Leptin Gene Polymorphisms and Their Phenotypic Associations

13

Vitamins and Hormones, Volume 71

Copyright 2005, Elsevier Inc. All rights reserve

Leptin Gene

Polymorphisms and

Their Phenotypic

Associations

T. van der Lende,* M. F. W. te Pas,*R. F. Veerkamp,* and S. C. Liefers

{

*Division of Animal Resources Development, Animal Sciences Group Wageningen UR

8200 AB Lelystad, The Netherlands{Animal Breeding and Genetics Group, Wageningen Institute of Animal Sciences

Wageningen University, 6700 AH Wageningen, The Netherlands

I.
I ntroduction
0083-d. DOI: 10.1016/S0083-67373

II.
S tructural Organization of the Leptin Gene and
Leptin Protein

I
II. P olymorphisms in the Human Leptin Gene
I
V. P olymorphisms in the Bovine Leptin Gene
V.
P olymorphisms in the Porcine Leptin Gene
V
I. C oncluding Remarks
R
eferences
of rapidly increasing prevalence of human ob
In an era esity and
associated health problems, leptin gene polymorphisms have drawn

much attention in biomedical research. Leptin gene polymorphisms

have furthermore drawn much attention from animal scientists for their

possible roles in economically important production and reproduction

traits. Of the polymorphisms reported for exonic, intronic, and

promoter regions of the leptin gene, 16 have been included in association

studies in humans, 19 in cattle, and 6 (all exonic or intronic) in pigs. In

6729/05 $35.0029(05)71013-X

374 van der Lende et al.

humans, associations have been found with overweight or (early‐onset)obesity, non‐insulin‐dependent diabetes mellitus, prostate cancer, and

non‐Hodgkin’s lymphoma. In cattle, associations have been found with

feed intake, milk yield traits, carcass traits, and reproduction‐relatedtraits, and in pigs with feed intake, average daily gain, carcass traits

(backfat/leanness), and reproduction performance traits. Many of the

polymorphisms were only included in a limited number of association

studies, or the phenotypes studied varied largely for a given

polymorphism between studies. Therefore, many of the associations

found for these polymorphisms need to be confirmed in future studies

before firm conclusions can be drawn. # 2005 Elsevier Inc.

I. INTRODUCTION

Leptin is a cytokine‐like hormone that is primarily synthesized and se-

creted by white adipose tissue (Masuzaki et al., 1995; Zhang et al., 1994).

Leptin produced in other tissues, for example, in the placenta (Green et al.,

1995; Hassink et al., 1997; Masuzaki et al., 1997; Senarıs et al., 1997), fundus

of the stomach (Bado et al., 1998), mammary epithelium (Chelikani et al.,

2003; Smith‐Kirwin et al., 1998), skeletal muscle (Wang et al., 1998, 1999),

and brain and pituitary (Jin et al., 2000; Morash et al., 1999; Wiesner et al.,

1999), likely acts in a paracrine/autocrine fashion at these sites (Considine,

2003). Leptin as a hormone has important functions in the regulation of

body weight (i.e., maintaining the balance between feed intake and energy

expenditure; Pelleymounter et al., 1995), reproduction (extensively reviewed

in Henson and Castracane, 2003), immune functions (Lord et al., 1998), and

bone formation and growth (Cornish et al., 2002; Hamrick et al., 2004;

Steppan et al., 2000). In an era of rapidly increasing prevalence of human

obesity and associated health problems such as, for example, non‐insulin‐dependent diabetes mellitus (NIDDM), cardiovascular disorders, and

hypertension, leptin has drawn much attention in biomedical research (see,

e.g., Peelman et al., 2004b; Rahmouni and Haynes, 2004). For completely

diVerent reasons, leptin has also drawn much attention from animal scien-

tists. In livestock production, traits such as feed intake, feed eYciency,

energy balance, fast lean growth (i.e., body composition), fertility, and

reproductive eYciency are very important for the profitability of milk and

meat production enterprises (Hossner, 1998).

The discovery in 1994 of the leptin gene and the identification of the

recessive mutations in this gene responsible for the obese phenotype and

various associated disorders in Jackson Laboratory C57BL/6J mice (Zhang

et al., 1994) and SM/Ckc‐þDAC mice (Moon and Friedman, 1997; Zhang

et al., 1994), that is, the ob allele and the ob2J allele, respectively, has

Leptin Gene Polymorphisms 375

triggered in biomedical and livestock research—for the above‐mentioned

reasons—the search for polymorphisms in the leptin gene of human and

livestock (to date, cattle and pig). More specifically, interest focused on the

possible associations of such polymorphisms with clinical traits (human) and

economically important traits (livestock). In livestock, the identification of

genetic markers that are positively associated with economically important

traits has the potential to be used in breeding programs to significantly alter

the rate of genetic improvement.

The objective of this chapter is to review the polymorphisms that have

been found in the leptin gene and its promoter region, as well as the observed

phenotypic associations of these polymorphisms, both in humans and live-

stock. Throughout this chapter, amino acid (aa) residues of leptin are

numbered according to their position in the 167‐aa leptin peptide (i.e., the

leptin peptide including a signaling peptide).

II. STRUCTURAL ORGANIZATION OF THELEPTIN GENE AND LEPTIN PROTEIN

The human leptin gene encodes a 3.5‐kb cDNA (Gong et al., 1996). The

leptin gene has three exons. The coding region is contained in exons 2 and 3,

as exon 1 is not translated. The first part of exon 2 encodes a signaling

peptide of 21 aa residues that is not represented in the mature leptin protein.

Leptin has 67% sequence identity among species such as human, gorilla,

chimpanzee, orangutan, rhesus monkey, dog, cow, pig, rat, and mouse

(Zhang et al., 1997).

To understand the regulation of leptin gene transcription, the leptin

promoter region has been isolated and characterized. To date, several im-

portant transcription factor binding domains have been identified in the

leptin‐promoter region of the human, rodent, and ruminant genes. These

include domains for CCAAT/enhancer binding proteins (Gong et al., 1996;

Hwang et al., 1996; Miller et al., 1996; Taniguchi et al., 2002), cAMP

response element‐binding protein (Gong et al., 1996), adipocyte determina-

tion diVerentiation dependent factor 1/sterol regulatory element binding

protein 1 (Kim et al., 1998), peroxisome proliferator activated receptor g(Hollenberg et al., 1997), hypoxia‐inducible factor 1 (Ambrosini et al., 2002;

Grosfeld et al., 2002; Meißner et al., 2003), SP1 (Fukuda and Iritani, 1999;

He et al., 1995; Mason et al., 1998), LP1 binding factor (Mason et al., 1998),

glucocorticoids (Gong et al., 1996), insulin (Meißner et al., 2003), and a

placental‐specific transcription factor (Bi et al., 1997). CCAAT/enhancer

binding protein is an important transcription factor for the transcription

of most genes expressed in adipose tissue and for other genes involved in

energy metabolism (Darlington et al., 1995). Several groups (Hwang et al.,

1996; Mason et al., 1998) mutated the CCAAT/enhancer binding protein site


of the leptin promoter in rat and mouse and demonstrated that this site was

functional in regulating leptin gene expression.

The leptin protein has a weight of approximately 16 kD. In human and

mice, two leptin proteins, one with 167 aa residues (167 aa leptin) and

another with 166 aa residues (166 aa leptin) have been found, diVering in

the presence or absence of a glutamine residue at position þ49 (Isse et al.,

1995; Zhang et al., 1994). These two variants are not a result of allelic

variation, or the existence of two diVerent leptin loci, but the result of

alternative splicing of mRNA (Isse et al., 1995; Oberkofler et al., 1997).

Although the absence of glutamine 49 has little influence on the secondary‐structure prediction of 166 aa leptin in comparison to 167 aa leptin, a

diVerence in function can, at present, not be ruled out (Oberkofler et al.,

1997). Structure prediction algorithms and nuclear magnetic resonance

analysis of a crystalline form of leptin revealed that leptin is a protein

with a four‐alpha‐helix bundle structure (helix A, B, C, and D) that is

similar to the structure of the hemopoietic cytokine‐family (Rock et al.,

1996; Zhang et al., 1997). It shows the highest structural similarity with the

cytokines of the interleukin 6 family and granulocyte colony‐stimulating

factor (Zabeau et al., 2003). The members of the interleukin 6 family of

cytokines interact with their receptors through three diVerent binding sites—I, II and III. Leptin contains a single disulfide bond that links two

cysteines (Cys96 and Cys146) within the C and D helices, and this bond

has been proven critical for the structural integrity and stability of leptin

(Rock et al., 1996).

The inactive leptin polypeptide in ob/ob mice misses the wild‐type leptindomains distal to aa residue 104. This indicates that leptin activity may be

localized, at least in part, in these 104þ domains. To investigate this, Grasso

et al. (1997) tested six overlapping peptide amides corresponding to aa

residues 106–167 of mouse leptin [i.e., LEP‐(106–120), LEP‐(116–130),LEP‐(126–140), LEP‐(136–150), LEP‐(146–160), and LEP‐(156–167)]. Thesepeptide amides were tested for their eVects on body weight and feed intake in

female C57BL/6J mice after peripheral injection. The results indicated that

only the first three peptide amides were biologically active. This strongly

indicates that leptin activity is localized, at least in part, in domains between

aa residues 106 and 140. In an earlier study, Samson et al. (1996) found no

eVects on feeding in rats after intracerebroventricular injection of the

C‐terminal 52 aa fragment (residues 116–167). According to Grasso et al.

(1997), the discrepancy between their results and the results of Samson et al.

(1996) may be caused by the size of the peptide tested by Samson et al. (1996)

or the cyclization of the peptide used by Samson et al. (1996) to conforma-

tionally constrain the peptide. The latter may have aVected interaction with

the leptin receptor and masked the activity of a smaller region between aa

residues 116–140. Next to the aa residue 116–167 fragment of leptin, Samson


et al. (1996) also tested the aa residue 22–56 and 57–92 fragments of leptin.

Significant, dose‐related and reversible inhibition of food intake was only

found following central administration of the aa residue 22–56 fragment.

According to the work of Imagawa et al. (1998), there are three leptin

structures that aVect the in vivo biological and in vitro receptor‐bindingactivities, being the N‐terminal aa sequence (residues 22–115), which is

essential for the biological and receptor binding activities; the C‐terminal

aa sequence (residues 116–166) with loop structure, which is important for

enhancing the activities of the N‐terminal region; and the C‐terminal disul-

fide bond, which is not needed for the activities of leptin. This conclusion

was drawn from experiments in which a mutant‐type human leptin (lacking

the C‐terminal disulfide bond), aa residues 22–115 and 115–166 were sepa-

rately injected intracerebroventricularly in C57BL/6J ob/ob mice or in vitro

incubated with coronal brain sections (autoradiography) and compared with

wild‐type leptin.Using site‐directed mutagenesis, Verploegen et al. (1997) and Peelman

et al. (2004a) studied the signaling and binding activity of diVerent leptinmutants to map the interactions between leptin and its receptor. Verploegen

et al. (1997) generated 37 human leptin mutants to study critical sites for

receptor binding and biological activity. All except four of the mutant leptins

showed similar receptor binding and biological activity as wild‐type leptin.

The Arg41Glu (designated R20Q by Verploegen et al., 1997) mutant showed

no receptor binding, whereas the Asp61Asn (D40N), Ser148Asp (S127D),

and Arg149Glu (R128Q) mutants did have normal receptor binding but

reduced, very weak, and no biological activity, respectively. These results

indicate that Arg41 (R20) is important for receptor binding and that Asp61

(D40), but especially Ser148 (S127) and Arg149 (R128), are involved in

biological activity once binding occurred. As far as Arg149Glu (R128Q) is

concerned, Brunner et al. (1999) and Raver et al. (2002) confirmed the

in vitro results of Verploegen et al. (1997). However, Brunner et al. (1999)

were unable to confirm the in vivo results of Verploegen et al. (1997). In fact,

in their study, Arg149Glu (R128Q) acted in vivo as an agonist rather than an

antagonist of leptin. In the second study, in which site‐directed mutagenesis

was used to study leptin‐receptor binding and activation, Peelman et al.

(2004a) generated and tested 31 leptin mutants. The mutations were located

within the areas of the leptin protein that resemble the binding sites I, II, and

III with which the interleukin 6 family of cytokines interact with their

receptors. Mutations in binding site I at the C‐terminus of helix D did not

aVect receptor binding but showed a modest eVect on signaling. Mutations

in binding site II at the surface of helices A and C impaired receptor binding

but had only a limited eVect on signaling. Site III mutations around the

N‐terminus of helix D impaired receptor activation without aVectingbinding to the receptor.


III. POLYMORPHISMS IN THE HUMANLEPTIN GENE

The single‐nucleotide polymorphisms that have been found in the

exons and introns of the human leptin gene are summarized in Table I. Of

the 10 polymorphisms described, four showed in at least one study an

association with overweight or (early‐onset) obesity [i.e., G(19)A, Gln25Gln,

Arg105Trp, and �133].

The G(19)A polymorphism, located in the untranslated exon 1, was first

described by Hager et al. (1998). In only one of the six studies investigating

the association of this polymorphism with obesity or overweight, such an

association was actually found (Table I; Li et al., 1999). In two recent

studies, associations of this polymorphism with glucose homeostasis in

response to regular exercise and risk for non‐Hodgkin’s lymphoma have

been found (Lakka et al., 2004; and Skibola et al., 2004, respectively). Serum

leptin levels were available in three studies, but only Hager et al. (1998)

found an association with the G(19)A polymorphism. After correction for

body mass index (BMI), obese subjects homozygous for the G‐allele showedsignificantly lower leptin concentrations compared to obese subjects either

heterozygous or homozygous for the A‐allele.The Gln25Gln polymorphism, caused by a silent A‐to‐G mutation, was

first described by MaVei et al. (1996). It was found in one heterozygous

subject out of 105 mainly obese subjects with various ethnic backgrounds.

The very low frequency of the mutation was confirmed by Shigemoto et al.

(1997), who found only one heterozygous subject among 84 obese Japanese

subjects (60 NIDDM subjects and 24 subjects with impaired glucose toler-

ance). A significant association of this mutation with morbid obesity has

more recently been reported by Ohshiro et al. (2000). In 53 morbidly obese

Japanese subjects, the frequency of the G allele was 0.09, whereas in 132

nonobese control subjects, the frequency of this allele was only 0.01 (i.e.,

slightly higher than the frequency reported by MaVei et al. [1996] and

Shigemoto et al. [1997]). Of the eight obese subjects in which the mutation

was found, three men and four women were heterozygous, and one woman

was homozygous. The carriers of the mutation in the control group, three

women, were heterozygous. Because in this study no other mutations

were found in exons 2 and 3, this silent mutation could be a marker in

linkage disequilibrium with a polymorphism near the coding region of the

leptin gene that contributes to the pathogenesis of morbid obesity (Ohshiro

et al., 2000).

The Arg105Trp missense mutation was found in a highly consangui-

neous Turkish family (Strobel et al., 1998). This mutation is at the same

location as the mutation that leads to a premature stop codon in ob/ob mice.

Recently, Jiang et al. (2004) reported the absence of this mutation in 548

subjects belonging to 82 white families, selected from the National Heart,

TABLE I. Single‐Nucleotide Polymorphisms in the Exonic and Intronic Regions of the

Human Leptin Gene and Their Phenotypic Associations

Polymorphism and

Study Population

Allele

frequency Associationsa

G(19)A

Hager et al.,

1998

395 unrelated

morbidly obese

and 121 lean,

nondiabetic

control subjects

Obese: G: 0.67,

A: 0.33; lean

controls:

G: 0.64,

A: 0.36

Morbid obesity

(N); serum

leptin levels

(Y)

Mammes et al.,

1998

117 French

Caucasians with

overweight

G: 0.62, A: 0.38 Overweight (N);

serum leptin

levels (N);

weight loss

after diet (N);

change in

serum leptin

levels in

response to

diet (N)

Karvonen et al.,

1998

141 obese Finns

and 65 control

Finns

G: 0.33, A: 0.67 Obesity (N)

Li et al., 1999 125 unrelated obese

North American

(NA) women and

86 average weight

NA women

Obese: G: 0.63,

A: 0.37; normal

weight: G: 0.75,

A: 0.25

Extreme obesity

(Y); degree of

obesity (Y)

Lucantoni et al.,

2000

205 obese and 61

normal weight

Italians

Obese: G: 0.64,

A: 0.36; normal

weight: G: 0.62,

A: 0.38

Obesity (N);

serum leptin

levels (N)

Mattevi et al.,

2002

336 nondiabetic

Brazilians of

European descent

Overweight or

obese: G: 0.61,

A: 0.39; normal

weight: G: 0.63,

A: 0.37

Overweight plus

obesity (N)

Lakka et al.,

2004

397 nondiabetic

Whites and 143

nondiabetic Blacks

(HERITAGE family

study)

Whites: G: 0.58,

A: 0.42; Blacks:

G: 0.59, A: 0.41

Glucose

homeostasis in

response to

regular

exercise (Yb)

Skibola et al.,

2004

376 Non‐Hodgkin’s

lymphoma (NHL)

patients and 805

controls

NHL: G: 0.68,

A: 0.32; control:

G: 0.64, A: 0.36

Risk for non‐Hodgkin’s

lymphoma (Y)

(Continues )


Phe17Leu [T(49)C]

Echwald et al.,

1997

156 Caucasians with

juvenile‐onsetobesity and 380

healthy young

Caucasians

Phe: 0.999;

Leu: 0.001

Juvenile‐onsetobesity (N)

Gln25Gln [A(75)G]

MaVei et al.,

1996

105 subjects

(majority obese)

with diverse ethnic

backgrounds

A: 0.995; G: 0.005 —

Shigemoto et al.,

1997

84 obese Japanese

[60 with non‐insulin‐dependent diabetes

mellitus (NIDDM)

and 24 with impaired

glucose tolerance]

A: 0.994; G: 0.006 —

Ohshiro et al.,

2000

53 morbidly obese

Japanese and 132

nonobese control

subjects

Morbidly obese:

A: 0.91, G: 0.09;

nonobese:

A: 0.99, G: 0.01

Morbid

obesity (Y)

C(102)A (Leu34Leu)

Mentioned by

Ohshiro et al., 2000

— — —

Ile45Val [A(133)G]

Onions et al., 1998 103 hypertensive

sibships from 73

families (167 African

American individuals)

Ile: 0.997;

Val: 0.003

Essential

hypertension

(N)

G(144)A (Thr48Thr)

Karvonen et al., 1998 200 obese Finns G: 0.997, A: 0.003 —

Val94Met [G(280)A]

Considine et al., 1996 68 obese and 38

lean subjects

Val: 0.995;

Met: 0.005

Obesity (N)

Arg105Trp [C(313)G]

Strobel et al., 1998 A highly

consanguineous

Turkish family

— Morbid obesity

(Y); gonad

development

(Y)

Val110Met [G(328)A]

Echwald et al.,

1997

156 Caucasians with

juvenile‐onsetobesity and 380

healthy young

Caucasians

Val: 0.9991;

Met: 0.0009


TABLE I. (Continued )

Polymorphism and

Study Population

Allele



Karvonen et al.,

1998

200 obese Finns Val: 0.9991;

Met: 0,0009

Obesity (N)

�133 (deletion of

glycine of the

normal

codon 133)

Farooqi et al., 1998;

Montague et al.,

1997

Two severely obese

children and

unaVected family

members from a

highly

consanguineous

pedigree

— Severe early

onset obesity

(Y)

Basepair counting according to gi38174529whereATGat location 56 is noted as start site¼ 1.aAssociations studied; (Y) ¼ association was found, (N) ¼ association was not found.

bThe association was only found within carriers of a specific mutation in the leptin receptor

gene (see text).

TABLE I. (Continued )

Polymorphism and

Study Population

Allele



Lung and Blood Institute Family Heart Study. This strongly indicates that

the Arg105Trp mutation is exceedingly rare in the general population. The

members of the Turkish family who were homozygous for this mutation

were morbidly obese and markedly hyperphagic, and had lower serum leptin

levels than normal family members. The adult homozygous family mem-

bers all had clinical signs of hypogonadism (Ozata et al., 1999; Strobel

et al., 1998; for serum leptin levels, see also Lahlou et al., 2002), indicating

that leptin may be a necessary signal for initiation of human puberty

(Strobel et al., 1998). Within this family, four living family members were

found who were homozygous for this mutation (one adult man, two adult

women and one child). However, in total, 11 individuals with the obese

phenotype were born within this family, and even though they were all

brought up under essentially the same overall conditions and environ-

ment and received similar medical care, seven died in childhood during the

course of infections (Ozata et al., 1999). In vitro cell culture studies with

transfected COS cells have indicated a defective secretion of the mutant

leptin protein (Strobel et al., 1998). This was confirmed by Rau et al.

(1999), using transfected Chinese hamster ovary cells. The mutant leptin

accumulated intracellularly. The destiny of this accumulated leptin is still

unknown.

The �133 frameshift mutation (glycine deletion) was found in two sev-

erely obese children belonging to a highly consanguineous Pakistani family.


Both children were homozygous for the mutation and had extremely low

serum leptin levels. Both had a normal birth weight but rapidly became

obese as a result of marked hyperphagia with impaired satiety (Montague

et al., 1997; see also Farooqi et al., 1998). In a study including 366 extremely

obese German children and adolescents (BMI > 99th BMI percentile; mean

BMI 32.5 � 5.9) Hinney et al. (1997) were unable to find a single carrier of

this mutation. The �133 frameshift mutation encodes a truncated leptin

polypeptide (�133 leptin) of 121 aa residues. Preliminary data indicated a

defect in the secretion of �133 leptin, explaining the very low serum leptin

levels in the children homozygous for this mutation (Montague et al., 1997).

In more elaborate transfection studies, using Chinese hamster ovary and

monkey kidney epithelium cells, Rau et al. (1999) established that only the

wild‐type leptin was secreted, but not �133 leptin. As a result of misfolding/

aggregation, �133 leptin accumulates intracellularly and is subsequently

degraded by the proteasome. Cotransfection experiments have shown that

the secretion of wild‐type leptin is not interfered with by �133 leptin (Rau

et al., 1999).

The polymorphisms that have been found in the promoter region of the

human leptin gene are summarized in Table II. Of the eight polymorphisms

described, four showed at least in one study an association with overweight

or (early‐onset) obesity [i.e., G(�2548)A, C(�1823)A/T, C(�633)T, and

C(�188)A]. The G(�2548)A mutation was first described by Mammes

et al. (1998), although at that time it was wrongly designated C(�2549)A

(see Mammes et al., 2000). The incorrect designation was also used by

Flehmig (1999), Le StunV et al. (2000) and Ren et al. (2004). As can be seen

from Table 2, this polymorphism has been included in 12 association studies

that included diverging traits. The frequency of the G allele in all studied

groups was approximately equal to or higher than that of the A allele (range,

0.49–0.75; Table II). An association of this polymorphism with overweight

or obesity has been found by Li et al. (1999), Mammes et al. (2000), and

Niet ers et al . (2000 ), but not by Ma mme s et al . (1998), Fleh mig (1999), Le

StunV et al. (2000), or Yiannakouris et al. (2003). Zhang et al. (2003) did not

find an association of this polymorphism with baseline weight indicators

(BMI, abdominal subcutaneous fat and intraabdominal fat), but they did

find associations with antipsychotic agent–induced weight gain and abdomi-

nal subcutaneous fat deposition during 10 weeks of treatment. In 6 of the 12

studies included in Table II (HoVstedt et al., 2002; Le StunV et al., 2000;

Mammes et al., 1998, 2000; Ren et al., 2004; Yiannakouris et al., 2003), the

association of circulating leptin levels and theG(�2548)A polymorphismwas

studied and actually found. It should be noted, however, that Mammes et al.

(2000) found this association only in men and that Yiannakouris et al. (2003),

who studied both total plasma leptin and free plasma leptin, only found an

association with free plasma leptin levels, and in this case only in women.

Until now, the association of the G(�2548)A polymorphism with NIDDM

TABLE II. Polymorphisms in the Promoter Region of the Human Leptin Gene and Their Phenotypic Associations

Polymorphism and Study Population Allele frequency Associationsa

G(�2548)Ab

Mammes et al., 1998 117 French Caucasians

with overweight

G: 0.56, A: 0.44 Overweight (N); serum leptin levels (Y);

weight loss after diet (Y in women);

change in serum leptin levels in response

to diet (N)

Li et al., 1999 125 unrelated extreme obese

North American (NA)

women and 86 average‐weightNA women

Obese: G: 0.65, A: 0.35;

normal weight: G: 0.49,

A: 0.51

Extreme obesity (Y); degree of obesity (N)

Flehmig, 1999 300 overweight subjects G: 0.55, A: 0.45 Weight (N); absolute and relative fat mass (N);

body mass index (N); diet‐induced changes in

weight, fat mass, and body mass index (N)

Mammes et al., 2000 109 overweight and 314

normal‐weight unrelatedsubjects from the Nancy

area in France

Overweight: G: 0.64,

A: 0.36; normal weight:

G: 0.54, A: 0.46

Overweight (Y); serum leptin levels (Y in men)

Le StunV et al., 2000 Cohort I: 140 Caucasian obese

girls; cohort II: 93 Caucasian

obese girls; controls: 116 lean

Caucasian adults

Cohort I: G: 0.51,

A: 0.49; cohort II:

G: 0.61, A: 0.39;

controls: G: 0.49,

A: 0.51

Obesity (N); serum leptin levels (Y); relationship

between serum leptin and BMI (Y)

HoVstedt et al., 2002 39 nonobese female subjects G: 0.49, A: 0.51 Serum leptin levels (Y); adipose tisuue leptin

secretion rate (Y); adipose tissue

leptin mRNA levels (Y)

Nieters et al., 2002 154 obese and 154 control subjects,

randomly selected from the

EPIC‐Heidelberg study

Obese: G: 0.49, A: 0.51;

controls: G: 0.57, A: 0.43

Obesity (Y)

(Continues )

383

Yiann ouris

et a 2003

118 healthy Greek high‐schoolstudents

G: 0.53, A: 0.47 Overweight (N); plasma leptin levels (N);

plasma free leptin levels (Y in women);

Zhan t al., 2003 128 Chinese Han untreated patients

with schizophrenia and 38 age‐and gender‐matched controls

Not given Baseline weight indicators (N); antipsychotic

agent–induced weight gain (Y); antipsychotic

agent–induced abdominal fat deposition (Y)

Ren e al., 2004 269 non‐insulin‐dependent diabetesmellitus (NIDDM) patients;

135 first‐degree relatives (nondiabetic);

85 healthy unrelated controls

NIDDM: G: 0.6 A: 0.35;

relatives: G: 0 1,

A: 0.29; Unre ted

controls: G: 0 5, A: 0.25

NIDDM (Y); fasting serum leptin levels (Y);

fasting insulin levels (Y); insulin

resistance (Y)

Ribei et al., 2004 150 prostate cancer (PC) patients and

118 healthy controls

PC patients G: 2, A: 0.48

Healthy contr s G: 0.64,

A: 0.36

Susceptibility to PC (Y); risk of advanced

disease (Y)

Skibo et al., 2004 376 non‐Hodgkin’s lymphoma (NHL)

patients and 805 controls

NHL: G: 0.54, 0.46;

control: G: 0. , A: 0.44

Risk for NHL (Yc )

T(�243

Mam `s et al., 1998 117 French Caucasians with

overweight

T: 0.99, G: 0.01 Overweight (N); serum leptin levels (N);

weight loss after diet (N); change in serum

leptin levels in response to diet (N)

T(�196

Li et , 1999 125 unrelated obese North

American (NA) women and

86 average‐weight NA women

Obese: T: 0.91, 0.09;

normal weigh T: 0.87,

C: 0.13

Extreme obesity (N); degree of obesity (N)

C(–1887

Mam `s et al., 1998 117 French Caucasians with

overweight

C: 0.91, T: 0.09 Overweight (N); serum leptin levels (N);


leptin levels in response to diet (Y in men)

TABL II. (Continued )

Polymo hism and Study Population Allele frequency Associationsa

384

ak

l.,

g e

t

ro

la

7)G

me

3)C

al.

)T

me

E

rp

5,

.7

la

.7

0.5

ol

A:

56

C:

t:

C(�1823)A/T

Mammes et al., 1998 117 French Caucasians with

overweight

C: 0.86, A: 0.14 Overweight (N); serum leptin levels (N);



Li et al., 1999 125 unrelated obese NA women and


Obese: C: 0.83, T: 0.17;

average weight: C: 0.92,

T: 0.08

Extreme obesity (Y); degree of obesity (N)

G(�1387)A


overweight

G: 0.59, A: 0.41 overweight (N); serum leptin levels (N);

weight loss after diet (N); change in

serum leptin levels in response to diet (N)

C(�633)T


overweight

C: 0.93; T: 0.07 Overweight (N); serum leptin levels (N);




86 average weight NA women

Obese: C: 0.94, T: 0.06;

normal weight: C: 0.94,

T: 0.06

Extreme obesity (N); degree of obesity (Y)

C(�188)A

Oksanen et al., 1997 249 morbidly obese and 141 lean

control Finns

Morbidly obese: C: 0.94,

A: 0.06; lean: C: 0.91,

A: 0.09

Obesity (N); serum leptin levels (N)


overweight

C: 0.94, A: 0.06 Overweight (N); serum leptin levels (N);





Obese: C: 0.93, A: 0.07;

normal weight: C: 0.94,

A: 0.06

Extreme obesity (N); degree of obesity (Y)

Yiannakouris

et al., 2003

118 healthy Greek high‐schoolstudents

C: 0.96, A: 0.04 Overweight (N); plasma leptin levels (N)

aAssociations studied; (Y) ¼ association was found, (N) ¼ association was not found.

bIn Mammes et al. (1998) wrongly designated as C(�2549)A, as indicated by Mammes et al. (2000). Note that Flehmig (1999), Le StunV et al. (2000),

and Ren et al. (2004) studied the same polymorphism and also used the designation C(�2549)A.cThe association was only found within carriers of a specific mutation in the leptin receptor gene (see text).

385


has only been studied by Ren et al. (2004). The frequency of the A allele was

found to be significantly higher in the NIDDM patients than in unrelated

normal control subjects (0.35 vs. 0.25, respectively). Next to an association

with fasting serum leptin levels, an association was also found with fasting

insulin levels and insulin resistance. With the increasing evidence that high

leptin levels are associated with immune dysfunction, the interest for associa-

tions between leptin gene polymorphisms and disease has increased. Recent

studies by Ribeiro et al. (2004) and Skibola et al. (2004) (Table II) have shown

an association between theG(-2548)A polymorphism and the susceptibility to

prostate cancer and the risk for non‐Hodgkin lymphoma, respectively. In the

study of Ribeiro et al. (2004), there was, moreover, an association with the

risk of developing advanced prostate cancer.

Association of each of the three polymorphisms C(�1823)A/T, C(�633)T,

and C(�188)A with extreme obesity has been found in a study by Li et al.

(1999). Their results are in contrast to the results of Mammes et al. (1998) (all

three polymorphisms) and Oksanen et al. (1997), as well as Yiannakouris

et al. (2003) [only C(�188)A], who found no associations with overweight or

obesity (Table II). Functional analysis of the C(�188)A polymorphism was

reported by Oksanen et al. (1998). Reporter‐gene constructs were used to

study the transcriptional activity of the leptin promoter driven by wild‐type(�188C) and variant (�188A) proximal promoter regions in 3T3‐L1 cells. No

diVerences were found for preadipocytes or for adipocytes. According to

these authors, their results do not exclude subtle eVects of this polymorphism

on leptin expression under more physiological conditions.

A few polymorphisms in the 3’ untranslated region of the human leptin

gene have been reported and were included in association studies. The results

of these studies are summarized in Table III. Of the three polymorphisms

included, only the tetranucleotide repeat showed an association with obesity

(in one out of the five studies that included this trait) and an association with

essential hypertension (only included in one study). This multiallelic tetra-

nucleotide repeat was first identified by Shinatani et al. (1996). In three of the

five studies in which the polymorphism was used, the 15 alleles found in each

of these studies had a length of either 121–145 base pairs (n ¼ 7) or 197–225

base pairs (n ¼ 8) and were referred to as class I and class II alleles,

respectively (De Silva et al., 1999; Shintani et al., 1996, 2002). In these

studies, individuals were grouped into three groups, depending on the length

of their alleles, with subjects homozygous for the shorter alleles designated

genotype I/I, subjects with both the shorter and the longer alleles designated

genotype I/II, and subjects homozygous for the longer alleles designated

genotype II/II. McGarvey et al. (2002) found 16 alleles, 5 with a length of

150–170 base pairs and 9 with a length of 218–250 base pairs. As can be seen

from Table III, McGarvey et al. (2002) found an association between this

polymorphism and obesity, this in contrast to Shintani et al. (1996), De Silva

et al. (1999), and Shintani et al. (2002). The frequency of individuals with

TABLE III. Polymorphisms in the 3’ Untranslated Region of the Human Leptin Gene and

Their Phenotypic Associations

Polymorphism and

Study Population Allele frequency Associationsa

C(538)T (33 bp

downstream from

stop codon)

Karvonen

et al., 1998

200 obese Finns

and 65 control

Finns

C: 0.98,

T: 0.02

Obesity (N)

A ! G (noncoding

region at base

number 9 downstream

from the stop codon)

Echwald et al., 1997 156 Caucasians

with juvenile‐onsetobesity and 380

healthy young

Caucasians

A: 0.9991;

G: 0.0009


Tetranucleotide

repeat at the 3’

untranslated region

Shintani et al., 1996 69 unrelated Japanese

subjects with

non‐insulin‐dependentdiabetes mellitus

(NIDDM) and 84

control subjects

NIDDM:

Class I: 0.30,

Class II: 0.70;

Control: Class I:

0.26, Class II:

0.74

NIDDM (N);

obesity (N);

overweight (N)

Ohman et al., 1999 105 sib pairs

concordant for

obesity from

92 families

Not given Obesity (N)

De Silva et al., 1999 232 nondiabetic

Nauruan males

Class I: 0.10;

Class II: 0.90

Obesity (N);

insulin

resistance (N)

McGarvey et al., 2002 181 unrelated

Samoans

Obese: 226, 0.04;

others: 0.96;

normal weight:

226, 0.16;

others: 0.84

Obesity (Y)

Shintani et al., 2002 205 Japanese patients

with essential

hypertension and

117 normotensive

subjects

Hypertension:

Class I, 0.29;

Class II, 0.71;

normotension:

Class I, 0.24;

Class II, 0.76

Obesity (N);

essential

hypertension

(Y); insulin

resistance (N);

serum leptin

levels (N)

aAssociations studied; (Y) ¼ association was found, (N) ¼ association was not found.



allele 226 at the leptin locus was significantly higher in the low‐BMI group

than in the high‐BMI group (0.16 vs. 0.04). Although Shintani et al. (1996)

did not find an association of this polymorphism with BMI, the researchers

did report a tendency that is in agreement with this result. In their control

subjects (subjects without NIDDM), the authors observed a nonsignificant

trend in which class II alleles (long‐base‐pair alleles) are more prevalent in

nonobese than in obese subjects (75% vs. 65%; n ¼ 148 and n ¼ 20 subjects,

respectively).

Neither Shintani et al. (1996) nor Shintani et al. (2002) found an associa-

tion of this tetranucleotide repeat polymorphism with insulin resistance, but

Shintani et al. (2002) did find an association with hypertension. The frequen-

cy of the I/I genotype was markedly higher in hypertensive than in normo-

tensive control subjects. In the same subjects, no association was found

between the polymorphism and body weight, degree of obesity, insulin

resistance, or serum leptin levels, which indicates that the association of

the polymorphism with hypertension is independent of obesity, insulin

resistance, and circulating leptin levels (Shintani et al., 2002).

IV. POLYMORPHISMS IN THE BOVINELEPTIN GENE

The polymorphisms that have been found in the exons and introns of the

bovine leptin gene are summarized in Table IV. Of the nine polymorphisms

described, four were not included in any association study, two were includ-

ed in one or two association studies, and three were included in four to six

association studies. Overall, associations have been found with feed intake

(Tyr7Phe and LEPSau3AI), milk yield traits (Arg25Cys and LEPSau3AI),

carcass (fat‐related) traits (Arg25Cys and LEPSau3AI), and reproduction‐related traits (LEPSau3AI). Because of the relatively low number of

studies and the large diversity in both breeds used and traits studied, definite

conclusions can not yet been drawn. In the only study that included plasma

leptin levels (Liefers et al., 2003), associations were actually found (Arg25Cys,

LepSau3AI, and Ala80Val). These associations were found during late

gestation, but not during lactation.

Single‐nucleotide polymorphisms in the promoter region of the bovine

leptin gene have to date only been reported by Liefers (2004). In the �1600‐to 0‐bp region of the promoter, a total of as many as 18 single‐nucleotidepolymorphisms and two deletions were found (see Table V). Of these

polymorphisms, 14 were studied in more detail (shown bold in Table V) to

establish possible associations with live weight traits, milk yield traits, feed

intake traits, energy balance during early lactation, and commencement of

ovarian activity after calving, as well as plasma leptin levels before and after

calving. Despite the close proximity between the polymorphisms, only three

TABLE IV. Polymorphisms in the Exonic and Intronic Regions of the Bovine Leptin Gene and Their Associations with Production and

Reproduction Traits


C(978)Tb

Lagonigro et al., 2003 169 Charolais � Holstein

crossbred bulls

C: 0.65, T: 0.35 —

C(1001)Gc


crossbred bulls

C: 0.35, G: 0.65 —

Tyr7Phe [A(1127)T]


crossbred bulls

Tyr: 0.86, Phe: 0.14 Feed intake (Y); carcass fat‐related traits (N)

Arg25Cysd [C(1180)T]

Buchanan et al., 2002 60 Angus bulls; 55 Charolais

bulls; 22 Hereford bulls;

17 Simmental bulls

Angus: Arg, 0.42;

Cys, 0.58; Charolais:

Arg, 0.66; Cys, 0.34;

Hereford: Arg, 0.45;

Cys, 0.55; Simmental:

Arg, 0.68; Cys, 0.32

Carcass fat content (Y); leptin mRNA

expression (Y)

Liefers et al., 2003 323 Holstein Friesian cows Arg: 0.67; Cys: 0.33 Serum leptin during late pregnancy (Y); serum

leptin during early lactation (N)


crossbred bulls

Arg: 0.65, Cys: 0.35 Feed intake (N); carcass fat‐related traits (N)

Buchanan et al., 2003 416 Holstein cows Arg: 0.54, Cys: 0.46 Milk yield traits (Y); milk somatic cell count linear

score (Y)

Liefers, 2004 613 Holstein Friesian cows Arg: 0.65; Cys: 0.35 Milk yield traits (N)

(Continues)

389

Nkrumah et al., 2004 26–30 steers of each of five

genetic lines (M1–M4, TX)

M1: Arg: 0.29, Cys: 71;

M2: Arg: 0.45, Cy 0.55;

M3: Arg: 0.52, Cy 0.48;

M4: Arg: 0.53, Cy 0.47;

TX: Arg: 0.58, Cy 0.42

Growth (N); feed intake (N); feed eYciency (N);

fat deposition rate (Y); body fat reserves (Y);

lean meat yield (Y); marbling (N); intermuscular

fat (N); carcass fat (N)

RFLP1, LEPSau3AI

[C(2059)T]

Pomp et al., 1997 Unrelated cattle representing

a variety of breeds

Within breeds: A‐all :

0.00– 0.82, B‐allel0.18–1.00

—

Liefers et al., 2002 613 Holstein Friesian cows C: 0.90, T: 0.10 Live weight traits (N); milk yield traits (Y); feed

intake traits (N); energy balance (N);

commencement of ovarian activity

after calving (N)

Liefers et al., 2003 323 Holstein Friesian cows C: 0.90, T: 0.10 Serum leptin during late pregnancy (Y); serum leptin

during early lactation (N)

Almeida et al., 2003 96 composite beef cows (5/8

Aberdeen Angus � 3/8 Nelore)

A‐allele 0.63 B‐allele .37 Calving interval (N); weight at first calving (Y)



þ Allele 0.06; � alle 0.94 Calving interval (Y); weight at first calving (Y)

Oprzadek et al., 2003 145 Black‐and‐White (Friesian)

bulls

A: 0.85, B: 0.07, C: 8 Growth (N); feed intake (Y); feed conversion (N);

carcass traits (Y)

LEPHinfI [C(2797)T/G]

Lien et al., 1997 6 bulls Not given —

LEPBsaAI [G(2857)A]

Lien et al., 1997 6 bulls Not given —

TABLE IV. (Continued )


390

0.

s:

s:

s:

s:

ele

e:

0

le

0.0


Aberdeen Angus � 3/8

Nelore)

0.58, 0.42 Calving interval (N); weight at first calving (N)

Ala80Vald [C(3100)T]

Haegeman et al., 2000 18–56 animals from each of

nine breeds and Belgian

Blue crossbreds

Wild type: 0.518–0.887;

mutant type: 0.113–0 82

—

Liefers et al., 2002 613 Holstein Friesain cows Ala: 0.75, Val: 0.25 Live weight traits (N); milk yield traits (N); feed

intake traits (N); energy balance (N);

commencement of ovarian activity after

calving (N)



0.85, 0.15 Calving interval (N); weight at first calving (N)

Liefers et al., 2003 323 Holstein Friesian cows Ala: 0.67, Val: 0.33 Serum leptin during late pregnancy (Y); serum leptin

during early lactation (N)


crossbred bulls

Ala: 0.46, Val: 0.54 Feed intake (N); carcass fat‐related traits (N)

Gln83Arg [A(3109)G]

Haegeman et al., 2000 Two Belgian Blue crossbred

animals

— —

Location of base pairs refers to Accession Number U50365.aAssociations studied; (Y) ¼ association was found, (N) ¼ association was not found.

bDesignated C(103)T by Lagonigro et al. (2003).

cDesignated C(126)G by Lagonigro et al. (2003).dReferred to as Arg4Cys and Ala59Val because 4 and 59 are the amino acid positions in e leptin protein without the 21–amino acid signaling peptide.

391

.4

th

TABLE V. Polymorphisms Found in the 1.6‐kb 5’‐Flanking Promoter Region of the Leptin

Gene of 20 Cows and a Comparison of the Submitted Sequence (AJ571671) with the Earlier

Published Sequence (AB070368) of Taniguchi et al. (2002)

Position AJ571671 SNP/DELa Allele frequency SNP AB070368

�1457 A G 0.46 G

�1452 A G G

�1446 T C C

�1392 G A G

�1255 AG DEL AG AG

�1238 G C 0.33 G

�1198 G no SNP DEL G

�1066 T A T

�963 C T 0.33 C

�901 A T A

�578 C G 0.44 G

�498 DEL C no SNP C

�483 G no SNP A

�415 G DEL G 0.27 G

�292 T C 0.47 C

�282 G T 0.10 T

�272 G A 0.37 G

�211 A G 0.10 G

�201 C T 0.12 T

�197 A C 0.19 A

�170 C T 0.40 C

�147 C T 0.47 T

�105 C G 0.42 G

Locations �1198, �489, and �483 were diVerent between AJ571671 and AB070368. Bold

mutations were genotyped for 613 animals, and allele frequencies are based on these data.

(Source: Liefers, 2004.)aDEL ¼ deletion of one or two base pairs.


of these polymorphisms showed any associations with the studied produc-

tion and reproduction traits, though diVerent from each other. Polymor-

phism A(�1457)G was associated with commencement of luteal activity

after calving and the change in live weight between the first week of lactation

and the minimum live weight after calving. Polymorphism C(�963)T was

associated with feed intake, dry matter intake, energy balance, and the

interval between calving and first estrus observed by the herdsman. Poly-

morphism C(�578)G was associated with milk protein percentage. Almost

all 14 polymorphisms were associated with serum leptin levels during late


gestation. Only G(�282)T was associated with serum leptin levels during

late gestation and early lactation, whereas C(�201)T was only associated

with serum leptin levels during early lactation (Liefers, 2004).

An An(TA)m polymorphism in the 5’ untranslated region of the bovine

leptin gene, first described by Wilkins and Davey (1997), has to our knowl-

edge not been used in any published association study. Wilkins and Davey

(1997) found in Holstein Friesian and Jersey cows a total of 17 alleles, with

frequencies between 0.01 and 0.26, whereas Hale et al. (1998) found in

Angus cattle only six alleles, with frequencies between 0.02 and 0.55.

V. POLYMORPHISMS IN THE PORCINELEPTIN GENE

In the pig, polymorphisms in the leptin gene have been studied in exonic

and intronic regions, but not yet in the promoter region. In total, seven

polymorphisms have been described (Table VI). For most of these poly-

morphisms, and in most of the breeds studied, one of the two alleles per

locus had a low to very low frequency (Table VI). For the production and

reproduction traits studied, associations were only found for C(867)T, A

(2845)T, and T(3469)C (Table VI). C(867)T was included in two association

studies. Associations with litter size and backfat thickness were found in the

study by Chen et al. (2004) in Duroc but not in Landrace and Yorkshire

animals. In the study of Jiang and Gibson (1999), which only included

backfat thickness in four pig breeds (including Duroc), no associations were

found. A(2845)T was included in one study only and was shown to be

associated in Landrace pigs, but not in Duroc and Yorkshire pigs, with total

feed intake during the growing period (i.e., from 30 to 105 kg body weight)

and with the estimated breeding value (i.e., genetic merit) for age at 100 kg

body weight (Kennes et al., 2001). The T(3469)C polymorphism was includ-

ed in eight association studies. Associations were found, although they were

not always conclusive, with production traits (Chen et al., 2004; Jiang and

Gibson, 1999; Kennes et al., 2001; Kulig et al., 2001; Szydlowski et al., 2004;

Urban et al., 2002) and reproduction traits (Chen et al., 2004; Kmiec et al.,

2003; Korwin‐Kossakowska et al., 2002), as indicated in Table VI. Overall,

the results of these studies indicate that the T(3469)C polymorphism may be

associated with carcass traits (backfat/leanness), average daily gain, litter

size, and semen production, but not consistently in all breeds studied. For

the associations found, the C‐allele in comparison to the T‐allele reduced

backfat thickness (Jiang and Gibson, 1999; Urban et al., 2002), increased

lean meat percentage (Kulig et al., 2001; Urban et al., 2002), reduced

intramuscular fat (Szydlowski et al., 2004), and increased loin weight

(Szydlowski et al., 2004). For average daily weight gain, Kennes et al.

(2001) found a positive eVect of the C‐allele, but in contrast, Urban et al.

TABLE VI. Polymorphisms in the Exonic and Intronic Regions of the Porcine Leptin Gene and Their Associations with Production and

Reproduction Traits


C(867)T

Jiang and Gibson, 1999 29 Duroc, 29 Hampshire,

30 Landrace, 32 Large White

Duroc: T: 0.55, C: 0.45;

Hampshire: T: 0.50,

C: 0.50; Landrace, T: 0.22,

C: 0.78; Large White,

T: 0.02, C: 0.98

Backfat at 100 kg (N)

Chen et al., 2004 170 Landrace sows and 455

Landrace boars, 62 Yorkshire

sows and 333 Yorkshire boars,

246 Duroc sows and 593 Duroc boars

Landrace: C: 0.77, T: 0.23;

Yorkshire: C: 0.74, T: 0.26;

Duroc: C: 0.65, T: 0.35

Litter size (Y in Duroc); average daily

gain (N); feed eYciency (N); backfat

thickness (Y in Duroc)

G(1112)A

Jiang and Gibson, 1999 29 Duroc, 29 Hampshire, 30 Landrace,

32 Large White

Duroc: G: 0.95, A: 0.05;

Hampshire: G: 0.90, A: 0.10;

Landrace: G: 0.93, A: 0.07;

Large White: G: 1.00, A: 0.00

Backfat at 100 kg (N)

A(2728)G

Kennes et al., 2001 86 Duroc, 160 Landrace,

118 Yorkshire

Duroc: G: 0.91, A: 0.09;

Landrace: G: 0.85,

A: 0.15; Yorkshire:

G: 1.00, A: 0.00

Average daily weight gain (N); feed

conversion (N); total feed intake (N);

average daily feed intake (N); backfat

at 100 kg (N); age at 100 kg (N);

EBV for backfat at 100 kg (N); EBV

for age at 100 kg (N)

A(2845)T


118 Yorkshire

Duroc: A: 0.68, T: 0.32;

Landrace: A: 0.93,

T: 0.07; Yorkshire: A:

1.00, T: 0.00


conversion (N); total feed intake

(Y in Landrace); average daily feed

intake (N); backfat at 100 kg (N);

age at 100 kg (N); EBV for backfat

at 100 kg (N); EBV for age at 100 kg

(Y in Landrace)

394

T(3469)C (Leu72Leu)

Stratil et al., 1997 Various Western pig breeds and Meishan

(6–14 animals per breed)

Western pig breeds:

T: 0.73–0.96, C: 0.04–0.27;

Meishan: T: 0, C: 1

—

Jiang and Gibson, 1999 29 Duroc, 29 Hampshire, 30 Landrace,

32 Large White

Duroc: T: 0.97, C: 0.03;

Hampshire: T: 0.88,

C: 0.12; Landrace: T: 0.93,

C: 0.07; Large White:

T: 0.74, C: 0.26

Backfat at 100 kg (Y in Large White)

Kulig et al., 2001 131 Polish Landrace sows T: 0.87, C: 0.13 Body weight (N); lean meat content (Y);

average daily weight gain (Y)


118 Yorkshire

DUROC: T: 0.91, C: 0.09;

Landrace: T: 0.94, C:

0.06; Yorkshire: T: 0.85,

C: 0.15

Average daily weight gain (Y in Landrace);

feed conversion (N); total feed intake (N);

average daily feed intake (N); backfat at

100 kg (N); age at 100 kg (N); EBV for

backfat at 100 kg (N); EBV for age at

100 kg (N)

Korwin‐Kossakowska

et al., 2002

L990 sows (444 first farrowings (FF)

and 890 later farrowings (LF)

FF: T: 0.86, C: 0.14; LF:

T: 0.87, C: 0.13

Total number of piglets born (Y in LF);

number of piglets born alive (Y in LF);

number of piglets surviving to day 21

(N); number of piglets weaned (N); litter

weight on day 21 (N); litter weight at

weaning (N)

Urban et al., 2002 117 Duroc T: 0.65, C: 0.35 Average daily gain birth–100 kg (Y);

average daily gain 30–100 kg (N);

backfat thickness (Y); area of musculus

longissimus lumborum et thoracis (N);

% lean meat (Y)

Kmiec et al., 2003 Duroc‐Pietrain crossbred boars T: 0.71, C: 0.29 Ejaculate volume (Y); ejaculate sperm

concentration (Y); percentage of

live sperm (Y); number of live sperm

per ejaculate (N)

(Continues )

395

Szydlowski et al., 2004 135 Polish Large White (PLW),

120 Polish Landrace (PL), 184

Synthetic line 990 (L990)

PLW: T: 0.89, C: 0.11;

PL: T: 0.90, C: 0.10;

L990: T: 0.89, C: 0.11

Average daily gain (N); feed conversion

ratio (N); abdominal fat (N); backfat

thickness (N); intramuscular fat (Y in

PLW); meat content (N); loin weight

(Y in L990); loin muscle area (N); ham

weight (N); ham cut weight (N)

Chen et al., 2004 170 Landrace sows and 455 Landrace

boars; 62 Yorkshire sows and

333 Yorkshire boars; 246 Duroc

sows and 593 Duroc boars

Landrace: C: 0.93, T: 0.07;

Yorkshire: C: 0.80,

T: 0.20; Duroc: C: 0.94,

T: 0.06

Litter size (Y in Landrace and Yorkshire);

average daily gain (Y in Landrace);

feed eYciency (Y in Yorkshire);

backfat thickness (N)

T(3714)G (Ala153Ala)

Jiang and Gibson, 1999 30 Erhualian T: 0.68, G: 0.32 —

T(3996)C

Kennes et al., 2001 86 Duroc, 160 Landrace, 118

Yorkshire

Duroc: T: 0.89, C: 0.11;

Landrace: T: 0.85,

C: 0.15; Yorkshire: T: 1.00,

C: 0.00


conversion (N); total feed intake (N);

average daily feed intake (N); backfat

at 100 kg (N); age at 100 kg (N); EBV

for backfat at 100 kg (N); EBV for age

at 100 kg (N)

Location of base‐pairs refers to Accession Number U66254.aAssociations studied; (Y) ¼ association was found, (N) ¼ association was not found.

TABLE VI. (Continued )


396


(2002) found a positive eVect of the T‐allele. Both the latter studies included

backfat as a trait, but only Urban et al. (2002) found an association with

T(3469)C (see Table VI). The three association studies that included repro-

duction traits (Chen et al., 2004; Kmiec et al., 2003; Korwin‐Kossakowska

et al., 2002) suggest that the T‐allele rather than the C‐allele is favorable forreproduction.

VI. CONCLUDING REMARKS

Of the polymorphisms reported in the exonic, intronic, and promoter

regions of the leptin gene and included in this overview (18 in humans, 29

in cattle, and 7 in pigs), the majority was included in at least one association

study (i.e., 16 in humans, 19 in cattle, and 6 in pigs). Considering the large

range of physiological functions of leptin, it is not surprising that various

phenotypic associations have been found with, for example, overweight or

(late‐onset) obesity, non‐insulin‐dependent diabetes mellitus, prostate can-

cer, and non‐Hodgkin’s lymphoma in humans; feed intake, milk yield traits,

carcass traits, and reproduction‐related traits in cattle; and average daily

gain, carcass traits (backfat thickness/leanness), and reproduction perfor-

mance traits in pigs. Either many of the polymorphisms were only included

in a limited number of association studies, or the phenotypes studied varied

largely for a given polymorphism between studies. Therefore, many of the

associations found for these polymorphisms need to be confirmed in future

studies before firm conclusions can be drawn. DiVerences in phenotypic

associations of a given leptin polymorphism between studies involving com-

parable traits or characteristics may be a result of diVerences in linkage

disequilibrium (or the absence of linkage disequilibrium) with a functional

mutation in the leptin gene itself (including the promoter region) or in genes

upstream or downstream of the leptin locus. Even if the polymorphism

studied is a functional polymorphism, associations in diVerent human po-

pulations or breeds of livestock may vary largely. Various studies have

shown that the ob/ob genotype in diVerent genetic backgrounds may lead

to diVerent phenotypes (Ewart‐Toland et al., 1999; Haluzik et al., 2004; Qiu

et al., 2001). Stoehr et al. (2004) reported large, heritable diVerences in body

weight and food intake between BTBR‐ob/ob and B6‐ob/ob mice and were

able to identify two loci, called modifier of obese (Moo1 and Moo2), that

explain the majority of the heritable variance in (BTBR � B6) F2‐ob/obmice. Two of the human association studies included in this review (Lakka

et al., 2004; Skibola et al., 2004; see Table I and Table II, respectively)

provide illustrative evidence that phenotypic associations of leptin gene

polymorphisms may already be influenced by allelic variation at a single

other unlinked locus (i.e., in these studies, the leptin receptor locus). Lakka

et al. (2004) found an association of the G(19)A polymorphism in the leptin


gene, with exercise‐induced change in fasting insulin blood level in carriers of

the Arg‐allele of the Lys109Arg polymorphism in the leptin receptor gene,

but not in subjects homozygous for the Lys‐allele. Likewise, Skibola et al.

(2004) found an association of the G(�2548)A polymorphism in the pro-

moter region of the leptin gene with the risk for non‐Hodgkin’s lymphoma in

subjects that were homozygous for the Arg‐allele of the Gln223Arg poly-

morphism in the leptin receptor gene, but not for carriers of the Gln‐allele. Acompletely diVerent phenomenon that may aVect the replication of associa-

tion studies was reported by Comings et al. (2001). The association of the

dinucleotide repeat D7S1875 (closely linked to the human leptin gene re-

ferred to as Lep1875) with the age of menarche depended on the age of the

mothers at the birth of the women studied. The Lep1875 by age of menarche

eVects were in opposite directions for subjects with a maternal age at birth of

less than 30 years compared to those with a maternal age at birth of 30 years

or more. The authors referred to this phenomenon as an ‘‘association

crossover eVect.’’

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Leptin Gene Polymorphisms and Their Phenotypic Associations

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