Sultan Qaboos University The genetics of familial hypercholesterolemia making things simple Fahad AL Zadjali, PhD [email protected] 20/10/2017 1
Aug 05, 2020
Sultan QaboosUniversity
The genetics of familial hypercholesterolemia
making things simple
Fahad AL Zadjali, PhD
[email protected]/10/2017
1
DISCLOSURE OF CONFLICT
No financial relationships with commercial
interests
20/10/2017
2
CONSANGUINITY increases risk of monogenic disorders
• Monogenic Familial Hypercholosterolemia is most common monogenic disease
• FH is severely underdiagnosed with <1 % of the population. genetic cascade screening
Tadmouri GO et. al. Reprod Health. 2009
Familial Hypercholesterolemia
Polygenic Monogenic
Single or doubleHits/mutations
multipleHits/mutations
Polygenic LDL-C score
Lipoprotein metabolism
WHO / Fredrickson classification of primary hyperlipidaemias
Familial hypercholestrolemia
Type IIA Familial Hypercholesterolemia
Michael M Page, Aust Prescr 2016
LDLRAP1
Defects in LDLR• Autosomal dominant hypercholesterolemia
(ADH1) classical FH
• Attributes to 60-90% of FH cases.
• Loss of function mutations
>1700 variants
LDLR HomeUniversity College Londonwww.ucl.ac.uk/ldlr
Population Specific Mutations
Alallaf F. et. al. Open Cardiovasc Med J. 2017
LDLR mutations in Saudi Arabia
Oman LDLR mutations:
Novel
cDNA Protein
c.G1145T p.G382V
c.1214_1216del p.405_406del
c.1319_1332del p.R440fs
c.711delC p.R237fs
c.C1502T p.A501V
c.T1054C p.C352R
c.271delG p.G91fs
c.504_510del p.D168fs
c.G1171A p.A391T
c.G1027A p.G343S
c.G1285A p.V429M
c.G397A p.D133N
Apo B 100 gene defects
• Autosomal dominant hypercholesterolemia 2 (ADH 2) or Familial defective apoB100 (FDB)
• Attributes to about 5% of FH cases
• Loss of function mutations
Amanda J 2004, clinical Chemistry
29 exons
2/3 of mutations are in exon 26LDLR-binding domain
Amanda J 2004, clinical Chemistry
Proprotein convertasesubtilisin/kexin type 9 (PCSK9)
• Autosomal dominant hypercholesterolemia 3 (ADH 3)
• Gain of function mutations ( around 50)
• attributes to 1-3% of FH cases.
• Promotes degradation of LDLR
Mapping of common natural mutation of PCSK9 to the surface of the molecule.
Eric N. Hampton et al. PNAS 2007;104:14604-14609
©2007 by National Academy of Sciences
Autosomal Recessive Hypercholesterolemia (ARH)LDLRAP1
• Very rare
• Only patients with homozygous or compound heterozygous LDLRAP1 mutations are affected
Genetic testing for Familial Hypercholesterolemia
Next generation sequencing
EDTA-blood tubeSaliva sample
39.3
37.6
2.6
20.5
LDLR
ApoB
PCSK9
LDLRAP1
no mutation
Spectrum of mutations in SQUH
Double heterozygous mutation
Homozygous FH
2 normal LDLR
1 normal1 defective
LDLR
X
normal HeFH
1 normal1 defective
LDLR
X
HeFH
X
2 defective LDLR
X
HoFH
X
Large deletion / duplication of LDLR
Thoracic Key ®
Multiplex Ligation-dependent Probe amplification
Run on samples with negative mutations from NGS and no double hit mutations
Polygenic Hypercholesterolemia
• Individuals with elevated LDL-C similar to HeFH
• No Mutation detected in the 4 known genes, No deletion/duplication of LDLR.
• Identification is important as it will comprise the efficiency of cascade screening
Meta-analysis of plasma lipid concentrations in >100,000 individuals of European descent
12 SNPs genotype and quantify
LDL-C polygenic score
Teslovich TM et. al. Nature 2010
Futema M, Clin Chem 2015
Talmud PJ, The lancet 2013
ControlVs
FH- no mutation
ControlVs
FH with mutation
FH with mutationVsFH- no mutation
Diagnostic workflow for cascade testing in patients with familial hypercholesterolemia
Talmud PJ, The lancet 2013
A village of low HDL
Conclusion
• FH is caused by mutation of 4 genes LDLR, apoB100, PCSK9, LDLRAP1
• Next generation sequencing is cost effective to sequence the entire region of the 4 genes
• Identified mutations apply cascade screening
for 1st degree relatives
• Non-identified mutations polygenic LDL-C score