Inherited Ataxias Molecular Pathways to Neurodegeneration Professor Yasser Metwally www.yassermetwally.com
Apr 22, 2015
Inherited Ataxias
Molecular Pathways to Neurodegeneration
Professor Yasser Metwally
www.yassermetwally.com
CLASSIFICATION OF THE HEREDITARY CLASSIFICATION OF THE HEREDITARY ATAXIASATAXIAS
(HARDING, 1981)(HARDING, 1981)Congenital Cerebellar AtaxiasMetabolic Ataxias Intermittent Metabolic Ataxias
Progressive Metabolic Ataxias (AVED)Ataxias Associated With Defective DNA Repair (AT)Degenerative Ataxias
Early Onset Inherited AtaxiasFriedreich’s AtaxiaEOCA (ARSACS, AOA-1, SCAN-1)Cerebellar Ataxia with HypogonadismProgressive Myoclonic AtaxiaOther Early Onset Ataxias
Late Onset Inherited AtaxiasADCA Type IADCA Type IIADCA Type IIIOther ADCA
Mitochondrial
Metabolic
Associated with Defective DNA Repair
Protein Folding & Degradation
Channelopathies
Toxic RNA
Others
Pathogenic Classification
Mitochondrial
Metabolic
Associated with Defective DNA Repair
Protein Folding & Degradation
Channelopathies
Toxic RNA
Others
Pathogenic Classification
Mitochondrial Ataxias
NUCLEAR GENES
• FRDA• MIRAS• IOSCA• ARCA2• SCA28
MITOCHONDRIAL GENES • MERRF• NARP• Kearns-Sayre syndrome
Mitochondrial Ataxias
NUCLEAR GENES
• Friedreich’s ataxia• MIRAS• IOSCA• ARCA2• SCA28
Mitochondrial AtaxiasÜber degenerative Atrophie der spinalen Hinterstränge; 1863
• Onset around puberty• Prominent ataxia and dysarthria • Inconstant nystagmus• Absent tendon reflexes• Late sensory loss and weakness• Scoliosis and pes cavus• Cardiac symptomsPrevalence 1:50,000
Carrier frequency 1:100
Ex 1 Ex 2 Ex 3 Ex 4 Ex 5a Ex 5b Ex 6
= Missense
= Truncation
GAA repeat
93%
7%
Homozygotes
Compound heterozygotes
FXN gene
Frequency Distribution of GAA
0300
600900
1200
0
10
20
30
40
Nu
mb
er
of
ch
rom
osom
es
GAA repeats
GAA1
GAA2
6 36Normal alleles
Expanded alleles60 1300
Frataxin
0
2
4
6
8
10
12
14
16
400 500 600 700 800 900 1000
GAA repeat number
Fra
taxi
n m
RN
A (
Arb
itra
ry U
nit
s)
0
5
10
15
20
25
30
35
A B C D E F G H Q R T
Fra
tax
in m
RN
A (
Arb
itra
ry u
nit
s)
Patients Controls
GAA expansion in the FXN gene causes frataxin mRNA reduction in FRDA patients
Frataxin reduction in FRDA patients
Iron Sulphur Centres
• Iron transport
• Iron storage
• Anti-oxidant
• Ox-Phos stimulation
• Fe-S centres biosynthesis
Frataxin deficiency
Oxidative stress
Oxidative stress
Increased Fe-S cluster byosynthesis
Reduction of Fe-Scluster proteins
Impaired energymetabolism
ROS productionFenton chemistry
Neurodegeneration
Fenton chemistry
Neurodegeneration
GAA1 Expansion is inversely correlated with onset age
r= -0.71r= -0.71
RR22 = 0.56 = 0.56
0
10
20
30
40
50
0 200 400 600 800 1000 1200
GAA1 repeats
Ag
e a
t on
set
Friedreich Ataxia Onset around puberty• Prominent ataxia and dysarthria • Inconstant nystagmus• Absent tendon reflexes• Late sensory loss and weakness• Scoliosis and pes cavus• Cardiac symptomsFRDA may show variant phenotype and the
molecular test should be considered in sporadic and autosomal recessive cases of ataxia, even with late onset and preserved tendon reflexes
DNA was extracted from EDTA-treated blood samples, and the (GAA)n repeat length in the first intron of the gene X25 was analyzed by PCR and separation on agarose gel. The size of alleles was estimated by leastsquare fit of fragment size to gel mobility.
NUCLEAR GENES
• FRDA• MIRAS• IOSCA• CoQ10 deficiency/ARCA2• SCA28
Mitochondrial Ataxias
Nuclear Mitochondrial Ataxias
Disease Acronym Gene Function
MITOCHONDRIAL RECESSIVE ATAXIA SYNDROME
MIRAS polymerase, dna, gamma; (POLG1)
Mitochondrial DNA replication
INFANTILE-ONSET SPINOCEREBELLAR ATAXIA
IOSCA
(mtDNA)-specific helicase (C10orf2)
Mitochondrial DNA replication
COENZYME Q10 DEFICIENCY
ARCA2
- mitochondrial parahydroxybenzoid-polyprenyltransferase (COQ2)
- decaprenyl diphosphate synthase subunit-1 gene (PDSS1)
- decaprenyl diphosphate synthase subunit-2 gene (PDSS2)
- aaarF-domain-containing kinase 3 (ADCK3/CABC1)
Coenzime Q Biosynthesis
Onset (years)Recessive ataxiaEpilepsyMental impairmentOphthalmoplegiaNeuropathyMyoclonusPyramidal signsOptic atrophyHearing loss HypogonadismHyperlactatemia
1-30++++++-----
MIRAS
1+++++--+++-
IOSCA
2-11+++-------+
ARCA2
Mitochondrial Ataxias
Cerebellar atrophy in ARCA 2
Cerebellar atrophy is present in MIRAS, IOSCA, and ARCA.It is absent or mild in FRDA.
NUCLEAR GENES
• FRDA• MIRAS • IOSCA• ARCA2• SCA28
Mitochondrial Ataxias
SCA28 – A Dominant Mitochondrial Ataxia
Genetics • mutations in the AFG3L2 (Afg3 like 2) gene (AAA family) • two m-AAA protease isoenzymes: a homo-oligomeric AFG3L2 complex and a hetero-oligomeric complex (paraplegin/AFG3L2) • dominant negative effect of AFG3L2 mutations • impaired quality system control of mitochondrial proteins
Phenotype• juvenile onset• slowly progressive ataxia• ophthalmoparesis
• cerebellar atrophy
Mitochondrial
Metabolic
Associated with Defective DNA Repair
Protein Folding & Degradation
Channelopathies
Toxic RNA
Others
Pathogenic Classification
INTERMITTENT ATAXIA
Deficiency of Urea CycleDisorders of Amino AcidDisorders of Pyruvate
PROGRESSIVE ATAXIA
Storage Diseases
Niemann-Pick type C KrabbeHexosaminidase A deficiency
KufsCholestanolosis (CTX)
Vitamin E Deficiency and Lipoprotein Disorders
AVED Abetalipoproteinemia Hypobetalipoproteinemia
Peroxysomal Diseases
Adrenomyeloneuropathy Refsum
Metabolic Ataxias
Metabolic Ataxias
• Rare disorders• Often autosomal recessive inheritance and early onset• Assay of enzymatic activities or measurement of serum or urine metabolite• Ataxia may be intermittent or progressive • Frequently associated to other neurological signs and multisystem involvement.
Mitochondrial Mitochondrial
MetabolicMetabolic
Associated with Defective DNA RepairAssociated with Defective DNA Repair
Protein Folding & DegradationProtein Folding & Degradation
ChannelopathiesChannelopathies
Toxic RNAToxic RNA
OthersOthers
Pathogenic Classification
Double Strand
• Ataxia Telangiectasia• AT like disorder
Single Strand
• AOA1• AOA2 (?)• SCAN1• Xeroderma Pigmentosum • Cockayne Syndrome
Disorders Associated with Defective DNA Repair
Neurological and non-neurological deficits
Absence of non-neurological deficits
Double Strand
• Ataxia Telangiectasia• AT like disorder
Associated with Defective DNA Repair
A-T is characterized by a triad of clinical manifestations:
a complex, progressive neurological syndrome
telangiectasias immunological deficiency
Onset (years)Recessive ataxiaOculomotor apraxiaNeuropathy Choreothetosis Mental impairment α-fetoprotein Cholesterol Albumin ImmunoglobulinsTelangiectasesMalignanciesEarly menopause
1-4++++-+--+++
-
AT
Single Strand
• AOA1• SCAN1• AOA2 (?)• Xeroderma Pigmentosum • Cockayne Syndrome
Disorders Associated with Defective DNA Repair
Ataxia oculomotor apraxia 1
AOA1 presents with early onset cerebellar ataxia, oculomotor apraxia, choreoathetosis, dystonia, axonal motor neuropathy, but no extra- neurological feature. Mild cognitive impairment may occur. In later stages, decreased serum albumin and increased total cholesterol may appear.
Aprataxin (APTX)
Imaging
[123I]FP-CIT
Diagnosis
We analyzed the PCR products by single-strand conformation polymorphism (SSCP) on PlusOne precast acrylamide gels (Pharmacia) with a Genephor electrophoresis device (Pharmacia) at two different running temperatures (5 °C and 20 °C) and then carried out silver staining. We sequenced the electrophoretic variants from both the forward and reverse strands after purification of the PCR products with the NucleoSpin Extract 2 in 1 kit (Macherey-Nagel GmbH). [Moreira et al. Nature Genetics 29, 189 - 193 (2001)]
Single Strand • AOA1 • SCAN1• AOA2 (?)• Xeroderma Pigmentosum • Cockayne Syndrome
Disorders Associated with Defective DNA Repair
121314 1615 17 1918 2021 232425 2622
TAGATG
123 4 5 6 7 89 10
Senataxin (SETX)
AOA2 presents with early onset cerebellar ataxia, oculomotor apraxia, choreoathetosis, dystonia, axonal motor neuropathy, but no extra- neurological feature. Early menopause may occur. Increased serum alphafetoprotein is a reliable peripheral marker.
Imaging
Back
Onset (years)Recessive ataxiaOculomotor apraxiaNeuropathy Choreothetosis Mental impairment α-fetoprotein Cholesterol Albumin ImmunoglobulinsTelangiectasesMalignanciesEarly menopause
1-4++++-+--+++
-
AT AOA12-30
++++
+/--++---
-
AOA210-22
++++-+++---
+
Double Strand
• Ataxia Telangiectasia• AT like disorder
Single Strand
• AOA1• AOA2 (?)• SCAN1• Xeroderma Pigmentosum • Cockayne Syndrome
Disorders Associated with Defective DNA Repair
Sporadic and autosomal recessive cases of ataxia with neuropathy negative for FRDA should be considered for screening of ataxia associated with defect of DNA repair (look for suggestive laboratory markers)