Clinical Features and Molecular Genetics of

Hereditary Cerebellar Ataxia

Franca Cambi, MD, PhD

Professor Neurology

University of Kentucky

Outlines• Clinical manifestations

• Differential Diagnosis

• Genotypes and Molecular Diagnosis

• Molecular mechanisms

• Current treatments

• Future treatments

1. SPORADIC ATAXIA

2. AUTOSOMAL DOMINANT ATAXIA

3. AUTOSOMAL RECESSIVE ATAXIA

4.X-LINKED ATAXIA

Presentation

Clinical Manifestations

Ataxia of gait

Dysarthria

Sensory deficits

Spasticity

Retinopathy and optic atrophy

Parkinsonian features

Epilepsy

PATIENT 1 47 year-old gentleman with 7-8 year-history of progressive problems with balance

Normal development, was very athletic

First symptom was slurring of speech

Followed by ataxia of gait

No sensory, memory, visual, sphincter deficits

Family History: negative, parents still alive, mother may have mild dementia. No history of consanguinity.

Blood tests prior to his visit: gliadin and tissue trans-glutaminase antibodies were negative. Transaminase, vitamin E, sed rate, ANA, Lyme titer, TSH, SSA, SSB, methylmalonic acid, homocysteine within normal limits.

MRI Patient 1

PATIENT 2

53 year-old gentleman with 10 year-history of progressive problems with balance

Normal development, was very athletic

First symptom was ataxia of gait

Followed by slurring of speech

Urinary urgency and cramps

Family History: Positive for cerebellar ataxia in 5 of his 7 siblings and in his mother deceased at 72. Earlier onset of disease in sibs (~35) and different severity of disease.

Patient 2

Differential Diagnosis1. Tumors in the posterior fossa

2. Paraneoplastic syndrome (Yo antibody)

3. Vitamin B12 deficiency

4. Multiple Sclerosis

5. Ataxia associated with gliadin and tissue transglutaminase antibodies (Sprue)

6. Vitamin E deficiency

7. Alcohol abuse

8. Late sequela of Dilantin use

9. Cerebellar variant of prion disease

10. Multisystem atrophy-C

Autosomal Dominant Cerebellar Ataxias(Harding’s Classification)

ADCAI ADCAII ADCAIII

Cerebellar syndrome Cerebellar syndrome Pure cerebellarWith involvement of other with pigmentary syndromeCNS systems retinopathy

GenotypesSCA1,2,3,4,12,13**,17,8,23*,25* SCA7

SCA5**,6,8,10+,11*,14**,26*,27**, 28*,29* 15, 16, 22*

* Gene not identified+ Repeat (ATCCT), associated with epilepsy**point mutation

Movement Disorders Vol 20, 11: 2005

Parameter SCA 1 SCA 2 SCA 3 SCA 4 SCA 5 SCA 6 SCA 7 SCA 8

N 13 19 20 14 16 27 7 11

Families, n (%) 5 (10) 10 (20) 17 (33) 2 (4) 1 (2) 10 (20) 2 (4) 4 (8)

Age at onset

   Mean ± SD (yr) 30 ± 9 29 ± 11 33 ± 11 36 ± 8 33 ± 10 47 ± 11 32 ± 8 37 ± 14

   Range (yr) 18-45 15-55 14-62 25-49 17-51 24-63 25-48 25-66

Disease duration

   Mean ± SD (yr) 11 ± 8 15 ± 11 9 ± 6 11 ± 10 17 ± 10 13 ± 9 8 ± 5 15 ± 11

   Range (yr) 2-25 1-37 0.5-25 1-32 4-30 0.5-30 3-18 0.5-37

No walking aid/wheelchair (%)

70 63 45 57 81 44 57 55

Progression to cane (n) 0 2 4 1 0 3 0 2

   Range (yr)  -  8-19 7-10 28  -  7-8  -  4-8

Age of Onset, Disease Duration and Rate of Progression

SCA 1 SCA 2 SCA 3 SCA 4 SCA SCA 6 SCA 7 SCA 8

Progression to cane (n) 0 2 4 1 0 3 0 2

   Range (yr)  -  8-19 7-10 28  -  7-8  -  4-8

Progression to walker (n) 1 3 1 1 0 2 0 1

   Range (yr) 9 13-28 12 8 0 17-23 0 31

Progression to wheelchair (n)

3 3 6 3 1 10 3 2

   Mean ± SD (yr) 13 ± 9 27 ± 9 13 ± 6 16 ± 12 5 17 ± 6 13 ± 6 21 ± 11

   Range (yr) 5-22 20-33 5-20 3-25 5 9-24 9-18 13-29

Genetic Features of SCADisease Gene Repeat Range Range

product normalpathologic

SCA1 ataxin1 CAG 6-44 39-83

SCA2 ataxin2 CAG 14-31 33-64

SCA3 ataxin3 CAG 12-40 54-86

SCA5 SPTBN2 point mutation (spectrin beta III)SCA6 CACNA1A CAG 4-20 20-31

SCA7 ataxin7 CAG 4-27 37->200

SCA8 kelch like CTG 15-91 100-155antisense

Genetic Features of SCADisease Gene Repeat Range Range

product normal pathologic

SCA10 ataxin10 ATTCT 6-44 39-83

SCA12 PPP2R2B CAG <29 66-93(brain specific ser-thr PP2)

SCA13 KCNC3 point mutations(voltage-dep K channel)

SCA14 PRKCG point mutations(protein kinase C gamma)

SCA17 TBP CAG 25-42 45 and 63(Tata box binding protein)

SCA27 FGF14 point mutations

(fibroblast growth factor)

CAG repeats in coding regions result in polyQ (polyglutamine stretches) in the protein product

Two Classes of Triplet Repeat Disorders

• 1) Translated Triplet Repeat Diseases

• 2) Untranslated Triplet Repeat Diseases

Translated (polyQ) triplet repeat disorders

• Disease Triplet repeatssequence

• HD CAG

• SCA 1,2,3,6,7,17 CAG

• DRPLA CAG

• Kennedy’s Disease (SBMA) CAG

Features of PolyQ Disorders

• Mode of inheritance is Autosomal Dominant except for SBMA, which is X-linked

• Neurodegeneration of specific neurons

• Mechanism of disease: Protein gain of function

Untranslated triplet repeat disorders

• Disease Triplet repeatsequence

• FRDA GAA (intron 1)

• SCA 8 CTG (3’ UTR)

• SCA10 ATTCT (intron)

• SCA12 CAG (5’ UTR)

• Myotonic Dystrophy CTG (3’ UTR)

• Fragile X MR/tremors-ataxia syndrome CGG (promoter)

Features of untranslated triplet repeat disorders

• Mode of inheritance: AD, AR and X-linked, likely reflects the mechanism of disease

• Neurodegeneration of specific neurons

• Systemic manifestations

• Multiple mechanisms of disease: loss of function and RNA dominant/gain of function

Untranslated Ataxic Disorders

Friedreich’s ataxia

Fragile X Tremors-Ataxia Syndrome (FXTAS)

SCA8, 10 and 12

Friedreich’s Ataxia (FRDA)

• Most common hereditary ataxia

• Autosomal Recessive

• Prevalence: 1 in 50,000-29,000

• Carrier rate:1 in 120-60

Essential Clinical Features(Harding)

• AR• Onset before 25 years• Progressive limb and gait ataxia• Absent DTR’s in legs• Axonal sensory neuropathy followed by

( 5 years)• Dysarthria, loss of proprioception, areflexia

of 4 limbs, extensor plantar response and pyramidal signs

Systemic Manifestations

• Cardiomyopathy

• Diabetes

• Hearing loss

• Scoliosis

• Pes cavus

• Amyotrophy

Other forms of FRDA

Late-onset FA, older than 20, more slowly progressive less frequent scoliosis and pes cavus

FRDA with retained reflexes, have all features except retain reflexes, less severe sensory neuropathy

Neuropathology

• Loss of large primary neurons in DRG early finding

• Degeneration of dorsal columns, corticospinal (distal to proximal) and spinocerebellar tracts, loss of axons in nerves

• MRI shows cord atrophy, normal cerebellum and brainstem

Cord pathology in FRDA

Early onset AR ataxiasAtaxia with ocular apraxia Type 1(AOA1) and Type 2 (AOA2)– Ocular apraxia, severe sensorimotor neuropathy,

cognitive deficits, hypoalbuminemia, hypercholesterolemia, increased α-fetoprotein (AOA2)

– Cerebellar atrophy on MRI– Mutations in aprataxin1 and senataxin, RNA helicase

Ataxia with vitamin E deficiency (α-tocoferol transfer protein)

Ataxia-telangectasia (phosphatidylinositol-kinase protein)

Molecular Genetics of FRDA

• 96% of cases carry expansion of GAA repeats in intron1 of the frataxin gene (120-1700) in both alleles

• 4% cases are compound heterozygotes and have 1 allele with GAA expansion and other allele with point mutations

• Variants of FRDA are caused by shorter expansions in frataxin

FRAX Molecular Diagnosis

Repeat length Interpretation

6-60 Normal

60-200 Premutation causing tremor-ataxia (FXTAS)

>200 Full mutations, completely penetrant in males and 50% penetrant in females

MOLECULAR DIAGNOSIS

Complete Ataxia Evaluation #690

Type of Disorder: Movement Disorders

Typical Presentation: Ataxia, poor coordination of hand, speech and eye movements, uncoordinated and unsteady gait

Disease(s) tested for:SCA1, SCA2, SCA3 (MJD), SCA6, SCA7, SCA8, SCA10, SCA13, SCA14 SCA17, AVED, MSS, Aprataxin, DRPLA & Friedreich's ataxias

Aprataxin DNA Sequencing Test , DRPLA DNA Test, Friedreich Ataxia DNA Test, MIRAS-Specific POLG1 DNA Test, SCA1 DNA Test, SCA10 DNA Test, SCA13 Select Exon DNA Test, SCA14 DNA Test, SCA17 DNA Test, SCA2 DNA Test, SCA3 (Machado-Joseph Disease) DNA Test, SCA6 DNA Test, SCA7 DNA Test, SCA8 DNA Test, SETX DNA Sequencing Test, SIL1 (Marinesco-Sjogren Syndrome) DNA Sequencing Test, TTPA (Ataxia with Vitamin E Deficiency) DNA Sequencing Test

Genetic Testing (Athena Diagnostics)

Autosomal Dominant Ataxia Evaluation #680

Type of Disorder: Movement Disorders

Typical Presentation: Ataxia, poor coordination of hand, speech and eye movements, uncoordinated and unsteady gait

Disease(s) tested for:SCA1, SCA2, SCA3 (MJD), SCA5, SCA6, SCA7, SCA8, SCA10, SCA13, SCA14, SCA17 & DRPLA

DRPLA DNA Test, SCA1 DNA Test, SCA10 DNA Test, SCA13 Select Exon DNA Test, SCA14 DNA Test, SCA17 DNA Test, SCA2 DNA Test, SCA3 (Machado-Joseph Disease) DNA Test, SCA5 Select Exon DNA Test, SCA6 DNA Test, SCA7 DNA Test, SCA8 DNA Test

Genetic Testing (Athena Diagnostics)

Frequency of SCA typesSCA3 is the most common (30-40%)AKA: Machado-Joseph DiseaseIn the US most common in East Coast, NE,

Rhode Island, Maryland, NC and in West Coast (CA), migration of Portuguese immigrants

SCA2 accounts for ~15-20%SCA1 accounts for ~10%Note: OPCA (MRI shows pontocerebellar

atrophy) is associated with SCA1 and 2SCA10, epilepsy

PATIENT 2

53 year-old gentleman with 10 year-history of progressive problems with balance

Normal development, was very athletic

First symptom was ataxia of gait

Followed by slurring of speech

Urinary urgency and cramps

Family History: Positive for cerebellar ataxia in 5 of his 7 siblings and in his mother deceased at 72. Earlier onset of disease in sibs (~35) and different severity of disease.

DNA testing: SCA2

PATIENT 1 47 year-old gentleman with 7-8 year-history of progressive problems with balance

Normal development, was very athletic

First symptom was slurring of speech

Followed by ataxia of gait

No sensory, memory, visual, sphincter deficits

Family History: negative, parents still alive, mother may have mild dementia. No history of consanguinity.

Blood tests prior to his visit: gliadin and tissue trans-glutaminase antibodies were negative. Transaminase, vitamin E, sed rate, ANA, Lyme titer, TSH, SSA, SSB, methylmalonic acid, homocysteine within normal limits.

DNA testing: SCA8

Copyright restrictions may apply.

Nemes, J. P. et al. Hum. Mol. Genet. 2000 9:1543-1551; doi:10.1093/hmg/9.10.1543

SCA8 Gene

Importance of Genetic Testing

Genetic Counseling for children and siblings

Prognosis

Future Treatments

Current Treatments

• Physical Therapy

• Speech and Swallowing Evaluation

• Supportive Devices: cane, walker, wheelchair

• Antioxidants

FUTURE TREATMENTS

Based on pathogenesis and tailored to the

genetic type

Two Classes of Triplet Repeat Disorders

Untranslated Triplet Repeat Diseases

Translated Triplet Repeat Diseases

GAA Expansion in frataxin gene

Mechanism of decreased frataxin expression

Reduced frataxin expression leads to mitochondrial dysfunction

Treatment for FRDA

• Frataxin is a mitochondrial protein that regulates iron metabolism in mitochondria

• Increased iron accumulation reacts with oxygen (H2O2-HOº,Fenton reaction) and causes oxidative stress

• Treatment with Fe chelators (?) and antioxidants (idebenone, analog of CoQ10)

Pandolfo M (2008) Drug Insight: antioxidant therapy in inherited ataxiasNat Clin Pract Neurol 4: 86–96 10.1038/ncpneuro0704

Table 2 Doses of idebenone used in the NIH phase II trial (placebo-controlled, double-blinded to assess tolerability and initial efficacy determination)

Translated (polyQ) triplet repeat disorders

• Disease Triplet repeatssequence

• HD CAG

• SCA 1,2,3,6,7,17 CAG

• DRPLA CAG

• Kennedy’s Disease (SBMA) CAG

Gain-of-function

“Although genetic evidence consistently indicates that a gain-of-function mechanism of pathogenesis is critical for each of the polyglutamine-induced diseases, the extent to which there might be a specific pathogenic pathway common among these disorders remains unresolved”.

Annu Rev Neurosci, 2007, Orr and Zoghbi

Gain-of-function

“It is becoming increasingly apparent that each polyglutamine disorder is, to a large degree, defined by the actions of the expanded polyglutamine tract in the context of the “host” protein (Gatchel & Zoghbi 2005, Orr 2001). Central to this idea is the concept that the normal function and interactions of each disease-associated polyglutamine protein are critical for defining the pathogenic pathway”.

Annu Rev Neurosci, 2007, Orr and Zoghbi

Gain-of-function: SCA1 as an example

• ATXN1 is widely expressed in all neurons and it localizes in the nucleus

• ATXN1 interacts with RNAs, shuttles between nucleus and cytoplasm and interacts with transcription factors

• The polyQ changes the properties of ATXN1 and its interactions with transcription factors leading to neurodegeneration

Gain-of-function in SCA1: alteration in transcription factors

Future Treatments for SCA Associated with polyQ

• Neuroprotective agents: high doses of CoQ10 and creatine (in testing for Huntington Disease)

• HDAC inhibitors (corrects abnormal transcription)

• Lithium (shown to be effective in mouse model of SCA1, affects transcription, inhibits GSK3)

• Genetic treatment aimed at reducing the amount of mutated gene for SCA: siRNA and microRNA as potential modulators