Genetic Mechanism of Conserved Ancestral Haplotype in SCA10

The Methodist Hospital Research Institute100 enrolled

Overview

Spinocerebellar ataxia type 10 (SCA10) is a hereditary ataxia whose ancestral mutation occurred in East Asia. The mutation is likely to have migrated during peopling of American continents from East Asia. We found a specific rare DNA variation associated with SCA10. We test whether this variation played a key role in the birth and subsequent spreading of SCA10 mutation.

Spinocerebellar ataxia type 10 (SCA10) is a rare ataxic disorder due to a large expansion of intronic (ATTCT)n repeat in ATXN10. SCA10 afflicts primarily Latin American (LA) populations of Native American Ancestry; recent discoveries of two East Asian (EA) SCA10 families suggests an Asian origin. SCA10 families from LA and EA share an ancestral haplotype that includes the G allele (allele frequency: 2-4% in EA and LA populations but 0% elsewhere) of a C/G/T single nucleotide polymorphism (SNP) at rs41524745 (https://www.ncbi.nlm.nih.gov/snp/rs41524547#frequency\_tab). Two characteristics suggest that rs41524745 has a functional role over the expansion: this SNP resides in the sequence encoding miR4762; and total linkage between the SNP and the SCA10 repeat, although they are \~35kb apart, a distance sufficient for multiple recombination events within the 15,000-20,000 years since human migration across Bering landmass. We studied DNA samples with G allele at rs41524547 from the 1000 Genomes repository and our own samples from general populations and surprisingly found 0-25% of these G(+) samples have SCA10 repeat expansions. Since our genotype-phenotype data suggest that SCA10 expansions with (ATTCC)n or (ATCCT)n(ATCCC)n repeat insertion in the 3' end of (ATTCT)n expansion exhibit full penetrance while pure (ATTCT)n expansion has reduced penetrance, the last one can be more common than previously expected. Hypotheses: (1) the G allele at rs41524547 predisposes the SCA10 (ATTCT)n repeat for expansion (Type A expansion), that remains mostly non-penetrant, and (2) the (ATTCT)n-(ATTCC)n (Type B) or (ATTCT)n(ATCCT)n-(ATCCC)n (Type C) repeat drives the SCA10 pathogenicity. To test the hypothesis, we propose three Aims in close collaborations between US and Brazilian SCA10 consortia: Aim 1. To determine the relationship between SCA10 and the G allele at rs41524547. Aim 2. To confirm that Type B and Type C expansions are pathogenic, but Type A expansions have significantly reduced pathogenicity. Aim 3. To determine if the G allele at rs41524547 reduces downstream recombination rates, protects against the toxicity of SCA10 RNA expansions, or promote expanded states of the SCA10 repeat. This effort will enable long term goals to: (1) identify people at risk for SCA10 by high-throughput screening of general populations for the G allele at rs41524547 in Brazil, (2) determine the frequency of non-penetrant SCA10 expansion alleles in Brazil, and (3) develop treatments of SCA10 based on results of this project. The proposed project requires complimentary expertise in multiple areas, including coordination of the clinical studies, along with recruitment plans and executions, management of tissue repository, maintenance and expansion of the clinical database, clinical MR technology and data analyses, which will be ongoing in both the US and Brazil.

Study Type

OBSERVATIONAL

Enrollment

100

Conditions

Spinocerebellar Ataxia Type 10

Interventions

Non-interventional studyOTHER

There are no treatments to stop or even slow down the progression of this disease although there are treatments that temporarily improve the symptoms, such as anti-seizure medications.

Eligibility

Sex: ALLMin age: 18 YearsHealthy volunteers:

Medical Language ↔ Plain English

Inclusion Criteria: 1. Signed informed consent (no study-related procedures may be performed before the subject has signed the consent form). 2. Participants of either sex aged ≥18 with presence of symptomatic ataxic disease with definite molecular diagnosis of SCA10 or whose first-degree relative has a molecular diagnosis of SCA10. 3. Asymptomatic participants of either sex aged ≥18 with definite molecular diagnosis of SCA10 (Premanifest carriers) or those whose first-degree relative has a molecular diagnosis of SCA10 (50%-at-risk relatives\*). 4. Participants capable of understanding and complying with protocol requirements. Exclusion Criteria: 1. Known genotype consistent with other inherited ataxias. 2. Concomitant disorder(s) or condition(s) that affects assessment of ataxia or severity of ataxia during this study. 3. Unwillingness to provide a DNA sample at study entry. 4. Inability to undergo MRI scanning, Weight over 300lbs, Presence of structural abnormalities such as subdural hematoma or primary or metastatic neoplasms, concurrent illnesses or treatment interfering with cognitive function such as stroke or normal pressure hydrocephalus.

Locations (3)

Houston Methodist Hospital

Houston, Texas, United States

RECRUITING

Universidade Federal do Paraná

Paraná, Curibita, Brazil

RECRUITING

Hospital de Clinicas de Porto Alegre

Porto Alegre, Brazil

RECRUITING

Outcomes

Primary Outcomes

Examine the disease progression in SCA10 as determined by change in the scale for the assessment and rating of ataxia score compared to healthy controls

Scale for the assessment and rating of ataxia (SARA) was evaluated in two large validation trials performed by the EUROSCA clinical group and was found to be easy to use, reliable and valid. SARA has eight categories with accumulative score ranging from 0 (no ataxia) to 40 (most severe ataxia).

Time frame: Baseline visit 1, Follow up visit (12-18 months after visit 1)

Examine the disease progression in SCA10 as determined by change in Spinocerebellar Ataxia Functional Index score compared to healthy controls

The Spinocerebellar Ataxia Functional Index (SCAFI) is composed of: 1. Timed 8 meter walk at maximum speed (8MW). Times are only given for two successfully completed trials. Discontinue the test if participant cannot complete trial in 3 minutes (more severe ataxia). 2. Timed dexterity test: 9-hole peg test (9HPT). Times are only given for two successfully completed trials for each hand. If participant cannot complete one trial in 5 minutes (more severe ataxia) discontinue 9-hole-peg test. 3. Timed speech test: PATA rate, a measure of speech performance. The participant is asked to repeat "PATA" as quickly and distinctly as possible for 10 seconds until told to stop. As soon as the participant begins speaking, start timer and begin counting the number of PATA repeats. Higher number (less dysarthria), lower number (more dysarthria). Discontinue if PATA articulation is too difficult to distinguish for counting or if participant cannot complete 10 seconds for two consecutive trials.

Time frame: Baseline visit 1, Follow up visit (12-18 months after visit 1)

Examine the disease progression in SCA10 as determined by change in Composite Cerebellar Functional Severity Score compared to healthy controls

The Composite Cerebellar Functional Severity (CCFS) score is a quantitative tool to measure cerebellar severity independently from age. It is an assessment in addition to a clinical examination and has demonstrated its usefulness in epidemiological studies, clinical trials, and patient follow-up that only take 5 minutes to be administrated. The CCFS is a combination of the time to perform 2 tasks; a 9-hole pegboard and a click test. It was validated in adults and children. CCFS scores range from 0.50 (normal/no ataxia) to 1.80 (more severe ataxia).

Central Contacts

Tetsuo Ashizawa, MD

CONTACT

713-441-8224 tashizawa@houstonmethodist.org

Titilayo Olubajo, CCRP

CONTACT

713-363-9803 tolubajo@houstonmethodist.org

Data from ClinicalTrials.gov

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