Objective: To describe and correlate the genotype and phenotype of patients diagnosed with SCAs.

Background: Spinocerebellar Ataxias (SCAs) are neurodegenerative diseases with autosomal dominant inheritance and phenotypic-genotypic heterogeneity. The most common SCA is the Machado-Joseph disease (SCA3), followed by SCA2, SCA1 and SCA6. SCA10 is more commonly found in Mexico and South America, particularly in populations with Amerindian descent.

Method: Data were collected from the records of our ataxia outpatient clinic considering the genetic diagnosis of SCA in the index case of each family. The inclusion criteria were met by 460 patients from 213 families. These patients were divided into four groups: SCA3, SCA10, Other SCAs and Without Mutation.

Results: The most frequent subtype was SCA3 (n=210, 45.7%), followed by SCA10 (n=84, 18.3%) and Other SCAs (n=61, 13.3%). Patients without a confirmed mutation represented a total of 105 cases (22.8%). Statistically significant (p<0.05) differences were observed for several symptoms when comparing SCA3 and SCA10. We highlight the presence of bulging eyes in 57.6% of patients with SCA3 and 1.2% with SCA10 (p<0.001); horizontal ophthalmoplegia in 67.5% of patients with SCA3 and 9.5% with SCA10 (p<0.001) and vertical ophthalmoplegia in 23.5% of patients with SCA3 and 1.3% with SCA10 (p<0.001). The prevalence of epilepsy in SCA10 patients was 4.8%.

Conclusion: We observed a high frequency of SCA10 when compared to data from other studies, which can be explained by a founder effect caused by the large number of Amerindian descendants in our region. In addition, we found several symptoms that may clinically differentiate SCA3 from SCA10, thus helping neurologists request the right confirmatory genetic test and define prognosis. Furthermore, the low prevalence of epilepsy in our SCA10 patients suggests a genetic variation of the disease, which is typically defined as an association between ataxia and epilepsy. This variation may be explained by a different pattern of interruptions in the mutated ATTCT genetic sequence and additional studies are required to confirm this hypothesis. Presented at the 70th AAN Annual Meeting in April 22, 2018 and at the XXVIII Brazilian Congress of Neurology in October 13, 2018.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/spinocerebellar-ataxias-in-southern-brazil-genotypic-and-phenotypic-evaluation-of-213-families/