The Complex Genetic Landscape of Hereditary Ataxias in Turkey and Implications in Clinical Practice.

BACKGROUND: The genetic and epidemiological features of hereditary ataxias have been reported in several populations; however, Turkey is still unexplored. Due to high consanguinity, recessive ataxias are more common in Turkey than in Western European populations. OBJECTIVE: To identify the prevalence and genetic structure of hereditary ataxias in the Turkish population. METHODS: Our cohort consisted of 1296 index cases and 324 affected family members. Polymerase chain reaction followed by Sanger sequencing or fragment analysis were performed to screen for the trinucleotide repeat expansions in families with a dominant inheritance pattern, as well as in sporadic cases. The expansion in the frataxin (FXN) gene was tested in all autosomal recessive cases and in sporadic cases with a compatible phenotype. Whole-exome sequencing was applied to 251 probands, selected based on the family history, age of onset, and phenotype. RESULTS: Mutations in known ataxia genes were identified in 30% of 1296 probands. Friedreich's ataxia was found to be the most common recessive ataxia in Turkey, followed by autosomal recessive spastic ataxia of Charlevoix-Saguenay. Spinocerebellar ataxia types 2 and 1 were the most common dominant ataxias. Whole-exome sequencing was performed in 251 probands with an approximate diagnostic yield of 50%. Forty-eight novel variants were found in a plethora of genes, suggesting a high heterogeneity. Variants of unknown significance were discussed in light of clinical data. CONCLUSION: With the large sample size recruited across the country, we consider that our results provide an accurate picture of the frequency of hereditary ataxias in Turkey. © 2021 International Parkinson and Movement Disorder Society.

Elevated Global DNA Methylation Is Not Exclusive to Amyotrophic Lateral Sclerosis and Is Also Observed in Spinocerebellar Ataxia Types 1 and 2.

Adult-onset neurological disorders are caused and influenced by a multitude of different factors, including epigenetic modifications. Here, using an ELISA kit selected upon careful testing, we investigated global 5-methylcytosine (5-mC) levels in sporadic and familial amyotrophic lateral sclerosis (sALS and fALS), spinocerebellar ataxia types 1 and 2 (SCA1 and SCA2), Huntington's disease, Friedreich's ataxia, and myotonic dystrophy type 1. We report a significant elevation in global 5-mC levels of about 2-7% on average for sALS (p < 0.01 [F(1, 243) = 9.159, p = 0.0027]) and various forms of fALS along with SCA1 (p < 0.01 [F(1, 83) = 11.285], p = 0.0012) and SCA2 (p < 0.001 [F(1, 122) = 29.996, p = 0.0001]) when compared to age- and sex-matched healthy controls. C9orf72 expansion carrier ALS patients exhibit the highest global 5-mC levels along with C9orf72 promoter hypermethylation. We failed to measure global 5-hydroxymethylcytosine (5-hmC) levels in blood, probably due to the very low levels of 5-hmC and the limitations of the commercially available ELISA kits. Our results point towards a role for epigenetics modification in ALS, SCA1, and SCA2, and help conclude a dispute on the global 5-mC levels in sALS blood.

Phenotypic and Genotypic Analysis of Hereditary Ataxia Patients in Sakarya City, Turkey.

INTRODUCTION: Hereditary ataxias are a group of heterogeneous diseases in regard to their clinical and genetic characteristics. Ataxia that progresses slowly may be accompanied by pyramidal and extrapyramidal findings, articulation disorders, ophthalmic movement disorders, neuropathic complaints, cognitive and behavioral abnormalies, and epilepsy. Definitive diagnosis in hereditary ataxias is based on molecular assays. History, clinical examination, laboratory and neuroimaging assist diagnosis. In our study, thirty-seven patients of suspected hereditary ataxia were examined with their clinical and genetic aspects, and the results compared with literature. METHOD: Our study included 37 patients in 22 families who presented to our center between 2010-2016, and whose familial history and phenotypic features indicated hereditary ataxia. The patients were studied for clinical findings, family tree, neuroimaging, and laboratory findings. Advanced genetic investigations were performed on peripheral venous blood samples for hereditary ataxia. RESULTS: Of the 37 patients included in our study, 21 were females and 16 were males. Genetic analyses resulted in spinocerebellar ataxia (SCA) in four families (10 patients), Friedrich ataxia (FA) in three families (eight patients), and recessive ataxia due to point mutation in one family (two patients). SCA subtyping revealed SCA 1, 2, 6 and 8 in our patients. The remaining 16 patients included in our study could not be solved so far and are under investigation. CONCLUSION: Hereditary ataxias are rare neurodegenerative disorders. Large genetic pool, ethnic and local differences complicate diagnosing even further. Our study contributes to the literature by reflecting phenotypic and genotypic characteristics of hereditary SCA patients in our region and reporting rare hereditary ataxia genotypes.