and the generous support of the patients and all individuals who donated biospecimens for study. L.M.M. is

A BS TRACT: 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.

BackgroundGerstmann‐Struassler‐Scheinker disease is one of the familial prion diseases secondary to mutations in the prion protein gene (PRNP). The clinical phenotype has a diverse spectrum and might show variation among cases with the same genotype. We report a patient with G131V mutation in the PRNP gene, who was initially considered to harbor familial Alzheimer’s disease, based on the family history, clinical presentation and imaging findings.MethodsA case with a G131V mutation in the PRNP gene is described, and the literature is reviewed.ResultsA 35‐year‐old man presented with personality changes, behavioral disturbances and cognitive complaints. A similar clinical phenotype was reported in the patient’s father, a paternal uncle and a paternal aunt. In conjunction with the observation of mild cerebral atrophy on magnetic resonance imaging and hypometabolism in bilateral temporal and parietal lobes on positron‐emission tomography studies, the diagnosis was initially considered as familial Alzheimer’s disease. However, whole‐exome sequencing of the index patient, confirmed with Sanger sequencing in his father and uncle, revealed the presence of a heterozygous G131V variant in the PRNP gene.ConclusionTo the best of our knowledge, this is the third report of a G131V mutation in the PRNP gene in the literature. Although ataxia and extrapyramidal findings accompanied dementia in patients reported in the previous literature, the members of the family in the present case primarily reported cognitive impairment, underscoring the importance of genetic evaluation in familial early‐onset dementia patients, regardless of clinical and imaging features suggestive of alternative pathologies.