Four Turkish families with hyperekplexia: A missense mutation and the exon 1-7 deletion in the GLRA1 gene.

BACKGROUND: Hyperekplexia is a disease that progresses with excessive startle attacks and is included in the differential diagnosis of epilepsy and many movement disorders. METHODS: The WES results were validated in available family members by Sanger sequencing, or in the case of deletion, PCR followed by agarose gel electrophoresis was performed. RESULTS: WES analysis revealed the previously reported homozygous c.277C>T p.Arg93Trp variant in the GLRA1 gene (ENST00000455880.2) in Family 1. In all other three families, the previously reported homozygous deletion of exons 1-7 of the GLRA1 gene was identified using CNV analysis based on the WES data. CONCLUSIONS: The homozygous exon1-7 deletion has been described several times in different populations and may be a founder mutation in the Kurdish people in Turkey. The family with Arg93Trp variant stems from the Black Sea region of Turkey where close consanguinity is common. These analyses are important to provide genetic counseling to families and for a better understanding of the pathophysiology of the disease.

Varied phenotypic spectrum presenting of paroxysmal exercise-induced dyskinesia: a Turkish family with SLC2A1 mutation.

INTRODUCTION: Paroxysmal exercise-induced dyskinesia (PED) is characterized by repeated episodes of involuntary movement disorders that are typically caused by prolonged walking or running and mostly caused by SLC2A1 gene mutations. Phenotypes vary from focal dystonia, ataxia, tremor, and complex non-kinesigenic movements to other movement disorders in patients with SLC2A1 mutation. Also, SLC2A1 mutations carriers may present with also other phenotypes such as epileptic seizure and migraine. CASE REPORTS: We report five patients with various phenotypic spectrums of PED in a Turkish family. Whole exome sequencing revealed a likely pathogenic synonymous variant p.Ser324Ser (c.972G > A) in the SLC2A1 gene (ENST00000426263.3) and the variant segregated in all affected family members. Also, other than PED, the phenotypical spectrum of affected individuals in this family includes epilepsy, mental retardation, and weakness. CONCLUSIONS: We concluded that family members with the same SLC2A1 gene mutation may show very heterogenous phenotypes. Clinicians should be aware of wide variety of symptoms of the patients with PED. We also emphasized that even if a mutation in the coding sequence does not make an amino acid change, it may cause the disease.

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.

A novel PNPLA6 mutation in a Turkish family with intractable Holmes tremor and spastic ataxia.

Autosomal recessive cerebellar ataxias are a group of rare neurological diseases with a genetic origin. Recently, the mutations in the PNPLA6 gene were suggested to lead to ataxia and also to other specific syndromes such as Boucher-Neuhauser (ataxia, hypogonadism, and chorioretinal dystrophy) or Gordon-Holmes Syndromes (ataxia, hypogonadism, and brisk reflexes) within a broad spectrum of neurodegenerative diseases. Here we report three patients from a single-family with a novel pathogenic mutation in the PNPLA6 gene which led to predominantly spastic-ataxia, and intractable Holmes tremor. The PNPLA6-related disease should be considered in the differential diagnosis of spastic-ataxias even in the absence of chorioretinal dystrophy, and hypogonadotropic hypogonadism. Further studies should unravel the factors which account for the phenotypic variability present in patients with PNPLA6 gene mutations.