Functional characterization of two KCND3 variants associated with SCA 19/22 ataxia in Latin American families.

backgroundSpinocerebellar ataxia 19/22 (SCA19/22) represents a rare autosomal dominant genetic disorder resulting in progressive ataxia and cerebellar atrophy. SCA19/22 is caused by variants in the KCND3 gene, which encodes a voltage-gated potassium channel subunit essential for cerebellar Purkinje cell function. To date, 22 variants have been reported worldwide, with incomplete functional studies.

resultsWe present four Chilean and Mexican cases in whom two single-nucleotide variants were identified through whole-exome sequencing of the probands. One variant (G371R) was initially cataloged as pathogenic and the other (S357W) as likely pathogenic according to the American College of Medical Genetics and Genomics criteria. The pathogenicity of the G371R variation was confirmed by in-silico mutagenesis. Our molecular models, that include electrostatic potential analysis and algorithms to analyze the pore dimensions (HOLE), indicated that the longer side chain of the arginine narrowed the channel's selectivity filter, while the positive charge modified its surface electrostatic potential, presumably preventing potassium flux. Functional characterization of the S357W variant was performed in AD293 cells. When overexpressed, K

conclusionsThis functional characterization of two KCND3 variants associated with SCA19/22 adds new evidence for the pathogenic role of Kv4.3 loss-of-function mutations and establishes a correlation between functional dominance and clinical severity in SCA19/22.