The First Case of Autosomal Recessive Cerebellar Ataxia with Prominent Paroxysmal Non‐kinesigenic Dyskinesia Caused by a Truncating FGF14 Variant in a Turkish Patient

Abstract Background ATX‐ FGF /SCA27A has been exclusively associated with heterozygous variants in the FGF14 gene, presenting with postural tremor, slowly progressive cerebellar ataxia, and psychiatric and behavioral disturbances. Objectives This study describes the first case of ATX‐ FGF /SCA27A linked to a biallelic frameshift variant in the FGF14 gene. Methods Whole‐exome sequencing (WES) was conducted using the Illumina NovaSeq 6000 platform, and the identified variant was confirmed using Sanger sequencing. Results We report the first case of autosomal recessive FGF14 ‐related cerebellar ataxia caused by a c.75del variant resulting in p.Leu26Serfs*51 truncation of the FGF14 protein. This variant was found in a patient born to consanguineous parents and presented with a complex congenital nonprogressive cerebellar disorder accompanied by neurodevelopmental delay, intellectual disability, and prominent drug‐responsive paroxysmal non‐kinesigenic dyskinesia. Segregation analysis confirmed that the homozygous variant was inherited from heterozygous parents who developed mild gait ataxia and tremor in their 40s. Conclusions Biallelic loss‐of‐function variants in FGF14 are a rare cause of inherited cerebellar ataxia and expand the current genetic spectrum of ATX‐ FGF14 . © 2024 International Parkinson and Movement Disorder Society.