First finding of familial spinal cerebellar Ataxia11 in China: clinical, imaging and genetic features

Abstract

Spinal cerebellar ataxia 11 (SCA11) is a rare disease, characterized by progressive cerebellar ataxia, abnormal eye sign. Four families have been reported in the past. We report on China's first family with spinocerebellar ataxia 11. A careful investigation of the clinical manifestations, brain imaging, and exome and Sanger sequencing were utilized to identify pathogenic genetic variants in a three-generation pedigree that includes 5 affected individuals. The proband and affected members began to develop cerebellar ataxia, dysarthria, nystagmus, and strabismus at approximately age 40 for no apparent reason. The lifespan of patients in the family is shortened. Brain MRIs showed cerebellar atrophy and slight atrophy of the bulbar medulla. Electromyography showed extensive neurogenic damage. Sensory evoked potentials of lower limbs showed damage to the spinal-brainstem-cortical conduction pathway. Genetic analysis revealed a novel point mutation (c.3290T>C) in the TTBK2 gene encoding tau-microtubule kinase 2, which led to an amino acid exchange (p.Val1097Ala). The missense mutation segregated with the phenotype. The mutation has a very low mutation rate in the population, the variant amino acids are highly conserved among species, and protein function damage prediction at the mutation site is detrimental and is highly likely to cause protein damage. The pathogenicity prediction of the mutation site shows that it is likely to cause disease. This variation is consistent with the diagnosis of SCA11. The first SCA11-affected family in China was characterized by gait instability, movement disorders and dysarthria with obvious cerebellar atrophy. The pathogenic allele was a c.3290T>C mutation in the TTBK2 gene.