Prevalence and clinicoradiological features of spinocerebellar ataxia type 34 in a Japanese ataxia cohort

Introduction: Spinocerebellar ataxia (SCA) type 34, a form of autosomal dominantly inherited ataxia, has recently been associated with mutations in the ELOVL4 gene. However, a genetic study of the prevalence of SCA34 in an ataxia cohort has never been reported. Methods: We performed a mutation screening of ELOVL4 in a cohort of 153 undiagnosed index ataxia patients, selected after excluding for common SCA types, in a series of 506 Japanese index ataxia patients. Results: Heterozygous mutation c.698C > T (p.T233M) was detected in an index patient with multisystem neurodegeneration including ataxia and erythrokeratodermia skin lesions, an archetypal skin phenotype in SCA34. The patient's father also presented with ataxia but not skin lesions. Although this mutation has been recently reported in a single English-Canadian patient, the present study confirms its cosegregation with the ataxia phenotype in the Japanese kindred. Brain magnetic resonance imaging (MRI) of the patient and his father revealed marked pontine and cerebellar atrophy as well as the hot cross bun sign, that is common in cerebellar type of multiple system atrophy and was also described in SCA34 patients harboring two other mutations: p.L168F and p.W246G. Conclusion: This represents the first genetic study of the prevalence of SCA34 in an ataxia cohort and demonstrates its low prevalence (0.2%) in ataxia patients. The broad SCA34 clinical spectrum suggests variable multisystem neurodegeneration. Clinicians should be aware of this rare disease entity, particularly if erythrokeratodermia or the hot cross bun sign in MRI are present in undiagnosed degenerative ataxia patients.