New Subtype of Spinocerebellar Ataxia With Altered Vertical Eye Movements Mapping to Chromosome 1p32

Importance: To provide clinical and genetic diagnoses for patients' conditions, it is important to identify and characterize the different subtypes of spinocerebellar ataxia (SCA). Objective: To clinically and genetically characterize a Spanish kindred with pure SCA presenting with altered vertical eye movements. Design: Family study of ambulatory patients. Electro-oculographic and genetics studies were performed in 2 referral university centers. Setting: Primary care institutional center in Spain. Participants: Thirty-six participants from a large Spanish kindred were clinically examined, and 33 family members were genetically examined. Detailed clinical data were obtained from 9 affected relatives. Two ataxic siblings and 2 asymptomatic family members were examined using an enhanced clinical protocol for a follow-up period of 7 years. Main Outcomes and Measures: High-density genome-wide single-nucleotide polymorphism arrays, along with microsatellite analysis, and genetic linkage studies were performed. Whole-exome sequencing was used for 2 affected relatives. For most patients, the initial symptoms included falls, dysarthria, or clumsiness followed by a complete cerebellar syndrome. For all 9 affected relatives, we observed altered vertical eye movements, as initial ocular signs for 3 of them and for the 2 asymptomatic family members, all having inherited the risk haplotype. Neuroimaging showed isolated cerebellar atrophy. Results: Initial genome-wide linkage analysis revealed suggestive linkage to chromosome 1p32. Multipoint analysis and haplotype reconstruction further traced this SCA locus to a 0.66-cM interval flanked by D1S200 and D1S2742 (z(max)=6.539; P < .0001). The causative mutation was unidentified by exome sequencing. Conclusions and Relevance: We report a new subtype of SCA presenting in patients as slow progressing ataxia with altered vertical eye movements linked to a 11-megabase interval on 1p32. The Human Genome Nomenclature Committee has assigned this subtype of ataxia the designation SCA37.