to determine the frequency and the phenotypical spectrum of SCA15 patients.
in the index cases of 333 families with autosomal dominant cerebellar ataxia (ADCA) negative for CAG repeat expansions in coding exons (SCA1,2,3,6,7,17 and dentatorubropallidoluysian atrophy), we searched for heterozygous rearrangements in ITPR1. Taqman PCR (258 index cases) or SNP genome-wide genotyping (75 index cases) were used.
a deletion of ITPR1 was found in 6/333 (1.8%) families, corresponding to 13 SCA15 patients. Age at onset ranged from 18 to 66 years with a mean of 35±16 years. The symptom at onset was mainly cerebellar gait ataxia, except for one patient presenting with isolated upper limb tremor. Although we tested a large cohort of families irrespective of their phenotype, the main clinical features of SCA15 patients were homogeneous and characterized by a very slowly progressive gait and limb cerebellar ataxia with dysarthria. However, pyramidal signs (two patients), and mild cognitive problems (two patients) were occasionally present. Ocular alterations consisted of nystagmus, mainly horizontal and gaze-evoked (ten patients), and saccadic pursuit (seven patients). Radiological findings showed global or predominant vermian cerebellar atrophy in all patients.
In this series ITPR1 deletions are rare and account for ~1% of all ADCA. The SCA15 phenotype mostly consists of a slowly progressive isolated cerebellar ataxia with variable age at onset; an additional pyramidal syndrome and problems in executive functions may be present in a minority of patients.