New mutations in protein kinase Cγ associated with spinocerebellar ataxia type 14

Autosomal dominant cerebellar ataxias (ADCA) arc a heterogeneous group of neurological disorders. Point mutations in the gene encoding protein kinase C gamma (PRKCG) are responsible for spinocerebellar ataxia 14 (SCA14). We screened for mutations in the PRKCG gene, in a large series of 284 ADCA index cases, mostly French (n=204) and German (n=48), in whom CAG repeat expansions in the known SCA genes were previously excluded. Six mutations were found that segregated with the disease and were not detected on 560 control chromosomes, including F643L (exon 18), already reported in another French kindred. Five new missense mutations were identified in exons 4 (C114Y/G123R/G123E), 10 (G360S) and 18 (V692G). All but one (V692G) were located in highly conserved regions of the regulatory or catalytic domains of the protein. All six SCA14 families were French and there was no evidence of reduced penetrance. The phenotype consisted in a very slowly progressive cerebellar ataxia with a mean age at onset of 33.5 +/- 14.2 years (range 15 to 60 years), occasionally associated with executive dysfunction, myoclonus, myorythmia, tremor or decreased vibration sense. SCA14 represented only 1.5% (7/454) of French ADCA families but none of the German families. It should, however, be considered in patients with slowly progressive ADCA, particularly when myoclonus and cognitive impairment are present.