A “dose” effect of mutations in the GBA gene on Parkinson's disease phenotype

Objective Mutations in the GBA gene are associated with Parkinson's disease (PD). A definite description of the clinical characteristics of PD patients who are compound heterozygotes or homozygotes for mutations in the GBA gene (GD-PD) requires further elucidation. Methods We assessed motor, cognitive, olfactory and autonomic functions as well as demographic data and medical history in a cohort of Ashkenazi Jewish PD patients who were screened for seven common mutations in the GBA gene. We then compared three groups of patients (matched for age and disease duration) who were distinguished by their GBA mutation status, idiopathic PD (iPD), GBA heterozygote PD (GBA-PD) and GD-PD. Results Out of a total of 1050 AJ PD patients screened, 12 were found to be either homozygotes or compound heterozygotes for mutations in the GBA gene. These patients had an earlier age of onset, more severe motor impairment, poorer cognition and lower olfactory scores. They also had a higher prevalence of REM sleep behavior disorder and higher frequencies of hallucinations compared to both GBA-PD and iPD. Conclusions The severity of PD phenotype is related to the burden of GBA mutations with GD-PD patients manifesting a more severe phenotype.