A molecular analysis of the GBA gene in Caucasian South Africans with Parkinson's disease

BACKGROUND The molecular basis of Parkinson's disease in South African population groups remains elusive. To date, substitutions in the GBA gene are the most common large-effect genetic risk factor for Parkinson's disease. The primary objective of this study was to determine the prevalence of GBA substitutions in South Africans with idiopathic Parkinson's disease. METHODS Participants were recruited from tertiary hospitals in the Gauteng Province in South Africa. All participants were screened for substitutions in GBA exon 8-11 and the full coding region was analysed in 20 participants. Peripheral β-glucocerebrosidase enzymatic activity of GBA-carriers was measured in mixed leukocytes. RESULTS Of 105 Caucasian Parkinson's disease participants (82.7% Afrikaner) with an average age of disease onset of 61.9 ± 12.2 years and 40 controls (age 73.4 ± 12.4 years) were included. Heterozygous GBA substitutions were identified in 12.38% of affected participants (p.G35A, p.E326K, p.I368T, p.T369M, p.N370S, p.P387L and p.K441N) and 5.00% of controls (p.E326K and p.T369M). The substitutions ranged from predicted benign to moderately damaging; with p.E326K and p.T369M most prevalent, followed by the Afrikaner Gaucher disease substitution p.P387L. Severe Gaucher disease mutations, like p.L444P, were absent in this cohort. Enzyme activity analysis revealed a nonsignificant reduction in the GBA-Parkinson's disease individuals (14.49 ± 2.30 nmol/h/mg protein vs. 15.98 ± 3.06 nmol/h/mg in control samples). GBA substitutions occur in both young-onset and late-onset Parkinson's cases in the cohort. CONCLUSION Mild GBA substitutions that may not cause Gaucher disease were a common risk factor for Parkinson's disease in the participant group.