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.