Effect of MDR1 haplotype on risk of Parkinson disease

Background: MDR1, a multidrug transporter, encodes a P-glycoprotein that regulates the bioavailability of xenobiotics and is highly expressed at the blood-brainbarrier. Two single nucleotide polymorphisms (SNPs) (e21/ 2677[G/T/A] and e26/3435[C/T]) in the MDR1 gene can lead to differences in MDR1 expression and function. Specific MDR1 alleles of the 2 SNPs are positively selected among ethnic Chinese but not in the white population. Objective: To determine whether specific haplotypes formed by SNPs e21/2677 and e26/3435 may protect against Parkinson disease (PD) among ethnic Chinese in Hong Kong. Design: Case-control study. Setting: Tertiary referral centers in Hong Kong. Subjects: One hundred eighty-five patients with PD and 206 control subjects. Interventions: The two SNPs were amplified in a single multiplex polymerase chain reaction. Five other SNPs that span 100 kilobases of the gene were also analyzed. Main Outcome Measures: Haplotypes frequencies, degree of haplotype association with the disease status, and estimated odds ratio for each haplotype with associated 95% confidence intervals. Results: In addition to 2677 G-->T/A (exon 21) and 3435 C-->T (exon 26), the other SNPs that were analyzed were -41 A-->G (intron -1), -145 C-->G (exon 1), -129 T-->C (exon 1), 1236 T-->C (exon 12), and 4036 A-->G (exon 28). Haplotypes containing SNPs e21/2677 and e26/ 3435 were found to be significantly associated with risk of PD. In particular, the 2677T-3435T haplotype was strongly associated with a reduced risk of PD (P<.001; x(2)=12.521; odds ratio, 0.33; 95% confidence interval, 0.19-0.59). Conclusions: An MDR1 haplotype containing SNPs e21/ 2677T and e26/3435T protects against PD in ethnic Chinese, compatible with the observation of a recent positive selection of the T alleles of these 2 SNPs in this ethnic population.