A heterozygous effect for PINK1 mutations in Parkinson's disease?

Objective: To investigate the significance of PINK1 mutations in sporadic Parkinson's disease (PD). Methods: We determined the frequency of PINK1 mutations by direct sequencing in a large series of PD patients with apparently sporadic disease (n = 768). Results: Twelve heterozygous mutations were identified, nine in PD patients and three in control subjects. Interpretation: Given the difficulty in interpreting the pathogenic significance of the heterozygous mutations that have already been reported in parkin and DJ-1, we first determined the frequency of heterozygous PINK1 mutations in the general population by sequencing a large number of control subjects (n = 768), then subsequently assessed their functional significance by examining their effects on stress-induced alterations to the mitochondrial membrane potential (Delta psi m). We demonstrate an enrichment of heterozygous mutations in sporadic PD patients compared with matched control subjects (1.2% in PD vs 0.4% in control subjects). Furthermore, we show that they adversely affect Delta psi m in a similar way to the familial G309D mutation. Although it remains difficult to conclusively demonstrate the pathogenicity of heterozygous mutations, the results of this study and the previously reported subdinical nigrostriatal dysfunction in carriers of heterozygous PINK1 mutations suggest the possibility that these heterozygous mutations are a significant risk factor in the development of later onset PD.