Analysis Of PLA2G6 Mutation In Early-onset Parkinsonism And Assay The Enzyme Activiy Of Mutated PLA2G6 Protein

Background:Parkinson's disease (PD) is one of the most frequent neurodegenerative disorders. The majority of cases of PD appear to be sporadic, thus specific genetic defects are linked to familial forms of PD. Early-onset parkinsonism (EOP) refers to a group of patients diagnosis with parkinsonism and the on-set age is less than 50 years. Previously, mutations in the genes encoding Parkin (PARK2), PINK1(PARK6), and DJ-1 (PARK7) were considered to be responsible for typical samples of EOP, while autosomal recessive parkinsonism associated with ATP13A2 (PARK9) and FBXO7(PARK15) often exhibit more complex phenotypes, including pyramidal signs, dementia, supranuclear vertical gaze palsy, and dystonia. Mutations in the PLA2G6 gene at the PARK14 locus have been reported in complicated parkinsonism patients. To assess the prevalence of and phenotypes associated with PLA2G6 gene mutations, we screened PLA2G6 mutations in a cohort of patients with EOP。Objective:We detected PLA2G6 gene mutations in a cohort of chinese patients diagnosed with EOP. Then we carried out DAT PET-CT and functional study in vitro.Methods:We selected 52 patients in which the Parkin, PINK1, DJ-1, ATP13A2, and FBXO7 gene mutations had been previously excluded.31 patients were sporadic cases and 12 were proband of AREP families. All patients came from the mainland of China. The entire PLA2G6 coding region and exon-intron boundaries were sequenced from genomic DNA templates. We then performed PET studies on individuals in the pedigree with a homozygous PLA2G6 mutation, and investigated the enzyme activity level of the mutation.Results:A novel homozygous missense mutation, c.G991T (p.D331Y) was identified in an autosomal recessive case. And we also find a novel heterozygous missense mutation c.G2036T (p.V679D) in a sporadic patient, and a novel heterozygous synonymous mutation in another patient. A younger sister of the p.D331 Y-carrying patient was also homozygous for the mutation, but was with no extra-pyramidal symptoms. A PET study showed a substantial reduction in dopamine transporter (DAT) binding in the p.D331Y patient, and a slight reduction in DAT binding in his sister and completely normal in other family members, this results proved that the PET results is co-segration with the gene type. In vitro, we experimentally demonstrate that the D331Y mutation caused an approximately 70% reduction in enzyme activity.Conclusions:1. There are EOP patients with novel PLA2G6 gene mutations in mainland China.2. DAT PET-CT study in the AREP family members with novel PLA2G6 gene mutation conformed the p.D331Y gene mutation is pathologic.3. The novel PLA2G6 p.D331Y gene mutation is assotiated with EOP patients with typical parkinson's disease clinical phenotypes.4. We further domostated that novel PLA2G6 gene mutation cause partly but not completed loss of enzyme activity of PLA2G6 protein, and indicated that partly loss of enzyme activity may be the reason why p.D331Y gene mutation cause the PD phenotype but not others.