Homozygous and compound heterozygous rare variants in VPS13C contribute to Lewy body diseases

Abstract

Background Dementia with Lewy bodies (DLB) and Parkinson’s disease (PD) are clinically, pathologically and etiologically overlapping disorders. They are included in the Lewy body disease (LBD) continuum characterized by α-synuclein-positive Lewy body pathology in neurons. Homozygous PTC mutations in Vacuolar Protein Sorting 13 homolog C gene (VPS13C) are associated with early-onset PD. Methods Whole genome sequencing of two affected siblings and healthy parents of family A with onset age below 50 years and DLB pathology confirmed at autopsy. Targeted resequencing of the VPS13C coding region in 844 LBD patients and 664 control individuals. Phasing cis-trans location of the compound heterozygous VPS13C variants. Analysis of VPS13C protein expression in lymphoblast cells and brain lysates. Immunohistochemistry and live cell labeling in HeLa and SH-SY5Y cells overexpressing wild type or mutant VPS13C. Results In the two affected siblings of family A, we identified compound heterozygous rare variants located in trans in VPS13C Rare VPS13C variants (MAF ≤ 1%), are significantly associated (p = 0.0233) in the LBD patient cohort using optimized sequence kernel association test (SKAT-O). We identified 11 carriers of compound heterozygous variants and 1 carrier of homozygous variants in VPS13C. Trans location of the variants in compound heterozygous carriers was confirmed in 4 and cis location in 3 patients. The frequency of patient carriers with bi-allelic variants mimicking recessive inheritance is 1.07% (9/844). In post-mortem brain tissue of two unrelated DLB carriers of compound trans heterozygous variants, we observed a reduction of VPS13C protein expression. Overexpressing of wild type or mutant VPS13C, in HeLa and SH-SY5Y cells, demonstrated that the mutations abolish the endosomal/lysosomal localization of VPS13C. Conclusions Our data indicate that rare alleles are associated with LBD, and when present bi-allelic in patients, these combinations have variable effects on expression and functioning of VPS13C. Apart from the recessive PTC mutations, some combinations of rare missense mutations might mimic recessive inheritance and explain part of the sporadic LBD patients. We propose that homozygous or compound heterozygous rare missense variants in VPS13C reducing VPS13C protein expression can contribute to risk of LBD.