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Vacuolar protein sorting 35 (VPS35) is a core component of the retromer complex, crucial to endosomal protein sorting and intracellular trafficking. We recently linked a mutation in VPS35 (p.D620N) to familial parkinsonism. Here, we characterize human VPS35 and retromer function in mature murine neuronal cultures and investigate neuron-specific consequences of the p.D620N mutation. We find VPS35 localizes to dendritic spines and is involved in the trafficking of excitatory AMPA-type glutamate receptors (AMPARs). Fundamental neuronal processes, including excitatory synaptic transmission, AMPAR surface expression and synaptic recycling are altered by VPS35 overexpression. VPS35 p.D620N acts as a loss-of-function mutation with respect to VPS35 activity regulating synaptic transmission and AMPAR recycling in mouse cortical neurons and dopamine neuron-like cells produced from induced pluripotent stem cells of human p.D620N carriers. Such perturbations to synaptic function likely produce chronic pathophysiological stress upon neuronal circuits that may contribute to neurodegeneration in this, and other, forms of parkinsonism., (© The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

A Saskatchewan multi-incident family was clinically characterized with Parkinson disease (PD) and Lewy body pathology. PD segregates as an autosomal-dominant trait, which could not be ascribed to any known mutation. DNA from three affected members was subjected to exome sequencing. Genome alignment, variant annotation and comparative analyses were used to identify shared coding mutations. Sanger sequencing was performed within the extended family and ethnically matched controls. Subsequent genotyping was performed in a multi-ethnic case-control series consisting of 2928 patients and 2676 control subjects from Canada, Norway, Taiwan, Tunisia, and the USA. A novel mutation in receptor-mediated endocytosis 8/RME-8 (DNAJC13 p.Asn855Ser) was found to segregate with disease. Screening of cases and controls identified four additional patients with the mutation, of which two had familial parkinsonism. All carriers shared an ancestral DNAJC13 p.Asn855Ser haplotype and claimed Dutch-German-Russian Mennonite heritage. DNAJC13 regulates the dynamics of clathrin coats on early endosomes. Cellular analysis shows that the mutation confers a toxic gain-of-function and impairs endosomal transport. DNAJC13 immunoreactivity was also noted within Lewy body inclusions. In late-onset disease which is most reminiscent of idiopathic PD subtle deficits in endosomal receptor-sorting/recycling are highlighted by the discovery of pathogenic mutations VPS35, LRRK2 and now DNAJC13. With this latest discovery, and from a neuronal perspective, a temporal and functional ecology is emerging that connects synaptic exo- and endocytosis, vesicular trafficking, endosomal recycling and the endo-lysosomal degradative pathway. Molecular deficits in these processes are genetically linked to the phenotypic spectrum of parkinsonism associated with Lewy body pathology.