A Novel α-Synuclein K58N Missense Variant in a Patient with Parkinson’s Disease

Parkinson's disease (PD) is a complex multifactorial disorder with a genetic component in about 15% of cases. Multiplications and point mutations in *SNCA* gene, encoding α-synuclein (aSyn), are linked to rare familial forms of PD. Our goal was to assess the clinical presentation and the biological effects of a novel K58N aSyn mutation identified in a patient with PD. We describe the clinical presentation associated with the novel mutation, together with genetic testing through whole exome sequencing (WES). Furthermore, we conducted extensive biophysical and cellular assays to assess the functional consequences of this novel variant. The patient exhibited typical features of sporadic PD with early onset and a benign disease course. WES showed a novel heterozygous missense variant in *SNCA*(NM_000345.4, c.174G>C; p.K58N). A positive family history of PD was evident, because both a parent and a grandparent had been diagnosed with PD but were deceased. The patient underwent deep brain stimulation surgery 13 years postdiagnosis, showing stable, long-term improvements in motor symptoms. Biophysical studies demonstrated K58N substitution causes local structural effects, disrupts membrane binding, and enhances aSyn in vitro aggregation. In cellular systems, K58N aSyn produces fewer inclusions per cell and does not form condensates. The variant increases aSyn cytoplasmic distribution and displays aberrant activity-dependent dynamic serine-129 phosphorylation. The clinical presentation associated with the novel K58N aSyn mutation suggests a relatively benign PD course consistent with the phenotypic spectrum of idiopathic PD. Overall, our molecular studies provide novel insight into the biology and pathobiology of aSyn.