2026/04/21 by Niccolò E. Mencacci, Georgia Minakaki, Reza Maroofian +36 · 1 voice
Medicine · Biochemistry, Genetics and Molecular Biology · Neuroscience · #Lysosomal Storage Disorders Research #Cellular transport and secretion #Neurological diseases and metabolism
paper · doi:10.1172/jci195336
openalex created_date 2025/05/08 · openalex publication_date 2026/04/21 · openalex updated_date 2026/07/26
BORCS5 encodes a subunit of the BLOC-One-Related Complex (BORC), which is known to promote anterograde movement and fusion of lysosomes. We identified 16 individuals from 9 families with bi-allelic BORCS5 variants, revealing a spectrum of neurodevelopmental and neurodegenerative phenotypes. Carriers of homozygous protein-truncating variants (PTVs), resulting in complete loss of BORCS5, presented with prenatally lethal arthrogryposis multiplex congenita, brain malformations, and neuropathological evidence of neuroaxonal dystrophy. Individuals with missense or splice-site variants presented differently, with microcephaly, developmental epileptic encephalopathy, optic atrophy, spasticity, and progressive movement disorders. In this group, brain MRI showed diffuse hypomyelination, corpus callosum abnormalities, and progressive global cerebral atrophy, consistent with neurodegeneration. Borcs5 KO in zebrafish resulted in microcephaly, motor deficits, and increased seizure susceptibility, mirroring the patients' clinical presentation. At the cellular level, only BORCS5 PTVs, but not missense variants, led to perinuclear lysosomal clustering and impaired lysosomal axonal trafficking in induced pluripotent stem cell-derived forebrain neurons. However, PTVs and missense variants were associated with reduced lysosomal proteolysis and activity of lysosomal hydrolases glucocerebrosidase and cathepsin B, indicating lysosomal dysfunction. Our study reveals a role for BORCS5 in modulation of lysosomal function, in addition to its known role in lysosome movement and fusion, possibly underlying the diverse clinical manifestations in individuals with BORCS5-related disorders.