Document Type
Article
Publication Date
5-3-2024
Identifier
DOI: 10.1093/brain/awad427; PMCID: PMC11068110
Abstract
BLOC-one-related complex (BORC) is a multiprotein complex composed of eight subunits named BORCS1-8. BORC associates with the cytosolic face of lysosomes, where it sequentially recruits the small GTPase ARL8 and kinesin-1 and -3 microtubule motors to promote anterograde transport of lysosomes toward the peripheral cytoplasm in non-neuronal cells and the distal axon in neurons. The physiological and pathological importance of BORC in humans, however, remains to be determined. Here, we report the identification of compound heterozygous variants [missense c.85T>C (p.Ser29Pro) and frameshift c.71-75dupTGGCC (p.Asn26Trpfs*51)] and homozygous variants [missense c.196A>C (p.Thr66Pro) and c.124T>C (p.Ser42Pro)] in BORCS8 in five children with a severe early-infantile neurodegenerative disorder from three unrelated families. The children exhibit global developmental delay, severe-to-profound intellectual disability, hypotonia, limb spasticity, muscle wasting, dysmorphic facies, optic atrophy, leuko-axonopathy with hypomyelination, and neurodegenerative features with prevalent supratentorial involvement. Cellular studies using a heterologous transfection system show that the BORCS8 missense variants p.Ser29Pro, p.Ser42Pro and p.Thr66Pro are expressed at normal levels but exhibit reduced assembly with other BORC subunits and reduced ability to drive lysosome distribution toward the cell periphery. The BORCS8 frameshift variant p.Asn26Trpfs*51, on the other hand, is expressed at lower levels and is completely incapable of assembling with other BORC subunits and promoting lysosome distribution toward the cell periphery. Therefore, all the BORCS8 variants are partial or total loss-of-function alleles and are thus likely pathogenic. Knockout of the orthologous borcs8 in zebrafish causes decreased brain and eye size, neuromuscular anomalies and impaired locomotion, recapitulating some of the key traits of the human disease. These findings thus identify BORCS8 as a novel genetic locus for an early-infantile neurodegenerative disorder and highlight the critical importance of BORC and lysosome dynamics for the development and function of the central nervous system.
Journal Title
Brain : a journal of neurology
Volume
147
Issue
5
First Page
1751
Last Page
1767
MeSH Keywords
Humans; Lysosomes; Female; Male; Neurodegenerative Diseases; Animals; Infant; Child, Preschool; Child; Zebrafish; Pedigree; ADP-Ribosylation Factors; Alleles; Mutation, Missense
Keywords
hereditary spastic paraplegia; leukodystrophy; lysosomes; neurodegeneration; neurodevelopmental disorder
Recommended Citation
De Pace R, Maroofian R, Paimboeuf A, et al. Biallelic BORCS8 variants cause an infantile-onset neurodegenerative disorder with altered lysosome dynamics. Brain. 2024;147(5):1751-1767. doi:10.1093/brain/awad427
Comments
Grants and funding
This work is written by (a) US Government employee(s) and is in the public domain in the US.
Publisher's Link: https://doi.org/10.1093/brain/awad427