Recessive variants in ESCRT-II component VPS25 alter vesicular transport and small extracellular vesicle processing...

The role of small extracellular vesicles (sEVs), such as exosomes, in cell-to-cell communication is increasingly recognized. Both during development and postnatally, sEVs have been shown to mediate a multitude of essential functions in the central nervous system. While abnormal sEV biogenesis has been observed in a number of neurodevelopmental disorders, a causal link has been largely lacking.

We clinically evaluated five families in which newborns presented with a novel neonatal-onset encephalopathy. Positional mapping, exome sequencing, and trio exome sequencing were utilized to identify the underlying genetic variants. Additionally, we utilized Vps25 hypomorphic mouse mutants and performed cellular assays to evaluate ESCRT-II interaction, cellular localization, and sEV secretion and cargo capacities.

The observed lethal encephalopathy is characterized by severe hypotonia, brain anomalies, and epilepsy. In families 1, 4, and 5 (multiplex consanguineous), we identified a novel homozygous missense variant in VPS25 as the likely candidate. Family 2 comprises a simplex case with two missense variants in trans in VPS25, one of which impacts the same residue as in the other three families. Family 3 also comprises a simplex case where we revealed a homozygous missense variant. VPS25 is an essential component of ESCRT-II, itself required for sEV biogenesis. We show that Vps25 hypomorphic mouse mutants recapitulate the developmental brain malformation observed in patients. We also show that mutant VPS25 is associated with abnormal ESCRT-II interaction, abnormal cellular localization, and highly abnormal sEVs. Specifically, mutant cells displayed engorged multivesicular bodies and were significantly defective in their capacity to secrete sEVs such as exosomes, while secreted sEVs contained altered cargo, lacking vital proteins for axon protection and maintenance.

We report a novel neurodevelopmental disorder caused by biallelic hypomorphic variants in VPS25. The consistent impact of these variants on sEV biogenesis suggests a potential pathomechanism. While future cases will further delineate the phenotypic spectrum, these findings offer a new perspective on abnormal sEVs as drivers of human neurodevelopmental disorders.