A homozygous MED11 C-terminal variant causes a lethal neurodegenerative disease

The study describes a novel genetic neurodegenerative disorder identified through exome or genome sequencing in 7 affected individuals from 5 unrelated families. The clinical phenotype included congenital microcephaly, severe respiratory distress at birth, profound neurodevelopmental delay, myoclonic seizures, exaggerated startle response, and progressive neurodegeneration leading to premature death in early infancy for some. A recurrent homozygous truncating variant (c.325C>T; p.Arg109Ter) in MED11 was identified as the cause. Functional studies using patient-derived fibroblasts showed the truncated protein escaped nonsense-mediated decay but was predicted to disrupt binding to other MED complex subunits (MED22, MED28, MED30C), potentially affecting complex stability. A zebrafish knockout model recapitulated key phenotypes, including microcephaly and early lethality. Limitations include the small sample size of human cases and the need for further functional studies to elucidate the precise pathogenic mechanism. The findings implicate MED complex integrity in human brain development and neurodegeneration.