Abstract
Protein glycosylation defects can present with early-onset brain malformations and muscular dystrophy or milder, late-onset muscular dystrophy. Here, we report a new glycosylation defect with an atypical phenotype of late-onset, progressive, severe brain atrophy and muscular dystrophy in a 47-year-old man. Exome sequencing revealed a homozygous highly deleterious c.478G>T (p.G160W) variant in the B3GNT4 gene. A knock-in mouse model replicated the patient's muscle histology. B3GNT4 is expressed at very low levels in the thalamus, and this region was selectively preserved in the patient. The study demonstrates the first disease associated with one of the seven B3GNT galactosyltransferases and the importance of B3GNT4 in adolescence to adult muscle and CNS development.