Mutations in ISPD cause Walker-Warburg syndrome and defective glycosylation of α-dystroglycan

Hans van Bokhoven and colleagues report mutations in the ISPD gene as a cause of Walker-Warburg syndrome. Knockdown of ispd in zebrafish causes hydrocephalus, reduced eye size, muscle degeneration and α-dystroglycan hypoglycosylation. Walker-Warburg syndrome (WWS) is an autosomal recessive multisystem disorder characterized by complex eye and brain abnormalities with congenital muscular dystrophy (CMD) and aberrant α-dystroglycan glycosylation. Here we report mutations in the ISPD gene (encoding isoprenoid synthase domain containing) as the second most common cause of WWS. Bacterial IspD is a nucleotidyl transferase belonging to a large glycosyltransferase family, but the role of the orthologous protein in chordates is obscure to date, as this phylum does not have the corresponding non-mevalonate isoprenoid biosynthesis pathway. Knockdown of ispd in zebrafish recapitulates the human WWS phenotype with hydrocephalus, reduced eye size, muscle degeneration and hypoglycosylated α-dystroglycan. These results implicate ISPD in α-dystroglycan glycosylation in maintaining sarcolemma integrity in vertebrates.