• NEUROMUSCULAR
• MUSCLE DISEASE

Congenital myasthenic syndrome (CMS) caused by mutations in GMPPB shows features of dystroglycanopathy with elevated serum creatine kinase (CK) and mild cognitive delay.

In their JNNP paper, Rodriguez Cruz et al1 report clinical features of eight patients with CMS carrying mutations in GMPPB. GMPPB encodes a glycosynthetic enzyme, GDP-mannose pyrophosphorylase B, that catalyses the conversion of mannose-1-phosphate and GTP to GDP-mannose. GDP-mannose is an essential substrate for both N-glycosylation and O-mannosylation.2 Mutations in genes in the O-mannosylation pathway were originally identified in patients with congenital muscular dystrophies with hypoglycosylation of α-dystroglycan, which is also called dystroglycanopathies. α-Dystroglycan is an abundantly glycosylated membrane-bound extracellular molecule in the dystrophin-associated glycoprotein complex, and links the extracellular matrix molecules and cytoplasmic molecules immediately …