POMT1 mutation results in defective glycosylation and loss of laminin-binding activity in -DG

Walker–Warburg syndrome (WWS) is a congenital muscular dystrophy associated with neuronal migration disorder and structural eye abnormalities. The mutations in the O-mannosyltransferase 1 gene (POMT1) were identified recently in 20% of patients with WWS. The authors report on a patient with WWS and a novel POMT1 mutation. Their patient expressed -dystroglycan ( -DG) core protein, but fully glycosylated -DG antibody epitopes were absent, associated with the loss of laminin-binding activity. NEUROLOGY 2004;62:1009–1011 Walker–Warburg syndrome (WWS; MIM 236670), Fukuyama-type congenital muscular dystrophy (FCMD; MIM 253800), and muscle-eye-brain disease (MEB; MIM 253280) are closely related congenital muscular dystrophies (CMDs) with cobblestone lissencephaly and eye abnormalities. Although they are known to be caused by the mutations of different genes encoding putative glycosyltransferases,1 it now is clear that the mutations of each gene produce overlapping clinical phenotypes.2,3 In addition, they share a similar pattern of selective loss of -dystroglycan ( -DG) on immunohistochemical study.1 A recent study showed hypoglycosylation of -DG and loss of binding activity of -DG to laminin, neurexin, and agrin in FCMD, MEB, and the mutant myodystrophy (Large) mouse, suggesting a defect in the same post-translational modification pathway of glycosylation in -DG.4 Mutations in the O-mannosyltransferase 1 gene (POMT1) were implicated recently in 20% of patients with WWS.5 The laminin-binding site in -DG is thought to reside in O-mannosyl-linked carbohydrate side chains, which may require POMT1 for synthesis.6 We report our experience with a Japanese boy with WWS and a novel POMT1 mutation, who showed reduced glycosylation and loss of lamininbinding activity of -DG in skeletal muscle. Methods. Patient. The patient was a Japanese boy aged 3.5 years from apparently nonconsanguineous parents. No other family member was affected. Prenatal ultrasonography showed that the patient had a meningoencephalocele. He was born at gestational week 38 by Cesarean section with a body weight of 2,042 g. He was floppy with an enlarged head. He underwent surgery to remove a meningoencephalocele, and a ventriculoperitoneal shunt was added 21 days after birth. Mild microphthalmia and corneal clouding also were observed. Serum creatine kinase levels were markedly elevated to 600 to 31,000 IU/L (upper normal limit, 70 IU/L). He exhibited markedly delayed milestones. He could not control his head, roll over, or sit. He showed lack of facial expression with an inability to smile and never developed the ability to speak. Brain MRI revealed agyric frontal and temporo-occipital lobes mixed with pachygyric parietal cortex. Hypoplasia of brain stem and cerebellum also was observed (figure 1). EEG showed multifocal spikes, and the muscle biopsy showed marked increase in fatty tissue with evidence of necrosis and regeneration. The mutational analysis for fukutin and protein O-mannose -1,2-Nacetylglucosaminyl-transferase gene (POMGnT1) did not show any abnormalities. Immunohistochemistry and immunoblotting studies. The following antibodies were used: monoclonal anti-DG (VIA4-1, Upstate Biotechnology, Lake Placid, NY), polyclonal goat anti-DG (GT20ADG),4 monoclonal anti-DG (43DAG1/8D5, Novocastra Laboratories, Newcastle upon Tyne, UK), monoclonal antilaminin2 chain (5H2, Chemicon, Temecula, CA), monoclonal antidystrophin C-terminal (Dy8/6C5, Novocastra Laboratories), and monoclonal antisarcoglycan antibodies (Novocastra Laboratories). The detailed techniques of the immunohistochemistry, immunoblotting, and laminin overlay assays have been described previously.4,7 Mutation analysis. Genomic DNA was extracted from frozen muscle tissue using standard method with informed consent. Primer Additional material related to this article can be found on the Neurology Web site. Go to www.neurology.org and scroll down the Table of