Kelch-like homologue 9 mutation is associated with an early onset autosomal dominant distal myopathy.

Distal myopathies are a heterogeneous group of disorders characterized by progressive weakness and muscular atrophy, beginning in distal limb muscles and affecting proximal limb muscles at a later stage. We studied a large German kindred with 10 affected members. Weakness and atrophy of the anterior tibial muscles started between the ages of 8 and 16 years, followed by atrophy of intrinsic hand muscles. Progression was slow, and patients retained the ability to walk until the seventh decade. Serum creatinine kinase levels were increased in the range of 150-1400 U/l. Muscle biopsies showed myopathic changes, whereas immunohistochemistry showed normal expression of marker proteins for muscular dystrophies. Patients had reduced sensation with stocking-glove distribution in the distal limbs in later life. Nerve conduction studies revealed no evidence of neuropathy. Genome-wide linkage analysis in this family revealed a new locus for distal myopathy at 9p21.2-p22.3 (multipoint logarithm of the odds ratio=4.21). By positional cloning we found a heterozygous mutation L95F in the Kelch-like homologue 9 gene, encoding a bric-a-brac Kelch protein. Molecular modelling indicated that the mutation may interfere with the interaction of the bric-a-brac domain with Cullin 3. Coimmunoprecipitation experiments confirmed that the mutation reduces association with Cullin 3 in the Kelch-like homologue 9-Cullin 3-E3 ubiquitin ligase complex, which is involved in ubiquitin-dependent protein degradation. We identified a unique form of early onset autosomal dominant distal myopathy which is associated with a Kelch-like homologue 9 mutation and interferes with normal skeletal muscle through a novel pathogenetic mechanism.

Enzymatic diagnostic test for Muscle-Eye-Brain type congenital muscular dystrophy using commercially available reagents.

OBJECTIVES: Mutations disrupting the interaction of extra-cellular ligands and alpha-dystroglycan are responsible for an etiologically heterogeneous group of autosomal recessive congenital muscular dystrophies (CMD) that can have associated brain and eye abnormalities. The objective is to develop a diagnostic test for one of these CMDs, Muscle-Eye-Brain disease (MEB), due to mutations in the gene encoding Protein O-Mannosyl beta-1,2-N-acetylglucosaminyltransferase 1 (POMGnT1). DESIGN AND METHODS: POMGnT1 enzyme activity was determined in extracts of muscle biopsies from four MEB patients and various controls using commercially available reagents. RESULTS: All four MEB muscle samples showed a highly significant decrease in POMGnT1 activity relative to controls. CONCLUSIONS: The assay of POMGnT1 activity in MEB muscle provides a rapid and relatively simple diagnostic test for this disease. CMDs associated with brain malformations such as MEB, WWS and FCMD are heterogenous in clinical presentation and on radiologic examination, suggesting that POMGnT1 assays of muscle biopsies should be used as a screening procedure for MEB in all CMD patients associated with brain malformations.

Differential activation of mononuclear phagocytes in cerebellar malformation associated with Walker-Warburg syndrome.

Walker-Warburg syndrome (WWS) is an autosomal recessive disorder with alterations affecting the CNS that are characteristic of type-II lissencephaly and dysplasia/hypoplasia of the cerebellum. Other than these features, WWS is typically also accompanied by muscular dystrophy and abnormalities affecting the eyes. There is at present little information on the state of microglial and mononuclear phagocytic cell responses within the brain in WWS. In this case report, we present evidence for focal and differential activation of mononuclear phagocytes specifically confined to the dysplastic cerebellum of an infant at 5 months of age, diagnosed with WWS.

Intragenic deletion in the LARGE gene causes Walker-Warburg syndrome.

Intragenic homozygous deletions in the Large gene are associated with a severe neuromuscular phenotype in the myodystrophy (myd) mouse. These mutations result in a virtual lack of glycosylation of alpha-dystroglycan. Compound heterozygous LARGE mutations have been reported in a single human patient, manifesting with mild congenital muscular dystrophy (CMD) and severe mental retardation. These mutations are likely to retain some residual LARGE glycosyltransferase activity as indicated by residual alpha-dystroglycan glycosylation in patient cells. We hypothesized that more severe LARGE mutations are associated with a more severe CMD phenotype in humans. Here we report a 63-kb intragenic LARGE deletion in a family with Walker-Warburg syndrome (WWS), which is characterized by CMD, and severe structural brain and eye malformations. This finding demonstrates that LARGE gene mutations can give rise to a wide clinical spectrum, similar as for other genes that have a role in the post-translational modification of the alpha-dystroglycan protein.

Worldwide distribution and broader clinical spectrum of muscle-eye-brain disease.

Muscle-eye-brain disease (MEB), an autosomal recessive disorder prevalent in Finland, is characterized by congenital muscular dystrophy, brain malformation and ocular abnormalities. Since the MEB phenotype overlaps substantially with those of Fukuyama-type congenital muscular dystrophy (FCMD) and Walker-Warburg syndrome (WWS), these three diseases are thought to result from a similar pathomechanism. Recently, we showed that MEB is caused by mutations in the protein O-linked mannose beta1,2-N-acetylglucosaminyltransferase 1 (POMGnT1) gene. We describe here the identification of seven novel disease-causing mutations in six of not only non-Finnish Caucasian but also Japanese and Korean patients with suspected MEB, severe FCMD or WWS. Including six previously reported mutations, the 13 disease-causing mutations we have found thus far are dispersed throughout the entire POMGnT1 gene. We also observed a slight correlation between the location of the mutation and clinical severity in the brain: patients with mutations near the 5' terminus of the POMGnT1 coding region show relatively severe brain symptoms such as hydrocephalus, while patients with mutations near the 3' terminus have milder phenotypes. Our results indicate that MEB may exist in population groups outside of Finland, with a worldwide distribution beyond our expectations, and that the clinical spectrum of MEB is broader than recognized previously. These findings emphasize the importance of considering MEB and searching for POMGnT1 mutations in WWS or other congenital muscular dystrophy patients worldwide.

Mutations in the O-mannosyltransferase gene POMT1 give rise to the severe neuronal migration disorder Walker-Warburg syndrome.

Walker-Warburg syndrome (WWS) is an autosomal recessive developmental disorder characterized by congenital muscular dystrophy and complex brain and eye abnormalities. A similar combination of symptoms is presented by two other human diseases, muscle-eye-brain disease (MEB) and Fukuyama congenital muscular dystrophy (FCMD). Although the genes underlying FCMD (Fukutin) and MEB (POMGnT1) have been cloned, loci for WWS have remained elusive. The protein products of POMGnT1 and Fukutin have both been implicated in protein glycosylation. To unravel the genetic basis of WWS, we first performed a genomewide linkage analysis in 10 consanguineous families with WWS. The results indicated the existence of at least three WWS loci. Subsequently, we adopted a candidate-gene approach in combination with homozygosity mapping in 15 consanguineous families with WWS. Candidate genes were selected on the basis of the role of the FCMD and MEB genes. Since POMGnT1 encodes an O-mannoside N-acetylglucosaminyltransferase, we analyzed the possible implication of O-mannosyl glycan synthesis in WWS. Analysis of the locus for O-mannosyltransferase 1 (POMT1) revealed homozygosity in 5 of 15 families. Sequencing of the POMT1 gene revealed mutations in 6 of the 30 unrelated patients with WWS. Of the five mutations identified, two are nonsense mutations, two are frameshift mutations, and one is a missense mutation. Immunohistochemical analysis of muscle from patients with POMT1 mutations corroborated the O-mannosylation defect, as judged by the absence of glycosylation of alpha-dystroglycan. The implication of O-mannosylation in MEB and WWS suggests new lines of study in understanding the molecular basis of neuronal migration.