Gene/Protein Disease Symptom Drug Enzyme Compound
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Hereditary Inclusion Body Myopathy (HIBM) is an autosomal recessive, quadriceps sparing type commonly referred to as HIBM but also termed h-IBM or Inclusion Body Myopathy 2 (IBM2). The clinical manifestations begin with muscle weakness progressing over the next 10-20 years uniquely sparing the quadriceps until the most advanced stage of the disease. Histopathology of an HIBM muscle biopsy shows rimmed vacuoles on Gomori's trichrome stain, small fibers in groups and tubulofilaments without evidence of inflammation. In affected individuals distinct mutations have been identified in the GNE gene, which encodes the bifunctional enzyme uridine diphospho-N-acetylglucosamine (UDP-GlcNAc) 2-epimerase/N-acetyl-mannosamine (ManNAc) kinase (GNE/MNK). GNE/MNK catalyzes the first two committed steps in the biosynthesis of acetylneuraminic acid (Neu5Ac), an abundant and functionally important sugar. The generation of HIBM animal models has led to novel insights into both the disease and the role of GNE/MNK in pathophysiology. Recent advances in therapeutic approaches for HIBM, including administration of N-acetyl-mannosamine (ManNAc), a precursor of Neu5Ac will be discussed.
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PMID:Hereditary inclusion body myopathy: a decade of progress. 1959 68

Hereditary Inclusion Body Myopathy (HIBM2) is a chronic progressive skeletal muscle wasting disorder which generally leads to complete disability before the age of 50 years. There is currently no effective therapeutic treatment for HIBM2. Development of this disease is related to expression in family members of an autosomal recessive mutation of the GNE gene, which encodes the bifunctional enzyme UDP-GlcNAc 2-epimerase/ManNAc kinase (GNE/MNK). This is the rate limiting bifunctional enzyme that catalyzes the first 2 steps of sialic acid biosynthesis. Decreased sialic acid production, consequently leads to decreased sialyation of a variety of glycoproteins including the critical muscle protein alpha-dystroglycan (alpha-DG). This in turn severely cripples muscle function and leads to the onset of the syndrome. We hypothesize that replacing the mutated GNE gene with the wildtype gene may restore functional capacity of GNE/MNK and therefore production of sialic acid, allowing for improvement in muscle function and/or delay in rate of muscle deterioration. We have constructed three GNE gene/CMV promoter plasmids (encoding the wildtype, HIBM2, and Sialuria forms of GNE) and demonstrated enhanced GNE gene activity following delivery to GNE-deficient CHO-Lec3 cells. GNE/MNK enzyme function was significantly increased and subsequent induction of sialic acid production was demonstrated after transfection into Lec3 cells with the wild type or R266Q mutant GNE vector. These data form the foundation for future preclinical and clinical studies for GNE gene transfer to treat HIBM2 patients.
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PMID:Preclinical assessment of wt GNE gene plasmid for management of hereditary inclusion body myopathy 2 (HIBM2). 1978 87

The bifunctional enzyme UDP-GlcNAc 2-epimerase/ ManNAc kinase (GNE/MNK), encoded by the GNE gene, catalyzes the first two committed, rate-limiting steps in the biosynthesis of N-acetylneuraminic acid (sialic acid). GNE/MNK is feedback inhibited by binding of the downstream product, CMP-sialic acid in its allosteric site. GNE mutations can result in two human disorders, hereditary inclusion body myopathy (HIBM) or sialuria. So far, no active site geometry predictions or conformational transitions involved with function are available for mammalian GNE/MNK. The N-terminal GNE domain is homologous to various prokaryotic 2-epimerases, some of which have solved crystallographic structures. The C-terminal MNK domain belongs to the sugar kinases superfamily; its crystallographic structure is solved at 2.84 A and three-dimensional structures have also been reported for several other kinases. In this work, we employed available structural data of GNE/MNK homologs to model the active sites of human GNE/MNK and identify critical amino acid residues responsible for interactions with substrates. In addition, we modeled effects of GNE/MNK missense mutations associated with HIBM or sialuria on helix arrangement, substrate binding, and enzyme action. We found that all reported mutations are associated with the active sites or secondary structure interfaces of GNE/MNK. The Persian-Jewish HIBM founder mutation p.M712T is located at the interface alpha4alpha10 and likely affects GlcNAc, Mg2+, and ATP binding. This work contributes to further understanding of GNE/MNK function and ligand binding, which may assist future studies for therapeutic options that target misfolded GNE/MNK in HIBM and/or sialuria.
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PMID:Molecular modeling of the bifunctional enzyme UDP-GlcNAc 2-epimerase/ManNAc kinase and predictions of structural effects of mutations associated with HIBM and sialuria. 1991 66

Hereditary Inclusion Body Myopathy (HIBM, IBM2, MIM:600737) is an autosomal recessive adult onset progressive muscle wasting disorder. It is associated with the degeneration of distal and proximal muscles, while often sparing the quadriceps. The bifunctional enzyme UDP-GlcNAc 2-epimerase/ManNAc kinase (GNE/MNK), encoded by the GNE gene, catalyzes the first two committed, rate-limiting steps in the biosynthesis of N-acetylneunaminic acid (sialic acid). Affected individuals have been identified with mutations in the GNE gene. In the present study, the GNE coding region of 136 symptomatic patients were sequenced. A total of 41 patients were found to have GNE mutations. Eight novel mutations were discovered among seven patients. Of the eight novel mutations, seven were missense (p.I150V, p.Y186C, p.M265T, p.V315T, p.N317D, p.G669R, and p.S699L) and one was nonsense (p.W495X), all of which span the epimerase, kinase, and allosteric domains of GNE. In one patient, one novel mutation was found in the allosteric region and kinase domain of the GNE gene. Mutations in the allosteric region lead to a different disease, sialuria; however, this particular mutation has not been described in patients with sialuria. The pathological significance of this variation with GNE function remains unknown and further studies are needed to identify its connection with HIBM. These findings further expand the clinical and genetic spectrum of HIBM.
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PMID:Novel GNE mutations in autosomal recessive hereditary inclusion body myopathy patients. 2343 77