Zohar Argov

The UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase gene is mutated in recessive hereditary inclusion body myopathy

Hereditary inclusion body myopathy (HIBM; OMIM 600737) is a unique group of neuromuscular disorders characterized by adult onset, slowly progressive distal and proximal weakness and a typical muscle pathology including rimmed vacuoles and filamentous inclusions. The autosomal recessive form described in Jews of Persian descent is the HIBM prototype. This myopathy affects mainly leg muscles, but with an unusual distribution that spares the quadriceps. This particular pattern of weakness distribution, termed quadriceps-sparing myopathy (QSM), was later found in Jews originating from other Middle Eastern countries as well as in non-Jews. We previously localized the gene causing HIBM in Middle Eastern Jews on chromosome 9p12–13 (ref. 5) within a genomic interval of about 700 kb (ref. 6). Haplotype analysis around the HIBM gene region of 104 affected people from 47 Middle Eastern families indicates one unique ancestral founder chromosome in this community. By contrast, single non-Jewish families from India, Georgia (USA) and the Bahamas, with QSM and linkage to the same 9p12–13 region, show three distinct haplotypes. After excluding other potential candidate genes, we eventually identified mutations in the UDP-N-acetylglucosamine-2-epimerase/N-acetylmannosamine kinase (GNE) gene in the HIBM families: all patients from Middle Eastern descent shared a single homozygous missense mutation, whereas distinct compound heterozygotes were identified in affected individuals of families of other ethnic origins. Our findings indicate that GNE is the gene responsible for recessive HIBM.

Disorders of neuromuscular transmission caused by drugs

MORE than 30 drugs in current clinical use, other than those used in anesthesia, may interfere with neuromuscular transmission. This complication of drug therapy is unusual but has been well docume...

Secondary reduction in calpain 3 expression in patients with limb girdle muscular dystrophy type 2B and Miyoshi myopathy (primary dysferlinopathies)

Dysferlin is the protein product of the gene (DYSF) that is defective in patients with limb girdle muscular dystrophy type 2B and Miyoshi myopathy. Calpain 3 is the muscle-specific member of the calcium activated neutral protease family and primary mutations in the CAPN3 gene cause limb girdle muscular dystrophy type 2A. The functions of both proteins remain speculative. Here we report a secondary reduction in calpain 3 expression in eight out of 16 patients with a primary dysferlinopathy and clinical features characteristic of limb girdle muscular dystrophy type 2B or Miyoshi myopathy. Previously CAPN3 analysis had been undertaken in three of these patients and two showed seemingly innocuous missense mutations, changing calpain 3 amino acids to those present in the sequences of calpains 1 and 2. These results suggest that there may be an association between dysferlin and calpain 3, and further analysis of both genes may elucidate a novel functional interaction. In addition, an association was found between prominent expression of smaller forms of the 80 kDa fragment of laminin alpha 2 chain (merosin) and dysferlin-deficiency.

Bioenergetic heterogeneity of human mitochondrial myopathies: Phosphorus magnetic resonance spectroscopy study

Twelve adults with mitochondrial myopathies were studied by phosphorus magnetic resonance spectroscopy of muscle. All 12 had abnormal 31P-NMR findings; recovery from exercise was abnormal in 11 patients. At rest, the ratio of phosphocreatine to inorganic phosphate was reduced in 10. Exercise transfer characteristics were abnormal in all five patients who could exercise. Exercise-induced intracellular acidosis was subnormal in nine patients. The range of abnormalities indicates biochemical heterogeneity, with two possible groups: (1) primary defects of energy metabolism with marked 31P-NMR abnormalities, and (2) secondary, less specific 31P-NMR abnormalities.

Effects of thyroid hormones on skeletal muscle bioenergetics. In vivo phosphorus-31 magnetic resonance spectroscopy study of humans and rats.

The pathophysiology of the myopathy in dysthyroid states is poorly understood. We therefore tested the effects of thyroid hormones on muscle bioenergetics in humans and rats, using in vivo 31P NMR. Two hypothyroid patients had: low phosphocreatine to inorganic phosphate ratio (PCr/Pi) at rest, increased PCr depletion during exercise and delayed postexercise recovery of PCr/Pi. Eight thyroidectomized rats did not show abnormalities at rest, but muscle work induced by nerve stimulation resulted in a significantly (P less than 0.0001) lower PCr/Pi (35-45% of control) at each of the three stimulation frequencies tested (0.25, 0.5, and 1.0 Hz). Recovery rate was markedly slowed to one-third of normal values. Thyroxine therapy reversed these abnormalities in both human and rat muscle. Five patients and six rats with hyperthyroidism did not differ from normal controls during rest and exercise but had an unusually rapid recovery after exercise. The bioenergetic abnormalities in hypothyroid muscle suggest the existence of a hormone-dependent, reversible mitochondrial impairment in this disorder. The exercise intolerance and fatigue experienced in hypothyroid muscle may be due to such a bioenergetic impairment. The changes in energy metabolism in hyperthyroid muscle probably do not cause the muscular disease in this disorder.

Drug-induced peripheral neuropathies.

Review of the various drugs in current clinical use showed that over 50 of them may cause a purely sensory or mixed sensorimotor neuropathy. These include antimicrobials, such as isoniazid, ethambutol, ethionamide, nitrofurantoin, and metronidazole; antineoplastic agents, particularly vinca alkaloids; cardiovascular drugs, such as perhexiline and hydrallazine; hypnotics and psychotropics, notable methaqualone; antirheumatics, such as gold, indomethacin, and chloroquine; anticonvulsants, particularly phenytoin; and other drugs, including disulfiram, calcium carbimide, and dapsone. Patients receiving drug treatment who complain of paraesthesie, pain, muscle cramps, or other abnormal sensations and those without symptoms who are receiving drugs that are known or suspected to be neurotoxic should undergo neurological examination and studies of motor and sensory nerve conduction. This will allow the incidence of drug-induced peripheral neuropathy to be determined more precisely.

Splicing mutation in dysferlin produces limb-girdle muscular dystrophy with inflammation.

Mutations in dysferlin were recently described in patients with Miyoshi myopathy, a disorder that preferentially affects the distal musculature, and in patients with Limb-Girdle Muscular Dystrophy 2B, a disorder that affects the proximal musculature. Despite the phenotypic differences, the types of mutations associated with Miyoshi myopathy and Limb-Girdle Muscular Dystrophy 2B do not differ significantly. Thus, the etiology of the phenotypic variability associated with dysferlin mutations remains unknown. Using genetic linkage and mutation analysis, we identified a large inbred pedigree of Yemenite Jewish descent with limb-girdle muscular dystrophy. The phenotype in these patients included slowly progressive, proximal, and distal muscular weakness in the lower limbs with markedly elevated serum creatine kinase (CK) levels. These patients had normal development and muscle strength and function in early life. Muscle biopsies from 4 affected patients showed a typical dystrophic pattern but interestingly, in 2, an inflammatory process was seen. The inflammatory infiltrates included primarily CD3 positive lymphocytes. Associated with this phenotype, we identified a previously undescribed frameshift mutation at nucleotide 5711 of dysferlin. This mutation produced an absence of normal dysferlin mRNA synthesis by affecting an acceptor site and cryptic splicing. Thus, splice site mutations that disrupt dysferlin may produce a phenotype associated with inflammation.

Hereditary inclusion body myopathy The Middle Eastern genetic cluster

Background: Recessively inherited hereditary inclusion body myopathy (HIBM) with quadriceps sparing was initially described only in Jews originating from the region of Persia. The recent identification of the gene responsible for this myopathy and the common “Persian Jewish mutation” (M712T) enabled the re-evaluation of atypical phenotypes and the epidemiology of HIBM in various communities in the Middle East. Objective: To test for the M712T mutation in the DNA from HIBM patients in the Middle East. Methods: DNA from all suspected HIBM patients was tested for the M712T mutation. Unaffected members of families with genetically proven HIBM were studied too. In the majority of families, haplotype construction with markers spanning the 700-kb region of the HIBM gene was performed. Results: One hundred twenty-nine HIBM patients of 55 families (Middle Eastern Jews, Karaites, and Arab Muslims of Palestinian and Bedouin origin) were homozygous for the M712T mutation, and all carried the same haplotype. Five clinically unaffected subjects were also homozygous for the common mutation and haplotype, including two older adults (ages 50 and 68 years). Atypical features with this same mutation were marked quadriceps weakness in five patients, proximal weakness only in two patients, facial weakness in three patients, and a muscle biopsy showing perivascular inflammation in one patient. Conclusions: The phenotypic spectrum of recessive HIBM is wider than previously described, and the diagnostic criteria for this myopathy must be changed. The Middle Eastern cluster is the result of a founder mutation, with incomplete penetrance, that is approximately 1,300 years old and is not limited to Jews.

The homozygous M712T mutation of UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase results in reduced enzyme activities but not in altered overall cellular sialylation in hereditary inclusion body myopathy

Hereditary inclusion body myopathy (HIBM) is a neuromuscular disorder, caused by mutations in UDP‐N‐acetylglucosamine 2‐epimerase/N‐acetylmannosamine kinase, the key enzyme of sialic acid biosynthesis. In Middle Eastern patients a single homozygous mutation occurs, converting methionine‐712 to threonine. Recombinant expression of the mutated enzyme revealed slightly reduced N‐acetylmannosamine kinase activity, in agreement with the localization of the mutation within the kinase domain. B lymphoblastoid cell lines derived from patients expressing the mutated enzyme also display reduced UDP‐N‐acetylglucosamine 2‐epimerase activity. Nevertheless, no reduced cellular sialylation was found in those cells by colorimetric assays and lectin analysis, indicating that HIBM is not directly caused by an altered overall expression of sialic acids.

Muscle energy metabolism in McArdle's syndrome by in vivo phosphorus magnetic resonance spectroscopy

Five patients with McArdles syndrome were examined by phosphorus magnetic resonance spectroscopy (31P-NMR). Adenosine triphosphate (ATP) levels at rest were reduced by 22%, but did not fall further during exercise or contracture. The slope of work rate versus inorganic phosphate/phosphocreatine (Pi/PCr) was 42 ± 8 joules/min/Pi/PCr in three patients without muscle wasting, compared with 13 and 16 in patients with atrophy (normal, 30 to 50 joules/min/Pi/PCr). Recovery from exercise showed similar rates in patients (postischemic exercise 1.03 ± 0.17, post-aerobic 1.63 ± 0.17 PCr/Pi units per minute) and controls (1.0 ± 0.2 and 1.8 ± 0.2, respectively) independent of intracellular pH. Infusion of glucose improved exercise kinetics by 163 to 190%, but an oral load of protein had no effect. We conclude that (1) muscle mitochondria operate normally in vivo in this glycogenolytic disorder, suggesting a sufficient alternate fuel supply. (2) Blood-borne glucose may serve as one alternate fuel for the “second wind” phenomenon. (3) ATP control mechanisms are altered only at rest. (4) Recovery from exercise is relatively pH-independent.