Homozygosity for a nonsense mutation in the alpha-tropomyosin gene TPM3 in a patient with severe nemaline myopathy

Homozygosity for a nonsense mutation in the alpha-tropomyosin gene TPM3 in a patient with severe nemaline myopathy

Abstracts chromosome 2q, have to date been non-informative. Studies with a wider panel of antibodies to these proteins are in progress. Mutations in t...

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Abstracts chromosome 2q, have to date been non-informative. Studies with a wider panel of antibodies to these proteins are in progress. Mutations in the gene for the slow isoform of ~-tropomyosin (TPM3) result in the formation of nemaline rods, and future immunocytochemical studies may reveal the role of this protein in rod formation. Immunocytochemistry will continue to play an active role in the recognition of new abnormalities in the congenital myopathies and provide insight into their pathogenesis.

Keywords: Congenital myopathy; Immunocytochemistry CMI.4 Nemaline myopathy and the myotubular mynpathies Carina Wallgren-Pettersson


identified as the skeletal muscle calcium release channel, the ryanodine receptor (RYRI), this let to linkage studies in CCD families with markers form the RYR 1 genomic region on chromosome 19q 13.1. Linkage of CCD to RYR1 was established in a large Australian pedigree and confirmed in several European families. A few mutations in RYRI have been reported to co-segregate with CCD. However, no experimental evidence is available yet to document the functional alteration of the RYR1 channel and to explain the pathophysiology of CCD. Recently, several authors have reported on discordance of CCD and MHS in some families. This, together with the surprising genetic heterogeneity of MHS which has become apparent, has challenged the concept of a strict association between CCD and MHS.

Department of Medical Genetics, University of Helsinki, and the ENMC International Consortia for Nemaline and Myotubular Myopathy

CMI.6 Congenital myopathies with inclusion bodies Hans H. Goebel

Nemaline myopathy is clinically and genetically heterogeneous and will fall into more subcategories as the molecular genetic background and pathogenetic mechanisms are clarified. In the autosomal recessive form, there is locus heterogeneity; in addition to the probably most common autosomal recessive form showing linkage to chromosome 2q, there are at least three unrelated families with likely autosomal recessive inheritance in which molecular genetic results are not indicative of linkage to this region. An autosomal dominant form of nemaline myopathy is caused by a mutation in the alpha-tropomyosin gene TPM3, but there are other families with likely autosomal dominant inheritance in which no mutation has been found in this gene. In addition to these forms of nemaline myopathy, it has been suggested that there is a separate, neonatally fatal form, in some patients accompanied by arthrogryposis and/or intranuclear rods, and an adult-onset form, which may or may not be genetic in origin. The gene for the X-linked form of myotubular myopathy, MTM1, encodes the tyrosine phosphatase myotubularin. The MTM1 gene has fifteen exons and disease-specific alterations have been found in most of them. The incidence of new mutations is high. There is no obvious correlation between clinical severity and the nature of the mutation. In families with the Xlinked form in which the mutation has been characterised, it is possible to use mutation detection in order to confirm the diagnosis, determine carrier status and perform prenatal diagnosis. There is no evidence of genetic heterogeneity in the X-chromosomal form of myotubular myopathy. Three other genes related to the MTMI gene have been found, the Xchromosomal MTMRI gene, and the autosomal MTMR2 and MTMR3 genes. The genes for the autosomal dominant and autosomal recessive forms of myotubular (centronuclear) myopathy have not yet been identified.

Department of Neuropathology, Johannes-Gutenberg University, Mainz, Germany

Keywords: Nemaline (rod) myopathy; Myotubular myopathy; Centronuclear myopathy CMI.5 Genetics of central core disease and its relationship to malignant hyperthermia Clemens R. Mueller

Department of Human Genetics, University of Wuerzburg, Biozentrum, Am Hubland D-97074 Wuerzburg, Germany Central core disease (CCD, OMIM no. 117000) was the first of the congenital myopathies to be described as a separate entity about 40 years ago. The clinical presentation is highly variable and rather unspecific: generalized hypotonia at birth, delayed motor development, proximal muscle weakness, slow progression. Histology of muscle tissue discloses the hallmarking structural feature: marked type 1 fibre predominance and sharply demarcated central areas which interrupt the fibrillar architecture of the muscle fibres. These 'cores' are devoid of mitochondria and thus stain negative in oxidative reactions. Genetic transmission is compatible with autosomal dominant inheritance, though penetrance appears to be variable. Early reports had noted a strong association between CCD and susceptibility to malignant hyperthermia (MHS). When a first gene for MHS was

Based on morphological abnormalities, congenital myopathies can be classified into several categories: (1) enzyme histochemically abnormal appearance without structural pathology, e.g. congenital fibre type disproportion or congenital fibre type uniformity; (2) abnormally placed nuclei, e.g. myotubular and centronuclear myopathies, (3) disruption of physiological intrinsic features, largely sarcomeres, e.g. central cores and minicores; (4) abnormal inclusions within muscle fibres. This latter category of congenital myopathies is divergent. Several such inclusions are derived from pre-existing structures, most notably rods or nemaline bodies, although their intranuclear presence is unexplained. Other derivatives of Z-band material are cytoplasmic bodies and possibly related inclusions as spheroid bodies, sarcoplasmic bodies or Mallory body-like inclusions, recently termed hyaline bodies. These inclusions share accumulation of desmin, the muscle fibre-specific intermediate filament, and of other proteins, some of them physiological, but others quite abnormal. Respective abnormalities at nucleic acid levels have not yet been reported and mutations are unknown because respective genes have not been mapped or cloned although many families with such inclusions within muscle fibres including granulofilamentous material have been recorded. Inclusions without possible precursors are fingerprint bodies, reducing bodies, cylindrical spirals, and Zebra bodies the nosological connotation of which occasionally seems unclear. The filamentous body consisting of thin myofilaments, probably of acfin nature, is a non-specific feature, but excess of actin has recently been documented in a few instances in possibly a new form of congenital myopathy. Whether other non-actin proteins are also increased in this actin excess-related myopathy is still unexplored. It is largely for these congenital myopathies marked by diversity of heterogeneous inclusions that experimental models and tissue culture reproduction are necessary to further clarify formation and pathogenesis and thus significance of these inclusions for congenital myopathy pathology.

C O N G E N I T A L MYOPATHIES: O R A L PRESENTATION CMO.1 Homozygosity for a nonsense mutation in the alpha-tropomyosin gene TPM3 in a patient with severe nemaline myopathy P. Tan", J. Briner b, E. Boltshauser~, K. North d, M.R. Davis a, S.D. Wilton a, C. Wallgren-Pettersson~, N.G. Laing"

"Australian Neuromuscular Research Institute, QEII Medical Centre, Nedlands', Western Australia 6009; '~lnstitute.[or Clinical Pathology University Hospital, Zurich, Switzerland; cChildren's Hospital, Zurich Switzerland; aNew Children's Ho,vJital, Sydney, Australia," eFolkhalsan Institute of Medical Genetics, TopeliusT,atan 20, Helsinki, Finland Recently a missense mutation in the alpha-tropomyosin stow gene (TPM3) was shown to be associated with dominant nemaline myopathy in a large Australian kindred [Laing et al., Nat Genet 1995;9:75-79]. In



the course of screening 46 other nemaline myopathy families for TPM3 mutations, a patient who deceased at 21 months with a severe form of the disease was shown to be homozygous for an SSCP polymorphism. Sequencing of the SSCP polymorphic fragment and genomic DNA from the patient revealed homozygosity for a nonsense mutation at codon 31, changing a CAG coding for ghitamine to a TAG stop codon. The patient's parents are first cousins, reinforcing the recessive nature of the disorder. Thus, both dominant and recessive nemaline myopathy may result from mutations in the alpha-tropomyosin gene TPM3. The muscle biopsy in the current patient demonstrated type 2 fibre predominance and rod bodies only in type 1 muscle fibres, in which TPM3 is expressed. How the 30 amino-acid truncated peptide the patient would synthesise lead to muscle weakness, the formation of rod bodies and death at 21 months is unknown.

serious respiratory problems postoperatively, due to nocturnal hypoventilation. In 3 others nocturnal saturation measurements and polysomnography revealed nocturnal hypoventilation. Those patients were symptom-free during the day and were totally unaware of this problem. They are now treated by nasal mask ventilation overnight. One five-year-old patient was admitted to hospital several times for difficulties in overcoming respiratory tract infections. We want to stress the importance of detection of nocturnal hypoventilation in this patient group with clinically mild myopathy. The fairly good muscle power of the limbs and the good functional status of these patients may be misleading and make one overlook an underlying respiratory weakness. We also want to draw attention to the unusual association of mini-core myopathy with malignant hyperthermia, which is classically described in central core disease.

Keywords: Nemaline myopathy; a-Tropomyosin TPM3; Nonsense muta-

Keywords : Mini-core disease; Children; Nocturnal hypoventilation

tion CMO.2 Dystrophic central core disease or muscular dystrophy with central cores? A possible new autosomal recessive disorder with central core disease A. Manzur, F. Muntoni, C.A. Sewry, J. Ziprin, V. Dubowitz

Neuromuscular Unit, Department of Paediatric~, Hammersmith Hospital, London WI2 0NN, UK

CMO.4 Intermuscular variation in X-linked myotubular myopathy T.R. Helliwell a, I.H. Ellis h, R.E. Appleton ~

aDepartment of Pathology, University of Liverpool, bDepartment of Clinical Genetics, Royal Liverpool Children's Hospital, ¢Department of Paediatric Neurology, Royal Liverpool Children's Hospital, UK

CM0.3 Minicore myopathy: cave noctem! N. Goemans, G. Buyse, K. De Boeck, M. Lammens, P. Casaer

A 17y primagravida delivered a 3.5 kg male infant at term. There was polyhydramnios and reduced fetal movements during pregnancy, and a family history of male still-births and neonatal deaths. At birth there was profound, generalised hypotonia with few spontaneous movements, and poor suck and cough reflexes. He required venfilatory support because of poor respiratory effort and recurrent aspiration. At two months he had a pyloro-myotomy for pyloric stenosis and at 3 months a tracheostomy was performed. At 5 months he was visually alert and interactive, but remained ventilator-dependant. Biochemical investigations were normal and be has a normal male karyotype. Screening for myotonic dystrophy was negative. He died at six months from respiratory failure. The family was informative with four microsatellite markers closely-linked to the MTMI gene: FRAXF (immediately proximal), DXS7432 (possibly just distal), DXS1684 (distal) and 4E R/F (just distal to DXSl684). The disease associated haplotype is derived from the proband's deceased obligate carrier great grandmother's genotype. Biopsies of vastus lateralis at 1 and 6 weeks showed small type 1 fibres with a central accumulation of oxidative enzyme activity and glycogen, and 2% of fibres with central nuclei. A biopsy of biceps brachii at 6 weeks showed 15% fibres with central nuclei, and many others with central glycogen and mitochondria. Myosin ATPase differentiation of fibres types was good. Immunohistochemical labelling showed increased expression of desmin and utrophin in both muscles, with a few fibres showing vimentin positivity. Membranous and cytoplasmic NCAM labelling was more extensive and intense in biceps than in vastus lateralis. This patient demonstrates more marked intermuscular variation in the morphological and immunohistochemical phenotype of X-linked myotubular myopathy than has previously been reported. This may lead to diagnostic difficulty.

Department of Paediatric Neurology, Paediatric Pneumology and Neuropathology University Hospital, Leuven, Belgium

Keywords: Myotubular myopathy; Variation; Pathology

Central core disease is a well recognised, relatively mild, dominantly inherited, congenital myopathy, associated with the ryanodine receptor on chromosome 19. We report four isolated, unrelated cases with a non-progressive congenital myopathy, in whom muscle biopsy showed classical central cores, but in addition an overall dystrophic pattern, with marked proliferation of connective tissue and adipose tissue, and variation in fibre size. Creatine kinase was normal. The first case, who had a selective involvement of her muscle in relation to the dystrophic change, with a relatively normal histology in the rectus femoris and marked dystrophic change in the vastus lateralis, with similar incidence of cores in both muscles, has been previously documented [Dubowitz V. A Colour Atlas of Muscle Disorders in Childhood, 1989, p. 477]. In striking contrast to the increased echogenicity of the muscle in the index cases, ultrasound assessment of the parents in all four cases showed no increase in echo, and needle biopsy of the parents in two cases showed no pathological change. Mutation studies in the ryanodine receptor gene are planned. We consider this a form of central core disease with secondary dystrophic change, rather than a primary dystrophic disorder with incidental central cores. It may represent a new form of central core disease with autosomal recessive inheritance.

Keywords: Central core disease; Autosomal recessive; Muscular dystrophy

Mini-core disease is a congenital myopathy, characterised by the presence of multiple small areas of focal myofibrillar degenerative changes and focal decrease of mitochondrial oxidative enzyme activity. In contrast to the central cores, mini-cores never extend through the entire length of the fibre. This myopathy is considered as a mild, relatively non-progressive disease. We report 7 patients, 4 boys, 3 girls, with mini-core disease, Two patients are siblings, the others are isolated cases. 6/7 presented in childhood with symptoms of a mild myopathy, 1/7 with a 'King-Denborough' syndrome with barrel-shaped chest, typical facial appearance, short stature and malignant hyperthermia reaction during anaesthesia, confirmed by halothane and caffeine test in vitro. The myopathy remained fairly static in all, facial weakness with poor mimic was present in all but one, 4/7 developed scoliosis which needed surgical fixation. One patient had

CMO.5 MTMI gene mutations in Japanese patients with X-linked myotubular myopathy Ichizo Nishinoa, Yu-chi Goto a, Kiichi Arahata b, Ikuya Nonaka a

Departments of~'Ultrastructural Research and bNeuromuscular Research, National Institute of Neuroscience, National Center of Neurology and Psychiatry (NCNP), Kodaira, Tokyo, Japan X-linked myotubular myopathy (MTM1) is an intractable genetic disorder with muscle weakness and hypotonia from birth. Recently Laporte et al. (1996) isolated the MTMI gene by positional cloning and found mutations in this gene in seven European families using single strand conformation polymorphism (SSCP) analysis of genornic DNA. We newly