Mutations in MYH7 cause Multi-minicore Disease (MmD) with variable cardiac involvement.

Central Core Disease (CCD) and Multi-minicore Disease (MmD) (the "core myopathies") have been mainly associated with mutations in the skeletal muscle ryanodine receptor (RYR1) and the selenoprotein N (SEPN1) gene. A proportion of cases remain unresolved. Mutations in MYH7 encoding the beta myosin heavy chain protein have been implicated in cardiac and, less frequently, skeletal muscle disorders. Here we report four patients from two families with a histopathological diagnosis of MmD, presenting in childhood with slowly progressive muscle weakness, more proximal in Family 1 and more distal in Family 2, and variable degrees of cardiorespiratory impairment evolving later in life. There was also a strong family history of sudden death in the first family. Muscle biopsies obtained in early childhood showed multiple minicores as the most prominent feature. Sequencing of the MYH7 gene revealed heterozygous missense mutations, c.4399C>G; p.Leu1467Val (exon 32) in Family 1 and c.4763G>C; p.Arg1588Pro (exon 34) in Family 2. These findings suggest MYH7 mutations as another cause of a myopathy with multiple cores, in particular if associated with dominant inheritance and cardiac involvement. However, clinical features previously associated with this genetic background, namely a more distal distribution of weakness and an associated cardiomyopathy, may only evolve over time.

Remission of clinical signs in early duchenne muscular dystrophy on intermittent low-dosage prednisolone therapy.

We report a 5-year follow-up of two 4-year-old boys with classical Duchenne dystrophy, with an out-of-frame deletion in the Duchenne gene and absence of dystrophin in their muscle, who had a quite remarkable response to an intermittent, low-dosage, regime of prednisolone (0.75 mg/kg/day for 10 days each month, or alternating 10 days on and 10 days off). In the first case there was complete remission of all clinical signs of dystrophy, sustained almost fully up to the present time; in the second, the initial response was almost as marked, sustained for almost 5 years, before showing a fairly rapid decline over the ensuing year that resulted in loss of independent ambulation at the age of 10. Both boys remained around the 50th centile for height and weight, and showed no evidence of demineralization of bone on consecutive dual X-ray absorptiometry scanning of the spine, nor any signs of chronic prednisolone toxicity. These carefully documented individual cases suggest there may be an optimal window for treatment in the early stages of the disease, and further larger scale controlled studies should be targeted more selectively at this stage of the disease. This report also confirms that our regime of low dosage, intermittent prednisolone, with cycles of 10 days of treatment, either per month or alternating with 10 days off treatment, is well tolerated and can therefore be recommended for long-term use in children with Duchenne muscular dystrophy.

Autosomal recessive inheritance of RYR1 mutations in a congenital myopathy with cores.

Central core disease (CCD) is a congenital myopathy due to dominant mutations in the skeletal muscle ryanodine receptor gene (RYR1). The authors report three patients from two consanguineous families with symptoms of a congenital myopathy, cores on muscle biopsy, and confirmed linkage to the RYR1 locus. Molecular genetic studies in one family identified a V4849I homozygous missense mutation in the RYR1 gene. This report suggests a congenital myopathy associated with recessive RYR1 mutations.

Facioscapulohumeral (FSHD1) and other forms of muscular dystrophy in the same family: is there more in muscular dystrophy than meets the eye?

We report on two unrelated Brazilian families with members affected by two different forms of muscular dystrophy. In the first one, the 35-year-old male proband has limb-girdle muscular dystrophy with proximal weakness, elevated creatine kinase and a myopathic muscle biopsy. All the proteins known to be associated with limb-girdle muscular dystrophy were normal. Two of his sisters also complained of muscle weakness. The oldest sister showed clinical signs consistent with facioscapulohumeral muscular dystrophy, confirmed through molecular analysis. She presented a 30 kb EcoRI/BlnI fragment which was found in another six relatives, but surprisingly not in the affected proband or the other sister. In the second family, a 57-year-old male with a typical facioscapulohumeral muscular dystrophy phenotype has a 17 kb EcoRI/BlnI fragment, which was also present in other affected relatives. However in a 14-year-old severely affected male cousin, confined to a wheelchair since age 12, but without facial weakness, the small fragment was absent. These families illustrate the importance of testing all affected individuals in a family.

Selective muscle involvement on magnetic resonance imaging in autosomal dominant Emery-Dreifuss muscular dystrophy.

OBJECTIVE: The aim of this study was to evaluate the spectrum of muscle involvement on MRI in patients with autosomal dominant Emery-Dreifuss muscular dystrophy (EDMD2) due to mutations in the lamin A/C gene and to compare it to the pattern found in other conditions with similar phenotype. PATIENTS AND METHODS: Nine patients with a diagnosis of EDMD2 had MRI scanning of their leg muscles. Seven other patients, four with the X-linked form of Emery-Dreifuss muscular dystrophy (EDMD) and three with an Emery-Dreifuss-like phenotype but no detectable mutations in either the emerin or the lamin A/C gene were also scanned as disease controls. RESULTS: All patients with EDMD2 showed a characteristic involvement of the posterior calf muscles. The medial head of the gastrocnemius was always predominantly involved while the lateral head was relatively spared. This pattern was more obvious in mildly affected patients in whom the other calf muscles were spared or only mildly involved but was also recognisable in the patients with more advanced disease. In contrast, none of the patients with the X-linked EDMD or with Emery-Dreifuss-like phenotype but no mutation in either genes showed this pattern of muscle involvement. CONCLUSIONS: Our results suggest that patients with EDMD2 have a specific pattern of muscle involvement and that muscle MRI can be used, in combination with other techniques, to distinguish various genetic forms of Emery-Dreifuss muscular dystrophy.

Neonatal arthrogryposis and absent limb muscles: a muscle developmental gene defect?

We describe a child who presented at birth with arthrogryposis. Following a muscle biopsy a diagnosis of congenital muscular dystrophy was made and a skin biopsy 12 years later confirmed the presence of merosin. Her clinical picture was unusual, however, for merosin-positive congenital muscular dystrophy. She had extreme wasting and weakness of her arms and legs. In contrast, she had good neck and trunk control, and no facial or respiratory muscle weakness. We have used magnetic resonance imaging to examine the pattern of muscle involvement in this case. No recognizable muscle could be identified in the limbs. In contrast, the axial muscles were preserved. This striking pattern of virtual absence of muscles in the limbs with sparing of the axial muscle suggests that a gene responsible for the migration and/or proliferation of limb muscle precursor cells may be involved in the disease process. It is recognized that merosin-positive congenital muscular dystrophy is a heterogeneous disease. Magnetic resonance imaging is a useful tool for examining in detail the pattern of muscle involvement and identifying individual phenotypes. Understanding more about which muscles are affected in children with congenital myopathies may provide information on the underlying pathological process and help in the search for candidate proteins and genes.

Characterisation of novel point mutations in the survival motor neuron gene SMN, in three patients with SMA.

We report two novel mutations in three cases of spinal muscular atrophy (SMA), including two distant cousins who followed an unexpectedly severe course. Diagnosis was confirmed by reduced SMN protein and full-length SMN mRNA levels. Sequencing of the non-deleted SMN1 gene revealed a single G insertion at the end of exon 1 in the two cousins and a novel G275S exon 6 missense mutation in the milder case.

Early white matter changes on brain magnetic resonance imaging in a newborn affected by merosin-deficient congenital muscular dystrophy.

In 1996 we reported sequential magnetic resonance imaging study in an infant with merosin-deficient congenital muscular dystrophy with normal brain magnetic resonance imaging at 3 weeks and white matter changes by 6 months. We now report an infant with merosin-deficient congenital muscular dystrophy with a mild degree of white matter changes already present on brain magnetic resonance imaging at 5 days of age. The difference may be due to a difference in the T2 sequences used. The images in this present case were obtained with a fast spin echo sequence (echo time: 210 ms). The increased T2 weighted may be responsible for a better detection of the white matter changes at an early stage, when they can be missed on conventional, less weighting T2 sequences. These results suggest that, by using appropriate sequences, mild white matter changes may be detectable on brain magnetic resonance imaging in the first days of life in infants with merosin-deficient congenital muscular dystrophy.

Mild phenotype of nemaline myopathy with sleep hypoventilation due to a mutation in the skeletal muscle alpha-actin (ACTA1) gene.

Nemaline myopathy is a clinically and genetically heterogeneous condition. The clinical spectrum ranges from severe cases with antenatal or neonatal onset and early death to late onset cases with only slow progression. Three genes are known to cause nemaline myopathy: the genes for nebulin (NEB) on chromosome 2q22, slow alpha-tropomyosin (TPM3) on chromosome 1q21 and skeletal muscle alpha-actin (ACTA1) on chromosome 1q42. We present a 39-year-old lady with a mild form of nemaline myopathy, whom we have followed over a period of 25 years. She presented at the age of 7 years with symptoms of mild axial and proximal muscle weakness. The overall course was essentially static, but at 36 years, she went into life-threatening respiratory failure, for which she is currently treated with night-time ventilation. Muscle biopsies at 12, 17 and 39 years of age showed typical nemaline rods, particularly in type 1 fibres. Areas with unevenness of oxidative stain were present in the second and third biopsies. The presence of rods and core-like areas was confirmed on electron microscopy. There was no detectable alteration in actin expression immunocytochemically. A dominant missense mutation in the skeletal muscle alpha-actin gene (ACTA1) was found. This case illustrates the clinical and genetic heterogeneity of nemaline myopathy, and one phenotype of the wide spectrum of severity caused by mutations in the skeletal muscle alpha-actin (ACTA1) gene. In addition, it shows the diversity of pathological features that can occur in congenital myopathies due to mutations in the same gene.

What is muscular dystrophy? Forty years of progressive ignorance.

This lecture traces recent advances in knowledge of the muscular dystrophies, as well as their increasing complexity. They are described through the eyes of the author from his first exposure to and complete ignorance of the disease in the late 1950s, through the advent of modern techniques, to the molecular genetic revolution, with the recognition of individual genes and proteins for disorders within the muscular dystrophy umbrella. There initially seemed to be a logical sequence of linked membrane proteins from dystrophin in Duchenne and Becker dystrophy, through the dystrophin-associated glycoproteins (sarcoglycans) in some of the limb girdle muscular dystrophies (LGMD), to the extracellular matrix protein merosin (alpha-2 laminin) in congenital muscular dystrophy (CMD). The first spoke in the wheel came with the discovery of a calcium activated protease enzyme, calpain 3, in one form of LGMD, and subsequently another novel non-membrane protein, dysferlin, in another. There are currently at least eight distinct genetic forms of LGMD alone, and another eight separate genetic entities in the CMD group. This has highlighted our ignorance of the pathogenesis of the muscular dystrophies in relation to a diverse array of protein deficiencies. To compound things further, the X-linked and dominant forms of Emery-Dreifuss muscular dystrophy have recently been linked to emerin and lamin A/C, respectively, two proteins of the nuclear membrane, opening up yet another new ballpark of discovery.

Brain magnetic resonance imaging abnormalities in merosin-positive congenital muscular dystrophy.

We report the brain magnetic resonance imaging (MRI) findings in 23 patients with merosin-positive congenital muscular dystrophy (CMD). Twelve patients had normal scans. Eight other children had essentially normal scans but showed mild non-specific periventricular white matter changes. Three children had structural abnormalities on imaging. The first patient, a 15-month-old boy with hypotonia, muscle weakness and global development delay, had moderate cerebellar atrophy and mild dilatation of the lateral ventricles. The second child, a 3-year-old ambulant girl with subtle learning problems, had mild cerebellar hypoplasia and a large subarachnoid space when scanned at 16 months. The third patient, a 15-year-old ambulant male with normal intelligence and complex partial seizures, had polymicrogyria of both temporoparietal lobes on brain MRI. The clinical features and motor ability of children with merosin-positive CMD are variable, although usually milder than merosin-deficient CMD. Our findings confirm that central nervous system involvement can occur in some merosin-positive cases. We suggest performing brain MRI in children with merosin-positive CMD, as this may help in our understanding of this very heterogeneous disease.

Minicore myopathy in children: a clinical and histopathological study of 19 cases.

Minicore myopathy is a congenital myopathy characterized by multifocal areas of degeneration in muscle fibres. Genetic heterogeneity expected on the basis of clinical variability awaits further resolution. We reviewed 19 cases in order to further delineate the phenotype. Marked hypotonia was the predominant presenting feature, with evidence of antenatal onset in 30% of cases. Weakness was most pronounced axially and proximally, often more severely affecting the shoulder girdle. Mild facial involvement was frequent. Varying degrees of scoliosis were obvious in all patients older than 10 years. In addition, two patients who were also the most severely affected had complete external ophthalmoplegia. One patient showed marked distal involvement. Respiratory failure developed in half of all patients after 10 years of age and correlated strongly with the degree of scoliosis. Cardiac involvement occurred mainly secondary to respiratory impairment. The course appeared static in most cases. Loss of independent walking was observed only in one case at the age of 10 years. On ultrasound scan, differential involvement within the quadriceps was documented in several patients. Variability in fibre size, type 1 predominance and atrophy with occasional type 2 hypertrophy were prominent but nonspecific histological changes. Apart from typical minicores, a marked increase in internal nuclei was the most prominent histological feature. With the exception of one family in which two generations were affected, inheritance appeared autosomal-recessive or sporadic in all cases.

High resolution magnetic resonance imaging of the brain in the dy/dy mouse with merosin-deficient congenital muscular dystrophy.

Magnetic resonance imaging (MRI) abnormalities in the cerebral white matter are a consistent feature of merosin-deficient human congenital muscular dystrophy, a disease caused by a primary defect in the expression of the laminin alpha2 chain of merosin. To investigate the relationship between imaging changes and merosin deficiency we undertook a MRI study in the dy/dy mouse, an animal model for this form of human congenital muscular dystrophy. High resolution in vivo imaging was performed on anaesthetized animals (two homozygous dy/dy mutants and two heterozygous dy/DY controls, aged 2.5 months) in a dedicated 11.7T magnetic resonance imaging scanner. T(1) and T(2) weighted images were normal in all mice and white matter changes were not seen at a stage of maturity when MRI changes are already very striking in human patients. Cerebral MRI abnormalities do not appear to be a feature of dy/dy mice, despite the virtual absence of merosin expression in the dy/dy mouse brain. Possible causes for this absence of MRI changes, and implications for the pathogenesis of the MRI changes in humans are reviewed.

Diaphragmatic spinal muscular atrophy with bulbar weakness.

We present the clinical and histopathological features of a child affected by diaphragmatic spinal muscular atrophy. The child was born with mild distal arthrogryposis, mild hypotonia and developed marked diaphragmatic and bulbar muscle weakness in the first week of life. Electrophysiological and pathological investigations performed at presentation were not conclusive, while the investigations performed at 3 months showed a clear neurogenic picture. Genetic studies excluded involvement of the SMN gene, or of other genes located on chromosome 5q, confirming that this syndrome represents a different entity from typical proximal spinal muscular atrophy.

Assignment of a form of congenital muscular dystrophy with secondary merosin deficiency to chromosome 1q42.

We have previously reported an autosomal recessive form of congenital muscular dystrophy, characterized by proximal girdle weakness, generalized muscle hypertrophy, rigidity of the spine, and contractures of the tendo Achilles, in a consanguineous family from the United Arab Emirates. Early respiratory failure resulting from severe diaphragmatic involvement was present. Intellect and the results of brain imaging were normal. Serum creatine kinase levels were grossly elevated, and muscle-biopsy samples showed dystrophic changes. The expression of the laminin-alpha2 chain of merosin was reduced on several fibers, but linkage analysis excluded the LAMA2 locus on chromosome 6q22-23. Here, we report the results of genomewide linkage analysis of this family, by use of homozygosity mapping. In all four affected children, an identical homozygous region was identified on chromosome 1q42, spanning 6-15 cM between flanking markers D1S2860 and D1S2800. We have identified a second German family with two affected children having similar clinical and histopathological features; they are consistent with linkage to the same locus. The cumulative LOD score was 3.57 (straight theta=.00) at marker D1S213. This represents a novel locus for congenital muscular dystrophy. We suggest calling this disorder "CMD1B." The expression of three functional candidate genes in the CMD1B critical region was investigated, and no detectable changes in their level of expression were observed. The secondary reduction in laminin-alpha2 chain in these families suggests that the primary genetic defect resides in a gene coding for a protein involved in basal lamina assembly.