Kenneth Ricker

Myotonic dystrophy type 2 Molecular, diagnostic and clinical spectrum

Background: Myotonic dystrophy types 1 (DM1) and 2 (DM2/proximal myotonic myopathy PROMM) are dominantly inherited disorders with unusual multisystemic clinical features. The authors have characterized the clinical and molecular features of DM2/PROMM, which is caused by a CCTG repeat expansion in intron 1 of the zinc finger protein 9 (ZNF9) gene. Methods: Three-hundred and seventy-nine individuals from 133 DM2/PROMM families were evaluated genetically, and in 234 individuals clinical and molecular features were compared. Results: Among affected individuals 90% had electrical myotonia, 82% weakness, 61% cataracts, 23% diabetes, and 19% cardiac involvement. Because of the repeat tract’s unprecedented size (mean ∼5,000 CCTGs) and somatic instability, expansions were detectable by Southern analysis in only 80% of known carriers. The authors developed a repeat assay that increased the molecular detection rate to 99%. Only 30% of the positive samples had single sizeable expansions by Southern analysis, and 70% showed multiple bands or smears. Among the 101 individuals with single expansions, repeat size did not correlate with age at disease onset. Affected offspring had markedly shorter expansions than their affected parents, with a mean size difference of −17 kb (−4,250 CCTGs). Conclusions: DM2 is present in a large number of families of northern European ancestry. Clinically, DM2 resembles adult-onset DM1, with myotonia, muscular dystrophy, cataracts, diabetes, testicular failure, hypogammaglobulinemia, and cardiac conduction defects. An important distinction is the lack of a congenital form of DM2. The clinical and molecular parallels between DM1 and DM2 indicate that the multisystemic features common to both diseases are caused by CUG or CCUG expansions expressed at the RNA level.

Proximal myotonic myopathy: A new dominant disorder with myotonia, muscle weakness, and cataracts

We describe three families with a dominantly inherited disorder. Affected individuals have myotonia, proximal muscle weakness, and cataracts. There was no abnormal CTG repeat expansion of the myotonic dystrophy (DM) gene in DNA from blood and muscle. The structure of the three families permitted linkage analysis, and there is no linkage to the gene loci for DM or to the loci for the muscle chloride channel disorders or muscle sodium channel disorders. The collection of symptoms in these three families seems to represent a new disorder.

Mutations in CAV3 cause mechanical hyperirritability of skeletal muscle in rippling muscle disease

Hereditary rippling muscle disease (RMD) is an autosomal dominant human disorder characterized by mechanically triggered contractions of skeletal muscle. Genome-wide linkage analysis has identified an RMD locus on chromosome 3p25. We found missense mutations in positional candidate CAV3 (encoding caveolin 3; ref. 5) in all five families analyzed. Mutations in CAV3 have also been described in limb-girdle muscular dystrophy type 1C (LGMD1C; refs. 6,7), demonstrating the allelism of dystrophic and non-dystrophic muscle diseases.

EFFECT OF IMMUNOSUPPRESSIVE DRUGS (AZATHIOPRINE)

For more than 18 years, we have been treating myasthenic patients with cytostatic drugs. We began with 6-mercaptopurin, actinomycin and ametopterin but we were forced to discontinue routine usage when serious side effects became evident. For the last 1 1 years, we have been using azathioprine at a dosage of 150-200 mg daily and have published our experiences with the drug at various times, mainly in German journals.l, * In 1978 we were able to report our results with azathioprine at the Plasmapheresis Conference in San Francisco; 5 , since then, many myasthenia clinics have accepted azathioprine usage; however, mostly in connection with plasmaphere~is.~-T Little new data have been uncovered during the last years concerning azathioprine treatment. First impressions about cytostatic drugs in myasthenia were published originally by Mertens in 1969; the experiences of other European authors O-I2 and our own multicenter-study results in 1976 2, have been mainly affirmed.

Stiff man syndrome: Clinical and laboratory findings in eight patients

The clinical, biochemical, neuroimaging and neurophysiological findings of eight patients with stiff man syndroms (SMS) [four of six being tested with autoantibodies against glutamic acid decarboxylase (GAD)] are presented. In two patients (one GAD-positive, one GAD-negative), transient oculomotor disturbances suggested progressive encephalomyelitis with rigidity and myoclonus (PERM) as differential diagnosis. The catalogue of characteristic clinical symptoms of SMS is extended by three new symptoms: (1) an aura-like feeling reported by five patients to precede spontaneous spasmodic attacks; (2) a stereotyped motor pattern seen in seven patients during spasmodic jerks, consisting of brief opisthotonos, stiffening of the slightly abducted legs and inversion of the plantar-flexed feet; (3) a paroxysmal fear when crossing a free space unaided, or even thinking of it. Clinical findings did not enable us to discriminate between patients tested GAD-positive or GAD-negative. Cerebrospinal fluid contained elevated immunoglobulin levels or cell counts, or both, in the majority of patients. Autopsy of one patient revealed scattered lymphocyte cuffs around leptomeningeal, intracerebral and particularly intraspinal vessels, suggesting a mild inflammatory process. Whether SMS and PERM are closely related is discussed; they are possibly both manifestations of a spectrum of encephalomyelopathies having autoimmunity against GABAergic neurons in common.

Sudden cardiac death in myotonic dystrophy type 2

Medical records and follow-up data were reviewed in 297 genetically proven myotonic dystrophy type 2 (DM2) patients. Patients were selected by the criteria of cardiac sudden death before age 45. Sudden death occurred in four patients, three of whom were cardiological asymptomatic, and one with a history of heart failure. Cardiac histopathology showed dilated cardiomyopathy in all, and conduction system fibrosis in two patients. Pathogenetic CCUG ribonuclear inclusions were demonstrable in cardiomyocytes.

Muscle pathology in 57 patients with myotonic dystrophy type 2

We evaluated muscle biopsies from 57 patients with genetically confirmed myotonic dystrophy type 2/proximal myotonic myopathy (DM2/PROMM). Light microscopy showed myopathic together with “denervation‐like” changes in almost all biopsies obtained from four different muscles: increased fiber size variation, internal nuclei, small angulated fibers, pyknotic nuclear clumps, and predominant type 2 fiber atrophy. Quantitative morphometry in 18 biopsies that were immunostained for myosin heavy chain confirmed a predominance of nonselective type 2 fiber atrophy. These histological changes were similar in all patients regardless of the site of biopsy, the predominant clinical symptoms and signs, and the clinical course. It is likely that, in a number of undiagnosed patients, DM2 is the underlying disorder. With a better understanding of the histopathological pattern in DM2, biopsies from patients with undiagnosed neuromuscular disorders can now be reevaluated. Muscle Nerve 29: 275–281, 2004

Myotonic Dystrophy Type 2: Human Founder Haplotype and Evolutionary Conservation of the Repeat Tract

Myotonic dystrophy (DM), the most common form of muscular dystrophy in adults, can be caused by a mutation on either chromosome 19 (DM1) or 3 (DM2). In 2001, we demonstrated that DM2 is caused by a CCTG expansion in intron 1 of the zinc finger protein 9 (ZNF9) gene. To investigate the ancestral origins of the DM2 expansion, we compared haplotypes for 71 families with genetically confirmed DM2, using 19 short tandem repeat markers that we developed that flank the repeat tract. All of the families are white, with the majority of Northern European/German descent and a single family from Afghanistan. Several conserved haplotypes spanning >700 kb appear to converge into a single haplotype near the repeat tract. The common interval that is shared by all families with DM2 immediately flanks the repeat, extending up to 216 kb telomeric and 119 kb centromeric of the CCTG expansion. The DM2 repeat tract contains the complex repeat motif (TG)(n)(TCTG)(n)(CCTG)(n). The CCTG portion of the repeat tract is interrupted on normal alleles, but, as in other expansion disorders, these interruptions are lost on affected alleles. We examined haplotypes of 228 control chromosomes and identified a potential premutation allele with an uninterrupted (CCTG)(20) on a haplotype that was identical to the most common affected haplotype. Our data suggest that the predominant Northern European ancestry of families with DM2 resulted from a common founder and that the loss of interruptions within the CCTG portion of the repeat tract may predispose alleles to further expansion. To gain insight into possible function of the repeat tract, we looked for evolutionary conservation. The complex repeat motif and flanking sequences within intron 1 are conserved among human, chimpanzee, gorilla, mouse, and rat, suggesting a conserved biological function.

Linkage of proximal myotonic myopathy to chromosome 3q.

Article abstract We performed genetic linkage analysis in nine German proximal myotonic myopathy (PROMM) families using DNA-markers D3S1541 and D3S1589 from the region of the recently discovered gene locus of myotonic dystrophy type 2 (DM2) on chromosome 3q. Two-point analysis supplied an lod score of 5.9. We conclude that a gene causing PROMM is located on chromosome 3q. PROMM and DM2 may be allelic disorders or may be caused by closely linked genes.

A sporadic case of rippling muscle disease caused by a de novo caveolin-3 mutation

Objective: To determine the cause of sporadic rippling muscle disease (RMD) in a 24-year-old patient. Background: RMD is a rare myopathy characterized by percussion-induced rapid muscle contractions (PIRC), muscle mounding, and rippling waves. We have recently found that autosomal dominant RMD is caused by mutations in the caveolin-3 gene (CAV3) on chromosome 3p25. Possibly, increased activity of neuronal nitric oxide synthase (nNOS) contributes to the clinical characteristics of increased mechanical muscle hyperexcitability. Methods: Clinical examination, mutational analysis, and immunohistochemistry of muscle tissue were performed in a patient with sporadic RMD. Results: The authors observed a de novo CAV3 missense mutation Arg26Gln. Immunohistochemistry showed reduced caveolin-3 surface expression in a muscle biopsy. In addition, the authors found normal sarcolemmal nNOS expression and a reduced expression of α-dystroglycan in muscle fibers. Conclusions: These data confirm that RMD is caused by CAV3 mutations. Moreover, there is evidence that CAV3 mutations may also be found in patients without a positive family history of RMD.