Myotone Dystrophien – Phänotypen, Pathogenese, Diagnostik und Therapie

Zwei Formen der myotonen Dystrophie (DM1, DM2) sind bisher beschrieben. 1992 konnte als genetische Ursache der DM1 ein abnorm expandiertes CTG-Triplettrepeat im 3´-UTR (untranslated region) des Dystrophia myotonica Proteinkinasegens (DMPK) auf Chromosom 19 gefunden werden. Die DM2 wurde 1994 durch Ricker und Thornton beschrieben und 2001 konnte ein abnorm expandiertes Tetranukleotid CCTG-Repeat im Intron 1 des Zinkfinger-9-Gens (ZNF-9) auf Chromosom 3q als kausal identifiziert werden. Multisystemische Symptome betreffen Skelettmuskulatur, Gehirn, Auge, Herz und Endokrinum. Der heterogenen Ätiologie mit zwei genetischen Loci liegt pathogenetisch eine RNA-Prozessierungsstörung mit alternativem Spleißen von organspezifischen Genen zugrunde (sogenanntes Konzept der Spleißeopathie).

Unser Symposium umfasste Beiträge zu aktuellen Aspekten der Klinik, Diagnostik, Bildgebung, Geburtshilfe und Schwangerschaft, molekularen RNA-Pathogenese sowie symptomatischen und molekularen Therapieoptionen.

Brain imaging and neuropsychology in late-onset dementia due to a novel mutation (R93C) of valosin-containing protein

Inclusion body myopathy with Paget disease of bone and frontotemporal dementia (IBMPFD, MIM 167320) is a recently identified autosomal dominant disorder due to mutations in the valosin-containing protein (VCP) that affects muscle, bone and brain. Brain involvement and neuropsychological findings of IBMPFD have not been described in detail. A patient carried a novel heterozygous base pair change, 47832C>T, in the VCP gene that resulted in substitution of an arginine residue by cysteine at position 93 (R93C). He presented first with myopathy while bone involvement remained subclinical. The patient developed behavioral abnormalities in his 60s and showed frank personality change with fluent empty speech at the age of 74 years. This syndrome was best classified as semantic dementia. Magnetic resonance imaging disclosed slight but progressive cerebral atrophy with prominent callosal and frontal white matter loss. Positron emission tomography demonstrated glucose hypometabolism of the frontal and temporal lobes disproportionate to their structural involvement. This first comprehensive clinical and neuroimaging study in IBMPFD may raise the awareness among clinicians as well as basic scientists for this exemplary genetic model of dementia.

Adult-onset glycogen storage disease type 2: clinico-pathological phenotype revisited

The need for clinical awareness and diagnostic precision of glycogen storage disease type 2 (GSD2) has increased, as enzyme replacement therapy has become available. So far, only small series have reported the muscle pathology of late-onset GSD2. We reassessed 43 muscle biopsies of 38 GSD2 patients. In all patients the diagnosis of GSD2 has been established by biochemistry and/or mutational analysis of the GAA gene. Additionally to the expected morphological features, ultrastructural analysis revealed a high incidence of autophagic vacuoles, lipofuscin debris, structural Z-line disorganization and histological neurogenic-like pattern that were not thoroughly appreciated, previously. Comparing age at onset and morphology, excessive vacuolar and autophagic myopathy and mitochondrial disorganization of virtually all fibres is common in infants. At juvenile onset, a more moderate vacuolization without significant differences in overall morphology is notable. At late-onset, the spectrum of vacuolar myopathy is more divergent, ranging from almost normal to severe. Here pronounced secondary alterations are observed that include lipofuscin debris, autophagic vacuoles with residual lysosomal bodies and granular inclusions, structural mitochondrial and Z-line texture alterations. Moreover, there is a high incidence of subtle neurogenic-like alteration in all subtypes. Nineteen patients were genetically tested; in 15 patients the common leaky splicing mutation c.-45T>G (or IVS1-13T>G) in intron1 of the GAA gene was found on at least one allele, facilitating genetic screening. In our patients, GAA genotype appears not to be associated with secondary alterations such as autophagic vacuoles, structural alterations or neurogenic-like changes. These findings may have implications for our understanding of the pathogenesis of GSD2 and for assessing therapeutic success of enzyme replacement therapy.

Serum Levels of Matrix Metalloproteinases-2 and -9 and Their Tissue Inhibitors in Inflammatory Neuromuscular Disorders

We monitored serum levels of matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) before and during intravenously applied immunoglobulin (IVIG) therapy in 33 patients with chronic immune-mediated neuropathies and myopathies and 15 controls. Baseline MMP-2 and TIMP-2 serum levels were lower and MMP-9 and TIMP-1 serum levels higher in all patients compared to age-matched controls. Eight days after IVIG treatment, MMP-2, TIMP-2, and TIMP-1 serum levels increased, while MMP-9 serum levels decreased, indicating tissue repair. After 60 days, MMP-9 levels increased, MMP-2 approached normal levels, while TIMP-1 and TIMP-2 serum levels were below day 8 levels, indicating relapsing tissue damage. Comparing the MMP/TIMP results with the clinical courses, IVIG treatment tended to change MMP/TIMP levels in a way that paralleled clinical improvement and relapse. In sum, during a distinct time period, IVIG therapy seems to be able to modulate MMP-mediated tissue repair.

Prediction of response to IVIg treatment in patients with lower motor neurone disorders

The distinction between multifocal motor neuropathy, treatable by intravenous immunoglobulins (IVIg), and degenerative motor neurone disorders is often difficult. To find predictive factors for the response to IVIg treatment, 40 consecutive patients with pure lower motor neurone disorders (LMND) were prospectively examined. They all received at least two times IVIg (2 g/kg bodyweight). Prior to the first and before all the following treatments a standardized evaluation was performed including clinical examination, neurophysiological and laboratory evaluation. According to changes in the neurological examination and the Neuromuscular Symptom Score, the patients were divided into responders and non-responders after the second course of treatment. In our study, no single clinical, neurophysiological, or laboratory parameter was sensitive enough to predict response. The only single parameter that highly correlated with a positive response to treatment was an elevated GM1 antibody titre. Lack of response to IVIg treatment is likely in patients with generalization of electromyographic signs of denervation beyond the clinically involved site, proximal localization of the weakness, and an elevated level of the creatinekinase. Conduction blocks do not distinguish between both groups. We propose a scoring system combining clinical, serological and neurophysiological data in order to decide which patients with LMND may receive IVIg.

Outcome and effect of pregnancy in myotonic dystrophy type 2

The authors reviewed the obstetric histories of 42 women of 37 families with myotonic dystrophy type 2 (DM2). Nine women (21%) had the first symptoms during pregnancy and worsening in subsequent pregnancies. Of 96 pregnancies, 13% ended as early and 4% as late miscarriages. Preterm labor occurred in 50% of pregnancies resulting in 27% preterm deliveries in women with overt DM2 in pregnancy. There was no evidence of a congenital DM2.

Coenzyme Q10 deficiency and isolated myopathy

Three unrelated, sporadic patients with muscle coenzyme Q10 (CoQ10) deficiency presented at 32, 29, and 6 years of age with proximal muscle weakness and elevated serum creatine kinase (CK) and lactate levels, but without myoglobinuria, ataxia, or seizures. Muscle biopsy showed lipid storage myopathy, combined deficiency of respiratory chain complexes I and III, and CoQ10 levels below 50% of normal. Oral high-dose CoQ10 supplementation improved muscle strength dramatically and normalized serum CK.

Mutations in mtDNA-encoded cytochrome c oxidase subunit genes causing isolated myopathy or severe encephalomyopathy

We report on clinical, histological and genetic findings in two patients carrying novel heteroplasmic mutations in the mitochondrial cytochrome c oxidase subunit genes COII and COIII. The first patient, a 35 year-old man had a multisystemic disease, with clinical symptoms of bilateral cataract, sensori-neural hearing loss, myopathy, ataxia, cardiac arrhythmia, depression and short stature and carried a 7970 G>T (E129X) nonsense mutation in COII. A sudden episode of metabolic encephalopathy caused by extremely high blood lactate lead to coma. The second patient developed exercise intolerance and rhabdomyolysis at age 22 years. A heteroplasmic missense mutation 9789 T>C (S195P) was found in skeletal muscle, but not in blood and myoblasts pointing to a sporadic mutation. Our report of two patients with isolated COX deficiency and new mutations in COX subunit genes may help to draw more attention to this type of mtDNA defects and provide new aspects for counselling affected families.

Lipidsenker- und andere toxische Myopathien

A growing number of therapeutic agents and exogenous toxins are harmful to structure and function of human skeletal muscle. The clinical syndrome encompasses asymptomatic creatine kinase elevation, myalgia, exercise intolerance, muscle paresis and atrophy, and lastly acute rhabdomyolysis. Toxic myopathies are potentially reversible, hence a prompt recognition is particularly helpful for the early diagnosis and in conclusion elimination of a myopathy inducing toxin. Toxic myopathies may be classified as acute or chronic accordingly to the exposition time to a toxin. Main source of an exogenous induced toxic myopathy is chronic alcohol abuse. Alcohol excess induces acute and/or chronic neuropathy and myopathy, consequently muscle wasting and weakness occurs. Drug-induced myopathies are most frequently seen due to amplified utilization of corticosteroids or lipid lowering agents.

Mutations in the acid alpha-glucosidase gene (M. Pompe) in a patient with an unusual phenotype

Glycogenosis type II (Pompe disease) is a lysosomal storage disease caused by deficiency of acid alpha-glucosidase (acid maltase). The disease is autosomal recessive inherited and is clinically and genetically heterogenous. The authors describe a 30-year-old woman affected by late-onset Pompe disease with vascular affection resembling atherosclerotic angiopathy of the elderly. Genetic analysis revealed two novel mutations (Ala237Val and Gly293Arg) in the acid alpha-glucosidase gene in this patient.

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.

Novel missense mutation in the caveolin-3 gene in a Belgian family with rippling muscle disease

Rippling muscle disease (RMD) is a rare muscle disorder characterised by muscle stiffness, exercise induced myalgia, and cramp-like sensations. It is genetically heterogeneous and can be acquired, but most cases show autosomal dominant inheritance due to mutations in the caveolin-3 (CAV3) gene. We report a novel heterozygous missense mutation in CAV3 in a Belgian family with autosomal dominant RMD. A 40 year old woman complained of fatigue, exercise induced muscle pain, and muscle cramps since the age of 35. Neurological examination revealed percussion induced rapid muscle contractions (PIRCs) and localised muscle mounding on percussion; muscle rippling was not observed. Creatine kinase (CK) was elevated but electromyography and nerve conduction studies were normal. Fluorescence immunohistochemistry revealed reduced caveolin-3 and dysferlin staining in a quadriceps muscle biopsy. Western blot analysis confirmed severely reduced caveolin-3 levels, whereas dysferlin was normal. Sequence analysis of the two coding exons of CAV3 revealed a hitherto unreported heterozygous C82A transversion in the first exon, predicting a Pro28Thr amino acid exchange. Thr patient's first degree relatives did not present with neuromuscular complaints, but PIRCs, muscle mounding, and muscle rippling were found in the mother, who also carried the CAV3 mutation.

Matrix metalloproteinases in inflammatory myopathies: enhanced immunoreactivity near atrophic myofibers

OBJECTIVES

To further examine the role of proteolytic enzyme expression of matrix metalloproteinases (MMP) and T-cell markers in inflammatory myopathies and controls.

MATERIAL AND METHODS

We studied the expression of MMP-2, MMP-7, and MMP-9 in 19 cases of inflammatory myopathies and controls using immunocytochemistry.

RESULTS

Inflammatory myopathies showed distinct patterns of up-regulation of MMP. MMP-9 was strongly expressed in atrophic myofibers in all inflammatory myopathies. MMP-2 immunoreactivity was similar in its distribution, however, to a weaker intensity. In dermatomyositis the perifascicular atrophy showed pronounced MMP-9 immunoreactivity, probably reflecting denervated patterns of myofibers. Moreover, MMP-7 strongly immunolabeled invaded myofibers in polymyositis cases only.

CONCLUSION

These patterns confirm, that MMP-7 up-regulation is prominent in PM, while MMP-2 immunoreactivity is only slightly elevated in inflamed muscle. In general, MMP-9 up-regulation appears to be an important additional molecular event in the multistep process of all inflammatory myopathies.