K.J. Osterziel

Unequal allelic expression of wild-type and mutated β-myosin in familial hypertrophic cardiomyopathy

Familial hypertrophic cardiomyopathy (FHC) is an autosomal dominant disease, which in about 30% of the patients is caused by missense mutations in one allele of the β-myosin heavy chain (β-MHC) gene (MYH7). To address potential molecular mechanisms underlying the family-specific prognosis, we determined the relative expression of mutant versus wild-type MYH7-mRNA. We found a hitherto unknown mutation-dependent unequal expression of mutant to wild-type MYH7-mRNA, which is paralleled by similar unequal expression of β-MHC at the protein level. Relative abundance of mutated versus wild-type MYH7-mRNA was determined by a specific restriction digest approach and by real-time PCR (RT-qPCR). Fourteen samples from M. soleus and myocardium of 12 genotyped and clinically well-characterized FHC patients were analyzed. The fraction of mutated MYH7-mRNA in five patients with mutation R723G averaged to 66 and 68% of total MYH7-mRNA in soleus and myocardium, respectively. For mutations I736T, R719W and V606M, fractions of mutated MYH7-mRNA in M. soleus were 39, 57 and 29%, respectively. For all mutations, unequal abundance was similar at the protein level. Importantly, fractions of mutated transcripts were comparable among siblings, in younger relatives and unrelated carriers of the same mutation. Hence, the extent of unequal expression of mutated versus wild-type transcript and protein is characteristic for each mutation, implying cis-acting regulatory mechanisms. Bioinformatics suggest mRNA stability or splicing effectors to be affected by certain mutations. Intriguingly, we observed a correlation between disease expression and fraction of mutated mRNA and protein. This strongly suggests that mutation-specific allelic imbalance represents a new pathogenic factor for FHC.

Familial dilated cardiomyopathy

ZusammenfassungEine häufige Ursache der Herzinsuffizienz ist die dilatative Kardiomyopathie (DCM). Sie ist in ca. 20–30% genetisch bedingt. Eine Familienanamnese und eine kardiologische Untersuchung von Familienangehörigen sind daher bei jedem Patienten mit einer bisher in der Ätiologie ungeklärten DCM sinnvoll und empfehlenswert. Für die Klassifikation einer familiären DCM sollten die Kriterien der “Collaborative Research Group of the European Human and Capital Mobility Project on Familial Dilated Cardiomyopathy” zugrunde gelegt werden. Die Variabilität der Erkrankung ist selbst innerhalb einer Familie sehr groß, so dass Genotyp-Phänotyp-Korrelationen nur mit diesen Einschränkungen zu betrachten sind. Bisher sind Mutationen in 24 Genen bekannt, die zu einer familiären DCM führen können. Mutationen im β-Myosin, Troponin T und Lamin A/C sowie Dystrophin sind relativ häufige Ursachen der familiären DCM, während Muta tionen in allen anderen Genen selten als Ursache in Frage kommen. Ein systematisches Screening aller bekannten Gene würde nur etwa 20% der Fälle aufklären und ist derzeit noch zu aufwendig. Es ist zu hoffen, dass weitere Gene identifiziert und effizientere Screeningmethoden entwickelt werden. Denn erst ein anderes Verständnis der Pathogenese der DCM wird auch zu prinzipiell neuen Therapieoptionen für diese maligne verlaufende Erkrankung führen.AbstractDilated cardiomyopathy (DCM) is the most frequent form of primary myocardial diseases and the third most common cause of heart failure. Clinically, DCM is characterized by a progressive course of ventricular dilatation and systolic dysfunction. The life expectancy is limited and varies according to the underlying etiology with a median survival time of about 5 years after diagnosis. Myocarditis, immunologic abnormalities, toxic myocardial damage, and genetic factors are all assumed to be causes. Familial occurrence of DCM, mostly as an autosomal dominant trait, is more common than generally believed and is responsible for 20–30% of all cases of DCM. Candidate gene screening and linkage analyses in large families were successful in identifying 24 disease genes. There is a wide variability in the onset, course and severity of the disease even within the same family. In addition, genotype-phenotype correlations included only small numbers of affected. This implies that in most cases no conclusion can be drawn from the clinical manifestation of DCM to the responsible disease gene. Mutations in the β-myosin heavy chain and in cardiac troponin T are common causes of pure familial DCM. DCM associated with conduction disease is mainly due to mutations in lamin A/C and X-linked DCM is often caused by mutations in dystrophin. All other disease genes are rare causes of familial DCM. Genetic screening in all known disease genes is not possible, but more efficient screening methods are awaited in the near future. Until then, clinical examination of family members and, in case of familial DCM, genetic counseling are recommended in the work-up of patients with idiopathic DCM.

Die arrhythmogene rechtsventrikuläre Kardiomyopathie

ZusammenfassungDie arrhythmogene rechtsventrikuläre Kardiomyopathie (ARVC) ist durch eine lokalisierte oder generalisierte Degeneration und Atrophie des rechtsventrikulären Myokards mit nachfolgendem Ersatz durch Fett- und Bindegewebe charakterisiert. Klinisch steht das rezidivierende Auftreten von Kammertachykardien mit linksschenkelblockartiger Konfiguration im Vordergrund; in einem späteren Stadium der Erkrankung kann es zu einer Herzinsuffizienz kommen.Die Prognose der ARVC wird maßgeblich durch die auftretenden ventrikulären Tachyarrhythmien und die Möglichkeit des Auftretens eines plötzlichen Herztodes bestimmt. Letzterer scheint bevorzugt bei jungen, sportlich aktiven, bis dahin nicht selten kardial unauffälligen Patienten aufzutreten. Bei ca. 30–50% der Angehörigen von ARVC-Betroffenen finden sich Hinweise auf eine familiäre Manifestation der Erkrankung. Die ARVC ist eine genetisch gesehen ausgesprochen heterogene Erkrankung.Diagnostisch stehen die Arrhythmiediagnostik, charakteristische EKG-Befunde und der Nachweis ARVC-typischer Veränderungen des rechten Ventrikels (regionale/globale Kontraktionsstörungen, Aneurysmen, rechtsventrikuläre Fibrolipomatose) im Vordergrund. Mittlerweile konnten zwar erste krankheitsverursachende Gene identifiziert werden, eine genetische Diagnostik steht für die routinemäßige Anwendung aber nicht zur Verfügung.Die Erkrankung verläuft häufig progredient. Patienten mit schwerwiegender Symptomatik (Synkopen, hämodynamisch kompromittierende Kammertachykardien, überlebter plötzlicher Herztod) werden mit einem implantierbaren Kardioverter- Defibrillator behandelt. In Einzelfällen kann im Endstadium mit rechts- oder biventrikulärer Herzinsuffizienz eine Herztransplantation notwendig werden.AbstractArrhythmogenic right ventricular cardiomyopathy (ARVC) is a primary myocardial disorder that is characterized by localized or diffuse atrophy of predominantly right ventricular myocardium with subsequent replacement by fatty and fibrous tissue. Arrhythmias of right ventricular origin are the main clinical manifestation. Affected patients present with ventricular premature beats and nonsustained or sustained ventricular tachycardia demonstrating a left bundle branch block pattern. However, since ventricular tachycardia may also degenerate into ventricular fibrillation, sudden death may be the first manifestation of ARVC.In recent years, ARVC has been more and more recognized as an important and frequent cause of ventricular tachyarrhythmias and sudden cardiac death, particularly in young patients and athletes, with apparently normal hearts. Evidence of the disease is found in 30–50% of family members. ARVC is a genetically heterogeneous disease.The diagnosis is based on electrocardiographic abnormalities and the identification of regional or global right ventricular dysfunction and fibrolipomatosis. Although several potentially causative genes have been identified, currently, genetic testing is not part of the routine diagnostic work-up.An implantable cardioverter-defibrillator is indicated in selected high-risk patients with ARVC (i. e., patients with life-threatening ventricular tachycardia or survivors of sudden cardiac death). The clinical course of the disease is often characterized by progression. In individual patients heart transplantation may become necessary.

Kardiale Manifestationen bei Muskeldystrophien

Muscular dystrophies (MD) are a clinically and genetically heterogenous disease group. In the last few years, remarkable progress has been made in understanding the close und various relations between skeletal muscle disease and heart muscle disease. Cardiac involvement has been documented in a number of primary MDs and is even the dominant feature in some of them. The myocardium can be affected in the form of a dilated cardiomyopathy while the conduction system can be affected resulting in arrhythmias and conduction defects. Many patients with MD die because of cardiac complications like sudden cardiac death or congestive heart failure. Detailed clinical data about cardiac involvement are available for Duchenne/Becker MD, Emery-Dreifuss MD, myotonic dystrophy, and the different limb girdle MDs. Cardiac manifestations were also found in congenital MD, central core disease, proximal myotonic myopathy, and nemaline myopathy. No data about cardiac abnormalities are available in oculopharyngeal MD and rippling muscle disease. The heart of patients with primary MD should be carefully investigated because of the life-threatening events caused by cardiac complications. There is a strong need for a close collaboration between neurologists and cardiologists in order to provide optimal disease management for the affected patients. Die Muskeldystrophien (MD) stellen sich als eine klinisch und genetisch sehr heterogene Krankheitsgruppe dar. In den vergangenen Jahren wurde zunehmend erkannt, dass es vielfältige und enge Beziehungen zwischen Muskeldystrophien und Kardiomyopathien gibt. Eine kardiale Beteiligung ist bei vielen unterschiedlichen primären MD-Formen gefunden worden und stellt bei einigen einen dominierenden Aspekt der Erkrankung dar. Die Herzbeteiligung betrifft meist das Myokard in Form einer dilatativen Kardiomyopathie und/oder das Reizleitungssystem in Form bradykarder Rhythmusstörungen. Viele Patienten mit MD versterben aufgrund dieser Manifestationen am Pumpversagen oder am plötzlichem Herztod. Bei der Duchenne/Becker MD, der Emery-Dreifuss MD, der myotonen Dystrophie und den Gliedergürtel- MDs ist die kardiale Manifestation detailiert und umfassend beschrieben worden. Eine Herzbeteiligung ist ebenfalls gefunden worden bei der kongenitalen MD, der Central Core Disease, der proximalen myotonen Myopathie und der Nemalin-Myopathie. Bei einigen seltenen Formen wie der okulopharyngealen MD und der Rippling Muscle Disease liegen keine Erkenntnisse zur Herzbeteiligung vor. Die kardiale Diagnostik sollte eine zentrale Rolle bei der Untersuchung von Patienten mit Muskelerkrankungen spielen, da kardiale Komplikationen oft lebensbedrohend sein können. Diagnostik und Therapie von Muskeldystrophien sollten in enger Zusammenarbeit von Neurologen und Kardiologen interdisziplinär erfolgen, um eine optimale Betreuung der Patienten zu gewährleisten.

A new LMNA mutationcausing limb girdlemuscular dystrophy 1B

Sirs: We describe a family with adult-onset limb girdle muscular dystrophy 1B (LGMD1B) due to a new mutation in LMNA encoding for lamin A/C. Lamins A/C maintain nuclear shape and provide a structural support for chromosomes [7]. Mutations in LMNA cause a variety of diseases, now called laminopathies: autosomaldominant and autosomal-recessive Emery-Dreifuss muscular dystrophy (AD-EDMD and AR-EDMD) [1], limb girdle muscular dystrophy 1B (LGMD1B) [8], dilated cardiomyopathy (DCM) with conduction defect [3], familial partial lipodystrophy type Dunnigan (FPLP) [11], CharcotMarie-Tooth neuropathy 2B1 (CMT2B1) [10], and several progeria syndromes [2, 9].The molecular mechanisms leading to these different clinical phenotypes are not understood. It appears that different parts of the molecule play different roles in their interaction with other molecules and stability of the protein [4, 7]. The 48 year old female index patient was well until she was 35 years of age when she noticed difficulty in climbing stairs. The muscular weakness was slowly progressive and was accompanied by mild dyspnea. She denied any stiffness or rigidity of her back, elbows or ankles. The family history revealed that the father had died at a young age because of lung cancer but muscle weakness could not be recalled. Her mother was in good health. On physical examination manual muscle testing revealed a moderate limb-girdle weakness with the pelvic girdle being predominantly affected (hip-flexor paresis 3–4/5). There were no contractures (Fig. A and B). The 19 year old daughter had minimal limb girdle weakness without contractures. Cardiac examination was normal. The creatinkinase was 10-times above normal. Metabolically, there were no signs of insulin-resistance, hyperlipidemia or other abnormalities typical of lipodystrophy The muscle specimen showed signs of a mild dystrophy with a normal immunohistochemical analysis. Cardiac examination revealed permanent atrial fibrillation and AV-block III° after cardioversion. A pacemaker was implanted at age 49. Cardiac MRI was performed using a phased array cardiac surface coil. On CINE-MRI images wall motion abnormalities could be detected at the apex and inferoseptal wall of the left ventricle, as well as a delayed contrast enhancement in the same regions (Fig. C). The phenomenon of delayed myocardial enhancement on MRI was first used to detect areas of non-viable myocardium in chronic myocardial infarction [5]. To our knowledge, we are the first to describe this phenomenon in a patient with muscular dystrophy. For mutation analysis of LMNA all exons and the promoter region were amplified [3]. The analysis was confirmed by sequencing in both directions (Fig. D) and subsequently by restriction enzyme analysis (Fig. E). The identified missense mutation exchanges tryptophan at position 498 for cysteine (W498C). The mutation was found in the index patient and in both of her children. Her mother did not carry the mutation. LGMD1B is rare within the LMNA-associated neuromuscular disorders. Whereas only eight mutations have been found leading to LGMD1B the EDMD phenotype is caused by more than 40 mutations spread out over the entire gene [6, 12–14]. On the protein level, tryptophan 498 is located at the C-terminus of betastrand 6 within the globular domain of lamin A/C. At this position there is a conserved aromatic residue in lamins. The side chain of tryptophan 498 is located at the center of a cavity, surrounded by mainly hydrophobic side chains of different beta-strands that are not close in the lamin sequence but in tertiary structure. Interestingly, another mutation associated with the rare LGMD1B phenotype is also found in the globular domain of lamin A/C, Y481H [6]. Y481 is located on beta 5 in a cavity close to W498 (Fig. E). This might be coincidental but could also represent a mutational hotspot in LMNA for LGMD1B.

A new LMNA

Sirs: We describe a family with adult-onset limb girdle muscular dystrophy 1B (LGMD1B) due to a new mutation in LMNA encoding for lamin A/C. Lamins A/C maintain nuclear shape and provide a structural support for chromosomes [7]. Mutations in LMNA cause a variety of diseases, now called laminopathies: autosomaldominant and autosomal-recessive Emery-Dreifuss muscular dystrophy (AD-EDMD and AR-EDMD) [1], limb girdle muscular dystrophy 1B (LGMD1B) [8], dilated cardiomyopathy (DCM) with conduction defect [3], familial partial lipodystrophy type Dunnigan (FPLP) [11], CharcotMarie-Tooth neuropathy 2B1 (CMT2B1) [10], and several progeria syndromes [2, 9].The molecular mechanisms leading to these different clinical phenotypes are not understood. It appears that different parts of the molecule play different roles in their interaction with other molecules and stability of the protein [4, 7]. The 48 year old female index patient was well until she was 35 years of age when she noticed difficulty in climbing stairs. The muscular weakness was slowly progressive and was accompanied by mild dyspnea. She denied any stiffness or rigidity of her back, elbows or ankles. The family history revealed that the father had died at a young age because of lung cancer but muscle weakness could not be recalled. Her mother was in good health. On physical examination manual muscle testing revealed a moderate limb-girdle weakness with the pelvic girdle being predominantly affected (hip-flexor paresis 3–4/5). There were no contractures (Fig. A and B). The 19 year old daughter had minimal limb girdle weakness without contractures. Cardiac examination was normal. The creatinkinase was 10-times above normal. Metabolically, there were no signs of insulin-resistance, hyperlipidemia or other abnormalities typical of lipodystrophy The muscle specimen showed signs of a mild dystrophy with a normal immunohistochemical analysis. Cardiac examination revealed permanent atrial fibrillation and AV-block III° after cardioversion. A pacemaker was implanted at age 49. Cardiac MRI was performed using a phased array cardiac surface coil. On CINE-MRI images wall motion abnormalities could be detected at the apex and inferoseptal wall of the left ventricle, as well as a delayed contrast enhancement in the same regions (Fig. C). The phenomenon of delayed myocardial enhancement on MRI was first used to detect areas of non-viable myocardium in chronic myocardial infarction [5]. To our knowledge, we are the first to describe this phenomenon in a patient with muscular dystrophy. For mutation analysis of LMNA all exons and the promoter region were amplified [3]. The analysis was confirmed by sequencing in both directions (Fig. D) and subsequently by restriction enzyme analysis (Fig. E). The identified missense mutation exchanges tryptophan at position 498 for cysteine (W498C). The mutation was found in the index patient and in both of her children. Her mother did not carry the mutation. LGMD1B is rare within the LMNA-associated neuromuscular disorders. Whereas only eight mutations have been found leading to LGMD1B the EDMD phenotype is caused by more than 40 mutations spread out over the entire gene [6, 12–14]. On the protein level, tryptophan 498 is located at the C-terminus of betastrand 6 within the globular domain of lamin A/C. At this position there is a conserved aromatic residue in lamins. The side chain of tryptophan 498 is located at the center of a cavity, surrounded by mainly hydrophobic side chains of different beta-strands that are not close in the lamin sequence but in tertiary structure. Interestingly, another mutation associated with the rare LGMD1B phenotype is also found in the globular domain of lamin A/C, Y481H [6]. Y481 is located on beta 5 in a cavity close to W498 (Fig. E). This might be coincidental but could also represent a mutational hotspot in LMNA for LGMD1B.

Growth hormone therapy in heart failure

Clinical and experimental data in animals and patients with endstage heart failure due to dilated cardiomyopathy or ischemic heart disease suggest a beneficial role of growth factors like human recombinant growth hormone or insulin-like growth factor I. Their cardiac effects are an increase in myocardial mass and a decrease in systolic wall stress. Based on the results of animal studies and of preliminary studies in patients with dilated cardiomyopathy, double-blind and placebo-controlled studies have proven the increase in myocardial mass and a significant reduction of left ventricular wall stress, as demonstrated by magnetic resonance imaging. The risk of the additional therapy with human growth factors in this high-risk group of patients with a high mortality is justified, if this new approach becomes a possible alternative to cardiac transplantation or a bridge toward transplantation. If future randomized studies in larger patient groups with an individualized substitution therapy with growth hormone and/or IGF-I can demonstrate a beneficial effect on mortality and morbidity, this new therapeutic approach could become an attractive alternative in these high-risk patients.