MYBPH acts as modifier of cardiac hypertrophy in hypertrophic cardiomyopathy (HCM) patients.

Left ventricular hypertrophy is a risk factor for cardiovascular morbidity and mortality. Hypertrophic cardiomyopathy (HCM) is considered a model disease to study causal molecular factors underlying isolated cardiac hypertrophy. However, HCM manifests with various clinical symptoms, even in families bearing the same genetic defects, suggesting that additional factors contribute to hypertrophy. The gene encoding the cardiac myosin binding protein C (cMYBPC) is one of the most frequently implicated genes in HCM. Recently another myosin binding protein, myosin binding protein H (MYBPH) was shown to function in concert with cMYBPC in regulating cardiomyocyte contraction. Given the similarity in sequence, structure and the critical role MYBPH plays in sarcomere contraction, we proposed that MYBPH may be involved in HCM pathogenesis. Family-based genetic association analysis was employed to investigate the contribution of MYBPH in modifying hypertrophy. Seven single nucleotide polymorphisms and haplotypes in MYBPH were investigated for hypertrophy modifying effects in 388 individuals (27 families), in which three unique South African HCM-causing founder mutations (p.R403W and pA797T in ß-myosin heavy chain gene (MYH7) and p.R92W in the cardiac troponin T gene (TNNT2)) segregate. We observed a significant association between rs2250509 and hypertrophy traits in the p.A797T MYH7 mutation group. Additionally, haplotype GGTACTT significantly affected hypertrophy within the same mutation group. MYBPH was for the first time assessed as a candidate hypertrophy modifying gene. We identified a novel association between MYBPH and hypertrophy traits in HCM patients carrying the p.A797T MYH7 mutation, suggesting that variation in MYBPH can modulate the severity of hypertrophy in HCM.

Cardiac Myosin binding Protein C; Adrenergic Stimulation and Cardiac contractility

Myosin binding protein C remained a perplexing although integral component of the sarcomeric thick filament until the discovery that genetic defects in its corresponding gene is a frequent cause of hypertrophic cardiomyopathy. Basic science investigation subsequently revealed that it is one of the most potent regulators of cardiac contractility. Phosphorylation of its N-terminus upon adrenergic stimulation; causes increased order in myosin heads as well as increased ATPase activity; Fmax and Ca2+-sensitivity of contraction; while its dephosphorylation upon cholinergic stimulation or during low flow ischaemia leads to changes in the sarcomeric thick filament that diminish interaction between myosin heads and actin. This dynamic flux in phosphorylation upon adrenergic stimulation is not only crucial to normal cardiac function and structure; but also vital for protection against ischaemic injury. Genetically-driven deficiency or inadequacy in cMyBPC leads to severe cardiac dysfunction and structural changes; including cardiac hypertrophy and dilation; and particularly attenuates the adaptive increase in left ventricular contractility that follows on a-adrenergic stimulation or pressure overload; resulting in decreased systolic function; and reduced cardiac output

Mendelian-inherited heart disease: a gateway to understanding mechanisms in heart disease Update on work done at the University of Stellenbosch.

The presence of founder effects in South Africa for many single-gene diseases, which include heart diseases such as progressive familial heart block types I and II, hypertrophic cardiomyopathy and the long QT syndromes, afforded us the opportunity to identify causal genes and associated mutations through genetic mapping and positional cloning. From finding the genes, the emphasis has shifted to elucidating how primary defects cause disease and recognising factors that could explain the often pronounced phenotypic variability seen in persons carrying the same inherited defect. In some of these diseases, sudden unexpected death has been a frequent occurrence in young, apparently healthy individuals who had not been aware that they had inherited an underlying risk. Herein, we review progress in identifying genes, mutations and risk factors associated with the diseases mentioned.

Support for a trimeric collar of myosin binding protein C in cardiac and fast skeletal muscle, but not in slow skeletal muscle.

Myosin-binding protein C (MyBPC) is proposed to take on a trimeric collar arrangement around the thick filament backbone in cardiac muscle, based on interactions between cardiac MyBPC domains C5 and C8. We have now determined, using yeast two-hybrid and in vitro binding assays, that the C5:C8 interaction is not dependent on the 28-residue cardiac-specific insert in C5. Furthermore, an interaction of similar affinity occurs between domains C5 and C8 of fast skeletal muscle MyBPC, but not between these domains of the slow skeletal muscle protein. These data have implications for the role and quaternary structure of MyBPC in skeletal muscle.

Of Rain Men and Snowcakes : the Presentation; Pathology; Aetiology and Management of Autistic Spectrum Disorder

Over the past two decades; both the prevalence and our understanding of autism have increased exponentially. Autism encompasses a group of behaviourally defined develop- mental disorders; collectively known as autism spectrum disorder (ASD); which appear to be caused by the impact of environment during early life on genetically induced susceptibility. As paediatricians are consulted first by most parents of children with developmental delay; they should be able to discuss the pathology; aetiology and manage- ment of the disorder. Although much remains to be understood; research over the last 20 years has shown that this disorder is treatable; and that early medical/biomedical and behavioural intervention greatly improves the quality of life and outcomes of children with ASD

Race and gender representation of hypertrophic cardiomyopathy or long QT syndrome cases in a South African research setting.

We researched hypertrophic cardiomyopathy (HCM) and long QT syndrome (LQTS) as models for studying the pathophysiology of arrhythmias and hypertrophy, and in the process we have had the opportunity to compare local disease profiles with global patterns. We trawled our database entries over the past 20 years to identify all cases of heart muscle and arrhythmic disease. Among these, we separated the index cases from the rest of their family members, segregating for the relevant heart disease, so that numbers were not biased by family size, and analysed the race and gender composition of the HCM and LQTS sectors. The majority of HCM index cases (n = 90, 51.1% of HCM index cases) were of mixed ancestry (MA), with white Caucasian ancestry following closely behind with 74 cases (42.0%); only a few black African (n = 9, 5.1%) or Indian/Asian (n = 3, 1.7%) cases were seen or referred. The LQTS index cases were almost exclusively white Caucasian (n = 36, 88% of LQTS index cases), with four cases (9.8%) of MA, one (2.4%) of Indian/Asian and none of black African descent. These race demographics did not fit the national demographics for South Africa as a whole. In contrast, in both groups, gender biases (slightly more male than female HCM cases, and a 0.4 ratio of males to females in LQTS) previously reported elsewhere appeared to be replicated in our database. Genetic bias is an unlikely explanation for the skewed demographics in our database; a more likely explanation relates to various missed opportunities to diagnose, missed diagnoses and misdiagnoses, as well as the real population drainage of our main referral centre in the context of a differentiated healthcare system.

Violence in male patients with schizophrenia: risk markers in a South African population.

OBJECTIVE: We investigate the role of functional variants in the catecholamine-O-methyl transferase gene (COMT) and the monoamine oxidase-A gene (MOA-A), as well as previously identified non-genetic risk factors in the manifestation of violent behaviour in South African male schizophrenia patients. METHOD: A cohort of 70 acutely relapsed male schizophrenia patients was stratified into violent and non-violent subsets, based on the presence or absence of previous or current violent behaviour. Standardized violence rating scales were also applied and the COMT/NlaIII and MAO-A promoter region variable number of tandem repeats (VNTR) polymorphisms were genotyped. RESULTS: A multiple logistic regression model based on the clinical, genetic and socio-demographic variables indicated that delusions of control (OR = 3.7, 95% CI = 1.21-11.61) and the combined use of cannabis and alcohol (OR = 6.89, 95% CI = 1.28-37.05) were two significant predictors of violent behaviour in this schizophrenia population. No association was found between the tested polymorphisms and violent behaviour. CONCLUSIONS: Although the sample size may have limited power to exclude a minor role for these specific gene variants, such a small contribution would have limited clinical relevance given the strong significance of the non-genetic markers. These findings suggest that currently proactive management of violent behaviour in this schizophrenia population should continue to be based on clinical predictors of violence.

Mutations of the light meromyosin domain of the beta-myosin heavy chain rod in hypertrophic cardiomyopathy.

Familial hypertrophic cardiomyopathy (HCM) is caused by mutations in 9 sarcomeric protein genes. The most commonly affected is beta-myosin heavy chain (MYH7), where missense mutations cluster in the head and neck regions and directly affect motor function. Comparable mutations have not been described in the light meromyosin (LMM) region of the myosin rod, nor would these be expected to directly affect motor function. We studied 82 probands with HCM in whom no mutations had been found in MYH7 exons encoding the head and neck regions of myosin nor in the other frequently implicated disease genes. Primers were designed to amplify exons 24 to 40 of MYH7. These amplimers were subjected to temperature modulated heteroduplex analysis by denaturing high-performance liquid chromatography. An Ala1379Thr missense mutation in exon 30 segregated with disease in three families and was not present in 200 normal chromosomes. The mutation occurred on two haplotypes, indicating that it was not a polymorphism linked with another disease-causing mutation. The position of this residue within the LMM region of myosin suggests that it may be important for thick filament assembly or for accessory protein binding. A further missense mutation in exon 37, Ser1776Gly, segregated with disease in a single family and was absent from 400 population-matched control chromosomes. Because the Ser1776 residue occupies a core position in the myosin rod at which the substitution of glycine is extremely energetically unfavorable, it is likely to disrupt the coiled-coil structure. We conclude that mutation of the LMM can cause HCM and that such mutations may act through novel mechanisms of disease pathogenesis involving myosin filament assembly or interaction with thick filament binding proteins.

Obsessive-compulsive disorder and a novel polymorphism adjacent to the oestrogen response element (ERE 6) upstream from the COMT gene.

Family and twin studies have consistently provided evidence for involvement of genetic mechanisms in obsessive-compulsive disorder (OCD). This has given rise to association studies involving several candidate genes in an endeavour to identify susceptibility factors. One of the more promising candidate genes appears to be the catecol-O-methyltransferase (COMT) gene. Recent association studies in North American and Afrikaner populations have reported a likely association between a functional polymorphism of COMT (linked with COMT enzyme activity levels) and OCD. COMT expression has been demonstrated to be regulated by oestrogen through the oestrogen-response elements (EREs) in the promoter region of the gene. In the light of this association, the authors tested for an association between a novel polymorphism (C --> T transition) adjacent to ERE 6 in the promoter area of COMT and OCD in 48 Afrikaners and 48 ethnically matched controls. The C --> T transition was not significantly associated with OCD (P = 0.93) or gender (P = 0.67). These findings, although limited by a small sample size, suggest that the novel polymorphism adjacent to ERE 6 in the promoter area of COMT does not play a major role in the genetic predisposition to OCD.

Association between a catechol-o-methyltransferase polymorphism and obsessive-compulsive disorder in the Afrikaner population.

BACKGROUND: It has been proposed that the catechol-o-methyl transferase gene (COMT) may play a role in the pathogenesis of obsessive-compulsive disorder (OCD). Whereas studies in a North American population showed that the low activity (L) allele of a functional polymorphism in COMT was associated with OCD in male patients, this result was not supported by studies in a Japanese population. The present association study assessed the risk for OCD conferred by this COMT polymorphism in a geographically different patient group, namely, the relatively genetically homogeneous Afrikaner population of South Africa. METHODS: Fifty-four unrelated OCD patients and fifty-four sex-matched controls were recruited from the same Afrikaner community. Patients and controls were phenotyped (DSM-IV) and genotyped for a NlaIII polymorphism with H (high activity) or L (low activity) alleles in the COMT gene. RESULTS: The H/L genotype was significantly more common than expected in the OCD patient group (P = 0.0017). LIMITATIONS: Replication studies with related individuals may be useful in discovering factors underpinning the H/L genotype abundance in the Afrikaner population. CONCLUSIONS: These results emphasise the need for further studies in genetically homogeneous populations to help define the complex etiology of this disease.

Hypertrophic cardiomyopathy repealing tenets in South Africa.

Hypertrophic cardiomyopathy (HCM), a common primary cardiac disorder with an increased risk of sudden death, affects all population groups in South Africa. Distinct causal mutations in multiple sarcomeric protein-encoding genes correlate with the risk of sudden death. Such genotype/phenotype correlations cannot be extrapolated geographically or ethnically, necessitating the generation of South African-specific data. We used DNA-based techniques to search for the causal mutations in a panel of South African HCM-affected subjects (37 with unequivocal HCM, 47 with HCM-like disease). Mutations detected were traced in family members and carriers assessed by echocardiography and electrocardiography. Nine different HCM-causing mutations (5 unique to South Africa, 3 showing a founder effect) were identified in 3 genes in 24 index cases (57% HCM group, 6% HCM-like group). The different mutations were associated with variable hypertrophy, independent of the risk of sudden death. The disease was generally familial and many at-risk mutation carriers did not meet clinical diagnostic criteria for HCM. Rigorous diagnosis of index cases facilitates detection of causal mutations, which allows for unequivocal DNA-based diagnosis of at-risk family members, regardless of age or clinical status. This permits focused patient management, informed prognostication and realistic counselling for this insidious disease, as well as time and cost savings.

The origins of hypertrophic cardiomyopathy-causing mutations in two South African subpopulations: a unique profile of both independent and founder events.

Hypertrophic cardiomyopathy (HCM) is an autosomal dominantly inherited disease of the cardiac sarcomere, caused by numerous mutations in genes encoding protein components of this structure. Mutation carriers are at risk of sudden cardiac death, mostly as adolescents or young adults. The reproductive disadvantage incurred may explain both the global occurrence of diverse independent HCM-associated mutations and the rare reports of founder effects within populations. We have investigated whether this holds true for two South African subpopulations, one of mixed ancestry and one of northern-European descent. Previously, we had detected three novel mutations-Ala797Thr in the beta-myosin heavy-chain gene (betaMHC), Arg92Trp in the cardiac troponin T gene (cTnT), and Arg645His in the myosin-binding protein C gene (MyBPC)-and two documented betaMHC mutations (Arg403Trp and Arg249Gln). Here we report three additional novel mutations-Gln499Lys in betaMHC and Val896Met and Deltac756 in MyBPC-and the documented betaMHC Arg719Gln mutation. Seven of the nine HCM-causing mutations arose independently; no conclusions can be drawn for the remaining two. However, the betaMHC Arg403Trp and Ala797Thr and cTnT Arg92Trp mutations were detected in another one, eight, and four probands, respectively, and haplotype analysis in families carrying these recurring mutations inferred their origin from three common ancestors. The milder phenotype of the betaMHC mutations may account for the presence of these founder effects, whereas population dynamics alone may have overridden the reproductive disadvantage incurred by the more lethal, cTnT Arg92Trp mutation.

Properties of mutant contractile proteins that cause hypertrophic cardiomyopathy.

Hypertrophic cardiomyopathy (HCM) is one of the most frequently occurring inherited cardiac disorders, affecting up to 1 in 500 of the population. Molecular genetic analysis has shown that HCM is a disease of the sarcomere, caused by mutations in certain contractile protein genes. To date seven disease-associated genes have been identified, those encoding beta-myosin heavy chain, both regulatory and essential myosin light chains, myosin binding protein-C, cardiac troponin T, cardiac troponin I and alpha-tropomyosin. Here we review the analyses of how these mutations affect the in vitro contractile protein function and the hypotheses derived to explain the development of the disease state.

Identification of a new missense mutation in MyBP-C associated with hypertrophic cardiomyopathy.

Hypertrophic cardiomyopathy is a primary cardiac disease, characterised by idiopathic myocardial hypertrophy, and is caused by defects in sarcomeric protein encoding genes. One of these genes is cardiac myosin binding protein C (MyBP-C), in which a number of splice site and duplication mutations causing HCM have been described. During mutation screening of a South African HCM population by PCR-SSCP, a missense mutation, Arg654His, was detected in one proband. Although the mutation was present in his three adult children, only the proband himself was markedly affected. This is the first report of a disease associated missense mutation in MyBP-C which does not affect the myosin or titin binding domains.