AKAP9 is a genetic modifier of congenital long-QT syndrome type 1

BACKGROUND

Long-QT syndrome (LQTS), a cardiac arrhythmia disorder with variable phenotype, often results in devastating outcomes, including sudden cardiac death. Variable expression, independently from the primary disease-causing mutation, can partly be explained by genetic modifiers. This study investigates variants in a known LQTS-causative gene, AKAP9, for potential LQTS-type 1-modifying effects.

METHODS AND RESULTS

Members of a South African LQTS-type 1 founder population (181 noncarriers and 168 mutation carriers) carrying the identical-by-descent KCNQ1 p.Ala341Val (A341V) mutation were evaluated for modifying effects of AKAP9 variants on heart rate-corrected QT interval (QTc), cardiac events, and disease severity. Tag single nucleotide polymorphisms in AKAP9 rs11772585, rs7808587, rs2282972, and rs2961024 (order, 5'-3'positive strand) were genotyped. Associations between phenotypic traits and alleles, genotypes, and haplotypes were statistically assessed, adjusting for the degree of relatedness and confounding variables. The rs2961024 GG genotype, always represented by CGCG haplotype homozygotes, revealed an age-dependent heart rate-corrected QT interval increase (1% per additional 10 years) irrespective of A341V mutation status (P=0.006). The rs11772585 T allele, found uniquely in the TACT haplotype, more than doubled (218%) the risk of cardiac events (P=0.002) in the presence of A341V; additionally, it increased disease severity (P=0.025). The rs7808587 GG genotype was associated with a 74% increase in cardiac event risk (P=0.046), whereas the rs2282972 T allele, predominantly represented by the CATT haplotype, decreased risk by 53% (P=0.001).

CONCLUSIONS

AKAP9 has been identified as an LQTS-type 1-modifying gene. Variants investigated altered heart rate-corrected QT interval irrespective of mutation status, as well as cardiac event risk, and disease severity, in mutation carriers.

Long QT syndrome in South Africa: the results of comprehensive genetic screening

Congenital long QT syndrome (cLQTS) is a genetic disorder predisposing to ventricular arrhythmia, syncope and sudden death. Over 700 different cLQTS-causing mutations in 13 genes are known. The genetic spectrum of LQTS in 44 South African cLQTS patients (23 known to carry the South African founder mutation p.A341V in KCNQ1) was established by screening for mutations in the coding regions of KCNQ1, KCNH2, KCNE1, KCNE2 and SCN5A, the most frequently implicated cLQTS-causing genes (five-gene screening). Fourteen disease-causing mutations were identified, eight (including the founder mutation) in KCNQ1, five in KCNH2 and one in KCNE1. Two mutations were novel. Two double heterozygotes were found among the 23 families (8.5%) carrying the founder mutation. In conclusion, cLQTS in South Africa reflects both a strong founder effect and a genetic spectrum similar to that seen in other populations. Consequently, five-gene screening should be offered as a standard screening option, as is the case internationally. This will disclose compound and double heterozygotes. Fivegene screening will most likely be even more informative in other South African sub-populations with a greater genetic diversity.

MicroRNAs in cardiac arrhythmia: DNA sequence variation of MiR-1 and MiR-133A in long QT syndrome

Long QT syndrome (LQTS) is a genetic cardiac condition associated with prolonged ventricular repolarization, primarily a result of perturbations in cardiac ion channels, which predisposes individuals to life-threatening arrhythmias. Using DNA screening and sequencing methods, over 700 different LQTS-causing mutations have been identified in 13 genes worldwide. Despite this, the genetic cause of 30-50% of LQTS is presently unknown. MicroRNAs (miRNAs) are small (∼ 22 nucleotides) noncoding RNAs which post-transcriptionally regulate gene expression by binding complementary sequences within messenger RNAs (mRNAs). The human genome encodes over 1800 miRNAs, which target about 60% of human genes. Consequently, miRNAs are likely to regulate many complex processes in the body, indeed aberrant expression of various miRNA species has been implicated in numerous disease states, including cardiovascular diseases. MiR-1 and MiR-133A are the most abundant miRNAs in the heart and have both been reported to regulate cardiac ion channels. We hypothesized that, as a consequence of their role in regulating cardiac ion channels, genetic variation in the genes which encode MiR-1 and MiR-133A might explain some cases of LQTS. Four miRNA genes (miR-1-1, miR-1-2, miR-133a-1 and miR-133a-2), which encode MiR-1 and MiR-133A, were sequenced in 125 LQTS probands. No genetic variants were identified in miR-1-1 or miR-133a-1; but in miR-1-2 we identified a single substitution (n.100A> G) and in miR-133a-2 we identified two substitutions (n.-19G> A and n.98C> T). None of the variants affect the mature miRNA products. Our findings indicate that sequence variants of miR-1-1, miR-1-2, miR-133a-1 and miR-133a-2 are not a cause of LQTS in this cohort.

The genetic basis of Brugada syndrome: a mutation update

Brugada syndrome (BrS) is a condition characterized by a distinct ST-segment elevation in the right precordial leads of the electrocardiogram and, clinically, by an increased risk of cardiac arrhythmia and sudden death. The condition predominantly exhibits an autosomal dominant pattern of inheritance with an average prevalence of 5:10,000 worldwide. Currently, more than 100 mutations in seven genes have been associated with BrS. Loss-of-function mutations in SCN5A, which encodes the alpha-subunit of the Na(v)1.5 sodium ion channel conducting the depolarizing I(Na) current, causes 15-20% of BrS cases. A few mutations have been described in GPD1L, which encodes glycerol-3-phosphate dehydrogenase-1 like protein; CACNA1C, which encodes the alpha-subunit of the Ca(v)1.2 ion channel conducting the depolarizing I(L,Ca) current; CACNB2, which encodes the stimulating beta2-subunit of the Ca(v)1.2 ion channel; SCN1B and SCN3B, which, in the heart, encodes beta-subunits of the Na(v)1.5 sodium ion channel, and KCNE3, which encodes the ancillary inhibitory beta-subunit of several potassium channels including the Kv4.3 ion channel conducting the repolarizing potassium I(to) current. BrS exhibits variable expressivity, reduced penetrance, and "mixed phenotypes," where families contain members with BrS as well as long QT syndrome, atrial fibrillation, short QT syndrome, conduction disease, or structural heart disease, have also been described.

Abnormal blood pressure response to exercise occurs more frequently in hypertrophic cardiomyopathy patients with the R92W troponin T mutation than in those with myosin mutations

Abnormal blood pressure response to exercise is reported to occur in up to a third of hypertrophic cardiomyopathy (HCM) cases and is associated with an increased risk of death, particularly in the young, but it is not known whether the HCM-causing mutation influences blood pressure response to exercise. The purpose of this article is to ascertain whether the blood pressure response to exercise differs among carriers of the R92W mutation in the cardiac troponin T gene (TNNT2), which has been associated with an increased risk of sudden cardiac death in young males; carriers of mutations in the cardiac β-myosin heavy chain gene (MYH7); and their noncarrier relatives. Thirty R92W_TNNT2 carriers, 51 MYH7 mutation carriers, and 68 of their noncarrier relatives were subjected to bicycle ergonometric exercise testing to assess blood pressure response to, as well as heart rate recovery after, exercise. Additional echocardiographic and demographic details were documented for all participants. R92W_TNNT2 carriers demonstrated significantly more abnormal blood pressure responses to exercise (P = .021; odds ratio 3.03; confidence interval 1.13–8.12) and smaller increases in systolic blood pressure than MYH7 mutation carriers or related noncarrier control individuals. Although abnormal blood pressure response occurred at similar frequencies in males in all groups (23%–26%), the percentage of R92W_TNNT2 females with abnormal blood pressure response was 64%, compared with 25% for MYH7 and 22% for noncarriers. Therefore, these results show that blood pressure response to exercise is influenced by genotype and gender in patients with HCM.

Investigating the role of the brain-derived neurotrophic factor (BDNF) val66met variant in obsessive-compulsive disorder (OCD)

Although evidence from family studies suggest that genetic factors play an important role in mediating obsessive-compulsive disorder (OCD), results from genetic case-control association analyses have been inconsistent. Discrepant findings may be attributed to the lack of phenotypic resolution, and population stratification. The aim of the present study was to investigate the role that the val66met variant within the gene encoding brain-derived neurotrophic factor (BDNF) may play in mediating the development of selected OCD subtypes accounting for the aforementioned confounding factors. One hundred and twelve OCD subjects and 140 controls were selected from the South African Afrikaner population. A significant association was observed in the male subgroup, with the met66 allele implicated as the risk allele in the development of OCD. This allele was also found to be associated with an earlier age at onset of OCD in males. On the other hand, the val66val genotype was associated with more severe OCD in the female population. No evidence of population stratification was observed in Afrikaner control subjects. These preliminary results point towards genetically distinct characteristics of OCD mediated by dysfunctions in BDNF. The present investigation forms part of ongoing research to elucidate the genetic components involved in the aetiology of OCD and OCD-related characteristics.

Genetic variation in angiotensin-converting enzyme 2 gene is associated with extent of left ventricular hypertrophy in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy, a common, inherited cardiac muscle disease, is primarily caused by mutations in sarcomeric protein-encoding genes and is characterized by overgrowth of ventricular muscle that is highly variable in extent and location. This variability has been partially attributed to locus and allelic heterogeneity of the disease-causing gene, but other factors, including unknown genetic factors, also modulate the extent of hypertrophy that develops in response to the defective sarcomeric functioning. Components of the renin-angiotensin-aldosterone system are plausible candidate hypertrophy modifiers because of their role in controlling blood pressure and biological effects on cardiomyocyte hypertrophy.

Troponin T and beta-myosin mutations have distinct cardiac functional effects in hypertrophic cardiomyopathy patients without hypertrophy

AIMS

The validity of genotype:phenotype correlation studies in human hypertrophic cardiomyopathy (HCM) has recently been questioned, yet animal models and in vitro studies suggest distinct effects for different mutations. The aims of this study were to investigate whether distinct HCM-mutations have different consequences for cardiac structure and function in the absence of the confounding effects of hypertrophy.

METHODS AND RESULTS

Individuals aged 20-65 belonging to 21 R92W(TNNT2), R403W(MYH7), or A797T(MYH7) mutation-bearing families were investigated with 2D, M-mode, and Doppler echocardiography. Cardiac structural and functional parameters were compared between prehypertrophic mutation-carriers and their non-carrier family members, with concomitant adjustment for appropriate covariates. Findings were evaluated against existing animal and in vitro functional data. The distinct functional effect of the R92W(TNNT) mutation was a relative increase in systolic functional parameters, that of the A797T(MYH7) mutation was reduced diastolic function, while the R403W(MYH7) mutation reduced both systolic and diastolic function. The observed early effects of the R92W(TNNT2) mutation mechanistically fit with prolonged force-transients precipitated by increased Ca(2+) sensitivity of the thin filament, and that of the MYH7 mutations with local ATP depletion.

CONCLUSION

Evaluation of the impact of the mutations on cardiac structure and function in prehypertrophic mutation-carriers, relative to the baseline norm provided by their non-carrier family members, best recapitulated existing animal and in vitro functional data, while inclusion of mutation-carriers with hypertrophy obscured such findings. The results prompt speculation that timely treatment aimed at ameliorating Ca(2+) sensitivity for R92W(TNNT2)-carriers, and energy depletion for MYH7 mutation-carriers, may offer a plausible approach for preventing progression from a preclinical into a decompensated state.

Long-term follow-up of R403WMYH7 and R92WTNNT2 HCM families: mutations determine left ventricular dimensions but not wall thickness during disease progression

BACKGROUND

The clinical profile and prognosis of patients with hypertrophic cardiomyopathy, a primary cardiac muscle disease caused mostly by mutations in sarcomeric protein-encoding genes, have been linked to particular disease-causing mutations in the past. However, such associations are often based on cross-sectional observations, as longitudinal studies of the progression of the disease in genotypically defined patients are sparse. Most importantly, the relative contribution of age, gender and genetic cause to disease profile and progression has not yet been reported, and the question remains whether one or more of these factors could mask the effect of the other(s).

METHODS

We previously described cross-sectional family studies of two hypertrophic cardiomyopathy (HCM)-causing mutations, R92W(TNNT2) and R403W(MYH7), both associated with minimal hypertrophy, but with widely different life expectancies. We re-investigated 22 and 26 R92W(TNNT2) and R403W(MYH7) mutation carriers in these and additional South African R92W(TNNT2) families after a mean 11.08 +/- 2.79 years, and compared the influence of the two mutations, in the context of age and gender, on disease progression.

RESULTS

We demonstrated a positive correlation between age and interventricular septal thickness for both mutations, with more than a third of all mutation carriers developing clinically recognised hypertrophy only after the age of 35 years. This period of hypertrophically silent HCM also coincided with the years in which most sudden cardiac deaths occurred, particularly in male R92W(TNNT2) carriers. Statistical analyses indicated that the particular mutation was the strongest determinant of left ventricular remodelling; particularly, LVESD increased and EF reduction was noted in the majority of R403W(MYH7) carriers, which may require clinical follow-up over the longer term.

CONCLUSIONS

Statistical modelling of follow-up data suggests that an interplay between unidentified, possibly gender-associated factors, and the causal mutation are the determinants of eventual cardiac function and survival, but not of the extent of hypertrophy, and emphasises the need for long-term follow-up even in individuals with apparently mild disease.

Genetic correlates in trichotillomania--A case-control association study in the South African Caucasian population

BACKGROUND

Trichotillomania (TTM), a prevalent and disabling psychiatric disorder characterized by repetitive hair-pulling, is presently classified as an impulse control disorder (ICD). Some have argued, however, that TTM is an obsessive-compulsive spectrum disorder (OCSD). There is some evidence that both disorders (OCD and TTM) are mediated by serotonergic (5-HT) and dopaminergic pathways.

METHODS

The aim of the present investigation was to assess the role of candidate genes encoding components within the 5-HT and dopaminergic neurotransmitter pathways in mediating TTM. South African Caucasian TTM subjects (n=39), OCD (n=250) and control subjects (n=152) were genotyped for variants in 5-HT and dopaminergic candidate genes.

RESULTS

Both genotypic and allelic distributions of the 5-HT receptor 2A (5-HT2A) T102C variant were found to be significantly different between the TTM and control subjects (p=0.028 and p=0.024, respectively), and a trend towards significance was noted between the TTM and OCD subjects (p=0.084 and p=0.080 for genotype and allele analyses, respectively), with the T102T-genotype found to confer susceptibility to the development of TTM.

CONCLUSION

This investigation provides preliminary evidence for the involvement of 5-HT2A in the molecular aetiology of TTM and supports the need for further replication in a larger dataset. The present data are consistent with previous findings that 5-HT2A plays a role in mediating impulse dyscontrol.

Cluster analysis of obsessive-compulsive spectrum disorders in patients with obsessive-compulsive disorder: clinical and genetic correlates

BACKGROUND

Comorbidity of certain obsessive-compulsive spectrum disorders (OCSDs; such as Tourette's disorder) in obsessive-compulsive disorder (OCD) may serve to define important OCD subtypes characterized by differing phenomenology and neurobiological mechanisms. Comorbidity of the putative OCSDs in OCD has, however, not often been systematically investigated.

METHODS

The Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition , Axis I Disorders-Patient Version as well as a Structured Clinical Interview for Putative OCSDs (SCID-OCSD) were administered to 210 adult patients with OCD (N = 210, 102 men and 108 women; mean age, 35.7 +/- 13.3). A subset of Caucasian subjects (with OCD, n = 171; control subjects, n = 168), including subjects from the genetically homogeneous Afrikaner population (with OCD, n = 77; control subjects, n = 144), was genotyped for polymorphisms in genes involved in monoamine function. Because the items of the SCID-OCSD are binary (present/absent), a cluster analysis (Ward's method) using the items of SCID-OCSD was conducted. The association of identified clusters with demographic variables (age, gender), clinical variables (age of onset, obsessive-compulsive symptom severity and dimensions, level of insight, temperament/character, treatment response), and monoaminergic genotypes was examined.

RESULTS

Cluster analysis of the OCSDs in our sample of patients with OCD identified 3 separate clusters at a 1.1 linkage distance level. The 3 clusters were named as follows: (1) "reward deficiency" (including trichotillomania, Tourette's disorder, pathological gambling, and hypersexual disorder), (2) "impulsivity" (including compulsive shopping, kleptomania, eating disorders, self-injury, and intermittent explosive disorder), and (3) "somatic" (including body dysmorphic disorder and hypochondriasis). Several significant associations were found between cluster scores and other variables; for example, cluster I scores were associated with earlier age of onset of OCD and the presence of tics, cluster II scores were associated with female gender and childhood emotional abuse, and cluster III scores were associated with less insight and with somatic obsessions and compulsions. However, none of these clusters were associated with any particular genetic variant.

CONCLUSION

Analysis of comorbid OCSDs in OCD suggested that these lie on a number of different dimensions. These dimensions are partially consistent with previous theoretical approaches taken toward classifying OCD spectrum disorders. The lack of genetic validation of these clusters in the present study may indicate the involvement of other, as yet untested, genes. Further genetic and cluster analyses of comorbid OCSDs in OCD may ultimately contribute to a better delineation of OCD endophenotypes.

Corrigendum to "gender in obsessive-compulsive disorder: clinical and genetic findings" [Eur. Neuropsychopharmacol. 14 (2004) 105-113]

BACKGROUND

There is increasing recognition that obsessive-compulsive disorder (OCD) is not a homogeneous entity. It has been suggested that gender may contribute to the clinical and biological heterogeneity of OCD.

METHODS

Two hundred and twenty patients (n=220; 107 male, 113 female) with DSM-IV OCD (age: 36.40 +/- 13.46) underwent structured interviews. A subset of Caucasian subjects (n=178), including subjects from the genetically homogeneous Afrikaner population (n=81), and of matched control subjects (n=161), was genotyped for polymorphisms in genes involved in monoamine function. Clinical and genetic data were statistically analyzed across gender.

RESULTS

Compared with females, males with OCD (1) had an earlier age of onset, and a trend toward having more tics and worse outcome, (2) had somewhat differing patterns of OCD symptomatology and axis I comorbidity, and (3) in the Caucasian group, were more likely to have the high activity T allele of the EcoRV variant of the monoamine oxidase A (MAO-A) gene compared to controls, and (4) in the Afrikaner subgroup, were more frequently homozygous for the G allele at the G861C variant of the 5HT1Dbeta gene than controls. Females with OCD (1) reported more sexual abuse during childhood than males, (2) often noted changes in obsessive-compulsive symptoms in the premenstrual/menstrual period as well as during/shortly after pregnancy, and with menopause, and (3) in the Caucasian subgroup, were more frequently homozygous for the low activity C allele of the EcoRV variant of the MAO-A gene compared to controls, with this allele also more frequent in female patients than controls.

CONCLUSION

This study supports the hypothesis that gender contributes to the clinical and biological heterogeneity of OCD. A sexually dimorphic pattern of genetic susceptibility to OCD may be present. Further work is, however, needed to delineate the mechanisms that are responsible for mediating the effects of gender.

Early- versus late-onset obsessive-compulsive disorder: investigating genetic and clinical correlates

There is increasing evidence that obsessive-compulsive disorder (OCD) is mediated by genetic factors. Although the precise mechanism of inheritance is unclear, recent evidence has pointed towards the involvement of the serotonergic and dopaminergic systems in the disorder's development. Furthermore, early-onset OCD appears to be a subtype that exhibits distinct clinical features and that is associated with greater familial loading. In the present investigation, South African OCD patients (n=252) were stratified according to age of onset and were clinically assessed. Additionally, selected variants in genes encoding serotonergic and dopaminergic components were investigated in a Caucasian OCD subset (n=180). This subgroup was further stratified to evaluate the role that these candidate genes may play in the genetically homogeneous Afrikaner subset (n=80). Analysis of the clinical data revealed an association between early age of onset and an increased frequency of tics, Tourette's disorder, and trichotillomania (TTM). The genetic studies yielded statistically significant results when the allelic distributions of genetic variants in the dopamine receptor type 4 gene (DRD4) were analysed in the Caucasian OCD cohort. These data support a role for the dopaminergic system, which may be relevant to the development of early-onset OCD.

Dissociative experiences in obsessive-compulsive disorder and trichotillomania: clinical and genetic findings

A link between dissociation proneness in adulthood and self-reports of childhood traumatic events (including familial loss in childhood, sexual/physical abuse and neglect) has been documented. Several studies have also provided evidence for an association between dissociative experiences and trauma in patients with various psychiatric disorders, including post-traumatic stress disorder, borderline personality, dissociative identity and eating disorders. Based on the relative paucity of data on dissociation and trauma in obsessive-compulsive disorder (OCD) and trichotillomania (TTM), the primary objective of this study was to examine the relationship between trauma and dissociative experiences (DE) in these two diagnostic groups. Furthermore, the availability of clinical and genetic data on this sample allowed us to explore clinical and genetic factors relevant to this association. A total of 110 OCD and 32 TTM patients were compared with respect to the degree of dissociation (using the Dissociative Experiences Scale [DES]) and childhood trauma (using the Childhood Trauma Questionnaire [CTQ]). Patients were classified on the DES as either "high" (mean DES score >/= 30) or "low" (mean DES score < 30) dissociators. Additional clinical and genetic factors were also explored with chi-square and t tests as appropriate. A total of 15.8% of OCD patients and 18.8% of TTM patients were high dissociators. OCD and TTM groups were comparable on DES and CTQ total scores, and in both OCD and TTM groups, significant positive correlations were found between mean DES scores and mean CTQ subscores of emotional abuse, physical abuse, sexual abuse, and physical neglect. In the OCD group, high dissociators were significantly younger than low dissociators, and significantly more high dissociators than low dissociators reported a lifetime (current and past) history of tics (P <.001), Tourette's syndrome (P =.019), bulimia nervosa (P =.003), and borderline personality disorder (P =.027). In the TTM group, significantly more high dissociators than low dissociators reported (lifetime) kleptomania (P =.005) and depersonalisation disorder (P =.005). In the Caucasian OCD patients (n = 114), investigation of genetic polymorphisms involved in monoamine function revealed no significant differences between high and low dissociator groups. This study demonstrates a link between childhood trauma and DE in patients with OCD and TTM. High dissociative symptomatology may be present in a substantial proportion of patients diagnosed with these disorders. High dissociators may also be differentiated from low dissociators on some demographic features (e.g., lower age) and comorbidity profile (e.g., increased incidence of impulse dyscontrol disorders). Additional work is necessary before conclusions about the role of monoaminergic systems in mediating such dissociation can be drawn.

Progressive familial heart block type II (PFHBII): a clinical profile from 1977 to 2003

An evaluation of a 38-year-old Caucasian woman, who was referred to Tygerberg Hospital (Western Cape Province, RSA) with Wenckebach second-degree or possibly complete atrioventricular (AV) block that had progressed from first-degree AV block, identified a family history of the cardiac conduction system disorder progressive familial heart block type II (PFHBII). This prompted a retrospective clinical review of the subjects described in the original study, as well as additional family members who had not been examined in the original study. Progression of clinical features was observed, but more importantly, PFHBII was clinically redefined as an AV nodal disorder, which may progress to dilated cardiomyopathy (DCM).

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.

Gender in obsessive-compulsive disorder: clinical and genetic findings

BACKGROUND

There is increasing recognition that obsessive-compulsive disorder (OCD) is not a homogeneous entity. It has been suggested that gender may contribute to the clinical and biological heterogeneity of OCD.

METHODS

Two hundred and twenty patients (n=220; 107 male, 113 female) with DSM-IV OCD (age: 36.40+/-13.46) underwent structured interviews. A subset of Caucasian subjects (n=178), including subjects from the genetically homogeneous Afrikaner population (n=81), and of matched control subjects (n=161), was genotyped for polymorphisms in genes involved in monoamine function. Clinical and genetic data were statistically analyzed across gender.

RESULTS

Compared with females, males with OCD (1) had an earlier age of onset, and a trend toward having more tics and worse outcome, (2) had somewhat differing patterns of OCD symptomatology and axis I comorbidity, and (3) in the Caucasian group, were more likely to have the high activity T allele of the EcoRV variant of the monoamine oxidase A (MAO-A) gene compared to controls, and (4) in the Afrikaner subgroup, were more frequently homozygous for the C allele at the G861C variant of the 5HT(1D beta) gene than controls. Females with OCD (1) reported more sexual abuse during childhood than males, (2) often noted changes in obsessive-compulsive symptoms in the premenstrual/menstrual period as well as during/shortly after pregnancy, and with menopause, and (3) in the Caucasian subgroup, were more frequently homozygous for the low activity C allele of the EcoRV variant of the MAO-A gene compared to controls, with this allele also more frequent in female patients than controls.

CONCLUSION

This study supports the hypothesis that gender contributes to the clinical and biological heterogeneity of OCD. A sexually dimorphic pattern of genetic susceptibility to OCD may be present. Further work is, however, needed to delineate the mechanisms that are responsible for mediating the effects of gender.

Molecular genetics of cardiomyopathy: changing times, shifting paradigms

Congestive heart failure is a major problem in developed and developing countries alike. Primary dysfunction of the heart muscle accounts for a significant proportion of patients with a non-ischaemic cause of heart failure. Application of genetic techniques has facilitated identification of some molecular causes of the inherited form of these diseases, dramatically increasing our understanding of the pathogenesis of these primary, previously termed 'idiopathic', cardiomyopathies over the last few decades. Knowledge of the different causes is beginning to coalesce into aetiological principles underlying the clinically distinguished cardiomyopathies. Hypertrophic cardiomyopathy (HCM) now appears to be a disease caused by a dysfunctional sarcomere, dilated cardiomyopathy (DCM), a disease of myocytic structural instability, and arrhythmogenic right ventricular cardiomyopathy, a disease of accelerated myocyte death. The aetiology of both HCM and DCM probably also involves cardiac energy imbalances, while additional factors modify the clinical expression in all cardiomyopathies. Even though our knowledge of the genetic aetiology of the cardiomyopathies is still incomplete, it already has relevant clinical significance. Elucidation of the full genetic contribution to the development and progression of the cardiomyopathies represents a new challenge in the study of these diseases, and will undoubtedly lead to new therapeutic approaches in the not-too-distant future.

Investigating the role of dopaminergic and serotonergic candidate genes in obsessive-compulsive disorder

There is increasing evidence that the aetiology of obsessive-compulsive disorder (OCD) has a marked genetic component, although the precise mechanism of inheritance is unclear. Clinical and pharmacological studies have implicated the serotonergic and dopaminergic systems in disease pathogenesis. This study investigated the role of attractive candidate genes in the serotonergic and dopaminergic pathways in the development of OCD. The distribution of selected polymorphic variants in the serotonin receptor type 2A and 1Dbeta (5-HT(2A), 5-HT(1Dbeta)), dopamine transporter (DAT), dopamine receptor type 4 (DRD4) and monoamine-oxidase A (MAO-A) genes were analysed in 71 OCD cases and 129 control individuals in the genetically homogeneous Afrikaner population, by means of case-control association studies. Although no statistically significant genotypic or allelic associations were detected, the data yielded interesting preliminary results that warrant further discussion and investigation.

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.

Obsessive-compulsive disorder and the promoter region polymorphism (5-HTTLPR) in the serotonin transporter gene (SLC6A4): a negative association study in the Afrikaner population

A polymorphism (5-HTTLPR) in the promoter region of the serotonin transporter gene (SLC6A4) has been reported to have functional significance and to be associated with obsessive-compulsive disorder (OCD). However, other studies have generated confounding results. A study was undertaken to re-evaluate this association in subjects drawn from the relatively genetically homogeneous Afrikaner population of South Africa. Fifty-four OCD patients of Afrikaner descent and 82 ethnically matched control individuals were phenotyped and genotyped. No significant association was found between the distribution of the 5-HTTLPR genotypes at the SLC6A4 locus and OCD. A similar result (p = 0.108) was generated when a meta-analysis of the 5-HTTLPR polymorphism, combining the current study with a previously reported Caucasian group, was performed; the meta-study comprised 129 OCD patients and 479 control individuals. However, both studies lacked power. Therefore, evidence that variation in SLC6A4 plays a significant role in the development of OCD in the population groups studied is inconclusive. Future association studies in Caucasian populations may extend the power of such meta-analyses and assist in delineating the role of SLC6A4 in OCD.

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.

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.

Sudden death due to troponin T mutations

OBJECTIVES

This study was designed to verify initial observations of the clinical and prognostic features of hypertrophic cardiomyopathy caused by cardiac tropnin T gene mutations.

BACKGROUND

The most common cause of sudden cardiac death in the young is hypertrophic cardiomyopathy, which is usually familial. Mutations causing familial hypertrophic cardiomyopathy have been identified in a number of contractile protein genes, raising the possibility of genetic screening for subjects at risk. A previous report suggested that mutations in the cardiac troponin T gene were notable because they were associated with a particularly poor prognosis but only mild hypertrophy. Given the variability of some genotype:phenotype correlations, further analysis of cardiac troponin T mutations has been a priority.

METHODS

Deoxyribonucleic acid from subjects with hypertrophic cardiomyopathy was screened for cardiac troponin T mutations using a ribonuclease protection assay. Polymerase chain reaction-based detection of a novel mutation was used to genotype members of two affected pedigrees. Gene carriers were examined by echocardiography and electrocardiology, and a family history was obtained.

RESULTS

A novel cardiac troponin T gene mutation, arginine 92 tryptophan, was identified in 19 of 48 members of two affected pedigrees. The clinical phenotype was characterized by minimal hypertrophy (mean [+/-SD] maximal ventricular wall thickness 11.3 +/- 5.4 mm) and low disease penetrance by clinical criteria (40% by echocardiography) but a high incidence of sudden cardiac death (mean age 17 +/- 9 years).

CONCLUSIONS

These data support the observation that apparently diverse cardiac troponin T gene mutations produce a consistent disease phenotype. Because this is one of poor prognosis, despite deceptively mild or undetectable hypertrophy, genotyping at this locus may be particularly informative in patient management and counselling.

Evidence of a long QT founder gene with varying phenotypic expression in South African families

We report five South African families of northern European descent (pedigrees 161, 162, 163, 164, and 166) in whom Romano-Ward long QT syndrome (LQT) segregates. The disease mapped to a group of linked markers on chromosome 11p15.5, with maximum combined two point lod scores, all generated at theta = 0, of 15.43 for the D11S922, 10.51 for the D11S1318, and 14.29 for the tyrosine hydroxylase (TH) loci. Recent studies have shown that LQT is caused by an Ala212Val mutation in a potassium channel gene (KVLQT1) in pedigrees 161 to 164. We report that the same mutation is responsible for the disease in pedigree 166. Haplotype construction showed that all the families shared a common haplotype, suggesting a founder gene effect. DNA based identification of gene carriers allowed assessment of the clinical spectrum of LQT. The QTc interval was significantly shorter in both carriers and non-carriers in pedigree 161 (0.48 s and 0.39 s, respectively) than the same two groups in pedigree 161 (0.52 s and 0.42 s, respectively). The spectrum of clinical symptoms appeared more severe in pedigree 162. The possible influence of modulating genetic factors, such as HLA status and sex of family members, on the expression of an LQT founder gene is discussed.

Clinical and prognostic evaluation of familial hypertrophic cardiomyopathy in two South African families with different cardiac beta myosin heavy chain gene mutations

BACKGROUND

Familial hypertrophic cardiomyopathy is the most common inherited cardiac disorder, with sudden cardiac death at a young age the most frequent cause of death in affected individuals. Some cases of familial hypertrophic cardiomyopathy are caused by missense mutations of the beta myosin heavy chain (beta MHC) gene on chromosome 14 and at least 17 such mutations have been described. Recent reports suggest that a correlation exists between a specific beta MHC gene mutation and prognosis in familial hypertrophic cardiomyopathy. This premise is currently being used as a basis to provide counselling for affected families. This mutation/prognosis association, however, has not been widely assessed as yet. The clinical and prognostic features of two South African families of mixed racial descent, in which different beta MHC gene mutations were segregating, were studied to evaluate this correlation. The results were compared with those of previously published reports of European families carrying the same mutations.

METHODS

The beta MHC gene missense mutations in two affected families were identified by single strand conformation polymorphism analysis and sequencing (pedigree 106: Arg403Trp; pedigree 108: Arg249Gln). All family members were subjected to genotypic analysis using polymerase chain reaction amplification and restriction enzyme based mutation detection techniques. Clinical, electrocardiographic, and echocardiographic studies were performed on genotypically affected individuals in these two kindreds.

RESULTS

The number of individuals identified in pedigree 106 with the Arg403Trp mutation was 32.10 individuals bore the Arg249Gln mutation in pedigree 108. The penetrance rate in adults (equal to or greater than 16 years), using the strict echocardiographic criterion of maximum left ventricular wall thickness > or = 13 mm, was 25% for pedigree 106 and 33% for pedigree 108. Familial hypertrophic cardiomyopathy compatible electrocardiographic and echocardiographic abnormalities were seen in 60% of genotypically positive individuals aged > or = 16 years in pedigree 106 and 80% in pedigree 108. The prognosis was uniformly benign in the two families. For pedigree 106 this corresponded to a report of no early sudden cardiac deaths in a French family with the Arg403Trp mutation. For pedigree 108 the absence of such deaths was in apparent contrast to the four cases reported in 24 genotypically affected individuals in a study of a kindred of European ancestry bearing the Arg249Gln mutation.

CONCLUSION

This study of a large South African kindred confirmed the benign nature of the Arg403Trp mutation suggested in a previous report. The number and the relatively young age of affected individuals in a second South African family must be considered when comparing the absence of familial hypertrophic cardiomyopathy associated deaths with the intermediate survival reported for the Arg249Gln mutation in a European family. This investigation lends support to current evidence relating specific beta MHC gene mutations to prognosis, which may be used as a basis to provide counselling for affected families.

Gene for progressive familial heart block type I maps to chromosome 19q13

BACKGROUND

Progressive familial heart block type I (PF-HBI) is a dominantly inherited cardiac bundle-branch conduction disorder that has been traced through nine generations of a large South African kindred. Similar conduction disorders have been reported elsewhere; however, the cause of these diseases is unknown. The aim of the present study was to determine by linkage analysis the approximate chromosomal position of the gene causing PFHBI, thereby allowing family-based diagnosis and the development of positional cloning strategies to identify the causative gene.

METHODS AND RESULTS

Eighty-six members of three pedigrees, 39 members of which were affected with PFHBI, were genotyped at four linked polymorphic marker loci mapped to chromosome 19, bands q13.2-q13.3 (chromosome 19q13.2-13.3). Maximum two-point logarithm of the odds scores (which represent the logarithm of the odds ratio of detecting linkage versus nonlinkage) generated were 6.49 (theta = 0) for the kallikrein locus, 5.72 (theta = 0.01) for the myotonic dystrophy locus, 3.44 (theta = 0) for the creatine kinase muscle-type locus and 4.51 (theta = 0.10) for the apolipoprotein C2 locus. The maximum multipoint logarithm of the odds score was 11.6, with the 90% support interval positioning the PFHBI locus within a 10 cM distance centering on the kallikrein 1 locus.

CONCLUSIONS

The gene for PFHBI maps to an area of approximately 10 cM on chromosome 19q13.2-13.3. There are several candidate genes in this interval; although a recombination event ruled out the myotonic dystrophy locus from direct involvement with PFHBI, the proximity of these two loci may be relevant to the observed cardiac abnormalities of myotonic dystrophy. The results provide a means of DNA-based diagnosis in the families studied and a foundation for cloning studies to identify the causative gene.

Polymerase chain reaction-based detection of MN blood group-specific sequences in the human genome

The MN blood group antigens have traditionally been detected by serotyping; however, development of a DNA-based method offers flexibility in the determination of this highly polymorphic system. Genotyping the MN blood group antigens was performed by polymerase chain reaction amplification of the specific alleles (PASA) in the human genome. In separate paired reactions, M or N allele-specific oligonucleotide primers were amplified with a common distal primer. Only in the presence of the homologous template was a 781-base pair polymerase chain reaction amplification product visible after agarose gel electrophoresis and ethidium bromide staining. This method of genotyping could be performed using either 1 microgram of extracted DNA or 0.5 microL of whole blood, and the results showed 100-percent correlation with those obtained by serotyping. PASA-based genotyping of MN blood group antigens, which requires a small amount of starting material, has application in linkage and population studies and in forensic medicine.

PCR-based detection of a polymorphic HaeIII site in intron VII of the human albumin (ALB) gene

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Synthesis of a wild-type and three mutant Cucurbita maxima trypsin inhibitor-encoding genes by a single-strand approach

A single-strand approach to gene assembly, based on a modification of an in vitro complementary oligodeoxyribonucleotide template-directed ligation of the desired sequence to a linearized vector [Chen et al., Nucleic Acids Res. 18 (1990) 871-878], is described. The gene coding for the wild-type Cucurbita maxima trypsin inhibitor of 29 amino acid residues [Bode et al., FEBS Lett. 242 (1989) 285-292], as well as three mutant forms of the gene, in which two of the three disulfide bonds have been replaced singly or as a pair, have been synthesized in a single synthesis run with minimal manual intervention. Subsequent to ligation to pUC9 and in vivo gapped duplex repair by Escherichia coli, their sequences have been verified.

A modified protoplast-regeneration protocol facilitating the detection of cloned exoenzyme genes in Bacillus subtilis

Incorporation of starch or casein into protoplast-regeneration medium facilitated shotgun cloning of alpha-amylase and neutral protease genes from an unidentified Bacillus sp. in Bacillus subtilis by polyethylene glycol-induced protoplast transformation. This modification and the use of the plasmid vector pPL603b enabled us to simultaneously select for promoter-bearing recombinant plasmids that expressed amylase or protease activity. The inserts were found to be 4 and 4.6 kb, respectively. Although protease activity directed by the cloned gene was only 2- to 4-fold higher than for the donor strain, that of alpha-amylase was 28-fold higher.

Effects of cystine or glutamine restriction on human diploid fibroblasts in culture

Amino-acid restriction was studied using a strain of human diploid fibroblasts (HDF) isolated from fetal skin. HDF populations were maintained at reduced proliferation rates by lowering cystine or glutamine concentrations of Eagle's MEM. Effects of this treatment on mean cell diameters, total cell protein and specific activity of acid phosphatase were assessed. Threshold levels of cystine required for maintenance were found to be markedly influenced by type and/or batch of serum used irrespective of their free cystine content. A 96-hr exposure of passage 25 cells to medium 0.01 or 0.005 mM in cystine resulted in an increased mean cell diameter and a greater heterogeneity of cell size. This was accompanied by an increase in the total cellular protein. A 48-hr exposure, followed by return to control serial cultivation, induced persistent change in mean cell diameter without affecting the total life span (49 passages over 165 days). The mean size of untreated cells increased with serial passage reaching a size similar to treated cells only at passage 44. Acid-phosphatase specific activities were higher in cells maintained under conditions restrictive in cystine. None of the above changes were observed when glutamine concentrations were reduced to 0.0025 mM, a level required to inhibit division rates. The possible relevance of these findings to the phenomenon of in vitro cell senescence is discussed.