Clinical features of arrhythmogenic right ventricular dysplasia/cardiomyopathy associated with mutations in plakophilin-2

BACKGROUND

Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is an inherited cardiomyopathy characterized by right ventricular dysfunction and ventricular arrhythmias. A recent study reported mutations in PKP2, encoding the desmosomal protein plakophilin-2, associated with ARVD/C. The purpose of our study was to validate the frequency of PKP2 mutations in another large series of ARVD/C patients and to examine the phenotypic characteristics associated with PKP2 mutations.

METHODS AND RESULTS

DNA from 58 ARVD/C patients was sequenced to determine the presence of mutations in PKP2. Clinical features of ARVD/C were compared between 2 groups of patients: those with a PKP2 mutation and those with no detectable PKP2 mutation. Thirteen different PKP2 mutations were identified in 25 (43%) of the patients. Six of these mutations have not been reported previously; 4 occurred in multiple, apparently unrelated, families. The mean age at presentation was lower among those with a PKP2 mutation (28+/-11 years) than in those without (36+/-16 years) (P<0.05). The age at median cumulative symptom-free survival (32 versus 42 years) and at the median cumulative arrhythmia-free survival (34 versus 46 years) was lower among patients with a PKP2 mutation than among those without a PKP2 mutation (P<0.05). Inducibility of ventricular arrhythmias on an electrophysiology study, diffuse nature of right ventricular disease, and presence of prior spontaneous ventricular tachycardia were identified as predictors of implanted cardioverter/defibrillator (ICD) intervention only among patients without a PKP2 mutation (P<0.05).

CONCLUSIONS

Our study highlights the clinical relevance of PKP2 mutations in ARVD/C. Presence of a PKP2 mutation in ARVD/C correlates with earlier onset of symptoms and arrhythmia. Patients with a PKP2 mutation experience ICD interventions irrespective of the classic risk factors determining ICD intervention in ARVD/C patients.

Nesiritide Therapy in a Term Neonate with Renal Disease

A term (39-wk-old) male neonate exhibited respiratory distress and anuria within 2 days of birth. The patient was diagnosed with pulmonary hypertension, polycystic kidney disease, and heart failure; his initial B-type natriuretic peptide concentration was 2460 pg/ml. After minimal response to loop diuretics, the patient was given an infusion of nesiritide 0.01 microg/kg/minute, with no loading dose. Urine output increased over 400%, and cardiac function improved. Nesiritide was titrated to 0.03 microg/kg/minute with no hypotension, decreased renal function, or adverse cardiac sequelae over the next 6 days. No subsequent changes in cardiac function occurred during the infant's stay in a progressive care unit, but he died at age 5.5 months due to sepsis. This case report demonstrates the successful first use of nesiritide therapy in a neonate with renal disease. Further studies are warranted to evaluate the safety and administration of this agent in the neonatal patient population.

Leukocyte Suppression is Associated with Improved Clinical Outcomes in Children’s Status after Orthotopic Heart Transplantation

BACKGROUND

Leukocyte suppression is a sequela of immunosuppressive therapy after orthotopic heart transplantation and may result in discontinuation of anti-proliferative agents. Clinical outcomes in this patient population have not been well delineated.

METHODS

This study was a retrospective review of children who underwent orthotopic heart transplantation at our institution from 1986 to 2003. Leukocyte suppression was defined as a white blood cell count <5,000, prompting the withdrawal of anti-proliferative agents. The population was divided into 2 groups, leukosuppressed (LS) and non-leukosuppressed (NLS), and their clinical outcomes were compared.

RESULTS

The study included 109 patients, of which 44 (40%) became leukosuppressed. The 2 groups were similar regarding demographic data and initial management. The LS Group had a significantly decreased incidence of rejection, being 7 times less likely to have recurrent rejection (p = 0.001). The median time to rejection was 0.8 +/- 0.6 years for the NLS Group, whereas the median time to rejection was not yet reached at 17 years for the LS Group. The LS Group also tended toward a decreased incidence of retransplantation or death (p = 0.06). The organ "half-life" in the NLS Group was 7.5 years vs 12.5 years in the LS Group. There was no difference between the 2 groups in regards to other adverse effects of immunosuppression.

CONCLUSIONS

Children who have undergone orthotopic heart transplantation and subsequently become leukosuppressed have a lower incidence of rejection and a tendency toward less organ loss than children who do not become leukosuppressed, without having an increased incidence of adverse side effects.

Spectrum of CHD7 mutations in 110 individuals with CHARGE syndrome and genotype-phenotype correlation

CHARGE syndrome is a well-established multiple-malformation syndrome with distinctive consensus diagnostic criteria. Characteristic associated anomalies include ocular coloboma, choanal atresia, cranial nerve defects, distinctive external and inner ear abnormalities, hearing loss, cardiovascular malformations, urogenital anomalies, and growth retardation. Recently, mutations of the chromodomain helicase DNA-binding protein gene CHD7 were reported to be a major cause of CHARGE syndrome. We sequenced the CHD7 gene in 110 individuals who had received the clinical diagnosis of CHARGE syndrome, and we detected mutations in 64 (58%). Mutations were distributed throughout the coding exons and conserved splice sites of CHD7. Of the 64 mutations, 47 (73%) predicted premature truncation of the protein. These included nonsense and frameshift mutations, which most likely lead to haploinsufficiency. Phenotypically, the mutation-positive group was more likely to exhibit cardiovascular malformations (54 of 59 in the mutation-positive group vs. 30 of 42 in the mutation-negative group; P=.014), coloboma of the eye (55 of 62 in the mutation-positive group vs. 30 of 43 in the mutation-negative group; P=.022), and facial asymmetry, often caused by seventh cranial nerve abnormalities (36 of 56 in the mutation-positive group vs. 13 of 39 in the mutation-negative group; P=.004). Mouse embryo whole-mount and section in situ hybridization showed the expression of Chd7 in the outflow tract of the heart, optic vesicle, facio-acoustic preganglion complex, brain, olfactory pit, and mandibular component of the first branchial arch. Microarray gene-expression analysis showed a signature pattern of gene-expression differences that distinguished the individuals with CHARGE syndrome with CHD7 mutation from the controls. We conclude that cardiovascular malformations, coloboma, and facial asymmetry are common findings in CHARGE syndrome caused by CHD7 mutation.

Administration of a Large Nesiritide Bolus Dose in a Pediatric Patient: Case Report and Review of Nesiritide Use in Pediatrics

Nesiritide (recombinant B-type natriuretic peptide) is often given for symptomatic relief of acute decompensated heart failure in adults. The literature describing the safety or efficacy of nesiritide in children is minimal, and we know of no data that describe the effects of a nesiritide overdose in adults or children. A 3-year-old, 10.9-kg girl was admitted to the pediatric intensive care unit with the diagnosis of dilated cardiomyopathy and acute decompensated heart failure. She received several vasoactive infusions during her admission, including nesiritide. On hospital day 47 (day 45 of nesiritide therapy), the patient received an 18-fold overdose of nesiritide, with no hemodynamic, cardiac, or renal sequelae. She subsequently underwent successful cardiac transplantation. The nesiritide treatment duration was longer for this patient than the 45 days previously reported in a pediatric patient. No hemodynamic instability or cardiac or renal sequelae were associated with the large, inadvertent bolus in our patient. This case report demonstrates the lack of adverse events in a pediatric patient administered nesiritide beyond the recommended dosing parameters. Increased vigilance is always advised when administering drugs not commonly given to pediatric patients.

Inflammatory cardiomyopathy: there is a specific matrix destruction in the course of the disease

Cardiomyopathies are responsible for a high proportion of cases of congestive heart failure and sudden death, as well as for the need for transplantation. Understanding of the causes of these disorders has been sought in earnest over the past decade. We hypothesized that DCM is a disease of the cytoskeleton/sarcolemma, which affects the sarcomere. Evaluation of the sarcolemma in DCM and other forms of systolic heart failure demonstrates membrane disruption; and, secondarily, the extracellular matrix architecture is also affected. Disruption of the links from the sarcolemma to ECM at the dystrophin C-terminus and those to the sarcomere and nucleus via N-terminal dystrophin interactions could lead to a "domino effect" disruption of systolic function and development of arrhythmias. We also have suggested that dystrophin mutations play a role in idiopathic DCM in males. The T-cap/MLP/alpha-actinin/titin complex appears to stabilize Z-disc function via mechanical stretch sensing. Loss of elasticity results in the primary defect in the endogenous cardiac muscle stretch sensor machinery. The over-stretching of individual myocytes leads to activation of cell death pathways, at a time when stretch-regulated survival cues are diminished due to defective stretch sensing, leading to progression of heart failure. Genetic DCM and the acquired disorder viral myocarditis have the same clinical features including heart failure, arrhythmias, and conduction block, and also similar mechanisms of disease based on the proteins targeted. In dilated cardiomyopathy, the process of progressive ventricular dilation and changes of the shape of the ventricle to a more spherical shape, associated with changes in ventricular function and/or hypertrophy, occurs without known initiating disturbance. In those cases in which resolution of cardiac dysfunction does not occur, chronic DCM results. It has been unclear what the underlying etiology of this long-term sequela could be, but viral persistence and autoimmunity have been widely speculated.

Possible association of the human KCNE1 (minK) gene and QT interval in healthy subjects: evidence from association and linkage analyses in Israeli families

QT interval prolongation is associated with increased risk of sudden and non-sudden cardiac death. Potassium channel gene variants are associated with inherited long QT syndromes. Using linkage and association analyses, we investigated whether variants in the potassium channel subunit KCNE1 are associated with QTc intervals in an unselected population sample of 80 kindreds living in kibbutz settlements in Israel. Variance-component linkage analysis revealed weak evidence of linkage of KCNE1 polymorphisms with QTc intervals. Family-based association analysis showed a significant association between the G38S polymorphism and QTc interval. Further quantitative trait association analysis demonstrated a significant residual heritability component (h(2)= 0.33), and that the effect of the G38S variant allele is modified by gender. Estimated maximum likelihood parameters from these models indicated that male gender, age, hypertension, diabetes, hypercholesterolemia, fibrinogen and BMI were positively associated with QTc interval; level of education and cigarette smoking showed an inverse association. Both erythrocyte membrane n-6 and n-3 fatty acids showed a significant inverse association with QTc interval. While more than 15.8% of QTc variability was contributed by covariates, another 4.7% was explained by dietary factors, the G38S polymorphism explained 2.2%, and approximately 36% was explained by polygenes. An in silico analysis showed also that the novel V80 SNP, another KCNE1 synonymous variant, abolishes the recognition for a splicing enhancer, which may lead to an increased effect of the G38S mutation. These results demonstrate that, in addition to polygenic background, dietary factors and other covariables, the KCNE1 G38S variant is involved in determining QTc levels in this population-based sample of families.

Clinical, genetic, and electrophysiologic characteristics of a new PAS-domain HERG mutation (M124R) causing Long QT syndrome

OBJECTIVES

To describe the clinical, genetic, and electrophysiologic characteristics of a new PAS-domain HERG mutation (M124R) that has been identified in a single large Jewish family with Long QT syndrome (LQTS).

BACKGROUND

Many previously reported HERG mutations causing LQTS are located either in the C-terminus, or in the pore region. Relatively fewer clinical data are available on N-terminus (PAS-domain) mutation carriers.

METHODS

Clinical data were available in 76 family members (aged 1-93 years, 69 alive) over 18 years of follow-up, while electrocardiographic data were available in 57, and genetic data in 45 family members. Cellular electrophysiology was assessed in transfected Chinese Hamster Ovary (CHO) cells using the whole-cell patch-clamp technique.

RESULTS

Thirty-six family members were phenotypically categorized as nonaffected, 3 as equivocal, and 20 as affected. Mean QTc was 410+/-23, 440+/-10, and 498+/-41 ms, respectively, in these three subgroups. Eight out of 20 affected family members were symptomatic: five had only syncope, two had aborted cardiac arrest, and one sudden death. Genetic analyses identified the M124R point mutation in all affected members tested (n=16), while all those tested with nonaffected (n=26) and equivocal (n=3) phenotype did not carry the mutation. The M124R mutation reduced the HERG tail-current density by 65%, significantly accelerated the deactivation kinetics, and caused a negative shift in the voltage dependence of activation.

CONCLUSIONS

A new PAS-domain HERG mutation (M124R) was identified as causing LQTS in a large Jewish family, with high penetrance and frequent disease-related symptoms. This mutation markedly decreased the tail-current density and accelerated the deactivation kinetics of the HERG channel in transfected CHO cells.

Symptom Complex is Associated with Transplant Coronary Artery Disease and Sudden Death/Resuscitated Sudden Death in Pediatric Heart Transplant Recipients

BACKGROUND

Transplant coronary artery disease (TCAD) is a common sequela of heart transplantation. Symptom complexes associated with TCAD have not been well described. The purpose of this study was to determine if somatic complaints are associated with TCAD in pediatric heart transplant recipients.

METHODS

We reviewed the medical records of all patients who underwent heart transplantation at our institution from November 1984 to December 2000. TCAD was defined as any interval narrowing of coronary arteries by angiography since the previous study or at least 50% luminal obstruction of 1 or more coronary arteries by histologic examination of explanted or autopsied hearts.

RESULTS

Ninety-nine patients received heart transplants, and follow-up data were available in 80. Sixty-six patients met study criteria. Complaints of abdominal (82%), chest (45%), abdominal and chest (27%), and arm (9%) pain were made by 22 (33%) of 66 patients, and TCAD was present in 27 (41%). Of the 22 patients with pain, TCAD was present in 18, for a positive predictive value of 82% (95% confidence interval [CI] 60%-95%). The relative risk of TCAD being present in patients with a history of pain was 4 times that of patients without pain (p < 0.001). Sudden death or resuscitated sudden death occurred in 15 (68%) of 22 patients with pain vs 4 (9%) of 44 without pain (p < 0.001).

CONCLUSIONS

The symptom complex of abdominal, chest and/or arm pain is strongly associated with the presence of TCAD and sudden death or resuscitated sudden death in pediatric heart transplant recipients.

Genetic predictors and remodeling of dilated cardiomyopathy in muscular dystrophy

BACKGROUND

Dystrophin gene mutations cause 2 common muscular dystrophies, Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD). Both are frequently associated with dilated cardiomyopathy (DCM) and premature death. We hypothesized that early diagnosis and treatment of DCM in DMD/BMD patients would lead to ventricular remodeling and that specific dystrophin gene mutations would predict cardiac involvement.

METHODS AND RESULTS

Sixty-nine boys with DMD (n=62) and BMD (n=7) (mean age, 12.9 and 13.7 years, respectively) were referred to our Cardiovascular Genetics Clinic for evaluation, including echocardiography and DNA analysis. Follow-up evaluations were scheduled yearly until the first abnormal echocardiogram indicative of DCM and quarterly thereafter. After the first abnormal echocardiogram, angiotensin-converting enzyme inhibitor or beta-blocker therapy was started. beta-Blockers were added if echocardiography showed no ventricular remodeling in angiotensin-converting enzyme inhibitor-treated patients after 3 months. DCM was diagnosed in 31 subjects (DMD, 27/62, 44%; BMD, 4/7, 57%) (mean age at onset, 15.4+/-2.8 years; range, 10.4 to 21.2 years). All 31 subjects were begun on pharmacological therapy after diagnosis. On follow-up (n=29), 2 subjects (both DMD) showed stable DCM, 8 subjects (all DMD) showed improvement, and 19 subjects (16 DMD; 3 BMD) showed normalization of left ventricular size and function (total improvement, 27/29 [93%]). DNA analysis in 47 cases (68%) revealed a significant association between DCM and exon 12 and 14 to 17 mutations, possible protection against DCM by exon 51 to 52 mutations, and a trend toward significant association between onset of DCM and exon 31 to 42 mutations. Statistical significance was based on nominal probability values.

CONCLUSIONS

Early diagnosis and treatment of DCM may lead to ventricular remodeling in DMD/BMD patients. Specific dystrophin gene mutations appear to be predictive of cardiac involvement, while other mutations may protect against or inhibit development of DCM. Further studies evaluating the impact of early intervention strategies on left ventricular geometry and function in muscular dystrophy patients seem warranted.

A cardiac myosin binding protein C mutation in the Maine Coon cat with familial hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is one of the most common causes of sudden cardiac death in young adults and is a familial disease in at least 60% of cases. Causative mutations have been identified in several sarcomeric genes, including the myosin binding protein C (MYBPC3) gene. Although numerous causative mutations have been identified, the pathogenetic process is still poorly understood. A large animal model of familial HCM in the cat has been identified and may be used for additional study. As the first spontaneous large animal model of this familial disease, feline familial HCM provides a valuable model for investigators to evaluate pathophysiologic processes and therapeutic (pharmacologic or genetic) manipulations. The MYBPC3 gene was chosen as a candidate gene in this model after identifying a reduction in the protein in myocardium from affected cats in comparison to control cats (P<0.001). DNA sequencing was performed and sequence alterations were evaluated for evidence that they changed the amino acid produced, that the amino acid was conserved and that the protein structure was altered. We identified a single base pair change (G to C) in the feline MYBPC3 gene in affected cats that computationally alters the protein conformation of this gene and results in sarcomeric disorganization. We have identified a causative mutation in the feline MYBPC3 gene that results in the development of familial HCM. This is the first report of a spontaneous mutation causing HCM in a non-human species. It should provide a valuable model for evaluating pathophysiologic processes and therapeutic manipulations.

Danon disease as an underrecognized cause of hypertrophic cardiomyopathy in children

BACKGROUND

Some patients with hypertrophic cardiomyopathy (HCM) or left ventricular hypertrophy also present with skeletal myopathy and Wolff-Parkinson-White (WPW) syndrome; mutations in the gene encoding the lysosome-associated protein-2 (LAMP-2) have been identified in these patients, suggesting that some of these patients have Danon disease. In this study we investigated the frequency of LAMP2 mutations in an unselected pediatric HCM population.

METHODS AND RESULTS

LAMP2 was amplified from genomic DNA isolated from peripheral lymphocytes of 50 patients diagnosed with HCM and analyzed by direct DNA sequencing. In 2 of the 50 probands (4%), nonsense mutations were identified. In 1 family the proband initially presented with HCM as a teenager, which progressed to dilated cardiomyopathy (DCM) and heart failure. Skeletal myopathy and WPW were also noted. The teenage sister of the proband is a carrier of the same LAMP2 mutation and has HCM without skeletal myopathy or WPW. The other proband presented with HCM, WPW, and skeletal myopathy as a teenager, whereas his carrier mother developed DCM during her 40s. Skeletal and cardiac muscle sections revealed the absence of LAMP-2 on immunohistochemical staining.

CONCLUSIONS

LAMP2 mutations may account for a significant proportion of cases of HCM in children, especially when skeletal myopathy and/or WPW is present, suggesting that Danon disease is an underrecognized entity in the pediatric cardiology community.

Radio-Frequency Catheter Ablation of Accessory Pathway Mediated Tachycardia in a Child After Orthotopic Heart Transplantation

Successful radio-frequency catheter ablation of accessory pathway mediated supraventricular tachycardia in the transplanted heart has been reported sporadically in adults, but has not been reported in children. This is the first report of a child having received a donor heart with manifest pre-excitation and who subsequently underwent successful radio-frequency ablation of the accessory pathway.

Detection of viral deoxyribonucleic acid in amniotic fluid: association with fetal malformation and pregnancy abnormalities

OBJECTIVE

To first test the hypothesis that the presence of viral nucleic acid in amniotic fluid (AF) is associated with an abnormal pregnancy outcome, and second, to determine if the overall rate of polymerase chain reaction (PCR) positivity and the distribution of virus types vary geographically.

STUDY DESIGN

Cytomegalovirus (CMV), parvovirus B19, adenovirus, enterovirus, herpes simplex virus, Epstein-Barr virus, and respiratory syncytial virus nucleic acids were sought in 423 AF samples obtained for clinical indications: 284 from the East Coast (EC) and 139 from the Midwest (MW).

RESULTS

Gestational age at sampling was 19.1 weeks for EC and 20.1 weeks for MW. 13.5% of karyotypically normal singleton pregnancies (57/423) had a positive AF PCR. 11% of AF PCR from the EC while 18% of AF PCR from the MW were positive (p = 0.06). The most commonly detected viruses were adenovirus (77%), enterovirus (12%), and CMV and parvovirus B19 (5% each). Twenty-four percent of sonographically abnormal pregnancies (33/136) had a positive AF PCR compared to only 8.4% (24/287) of normal pregnancies (p < 0.001).

CONCLUSION

A positive AF PCR is associated with an increased rate of fetal structural malformations, intrauterine growth restriction, hydrops and other fetal abnormalities. There were no significant geographic differences in the incidence of AF viral PCR positivity.

Left ventricular noncompaction cardiomyopathy in association with trisomy 13

In recent years, left ventricular noncompaction (LVNC) has been recognized as a distinct form of cardiomyopathy with its own clinical presentation and natural history. More than 100 cases of LVNC have been described in children. Although LVNC has been described in association with metabolic disorders such as Fabry's disease or genetic disorders such as Roifman's syndrome, this case represents the first report of LVNC in a child with trisomy 13.

Diagnostic value of epinephrine test for genotyping LQT1, LQT2, and LQT3 forms of congenital long QT syndrome

OBJECTIVES

The aim of this study was to test the hypothesis that epinephrine test may have diagnostic value for genotyping LQT1, LQT2, and LQT3 forms of congenital long QT syndrome (LQTS).

BACKGROUND

A differential response of dynamic QT interval to epinephrine infusion between LQT1, LQT2, and LQT3 syndromes has been reported, indicating the potential diagnostic value of the epinephrine test for genotyping the three forms.

METHODS

The responses of 12-lead ECG parameters to epinephrine were retrospectively examined in 15 LQT1, 10 LQT2, 8 LQT3, and 10 healthy volunteers to select the best ECG criteria for separating the four groups. The epinephrine test then was prospectively conducted in 42 probands clinically affected with LQTS, their 67 family members, and 10 new volunteers. The best criteria were applied in a blinded fashion to prospectively separate a different group of 31 LQT1, 23 LQT2, 6 LQT3, and 30 Control patients (10 genotype-negative LQT1, 10 genotype-negative LQT2 family members, and 10 volunteers).

RESULTS

The sensitivity (penetrance) by ECG diagnostic criteria was lower in LQT1 (68%) than in LQT2 (83%) or LQT3 (83%) before epinephrine and was improved with steady-state epinephrine in LQT1 (87%) and LQT2 (91%) but not in LQT3 (83%), without the expense of specificity (100%). The sensitivity and specificity to differentiate LQT1 from LQT2 were 97% and 96%, those from LQT3 were 97% and 100%, and those from Control were 97% and 100%, respectively, when Delta mean corrected Q-Tend >/=35 ms at steady state was used. The sensitivity and specificity to differentiate LQT2 from LQT3 or Control were 100% and 100%, respectively, when Delta mean corrected Q-Tend >/=80 ms at peak was used.

CONCLUSIONS

Epinephrine infusion is a powerful test to predict the genotype of LQT1, LQT2, and LQT3 syndromes as well as to improve the clinical diagnosis of genotype-positive patients, especially those with LQT1 syndrome.

Inheritance analysis of congenital left ventricular outflow tract obstruction malformations: Segregation, multiplex relative risk, and heritability

The left ventricular outflow tract (LVOTO) malformations, aortic valve stenosis (AVS), coarctation of the aorta (COA), and hypoplastic left heart (HLH) constitute a mechanistically defined subgroup of congenital heart defects that have substantial evidence for a genetic component. Evidence from echocardiography studies has shown that bicuspid aortic valve (BAV) is found frequently in relatives of children with LVOTO defects. However, formal inheritance analysis has not been performed. We ascertained 124 families by an index case with AVS, COA, or HLH. A total of 413 relatives were enrolled in the study, of which 351 had detailed echocardiography exams for structural heart defects and measurements of a variety of aortic arch, left ventricle, and valve structures. LVOTO malformations were noted in 30 relatives (18 BAV, 5 HLH, 3 COA, and 3 AVS), along with significant congenital heart defects (CHD) in 2 others (32/413; 7.7%). Relative risk for first-degree relatives in this group was 36.9, with a heritability of 0.71-0.90. Formal segregation analysis suggests that one or more minor loci with rare dominant alleles may be operative in a subset of families. Multiplex relative risk analysis, which estimates number of loci, had the highest maximum likelihood score in a model with 2 loci (range of 1-6 in the lod-1 support interval). Heritability of several aortic arch measurements and aortic valve was significant. These data support a complex but most likely oligogenic pattern of inheritance. A combination of linkage and association study designs is likely to enable LVOTO risk gene identification. This data can also provide families with important information for screening asymptomatic relatives for potentially harmful cardiac defects.

Monolysocardiolipins accumulate in Barth syndrome but do not lead to enhanced apoptosis

Barth syndrome (BTHS) is an X-linked recessive disorder that is biochemically characterized by low cellular levels of the mitochondrial phospholipid cardiolipin (CL). Previously, we discovered that the yeast disruptant of the TAZ ortholog in Saccharomyces cerevisiae not only displays CL deficiency but also accumulates monolysocardiolipins (MLCLs), which are intermediates in CL remodeling. Therefore, we set out to investigate whether MLCL accumulation also occurs in BTHS. Indeed, we observed MLCL accumulation in heart, muscle, lymphocytes, and cultured lymphoblasts of BTHS patients; however, only very low levels of these lysophospholipids were found in platelets and fibroblasts of these patients. Although the fatty acid composition of the MLCLs was different depending on the tissue source, it did parallel the fatty acid composition of the (remaining) CLs. The possible implications of these findings for the two reported CL remodeling mechanisms, transacylation and deacylation/reacylation, are discussed. Because MLCLs have been proposed to be involved in the initiation of apoptosome-mediated cell death by the sequestration of the proapoptotic protein (t)BH3-interacting domain death agonist (Bid) to the mitochondrial membrane, we used control and BTHS lymphoblasts to investigate whether the accumulation of MLCLs results in higher levels of apoptosis. We found no differences in susceptibility to death receptor-mediated apoptosis or in cellular distribution of Bid, cytochrome c, and other parameters, implying that MLCL accumulation does not lead to enhanced apoptosis in cultured BTHS lymphoblasts.

A family-based association study of congenital left-sided heart malformations and 5,10 methylenetetrahydrofolate reductase

BACKGROUND

Aortic valve stenosis (AVS), coarctation of the aorta (CoA), and hypoplastic left heart syndrome (HLHS) are obstructive malformations of the left ventricular outflow tract that account for a significant proportion of infant mortality. Two previous small case-control studies suggested methylenetetrahydrofolate reductase (MTHFR) polymorphisms may be associated with this group of malformations.

METHODS

We used a family-based association design with inclusion criteria of nonsyndromic diagnosis of AVS, CoA, and HLHS, powered to detect an odds ratio for the heterozygote of <1.5. A total of 207 affected offspring-parent trios were genotyped by restriction fragment length polymorphisms at the two common polymorphic loci C677T and A1298C.

RESULTS

Error rate estimation based on replicate samples was 0.76%. Mendelian inconsistency at either polymorphism was noted in 10 trios, for a calculated undetected error rate of 1.95%. A total of 197 trios were analyzed using the transmission disequilibrium test. Significant association was not found between both the C677T or A1298C polymorphisms and presence of a heart defect, whether analyzed as a group, or by sex, ethnicity, or specific diagnosis. A log-linear analysis did not find increased relative risk based on the maternal genotype.

CONCLUSIONS

We were unable to replicate previous association studies and concluded that neither the affected nor the maternal MTHFR genotype, by itself, is a major risk factor for congenital left ventricular outflow tract malformations.

Regulatory mutations in transforming growth factor-beta3 gene cause arrhythmogenic right ventricular cardiomyopathy type 1

OBJECTIVE

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a genetically heterogeneous disorder characterized by fibro-fatty replacement of the right ventricular myocardium, associated with high risk of sudden death. The objective of this study is to identify the gene involved in ARVD1, which has been elusive ever since its locus was mapped to chromosome 14q24.3.

METHODS AND RESULTS

Mutation screening of the promoter and untranslated regions (UTRs) of the transforming growth factor-beta3 (TGFbeta3) gene was performed by direct sequencing of genomic DNA of one index case belonging to an ARVD1 family including 38 members in four generations. We detected a nucleotide substitution (c.-36G>A) in 5' UTR of TGFbeta3 gene, invariably associated with the typical ARVC clinical phenotype in the affected family members, according to the established diagnostic criteria. Investigation extended to 30 unrelated ARVC patients, performed by denaturing high-performance liquid chromatography (DHPLC), led to the identification of an additional mutation (c.1723C>T) in the 3' UTR of one proband. Neither nucleotide change was found in 300 control subjects. In vitro expression assays with constructs containing the mutations showed that mutated UTRs were twofold more active than wild-types.

CONCLUSION

We identified TGFbeta3 as the disease gene involved in ARVD1. The identification of a novel ARVC gene will increase the power of the genetic screening for early diagnosis of asymptomatic carriers among relatives of ARVC patients.