Loss-of-function mutations in growth differentiation factor-1 (GDF1) are associated with congenital heart defects in humans

Congenital heart defects (CHDs) are among the most common birth defects in humans (incidence 8-10 per 1,000 live births). Although their etiology is often poorly understood, most are considered to arise from multifactorial influences, including environmental and genetic components, as well as from less common syndromic forms. We hypothesized that disturbances in left-right patterning could contribute to the pathogenesis of selected cardiac defects by interfering with the extrinsic cues leading to the proper looping and vessel remodeling of the normally asymmetrically developed heart and vessels. Here, we show that heterozygous loss-of-function mutations in the human GDF1 gene contribute to cardiac defects ranging from tetralogy of Fallot to transposition of the great arteries and that decreased TGF- beta signaling provides a framework for understanding their pathogenesis. These findings implicate perturbations of the TGF- beta signaling pathway in the causation of a major subclass of human CHDs.

Mutations in desmoglein-2 gene are associated with arrhythmogenic right ventricular cardiomyopathy

BACKGROUND

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited cardiomyopathy characterized by progressive myocardial atrophy with fibrofatty replacement. The recent identification of causative mutations in plakoglobin, desmoplakin (DSP), and plakophilin-2 (PKP2) genes led to the hypothesis that ARVC is due to desmosomal defects. Therefore, desmoglein-2 (DSG2), the only desmoglein isoform expressed in cardiac myocytes, was screened in subjects with ARVC.

METHODS AND RESULTS

In a series of 80 unrelated ARVC probands, 26 carried a mutation in DSP (16%), PKP2 (14%), and transforming growth factor-beta3 (2.5%) genes; the remaining 54 were screened for DSG2 mutations by denaturing high-performance liquid chromatography and direct sequencing. Nine heterozygous DSG2 mutations (5 missense, 2 insertion-deletions, 1 nonsense, and 1 splice site mutation) were detected in 8 probands (10%). All probands fulfilled task force criteria for ARVC. An endomyocardial biopsy was obtained in 5, showing extensive loss of myocytes with fibrofatty tissue replacement. In 3 patients, electron microscopy investigation was performed, showing intercalated disc paleness, decreased desmosome number, and intercellular gap widening.

CONCLUSIONS

This is the first investigation demonstrating DSG2 gene mutations in a significant number of ARVC-unrelated probands. Cardiac phenotype is characterized clinically by typical ARVC features with frequent left ventricular involvement and morphologically by fibrofatty myocardial replacement and desmosomal remodeling. The presence of mutations in desmosomal encoding genes in 40% of cases confirms that many forms of ARVC are due to alterations in the desmosome complex.

Identification and functional analysis of ZIC3 mutations in heterotaxy and related congenital heart defects

Mutations in the zinc finger transcription factor ZIC3 cause X-linked heterotaxy and have also been identified in patients with isolated congenital heart disease (CHD). To determine the relative contribution of ZIC3 mutations to both heterotaxy and isolated CHD, we screened the coding region of ZIC3 in 194 unrelated patients, including 61 patients with classic heterotaxy, 93 patients with heart defects characteristic of heterotaxy, and 11 patients with situs inversus totalis. Five novel ZIC3 mutations in three classic heterotaxy kindreds and two sporadic CHD cases were identified. None of these alleles was found in 97 ethnically matched control samples. On the basis of these analyses, we conclude that the phenotypic spectrum of ZIC3 mutations should be expanded to include affected females and CHD not typical for heterotaxy. This screening of a cohort of patients with sporadic heterotaxy indicates that ZIC3 mutations account for approximately 1% of affected individuals. Missense and nonsense mutations were found in the highly conserved zinc finger-binding domain and in the N-terminal protein domain. Functional analysis of all currently known ZIC3 point mutations indicates that mutations in the putative zinc finger DNA binding domain and in the N-terminal domain result in loss of reporter gene transactivation. It is surprising that transfection studies demonstrate aberrant cytoplasmic localization resulting from mutations between amino acids 253-323 of the ZIC3 protein, indicating that the pathogenesis of a subset of ZIC3 mutations results at least in part from failure of appropriate nuclear localization. These results further expand the phenotypic and genotypic spectrum of ZIC3 mutations and provide initial mechanistic insight into their functional consequences.

Is adenovirus a fetal pathogen?

OBJECTIVES

The purpose of this study was to test the relationship between adenovirus genetic material in the amniotic fluid and adverse pregnancy outcome.

STUDY DESIGN

This was a prospective, observational study of women who were referred in the second trimester of gestation for either genetic amniocentesis or evaluation of fetal malformation. A 2-mL aliquot of amniotic fluid was subjected to multiplex polymerase chain reaction for a panel of viruses that included adenovirus and human genome controls. Fetuses with an abnormal karyotype were excluded from analysis.

RESULTS

The prevalence of adenovirus was similar in normal (39/652) and anomalous fetuses (23/364; chi(2) test, P=.376). There was significant seasonal variation in the prevalence in both normal and anomalous fetuses (chi(2) exact test, P<.001), but no significant difference between groups. The monthly proportion of patients who underwent amniocentesis remained constant throughout the year (mean, 8.3%; chi(2) test, P=.67). Central nervous system anomalies and echogenic liver foci were significantly more common among fetuses with positive amniotic fluid polymerase chain reaction results for adenovirus (P<.005, respectively).

CONCLUSION

Adenovirus is found in a similar prevalence and seasonal variation in sonographically normal and abnormal pregnancies. Although a specific fetal presentation was not identified, echogenic liver lesions with or without hydrops and neural tube defects were significantly more common in the presence of adenovirus. The significance of these findings deserves further study.

Prevalence of viral DNA in amniotic fluid of low-risk pregnancies in the second trimester

AIM

The association between fetal viral infection and adverse pregnancy outcome is well documented. However, the prevalence of common viral pathogens in the amniotic fluid of normal pregnancies is not established. The purpose of this study was to determine this prevalence in asymptomatic patients.

METHODS

This was a prospective observational study of patients at low risk for viral infection who were referred for second-trimester genetic amniocentesis. In patients with normal fetal anatomy on ultrasound and a normal fetal karyotype, a 2-ml aliquot of amniotic fluid obtained at amniocentesis was analyzed by multiplex polymerase chain reaction for cytomegalovirus (CMV), parvovirus B19, adenovirus, enterovirus, herpes simplex virus (HSV), respiratory syncytial virus (RSV) and Epstein-Barr virus (EBV).

RESULTS

Among 686 patients, advanced maternal age was the most common indication for genetic testing (n = 469, 68.4%), followed by elevated aneuploidy risk on triple screen (n = 164, 23.9%), elevated maternal serum alpha-fetoprotein (n = 20, 2.9%), previous aneuploidy (n = 16, 2.3%) and family history of inheritable disease (n = 14, 2.1%). Forty-four (6.4%) amniotic fluid samples were positive for viral genome. A single genome was amplified in 41 samples (93%). In three samples, two viral genomes were identified. Adenovirus was most frequently identified (37/44), followed by CMV (5/44), EBV (2/44), enterovirus (2/44) and RSV (1/44). Parvovirus and HSV were not identified. There was a bimodal seasonal variation in prevalence, with the highest prevalence during the summer and late winter.

CONCLUSION

Viral genome is commonly found in amniotic fluid with a sonographically normal fetus, and the prevalence follows a seasonal pattern. The mechanism, significance and effects of this asymptomatic viral presence require further study.

Arrhythmogenic right ventricular cardiomyopathy type 1 (ARVD1): confirmation of locus assignment and mutation screening of four candidate genes

Arrhythmogenic right ventricular cardiomyopathy type 1 (ARVD1) is an autosomal dominant disorder characterised by progressive degeneration of right ventricular myocardium, arrhythmias and risk of sudden death. By linkage analysis, we previously mapped the involved gene to chromosome 14q24.3. In the present study we report on linkage analysis of one additional and unrelated family, which enabled to confirm previous locus assignment. Another family is reported, in which genetic and clinical data suggest linkage to the same locus. Direct sequencing of DNA from individuals belonging to established ARVD1 families failed to detect causative mutations in exonic sequences of four genes (POMT2, TGFbeta3, KIAAA1036 and KIAA0759) expressed in the heart and which defects could possibly induce plasma membrane instability or apoptosis, key features of ARVD pathogenesis.

PTPN11 mutations in Noonan syndrome type I: detection of recurrent mutations in exons 3 and 13

We surveyed 16 subjects with the clinical diagnosis of Noonan Syndrome (NS1) from 12 families and their relevant family members for mutations in PTPN11/SHP2 using direct DNA sequencing. We found three different mutations among five families. Two unrelated subjects shared the same de novo missense substitution in exon 13 (S502T); an additional two unrelated families had a mutation in exon 3 (Y63C); and one subject had the amino acid substitution Y62D, also in exon 3. None of the three mutations were present in ethnically matched controls. In the mature protein model, the exon 3 mutants and the exon 13 mutant amino acids cluster at the interface between the N' SH2 domain and the phosphatase catalytic domain. Six of eight subjects with PTPN11/SHP2 mutations had pulmonary valve stenosis while no mutations were identified in those subjects (N = 4) with hypertrophic cardiomyopathy. An additional four subjects with possible Noonan syndrome were evaluated, but no mutations in PTPN11/SHP2 were identified. These results confirm that mutations in PTPN11/SHP2 underlie a common form of Noonan syndrome, and that the disease exhibits both allelic and locus heterogeneity. The observation of recurrent mutations supports the hypothesis that a special class of gain-of-function mutations in SHP2 give rise to Noonan syndrome.

Long-term follow-up of individuals with the electrocardiographic pattern of right bundle-branch block and ST-segment elevation in precordial leads V1 to V3

BACKGROUND

The electrocardiographic pattern of right bundle-branch block with ST-segment elevation in leads V1 to V3 is increasingly recognized among patients who have aborted sudden cardiac death, but also in asymptomatic individuals, raising questions about its prognostic significance.

METHODS AND RESULTS

The clinical, electrophysiological, and follow-up data of 334 patients with the Brugada phenotype were analyzed. A total of 79 women and 255 men with a mean age at diagnosis of 42+/-16 years were studied. The abnormal ECG was recognized after a resuscitated cardiac arrest in 71 patients (group A), after a syncopal episode in 73 patients (group B), and in 190 asymptomatic individuals (group C). Sustained ventricular arrhythmias were inducible in 83%, 63%, and 33% of patients in group A, group B, and group C, respectively. During 54+/-54 and 26+/-36 months of follow-up, respectively, 62% of patients in group A and 19% of group B patients had a new arrhythmic event. Inducibility of ventricular arrhythmias was the only predictor of arrhythmia occurrence in both groups. During a mean follow-up of 27+/-29 months, 8% of group C individuals had a first arrhythmic event. In these individuals, inducibility of ventricular arrhythmias and a basal abnormal ECG were predictors of arrhythmia occurrence.

CONCLUSIONS

An ECG showing right bundle-branch block and ST-segment elevation in the right precordial leads is a marker of malignant ventricular arrhythmias and sudden death. Recurrence of malignant arrhythmias is high after the occurrence of symptoms. Among asymptomatic individuals, those with a spontaneously abnormal ECG and inducible to ventricular arrhythmias have the poorer prognosis.

Loss-of-function mutations in the EGF-CFC gene CFC1 are associated with human left-right laterality defects

All vertebrates display a characteristic asymmetry of internal organs with the cardiac apex, stomach and spleen towards the left, and the liver and gall bladder on the right. Left-right (L-R) axis abnormalities or laterality defects are common in humans (1 in 8,500 live births). Several genes (such as Nodal, Ebaf and Pitx2) have been implicated in L-R organ positioning in model organisms. In humans, relatively few genes have been associated with a small percentage of human situs defects. These include ZIC3 (ref. 5), LEFTB (formerly LEFTY2; ref. 6) and ACVR2B (encoding activin receptor IIB; ref. 7). The EGF-CFC genes, mouse Cfc1 (encoding the Cryptic protein; ref. 9) and zebrafish one-eyed pinhead (oep; refs 10, 11) are essential for the establishment of the L-R axis. EGF-CFC proteins act as co-factors for Nodal-related signals, which have also been implicated in L-R axis development. Here we identify loss-of-function mutations in human CFC1 (encoding the CRYPTIC protein) in patients with heterotaxic phenotypes (randomized organ positioning). The mutant proteins have aberrant cellular localization in transfected cells and are functionally defective in a zebrafish oep-mutant rescue assay. Our findings indicate that the essential role of EGF-CFC genes and Nodal signalling in left-right axis formation is conserved from fish to humans. Moreover, our results support a role for environmental and/or genetic modifiers in determining the ultimate phenotype in humans.

Clinic-based study of plexiform neurofibromas in neurofibromatosis 1

Individuals with neurofibromatosis 1 (NF1) develop both benign and malignant tumors at an increased frequency. One of the most common benign tumors in NF1 is the plexiform neurofibroma. These tumors cause significant morbidity and mortality on account of their propensity to grow and affect adjacent normal tissues. To determine the clinical profile of plexiform neurofibromas in NF1, we conducted a retrospective review of 68 NF1 patients with plexiform neurofibroma. In our series, 44% of tumors were detected by 5 years of age and most were located in the trunk and extremities. Only two patients developed malignant peripheral nerve sheath tumors in their preexisting plexiform neurofibromas. Lastly, we demonstrate that there were no specific clinical features of NF1 associated with the presence of plexiform neurofibroma. These results underscore the importance of careful serial examinations in the evaluation of patients with NF1.

Predicting outcome after listing for heart transplantation in children: comparison of Kaplan-Meier and parametric competing risk analysis. Pediatric Heart Transplant Study Group

After listing for pediatric heart transplantation, at any point in time one of the following possibilities could have occurred; death, transplantation, removal from the list because of clinical improvement, or continuing to wait. In the setting of those competing outcomes, the Kaplan-Meier estimate portrays the time-relatedness of an event while ignoring the effect of the other possible outcomes. The competing outcomes method, however, depicts the time relatedness of an event while solving for all possible events simultaneously. The competing outcomes method may potentially provide more accurate information regarding the actual proportion of patients experience an outcome after listing.

Multiple mechanisms in the long-QT syndrome. Current knowledge, gaps, and future directions. The SADS Foundation Task Force on LQTS

The congenital long-QT syndrome (LQTS) is characterized by prolonged QT intervals, QT interval lability, and polymorphic ventricular tachycardia. The manifestations of the disease vary, with a high incidence of sudden death in some affected families but not in others. Mutations causing LQTS have been identified in three genes, each encoding a cardiac ion channel. In families linked to chromosome 3, mutations in SCN5A, the gene encoding the human cardiac sodium channel, cause the disease, Mutations in the human ether-à-go-go-related gene (HERG), which encodes a delayed-rectifier potassium channel, cause the disease in families linked to chromosome 7. Among affected individuals in families linked to chromosome 11, mutations have been identified in KVLQT1, a newly cloned gene that appears to encode a potassium channel. The SCN5A mutations result in defective sodium channel inactivation, whereas HERG mutations result in decreased outward potassium current. Either mutation would decrease net outward current during repolarization and would thereby account for prolonged QT intervals on the surface ECG. Preliminary data suggest that the clinical presentation in LQTS may be determined in part by the gene affected and possibly even by the specific mutation. The identification of disease genes in LQTS not only represents a major milestone in understanding the mechanisms underlying this disease but also presents new opportunities for combined research at the molecular, cellular, and clinical levels to understand issues such as adrenergic regulation of cardiac electrophysiology and mechanisms of susceptibility to arrhythmias in LQTS and other settings.