Dominant mode of inheritance in atrial septal defect

The pathogenesis of atrial and atrioventricular septal defects with special emphasis on the role of the dorsal mesenchymal protrusion

Partitioning of the four-chambered heart requires the proper formation, interaction and fusion of several mesenchymal tissues derived from different precursor populations that together form the atrioventricular mesenchymal complex. This includes the major endocardial cushions and the mesenchymal cap of the septum primum, which are of endocardial origin, and the dorsal mesenchymal protrusion (DMP), which is derived from the Second Heart Field. Failure of these structures to develop and/or fully mature results in atrial septal defects (ASDs) and atrioventricular septal defects (AVSD). AVSDs are congenital malformations in which the atria are permitted to communicate due to defective septation between the inferior margin of the septum primum and the atrial surface of the common atrioventricular valve. The clinical presentation of AVSDs is variable and depends on both the size and/or type of defect; less severe defects may be asymptomatic while the most severe defect, if untreated, results in infantile heart failure. For many years, maldevelopment of the endocardial cushions was thought to be the sole etiology of AVSDs. More recent work, however, has demonstrated that perturbation of DMP development also results in AVSD. Here, we discuss in detail the formation of the DMP, its contribution to cardiac septation and describe the morphological features as well as potential etiologies of ASDs and AVSDs.

Familial atrial septal defect in the oval fossa with progressive prolongation of the atrioventricular conduction caused by mutations in the NKX2.5 gene

OBJECTIVE

To search for a genetic basis in a family with autosomal dominantly inherited atrial septal defect in combination with increasing conduction anomalies.

DESIGN

We searched for mutations in the NKX2.5 gene by sequencing of desoxyribonucleic acid in a previously investigated family.

PATIENTS

All family members were included if they, after informed consent, had decided to participate in the genetic testing. A blood sample was sent from local doctors for analysis of potential mutations. Patients with cardiac anomalies were examined in our hospital. For those family members without cardiac anomalies, we relied on local information.

RESULTS

We identified the mutation Q149X in the NKX2.5 gene on chromosome 5q35 in all patients with atrial septal defect and disturbances of atrioventricular conduction. No family member without an atrial septal defect possessed the mutation, including a member with transposed arterial trunks.

CONCLUSION

We have identified a mutation in the NKX2.5 gene responsible for autosomal dominantly inherited atrial septal defect in the oval fossa combined with disturbances of atrioventricular conduction in 7 patients spanning 4 generations.

Mutations in mammalian tolloid-like 1 gene detected in adult patients with ASD

Atrial septal defect (ASD) is an incomplete septation of atria in human heart causing circulatory problems. Its frequency is estimated at one per 10 000. Actions of numerous genes have been linked to heart development. However, no single gene defect causing ASD has yet been identified. Incomplete heart septation similar to ASD was reported in transgenic mice with both inactive alleles of gene encoding mammalian zinc metalloprotease a mammalian tolloid-like 1 (tll1). Here, we have screened 19 ASD patients and 15 healthy age-matched individuals for mutations in TLL1 gene. All 22 exons were analyzed exon by exon for heteroduplex formation. Subsequently, DNA fragments forming heteroduplexes were sequenced. In four nonrelated patients, three missense mutations in coding sequence, and one single base change in the 5'UTR have been detected. Two mutations (Met182Leu, and Ala238Val) were detected in ASD patients with the same clinical phenotype. As the second mutation locates immediately upstream of the catalytic zinc-binding signature, it might change the enzyme substrate specificity. The third change, Leu627Val in the CUB3 domain, has been found in an ASD patient with interatrial septum aneurysm in addition to ASD. The CUB3 domain is important for substrate-specific recognition. In the remaining 15 patients as well as in 15 reference samples numerous base substitutions, deletions, and insertions have been detected, but no mutations changing the coding sequence have been found. Lack of mutations in relation to ASD of these patients could possibly be because of genetic heterogeneity of the syndrome.

The familial form of atrial septal defect

BACKGROUND

The secundum atrial septal defect accounts for 10% of congenital heart disease. Familial occurrence is rare and may present as an isolated lesion or with conduction and skeletal abnormalities. Predisposing genes were described.

OBJECTIVES

To evaluate familial defect's prevalence and associated anomalies and assess the yield of screening.

METHODS

Family history, physical, electrocardiographic and echocardiographic evaluation of 286 ASD patients and families regarding heart disease, conduction and skeletal anomalies were performed.

RESULTS

Eleven new families with familial defects were identified yielding 28 patients. The rate of transmission was 40-100%, suggestive of autosomal dominant inheritance. Parents were healthy in four families with multiple offspring with ASDs. Two families had ASDs with atrioventricular conduction abnormalities in five of six subjects, not requiring pacing. One subject had skeletal malformation. Ten patients had surgery, 12 had transcatheter ASD closure and six await treatment.

CONCLUSIONS

In view of the high prevalence of familial occurrence of secundum ASD (10% of all ASD patients), we recommend screening all first degree relatives of ASD patients for cardiac, conduction and skeletal anomalies. Although a routine genetic investigation is not yet available, genetic patterns of inheritance may be compatible with autosomal dominant inheritance. Healthy parents of affected offspring may suggest a variable gene penetrance or past spontaneous ASD closure. Conduction anomalies may be present or may develop throughout life, and thus should be periodically screened for.

Familial recurrence of congenital heart disease in patients with ostium secundum atrial septal defect

AIMS

Ostium secundum atrial septal defect (osASD) is one of the most common cardiac malformations. Few data are available on the familial recurrence of congenital heart disease (CHD), in particular, in a large group of patients with isolated osASD. The aim is to investigate the familial recurrence of CHD in up to third-degree relatives from a large sample of consecutively enrolled patients with osASD, taking into account the influence of degree of relatedness (as number of relatives).

METHODS AND RESULTS

From January 1998 to December 2002, we enrolled 583 patients with osASD and 408 healthy subjects, referred to our tertiary centre. We hypothesized that a positive family history required at least one relative with CHD to constitute a risk factor. In this model of analysis, the null hypothesis is a similar familial history between cases and controls. Among 583 patients with osASD, 109 (19%) had at least one relative with CHD. Among the 408 healthy subjects studied, only 23 (6%) had a family history of CHD. A familial recurrence of CHD was demonstrated in 72 of 312 (23%) patients with isolated osASD and in 37 of 271 (13.6%) patients with non-isolated osASD. Familial recurrence of isolated osASD was demonstrated in 22 of 312 patients (7%) with an isolated osASD and only in six of 271 patients (2.2%) with non-isolated osASD. The familial recurrence risk of isolated osASD in patients with isolated osASD was higher in sibs, especially in sisters (33.3%).

CONCLUSION

This study underscores the role of genetic factors in the determination of CHD, particularly osASD. Our results could represent the basis for further studies to calculate a 'value of family history' to adapt the familial recurrence to the real size of each family group. In this way, we could select families with a 'tendency' to develop CHD, particularly osASD. In these families, we could analyse the genetic pattern to establish abnormalities and the bases of CHD.

Reduced penetrance, variable expressivity, and genetic heterogeneity of familial atrial septal defects

BACKGROUND

Secundum atrial septal defect (ASD) is a common congenital heart malformation that occurs as an isolated anomaly in 10% of individuals with congenital heart disease. Although some embryological pathways have been elucidated, the molecular etiologies of ASD are not fully understood. Most cases of ASD are isolated, but some individuals with ASD have a family history of this defect or other congenital heart malformations.

METHODS AND RESULTS

Clinical evaluation of three families identified individuals with ASD in multiple generations. ASD was transmitted as an autosomal dominant trait in each family. ASD was the most common anomaly, but other heart defects occurred alone or in association with ASD in individuals from each kindred. Genome-wide linkage studies in one kindred localized a familial ASD disease gene to chromosome 5p (multipoint LOD score=3.6, theta=0.0). Assessment of 20 family members with the disease haplotype revealed that 9 had ASD, 8 were clinically unaffected, and 3 had other cardiac defects (aortic stenosis, atrial septal aneurysm, and persistent left superior vena cava). Familial ASD did not map to chromosome 5p in two other families.

CONCLUSIONS

Familial ASD is a genetically heterogeneous disorder; one disease gene maps to chromosome 5p. Recognition of the heritable basis of familial ASD is complicated by low disease penetrance and variable expressivity. Identification of ASD or other congenital heart defects in more than one family member should prompt clinical evaluation of all relatives.

Genetic study of congenital heart defects in Northern Ireland (1974-1978)

Congenital heart defects are a major congenital abnormality and are assuming increasing importance. A study was undertaken to estimate the incidence of congenital heart defects in Northern Ireland over a five year period (1974-1978), to determine the age at diagnosis and to assess the risk of recurrence in sibs. An incidence rate of 7.3 per 1000 total births was found. This reduced to 3.1 per 1000 total births if only invasive methods of diagnosis (catheter studies, surgery, or necropsy) were considered. The overall risk of recurrence for sibs (excluding index patients with chromosomal abnormalities and syndromes) was 3.1%. In addition, excluding families with an affected parent and child gave a recurrence risk of 2.6%. By 6 weeks of age 63% of index patients had been diagnosed and this figure had risen to 88% by 1 year. This has important implications for studies which include only congenital heart defects diagnosed in the first year of life. Of 388 patients with a congenital heart defect confirmed by invasive criteria, 96 (24.7%) were found to have an extracardiac abnormality (ECA). Excluding those with epilepsy or mental handicap as the sole ECA left 91 (23.5%) with an ECA. This highlights the importance of looking for other abnormalities in a child with a congenital heart defect. The 388 index patients had 952 sibs of whom 72 (7.6%) had an ECA. Excluding those with minor abnormalities (inguinal hernias, undescended testes) as the sole ECA left 62 (6.5%) with a major ECA. In addition, excluding those with epilepsy or mental handicap as the sole ECA left 51 (5.4%) with a major ECA. Since parents are often reassured after the birth of a child with a congenital heart defect that their risk of having a child with a noncardiac abnormality is no greater than the general population this finding has important implications for genetic counselling.

Familial atrial septal defect with prolonged atrioventricular conduction

This report describes a family with frequent recurrence of congenital heart disease in multiple generations. Eight members had atrial septal defect (ASD) of the fossa ovalis type and seven members had other forms of congenital heart disease. One branch of the pedigree showed a predominance of ASD with prolonged atrioventricular (A-V) conduction and initially suggested an autosomal dominant gene effect. A variety of other forms of congenital heart disease were found in several first degree relatives of those with ASD as well as in more distant relatives. The variability of congenital heart disease in this pedigree is compatible with the polygenic mode of inheritance. Definition of the inheritability of congenital heart disease in a specific family has important consequences in the determination of the recurrence risks for all family members.

Association of secundum atrial septal defect with abnormalities of atrioventricular conduction or left axis deviation. Genetic study of 10 families

A genetic analysis was made of 10 families in which the propositi had a secundum atrial septal defect associated with abnormal atrioventricular conduction (first, second, or third degree heart block) or unexplained left axis deviation or a combination of these conduction disturbances. Diagnostic information was available on 51 (81%) of the first degree relatives. Three of the families appeared to be examples of a new syndrome which, with variable expression, was inherited as a non-sex-linked autosomal dominant. The main features were a secundum atrial septal defect; disease of the conducting tissue, which in some cases was progressive; unexplained left axis deviation; and unexpected death. These families did not seem to be examples of the Holt-Oram syndrome, for the upper limbs were clinically and radiologically normal in the 19 members examined. The importance of recognizing this syndrome is the occurrence of progressive disease of the conducting tissue and the risk of sudden death. When, therefore, unexplained left axis deviation or prolonged atrioventricular conduction is found in association with a secundum atrial septal defect all available relatives should be examined. In the remaining seven families there was only one affected first degree relative out of 39 examined. He was the son of one of the propositi and had paroxysmal coronary sinus rhythm with an intact atrial septum.

Secundum type atrial septal defect with prolonged PR interval and autosomal dominant mode of inheritance

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Genetics of atrial septal defect

Of 109 cases of atrial septal defect, cases with an isolated defect (92 cases) showed a female preponderance (sex ratio 0·64), but there was a higher risk to the sibs of the male patients, suggesting a multifactorial mechanism. Dermatoglyphs showed a large number of whorls on the fingers. In 17 cases there were multiple malformations, such as Holt-Oram syndrome (hypoplastic and triphalangic thumb, with ostium secundum atrial septal defect), polydactyly plus ostium primum defect, and tracheo-oesophageal fistula.