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

Electrical disorders in atrial septal defect: genetics and heritability

Atrial septal defect (ASD) is one of the most common types of congenital heart diseases (CHDs). Most ASDs occur sporadically, but some are inherited and associated with cardiac conduction defects such as atrioventricular block (AVB) or bundle branch block. Mutations in genes encoding transcription factor gene TBX5 and NKX2-5, were found in Holt-Oram syndrome (HOS) and ASD with atrioventricular (AV) conduction defects, respectively. HOS is characterized by upper limb anomaly in addition to ASD and AVB (heart-hand syndrome). ASD associated with NKX2-5 is rare but is reported to cause sudden cardiac death (SCD) or cardiomyopathy. We provide a review of these two diseases.

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.

Congenital cardiovascular malformations: questions on inheritance. Baltimore-Washington Infant Study Group

The Baltimore-Washington Infant Study, an epidemiologic investigation of congenital heart disease, searches for genetic and environmental risk factors. Among 2,102 infants with heart disease, 17.5% had a noncardiac abnormality of chromosomal or genetic origin, whereas among 2,328 control infants, only 0.7% had a genetic abnormality. Familial cardiovascular malformations encountered can be grouped into five distinct etiologic mechanisms. Single gene effects may be responsible for the specific histologic and biochemical changes in familial atrial septal defect with conduction disturbance and also in idiopathic ventricular hypertrophy. Left heart lesions showed familial concordance by the presumed morphogenetic mechanism of abnormal embryonic blood flow with phenotypes of varying severity. Pulmonary stenosis appeared with familial heritable disorders, as well as a partially concordant lesion with tetralogy of Fallot. Ventricular septal defect with transposition of the great arteries (one sibling pair) and with truncus arteriosus (two sibling pairs) indicate forme fruste expression of conotruncal defects. Endocardial cushion defect occurred with and without Down's syndrome in members of three families, suggesting inheritance of a defect affecting cellular migration. Heritable blood coagulopathies occurred in case families and not in control families. The associated of hemophilia and transposition, observed also by others, is extremely unlikely by chance and suggests genetic errors of endothelial cell function. The description of specific families from a population-based study emphasizes biologic questions on the nature of the inheritance of cardiovascular malformations.

Evidence of congenital heart disease in the offspring of parents with atrioventricular defects

Fifty-two of the 56 offspring from 90 patients with proven atrioventricular defects were examined. There were five with congenital heart disease. The defects were concordant in three and discordant in two. The mother was the affected propositus in all cases. In this relatively small sample the incidence of congenital heart disease in the offspring of parents with atrioventricular defects was 9.6%, or 14.3% if only the female propositi were considered. This is a much higher figure than that reported for the simple forms of isolated congenital heart disease.

Atrioventricular nodal dysfunction in patients with atrial septal defect. Abnormalities of conduction and reciprocal rhythms

Electrophysiologic studies were performed in 17 unselected patients (mean age, 20 years) with atrial septal defect (ASD) of the ostium secundum type. In nine (52.9 percent) signs were found of atrioventricular (A-V) nodal dysfunction, in seven (41.1 percent) prolonged A-H interval, and in three (17.6 percent) prolonged effective refractory period of A-V node and in five (29.4 percent) A-V nodal tachycardia and reentry. Three of the four cases showed anterograde conduction (Ae-H interval) faster than retrograde conduction (H-A3 interval) during the tachycardia. In one patient with reentry a similar phenomenon was observed. In the remaining patient the conduction time was reversed (Ae-H longer than H-Ae). In two patients infrahisian and intrahisian block (first and second degree) with persistence of the tachycardia was observed. Patent or latent abnormalities in A-V node function are a frequent finding in patients with ASD. In the sinus node, any kind of significant abnormality can be found.

Left axis deviation: a reassessment

This report deals with the ramifications of the concept of left axis deviation. In early life, the leftward shift of the frontal plane QRS axis is determined chiefly, if not solely, by the relative weights of the ventricles. Once adult ventricular weight ratios are reached, there is a long period of axis stability, then a gradual leftward drift of the QRS, governed principally by left anterior fascicular conduction. Thus, the normal QRS axis is age-dependent, and left axis deviation must be considered accordingly.

Congenitally bicuspid aortic valves. Clinicogenetic study of 41 families

The families of 41 patients with surgically proved isolated bicuspid aortic valves were examined. There were 275 first degree relatives of whom 220 were living, and 188 (85.5%) of these were examined. Seven first degree relatives were found to have aortic valve disease, and in a further 11 there was 'doubtful' evidence of bicuspid aortic valves. In 6 families there was more than 1 affected member and in an additional 7 families there was 1 or more 'doubtful' first degree relative. The minimum family incidence was therefore 14.6 per cent, or 31.7 per cent if 'doubtful' cases were included. The inheritance is most probably multifactorial, but occasionally the condition may occur as an autosomal dominant. The difficulties of diagnosing bicuspid aortic valves before the development of obstruction of left ventricular outflow were encountered and are discussed. The association of a bicuspid aortic valve with asymmetric septal hypertrophy, hypertrophic cardiomyopathy, and Marfan's syndrome was also noted.

Formes frustes of Marfan's syndrome presenting with severe aortic regurgitation. Clinicogenetic study of 18 families

Eighteen patients who presented with severe aortic regurgitation and dilatation of the ascending aorta were found to be formes frustes of Marfan's syndrome and formed the basis for this clinicogenetic study. All had aortic valve replacement and reconstruction of part of the ascending aorta. The diagnosis was confirmed by histological examination of the aortic tissue. There were 126 first degree relatives; 85 were living and 67 (78-8%) of these were examined. Limited information was available about 32 of the 41 relatives who had died. No relative had the classical clinical features of Marfan's syndrome but stigmata of the disease were found in 25 (37-3%) of the 67 first degree relatives examined. In 21, the abnormality was confined to the cardiovascular system, the skeleton, or the eye, but in 4, abnormalities involved 2 systems. Cardiovascular abnormalities affecting the aortic valve or aortic wall were present in 6 (9-0%) of the 67 first degree relatives examined. One or more of the skeletal indices measured (height-span difference, metacarpal index, phalangeal index) was abnormal in 18 (26-9%) and ocular abnormalities were found in 5 of 51 (9-8%) examined. There were no relatives with dislocation of the lens or iridodonesis. Using strict diagnostic criteria, a minimum of 37-3 per cent of the first degree relatives examined were affected; this involved 12 of the 18 families studied. There was nothing in our data to suggest that the formes frustes of the disease had a different mode of inheritance from the classical syndrome.