Recurrence of congenital heart defects among siblings-a nationwide study.

Congenital heart defects (CHD) constitute the largest group of congenital malformations. In most families, only one person has CHD; however, the risk of CHD increases for children born into families already affected. In this study, all births from 1994 through 2009 were identified in the Medical Birth Registry of Norway, including supplemental information on CHD from clinical and administrative registers, as part of the CVDNOR project. By using the unique personal identification number of each parent we were able to link 16,078 pairs of twins, 445,584 pairs of full siblings, and 106,840 pairs of half-siblings. Sibling recurrence risk ratio (RRR) was calculated using CHD status in the oldest sibling as exposure and CHD status in the younger sibling as outcome, adjusted for year of birth, maternal age, and maternal diabetes. Among full sibling pairs with CHD in the older sibling, the younger sibling had CHD in 4.1% compared to 1.1% of the pairs without CHD in the older sibling (adjusted RRR 3.6; 95% confidence interval (CI) 3.1-4.1). In same-sex twins the RRR was 14.0 (95% CI 10.6-18.6), and in opposite-sex twins the RRR was 11.9 (95% CI 7.1-19.9). For half-siblings the RRR was 1.5 (95% CI 0.8-2.8). When restricting to severe types of CHD, the RRR was 6.9 (95% CI 4.9-9.8) for full siblings. In 50% of the pairs with recurrent CHD, the siblings had similar types of CHD. The high relative risk of recurrence indicates that familial risk factors are important in the etiology of CHD.