Occurrence of cardiac malformations in relatives of children with transposition of the great arteries

Transposition of the great arteries (TGA) is the most common cyanotic cardiac malformation, representing 5-7% of all cardiac malformations. Previous estimates of the frequency of cardiac malformations in sibs of probands range from 0-1.7%. This study ascertained the frequency of congenital cardiac malformations in relatives of 271 probands with TGA, who were grouped according to the type of TGA present. These include dextro (d- TGA), levo (l-TGA), complex TGA, and asplenia with TGA. In the d-TGA cases there were 369 sibs, one of whom had a cardiac malformation (0.27%). There were 50 sibs in the 1-TGA group, with one sib having a cardiac malformation (2.00%). Cardiac malformations were found in 2 of 143 (1.40%) sibs of the complex TGA index cases, and 1 of 50 (2.00%) sibs in the asplenia with TGA group. The overall recurrence risk of cardiac malformations in sibs of TGA probands was 0.82%. Cardiac malformations in parents of probands were found in 0.29% of d-TGA, 0% of 1-TGA, 1.54% of complex TGA, and 0% of asplenia with TGA, giving an overall parental occurrence of 0.55%. This is the first study to provide information on the different types of TGA in evaluating sib occurrence. It provides necessary genetic counseling information for families of probands with TGA.