Objectives Congenital heart defects (CHD) accompany patients all their life and are assumed to have an impact on mental health. Epigenetics and socio-economic aspects as well as family influences, however, are confounding factors, making the exact influence of CHD difficult to define. This study aims to specify the impact of CHD on mental health neutralizing genetic and environmental factors by investigating twin siblings.

Methods Out of the “Same Same, but different?” project the parents of 25 pairs of twin siblings (one with CHD (13 moderate/12 complex severity) and the other without, 30 girls (60%), 10.2±4.2 years) filled in the strength and difficulties questionnaire (SDQ) for mental health for both of their children. The SDQ consists of five dimensions and a total difficulties score for mental health. The CHD severity classification of Warnes et al. was used and statistical analyses were conducted using the software SPSS V.25.

Results In all 50 children, the total difficulties score showed 82% normal scores, 12% borderline and 6% abnormal. In the sub-dimensions, they showed scores of 68% normal, 18% borderline and 14% abnormal in the dimension of emotional symptoms, 78% normal, 12% borderline and 10% abnormal in conduct problems dimension, 80% normal, 2% borderline and 18% abnormal in hyperactivity, 76% normal, 6% borderline and 18% abnormal in peer relationship problems an in prosocial behaviour 90% normal, 4% borderline and 6% abnormal. For 27 (54%) children, parents reported conspicuous behaviour, which in 7 (14%) children led to clear family burdens, in 11 (22%) to slight family burdens, and in 9 (18%) to no burdens. The direct twin sibling comparison using the paired-sample t-test showed significant differences in total difficulties score (p=.008), in peer relationship problems (p=.018) and hyperactivity (p=.008). The other dimension showed no significant difference between the twins.

Conclusion Children with CHD suffer from mental health problems in a direct comparison with their twin siblings in terms of total difficulties score, peer relationship problems, and hyperactivity and the parents reported on family burdens that cannot be ignored. These results underline the importance of psychological guidance for the whole family.