Congenital dislocation of the hip joint in Norway V. Evaluation of genetic and environmental factors

The incidence of congenital dislocation of the hip joint (CDH) in Norway is high. Environmental factors and familial occurrence of CDH have been studied in 1147 probands with neonatal CDH and in 784 probands with late-diagnosis CDH. The proportion of affected sibs was 6 per cent in neonatal CDH and 8.5 per cent in late-diagnosis CDH. In 51 families, patients with neonatal CDH had sibs with late-diagnosis CDH, most of whom had been screened for CDH in the neonatal period. The distribution in families was computable with a polygenic mode of inheritance, and the heritability of CDH was calculated to be 74 per cent.
Breech presentation, the most important environmental factor, was observed in 15.7 per cent of the neonatal and in X.3 per cent of the late-diagnosis cases. A significant seasonal trend in month of birth was found in late-diagnosis CDH, with a maximum in early October. A higher percentage of birth rank one was found in CDH, but this was mostly due to an association between birth rank one and breech presentation. Probands with familial occurrence were significantly more often severely affected than those with no affected relatives. When several environmental factors were present in the history of a proband, the disorder tended to be more serious, and a familial occurrence of CDH was less likely. Concomitant anomalies were frequently found in CDH.