We present 14 familial cases from five Finnish families affected with a life-threatening congenital diaphragmatic defect (CDD) and review data on 53 previously published familial cases. CDD occurred in three sibs and their half brother's son, and probably in all four offspring of parents consanguineous as both first and second cousins. In the remaining three Finnish families and in the vast majority of the previously reported familial cases, only two sibs were affected. Two thirds of those affected were males both in the Finnish and the overall series.
Pedigree data, delayed fusion of the diaphragm as the primary pathogenetic mechanism, varying anatomical structure of the defective hemidiaphragm, association with other congenital anomalies, and data on animal experiments are more in accordance with multifactorial determination than with recessive inheritance. This does not exclude other genetic causes in some familial cases.
The recurrence risk for sibs after one affected sib is about 2%. As the prognosis, especially in familial cases of CDD has remained grave, the development of fetal surgical treatment is desirable. This emphasizes the future role of prenatal diagnosis by ultrasound.