Editor—Congenital diaphragmatic hernia (CDH) is seen in 1/2000 to 1/5000 fetuses and liveborn infants.1 2Around 60% of fetuses diagnosed by antenatal ultrasound scanning at 20 weeks' gestation die in utero and the mortality rate in those surviving to term remains 30-50%. Coexistent major structural malformations are seen in a large proportion of cases, the commonest in liveborn infants being cardiac anomalies and neural tube defects.3

The genetic contribution to the aetiology of CDH is poorly understood. Although no large scale, population based, offspring recurrence study exists, familial clustering of CDH has been attributed to polygenic inheritance, which predicts an offspring recurrence risk of 1-2%. Familial congenital diaphragmatic hernia is, however, well described with autosomal dominant inheritance in most reported families, although no linkage studies have been performed. Candidate genes may therefore be localised by studying the large proportion of patients with CDH and an underlying chromosome abnormality. Autosomal trisomies, typically of chromosomes 13, 18, and 21, account for many of these cases. More complex structural rearrangements have also been reported in some series, although many of these cases have additional organ malformations.4-6 However, a number of de novo structural anomalies associated with CDH have been documented, defining candidate loci for future study; these are summarised in table1.