Decreased prevalence of hypoplastic left heart syndrome in Malta.

Hypoplastic left heart syndrome (HLHS) is the most severe form of congenital heart disease (CHD), which until recently was considered to be fatal. However, surgical intervention is now possible using neonatal heart transplantation or three-stage palliative surgery (Norwood's staged operations). In Malta, during the period 1977-1994, there were four cases of classic HLHS, with an additional three cases of HLHS-like cases. The birth prevalence of classical HLHS was 0.04 per 1000 live births, whereas that of combined HLHS-like cases was 0.06 per 1000 live births for the same period. One neonate with HLHS is expected every 3 or 4 years. Despite a high rate of ascertainment of CHD, the birth prevalence of HLHS in Malta was significantly lower than that quoted in historical studies (p < 0.006) and in the European Congenital Anomalies and Twins Registry (p < 0.002). Malta has the expected birth prevalence of CHD, but the spectrum of CHD exhibits a predominance of lesions causing right ventricular outflow obstruction and a deficit of lesions causing left ventricular outflow tract obstruction. CHD is caused by a genetic-environmental interaction. The low rate of HLHS in Malta appears to be a true divergence from the usual observed spectrum of CHD and may be caused by genetic and/or environmental factors.