We propose that ACD/MPV results from haploinsufficiency of FOXF1 and that the differences in the associated malformations between groups 1 and 3 relate to haploinsufficiency for FOXC2 and FOXL1. Point mutations in FOXC2, probably leading to its haploinsufficiency, are responsible for lymphoedema-distichiasis syndrome;21,22 a small proportion of these patients also have congenital heart defects (6.8% in one series,21 including tetralogy of Fallot and ventricular septal defect but not hypoplastic left heart). The gene discussed is FOXF1; the disease is Tetralogy of Fallot.