ABSTRACT
Associated anomalies consisting mainly of urinary tract anomalies occur in one to 20 per cent. Association with Smith-Lemli-Opitz syndrome and various chromosomal disorders, including trisomy 18, trisomy 21 and Turner syndrome, is well documented. Association with asymptomatic joint hypermobility suggests a systemic abnormality of extracellular matrix. Familial occurrence is well described. With an affected mother, there is a 20 per cent risk for a son and a seven per cent risk for a daughter to develop pyloric stenosis. With an affected father, the respective risks are five and 2.5 per cent. The neuronal nitric oxide synthase (NOS1) gene has been described as a susceptible locus for pyloric stenosis.
