THE EPIDEMIOLOGY OF INFANTILE HYPERTROPHIC PYLORIC-STENOSIS

Infants with infantile hypertrophic pyloric stenosis (IHPS) born from 1983 to 1988 and recorded in the California Birth Defects Monitoring P rogram (CBDMP) database were compared with their birth cohort by demog raphic characteristics and selected associated birth defects. We ident ified 1963 cases of IHPS for a cumulative incidence of 1.9 per 1000 li vebirths. The cumulative incidence per 1000 livebirths was 2.4 in Whit e, 1.8 in Hispanic, 0.7 in Black, and 0.6 in Asian infants. Between we eks 3-12 after birth, 1871 (95%) IHPS cases were diagnosed. Premature infants were diagnosed with IHPS later than term or postterm infants. The incidence of IHPS declined for those born to maternal age groups o f greater than or equal to 25 years and, independently, for successive birth ranks. The probandwise concordance rate for IHPS in monozygous twins was less than unity (0.25-0.44), although higher than the concor dance for dizygous twins (0.05-0.10). The incidence of Smith-Lemli-Opi tz syndrome (SLO) diagnosed in infants with IHPS (3 of 1963) was 157-f old higher than the incidence of SLO diagnosed in the CBDMP population . IHPS occurs in all of the largest racial and ethnic groups in Califo rnia, most frequently in White and Hispanic infants. Pyloric stenosis presents only within a brief phase of development, which may be delaye d in premature infants. A predominant discordance of disease state in monozygous twins implies an aetiological role for undetermined environ mental factors. The association between SLO, caused by deficient chole sterol synthesis, and IHPS deserves additional study. Infants with sus pected SLO require close observation for the onset of IHPS.