The continuing enigma of pyloric stenosis of infancy: a review.

Striking features of the descriptive epidemiology of pyloric stenosis of infancy have been identified but until recently have not suggested any useful etiologic lead. The disease first received serious attention approximately 100 years ago and has since occurred throughout the Western world at a rate between 2 and 5 per thousand live births; it appears to be uncommon elsewhere. Its age distribution is essentially limited to the period between the third and eighth weeks after birth. It is 4 to 5 times more common in boys than girls. It is less common in blacks than whites in the United States and less common among Asians than whites in the United States and elsewhere. Its incidence is highest in first-born infants. Evidence on a role for maternal age is not consistent. The disease re-occurs in families with sufficient frequency to incite the interest of geneticists, although no genetic model yet proposed offers a better basis for counseling than do the empiric observations on which it is based. Monozygous twins are concordant for the disease not much more frequently than are dizygous twins, and indeed not a great deal more often than nontwin siblings, which should prompt a search for environmental explanations of the disease's familial nature. Sharp declines in the incidence of the disease in Denmark and Sweden during the 1990s led to the hypothesis that infants sleeping in the prone position-a practice discouraged with some success by Scandinavian campaigns to reduce the frequency of sudden infant death syndrome (SIDS)-may also be at increased risk of pyloric stenosis. If supported, this hypothesis may offer the first-ever possibility of reducing the frequency of this disease, as well as SIDS. If the hypothesis is not supported, the recent declines in the disease in Denmark and Sweden add another facet to its enigmatic nature.