It has been suggested by Cockayne,1 Sheldon2 and Penrose2a that the condition of pyloric stenosis has a genetic basis, and although four fifths of the examples occur in males the factor is probably not sex linked. Cockayne added that "the way in which the condition is inherited is still uncertain and an environmental factor may be necessary for its production in addition to the genetic one."
Sheldon collected records of the condition in 36 sets of twins. Although the analysis of the type of twinning is for the most part inadequate, the evidence indicates that in the case of uniovular twins both infants are affected (with 1, or possibly 2, exceptions), while in the case of binovular twins the condition is likely to occur in only 1 infant. Sheldon made the significant observation that in a population of 1,000 infants with pyloric stenosis the proportion of twins
FORD N, BROWN A, McCREARY JF. EVIDENCE OF MONOZYGOSITY AND DISTURBANCE OF GROWTH IN TWINS WITH PYLORIC STENOSIS. Am J Dis Child. 1941;61(1):41-53. doi:10.1001/archpedi.1941.02000070050004