The inheritance of pyloric stenosis explained by a multifactorial threshold model with sex dimorphism for liability

The inheritance of pyloric stenosis is explained by a multifactorial threshold model with an underlying assumption that the liability for the disease is distributed in males and females showing a sex dimorphism. From the available data on familial occurrences of pyloric stenosis, it is shown, that an extra maternal effect is not required to explain the familial risk of pyloric stenosis, as opposed to the earlier literature. Explicit expressions for familial risks of a discontinuous trait exhibiting dimorphism of liability are presented, based on a model originally proposed by Rice et al [1981], which do not require the approximation of univariate normality of a conditional bivariate normal distribution.