Human Pathological Conditions Determined by Any One of Several Genes

Abstract

IT is a striking fact that in many inherited human pathological conditions more than one type of inheritance is found. To quote only two examples, retinitis pigmentosa may be either dominant or recessive, and congenital stationary night blindness may be dominant, recessive, or sex-linked.¹ In a collection of human pedigrees of a condition showing dominant inheritance there is no possibility of determining whether a single dominant factor is involved in all cases, or whether the condition may be determined by any one of several dominant factors. This is also true of sex-linked inheritance, but in the case of a condition which behaves as a recessive, a test is available. The incidence of first-cousin marriages amongst the normal parents of affected offspring can be related to the incidence of the condition in the general population. The formula in use was proposed by Lenz² and Dahlberg.³