Differences in recurrence risk by birth order of the first affected child provide evidence of genetic heterogeneity

Genetic heterogeneity has adverse implications for detecting linkage, determining mode of transmission, and estimating segregation ratios. This paper describes a new method for detecting genetic heterogeneity by mode of inheritance. The expected birth order of the first affected child within a sibship is related to segregation ratio "p." The probability of a first affected child having a given ordinal position decreases through the birth order …