Likelihood-based models for genetic linkage analysis using affected sib pairs

Risch [Am J Hum Genet 1990;46:229-253] recently developed a likelihood method for testing genetic linkage using affected sib pairs. This paper proposes a reparameterization of the Risch likelihood in terms of genetic variance components divided by the affected-sib-pair ascertainment probability. The new parameters allow for ease of interpretation, particularly for multilocus models. A single-degree-of-freedom test of the total disease genetic effect at a marker locus can be constructed that has power comparable to the likelihood ratio 'triangle' test. Extension of the models to other types of relative pairs is also discussed. The models may be used in genome scanning and in studying single or multilocus models of inheritance.