Extensions to multivariate normal models for pedigree analysis

Abstract

mal models for pedigree analysis. II. Modeling the effect of shared environ-ment in the analysis of variation in blood lead levels. Am J Epidemiol 1983;117:344-55. A multivariate normal model for pedigree analysis is applied to blood lead measurements from 617 individuals in 80 families in Melbourne, Australia, studied in 1977-1978. A new method is introduced for estimating time depen-dence of the family covariance matrix for blood lead levels; this time depen-dence can be interpreted as arising from the effects of common family envi-ronment on blood lead levels. Methods for the testing of assumptions and detection of outlying pedigrees and outlying individuals are applied. No cor-relation between blood lead levels of spouses was observed, but an effect of shared family environment was suggested by the difference between an es-timated sibling correlation of about 0.5 for young sibling pairs living together and of about 0.1 for older siblings no longer living together. As there was no significant polygenic additive effect, the non-zero correlation between older siblings is more likely to be due to continuing effects of (environmental) fac-tors shared in youth, rather than to a polygenic dominant effect. It is estimated that smoking 20 cigarettes per day is associated with an increase of about 12 per cent in blood lead level. analysis of variance; lead; smoking; statistics A major aim of pedigree analysis is to the effect of common genes, and that apportion the covariation of a quantita- which might be "explained " by the effect tive trait within and between families of common environment. Pedigree analy-into that which might be "explained " by sis based on maximizing the likelihood of a multivariate normal model (1 — 3) chooses the most likely combination of ef-Received for publication February 24,1982, and in fects t h a t flt t h e observed familial pat