Pi-Gm linkage: evidence for linkage in males but not in females and for an effect of the S allele of the Pi system.

Linkage between the Pi (alpha 1-antitrypsin) and Gm (immunoglobulin heavy chain) loci was studied in thirty-four families including forty-one informative parents and 142 children. In females, the results did not provide evidence for linkage (posterior probability of non-linkage 0.98). In contrast, in males, there was strong evidence for linkage (peak lod 3.9 at theta = 0.18, posterior probability of linkage 0.98). The two populations appeared to be significantly different (0.001 less than P less than 0.01) with respect to the heterogeneity criterion of Morton. In addition, the effect of the possession of the S allele (associated with significantly decreased serum alpha 1-antitrypsin levels) was studied in fifteen informative parents and fifty-three children of the same group. No evidence for or against linkage was found in females, but in males close linkage between Pi S and Gm was demonstrated (peak lod 7.7 at theta = 0.05, posterior probability of linkage 0.9999). These data indicate significant linkage between Pi and Gm in males but not females and close linkage between the Pi S and Gm markers in males.