Summary
A pedigree-based maximum likelihood method developed by Lange et al. (12) was used
to study the contribution of a newly defined di-allelic polymorphism in histidine-rich
glycoprotein (HRG) to the plasma levels of HRG. In four families (n = 99) and 20 volunteers
we found a heritability of 70%, an age effect of 3% and an effect of individual environmental
factors of 27%. These results are remarkably similar to the results found in a previous
parent-twin study in which a heritability of 69% and an effect of random environment
of 31% was found. The overall genetic influence in the present study can be subdivided
into an effect of 59% by the HRG phenotype and 11% by residual genetic factors. The
influence of the HRG phenotype of 59% can entirely be explained by adding up the effect
of the two alleles that make up the phenotype. These results indicate a codominant
inheritance pattern of HRG levels in which the genetic influence can almost completely
be ascribed to the additive effect of the di-allelic HRG locus whereas only a small
part is due to other loci.
