An inherited X-linked serum system in man; the Xm system.

The detection of an inherited X-linked serum system in man, disclosed by a heteroantisenim made specific by absorption, is described. These studies suggest that the antigen, demonstrated by the specific antiserum, resides in the alpha(2)-macroglobulin fraction of serum. The system has been named the Xm system, where X refers to the localization of the gene on the X chromosome, and the m indicates that the antigen is part of the alpha(2)-macroglobulin fraction. The distribution of phenotypes in unrelated individuals from 4 populations, as well as studies performed in families are consistent with an X-linked dominant mode of inheritance. One Xm(a-) daughter was found in a family where the father was Xm(a+). This finding is discussed with particular reference to the possible influence of sex and age on the development of the phenotype. This common X-linked marker is likely to prove useful in mapping the human X chromosome.