The human X-chromosome and the levels of serum immunoglobulin M

The serum concentrations of immunoglobulins G, A and M were measured in a sample of 93 pairs of monozygotic twins, their spouses, and their offspring. The hypothesis that the human X-chromosome carries genes which control the levels of immunoglobulin M was tested with three different approaches. Our results indicate that environmental factors are primarily responsible for the observed variation in the levels of IgG and IgA. The variance of IgM seems to be mostly the result of X-linked gene effects, with women having higher IgM levels than men.