Abstract
Serum levels of immunoglobulins (Ig) G, M, and A were determined in 28 women with an additional X-chromosome (XXX), and in equal numbers of age-matched normal women and men. Mean IgM levels were found to be highest in the XXX group, intermediate in normal women, and lowest in men; these differences were statistically significant. Mean IgM values obtained from seven XXY and three XXXY cases were almost identical with those of normal women and XXX women respectively. No such sex linkage was observed for IgA and IgG levels. These results support the suggestion that the serum level of IgM is related to the number of X chromosomes present.