Lefranc et al. (1982) found that immunoglobulins were confined to IgM, IgD, IgG3, IgE and IgA2 in a healthy Tunisian person and in 2 Tunisian brothers apparently unrelated to the first case. The results of Southern hybridization suggested deletion of the gamma-1, gamma-2 and gamma-4 genes, a pseudoepsilon gene and the alpha-1 gene. The probable order of the groups of cosmid clones is 5-prime region A to region B 3-prime, as the deletion presumably starts downstream of gamma-3 (in region A) and ends upstream of the active epsilon gene. IgA2 allotypes determined serologically have their counterparts in restriction fragment length polymorphism.Kunkel et al. (1969) defined a system they called Am(2). The Am(2) and Gm systems, involving IgA and IgG, respectively, appear to be closely linked in man. Gamma A and gamma G markers are closely linked in the mouse also.