Gene deletions within the human immunoglobulin heavy chain constant region gene cluster.

Gene deletions due to unequal crossing-over events represent a not uncommon cause of immunoglobulin isotype deficiency. A variety of deleted haplotypes has been ascertained in the Italian population by means of screening for different Ig isotypes followed by Southern blot analysis of the deficient probands. The total frequency of gene deletions involving the gamma 2 and/or gamma 4 genes amounts to about 1/60; among these, a higher frequency was observed for multigene compared with single gene deletions. Carriers of multiple deficiencies due to gene deletions are able to activate compensation mechanisms, avoiding the usual pathological consequences of the deficiency.