Inheritance of a large deletion within the human immunoglobulin heavy chain constant region gene complex and immunological implications.

A deletion of the immunoglobulin heavy chain (IgH) pseudo-gamma, gamma-2, gamma-4, epsilon, and alpha-2 constant region gene segments was found to segregate unchanged in three generations of a family. The IgG1 locus on the IgH allele carrying the deletion was expressed to the same extent as its normal counterpart. One individual who was heterozygous for the deletion had an IgG2 deficiency, whereas the four other heterozygous individuals had serum levels of IgG2 and IgG4 within the normal ranges. IgA2 levels were low or below the normal range in all heterozygous individuals. The data indicate that the expression of some Ig isotypes can be decreased by hemizygous deletions, possibly due to a lower probability for switching.