Uncommon Gm* haplotypes in the Tunisian population: further contribution to the genetics of the IgG immunoglobulins.

In this work, eight family studies were conducted to establish the suspected unusual Gm* haplotypes in 13 persons (among 418) showing uncommon Gm phenotypes. Usually, the Gm (21 and 28)--or Gm (g1 and g5)--allotypes are both present or absent. Exceptions to this rule were observed: on the one hand, only the Gm (28) allotype was present in 12 persons, and on the other hand, only the Gm (21) allotype was found in 1 person. Such events could be explained, in some cases, by equal crossovers or point mutations, and, more generally and very likely, by gene conversions. Other interesting results are also presented, as, on the one hand, silent genes homozygous at the C gamma 4 locus and, on the other hand, a homozygous multigene deletion encompassing the C alpha 1, psi gamma, C gamma 2 and C gamma 4 loci.