Gm, Am and Km allotypes were investigated in two Tunisian populations (236 samples from Mahdia and 142 samples from Sfax). These populations descend from immigrants and, therefore, the results were compared with those obtained in other populations living in the Near East and in North Africa. The subclass heavy chain allotypes G1m, G2m, G3m and A2m are inherited in fixed combinations. There were five main and four minor Gm-Am haplotypes that could be deduced from the phenotypes. This led to the conclusion that the populations studied are Caucasoids with some African admixture (about 10%) and a very low oriental contribution. Furthermore, there were 11 samples which showed 8 uncommon Gm-Am phenotypes. These could be explained by the assumption of five different uncommon Gm-Am haplotypes. Four of these may have arisen by equal crossing over of prevalent haplotypes. The fifth may be the result of unequal crossing over of prevalent haplotypes. The fifth may be the result of unequal crossing over, since it was proven, by family study, that more markers are transmitted together than are present in the prevalent haplotypes.
The locus for human immunoglobulin heavy chain constant region genes (IgCH) is characterized by a significant frequency of deleted or duplicated haplotypes, due to unequal crossing-over events. Four types of deletions and one duplication have been reported so far. We describe here a molecular study of four cases of IgCH deletions. Two of the three types of deletions are reported here for the first time. Analysis of genetic markers associated with the deleted haplotypes pointed to the independent origin of similar deletions and the involvement of intergenic sequences in the mispairing-recombination process. The reduced or absent transcription of the C gamma 4 gene in two C gamma 2-deleted haplotypes offers an insight into the requirements for the isotype switch mechanism.
Immunoglobulin allotypes G1m, G2m, G3m, A2m and Km were determined in patients with a single head and neck cancer and in head and neck cancer patients with multiple primary tumours. Frequencies were compared with those of healthy controls. In all 39 patients with multiple primary tumours studied, Km(1) was absent vs. 82% and 75% absence in healthy controls and patients with a single head and neck cancer, respectively. This difference is highly significant. We conclude that head and neck cancer patients lacking the Km(1) are susceptible to the development of new cancers, and therefore should be screened thoroughly for more tumours.
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