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In a hypercholesterolemic Lebanese family, an uncommon Gm haplotype carrying an unexpected C gamma 1 gene was inherited by only one of 10 siblings. A new recombination during the maternal or paternal meiosis could explain its formation. According to this hypothesis, our data would be informative for the linkage relationship between the gamma-cistrons and the alpha 2-cistron. The latter might be located near the N-terminal side of the gamma-cistron linkage group, and the sequence of genes would be alpha 2, gamma 4, gamma 3, and gamma 1. A mutation could also effect the change from G1m(17) (codons AAA and AAG) TO G1m(3) (codons AGA and AGG). Another alternative is to postulate a constitutive expression of a C gamma 1 structural gene which, normally, would not be expressed. The uncommon derepression could be the consequence of uncommon cellular response to environmental, pathological or metabolic perturbation of a regulatory mechanism.

Grubb and Laurell1, Harboe and Lundevall2 and Harboe3 have described the serum groups Gma, Gmx and Gmb with the help of some rheumatoid-arthritic sera which were able to agglutinate O Rh + red cells sensitized with an incomplete anti-D. Also with an anti-D rheumatoid-arthritic serum complex, Steinberg and Giles4 have discovered a new factor (Gm-like) only present in the Negro sera but absent in the Whites. Roparbz et al. 5 have demonstrated that some sera withdrawn from healthy donors could be used for the Gm groups typings; in fact, such sera sometimes possess a very pure anti-Gm specificity.

SINCE Grubb and Laurell discovered the Gm factor in 1956 (ref. 1), all those who have worked in this field have carried out the tests with sera from patients suffering from rheumatoid-arthritic diseases. Thus Harboe and Lundevall2 and then Harboe3 found and described the Gmx and Gmb factors in 1959. Also using a rheumatoid-arthritic serum, Steinberg4 was able to demonstrate in the sera of Negroes the presence of a Gm-like factor, a factor which is not found in the white population. In 1959, however, Grubb found an anti-Gm factor in the serum of a young girl who was suffering from hepatitis with plasma cells5.