From a study of 320 individuals superoxide dismutase (SOD) variants are shown to be present in Iraq, and it is suggested that this genetic system may be useful for the study of historical population movement in the Middle East. The esterase D gene frequencies show no significant heterogeneity among the different regions of the country.

The effects of ABO compatibility mating, secretor, and haptoglobin subtypes on the levels of immunoglobulin have been determined in an Iraqi population. An interaction between the secretor and Lewis subtypes and levels of immunoglobulin was demonstrated. The IgG levels of the non-secretor group were lower than those of secretors. In contrast, haptoglobin subtypes displayed no significant effect on immunoglobulin levels. The interactions may indicate the indirect importance of these genetic markers in the evolution of resistance to infections.

The extent of the contribution of genetic and environmental factors to the variation in levels of serum immunoglobulin G, A, M and E was studied among families of Arabs and Kurds of Iraq. Heritability (h2) values were calculated from offspring-parent, offspring-mid-parent and sib-sib comparisons and were all positive and moderate. All values were significant for all four immunoglobulins, being generally lower in Arabs than in Kurds. The h2 estimate based on offspring-parent and offspring-mid-parent were generally lower than those based on sib-sib comparisons, suggesting that these values were inflated by the common environment of full sibs. Genetic correlations between IgG--IgE and IgG--IgA were relatively high, reflecting a common regulation in the level of these immunoglobulins. IgM showed low genetic correlation with other immunoglobulins. All environment correlations were positive, and rather higher in the Kurds than the Arabs, indicating that environmental factors influence the level of all four classes of immunoglobulins.

Heterogeneity of gene frequencies in the polymorphism of the third component of complement among local samples in Iraq is analysed. It appears to derive essentially from population and not from regional differences.