Susceptibility to lung tuberculosis--a population-genetic study.

The aim of this study was to compare the genetic structure of lung tuberculosis (LTB) patients (Pts) to healthy controls i.e. to evaluate dependency of LTB occurrence and course of the disease in regard to subject's genetic constitution. The study group consisted of 100 LTB Pts, while the same number of healthy non-sibling individuals served as controls. The groups were analyzed with respect to homozygous recessive characteristics (HRC) that served as genetic markers, which were studied in each subject. Twenty-three HRCs were chosen according to HRC-test rules. The results show significant difference in average HRC number between two samples, a decreased number in Pts group, total cumulative chi2 difference (p<0.001) and frequency distribution (p = 0.0027). We conclude that the analyzed groups make two different samples in regard to their population-genetic structure. It means that they may give a different response to similar environmental agents. A significantly decreased HRC number in the Pts group may be a manifestation of their decreased degree of homozygosity and indicate a dominant factor inluence in predisposition to LTB. It is possible that individuals with such genetic and physiological constitution are more liable to infection/disease caused by M. tuberculosis. Deviation from optimal degree of homozygosity appoints to possibility of altered genetic-physiological organism homeostasis and its altered reaction norm that leads to illness. Particular phenotype distribution analysis of significantly decreased frequency of HRC and characteristic expression (eye and hair colour) suggest that there is a possibility of related gene alleles association with genetic basis for susceptibility to TB in humans.