Lung cancer (LC) is the most frequent type of cancer in men [1]. Despite therapeutic possibilities, this devastating disease remains the leading cause of cancer death in the world with more than 1.2 mil­lion new cases diagnosed every year [2]. Its etiology has been mentioned as an example of ecogenetics in oncology with tobacco smoking as the major risk factor [3]. Lung cancer is an etiologically complex disease in which multiple genes are involved in the pathogenesis via different pathways [4,5]. Some of the major susceptibility loci which influence LC risk have been localized [5-10]. Such susceptibil­ity genes are of considerable scientific interest, but do not confer high enough risks to be clinically rel­evant [6].

Tuberculosis (TB), an infectious disease caused by Mycobacterium tuberculosis complex, was de­clared a global emergency in 1993 and is still a problem due to the increasing number of immune-deficient persons in the world and the development of multi-drug resistant TB [11,12]. It is estimated that one-third of the world population is infected with TB bacillus [11,12]. Often the antibodies pres­ent in the human organism are strong enough to prevent the establishment of the disease. Although a variety of studies have suggested that host genetic factors may be a key to determining susceptibility/ resistance to M. tuberculosis, those that have as­sessed variants of the natural resistance-associated macrophage protein 1 gene (NRAMP1) and their association with TB in humans have yielded con­flicting results [13-19]. It is likely that NRAMP1 polymorphisms may be associated with progression to severe forms of pulmonary TB rather than with susceptibility to M. tuberculosis infection [18,19]. Recent findings suggest that persons carrying the monocyte chemo-attractant protein-1 (MCP-1) gen­otype GG produce high concentrations of MCP-1, which inhibits production of IL-12p40 in response to M. tuberculosis and increases the likelihood that M. tuberculosis infection will progress to active pul­monary TB [20]. Thus, despite the known infectious cause, the etiology of TB remains complex, and several host genes have been shown to contribute to the development of clinical disease [19,21,22]. Our previous population-genetic research indicated a possible role for a dominant factor influence in TB [17]. Although the molecular basis of genetic predisposition to pulmonary TB in adults remains largely elusive, a genome-wide linkage study pro­vided direct molecular evidence that the genetic component involves at least one major locus with a dominant susceptibility allele [21]. Genes which are involved in susceptibility to TB include: 12q14, 2q35, 15q11-q13 (OMIM numbers 607948, 607949, 300259), and 8q12-q13 [23].

In population-genetic investigations, a great number of morpho-physiological characters serve as genetic markers. Individual variation is a phenome­non, which can easily be noticed when we carefully observe the same species of organisms. Thus, hu­man populations vary in regard to face shape, skin pigmentation, height, hair color, blood types as well as functions and abilities. Some of these characters are expressed in a recessive or dominant type and are called qualitative traits [24]. Thus, blue eyes are a recessive trait, brown eyes are a dominant one, and inability to recognize the bitter taste of phenyl-thio-carbamide (PTC), left-handedness and fixed ear lobe are recessive traits. We applied this method to estimate the proportion of a variety of homozygous-recessive characters (HRCs) tests in two groups of patients with respiratory diseases and in a healthy control group.

We hypothesized that there is a difference in the population-genetic structure of LC patients, patients who develop active pulmonary TB and healthy controls. Our aims were a) to analyze and compare the population-genetic structure of these three groups using a number of qualitative morpho-physiological traits; b) to evaluate the degree of ge­netic homozygosity in these three groups according to the frequency of homozygous-recessive traits; c) to investigate the frequency of independent genetic determinants such as the ABO blood type in these three groups.