Vitamin D receptor and interleukin-1 receptor antagonist gene polymor- phism in spinal tuberculosis

Our earlier studies revealed that both MHC (Major Histocompatibility Complex) and non-MHC genes are associated with the susceptibility to pulmonary tuberculosis (TB). To find out whether non-MHC genes such as vitamin D receptor (VDR) and interleukin-1 receptor antagonist (IL-1RA) genes are associated with the susceptibility to spinal TB (extrapulmonary form of TB), the present study was carried out in spinal TB patients (n = 66) and spouses of TB patients (spinal-TB and pulmonary-TB) (n = 80) (family contacts). A trend towards an increased per cent genotype frequency of IL-1RA genotype variant 22 (12.1%) was seen in spinal TB patients when compared to the controls (3.8%) (spouses of the patients) (P = 0.057; odds ratio 3.5). No difference was observed in the frequency of VDR genotypes between the overall spinal TB patients and the family contacts. However, the VDR mutant genotype tt was seen at a higher frequency in female patients with TB spine (TBS) (12.8%) than female contacts (4.2%) (P > 0.05 not significant; odds ratio 3.5). Among the contacts, a significantly increased frequency of wild type genotype TT (wild homozygotes) was seen in female contacts (55.1%) than male contacts (16.1%) (P = 0.0012). Similarly a significant decrease in tt genotype was seen in female contacts (4.1%) than male contacts (25.8%) (P = 0.012). The present study suggests that IL-1RA genotype 22 may be associated with the susceptibility to spinal TB. Moreover, vitamin D receptor tt genotype may be associated with the susceptibility to spinal TB in female patients. The study reveals that multicandidate genes may be associated with the susceptibility to spinal TB.