The TNP1 haplotype - GCG is associated with azoospermia

Transition nuclear proteins (TNP1 and TNP2) are the major nuclear proteins that replace somatic histones during spermatogenesis. TNPs are required for the maintenance of normal spermatogenesis. Moreover, spermatogenesis was found to be compromised in both Tnp1 and Tnp2 null mice. As no study is available on the role of these genes in Indian infertile men, we have sequenced the entire TNP1 and TNP2 genes in 320 infertile men and 280 control fertile men drawn from two states in India. We identified 18 variants, including 8 previously known and 10 novel. Of the 10 novel variants, 3 were found only in azoospermic men, of which 2 (g.-688A>T in TNP1 and g.1030G>A in TNP2) were predicted to affect the transcription factor binding sites and therefore can cause deregulation of gene expression. Haplotype association analysis showed a significant omnibus association (omnibus χ2 = 7.87, p = 0.0195) for the single nucleotide polymorphisms (SNPs) in the TNP1 gene with azoospermia. The frequency of the haplotype GCG (H3) was increased in azoospermic men (53.1%) compared with fertile men (43%; χ2 = 7.964, p = 0.005). However, similar analysis of the TNP2 gene did not show any association with infertility. Furthermore, expression analysis of the TNP1 gene in obstructive azoospermic men showed that haplotypes of the TNP1 gene do not affect its expression level. Our results suggest that the individual SNPs of the TNP1 and TNP2 genes are not associated with infertility; however, the haplotype GCG of the TNP1 gene is a risk factor for azoospermia.