Associations of Y-chromosome subdeletion gr/gr with the prevalence of Y-chromosome haplogroups in infertile patients

Abstract

Microdeletions in azoospermia factor (AZF) region on distal Yq are associated with male infertility and spermatogenic failure due to intra-chromosomal homologous recombination between large nearly identical repeat amplicons and are found in ∼10% of azoospermic and severe oligozoospermic cases. Although AZFc is deleted in azoospermia or oligozoospermia, no definitive conclusion has been drawn for the role of partial AZFc deletions to spermatogenic failure. Therefore, this study is planned to investigate the role of gr/gr subdeletions in individuals with spermatogenic failure and to find its relationship with Y chromosome haplogroups (HGs) in infertile men from Indian population. It is a case-control study involving 236 azoospermic, 182 oligospermic and 240 healthy normozoospermic men. We found 18 gr/gr, 11 b1/b3 and 2 b2/b3 subdeletions in azoospermic patients and 12 gr/gr, 5 b1/b3 and 4 b2/b3 subdeletions in oligospermic patients. However, we also found seven gr/gr deletions in normozoospermic men. Seven patients each with spermatogenic arrest and oligospermia who carry gr/gr subdeletions have deleted DAZ3/DAZ4 genes. A total of 11 patients with sertoli cell-only syndrome (SCOS) and 5 oligospermic patients with gr/gr subdeletions also have DAZ1/DAZ2 genes deleted indicating that deletions of DAZ genes contributed differently to damage to spermatogenic process. L1 HG is found in patients showing b1/b3 subdeletions, whereas HG H1a2 and H1b were found in normozoospermic individuals with gr/gr subdeletions. Our results provide evidence of association between the occurrence of subdeletions and male infertility as well as the severity of the spermatogenic failure.

Figure 1

(a) The AZFc region of Y chromosome showing different subdeletions: gr/gr and b1/b3 subdeletions in infertile patients. Repeat sequences are shown with arrows along with the position of various STS markers used in this study. The central bar depicts the organization of the amplicons, including those labeled b1 through b4. It also shows more details about the location of different multicopy genes modified from Skaletsky et al., (b) b2/b3 subdeletion in infertile patients. Two pathways can lead to this type of deletion. Either gr/gr inversion (g1, r1, r2 recombining with r3, r4 and g3) followed by b2/b3 deletion via homologous recombination or b2/b3 inversion followed by rg/rg deletion via homologous recombination.

Figure 2

Examples of capillary electrophoretograms showing different gene dosages for the CDY1/CDY2 and DAZ/DAZL genes. The x-axis shows length of PCR products (base pairs), whereas y-axis shows fluorescent intensity (arbitrary units). The gene dosage of CDY1 and DAZ can be calculated by the comparison of peak area with CDY2 and DAZL, respectively, as the latter acts as internal standard with known number of copies. (a) The peak area of CDY1 is compared with that of CDY2 (corresponding to two copies). A CDY1/CDY2 pattern of 1:1 indicates two CDY1 copies (‘normal' CDY1 gene dosage according to the reference sequence; top left), 0.5:1 indicates one CDY1 copy (middle left) and 1.5:1 indicates three CDY1 copies (bottom left). (b) The peak area of DAZ is compared with that of DAZL (corresponding to two copies). DAZ/DAZL pattern of 2:1 indicates four DAZ copies (‘normal' DAZ gene dosage according to the reference sequence; top right), 1:1 indicates two DAZ copies (middle right) and 3:1 indicates six DAZ copies (bottom right).

Figure 3

The genealogical tree of human Y chromosome and branches in which gr/gr and b2/b4 deletions were observed in patients and controls. The designation for the branches is based on the Y Chromosome Consortium (2002), which later on is updated by Jobling and Taylor-Smith. ^*, Indicate that haplogroup may not be monophyletic; ^¶, indicate the haplogroup found in patients and controls with subdeletions, such as gr/gr, b1/b3 and b2/b3.