Microdeletions of the Y chromosome are the second most frequent genetic cause of spermatogenetic failure in infertile men after the Klinefelter syndrome. Microdeletions occur in about one in 4000 men in the general population but its frequency is significantly increased among infertile men. The molecular diagnosis of Y-chromosomal microdeletions is recommended in the workup of male infertility in men with azoospermia or severe oligozoospermia. Azoospermic men have a higher incidence of microdeletions than oligozoospermic men. The following recurrent microdeletions in the azoospermia factors (AZF) of the Y chromosome are clinically relevant and are found in men with severe oligo-or azoospermia
– AZFa,
– AZFb (P5/proximal P1),
– AZFbc (P5/distal P1 or P4/distal P1)
– AZFc (b2/b4)

Deletions in these regions remove one or more of the candidate genes (DAZ, RBMY, SP9Y, and DBY) and cause severe testiculopathy leading to male infertility. The most frequent deletion type is the AZFc region deletion (~80%) followed by AZFa (0.5–4%), AZFb (1–5%) and AZFbc (1–3%) deletion. Deletions which are detected as AZFabc are most likely related to abnormal karyotype such as 46, XX male or iso(Y).

Detection of microdeletions is performed by polymerase chain reaction (PCR) amplification of selected regions of the Y chromosome. At least two STS loci in each AZF region should be analysed for molecular screening. However, in light of novel data on genotype–phenotype correlations, the extension analysis for the AZFa and AZFb deletions is now routinely recommended.