Genetics
Genetic factors can cause  pretesticular, testicular, and post-testicular azoospermia  (or oligospermia)  and include the following situations: The frequency of chromosomal abnormalities is inversely proportional to the semen count, thus males with azoospermia are at risk to have a 10–15% (other sources citing 15–20% incidence) abnormalities on karyotyping versus about <1 % in the fertile male population.Pretesticular azoospermia may be caused by congential hypopituitarism, Kallmann syndrome, Prader-Willi syndrome and other genetic conditions that lead to GnRH or gonadotropin deficiency. Testicular azoospermia is seen in Klinefelter syndrome (XXY) and the XX male syndrome. In addition, 13% of men with azoospermia have a defective spermatogenesis that is linked to defects of the Y chromosome. Such defects tend to be de novo micro-deletions and affect usually the long arm of the chromosome. A section of the long arm of the Y chromosome has been termed Azoospermia Factor (AZF) at Yq11 and subdivided into AZFa, AZFb,  AZFc and possibly more subsections. Defects in this area can lead to oligospermia or azoospermia, however, a tight genotype-phenotype correlation has not been achieved. Spermatogenesis is defective with gene defects for the androgen receptor.Post-testicular azoospermia can be seen with certain point mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene commonly associated with congenital vas deferens abnormalities.Genetic counselling is indicated for men with genetic causes of azoospermia. In terms of reproduction, it needs to be considered if the genetic defect could be transmitted to the offspring. BRD7
BRD7, a transcription regulatory protein, is normally highly expressed in the testis.
Absent or reduced expression of BRD7 protein was observed in the testes of azoospermia patients exhibiting spermatogenesis arrest. Homozygous knockout mice [BRD7(-/-)] are infertile and have higher levels of apoptosis and DNA damage in their germline cells. Gene polymorphisms
The human breast cancer susceptibility gene 2 (BRCA2) is employed in DNA repair. A common single nucleotide polymorphism in BRCA2 is associated with idiopathic male infertility with azoospermia.Four genes involved in DNA double-strand break repair and chromosome synapsis (TEX11, TEX15, MLH1 and MLH3) have key roles in genomic integrity, meiotic recombination and gametogenesis. Polymorphisms in these genes were tested for associations with male infertility. Single nucleotide polymorphisms in two of these genes (TEX11 and MLH3) were found to be associated with male infertility involving azoospermy or oligospermia. Diagnosis
Azoospermia is usually detected in the course of an infertility investigation. It is established on the basis of two semen analysis evaluations done at separate occasions (when the seminal specimen after centrifugation shows no sperm under the microscope) and requires a further work-up.The investigation includes a history, a physical examination including a thorough evaluation of the scrotum and testes, laboratory tests, and possibly imaging. History includes the general health, sexual health, past fertility, libido, and sexual activity. Past exposure to a number of agents needs to be queried including medical agents like hormone/steroid therapy, antibiotics, 5-ASA inhibitors (sulfasalazine), alpha-blockers, 5 alpha-reductase inhibitors, chemotherapeutic agents, pesticides, recreational drugs (marijuana, excessive alcohol), and heat exposure of the testes. A history of surgical procedures of the genital system needs to be elicited.