Men with this condition may exhibit azoospermia (no sperm production), oligozoospermia (small number of sperm production), or they may produce abnormally shaped sperm (teratozoospermia). This case of infertility occurs during the development of gametes in the male. Where a normal healthy male will have both an X and a Y chromosome, affected males have genetic deletions in the Y chromosome. These deletions affect protein production that is vital for spermatogenesis. Studies have shown that this is an inherited trait; if a male is fathered by a man who also exhibited Y chromosome deletions then this trait will be passed down. These individuals are thereby "Y-linked". Daughters are not affected and cannot be carriers due to their lack of a Y chromosome. Other
Age group 12–49 (Paternal age effect)
Aneuploidy, an abnormal number of chromosomes
Centriole
Neoplasm, e.g. seminoma
Idiopathic failure
Cryptorchidism
Trauma
Hydrocele, particularly hydrocele testis
Hypopituitarism in adults, and hypopituitarism untreated in children (resulting in growth hormone deficiency and proportionate dwarfism.) Mumps
Malaria
Testicular cancer
Defects in USP26 in some cases
Acrosomal defects affecting egg penetration
Idiopathic oligospermia – unexplained sperm deficiencies account for 30% of male infertility. Pre-testicular causes
Pre-testicular factors refer to conditions that impede adequate support of the testes and include situations of poor hormonal support and poor general health including:

Varicocele
Varicocele is a condition of swollen testicle veins.It is present in 15% of normal men and in about 40% of infertile men. It is present in up to 35% of cases of primary infertility and 69–81% of secondary infertility. Hypogonadotropic hypogonadism due to various causes
Obesity increases the risk of hypogonadotropic hypogonadism.
Scrotum ultrasonography may also detect testicular lesions suggestive of malignancy. A decreased testicular vascularization is characteristic of testicular torsion, whereas hyperemia is often observed in epididymo-orchitis or in some malignant conditions such as lymphoma and leukemia. Doppler ultrasonography useful in assessing venous reflux in case of a varicocele, when palpation is unreliable or in detecting recurrence or persistence after surgery, although the impact of its detection and surgical correction on sperm parameters and overall fertility is debated.Dilation of the head or tail of the epididymis is suggestive of obstruction or inflammation of the male reproductive tract. Such abnormalities are associated with abnormalities in sperm parameters, as are abnormalities in the texture of the epididymis. Scrotal and transrectal ultrasonography (TRUS) are useful in detecting uni- or bilateral congenital absence of the vas deferens (CBAVD), which may be associated with abnormalities or agenesis of the epididymis, seminal vesicles or kidneys, and indicate the need for testicular sperm extraction. TRUS plays a key role in assessing azoospermia caused by obstruction, and detecting distal CBAVD or anomalies related to obstruction of the ejaculatory duct, such as abnormalities within the duct itself, a median cyst of the prostate (indicating a need for cyst aspiration), or an impairment of the seminal vesicles to become enlarged or emptied. Prevention
Some strategies suggested or proposed for avoiding male infertility include the following:

Avoiding smoking as it damages sperm DNA
Avoiding heavy marijuana and alcohol use. Avoiding excessive heat to the testes.