Causes of Hypogonadism
Testosterone deficiency (hypogonadism, low T) may be present at birth (congenital) or may develop later (acquired). Low T is classified by the location of its cause along the hypothalamic-pituitary-gonadal axis:
- Primary, disruption in the testicles
- Secondary, disruption in the pituitary
- Tertiary, disruption in the hypothalamus
The most common congenital cause is Klinefelter's syndrome. This condition, which is caused by an extra X chromosome, results in infertility, sparse facial and body hair, abnormal breast enlargement (gynecomastia), and small testes.
Congenital hormonal disorders such as leutenizing hormone-releasing hormone (LHRH) deficiency and gonadotropin-releasing hormone (GnRH) deficiency (e.g., Kallmann's syndrome) also may cause testosterone deficiency.
Other congenital causes include absence of the testes (anorchism; also may be acquired) and failure of the testicles to descend into the scrotum (cryptorchidism).
Acquired causes of testosterone deficiency include the following:
- Damage occurring during surgery involving the pituitary gland, hypothalamus, or testes
- Glandular malformation
- Head trauma that affects the hypothalamus
- Infection (e.g., meningitis, syphilis, mumps)
- Isolated LH deficiency (e.g., fertile eunuch syndrome)
- Radiation therapy
- Testicular trauma
- Tumors of the pituitary gland, hypothalamus, or testicles
Studies have shown that men who are overweight or obese and those with diabetes or hypertension (high blood pressure) may be twice as likely to have low testosterone levels.