A genetic deficiency in testosterone production. Affects between 1 in 500 and 1 in 1000 men.
Injury to the testes
The testes are prone to injury because they hang outside the body and are not protected by bone or muscle. Damage to testes can cause reduced testosterone production.
The testes develop within the abdomen and descend into the scrotum shortly before birth. In some cases one or both of the testes may not descend at birth (this happens in about 1 in 4 boys born prematurely and 1 in 20 boys born at term). The condition usually corrects itself naturally within the first year of life but if not corrected in early childhood, the testes may not develop properly.
Sometimes a mumps infection will involve the testes as well as the saliva glands. If this happens during adolescence or adulthood, long-term damage may occur that affects testosterone production.
Cancer and cancer treatment
Cancer of the testes or pituitary tumours can lead to low testosterone. Chemotherapy or radiation therapy can also interfere with testosterone production.
Hormone system imbalance
Kallmann syndrome involves abnormal development of the hypothalamus and is a risk factor for low testosterone. Pituitary disorders can impair the release of hormones affecting normal testosterone production.
Chronic illnesses such as liver or kidney disease, diabetes, metabolic syndrome and rheumatoid arthritis may be risk factors for low testosterone.In some instances it is not clear whether the chronic illness is a cause or a consequence of low testosterone.
Men normally experience some decline in testosterone level as they age.
Haemochromatosis is a genetic disorder that causes the body to absorb too much iron from the diet. This iron can be deposited in various body organs including the hypothalamus, pituitary and testes. It is now recognized as a common disorder and 1 in 200 people in Northern Europe may be at risk of developing iron overload.