Causes of testosterone deficiency?

Testosterone deficiency results from the testes being unable to produce the normal levels of testosterone.
This deficiently can be physiological or pathological. Physiological deficiency occurs with age. As a man ages, the amount of testosterone in his body gradually declines. This natural decline starts after the age of 30 and continues throughout the life.
In healthy male population 20–40 years of age, the level of early morning testosterone should be 21.8 nmol/L (627 ng/dL).

Pathological deficiency is caused by some other condition and the most common causes are:

1.    Injury or infection of the testicles
2.    Chemotherapy or radiation treatment for cancer
3.    Genetic abnormalities such as Klinefelter's Syndrome
4.    Hemochromatosis caused by too much iron in the body
5.    Dysfunction of the pituitary gland (a gland in the brain that produces many important hormones)
6.    Inflammatory diseases such as sarcoidosis  
7.    Medications, especially hormones used to treat prostate cancer and corticosteroid drugs
8.    Chronic illness
9.    Chronic kidney failure
10.    Liver cirrhosis
11.    Stress
12.    Alcoholism

What Are the Symptoms of Testosterone Deficiency?

Testosterone deficiency has many effects on the body. The most common effects of the testosterone deficiency on man are:

• Decrease of sex drive
• Erectile dysfunction
• Feelings of depression
• Decreased sense of well-being
• Difficulties with concentrating

There are also several other changes that occur in the body such as:

• Decrease in muscle mass, with an increase in body fat
• Changes in cholesterol levels
• Decrease in hemoglobin and possibly mild anemia
• Fragile bones (osteoporosis)
• Decrease in body hair

Primary testicular failure is causing a condition called hyper-gonadotropic hypogonadism. In this condition testosterone levels are low and pituitary gonadotropic hormones are elevated.

In secondary or hypogonadotropic hypogonadism, there is a decreased secretion of pituitary gonadotropic hormones.

• Pre-pubertal hypogonadism is characterized by infantile genitalia and lack of virilization,
• Hypogonadism after puberty results in a diminished libido, erectile dysfunction, infertility, gynecomastia, impaired masculinization, changes in body composition, reductions in body and facial hair, and osteoporosis.