Reifenstein syndrome is an inherited disorder that causes underdevelopment of the male reproductive tract and sexual dysfunction in males, which includes an inability to make sperm, undescended testicles (the testicles do not descend into the scrotum), and development of breasts. See also testicular feminization.

Reifenstein syndrome is one of a group of diseases in which the body is unable to respond appropriately to the male sex hormones (androgens), which include testosterone.

In this genetic disease, the affected gene codes for the androgen receptor, which is the key protein that allows cells to respond to androgens. This particular mutation makes the cells less responsive to these hormones -- hence the alternative name, Partial Androgen Insensitivity Syndrome.

By default, human babies develop female genitalia. It is only when androgens are made by the testes of male fetuses that male sexual organs arise. As a result, boys with the most severe cases of Reifenstein syndrome may appear to be girls at birth even though they are genetically male, or they may have very small penises.

The disease is inherited in an x-linked recessive manner, which means that women are not affected but may carry the gene, and males who inherit the gene from their mothers will have the condition.