A related condition is follicle-stimulating hormone (FSH) insensitivity, which presents with similar symptoms to those of Leydig cell hypoplasia but with the symptoms in the respective sexes reversed (i.e., hypogonadism and sexual infantilism in females and merely problems with fertility in males). Despite their similar causes, FSH insensitivity is considerably less common in comparison to LH insensitivity.
A 46,XY (biologically male) woman with complete insensitivity to LH, resulting in fully feminized genitalia at birth. Puberty appears to have commenced, likely due to estrogen replacement therapy.
Leydig cell hypoplasia is caused by genetic mutations in LHCGR, a gene which encodes the LH/hCG receptor. LH normally acts through the LH/hCG receptor to stimulate the growth of Leydig cells in the testicles and the production of androgens such as testosterone and dihydrotestosterone (DHT) by these cells. In Leydig cell hypoplasia however, there is a reduced capacity for the LH/hCG receptor to respond to LH. This results in hypoplasia or absence of Leydig cells, testicular atrophy, and lower than normal androgen levels. In the most severe form of the condition in which there is a complete lack of response of the Leydig cells to LH, androgen production by the testicles is virtually negligible and secondary sexual characteristics entirely fail to develop at puberty.
Patients with Leydig cell hypoplasia may be treated with hormone replacement therapy (i.e., with androgens), which will result in normal sexual development and the resolution of most symptoms. In the case of 46,XY (biologically male) individuals who are phenotypically female and/or identify as the female gender, estrogens should be given instead. Surgical correction of the genitals in 46,XY males may be required, and, if necessary, an orchidopexy (relocation of the undescended testes to the scrotum) may be performed as well.