Familial peripheral male-limited precocious puberty

Familial male-limited precocious puberty (FMPP), also known as testotoxicosis or familial peripheral male-limited precocious puberty, is a rare genetic disorder characterized by gonadotropin-independent precocious puberty occurring exclusively in males. The condition is caused by activating mutations in the LHCGR gene (luteinizing hormone/choriogonadotropin receptor gene) on chromosome 2p21, which leads to constitutive activation of the LH receptor in Leydig cells of the testes. This results in autonomous testosterone production independent of the hypothalamic-pituitary-gonadal axis. Affected boys typically present between ages 1 and 4 years with signs of early puberty including rapid growth, advanced bone age, penile enlargement, pubic hair development, acne, and increased muscle mass. Testicular enlargement may be present but is typically modest compared to central precocious puberty, as the seminiferous tubules are not stimulated. The endocrine system is primarily affected, with downstream effects on the skeletal system and reproductive organs. Without treatment, premature epiphyseal fusion leads to short adult stature despite initial rapid growth. Serum testosterone levels are elevated to pubertal or adult ranges, while gonadotropin (LH and FSH) levels remain prepubertal, distinguishing this condition from central (gonadotropin-dependent) precocious puberty. Females who carry the mutation are unaffected, as constitutive LH receptor activation does not produce a clinical phenotype in the absence of Leydig cells. Treatment strategies aim to reduce testosterone production or block its effects. Commonly used therapies include combinations of anti-androgens (such as spironolactone or bicalutamide) with aromatase inhibitors (such as anastrozole or letrozole) to slow bone maturation and preserve adult height potential. Ketoconazole, which inhibits steroidogenesis, has also been used. If secondary central precocious puberty develops due to prolonged sex steroid exposure advancing hypothalamic maturation, GnRH agonist therapy may be added. Early diagnosis and treatment are important to optimize growth outcomes and manage psychosocial effects of premature sexual development.

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