SUN-LB15 A Case of Familial Male-Limited Precocious Puberty With a Novel Mutation

Introduction: Familial Male-Limited Precocious Puberty (FMPP), also known as testotoxicosis, is a rare cause of precocious puberty in males. It is caused by a mutation in the luteinizing hormone/chorionic gonadotropin receptor (LHCGR) gene, resulting in the receptor to be constitutively activated. This results in precocious puberty in males with rapid skeletal maturation and compromised final adult height if not treated. A combination on anti-androgens and aromatase inhibitors are the mainstay of treatment. Case: A 16-month-old male presented to our clinic due to concerns of precocious puberty. Pubic hair was noted at 6 months of age along with rapid growth acceleration. There was no known exposure to testosterone and no family history of early puberty or subnormal adult height. Upon presentation, his height was over the 99(th) percentile while his target height is at the 50(th) percentile. Physical examination revealed prepubertal testes with pubic hair at Tanner stage II. A bone age was reported as 12-18 months at a chronologic age of 12 months. Initial lab evaluation revealed normal serum levels of 17 OHP, androstenedione and DHEA-S with a slightly elevated serum LH (0.7mIU/ml), and very elevated serum testosterone level (289ng/dl). Leuprolide and ACTH stimulation tests as well as MRI of the abdomen and pelvis were normal. Serum levels of AFP, β-hCG and IGF-1 were also normal. Bone age advanced to 6 years at a chronological age of 21 months and to 8 years by 26 months of age. At 26 months of age, his stretched penile length measured 11cm. LH receptor testing was obtained, which revealed a novel heterozygous missense mutation in the LHCGR gene (c.1733A>C; p.Asp.578Ala). The mutation was reported to be a variant of unknown significance though likely in the pathological end of the spectrum by variant analysis with SIFT and PolyPhen. He was started on treatment with anastrozole 1 mg daily and bicalutamide 25 mg daily at 2 and 9/12 years of age. Pubertal progression, linear growth and skeletal maturation slowed down with treatment. His bone age remained stable at 13 years from the age of 2 and 10/12 years to 4 years old. Pubertal stage and stretched penile length have also remained stable on treatment. He is tolerating treatment well. Conclusion: We report a novel mutation in the LHCGR gene causing FMPP in a 6-month-old male who is responding very well to a combination of bicalutamide and anastrazole with marked decrease in growth velocity, pubertal progression and skeletal advancement.