Objective To report the clinical characteristics of a familial male-limited precocious puberty (FMPP) child, and to analyze the mutation in luteinizing hormone/choriogonadotropin receptor (LHCGR) gene.

Methods The clinical data including sexuality and related laboratory examination results of a child aged 2 years and 5 months were collected. DNA was extracted from blood samples of the proband and his parents. The 11th exons of LHCGR gene were sequenced using a Genetic Analyzer.

Results The height of the child was 98 cm. Testicular volume was 3.5 mL bilaterally, penile size was 7 cm×2 cm, Tanner stage was PH2, basal testosterone level was 3.09 ng/mL, basal LH < 0.1 mU/mL, basal follicle-stimulating hormone (FSH) was 0.2 mU/mL, gonadotropin releasing hormone (GnRH) stimulation test revealed that the peak of LH was 0.88 mU/mL and the peak of FSH was 1.35 mU/mL. Upon sequencing exon 11 of the LHCGR, a heterozygous point mutation of nucleotide 1723 from A to C was detected, which resulted in an amino acid transition from Ile to Leu at position 575. The same point mutation was detected in the patient's mother, but did not have any influence on her puberty development.

Conclusions A novel point mutation of the LHCGR gene has been identified in a family affected with FMPP. The c.1723A>C mutant LHCGR was confirmed to be constitutively active, which has led to maturation and proliferation of Leydig cells. The mother had the same genotype but different phenotypes, which may be due to that the hormone estrogen and the follicular development need both LH and FSH to participate, and before puberty, female gonads do not express or low express LHCGR.