Familial male-limited precocious puberty (
FMPP) is an autosomal dominant disorder characterized by marked elevation of serum
testosterone despite low levels of
gonadotropin. Recently, a single point mutation in the
LH/hCG receptor (LH/CGR) gene was found in
FMPP families that constitutively activates the LH/CGR, causing Leydig cell activation and
precocious puberty. Among the Japanese population, only four sporadic cases of
male-limited precocious puberty have been reported. In the current study, we examined one of the four reported Japanese patients with sporadic
male-limited precocious puberty and found the same mutation as that in the
FMPP families. Genomic
DNA was isolated, and the polymerase chain reaction (PCR) was performed to amplify a fragment of LH/CGR
DNA encoding
amino acid residues that include transmembrane helixes 5 and 6. Sequencing of the PCR products revealed a heterozygous
adenosine-
guanine transition at
nucleotide 1733 in
codon 578. The mutation encodes an aspartic acid578-glycine substitution in transmembrane helix 6. The mutant LH/CGR, created by site-directed mutagenesis in vitro, exhibited constitutively higher cAMP levels in transfected COS-7 cells than the wild-type LH/CGR, as described previously; however, basal
inositol phosphate levels were not increased by transfection with
complementary DNA for the mutant receptor. The concentration and affinity of [125I]hCG-binding sites were similar in cells transfected with the mutant and wild-type LH/CGR complementary DNAs, indicating that the mutant did not alter the production of receptor or its ability to bind human LH/CG. The sporadic occurrence of this case was confirmed by further studies. The mutation creates a recognition site for the
restriction endonuclease MspI. Restriction digestion was positive for the mutant not digested by MspI, indicating that the patient's mutant allele was not inherited from his parents.
DNA analysis of the patient and the parents, using microsatellite repeat markers, was compatible with
biological paternity and maternity. We conclude that the aspartic acid578-->
glycine mutation in the LH/CGR has arisen in the Japanese population and is the cause of a sporadic case of
male-limited precocious puberty.