A SPORADIC CASE OF MALE-LIMITED PRECOCIOUS PUBERTY HAS THE SAME CONSTITUTIVELY ACTIVATING POINT MUTATION IN LUTEINIZING-HORMONE CHORIOGONADOTROPIN RECEPTOR GENE AS FAMILIAL CASES

Familial male-limited precocious puberty (FMPP) is an autosomal domina nt disorder characterized by marked elevation of serum testosterone de spite low levels of gonadotropin. Recently, a single point mutation in the LH/hCG receptor (LH/CGR) gene was found in FMPP families that con stitutively activates the LH/CGR, causing Leydig cell activation and p recocious puberty. Among the Japanese population, only four sporadic c ases of male-limited precocious puberty have been reported. In the cur rent study, we examined one of the four reported Japanese patients wit h sporadic male-limited precocious puberty and found the same mutation as that in the FMPP families. Genomic DNA was isolated, and the polym erase chain reaction (PCR) was performed to amplify a fragment of LH/ CGR DNA encoding amino acid residues that include transmembrane helixe s 5 and 6. Sequencing of the PCR products revealed a heterozygous aden osine-guanine transition at nucleotide 1733 in codon 578. The mutation encodes an aspartic acid(678)-glycine substitution in transmembrane h elix 6. The mutant LH/CGR, created by site-directed mutagenesis in vit ro, exhibited constitutively higher cAMP levels in transfected COS-7 c ells than the wild-type LH/CGR, as described previously; however, basa l inositol phosphate levels were not increased by transfection with co mplementary DNA for the mutant receptor. The concentration and affinit y of [I-125]hCG-binding sites were similar in cells transfected with t he mutant and wild-type LH/CGR complementary DNAs, indicating that the mutant did not alter the production of receptor or its ability to bin d human LH/CG. The sporadic occurrence of this case was confirmed by f urther studies. The mutation creates a recognition site for the restri ction endonuclease MspI. Restriction digestion was positive for the mu tant allele in the patient; however, the PCR products of his parents w ere not digested by MspI, indicating that the patient's mutant allele was not inherited from his parents. DNA analysis of the patient and th e parents, using microsatellite repeat markers, was compatible with bi ological paternity and maternity. We conclude that the aspartic acid(5 78)-->glycine mutation in the LH/CGR has arisen in the Japanese popula tion and is the cause of a sporadic case of male-limited precocious pu berty.