A NEW CONSTITUTIVELY ACTIVATING POINT MUTATION IN THE LUTEINIZING-HORMONE CHORIOGONADOTROPIN RECEPTOR GENE IN CASES OF MALE-LIMITED PRECOCIOUS PUBERTY

A single point mutation that encodes an aspartic acid (Asp(578)) to gl ycine substitution in the LH/CG receptor (LH/CGR) gene, D578G, was rec ently found in American patients with familial male-limited precocious puberty and in a Japanese patient with a sporadic form of the disorde r. Transfection of the mutant, compared to the wild-type, LH/CGR compl ementary DNA into COS-7 cells results in higher basal cAMP production, but a normal agonist-induced response; the mutation is, therefore, pr oposed to constitutively activate Leydig cells and elevate serum testo sterone, despite low levels of gonadotropin. In the current study we e xamined two additional Japanese patients with male-limited precocious puberty without a family history of the disease. We describe a heteroz ygous cytosine (C) to thymine (T) transition at nucleotide 1715 in bot h; the mutation encodes an alanine to valine substitution in codon 572 of transmembrane helix 6, A572V. Transfected into COS-7 cells, the A5 72V mutant exhibited the same constitutively high basal cAMP levels an d normal agonist-induced cAMP response as the D578G mutant. We conclud e that the constitutively higher cAMP levels caused by the A572V mutat ion led to Leydig cell activation and male-limited precocious puberty, as in the previously described D578G mutation. As the mother of one o f the two patients had the same heterozygous mutation, this patient re presents the first recognized case of inherited male-limited precociou s puberty in the Japanese population. The previously described D578G m utant did not increase basal or agonist-induced inositol phosphate pro duction in transfected COS-7 cells, or the number of LH/CGRs or their affinity for LH/CG. In contrast, transfection of the A572V mutation in COS-7 cells exhibited significantly higher inositol phosphate levels basally and at 10(-11) mol/L hCG, but significantly lower inositol pho sphate levels at 10(-7) mol/L hCG. These data suggest that the A572V m utation of the LH/CGR may have effects on the guanine nucleotide bindi ng protein which activates phospholipase C (G(q)) coupling and phospho lipase-C activation in addition to its effects on G(s) coupling and ac tivation of adenylyl cyclase. A572V-transfected cells also exhibited a higher affinity, despite an apparent decrease in the number of bindin g sites, for [I-125]hCG, compared to transfectants with the wild-type LH/CGR. We hypothesize that these differences between the A572V and D5 78G mutations reflect a greater impact of the A572V mutation on recept or conformation.