GENETIC-HETEROGENEITY OF CONSTITUTIVELY ACTIVATING MUTATIONS OF THE HUMAN LUTEINIZING-HORMONE RECEPTOR IN FAMILIAL MALE-LIMITED PRECOCIOUS PUBERTY

Genomic DNA from 32 unrelated families with male-limited precocious puberty was examined for the previously described Asp-578 --> Gly, Met-571 --> Ile, and Thr-577 --> Ile mutations in transmembrane helix 6 of the human luteinizing hormone receptor (hLHR). Twenty-eight families had the inherited form of the disorder, and of these, 24 were found to have the Asp-578 --> Gly mutation. Four additional mutations were found among the remaining four families with the inherited form and in four sporadic cases of the disorder: an A --> C transversion resulting in substitution or leucine for Ile-542 in the fifth transmembrane helix, an A --> G transition resulting in substitution of glycine for Asp-564 in the third cytoplasmic loop, a G --> T transversion resulting in substitution of tyrosine for Asp-578 in the sixth transmembrane helix, and a T --> C transition resulting in substitution of arginine for Cys-581 in the sixth transmembrane helix. Human embryonic kidney cells transfected with cDNAs for each of the mutant hLHRs, created by PCR-based mutagenesis of the wild-type hLHR cDNA, exhibited increased levels of basal cAMP production in the absence of agonist, indicating constitutive activation of the mutant hLHRs. Three of the additional mutations had specific features: Ile-542 --> Leu and Cys-581 --> Arg appeared ligand-unresponsive, whereas Asp-578 --> Tyr appeared to correlate genotype with phenotype. We conclude that the region spanning nt 1624-1741 of exon 11 is a hotspot for heterogeneous point mutations that constitutively activate the hLHR and cause male-limited precocious puberty.