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 pu berty was examined for the previously described Asp-578 --> Gly, Met-5 71 --> Ile, and Thr-577 --> Ile mutations in transmembrane helix 6 of the human luteinizing hormone receptor (hLHR). Twenty-eight families h ad the inherited form of the disorder, and of these, 24 were found to have the Asp-578 --> Gly mutation. Four additional mutations were foun d among the remaining four families with the inherited form and in fou r 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-56 4 in the third cytoplasmic loop, a G --> T transversion resulting in s ubstitution 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 tr ansfected with cDNAs for each of the mutant hLHRs, created by PCR-base d mutagenesis of the wild-type hLHR cDNA, exhibited increased levels o f basal cAMP production in the absence of agonist, indicating constitu tive activation of the mutant hLHRs. Three of the additional mutations had specific features: Ile-542 --> Leu and Cys-581 --> Arg appeared l igand-unresponsive, whereas Asp-578 --> Tyr appeared to correlate geno type with phenotype. We conclude that the region spanning nt 1624-1741 of exon 11 is a hotspot for heterogeneous point mutations that consti tutively activate the hLHR and cause male-limited precocious puberty.