A NOVEL MUTATION OF THE HUMAN LUTEINIZING-HORMONE RECEPTOR IN 46XY AND 46XX SISTERS

We report a novel homozygous mutation of the LH receptor (LHR) gene in three siblings: two 46XY and one 46XX. The 46XY siblings presented wi th female external genitalia, primary amenorrhea, and lack of breast d evelopment. Hormonal evaluation revealed a markedly elevated LH level with a low testosterone level, which failed to increase after human CG stimulation. Enzymatic deficiencies of testosterone biosynthesis were eliminated as possible etiologies. Histologic analysis of the inguina l gonads in a 46XY sibling revealed no Leydig cells; Sertoli cells, sp ermatogonia, and primary spermatocytes were seen. The 46XX sibling had female external genitalia, normal breast development, and primary ame norrhea. Hormonal analyses showed markedly elevated LH levels and low plasma 17 beta-estradiol levels. Genetic analysis of the LHR revealed a homozygous missense mutation at exon 11 of the LHR gene. Guanine was replaced by adenine (GAA-->AAA), resulting in a substitution of lysin e for glutamic acid (glu) at amino acid position 354 of the receptor. This mutation is; located in the extracellular domain adjacent to the first transmembrane helix of the LHR. Glutamic acid at position 354 of the LHR has been highly conserved throughout evolution. Functional an alysis of the LHR mutation, using an in vitro mutagenesis-transfection assay, demonstrated complete loss of function, indicated by the lack. of cAMP production after human CG stimulation in transfected human em bryonic kidney 293 cells. Screening of family members demonstrated het erozygosity for the mutation, indicating autosomal recessive inheritan ce. Delineation of the specific genetic defect in this family confirms recent reports that a single mutation in the LHR gene causes male pse udahermaphraditism in 46XY subjects and primary amenorrhea in 46XX sub jects. More importantly, it also defines a new region of the LHR molec ule that is critical for biologic activity.