A missense (T577I) mutation in the luteinizing hormone receptor gene associated with familial male-limited precocious puberty

Testotoxicosis without Testicular Mass: Revealed by Peripheral Precocious Puberty and Confirmed by Somatic LHCGR Gene Mutation

Purpose: Testotoxicosis is an autosomal dominant form of limited gonadotropin-independent precocious puberty in boys. It is caused by a heterozygous constitutively activating mutation of the LHCGR gene encoding the luteinizing/hormone receptor (LHR). Some twenty mutations of the LHCGR gene have been reported. Most of them are constitutive mutations isolated from blood leukocyte DNA, although others are somatic, found only in testicular tumoural tissue. In all the previously reported cases of these somatic mutations, the tumour, whether a nodular Leydig cell adenoma or hyperplasia, was easily visible on testicular ultrasonography. The aim of this study was to describe an unusual presentation of a patient with the clinical and hormonal characteristics of testotoxicosis but no well-circumscribed lesion at testicular ultrasonography.Materials and Methods: Molecular analysis of the LHCGR gene was performed by direct sequencing of DNA extracted from peripheral leucocytes and testicular biopsy.Results: Molecular analysis didn't find any LHR mutation in blood, whereas it revealed for the first time a somatic D578H mutation in testicular tissue despite no evidence of a nodular aspect at testis ultrasonography.Conclusions: This observation underlines the need to look for a somatic LHCGR gene mutation from the testicular biopsies of all boys with testotoxicosis with no constitutive LHCGR gene mutation identified from blood DNA, even in the absence of circumscribed testicular lesion at ultrasonography. In addition, based on the known link between LHR mutations and testicular tumourigenesis, yearly ultrasound monitoring of the testes should be considered for these patients.

Cosegregation of a novel mutation in the sixth transmembrane segment of the luteinizing/choriogonadotropin hormone receptor with two Brazilian siblings with severe testotoxicosis

PURPOSE

Testotoxicosis is an autosomal dominant form of gonadotropin-independent precocious puberty caused by heterozygous constitutively activating mutations of the luteinizing hormone/choriogonadotropin receptor (LHCGR) gene. The aim of this study was to describe two Brazilian siblings with testotoxicosis, to confirm the molecular diagnosis, and to perform an in silico analysis of a novel mutation in the hot spot of the LHCGR gene.

MATERIALS AND METHODS

Molecular analysis of the mutation on the LHCGR gene was performed by direct Sanger sequencing, followed by an in silico analysis using HOPE bioinformatics tool to predict a functional defect of the mutant.

RESULTS

Both patients presented with gonadotropin-independent precocious puberty before the age of four years. Genetic analysis revealed a novel non-maternally inherited p.Asp578Val mutation of the LHCGR gene. An in silico analysis showed that the p.Asp578Val mutation disturbed amino acid physicochemical features regarding its size, charge, and hydrophobicity value.

CONCLUSIONS

Clinical and hormonal profile of the siblings here evaluated was not different while compared to those patients previously described. An in silico mutation analysis reinforced the causative role of recurrent activating mutations in the intracellular loop and transmembrane helices of the LHCGR. The segregation of this mutation with the offsprings' phenotype indicated that it is causative.

Constitutive activity in gonadotropin receptors

Constitutively active mutants (CAMs) of gonadotropin receptors are, in general, rare conditions. Luteinizing hormone-choriogonadotropin receptor (LHCGR) CAMs provoke the dramatic phenotype of familial gonadotropin-independent isosexual male-limited precocious puberty, whereas in females, there is not yet any identified phenotype. Only one isolated follicle-stimulating hormone receptor (FSHR) CAM (Asp567Gly) has so far been detected in a single male patient, besides other FSHR weak CAMs linked to pregnancy-associated ovarian hyperstimulation syndrome or to impaired desensitization and internalization. Several animal models have been developed for studying enhanced gonadotropin action; in addition to unraveling valuable new information about the possible phenotypes of isolated FSHR and LHCGR CAMs in women, the information obtained from these mouse models has served multiple translational goals, including the development of new diagnostic and therapeutic targets as well as the prediction of phenotypes for mutations not yet identified in humans. Mutagenesis and computational studies have shed important information on the physiopathogenic mechanisms leading to constitutive activity of gonadotropin receptors; a common feature in these receptor CAMs is the release of stabilizing interhelical interactions between transmembrane domains (TMDs) 3 and 6 leading to an increase, with respect to the wild-type receptor, in the solvent accessibility at the cytosolic extension of TMDs 3, 5, and 6, which involves the highly conserved Glu/Asp-Arg-Tyr/Trp sequence. In this chapter, we summarize the structural features, functional consequences, and mechanisms that lead to constitutive activation of gonadotropin receptor CAMs and provide information on pharmacological approaches that might potentially modulate gonadotropin receptor CAM function.

Effectiveness of anastrozole and cyproterone acetate in two brothers with familial male precocious puberty

Testotoxicosis is a rare form of precocious puberty caused by a constitutively activating mutation in the luteinizing hormone receptor (LHR) gene. Symptoms include rapid virilization, accelerated growth and reduced adult height. We describe a rare association of testotoxicosis with a metaphyseal chondrodysplasia called cartilage-hair hypoplasia (CHH) and report two brothers with testotoxicosis after 4 years of treatment. The brothers had a T577I mutation in the LHR gene. One brother also presented CHH. The older brother was treated with ketoconazole, then with the aromatase inhibitor anastrozole and the anti-androgen cyproterone acetate. The younger brother received this combination as first-line therapy. Clinical improvements included reductions in growth velocity and bone maturation rate, which should result in taller adult stature. Tolerance was good.

CONCLUSION

Combined treatment with anastrozole and cyproterone acetate is effective in improving the prognosis of adult height in testotoxicosis.

Mutations in theDrosophilaglycoprotein hormone receptor,rickets, eliminate neuropeptide-induced tanning and selectively block a stereotyped behavioral program

Adult insects achieve their final form shortly after adult eclosion by the combined effects of specialized behaviors that generate increased blood pressure, which causes cuticular expansion, and hormones, which plasticize and then tan the cuticle. We examined the molecular mechanisms contributing to these processes in Drosophila by analyzing mutants for the rickets gene. These flies fail to initiate the behavioral and tanning processes that normally follow ecdysis. Sequencing of rickets mutants and STS mapping of deficiencies confirmed that rickets encodes the glycoprotein hormone receptor DLGR2. Although rickets mutants produce and release the insect-tanning hormone bursicon, they do not melanize when injected with extracts containing bursicon. In contrast, mutants do melanize in response to injection of an analog of cyclic AMP, the second messenger for bursicon. Hence, rickets appears to encode a component of the bursicon response pathway, probably the bursicon receptor itself. Mutants also have a behavioral deficit in that they fail to initiate the behavioral program for wing expansion. A set of decapitation experiments utilizing rickets mutants and flies that lack cells containing the neuropeptide eclosion hormone, reveals a multicomponent control to the activation of this behavioral program.

Mutations of gonadotropins and gonadotropin receptors: elucidating the physiology and pathophysiology of pituitary-gonadal function

The recent unraveling of structures of genes for the gonadotropin subunits and gonadotropin receptors has provided reproductive endocrinologists with new tools to study normal and pathological functions of the hypothalamic-pituitary-gonadal axis. Rare inactivating mutations that produce distinctive phenotypes of isolated LH or FSH deficiency have been discovered in gonadotropin subunit genes. In addition, there is a common polymorphism in the LHbeta subunit gene with possible clinical significance as a contributing factor to pathologies of LH-dependent gonadal functions. Both activating and inactivating mutations have been detected in the gonadotropin receptor genes, a larger number in the LH receptor gene, but so far only a few in the gene for the FSH receptor. These mutations corroborate and extend our knowledge of clinical consequences of gonadotropin resistance and inappropriate gonadotropin action. The information obtained from human mutations has been complemented by animal models with disrupted or inappropriately activated gonadotropin ligand or receptor genes. These clinical and experimental genetic disease models form a powerful tool for exploring the physiology and pathophysiology of gonadotropin function and provide an excellent example of the power of molecular biological approaches in the study of pathogenesis of diseases.

Constitutively active mutations of G protein-coupled receptors: the case of the human luteinizing hormone and follicle-stimulating hormone receptors

Activating mutations of the luteinizing hormone receptor (LHR) and the follicle-stimulating hormone receptor (FSHR) have been known for several years. These activating mutations permanently stimulate, in the absence of their cognate ligand, the receptor signaling pathways. In the case of the LHR, the induced chronic stimulation causes sporadic and familial pseudoprecocious puberty, a phenotype observed only in males. The absence of a female phenotype is probably due to the requirement for FSH in the induction of LHR expression. For the FSHR, one activating mutation was found in a patient with normal spermatogenesis without detectable gonadotropins. Whether activating mutations of the gonadotropin receptors are involved in tumor development is not yet clear. Activating mutations of the FSHR were supposedly involved but not found in ovarian tumors. For the LHR, only one patient with a seminoma and an activating mutation was described. The different occurrence of activating mutations of the LHR compared to the FSHR is surprising, since the two genes are adjacently located on chromosome 2 and should therefore be affected by a similar mutation rate. It might well be that mutations occur with the same frequency, but that activating mutations of the FSHR do not result in any particular phenotype.

A limited repertoire of mutations of the luteinizing hormone (LH) receptor gene in familial and sporadic patients with male LH-independent precocious puberty

Herein, we report mutation analysis of the LH receptor gene in 17 males with LH-independent precocious puberty, of which 8 were familial and 9 had a negative family history. A total of 7 different mutations (all previously reported) were detected in 12 patients. Among 10 European familial male-limited precocious puberty (FMPP) patients who had a LH receptor gene mutation, none had the Asp578Gly mutation, which is responsible for the vast majority of cases in the U.S. The restricted number of activating mutations of the LH receptor observed in this and other studies of FMPP strongly suggests that an activating phenotype is associated with very specific sites in the receptor protein. Clinical follow-up of the 5 patients who did not have LH receptor mutations shows that such cases most likely do not have true FMPP. LH receptor mutation analysis provides a sensitive tool for distinguishing true FMPP from other causes of early-onset LH-independent puberty in males.

Molecular genetic, biochemical, and clinical implications of gonadotropin receptor mutations

Human reproductive function is regulated mainly by luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Mutations of the human LH/ chorionic gonadotropin receptor (LHR) and the FSH receptor (FSHR) leading to either constitutive activation or inactivation of the receptors have been identified. All activating mutations of the LHR and the FSHR are located within the exon encoding the transmembrane domain while the inactivating mutations are scattered throughout the coding sequence. A number of activating and inactivating mutations of the LHR have been found while only one activating and three inactivating mutations of the FSHR are known. Activating mutations of the LHR cause familial male-limited precocious puberty (FMPP) while that of the FSHR has been shown to restore the reproductive capability of a hypophysectomized male. Inactivating mutations of the LHR cause Leydig cell hypoplasia (LCH) in males while that of the FSHR causes hereditary hypergonadotropic ovarian dysgenesis (ODG) in females. Activating mutations of both receptors are dominant while inactivating mutations are recessive. Genotype-phenotype correlation is best established for the inactivating mutations of LHR. Severity of clinical phenotype in LCH correlates with the amount of residual activity of the mutated LHR. Comparison of the clinical impact of the activating and the inactivating mutations of the receptors indicates that male reproductive capacity depends primarily on LH while female reproductive capacity depends primarily on FSH.

New aspects in the diagnosis and treatment of pubertal disorders

Recent developments in biochemistry, genetics, and clinical research have produced a profound effect on the understanding of normal and abnormal puberty. This article is intended to point out selected new developments that affect the understanding of puberty and clinical practice in disorders of puberty.