Mother-to-Son Transmission of a Luteinizing Hormone Receptor ...

G Freund Publishing House Ltd., London

Journal of Pediatric Endocrinology & Metabolism, 22, 275-279 (2009)

Mother-to-Son Transmission of a Luteinizing Hormone Receptor Activating Mutation in a Prepubertal Child with Testotoxicosis Marumudi Eunice, Pascal Philibert1, Bindu Kulshreshtha, Fran9oise Audran1, Fran9oise Paris1, Charles Sultan1 and Ariachery C. Ammini Department of Endocrinology and Metabolism, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India and 'Service d' Hormonologie du developpement et de la reproduction, Hopital Lapeyronie, Montpellier, France ABSTRACT

INTRODUCTION

Aim: To identify the LHR gene mutation in a prepubertal child with testotoxicosis. Methods: Standard RIA procedure was used for estimating LH, FSH and testosterone levels. Molecular analysis was done by standard PCR using different sets of primers and reaction conditions specific for the LHR gene. Direct sequencing was done using the ABI Prism Dye terminator sequencing kit and the ABI 310 sequencing apparatus. Results: We found a heterozygous mutation of the LHR gene in exon 11 of the second transmembrane region, Met-*Thr at the 398 position (M398T). The same mutation was also found in the proband's mother. Conclusion: To our knowledge, this is the first molecular characterization of maternally inherited testotoxicosis in a 5% year-old boy from the Indian subcontinent.

Testotoxicosis is a condition characterized by male limited gonadotropin-independcnt sexual precocity. This disorder is caused by activating mutations in the luteinizing hormone (LH) receptor gene inherited in an autosomal dominant fashion. The human LII receptor (LHR) gene is a member of the G protein-coupled receptor family with seven transmembrane helices and 11 exons1'2. The majority of the mutations are found in transmembrane helix VI of the LHR gene3'8. Affected males present with sexual precocity by the age of 34 years. We describe here a 5'/2 year-old boy with testotoxicosis. Direct sequencing analysis revealed an activating mutation in the second transmembrane region of exon 11 of the LHR giving a methionine to threonine mutation at the amino acid 398 position.

KEY WORDS

The parents of the proband sought medical attention for the first time when he was 3 years old for sexual precocity and aggressive behavior. MRI of the brain revealed no abnormality. He was advised to take monthly injections of luprolide acetate 3.75 mg at the age of 4/2 years. He took this treatment for a period of 4 months. There was, however, no change in his behavior and he gained 5 cm height during this period. As there was no improvement, this treatment was stopped and the patient was referred to the endocrine services of this hospital at the age of 5 years (1 month after stopping LH releasing hormone [LHRH) treatment). Height records prior to the past 5 months were not available. Physical examination revealed a

maternal transmission, LHR gene mutation, testotoxicosis

Reprint address: Dr. A.C. Ammini, M.D., D.M. Department of Endocrinology and Metabolism All India Institute of Medical Sciences New Delhi-II0029, India e-mail: [email protected]

PATIENT REPORT

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muscular child, height 122 cm, with pubic hair Tanner stage 3, testicular volume 10 ml bilaterally and stretched phallic length of 8 cm. The proband's mother underwent menarche at the age of 16 years, and had had regular periods. She had three spontaneous pregnancies. The first child was stillborn, and an older brother was 8 years. The proband is the youngest child. Examination of the mother revealed a normal female phenotype with normal secondary sexual characters and no clinical evidence of hyperandrogenism. She was more anxious about the child than the father. Present height and body mass index were 161 cm and 27.2 kg/m2, respectively.

RESULTS

Hormonal analysis

Basal testosterone, LI I and FSH levels were 451.1 nmol/1, undetectable, and 0.3 IU/1, respectively. 17-Hydroxyprogesterone (2.36 nmol/1), betahuman chorionic gonadotropin (hCG) (Thr(ACG) substitution at the 398 position in the proband's mother. B. Electropherogram showing the heterozygous mutation Met (ATG)->Thr(ACG) substitution at the 398 position in the proband.

Children with testotoxicosis present with accelerated growth and precocious virilization of external genitalia. The testicular volumes described in this condition normally range from 3-6 ml . This is due to LHR-mediated Leydig cell hyperplasia. Higher volumes are unusual because of lack of trophic effect of FSH on tubular maturation. Early Leydig cell maturation and Leydig cell hyperplasia has been described in patients with testotoxicosis". Germ cells were seen in various stages,

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but they showed disorganization of maturation and spermatid abnormalities. The present proband was found to have a heterozygous M398T mutation in the eleventh exon of the LHR gene. This mutation was caused by a single base substitution of T to C nucleotide at the 1192 position. This mutation has been found in a familial male limited precocious puberty kindred and a patient from the UK, two kindreds from Germany, one from Sicily and a patient from Japan7'8'12. Bilateral testicular volume in the present case was found to be 10 ml, which is rare. One such case of testotoxicosis was described in Japan13. That case was also found to have the 'Same point mutation at the M398T position. This mutant receptor shows increased basal activity (3.6-fold compared with the wild-type LHR)14. The M398T mutant exhibits higher basal cAMP levels compared to other site directed mutants at the same position". Apart from cAMP activation, the M398T mutant can also activate other intracellular pathways (Gq coupling and phospholipase C activation). It is possible that a greater testicular volume is a consequence of the activation of multiple intracellular pathways and greater LHR mediated cell proliferation. The mutation M398T peculiarly exhibits incomplete penetrance; not all carriers of the mutation show sexual precocity9'15. These authors speculate that the incomplete penetrance may indicate interaction with a modifier gene that modulates the activating effect of the LHR. A nine generation pedigree study has shown that testotoxicosis is a male-limited, autosomal dominant trait, which is transmitted through affected males or carrier females to their sons16. In our study, we found the same mutation in the proband's mother, who had normal female phenotype, menstrual periods and fertility. Only menarche was slightly delayed. Possibly, FSH rather than LH has a greater role in female ovarian physiology. The sexually dimorphic phenotypic manifestations of LHR activation in transgenic mice have been well characterized17. Female transgenic models overexpressing the hCG receptor showed precocious puberty, menstrual irregularities and an altered ovarian sex steroid profile. Male transgenic mice, however, show less severe phenotypic mani-

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festations and had only lowered testicular volumes compared to wild-type mice. In contrast, human males develop precocious puberty and testicular tumors, whereas the carrier females are not affected18'19. The reasons for this species disparity in phenotypic manifestations are unclear. In conclusion, we found a heterozygous mutation in this boy with testotoxicosis in exon 11 with a substitution of methionine by threonine at the 398 position of the second transmembrane region of the LHR, which is outside the commonly occurring mutational hotspot region. His mother was found to have the same mutation in heterozygous form, with normal female phenotype and pituitary gonadal function. This is the first report of molecular genetic analysis of a boy with testotoxicosis from the Indian subcontinent. ACKNOWLEDGEMENT

We acknowledge the help of Dr V. Padmavathamma and E.P. Praveen for sample collection and DNA isolation.

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ACTIVATING LUR GENE MUTATION IN A BOY WITH TESTOTOXICOSIS

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