P–577 Impaired double strand DNA repair in isolated Primary Ovarian Insufficiency with homozygous nonsense mutation of SPIDR

Study question

To identify the etiology of isolated Primary Ovarian Insufficiency (POI) in a patient from an Indian consanguineous family.

Summary answer

A homozygous nonsense mutation of SPIDR in the patient yielded chromosomal instability: first evidence of a role of this gene in DNA repair.

What is known already

POI, affecting 1% of women under 40, is a public health problem. To date ∼ 70% of cases remain idiopathic. The leap due to exome sequencing, led to the identification of ∼ 80 genes, often in single or few cases. SPIDR was recently identified as a scaffolding protein connecting RAD51, a central player in homologous recombination, to BLM, a helicase implicated in the integrity of the genome. But its precise role is still unknown. A SPIDR mutation was previously associated with POI. However, contradictory conclusions were reported on the mechanism of SPIDR action and on its pathogenic role in POI.

Study design, size, duration

Prospective genetic study of a cohort of 150 pateints with POI worldwide using a custom-made targeted next generation sequencing (NGS) panel comprising 60 known POI-causing genes. A single patient was found mutated in SPIDR. Cytogenetic studies were performed to analyse the consequences of the mutation on DNA repair and sister chromatide exchanges (SCE).

Participants/materials, setting, methods

The patient with SPIDR mutation had POI with primary amenorrhea, delayed puberty and streaks ovaries. She was born to consanguineous Indian parents. No other mutation was detected in our cohort of 150 patients with POI. Targeted NGS was performed in the proposita. Familial segregation was performed by Sanger sequencing. Mitomycin C (MMC)-induced chromosomal breakages were studied and a sister chromatid exchange (SCE) assay was performed in patient’s peripheral lymphocytes.

Main results and the role of chance

We identified a novel homozygous nonsense mutation in the exon 7 of SPIDR (KIAA0146) c.814C>T, R272*, predicted to yield either a truncated protein, or a non-sense-mediated mRNA decay. The patient’s cells display increased chromosomal fragility with high MMC-induced chromosomal breaks when compared to a control. Remarkably, there was no increased SCE. In the previous report of a SPIDR mutation in POI, no cytogenetic studies were performed, and contradictory results were obtained on a homologous recombination test between the two sisters, either enhanced or reduced. In conclusion, we show here that inactivation of SPIDR results in a defect of double strand DNA damage repair, similar to alteration of the RAD51 pathway. There was no increased SCE, the hallmark of the BLM pathway. This observation has major consequences for this patient’s care : indeed mutations of DNA-repair genes may also yield to tumors/cancers. A long follow-up of the patient is needed in a multidisciplinary team to detect possible comorbidities. Indeed, even in the absence of somatic symptomatology, the patient has enhanced chromosomal instability highlighted by cytogenetic studies, that may yield tumor-predisposition.

Limitations, reasons for caution

No other mutation of SPIDR in the replication cohort of 150 POI patients. SPIDR mutation are thus very rare world-wide.

Wider implications of the findings: This is the first evidence of chromosomal instability associated with SPIDR defect, providing strong evidence for a role of SPIDR in double strand DNA damage repair in humans and for its causal role in POI. Our study improves the knowledge on SPIDR function and confirms its involvement in POI worldwide.

Trial registration number

Not applicable

Array comparative genomic hybridization analysis of small supernumerary marker chromosomes in human infertility

Small supernumerary marker chromosomes (sSMC) are structurally abnormal chromosomes that cannot be unambiguously identified by conventional banding cytogenetics. This study describes four patients with sSMC in relation with infertility. Patient 1 had primary infertility. His brother, fertile, carried the same sSMC (patient 2). Patient 3 presented polycystic ovary syndrome and patient 4 primary ovarian insufficiency. Cytogenetic studies, array comparative genomic hybridization (CGH) and sperm analyses were compared with cases previously reported. sSMC corresponded to the 15q11.2 region (patients 1 and 2), the centromeric chromosome 15 region (patient 3) and the 21p11.2 region (patient 4). Array CGH showed 3.6-Mb gain for patients 1 and 2 and 0.266-Mb gain for patient 4. Sperm fluorescent in-situ hybridization analyses found ratios of 0.37 and 0.30 of sperm nuclei with sSMC(15) for patients 1 and 2, respectively (P < 0.001). An increase of sperm nuclei with disomy X, Y and 18 was noted for patient 1 compared with control and patient 2 (P < 0.001). Among the genes mapped in the unbalanced chromosomal regions, POTE B and BAGE are related to the testis and ovary, respectively. The implication of sSMC in infertility could be due to duplication, but also to mechanical effects perturbing meiosis.

Discordant expression of familial amyloid polyneuropathy in monozygotic Brazilian twins

Discordant expression of Familial Amyloid Neuropathy (FAP) in monozygotic twins is a rare event. Only five such cases have been described in the literature so far. We report the clinical, neurophysiologic and autonomic findings of Brazilian monozygotic twins discordant for the expression of FAP type I. Twin I first presented symptoms at the age of 21, when his brother was completely asymptomatic. Twin 2 only presented symptoms at the age of 25, almost four years after his brother. Both brothers eventually developed the complete phenotype of FAP type I. The occurrence of monozygotic twins discordant for the expression of FAP type I suggests that other factors beside TTR gene mutations should play an important role in the pathogenesis of this condition. Environmental factors, as well as modifier genetic loci are likely to modulate the expression of FAP type I and the study of cases such as the one presented here may help to identify some of these factors.

On the origin of the transthyretin Val30Met familial amyloid polyneuropathy

Transthyretin (TTR) familial amyloid polyneuropathy is a severe autosomal dominant neuropathy of adulthood, frequently linked to the pathogenic Val30Met variant of the TTR gene. The condition was initially described in northern Portugal, which is the first focus of the disease. Other important clusters of families are found in Sweden, Japan and South America. The origin of the Val30Met mutation and its distribution through the populations remains unclear. In the present work, we aimed at refining the history of the Val30Met mutation in patients affected with TTR amyloid neuropathy from Portugal, Sweden and Brazil. The decay of haplotype sharing was studied in 60 patients to estimate the age of the Most Recent Common Ancestor (MRCA) of mutation carriers in these populations. Our results showed a common haplotype in Portuguese and Brazilian patients and an age estimate of the MRCA of 750 and 650 years, respectively. In contrast, a different haplotype was found in the Swedish Val30Met patients with a corresponding age estimate for the MRCA, of 375 years. This work strengthens the hypothesis of different founders in Portuguese and Swedish Val30Met carriers and suggested a Portuguese origin of the Brazilian mutation. The age estimates of the MRCA are in line with the current historical knowledge of these populations.

Evaluation of different markers of the ovarian reserve in patients presenting with premature ovarian failure

Premature ovarian failure (POF) is a heterogeneous syndrome, possibly due to mutations of genes involved in the normal development of the ovary and/or the follicles. Based essentially on animal models, these mutations are associated with various ovarian histological phenotypes, from a complete absence of to a partial follicular maturation. The aims of our work were in one hand to determine if ovarian histology, compared to pelvic ultrasonography, would be helpful either in identifying which patients display an impaired follicular growth or in the orientation of the POF etiology; on the other hand, since developing follicles up to the antral stage are reported in POF and that Anti-Müllerian hormone (AMH) might be a good indicator of follicular presence, we decided to determine whether AMH should be a better marker to determine the presence of an ovarian reserve in POF patients. To try to answer to the first question, we studied first 166 patients suffering from POF with a normal karyotype. Vaginal ultrasonography (US) was performed in 134 patients and an ovarian biopsy was obtained in 67 women. The presence of follicles suggested at US was confirmed at histology in only 56% of the patients. Ovarian histology led to the distinction of two phenotypes (a) small-sized ovaries, deprived of follicles, and (b) normal-sized ovaries with partial follicular maturation. To confirm the value of ovarian biopsies, samples from 20 normal women have been studied, confirming that ovarian biopsy at random allow reliable assessment of follicular activity. To try to answer to the second question of our work, a cross sectional study analyzing serum AMH, ovarian histology and AMH immunoexpression in 48 POF patients, was performed. Serum AMH was significantly higher in women with more than 5 follicles at ovarian histology. Ovarian AMH immunostaining revealed a normal AMH expression in POF preantral follicles but a decrease expression at the early antral stages. In conclusion, ovarian histology appears to be a reliable tool to appreciate the follicular reserve, and helpful and complementary to clinical and hormonal phenotyping in order to orient the search for various genetic causes of POF syndrome. Finally, AMH levels in POF patients could identify women with persistent follicles.

Molecular pathology of the FSH receptor: new insights into FSH physiology

Manipulations of mouse genome have helped to elucidate gonadotrophin function but important differences subsist between rodent and human reproduction. Studies of patients with mutations of gonadotrophins or gonadotrophin receptors genes allow understanding their physiological effects in humans. The correlation of the clinical phenotypes of patients with in vitro studies of the mutated receptor residual function and histological and immunohistological studies of the ovarian biopsies permits to understand which stages of follicular development are under FSH control. Total FSH receptor (FSHR) inactivation causes infertility with an early block of follicular maturation remarkably associated with abundant small follicles as in prepubertal ovaries and demonstrates the absolute requirement of FSH for follicular development starting from the primary stage. Partial FSHR inactivation, characterized by normal-sized ovaries, can sustain follicular development up to the early antral stages but incremental levels of FSH stimulation seem to be required for antral follicular growth before selection. These findings contrast with the traditional view of an initial gonadotrophin-independent follicular growth prior to the preantral-early antral stages. The presence of numerous reserve follicles in the ovaries of these patients may permit a future treatment of their infertility. The study of reduced FSHbeta or FSHR activity in genetically modified male mice models and in men suggests a minor impact of the FSHR on masculine fertility. Further studies on patients with a demonstrated total FSHbeta or FSHR inactivation are required to elucidate reported differences in spermatogenesis impairment. Finally, the studies of mutations of gonadotrophins and their receptors demonstrate differences in gonadotrophin function between genetically modified rodents and humans which suggest prudence in extrapolating observations in rodents to human reproduction. Ovarian hyperstimulation syndrome (OHSS) can infrequently arise spontaneously during pregnancy, but most often it is an iatrogenic complication of ovarian stimulation treatments with ovulation drugs for in vitro fertilization. The first genetic cause of familial recurrent spontaneous OHSS was identified as a broadening specificity of the FSHR for hCG due to naturally occurring heterozygous mutations located unexpectedly in the transmembrane domain of the FSHR. Broadening specificity of a G protein-coupled receptor is extremely rare. These observations led to the identification of the etiology of this previously unexplained syndrome and permitted to conceive novel models of FSHR activation. Susceptibility to iatrogenic OHSS or its clinical severity may be associated with FSHR polymorphisms with slightly different activities in vivo as suggested by several studies. The study of larger cohorts is needed to evaluate the clinical impact of these observations in the management of patients undergoing IVF protocols.

Ultrastructural nuclear defects and increased chromosome aneuploidies in spermatozoa with elongated heads

BACKGROUND

Cellular and molecular mechanisms leading to elongated sperm heads are not known. We have analysed the nuclear status of spermatozoa with elongated heads.

METHODS

Fourteen men with at least 30% of spermatozoa with an elongated nucleus were studied and compared with five fertile men as controls. Sperm morphology was analysed by a quantitative ultrastructural analysis. Sperm chromosomal content was assessed by three-colour fluorescence in-situ hybridization (chromosomes X, Y, 18). Y chromosome microdeletion and karyotype were analysed.

RESULTS

Elongated sperm head rates of the patients were 46.9% (30-75 versus 0-2% in the control group) by light microscopy and 34.4% by electron microscopy. In all patients, the chromatin was poorly condensed in elongated sperm heads (50% of elongated nuclei). No anomalies of sperm biochemical markers were found. All the men showed normal karyotype (46,XY) and absence of Y chromosome microdeletion. Aneuploidy rates of gonosomes and chromosome 18 were significantly increased in patients (1.64- and 3.6-fold, P = 0.006 and 0.026, respectively).

CONCLUSIONS

This study demonstrates that impaired chromatin compaction and slightly increased chromosome aneuploidies are found in spermatozoa with an elongated head, suggesting possible mechanisms such as meiotic non-disjunctions or spermiogenesis anomalies.

Serum anti-Müllerian hormone expression in women with premature ovarian failure

BACKGROUND

Premature ovarian failure (POF) is generally irreversible. However, developing follicles up to the antral stage are reported in POF and anti-Müllerian hormone (AMH) might be a good indicator of follicular presence. This study analysed serum AMH, ovarian histology and AMH immunoexpression in POF patients.

METHODS

A cross-sectional study of 48 POF patients in an Endocrinology Department setting. Patients had an ovarian biopsy simultaneously with serum AMH sampling and/or ovarian AMH immunostaining.

RESULTS

Mean serum AMH was 1.04 +/- 1.66 ng/ml. Serum AMH was significantly higher in women with 15 or more follicles at ovarian histology (P = 0.001). Comparison of ovarian AMH immunostaining from POF patients and 10 normal controls revealed a normal AMH expression in POF pre-antral follicles, but a decreased expression at the early antral stages. Serum AMH was undetectable in 77% of the patients with 0-5 AMH immunopositive follicles and detectable in 100% of the patients with more than 15 AMH immunopositive follicles.

CONCLUSIONS

AMH levels in POF patients could identify women with persistent follicles. The decrease of AMH immunoexpression in POF antral follicles could suggest a defect of antral development.

[Wilson disease: clinical and biological aspects]

Wilson disease is an autosomal recessive disorder of copper excess. This illness results from mutations of the ATP7B gene (chromosome 13, MIM# 277900). The discovery of the gene allowed a better understanding of cytosolic copper trafficking and its relationship with ceruloplasmin synthesis. Symptomatic patients may present with hepatic, neurologic or psychiatric forms. Clinical and phenotypic evidences provide only presumptive arguments for this disease which can be routinely assessed by molecular analysis. This genetic disease which can be efficiently treated was formerly biologically suspected after a careful but sometimes invasive study of copper metabolism. Genetic advances can now give a definite answer using linkage analysis and research for disease-causing mutations. However, this diagnosis strategy is limited since currently over 320 mutations and 80 polymorphisms have been currently identified.

Cytogenetic, molecular and testicular tissue studies in an infertile 45,X male carrying an unbalanced (Y;22) translocation: case report

(Y;autosome) translocations have been reported in association with male infertility. Different mechanisms have been suggested to explain the male infertility, such as deletion of the azoospermic factor (AZF) on the long arm of the Y chromosome, or meiosis impairment. We describe a new case with a de novo unbalanced translocation t(Y;22) and discuss the genotype-phenotype correlation. A 36 year old male with azoospermia was found to have a mosaic 45,X/46,X, + mar karyotype. Fluorescence in situ hybridization (FISH) showed the presence of a derivative Y chromosome containing the short arm, the centromere and a small proximal part of the long-arm euchromatin of the Y chromosome and the long arm of chromosome 22. The unstable small marker chromosome included the short arm and the centromere of chromosome 22. This unbalanced translocation t(Y;22)(q11.2;q11.1) generated the loss of the long arm of the Y chromosome involving a large part of AZFb, AZFc and Yq heterochromatin regions. Testicular tissue analyses showed sperm in the wet preparation. Our case shows the importance of documenting (Y;autosome) translocations with molecular and testicular tissue analyses.

Significance of ovarian histology in the management of patients presenting a premature ovarian failure

BACKGROUND

Premature ovarian failure (POF) is a heterogeneous syndrome, possibly due to mutations of genes involved in the normal development of the ovary and/or follicles. Based essentially on animal models, these mutations are associated with various ovarian phenotypes, from a complete absence of follicles to a partial follicular maturation. The aim of the present study was to determine whether ovarian histology, compared to pelvic ultrasonography, would be helpful in identifying which patients display an impaired follicular reserve and/or growth, and in orientating the search for POF aetiology.

METHODS AND RESULTS

We studied a cohort of 61 patients suffering from POF with a normal karyotype. Their median age (range) at diagnosis was 26 years (15-39). The FSH plasma level was high, 67.0 IU/l (13-155). Estradiol and inhibin B plasma levels were low: 18.5 pmol/l (18.5-555) and 5 pg/ml (5-105) respectively. Both pelvic ultrasonography and ovarian biopsies were performed in each patient. The presence of follicles suggested at ultrasonography was confirmed at histology in 56% of the patients. Ovarian histology led to the distinction of two phenotypes: (i) small-sized ovaries, deprived of follicles; and (ii) normal-sized ovaries with partial follicular maturation. To confirm the value of ovarian biopsies, samples from 20 normal women were studied. These demonstrated that ovarian biopsy at random enables reliable assessment of follicular presence, especially when their size is <2 mm.

CONCLUSION

Ovarian histology appears to be a reliable tool in evaluating the follicular reserve, and helpful and complementary to clinical and hormonal phenotyping in orienting the search for the various genetic causes of POF syndrome.

Delayed puberty and primary amenorrhea associated with a novel mutation of the human follicle-stimulating hormone receptor: clinical, histological, and molecular studies

Inactivating mutations of the FSH receptor have been described in rare cases of premature ovarian failure. Only one mutation was associated with a complete phenotype, including delayed puberty, primary amenorrhea, and small ovaries. We describe here a new patient presenting a similar complete phenotype of premature ovarian failure, with high plasma FSH levels associated with very low estrogen and inhibin B levels. No biological response to high doses of recombinant FSH was detected. A novel homozygous Pro(519)Thr mutation was found in this patient. This mutation is located in the second extracellular loop of the FSH receptor, within a motif highly conserved in gonadotropin and TSH receptors. The mutation totally impairs adenylate cyclase stimulation in vitro. FSH binding experiments and confocal microscopy showed that this mutation alters the cell surface targeting of the mutated receptor, which remains trapped intracellularly. Histological studies of the ovaries of the patient showed an increase in the density of small follicles compared with age-matched normal women. A complete block in follicular maturation after the primary stage was also observed. Immunocytochemical studies allowed detection of the expression of c-Kit and proliferation cellular nuclear antigen, whereas no apoptosis was shown by the 3'-end-labeling method. This observation supports the concept that in humans FSH seems mandatory for the initiation of follicular growth only after the primary stage. In our patient complete FSH resistance yields infertility, which is remarkably associated with the persistence of a high number of small follicles.

Expression of the thyroid-stimulating hormone receptor in the folliculo-stellate cells of the human anterior pituitary

TSH secretion from the anterior pituitary is mainly regulated by TRH and thyroid hormones. We hypothesized that in addition the pituitary itself could modulate TSH production by sensing its own TSH release, enabling fine-tuning of TSH secretion. For such an ultra-short loop control, the pituitary should contain a TSH receptor (TSH-R). To find evidence for this we screened a human pituitary complementary DNA library with a digoxigenin-labeled TSH-R probe and found 2 positive clones of 32,000 plaques. One clone was sequenced and found to be completely identical to the thyroid TSH-R. Further proof was obtained by RT-PCR on a human anterior pituitary obtained at autopsy. In situ hybridization and immunohistochemistry confirmed the presence of TSH-R in the anterior pituitary at the messenger ribonucleic acid level as well as the protein level. Moreover, double labeling experiments revealed that TSH-R messenger ribonucleic acid as well as TSH-R protein colocalize with major histocompatibility complex class II expression of folliculo-stellate cells. We conclude that TSH-R is expressed in a subpopulation of folliculo-stellate cells in the human anterior pituitary. This finding suggests ultra-short loop regulation of TSH secretion. Putative recognition of the pituitary TSH-R by TSH-R antibodies might have clinical relevance in Graves' disease.

CCR2B-64I chemokine receptor allele and mother-to-child HIV-1 transmission or disease progression in children. French pediatric HIV infection study group

The beneficial role of a variant of the chemokine receptor CCR2B (CCR2B-641) in the evolution of HIV-1 infection in adults is still controversial. Furthermore, no studies have been performed in HIV-1-infected children. A multicenter and prospective study of 745 infants born to HIV-1-seropositive mothers was performed. The CCR2B-641 allele was studied in 525 non-African children among whom 523 had been previously genotyped for the CCR5delta32 allele and 220 African children. Of the 745 total, 376 children were infected and 369 were uninfected. In the complete population studied, the children homozygous for the CCR2B-64I allele and the heterozygous children were found distributed equally in the infected (respectively, 1.6% and 21%) and uninfected (respectively, 1.9% and 26.3%) groups (p < .22). Among 376 infected children, the incidence of stage C symptoms (U.S. Centers for Disease Control and Prevention [CDC] classification) or the progression of severe immune deficiency (CD4 <15%, CDC stage 3) was not significantly different in heterozygous infected children or children homozygous for the normal allele (p < .17 and p < .75, respectively). The same lack of protective effect was obtained when a separate analysis was performed in the non-African and African HIV-1-infected children.

New natural inactivating mutations of the follicle-stimulating hormone receptor: correlations between receptor function and phenotype

Premature ovarian failure occurs in almost 1% of women under age 40. Molecular alterations of the FSH receptor (FSHR) have recently been described. A first homozygous mutation of the FSHR was identified in Finland. More recently, we described two new mutations of the FSHR in a woman presenting a partial FSH-resistance syndrome (patient 1). We now report new molecular alterations of the FSHR in another woman (patient 2) who presented at the age of 19 with primary amenorrhea contrasting with normal pubertal development. She had high plasma FSH, and numerous ovarian follicles up to 3 mm in size were evidenced by ultrasonography. Histological and immunohistochemical examination of ovarian biopsies revealed the presence of a normal follicular development up to the antral stage and disruption at further stages. DNA sequencing showed two heterozygous mutations: Asp224Val in the extracellular domain and Leu601Val in the third extracellular loop of FSHR. Cells transfected with expression vectors encoding the wild type or the mutated Leu601Val receptors bound hormone with similar affinity, whereas binding was barely detectable with the Asp224Val mutant. Confocal microscopy showed the latter to have an impaired targeting to the cell membrane. This was confirmed by its accumulation as a mannose-rich precursor. Adenylate cyclase stimulation by FSH of the Leu601Val mutant receptor showed a 12+/-3% residual activity, whereas in patient 1 a 24+/-4% residual activity was detected for the Arg573Cys mutant receptor. These results are in keeping with the fact that estradiol and inhibin B levels were higher in patient 1 and that stimulation with recombinant FSH did not increase follicular size, estradiol, or inhibin B levels in patient 2 in contrast to what was observed for patient 1. Thus, differences in the residual activity of mutated FSHR led to differences in the clinical, biological, and histological phenotypes of the patient.

Autoantibodies interacting with purified native thyrotropin receptor

Native thyrotropin receptor (TSHR) was purified by immunoaffinity chromatography from membrane extracts of stably transfected L cells. An ELISA test was devised to study anti-TSHR autoantibodies directly. Comparison of native TSHR with bacterially expressed, denatured TSHR showed that the latter was not recognized by the autoantibodies, suggesting that they bind to conformational epitopes only present on the native receptor. The use of deglycosylated TSHR and of purified receptor ectodomain (alpha-subunit) showed that the autoantibodies recognized only the protein backbone moiety of the receptor and that their epitopes were localized entirely in its ectodomain. Autoantibodies were detected in 45 of 48 subjects with untreated Graves' disease and in 26 of 47 healthy volunteers. The affinity for the receptor was similar in the two groups (Kd = 0.25-1 x 10-10 M) and the autoantibodies belonged to the IgG class in all cases. Although the concentration of autoantibodies was higher in Graves' disease patients (3.50 +/- 0.36 mg.L-1) than in control subjects (1.76 +/- 0.21) (mean +/- SEM), there was an overlap between the groups. Receptor-stimulating autoantibodies (TSAb) were studied by measuring cAMP synthesis in stably transfected HEK 293 cells. Their characteristics (recognition of alpha-subunit, of deglycosylated TSHR, nonrecognition of bacterially expressed denatured receptor) were similar to those of the antibodies detected by the ELISA test. TSAb were only found in individuals with Graves' disease. The ELISA test measures total anti-TSHR antibodies, whereas the test using adenylate cyclase stimulation measures antibodies that recognize specific epitopes involved in receptor activation. Our observations thus disprove the hypothesis according to which Graves' disease is related to the appearance of anti-TSHR antibodies not present in normal subjects. Actually, anti-TSHR antibodies exist in many euthyroid subjects, in some cases even at concentrations higher than those found in patients with Graves' disease. What distinguishes the latter from normal subjects is the existence of subpopulation(s) of antibodies directed against specific epitope(s) of the receptor involved in its activation.

Luteinizing hormone/human chorionic gonadotrophin receptors in various epidermal structures

Two different monoclonal antibodies recognizing different epitopes were used to study the localization of luteinizing hormone/human chorionic gonadotrophin (LH/hCG) receptors in human skin. Immunolabelling was observed only in the epidermis and derived structures but not in the dermis. The basal, spinal and granular layers were stained, whereas no receptors were detected in the non-nucleated horny cells. In the growing (anagen) hair, immunostaining was found in the inner root sheath below the level of the sebaceous glands and in the outer root sheath above this level. In the resting (telogen) hair, only the latter staining was observed. In the sebaceous glands, only the thin cells close to the walls of the ducts were immunolabelled. In the eccrine sweat glands, the external clear cells were stained in the secretory portion of the gland, whereas only the cells close to the lumen were labelled in the ducts. The distribution of LH/hCG receptors was compared with that of steroidogenic enzymes (side chain cleavage cytochrome P450, adrenodoxin, 3-beta-hydroxy-5-ene steroid dehydrogenase Delta5-Delta4 isomerase, 17-hydroxylase cytochrome P450 and cytochrome P450 aromatase). Only partial overlaps were observed. The presence of LH receptor mRNA in the skin was confirmed by reverse transcription-polymerase chain reaction. Monoclonal antibodies raised against the human follicle-stimulating hormone receptor failed to detect the latter in the epidermal structures and in the dermis. The role of LH and hCG in skin modifications occurring during pregnancy and after the menopause is unknown. These hormones may possibly act by regulating steroidogenic enzymes or by modulating cell growth and differentiation.

CCR5 delta32 deletion and reduced risk of toxoplasmosis in persons infected with human immunodeficiency virus type 1. The SEROCO-HEMOCO-SEROGEST Study Groups

This study attempted to determine whether the CCR5 Delta32 deletion affected progression to certain first AIDS-defining illnesses in human immunodeficiency virus type 1-infected patients enrolled in the French SEROCO/HEMOCO/SEROGEST cohorts. Toxoplasmosis onset as a first AIDS-defining illness was significantly delayed in 253 heterozygous patients, compared with 1404 wild type patients. The relative risk of toxoplasmosis associated with heterozygosity was 0. 39 (95% confidence interval, 0.16-0.96) after adjustment for age, CD4 cell count, and primary specific prophylaxis. A nonsignificant protective trend was observed with regard to the onset of mycobacterial, cytomegalovirus, and herpesvirus diseases, but these events were less frequent than toxoplasmosis. Progression to other conditions (e.g., wasting, non-Hodgkin's lymphoma, Kaposi's sarcoma) was similar in the 2 groups as was the frequency of toxoplasmosis as a subsequent AIDS-defining illness. As chemokines are involved in numerous infectious processes, the Delta32 deletion could delay progression to certain opportunistic infections such as toxoplasmosis.

[Mechanisms of polarized targeting of the FSH receptor]

Gonadotropin and TSH receptors belong to a subgroup of G protein-coupled receptors. TSH and FSH receptor present a particular intracellular traffic: they present a polarized basolateral expression in thyroid follicular cells and in Sertoli cells respectively. By contrast, the LH receptor is expressed circumferentially in target gonadic cells. We expressed these receptors in MDCK cells (a well characterized model of polarized epithelial cells) to understand this difference of properties. We show that the three receptors have a polarized basolateral expression in these cells. All contain a basolateral targeting signal. Furthermore, gonadotropin receptors undergo a partial transcytosis which is not observed for the TSH receptor. We show that heterotrimeric G proteins play a role in this mechanism of transcytosis. This effect is not mediated by adenylate cyclase activation and involves a population of G proteins different from that involved in signal transduction. We thus used in vitro mutagenesis to delineate the basolateral localization signal of the FSH receptor. Surprisingly, the signal is localized in the C-terminal tail of the intracellular domain which is not conserved between the three receptors. It contains 14 amino-acids and its activity is mainly dependent on a tyrosine and a leucine residue. The basolateral localization signal of the FSHR is not colinear with its internalization signal. This signal is autonomous and dominant because, when transferred to an apically targeted membrane protein, the neurotrophin receptor, it redirects the chimeric construct to the basolateral domain of MDCK cells. The basolateral localization signal of the FSH receptor is thus the first signal identified for a G protein-coupled receptor and more generally for a hormone receptor.

Gonadotropin receptors

Gonadotropin receptors belong to a subgroup of G-protein coupled receptors characterized by a large extracellular domain responsible for the binding of the hormone. Soluble, hormone-binding, alternative splicing variants of the LH receptor, are present in high concentration. A mannose rich precursor form of LH and FSH receptor is accumulated inside target cells. FSH receptors are addressed to the basolateral domain of cells through specific signaling mechanisms. Gonadotropin receptors are also present in endothelial cells of target organ vessels and are involved in hormone transcytosis. Various genetic abnormalities of these receptors (and of the GnRH receptor) are discussed.

Loss of function mutations of the GnRH receptor: a new cause of hypogonadotropic hypogonadism

The association of hypogonadotropic hypogonadism with anosmia defines Kallmann's syndrome. The gene of the X-linked form of this syndrome has been cloned and several mutations described. However, the relatively small number of hypogonadotropic hypogonadic patients with Kallmann's gene defects supports the hypothesis that other genes may be involved. Idiopathic hypogonadotropic hypogonadism (IHH) is not associated with anosmia. The GnRH gene was excluded as a candidate gene in IHH since no abnormality was found in several patients. The action of the GnRH is mediated through a G-protein coupled receptor present in the cell membrane of gonadotropes. The GnRH receptor was thus another candidate gene. Recently, we described the first patient with partial hypogonadotropic hypogonadism without anosmia caused by loss of function mutations of the GnRH receptor. We compare this first family with a new family presenting complete hypogonadotropic hypogonadism and a variable degree of gonadotrope deficiency in the affected kindred, and discuss genotype-phenotype correlation.

The same molecular defects of the gonadotropin-releasing hormone receptor determine a variable degree of hypogonadism in affected kindred

Detailed endocrinological studies were performed in the three affected kindred of a family carrying mutations of the GnRH receptor gene. All three were compound heterozygotes carrying on one allele the Arg262Gln mutation and on the other allele two mutations (Gln106Arg and Ser217Arg). When expressed in heterologous cells, both Gln106Arg and Ser217Arg mutations altered hormone binding, whereas the Arg262Gln mutation altered activation of phospholipase C. The propositus, a 30-yr-old man, displayed complete idiopathic hypogonadotropic hypogonadism with extremely low plasma levels of gonadotropins, absence of pulsatility of endogenous LH and alpha-subunit, absence of response to GnRH and GnRH agonist (triptorelin), and absence of effect of pulsatile administration of GnRH. The two sisters, 24 and 18 yr old, of the propositus displayed, on the contrary, only partial idiopathic hypogonadotropic hypogonadism. They both had primary amenorrhea, and the younger sister displayed retarded bone maturation and uterus development, but both sisters had normal breast development. Gonadotropin concentrations were normal or low, but in both cases were restored to normal levels by a single injection of GnRH. In the two sisters, there were no spontaneous pulses of LH, but pulsatile administration of GnRH provoked a pulsatile secretion of LH in the younger sister. The same mutations of the GnRH receptor gene may thus determine different degrees of alteration of gonadotropin function in affected kindred of the same family.

Sequential cleavage and excision of a segment of the thyrotropin receptor ectodomain

The thyrotropin (TSH) receptor belongs to a subfamily of G protein-coupled receptors, which also includes luteinizing hormone and follicle-stimulating hormone receptors. The TSH receptor (TSHR) differs from the latter by the presence of an additional specific segment in the C-terminal part of its ectodomain. We show here that this insertion is excised in the majority of receptor molecules. Preparation of specific monoclonal antibodies to this region, microsequencing, enzyme-linked immunosorbent assay, and immunoblot studies have provided insight into the mechanisms of this excision. In the human thyroid gland, N termini of the transmembrane receptor beta subunit were found to be phenylalanine 366 and leucines 370 and 378. In transfected L cells a variety of other more proximal N termini were found, probably corresponding to incomplete excisions. The most extreme N terminus was observed to lie at Ser-314. These observations suggest that after initial cleavage at Ser-314 the inserted fragment of TSHR is progressively clipped out by a series of cleavage reactions progressing up to amino acids 366-378. The impossibility of recovering the excised fragment from purified receptor, cell membranes, or culture medium supports this interpretation. The cleavage enzyme has previously been shown to be inhibited by BB-2116, an inhibitor of matrix metalloproteases. However, we show here that it is unaffected by tissue inhibitors of metalloproteases. The cleavage enzyme is very similar to TACE (tumor necrosis factor alpha-converting enzyme) in both these characteristics. However, incubation of the TSH receptor with the purified recombinant catalytic domain of TACE, co-transfection of cells with TACE and TSHR expression vectors, and the use of mutated Chinese hamster ovary cells in which TACE is inactive suggested that the TSHR cleavage enzyme is different from TACE. TACE and TSHR cleavage enzyme may thus possibly be related but different members of the adamalysin family of metzincin metalloproteases.

A novel phenotype related to partial loss of function mutations of the follicle stimulating hormone receptor

A single natural loss of function mutation of the follicle stimulating hormone receptor (FSHR) has been described to date. Present in the Finnish population it markedly impairs receptor function, blocking follicle development at the primary stage and presenting as primary amenorrhea with atrophic ovaries. When Western European women with this phenotype were examined for FSHR mutations the result was negative, suggesting that other etiologies corresponding to this clinical pattern are markedly more frequent. We now describe a novel phenotype related to mutations provoking a partial loss of function of the FSHR. A woman with secondary amenorrhea had very high plasma gonadotropin concentrations (especially FSH), contrasting with normal sized ovaries and antral follicles up to 5 mm at ultrasonography. Histological and immunohistochemical examination of the ovaries showed normal follicular development up to the small antral stage and a disruption at further stages. The patient was found to carry compound heterozygotic mutations of the FSHR gene: Ile160Thr and Arg573Cys substitutions located, respectively, in the extracellular domain and in the third intracellular loop of the receptor. The mutated receptors, when expressed in COS-7 cells, showed partial functional impairment, consistent with the clinical and histological observations: the first mutation impaired cell surface expression and the second altered signal transduction of the receptor. This observation suggests that a limited FSH effect is sufficient to promote follicular growth up to the small antral stage. Further development necessitates strong FSH stimulation. The contrast between very high FSH levels and normal sized ovaries with antral follicles may thus be characteristic of such patients.

Genotypic-phenotypic variations in a series of 65 patients with familial amyloid polyneuropathy

OBJECTIVE

To investigate the genotypic-phenotypic variations in a series of patients with familial amyloid polyneuropathy (FAP).

BACKGROUND

Progress in molecular genetics has led to the identification of point mutations in the transthyretin (TTR) gene in FAP--a dominantly inherited neuropathy with a fatal outcome. These findings have modified the management of patients with small-fiber neuropathy and allow genetic counseling.

METHODS

We performed a clinical and molecular genetic study with screening of the TTR gene mutations and associated haplotypes in 65 patients from 29 unrelated families of French ancestry.

RESULTS

We detected nine heterozygous point mutations segregating with FAP. Fourteen families (48%) carried the common methionine (Met) 30 substitution. Seven kindreds (24%) had previously unreported TTR variants, namely asparagine 35, serine (Ser) 91, phenylalanine (Phe) 77, and Ser 116. At least two different haplotypes were associated with each of the following: Met 30, Phe 77, and valine 107, suggesting that multiple founders occurred for each variant. Only 35% of the index patients had affected relatives. Other patients had a sporadic presentation. All progressed to a severe sensorimotor and autonomic neuropathy with frequent cardiac involvement (80%). On average, a late age at onset (54.3 +/- 13.3 years) and a disease duration shorter than 10 years were observed for virtually all variants.

CONCLUSION

The heterogeneity of the TTR variants, the late age at onset, and the short duration of the disease found in our patients contrast with the presentation of FAP in Portugal. These findings must be taken into account in the management of both patients and asymptomatic carriers.

Absence of activating mutations in the GnRH receptor gene in human pituitary gonadotroph adenomas

The monoclonal origin of gonadotropin-secreting pituitary adenomas has been well demonstrated but only few molecular abnormalities have so far been recognized in these tumors. For many years, several authors have suggested a role for GnRH and/or GnRH receptors (GnRH-R) in the development of these pituitary adenomas. To test the hypothesis that mutant genes encoding a constitutively activated GnRH-R might be involved in the pathogenesis of these tumors, the sequence of the GnRH-R gene was analyzed in tumoral pituitary tissue obtained from ten patients (six female, four male). The pituitary gonadotropin-secreting adenoma was associated with in vivo hypersecretion of FSH, LH and/or free alpha-subunit (n = 7) or was clinically silent (normal plasma levels of gonadotropins or free alpha-subunit, n = 3). In all cases, immunocytochemical studies of the removed adenoma confirmed their gonadotroph nature by revealing positivity for FSH, LH and/or alpha-subunit. Genomic DNA was extracted from the pathological tissue obtained at neurosurgery. Eight sequencing primers were used to amplify the three exons of the GnRH-R gene from tumoral DNA. The entire coding sequence of the GnRH-R gene was sequenced in the ten adenomas. No mutation was found in any of the tumor specimens examined. In conclusion, mutations in the GnRH receptor coding sequence occur infrequently if at all in gonadotropin-secreting pituitary adenomas.

[Mechanisms of shedding of a soluble form of the TSH receptor]

The thyrotropin (TSH) receptor in human-thyroid glands is cleaved into an extracellular alpha subunit and a transmembrane beta subunit held together by disulfide bridges. An excess of the latter component relative to the former suggests shedding of the ectodomain. Indeed we observed such shedding in cultures of human thyrocytes and permanently transfected L or Chinese hamster ovary cells. Shedding was increased by inhibitors of endocytosis, recycling and lysosomal degradation suggesting that it was dependent on receptor residency at the cell surface. It was slightly increased by TSH and phorbol esters whereas forskolin and 8 bromo cAMP were without effect. The complete inhibition of soluble TSH receptor shedding by the specific inhibitor BB-2116 indicated that the cleavage reaction is catalyzed probably at the cell surface by a matrix metalloprotease-like enzyme. Shedding of the TSH receptor alpha domain is the consequence of two events: cleavage of the proreceptor into alpha and beta subunits and reduction of the disulfide bridge(s). The use of different specific inhibitors including monoclonal antibodies allowed us to implicate the enzyme protein disulfide isomerase in the reduction of TSHR disulfide bounds. The shed alpha subunit probably results in circulating TSH receptor ectodomain detected in human blood. This shedding mechanism might be implicated in the development of autoimmune diseases.

The basolateral localization signal of the follicle-stimulating hormone receptor

The follicle-stimulating hormone receptor (FSHR) is physiologically localized in the basolateral compartment of the membrane of Sertoli cells. This localization is also observed when the receptor is experimentally expressed in Madin-Darby canine kidney cells. We thus used in vitro mutagenesis and transfection into these polarized cells to delineate the basolateral localization signal of the receptor. The signal was localized in the C-terminal tail of the intracellular domain (amino acids 678-691) at a marked distance of the membrane. Mutation of individual amino acids highlighted the importance of Tyr684 and Leu689. The 14-amino acid sequence was grafted onto the p75 neurotrophin receptor and redirected this apical protein to the basolateral cell membrane compartment. Deletion of amino acids 677-695 did not modify the internalization of the FSHR, showing that the basolateral localization signal of the FSHR is not colinear with its internalization signal.

Gonadotropin receptors and the control of gonadal steroidogenesis: physiology and pathology

Over the past few years, knowledge of the structure of gonadotropin receptors and their mode of action has rapidly advanced. The cDNA corresponding to the luteinizeng hormone (LH) receptor (LHR) has been cloned, leading to the identification of a novel family of G-protein-coupled receptors. The follicle stimulating hormone (FSH) receptor (FSHR) was thereafter cloned by cross-hybridization with the LHR. Structure-function relationships have been studied by mutagenesis experiments in several laboratories. The cloning and chromosomal localization to chromosome 2p21 of the two human gonadotropin receptor genes has provided insights into their evolutionary relationships. The LHR and FSHR genes are very large and contain 10 and 11 exons respectively. The obtention of monoclonal antibodies against the receptors resulted in the characterization of the receptor proteins. These antibodies also allowed the study of receptor expression in target cells in physiological and pathological conditions. The internalization of the LHR has been studied by electron microscopy. A mechanism of receptor-mediated transcytosis through the endothelial cells of the testes has been described for the LHR. The polarized expression of receptors has been studied. The cloning of gonadotropin receptor genes has opened the field of genetic study of the receptors. Inactivating mutations of the LHR have been described in Leydig cell agenesis or hypoplasia. Different phenotypes, including complete pseudohermaphroditism, ambiguous genitalia and male phenotype, have been described. In the case of the FSHR, only one mutation has been reported in familial ovarian dysgenesis with primary amenorrhea. Related males have variable alterations of spermatogenesis and fertility. Constitutive mutations of the LHR have been reported in familial testotoxicosis. One similar mutation has also been described for the FSHR. Such mutations may lead to the development of a model of receptor activation.

Oncogenic potential of a mutant human thyrotropin receptor expressed in FRTL-5 cells

An abnormal stimulation of the cAMP pathway has been recognized as the primary event in various pathological situations that lead to goitrogenesis or thyroid tumors. Thyroid adenomas are monoclonal neoplasms that become independent of thyroid stimulating hormone (TSH) in their secretory function and growth. Mutated forms of the TSH receptor (TSHR) and the adenylyl cyclase-activating Gs alpha protein, which confer a constitutive activity on these proteins, have been observed in human adenomas. The FRTL-5 rat thyroid cell line is a permanent but untransformed line; the growth of which depends on the presence of TSH, and at least in part, on the stimulation of the cAMP pathway. In order to compare the oncogenic potential of the activated mutant Gs alpha protein and the constitutively activated TSHR, we have transfected FRTL-5 cells with an expression vector bearing either the cDNA of the Gs alpha gene carrying the A201S mutation or the cDNA of the TSH receptor carrying the M453T mutation recently identified in a case of congenital hyperthyroidism. The expression of these two cDNAs was driven by the bovine thyroglobulin gene promoter. We show that, although the expression of both the Gs alpha or TSHR mutant proteins leads to TSH-independent proliferation and to constitutive cAMP accumulation in FRTL-5 cells, only the mutant TSHR is able to induce neoplastic transformation, as demonstrated by growth in semi-solid medium and tumorigenesis in nude mice.

CCR5 chemokine receptor variant in HIV-1 mother-to-child transmission and disease progression in children. French Pediatric HIV Infection Study Group

CONTEXT

Studies suggest that adults with the CCR5delta32 deletion are less likely to become infected with the human immunodeficiency virus (HIV) and to develop HIV-related disease progression, but the effect of the mutation in children is not known.

OBJECTIVE

To study the effect of the CCR5 chemokine receptor mutant allele on mother-to-child transmission of HIV type 1 (HIV-1) and subsequent disease progression in infected children.

DESIGN

Multicenter, prospective study of infants born to mothers seropositive for HIV-1.

SETTING

A total of 52 medical centers participating in the French Pediatric HIV Cohort studies.

PARTICIPANTS

The CCR5delta32 deletion was studied in 512 non-African children, born between 1983 and 1996 to HIV-1-infected mothers. Among them, 276 children were infected and 236 were not.

MAIN OUTCOME MEASURES

HIV-1 infection status and, in infected children followed up since birth, incidence of category B and C disease events and severe immunosuppression as defined in the new pediatric Centers for Disease Control and Prevention (CDC) classification, according to CCR5 genotype.

RESULTS

The 32-base pair deleted allele was detected at a frequency of 0.05. Only 1 infant, not infected by HIV-1, was homozygous for the delta32 deletion. The 49 heterozygous children (9.6% of the total; 95% confidence interval [CI], 7.1-12.2) were equally distributed into the infected (9.8%) and uninfected (9.3%) groups. The incidence of stage C symptoms in heterozygous infected children was 9% at 36 months vs 28% in children homozygous for the normal allele (P<.004). The proportion of children at 8 years old with no stage B or C symptoms was 49% for heterozygous children and 11% for children homozygous for the normal allele (P<.003). The progression of severe immune deficiency (CD4 <15%, CDC stage 3) was also significantly different between the 2 groups (P<.001).

CONCLUSIONS

Heterozygosity for the CCR5delta32 deletion does not protect children from infection by the maternal virus but substantially reduces the progression of the disease in HIV-1-infected children.

Gonadotrophin and thyrotrophin receptors

Gonadotrophin and thyrotrophin receptors belong to a subgroup of G-protein-coupled receptors. These receptors are characterized by a large extracellular domain that is responsible for the binding of the hormone. Soluble receptors, such as some luteinizing hormone receptors, arise from premessenger RNA alternative splicing, or, in the case of thyroid-stimulating hormone (TSH) receptors, by the cleavage and shedding of the ectodomain. Follicle-stimulating hormone and TSH receptors are restricted to the basolateral domain of their target cells. These receptors are also present in endothelial cells of target organ vessels and are involved in hormone transcytosis. Various genetic abnormalities of these receptors have been described.

Comparison of immunocytochemical and molecular features with the phenotype in a case of incomplete male pseudohermaphroditism associated with a mutation of the luteinizing hormone receptor

We report the case of an infant who presented at birth with a hypoplastic phallus associated with hypospadias. Low testosterone production, normal serum levels of steroid precursors, and increased LH in response to LH-releasing hormone supported a defect in Leydig cell differentiation or function. Conventional microscopic study of the testes showed fibroblastic cells in the interstitium. However immunocytochemical analysis using anti-LH receptor and anti-P450c17 antibodies demonstrated that about one third of these cells were Leydig cells or precursors of Leydig cells. No histological feature could distinguish the latter cells from fibroblasts. A homozygous substitution of cysteine 133 for arginine was found in the extracellular domain of the receptor. This is the first naturally occurring missense mutation found in the extracellular domain of the LH receptor. COS-7 cells transfected with the mutant receptor exhibited a marked impairment of hCG binding, whereas some cAMP production could be observed at high hCG concentrations. We propose that the partial impairment of LH receptor function, as reflected by the presence of Leydig cells, was responsible for the incomplete male pseudohermaphroditism observed in our patient.

Basolateral localization and transcytosis of gonadotropin and thyrotropin receptors expressed in Madin-Darby canine kidney cells

The thyrotropin (TSH) and follicle-stimulating hormone (FSH) receptors are present mainly on the basolateral cell surface in the thyroid gland and in Sertoli cells, whereas in ovarian and in testicular cells, the luteinizing hormone (LH) receptors are distributed throughout the cell surface. When expressed in Madin-Darby canine kidney (MDCK) cells, all three receptors accumulated at the basolateral cell surface showing that they carry the corresponding targeting signals. The receptors were directly delivered to the basolateral surface of the MDCK cells. A minor fraction of the gonadotropin receptors but not of TSH receptors was secondarily targeted to the apical surface through transcytosis. The mechanisms of basolateral targeting and transcytosis were analyzed using the FSH receptor as a model. Both were insensitive to brefeldin A and pertussis toxin. Gs activation by AlF4- and cholera toxin provoked a marked enhancement of FSH receptor transcytosis. The population of Gs proteins involved in this mechanism was different from that involved in signal transduction since neither FSH nor forskolin mimicked the effects of AlF4- and cholera toxin. Gs activation provoked a similar effect on LH receptor distribution in MDCK cells, whereas it did not modify the compartmentalization of the TSH receptor. Hormone-specific transcytosis was observed in MDCK cells expressing the gonadotropin (FSH and LH) receptors and was increased after cholera toxin administration.

The LH/CG and FSH receptors: different molecular forms and intracellular traffic

Monoclonal antibodies have been raised against the LH/CG receptor [1] and have allowed to perform immunochemical studies of the receptor in target cells. Three different forms of the LH/CG receptor are physiologically expressed: a mature approximately 85 kDa transmembrane species corresponding to the full length receptor, a approximately 68 kDa high mannose containing species corresponding to a precursor which accumulates inside the cells, and truncated soluble approximately 45-48 kDa molecular weight species corresponding to the variant messanger RNAs generated by alternative splicing. Monoclonal antibodies against the human FSH receptor were also prepared. They allow to observe the existence of two forms of the FSH receptor in the ovaries: a major approximately 87 kDa species corresponding to the mature receptor and a minor approximately 81 kDa species corresponding to a high mannose rich precursor. No variant forms of the receptor corresponding to alternative mRNA transcripts were detected. The transport of hCG was examined in rat testicular microvasculature by electron microscopy and by analyzing the transfer of radiolabeled hormone and antireceptor antibodies. LH/CG receptors were present in endothelial cells and were involved in hormone transcytosis through these cells. Immunocytochemical experiments have shown that the FSH receptor has a polarized expression in the Sertoli cells of the testes whereas the LH/Cg receptor is spread on the surface of thecal granulosa and luteal cells in the ovary and Leydig cells in the testes. To study the mechanism of this polarization FSH, LH and TSH receptors were expressed in polarized MDCK cells. The mechanism of basolateral localization and of transcytosis of the receptors was studied using this model. The effect of hormone, cAMP and agents acting on G proteins was examined.

Four families with loss of function mutations of the thyrotropin receptor

We observed four families with loss of function mutations of the TSH receptor gene. One patient had a homozygous Pro162 Ala substitution. The three other were compound heterozygotes: 1) Gln324-->Stop and Asp410 Asn2), Cys41 Ser and Phe525 Leu, 3) Cys390 Trp and Trp546-->Stop. In all patients, the plasma TSH concentration was increased, whereas T3 and T4 concentrations were normal. The TSH levels were normal in the heterozygous parents. These results confirmed the recessive character of TSH receptor defects. Expression of the various mutated receptors in transfected COS-7 cells demonstrated the impairment of their function. We studied the expression of the receptors on the cell surface by immunofluorescence, their ability to bind hormone, and their capacity to activate adenylate cyclase. Some mutations allowed us to identify sites that are especially important for receptor function. The substitution Cys390 Trp abolished high affinity hormone binding. Receptor mutated at Asp410 Asn bound the hormone normally, but failed to activate adenylate cyclase. This result underscores the role of this acidic extracellular residue, close to the first transmembrane segment, in signal transmission. The Phe525 Leu substitution also markedly impaired adenylate cyclase activation, underlining the importance of the second intracellular loop in receptor signaling.

Cell surface protein disulfide-isomerase is involved in the shedding of human thyrotropin receptor ectodomain

In human thyroid glands the TSH receptor undergoes a cleavage reaction which yields to an extracellular alpha subunit and a membrane spanning beta subunit linked together by disulfide bridges. A similar reaction is observed in transfected L cells although some uncleaved monomers persist in these cells. We have recently shown that the alpha subunit of the TSH receptor undergoes partial shedding in human thyroid cells and heterologous cells permanently transfected with an expression vector encoding the receptor. This shedding is a two-step process. The first step consists in the cleavage of the proreceptor at the cell surface probably by a matrix metalloprotease and the second step in the reduction of the disulfide bridge(s) (Couet, J., Sar, S., Jolivet, A., Vu Hai, M. T., Milgrom, E., & Misrahi, M. 1996, J. Biol. Chem. 271, 4545-4552). We have used the transfected L cells to study the second step involved in sTSHR shedding. The membrane impermeant sulfhydryl reagent DTNB (5,5'-dithiobis(2-nitrobenzoic acid) allowed us to confirm that the reduction of the TSH receptor disulfide bonds occurred at the cell surface. The antibiotic bacitracin even at low concentrations also elicited a marked inhibition of TSH receptor shedding. This led us to implicate the enzyme protein disulfide isomerase (PDI, EC 5.3.4.1) in this process. We thus tested the inhibitory activity of specific monoclonal antibodies raised against PDI. All antibodies elicited a marked inhibition of sTSHR shedding. This confirmed that cell surface PDI is involved in the shedding of the TSH receptor ectodomain. The shed alpha subunit may be at the origin of circulating TSH receptor ectodomain detected in human blood.

Analysis of the thyrotropin receptor as a candidate gene in familial Graves' disease

Familial clustering of Graves' disease indicates a genetic etiology. Searches for genetic factors additional to the known human leukocyte antigen (HLA) association have implicated the gene for the TSH receptor (TSHR). We analyzed the linkage and association among three recently described microsatellite markers within the TSHR introns in Graves' disease in large multiply affected Welsh and English families (223 members, 44 affected individuals). Linkage analysis under a dominant model strongly rejected the hypothesis that TSHR is linked to Graves' disease in these families (lod score = -4.53). More detailed analyses also failed to provide evidence for linkage; these included combined segregation and linkage analysis, correction for HLA-DR3 status, allowance for the levels of thyroid autoantibodies in unaffected pedigree members, consideration of a recessive model for the disease, and linkage disequilibrium between disease and marker alleles. We also considered the possibility of a genetic heterogeneity of Graves' disease and thus analyzed separately the different families with a similar result. Although these results cannot eliminate a minor role of the TSHR gene locus in the genetics of Graves' disease, they argue against it being a major genetic determinant in this pathology.

Additional translocation (9;12)(p13;q24.1) in newly diagnosed chronic myeloid leukemia: complete cytogenetic remission after interferon therapy

We report the case of a patient with chronic phase CML who exhibited, in the same cells, beside the Philadelphia chromosome, an additional translocation between the other chromosome 9 and one of the chromosomes 12 [t(9;12)(p13;q24.1)]. Complete cytogenetic remission with disappearance of both karyotypic abnormalities was achieved after 18 months treatment with low dose (1.4 x 10(6) U/m2/day) recombinant alpha-interferon and has been sustained with maintenance therapy for 68+ months (actual follow-up). Clonality at diagnosis and recovery of polyclonal hematopoiesis in complete cytogenetic remission were demonstrated using the polymorphism at the human androgen receptor gene (Humara) locus on chromosome X. The role of the additional translocation in the response to low dose alpha-interferon therapy remains hypothetical.

A neomutation of the thyroid-stimulating hormone receptor in a severe neonatal hyperthyroidism

Until recently, neonatal hyperthyroidism has been considered to be related to the transplacental passage of thyroid-stimulating Ig present in the serum of the mother. We report here the case of a newborn who presented with severe hyperthyroidism, diffuse goiter, and important ocular signs (eyelid retraction and possibly proptosis). However, the absence of thyroid pathology in the parents and the lack of antithyroid antibodies in the mother and in the patient led us to suspect a nonimmune aetiology. Direct genomic sequencing of the last exon of the TSH receptor in the patient revealed a T-->C transversion yielding to a Met453-->Thr heterozygous substitution in the second transmembrane domain of the receptor. The mutation was absent in both parents. Eukaryotic expression analysis in COS-7 cells yielded a mutated receptor that produced constitutive activation of adenylate cyclase without enhancement of phospholipase C activity.