CYP24A1 Mutations in a Cohort of Hypercalcemic Patients: Evidence for a Recessive Trait.

CONTEXT: Loss-of-function mutations of CYP24A1 (which encodes the 25-OH-D3-24-hydroxylase) have recently been reported to cause hypercalcemia. OBJECTIVES: The aims of this study were: 1) to evaluate the frequency of CYP24A1 mutations in patients with medical history of hypercalcemia; 2) to show the clinical utility of a simultaneous assay of serum 25-hydroxyvitamin D3 (25-OH-D3) and 24,25-dihydroxyvitamin D3 (24,25-[OH]2D3) by liquid chromatography tandem mass spectrometry (LC-MS/MS); and 3) to investigate biochemical parameters in heterozygous gene carriers with CYP24A1 mutations. PATIENTS AND METHODS: We screened for CYP24A1 mutations in 72 patients with serum calcium levels > 2.6 mmol/L and PTH levels < 20 pg/mL and recruited 24 relatives after genetic counseling for subsequent investigations. Vitamin D metabolite concentrations were assessed in a subset of patients by LC-MS/MS and results expressed as a ratio (R) of 25-OH-D3:24,25-(OH)2D3. RESULTS: Twenty-five patients with hypercalcemia (35%) harbored CYP24A1 variations. Twenty (28%) had biallelic variations, mostly found in subjects with nephrocalcinosis or renal stones (19/20). Five patients, all neonates, were heterozygous, without renal disease. We describe 15 new variations leading to loss-of-function according to pathogenicity prediction programs, and we functionally characterized 5 of them in vitro. A dramatic increase of R, usually >80, was found in patients harboring biallelic mutations providing evidence in vivo for the loss of CYP24A1 activity. In contrast, R value remains <25 in patients without CYP24A1 mutations. Subjects carrying one mutant allele, hypercalcemic individuals, as well as gene-carrier relatives, had a detectable 24,25-(OH)2D3 level and R < 25, indicating normal 24-hydroxylase activity. CONCLUSION: CYP24A1 biallelic mutations are frequently found in patients presenting with hypercalcemia, low PTH, and renal disease. We confirm the accuracy and effectiveness of a novel blood test estimating the ratio between relevant vitamin D metabolites as a useful screening tool for CYP24A1 mutations. Haploinsufficiency is not associated with CYP24A1 deficiency.

[Overdose or hypersensitivity to vitamin D?]. / Surdosage ou hypersensibilité à la vitamine D ?

Vitamin D intoxication with severe hypercalcemia is rare in the neonatal and infancy period. Through nine cases of hypercalcemia, secondary to taking 600,000 units of vitamin D (Sterogyl(®)), a review of vitamin D requirements and possible mechanisms of toxicity including hypersensitivity to this vitamin will be discussed. We report nine cases of babies admitted to our department between the ages of 25 and 105 days for treatment of severe dehydration. The pregnancies were normal, with no incidents at delivery. Clinical signs were dominated by weight loss, vomiting, and fever. Examination on admission revealed dehydration whose degree ranged from 8 to 15% with preserved diuresis and loss weight between 100 and 1100 g. Laboratory tests objectified hypercalcemia between 113 and 235mg/L, hypercalciuria (urinary calcium/creatinine mmol/mmol >0.5), and a low-level of parathyroid hormone. The vitamin D values in nine patients were toxic (344-749 nmol/L; normal >50 nmol/L; toxicity if >250 nmol/L). Abdominal ultrasound objectified renal nephrocalcinosis in seven patients. The DNA study, performed in eight patients, did not reveal a mutation of the vitamin D 24-hydroxylase gene (CYP24A1). The treatment consisted of intravenous rehydration with treatment of hypercalcemia (diuretics and corticosteroids). Serum calcium returned to the normal range within 4-50 days, with weight gain progressively over the following weeks. The follow-up (2 years for the oldest case) showed the persistence of images of nephrocalcinosis. Genetic susceptibility and metabolic differences appear to modulate the threshold of vitamin D toxicity. However, respect for recommended doses, recognized as safe in a large study population, reduces the risk of toxicity.

Seasonal expression of KiSS-1 and the pituitary gonadotropins LHß and FSHß in adult male Libyan jird (Meriones libycus).

The molecular mechanisms operating on a seasonal time-scale and regulating functions such as reproduction are poorly understood in animals living in desert environments. Kisspeptin, the product of the KiSS-1 gene, plays a critical role in control of the hypothalamic-pituitary-gonad axis that orchestrates the reproductive system in vertebrates. We report a sequence analysis of KiSS-1 and the pituitary luteinising hormone-beta (LHß) and follicle-stimulating hormone-beta (FSHß) in the Libyan jird (Meriones libycus), a seasonal breeding rodent that is sexually active during spring and quiescent in fall. We also assessed gene expression by quantitative real-time reverse transcription-polymerase chain reaction during the non-breeding and breeding seasons. The KiSS-1 cDNA sequence analysis showed high homology between M. libycus and all other rodents (94%) and humans (92%). KiSS-1 expression was higher during the breeding season than that during the non-breeding season. In contrast, LHß and FSHß expression levels were higher during the non-breeding season in autumn and varied in an opposite manner with testicular, seminal vesicle weights and plasma testosterone levels. Our results extend the role for KiSS-1 in activating the HPG axis in this desert rodent in its natural biotope by relaying environmental cues as in other seasonal non-desert rodent models.

Evidence that FGFR1 loss-of-function mutations may cause variable skeletal malformations in patients with Kallmann syndrome.

PURPOSE: Loss-of-function mutations in FGFR1 have been identified in approximately 10% of the Kallmann syndrome (KS) patients. Previous reports have focused mainly on olfactory, reproductive, and some other features such as cleft lip/palate and dental agenesis. Given the ubiquitous expression of FGFR1 during development, other abnormal phenotypes might, however, have been overlooked in these patients. Here, we demonstrate skeletal phenotypic characterization of patients presented with KS and FGFR1 mutations. MATERIAL AND METHODS: Using the Sanger DNA sequencing technique a cohort of 29 KS patients was screened. RESULTS: Here, we report on 5 KS patients who carry FGFR1 mutations (Gly270Asp, Gly97Ser, Met161Thr, Ser685Phe and Ala167Ser/Ala167Ser). Three patients presented with skeletal abnormalities, i.e. spine (hemivertebra and butterfly vertebra) and limb (oligodactyly of the feet, fusion of the 4th and 5th metacarpal bones) malformations in two patients and one patient, respectively. The hand phenotype found in the patient cannot be thought of as a counter-type of the hand phenotype resulting from FGFR1 gain-of-function mutations. The skeletal anomalies identified in the 3 KS patients are close to those observed in Fgfr1 conditional knockout mice. CONCLUSIONS: This study demonstrates that FGFR1 loss-of-function mutations can be associated with skeletal abnormalities also in humans. Further investigations in KS patients who carry FGFR1 mutations are needed to evaluate the prevalence of skeletal defects in this genetic form of KS. Conversely, the presence of bone malformations in a KS patient should direct the geneticist towards a search for mutations in FGFR1.

Progressive osseous heteroplasia: a model for the imprinting effects of GNAS inactivating mutations in humans.

CONTEXT: Heterozygous GNAS inactivating mutations are known to induce pseudohypoparathyroidism type 1a when maternally inherited and pseudopseudohypoparathyroidism when paternally inherited. Progressive osseous heteroplasia (POH) is a rare disease of ectopic bone formation, and studies in different families have shown that POH is also caused by paternally inherited GNAS mutations. OBJECTIVE: Our purpose was to characterize parental origin of the mutated allele in de novo cases of POH and to draw phenotype/genotype correlations according to maternal or paternal transmission of a same GNAS mutation. DESIGN AND SETTING: We conducted a retrospective study on patients addressed to our referral center for the rare diseases of calcium and phosphorus metabolism. PATIENTS AND METHODS: We matched 10 cases of POH with cases of pseudohypoparathyroidism type 1a carrying the same GNAS mutations. MAIN OUTCOME MEASURES: The parental origin of the mutated allele was studied using informative intragenic polymorphisms and subcloning of PCR products. RESULTS: Paternal origin of GNAS mutations was clearly demonstrated in eight POH cases including one patient with mutation in exon 1. Genotype/phenotype analyses suggest that there is no direct correlation between the ossifying process and the position of the inactivating GNAS mutation. It is, however, more severe in patients in whom origin of the mutation is paternal. Severe intrauterine growth retardation was clearly evidenced in paternally inherited mutations. CONCLUSIONS: Clinical heterogeneity makes genetic counseling a delicate matter, especially in which paternal inheritance is concerned because it can lead to either a mild expression of pseudopseudohypoparathyroidism or a severe expression of POH.

[Epigenetics and pseudohypoparathyroidism]. / Épigénétique et pseudohypoparathyroïdies.

Parental imprinting and the type of the genetic alteration play a determinant role in the phenotype expression of GNAS locus associated to pseudohypoparathyroidism (PHP). This imprint is tissue-specific, mainly localized in the kidney and the thyroid. Only the maternal allele is expressed at this level. An alteration in the coding sequence of the gene leads to an haplo-insufficiency and a dysmorphic phenotype (Albright's syndrome). If the alteration is on the maternal allele, there is a hormonal resistance to the PTH at the kidney level and to the TSH at the thyroid level. The phenotype is known as a PHP1a. If the alteration is on the paternal allele, there are few clinical signs with no hormonal resistance and the phenotype is known as pseudo-pseudo-hypoparathyroidism (PPHP). Methylation anomalies of GNAS locus, in particular of exon 1A, are responsible for a lack of expression of Gαs at kidney and thyroid levels only. If these anomalies concern the maternal allele (the only one expressed) with a paternal pattern, there is no haplo-insufficiency and no dysmorphic syndrome. The hormonal resistance is yet again limited to PTH and TSH. The phenotype is known as PHP1b. In the familial forms, these methylation anomalies are associated with a deletion of the syntaxine 16 gene in the maternal allele. This gene contains probably the imprinting center of the locus.

FSHbeta gene mutation in a female with delayed puberty and hypogonadism: response to recombinant human FSH.

We report a woman with primary amenorrhoea and infertility associated with an isolated deficiency of pituitary FSH that does not respond to GnRH administration. Serum inhibin B was undetectable and antimullerian hormone (AMH) was within the normal range. Ultra sound examination revealed a small uterus and small ovaries with few small follicles. We identified an homozygous 1-bp (G) deletion at codon 79 in FSHbeta gene suggesting a complete loss of function. The patient underwent studies of ovarian responsiveness to recombinant human FSH according to the following protocol: 150UI/d for five days following by 75 UI/d for 10 days. Estradiol plasma level started to increase from day 5 associated to a sharp increase of inhibine B and a decrease of LH. During the same time, we observed an excessive development of multiple follicles resulting in an arrest of the treatment to avoid hyperstimulation. The present study confirm that follicles up to 5 mm in diameter had developed in the absence of FSH and that FSH is required for the growth of follicles beyond the two-layer granulose stage.

KiSS-1 and GPR54 genes are co-expressed in rat gonadotrophs and differentially regulated in vivo by oestradiol and gonadotrophin-releasing hormone.

Kisspeptin, the product derived from KiSS-1, and its cognate receptor, GPR54, both exert a role in the neuroendocrine control of reproduction by regulating gonadotrophin-releasing hormone (GnRH) secretion. In the present study, we demonstrate, using dual immunofluorescence with specific antibodies, that the KiSS-1 and GPR54 genes are both expressed in rat gonadotrophs. All luteinising hormone beta-immunoreactive (LH beta-ir) cells were stained by the KiSS-1 antibody but some kisspeptin-ir cells were not LH beta positive; thus, we cannot exclude the possibility that kisspeptins are expressed in other pituitary cells. All GPR54-ir are co-localised with LH beta cells, but only a subset of LH beta cells are stained with the GPR54 antibody. Using the real-time reverse transcription-polymerase chain reaction (RT-PCR), we found that the expression of KiSS-1 and GPR54 is differentially regulated by steroids. In the female, KiSS-1 mRNA levels dramatically decreased following ovariectomy (OVX), and this decrease was prevented by administration of 17beta-oestradiol (E(2)), but not by administration of GnRH antagonist or agonist. Administration of E(2) in OVX rats receiving either GnRH antagonist or agonist clearly shows that E(2) acts directly on the pituitary to positively control KiSS-1 expression. In OVX rats, administration of the selective oestrogen receptor (ER)alpha ligand propylpyrazoletriol, but not the selective ER beta ligand diarylpropionitrile, mimics this effect. By contrast, our study shows that GPR54 expression is positively regulated by GnRH and negatively controlled by chronic exposure to E(2). In summary, our data document for the first time that, in the female rat pituitary, KiSS-1 expression is up-regulated by oestradiol, similarly to that seen in the anteroventral periventricular nucleus of the hypothalamus. Conversely, GPR54 is up-regulated by GnRH, which exclusively targets gonadotrophs.

Clinical, biochemical, magnetic resonance imaging (MRI) and proton magnetic resonance spectroscopy (1H MRS) findings in a fourth case of combined D- and L-2 hydroxyglutaric aciduria.

We report the fourth case of combined D-and L-2-hydroxyglutaric aciduria presenting with neonatal encephalopathy and subependymal cysts.

Prostatic neuroendocrine tumor in multiple endocrine neoplasia Type 2B.

We report the unusual occurrence of a neuroendocrine prostatic tumor in two young males with multiple endocrine neoplasia (MEN) 2B. Immunohistochemistry of the tumor markers may help differentiate a primary neuroendocrine prostate tumor from the metastasis of a medullary thyroid carcinoma of poor prognosis. MEN 2B hallmarks (i.e. plasma thyrocalcitonin and urinary metanephrines) may be systematically investigated in neuroendocrine tumors of the prostate, and conversely prostate examination may be performed in the periodic screening of MEN 2B male patients.

Tryptophan missense mutation in the ligand-binding domain of the vitamin D receptor causes severe resistance to 1,25-dihydroxyvitamin D.

In this study, two related young children, brother and sister, exhibited severe vitamin D-resistant rickets without alopecia. Sequence analysis of the total vitamin D receptor (VDR) cDNA from skin fibroblasts revealed a substitution of the unique tryptophan of the VDR by arginine at amino acid 286 (W286R). Cultured skin fibroblasts of the two patients expressed normal-size VDR protein (immunocytochemistry and Western blotting) and normal length VDR mRNA (Northern blotting). But, these fibroblasts, as well as COS-7 cells transfected with the W286R mutant, failed to bind 3H 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. The tryptophan substitution did not affect VDR trafficking toward the nucleus but abolished the 24-hydroxylase gene response to 1,25(OH)2D3, even at 10(-6) M concentrations. In conclusion, this case report of a new family with hereditary vitamin D-resistant rickets (HVDRR) emphasizes the crucial role of the VDR tryptophan for ligand binding and for transactivation of 1,25(OH)2D3 target genes. It clearly shows the clinical significance of this VDR amino acid for calcium homeostasis and bone mineralization. This observation suggests further that the presence of a stable VDR-bound ligand may not be obligatory for normal hair follicle development.

Activating mutations of the calcium-sensing receptor: management of hypocalcemia.

Activating mutations of the calcium-sensing receptor (CaR) can cause isolated hypoparathyroidism. Treatment of hypocalcemia in these patients remains to be optimized, because the use of 1-hydroxylated vitamin D3 derivatives can cause hypercalciuria and nephrocalcinosis. We identified activating CaR mutations in 8 (42%) of 19 unrelated probands with isolated hypoparathyroidism. The severity of hypocalcemic symptoms at diagnosis was independent of age, mutation type, or mode of inheritance but was related to the degree of hypocalcemia; serum Ca was 1.97 +/- 0.08, 1.82 +/- 0.14, and 1.54 +/- 0.22 mmol/liter, respectively, in asymptomatic (n = 7), mildly symptomatic (n = 8), and severely symptomatic patients (n = 6). Hypocalcemia segregated with the CaR mutation, but no phenotype-genotype relationships were identified. Fourteen patients received regular 1-hydroxylated vitamin D3 treatment (mean duration, 7.2 +/- 4.9 yr). Nine had hypercalciuric episodes, which were associated with nephrocalcinosis in eight cases. Serum Ca during treatment predicted hypercalciuria and nephrocalcinosis poorly, because either or both of the latter could develop in hypocalcemic patients. Thus, mutational analysis of the CaR gene should be considered early in the work-up of isolated hypoparathyroidism. Treatment options should be weighed carefully in patients with serum Ca below 1.95 mmol/liter. The risk of nephrocalcinosis during treatment can be minimized by carefully monitoring urinary Ca excretion.

Familial medullary thyroid carcinoma with noncysteine ret mutations: phenotype-genotype relationship in a large series of patients.

Familial medullary thyroid carcinoma only is related to germline mutations in the protooncogene RET, mainly in exons 10, whereas noncysteine mutations (exons 13-15) are considered infrequent. We analyzed 148 patients from 47 familial medullary thyroid carcinoma only families, and we found noncysteine RET mutations in 59.5% of these families. Of the index cases with noncysteine mutations, 43.4% presented with a multinodular goiter and high basal calcitonin; they were older at diagnosis than those with mutation in exon 10 and had more multifocal medullary thyroid carcinoma, but no difference in size, bilaterality, presence of C cell hyperplasia, or nodal metastases was found. Gene carriers with noncysteine RET mutations had a lower incidence of medullary thyroid carcinoma (78.2% vs. 94.1%) than those with mutation in exon 10; 20.2% had C cell hyperplasia only, although thyroidectomized at an older age. In conclusion, familial medullary thyroid carcinoma with noncysteine RET mutations are not infrequent and are overrepresented in presumed sporadic medullary thyroid carcinoma, suggesting that RET analysis should routinely be extended to exons 13, 14, and 15. The phenotype is characterized by a late onset of the disease, suggesting a delayed appearance of C cell disease rather than a less aggressive form. In familial medullary thyroid carcinoma gene carriers, the optimal timing for thyroidectomy remains controversial. Based on these data, we propose that surgery should be performed before elevation of the basal calcitonin level, potentially as soon as the pentagastrin test becomes abnormal.

Mazabraud syndrome in two patients: clinical overlap with McCune-Albright syndrome.

Mazabraud syndrome is a rare sporadic disorder, mainly characterized by bone fibrous dysplasia and intramuscular myxomas. We report here two new cases of Mazabraud syndrome. One of our patients (Patient 1) also had café-au-lait spots and multinodular goiter suggestive of McCune-Albright syndrome. We review the 37 previously reported cases with Mazabraud syndrome and discuss the 6/37 patients with criteria of Mazabraud and McCune-Albright syndromes. Based on the clinical overlap between the two syndromes, we tested the GNAS1 gene in blood leukocytes and skin fibroblasts of Patient 1, but found no evidence of an activating mutation in the GNAS1 gene.

A new compound heterozygous mutation of the gonadotropin-releasing hormone receptor (L314X, Q106R) in a woman with complete hypogonadotropic hypogonadism: chronic estrogen administration amplifies the gonadotropin defect.

We describe a woman with complete hypogonadotropic hypogonadism and a new compound heterozygous mutation of the GnRH receptor (GnRHR) gene. A null mutation L314X leading to a partial deletion of the seventh transmembrane domain of the GnRHR is associated with a Q106R mutation previously described. L314X mutant receptor shows neither measurable binding nor inositol phosphate production when transfected in CHO-K1 cells compared to the wild-type receptor. The disease is transmitted as an autosomal recessive trait, as shown by pedigree analysis. Heterozygous patients with GnRHR mutations had normal pubertal development and fertility. The present study shows an absence of LH and FSH response to pulsatile GnRH administration (20 microg/pulse, sc, every 90 min). However, GnRH triggered free alpha-subunit (FAS) pulses of small amplitude, demonstrating partial resistance to pharmacological doses of GnRH. FSH, LH, and FAS concentrations were evaluated under chronic estrogen treatment and repeat administration of GnRH. Not only were plasma FSH, LH, and FAS concentrations decreased, but FAS responsiveness was reduced. This new case emphasizes the implication of the GnRH receptor mutations in the etiology of idiopathic hypogonadotropic hypogonadism. We also have evidence for a direct negative estrogen effect on gonadotropin secretion at the pituitary level, dependent on the GnRHR signaling pathway.

A large homozygous or heterozygous in-frame deletion within the calcium-sensing receptor's carboxylterminal cytoplasmic tail that causes autosomal dominant hypocalcemia.

Autosomal dominant hypocalcemia (ADH) can result from heterozygous missense activating mutations of the calcium-sensing receptor (CaSR) gene, a G-protein-coupled receptor playing key roles in mineral ion metabolism. We now describe an ADH kindred of three generations caused by a novel CaSR mutation, a large in-frame deletion of 181 amino acids within its carboxylterminal-tail from S895 to V1075. Interestingly, the affected grandfather is homozygous for the deletion but no more severely affected than heterozygous affected individuals. Functional properties of mutant and wild-type (WT) CaSRs were studied in transiently transfected, fura-2-loaded human embryonic kidney (HEK293) cells. The mutant receptor exhibited a gain-of-function, but there was no difference between cells transfected with mutant complementary DNA alone or cotransfected with mutant and WT complementary DNAs, consistent with the similar phenotypes of heterozygous and homozygous family members. Therefore, this activating deletion may exert a dominant positive effect on the WT CaSR. The mutant receptor's cell surface expression was greater than that of the WT CaSR, potentially contributing to its gain-of-function. This novel mutation in the CaSR gene provides the first known examples of a large naturally occurring deletion within a G-protein-coupled receptor's carboxylterminal-tail and of a homozygous, affected individual with ADH.

LH down-regulates gonadotropin-releasing hormone (GnRH) receptor, but not GnRH, mRNA levels in the rat testis.

The demonstration of an inhibitory effect of gonadotropin-releasing hormone (GnRH) agonists upon steroidogenesis in hypophysectomized rats and the presence of mRNA coding for GnRH and GnRH receptors (GnRH-R) in rat gonads suggests that GnRH can act locally in the gonads. To assess this hypothesis, we investigated the effects of GnRH analogs, gonadotropins and testosterone on the levels of both GnRH and GnRH-R mRNA in the rat testis. Using dot blot hybridization, we measured the mRNA levels 2 to 120 h after the administration of the GnRH agonist, triptorelin. We observed an acute reduction of both GnRH and GnRH-R mRNAs 24 h after the injection (about 38% of control). However, the kinetics for testis GnRH-R mRNA were different from those previously found for pituitary GnRH-R mRNA under the same conditions. Initially, the concentrations of serum LH and FSH peaked, then declined, probably due to the desensitization of the gonadotrope cells. In contrast, the GnRH antagonist, antarelix, after 8 h induced a 2.5-fold increase in GnRH-R mRNA, but not in GnRH mRNA, while gonadotropins levels were reduced. Human recombinant FSH had no significant effect on either GnRH or GnRH-R mRNA levels. Inversely, GnRH-R mRNA levels markedly decreased by 21% of that of control 24 h after hCG injection. Finally, 24 h after testosterone injection, a significant increase in GnRH-R mRNA levels (2.3 fold vs control) was found, but a reduction in the concentration of serum LH, probably by negative feedback on the pituitary, was observed. In contrast, GnRH mRNA levels were not significantly altered following testosterone treatment. Since LH receptors, GnRH-R and testosterone synthesis are colocalized in Leydig cells, our data suggest that LH could inhibit the GnRH-R gene expression or decrease the GnRH-R mRNA stability in the testis. However, this does not exclude the possibility that GnRH analogs could also affect the GnRH-R mRNA levels via direct binding to testicular GnRH-R. In contrast, the regulation of GnRH mRNA levels appeared to be independent of gonadotropins. Taken together, our results suggest a regulation of GnRH and GnRH-R mRNA specific for the testis.