[Pseudohypoparathyroidism and variants: A translational medicine success story]. / Pseudo-hypoparathyroïdie et ses variants - Un succès de la médecine translationnelle.

Pseudohypoparathyroidism (PHP) is an uncommon disorder which is characterized by end-organ PTH resistance. The genetic defect is located at the GNAS locus that encodes the alpha-subunit of the stimulatory G protein (Gαs) and several splice variants thereof. This complex locus undergoes parental specific methylation changes that result in tissue-specific silencing of the paternal allele. Heterozygous inactivating mutations that disrupt Gαs function or epigenetics changes that impair Gαs expression contribute to a wide clinical spectrum of the disease: PHP1A, PHP1B, osseous heteroplasia, osteodystrophy, obesity, intrauterine growth retardation… whose mechanisms at the molecular level remain unresolved.

Title: Pseudo-hypoparathyroïdie et ses variants - Un succès de la médecine translationnelle. Abstract: Les pseudohypoparathyroïdies (PHP) sont des maladies rares, caractérisées par une résistance à l'action rénale de la parathormone. Le défaut génétique est localisé au locus GNAS, qui code la sous-unité alpha stimulatrice des protéines G (Gαs). Ce locus est le siège de régulations complexes, épissage alternatif et empreinte parentale éteigant de façon tissu-spécifique l'expression de l'allèle paternel. Des mutations hétérozygotes perte de fonction, des épimutations responsables d'une perte d'expression sont associées à un large spectre pathologique : PHP1A, PHP1B, ossification hétérotopique, ostéodystophie, obésité, retard de croissance in utero, etc., dont les mécanismes restent encore incomplètement connus.

Overlapping Phenotypes Associated With CYP24A1, SLC34A1, and SLC34A3 Mutations: A Cohort Study of Patients With Hypersensitivity to Vitamin D.

Mutations in CYP24A1 (vitamin D 24-hydroxylase) and SLC34A1 (renal phosphate transporter NPT2a) cause autosomal recessive Infantile Hypercalcemia type 1 and 2, illustrating links between vitamin D and phosphate metabolism. Patients may present with hypercalciuria and alternate between chronic phases with normal serum calcium but inappropriately high 1,25-(OH)2D and appropriately low PTH, and acute phases with hypercalcemia with suppressed PTH. Mutations in SLC34A3 and SLC9A3R1 have been associated with phosphate wasting without hypercalcemia. The aims of this study were to evaluate the frequency of mutations in these genes in patients with a medical history suggestive of CYP24A1 mutation to search for a specific pattern. Using next generation sequencing, we screened for mutations in 185 patients with PTH levels < 20 pg/mL, hypercalcemia and/or hypercalciuria, and relatives. Twenty-eight (15%) patients harbored biallelic mutations in CYP24A1 (25) and SLC34A3 (3), mostly associated with renal disease (lithiasis, nephrocalcinosis) (86%). Hypophosphatemia was found in 7 patients with biallelic mutations in CYP24A1 and a normal phosphatemia was reported in 2 patients with biallelic mutations in SLC34A3. Rare variations in SLC34A1 and SLC34A3 were mostly of uncertain significance. Fifteen patients (8%) carried only one heterozygous mutation. Heterozygous relatives carrying SLC34A1 or SLC34A3 variation may present with biochemical changes in mineral metabolism. Two patients' genotype may suggest digenism (heterozygous variations in different genes). No variation was found in SLC9A3R1. As no specific pattern can be found, patients with medical history suggestive of CYP24A1 mutation should benefit from SLC34A1 and SLC34A3 analysis.

Differential diagnosis of vitamin D-related hypercalcemia using serum vitamin D metabolite profiling.

Genetic causes of vitamin D-related hypercalcemia are known to involve mutation of 25-hydroxyvitamin D-24-hydroxylase CYP24A1 or the sodium phosphate co-transporter SLC34A1, which result in excessive 1,25-(OH)2 D hormonal action. However, at least 20% of idiopathic hypercalcemia (IH) cases remain unresolved. In this case-control study, we used precision vitamin D metabolite profiling based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) of an expanded range of vitamin D metabolites to screen German and French cohorts of hypercalcemia patients, to identify patients with altered vitamin D metabolism where involvement of CYP24A1 or SLC34A1 mutation had been ruled out and who possessed normal 25-OH-D3 :24,25-(OH)2 D3 ratios. Profiles were compared to those of hypercalcemia patients with hypervitaminosis D, Williams-Beuren syndrome (WBS), CYP24A1 mutation, and normal subjects with a range of 25-OH-D levels. We observed that certain IH and WBS patients exhibited a unique profile comprising eightfold to 10-fold higher serum 23,25,26-(OH)3 D3 and 25-OH-D3 -26,23-lactone than normals, as well as very low serum 1,25-(OH)2 D3 (2-5 pg/ml) and elevated 1,24,25-(OH)3 D3 , which we interpret implies hypersensitive expression of vitamin D-dependent genes, including CYP24A1, as a general underlying mechanism of hypercalcemia in these patients. Because serum 25-OH-D3 and 24,25-(OH)2 D3 remained normal, we excluded the possibility that the aberrant profile was caused by hypervitaminosis D, but instead points to an underlying genetic cause that parallels the effect of Williams syndrome transcription factor deficiency in WBS. Furthermore, we observed normalization of serum calcium and vitamin D metabolite profiles at follow-up of an IH patient where 25-OH-D was reduced to 9 ng/ml, suggesting that symptomatic IH may depend on vitamin D nutritional status. Other hypercalcemic patients with complex conditions exhibited distinct vitamin D metabolite profiles. Our work points to the importance of serum vitamin D metabolite profiling in the differential diagnosis of vitamin D-related hypercalcemia that can rationalize expensive genetic testing, and assist healthcare providers in selecting appropriate treatment. © 2021 American Society for Bone and Mineral Research (ASBMR).

Maternal Transmission Ratio Distortion of GNAS Loss-of-Function Mutations.

Pseudohypoparathyroidism type 1A (PHP1A) and pseudopseudohypoparathyroidism (PPHP) are two rare autosomal dominant disorders caused by loss-of-function mutations in the imprinted Guanine Nucleotide Binding Protein, Alpha Stimulating Activity (GNAS) gene, coding Gs α. PHP1A is caused by mutations in the maternal allele and results in Albright's hereditary osteodystrophy (AHO) and hormonal resistance, mainly to the parathormone (PTH), whereas PPHP, with AHO features and no hormonal resistance, is linked to mutations in the paternal allele. This study sought to investigate parental transmission of GNAS mutations. We conducted a retrospective study in a population of 204 families with 361 patients harboring GNAS mutations. To prevent ascertainment bias toward a higher proportion of affected children due to the way in which data were collected, we excluded from transmission analysis all probands in the ascertained sibships. After bias correction, the distribution ratio of the mutated alleles was calculated from the observed genotypes of the offspring of nuclear families and was compared to the expected ratio of 50% according to Mendelian inheritance (one-sample Z-test). Sex ratio, phenotype of the transmitting parent, and transmission depending on the severity of the mutation were also analyzed. Transmission analysis was performed in 114 nuclear families and included 250 descendants. The fertility rates were similar between male and female patients. We showed an excess of transmission from mother to offspring of mutated alleles (59%, p = .022), which was greater when the mutations were severe (61.7%, p = .023). Similarly, an excess of transmission was found when the mother had a PHP1A phenotype (64.7%, p = .036). By contrast, a Mendelian distribution was observed when the mutations were paternally inherited. Higher numbers of females within the carriers, but not in noncarriers, were also observed. The mother-specific transmission ratio distortion (TRD) and the sex-ratio imbalance associated to PHP1A point to a role of Gs α in oocyte biology or embryogenesis, with implications for genetic counseling. © 2019 American Society for Bone and Mineral Research.

High frequency of paternal iso or heterodisomy at chromosome 20 associated with sporadic pseudohypoparathyroidism 1B.

Pseudohypoparathyroidism 1B (PHP1B) is caused by maternal epigenetic defects in the imprinted GNAS cluster. PHP1B can follow an autosomal dominant mode of inheritance or occur sporadically (spor-PHP1B). These latter patients present broad methylation changes of two or more differentially methylated regions (DMR) that, when mimicking the paternal allele, raises the suspicious of the occurrence of paternal uniparental disomy of chromosome 20 (upd(20)pat). A cohort of 33 spor-PHP1B patients was screened for upd(20)pat using comparative genomic hybridization with SNP-chip. Methylation analyses were assessed by methylation specific-multiplex ligation-dependent probe amplification. Upd(20)pat was identified in 6 patients, all exhibiting typical paternal methylation pattern compared to normal controls, namely a complete loss of methylation of GNAS A/B:TSS-DMR, negligible methylation at GNAS-AS1:TSS-DMR and GNAS-XL:Ex1-DMR and complete gain of methylation at GNAS-NESP:TSS-DMR. The overall frequency of upd(20) is 18% in our cohort when searched considering both severe and partial loss of imprinting. However, twenty five patients displayed severe methylation pattern and the upd(20)pat frequency reaches 24% when searching in this group. Consequently, up to day, upd(20)pat is the most common anomaly than other genetic alterations in spor-PHP1B patients. Upd(20)pat occurrence is not linked to the parental age in contrast to upd(20)mat, strongly associated with an advanced maternal childbearing age. This study provides criteria to guide further investigations for upd(20)pat needed for an adequate genetic counseling.

Molecular characterization of a recurrent 10.9 kb CYP24A1 deletion in Idiopathic Infantile Hypercalcemia.

Loss-of-function mutations in CYP24A1 (MIM 126065 20q13.2), the gene encoding the 24-hydroxylase responsible for 25-OH-D and 1,25-(OH)2D degradation, are identified in about 20% of patients presenting Idiopathic Infantile Hypercalcemia (IIH) (MIM 143880). Common features of this autosomal recessive condition included hypercalcemia with hypercalciuria, suppressed PTH and a high 25-OH-D3:24,25-(OH)2D3 ratio. Medical care mainly relies on sun protection and life-long contraindication of vitamin D to avoid complications such as early nephrocalcinosis and renal failure. Molecular diagnosis therefore keeps a crucial place in the diagnosis of IIH, and genetic counseling should be systematically recommended to prevent vitamin D administration in affected siblings. In this report is described the molecular characterization of a CYP24A1 deletion identified in two unrelated families. This highlights the potential role of CYP24A1 copy number variations (CNV) in IIH. Considering the presence of CNV affecting CYP24A1 in public databases, CNV analysis should be systematically added to the sequencing studies in IIH. Targeted Massively Parallel Sequencing (MPS) study coupled with a CNV detection tool called CovCop is a powerful method to detect genic rearrangement and improve genetic analysis.

Diagnosis and management of pseudohypoparathyroidism and related disorders: first international Consensus Statement.

This Consensus Statement covers recommendations for the diagnosis and management of patients with pseudohypoparathyroidism (PHP) and related disorders, which comprise metabolic disorders characterized by physical findings that variably include short bones, short stature, a stocky build, early-onset obesity and ectopic ossifications, as well as endocrine defects that often include resistance to parathyroid hormone (PTH) and TSH. The presentation and severity of PHP and its related disorders vary between affected individuals with considerable clinical and molecular overlap between the different types. A specific diagnosis is often delayed owing to lack of recognition of the syndrome and associated features. The participants in this Consensus Statement agreed that the diagnosis of PHP should be based on major criteria, including resistance to PTH, ectopic ossifications, brachydactyly and early-onset obesity. The clinical and laboratory diagnosis should be confirmed by a molecular genetic analysis. Patients should be screened at diagnosis and during follow-up for specific features, such as PTH resistance, TSH resistance, growth hormone deficiency, hypogonadism, skeletal deformities, oral health, weight gain, glucose intolerance or type 2 diabetes mellitus, and hypertension, as well as subcutaneous and/or deeper ectopic ossifications and neurocognitive impairment. Overall, a coordinated and multidisciplinary approach from infancy through adulthood, including a transition programme, should help us to improve the care of patients affected by these disorders.

Genetic and Epigenetic Defects at the GNAS Locus Lead to Distinct Patterns of Skeletal Growth but Similar Early-Onset Obesity.

Pseudohypoparathyroidism type 1A (PHP1A), pseudoPHP (PPHP), and PHP type 1B (PHP1B) are caused by maternal and paternal GNAS mutations and abnormal methylation at maternal GNAS promoter(s), respectively. Adult PHP1A patients are reportedly obese and short, whereas most PPHP patients are born small. In addition to parathyroid hormone (PTH) resistance, PHP1A and PHP1B patients may display early-onset obesity. Because early-onset and severe obesity and short stature are daily burdens for PHP1A patients, we aimed at improving knowledge on the contribution of the GNAS transcripts to fetal and postnatal growth and fat storage. Through an international collaboration, we collected growth and weight data from birth until adulthood for 306 PHP1A/PPHP and 220 PHP1B patients. PHP1A/PPHP patients were smaller at birth than healthy controls, especially PPHP (length Z-score: PHP1A -1.1 ± 1.8; PPHP -3.0 ± 1.5). Short stature is observed in 64% and 59% of adult PHP1A and PPHP patients. PHP1B patients displayed early postnatal overgrowth (height Z-score at 1 year: 2.2 ± 1.3 and 1.3 ± 1.5 in autosomal dominant and sporadic PHP1B) followed by a gradual decrease in growth velocity resulting in normal adult height (Z-score for both: -0.4 ± 1.1). Early-onset obesity characterizes GNAS alterations and is associated with significant overweight and obesity in adults (bodey mass index [BMI] Z-score: 1.4 ± 2.6, 2.1 ± 2.0, and 1.4 ± 1.9 in PPHP, PHP1A, and PHP1B, respectively), indicating that reduced Gsα expression is a contributing factor. The growth impairment in PHP1A/PPHP may be due to Gsα haploinsufficiency in the growth plates; the paternal XLαs transcript likely contributes to prenatal growth; for all disease variants, a reduced pubertal growth spurt may be due to accelerated growth plate closure. Consequently, early diagnosis and close follow-up is needed in patients with GNAS defects to screen and intervene in case of early-onset obesity and decreased growth velocity. © 2018 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research (ASBMR).

Genetic Diseases of Vitamin D Metabolizing Enzymes.

Vitamin D metabolism involves 3 highly specific cytochrome P450 (CYP) enzymes (25-hydroxylase, 1α-hydroxylase, and 24-hydroxylase) involved in the activation of vitamin D3 to the hormonal form, 1,25-(OH)2D3, and the inactivation of 1,25-(OH)2D3 to biliary excretory products. Mutations of the activating enzymes CYP2R1 and CYP27B1 cause lack of normal 1,25-(OH)2D3 synthesis and result in rickets whereas mutations of the inactivating enzyme CYP24A1 cause build-up of excess 1,25-(OH)2D3 and result in hypercalcemia, nephrolithiasis, and nephrocalcinosis. This article reviews the literature for 3 clinical conditions. Symptoms, diagnosis, treatment, and management of vitamin D-dependent rickets and idiopathic infantile hypercalcemia are discussed.

Pseudohypoparathyroidism type 1B associated with assisted reproductive technology.

Evidence suggests an increased incidence of imprinting disorders in children conceived by assisted reproductive technologies (ART). Maternal loss-of-methylation at GNAS exon A/B, observed in pseudohypoparathyroidism type 1b (PHP1B), leads to decreased expression of the stimulatory Gsα. We present a patient conceived by ART, who presented at age 4 years with delayed neurocognitive development and persistently increased creatine kinase (CK). At 6 years an elevated PTH was detected with normal calcium and a low 25(OH) vitamin D level (25OHD). Physical exam showed a narrow forehead, nasal bridge hypoplasia and micropenis. After normalizing vitamin D, PTH remained elevated and PHP1B was therefore considered as the underlying diagnosis. An almost complete loss-of-methylation was observed at GNAS exons A/B and AS, but not at exon XL, which was associated with a gain-of-methylation at exon NESP. There was no evidence of a microdeletion within the GNAS/STX16 region and analysis of several microsatellite markers for the GNAS region on Chr.20q revealed no evidence for paternal uniparental disomy (patUPD20q). Established facts Increased incidence of imprinting disorders in children conceived by assisted reproductive technologies (ART) Pseudohypoparathyroidism is caused by imprinting abnormalities. Novel Insights First report of a possible association between a methylation defects that causes PHP1B and assisted conception Increased creatine kinase level was associated with an increase in PTH concentration.

[Hypercalcemia and inactive mutation of CYP24A1. Case-study and literature review]. / Hypercalcémie par mutation inactivatrice du CYP24A1. Étude d'un cas et revue de la littérature.

We present the case of a family whose members have high levels of serum calcium (hypercalcaemia) by loss of function of the enzyme vitamin D 24-hydroxylase due to bi-allelic mutations in the CYP24A1 gene: c.443 T>C (p.Leu148Pro) and c.1187 G>A (p.Arg396Gln). 24-VITD hydroxylase is a key player in regulating the circulating calcitriol, its tissue concentration and its biological effects. Transmission is recessive. The estimated prevalence of stones in the affected subjects is estimated between 10 and 15%. The loss of peripheral catabolism of vitamin D metabolites in patients with an inactivating mutation of CYP24A1 is responsible for persistent high levels of 1,25-dihydroxyvitamin D especially after sun exposure and a charge of native vitamin D. Although there are currently no recommendations (French review) on this subject, this disease should be suspected in association with recurrent calcium stones with nephrocalcinosis, and a calcitriol-dependent hypercalcaemia with adapted low parathyroid hormone levels. Resistance to corticosteroid therapy distinguishes it from other calcitriol-dependent hypercalcemia. A ratio of 25-hydroxyvitamin D/24.25 hydroxyvitamin D>50, is in favor of hypercalcemia with vitamin D deficiency 24-hydroxylase. Genetic analysis of CYP24A1 should be performed at the second step. The current therapeutic management includes the restriction native vitamin D supplementation and the limitation of sun exposure. Biological monitoring will be based on serum calcium control and modulation of parathyroid hormone concentrations.

Vitamin D-Dependent Rickets Type 1B (25-Hydroxylase Deficiency): A Rare Condition or a Misdiagnosed Condition?

Vitamin D requires a two-step activation by hydroxylation: The first step is catalyzed by hepatic 25-hydroxylase (CYP2R1, 11p15.2) and the second one is catalyzed by renal 1α-hydroxylase (CYP27B1, 12q13.1), which produces the active hormonal form of 1,25-(OH)2 D. Mutations of CYP2R1 have been associated with vitamin D-dependent rickets type 1B (VDDR1B), a very rare condition that has only been reported to affect 4 families to date. We describe 7 patients from 2 unrelated families who presented with homozygous loss-of-function mutations of CYP2R1. Heterozygous mutations were present in their normal parents. We identified a new c.124_138delinsCGG (p.Gly42_Leu46delinsArg) variation and the previously published c.296T>C (p.Leu99Pro) mutation. Functional in vitro studies confirmed loss-of-function enzymatic activity in both cases. We discuss the difficulties in establishing the correct diagnosis and the specific biochemical pattern, namely, very low 25-OH-D suggestive of classical vitamin D deficiency, in the face of normal/high concentrations of 1,25-(OH)2 D. Siblings exhibited the three stages of rickets based on biochemical and radiographic findings. Interestingly, adult patients were able to maintain normal mineral metabolism without vitamin D supplementation. One index case presented with a partial improvement with 1alfa-hydroxyvitamin D3 or alfacalcidol (1α-OH-D3 ) treatment, and we observed a dramatic increase in the 1,25-(OH)2 D serum concentration, which indicated the role of accessory 25-hydroxylase enzymes. Lastly, in patients who received calcifediol (25-OH-D3 ), we documented normal 24-hydroxylase activity (CYP24A1). For the first time, and according to the concept of personalized medicine, we demonstrate dramatic improvements in patients who were given 25-OH-D therapy (clinical symptoms, biochemical data, and bone densitometry). In conclusion, the current study further expands the CYP2R1 mutation spectrum. We note that VDDR1B could be easily mistaken for classical vitamin D deficiency. © 2017 American Society for Bone and Mineral Research.

Improved Screening Test for Idiopathic Infantile Hypercalcemia Confirms Residual Levels of Serum 24,25-(OH)2 D3 in Affected Patients.

CYP24A1 mutations are now accepted as a cause of idiopathic infantile hypercalcemia (IIH). A rapid liquid-chromatography tandem mass spectrometry (LC-MS/MS)-based blood test enabling measurement of the 25-OH-D3 :24,25-(OH)2 D3 ratio (R) can identify IIH patients on the basis of reduced C24-hydroxylation of 25-OH-D3 by CYP24A1 in vivo. Although values of this ratio are significantly elevated in IIH, somewhat surprisingly, serum 24,25-(OH)2 D3 remains detectable. The current study explores possible explanations for this including: residual CYP24A1 enzyme activity in individuals with certain CYP24A1 genotypes, expression of alternative C24-hydroxylases, and the possibility of isobaric contamination of the 24,25-(OH)2 D3 peak on LC-MS/MS. We employed an extended 20-min run time on LC-MS/MS to study serum vitamin D metabolites in patients with IIH due to mutations of CYP24A1 or SLC34A1; in unaffected heterozygotes and dialysis patients; in patients with vitamin D deficiency; as well as in normal subjects exhibiting a broad range of 25-OH-D levels. We identified 25,26-(OH)2 D3 as a contaminant of the 24,25-(OH)2 D3 peak. In normals, the concentration of 24,25-(OH)2 D3 greatly exceeds 25,26-(OH)2 D3 ; however, 25,26-(OH)2 D3 becomes more significant in IIH with CYP24A1 mutations and in dialysis patients, where 24,25-(OH)2 D3 levels are low when CYP24A1 function is compromised. Mean R in 30 IIH-CYP24A1 patients was 700 (range, 166 to 2168; cutoff = 140) as compared with 31 in 163 controls. Furthermore, patients possessing CYP24A1 L409S alleles exhibited higher 24,25-(OH)2 D3 levels and lower R (mean R = 268; n = 8) than patients with other mutations. We conclude that a chromatographic approach which resolves 24,25-(OH)2 D3 from 25,26-(OH)2 D3 produces a more accurate R that can be used to differentiate pathological states where CYP24A1 activity is altered. The origin of the residual serum 24,25-(OH)2 D3 in IIH patients appears to be multifactorial. © 2017 American Society for Bone and Mineral Research.

A Large Inversion Involving GNAS Exon A/B and All Exons Encoding Gsα Is Associated With Autosomal Dominant Pseudohypoparathyroidism Type Ib (PHP1B).

Pseudohypoparathyroidism type Ib (PHP1B) is characterized primarily by resistance to parathyroid hormone (PTH) and thus hypocalcemia and hyperphosphatemia, in most cases without evidence for Albright hereditary osteodystrophy (AHO). PHP1B is associated with epigenetic changes at one or several differentially-methylated regions (DMRs) within GNAS, which encodes the α-subunit of the stimulatory G protein (Gsα) and splice variants thereof. Heterozygous, maternally inherited STX16 or GNAS deletions leading to isolated loss-of-methylation (LOM) at exon A/B alone or at all maternal DMRs are the cause of autosomal dominant PHP1B (AD-PHP1B). In this study, we analyzed three affected individuals, the female proband and her two sons. All three revealed isolated LOM at GNAS exon A/B, whereas the proband's healthy maternal grandmother and uncle showed normal methylation at this locus. Haplotype analysis was consistent with linkage to the STX16/GNAS region, yet no deletion could be identified. Whole-genome sequencing of one of the patients revealed a large heterozygous inversion (1,882,433 bp). The centromeric breakpoint of the inversion is located 7,225 bp downstream of GNAS exon XL, but its DMR showed no methylation abnormality, raising the possibility that the inversion disrupts a regulatory element required only for establishing or maintaining exon A/B methylation. Because our three patients presented phenotypes consistent with PHP1B, and not with PHP1A, the Gsα promoter is probably unaffected by the inversion. Our findings expand the spectrum of genetic mutations that lead to LOM at exon A/B alone and thus biallelic expression of the transcript derived from this alternative first GNAS exon. © 2017 American Society for Bone and Mineral Research.

Calcium pyrophosphate deposition disease revealing a hypersensitivity to vitamin D.

OBJECTIVE: Hypersensitivity to vitamin D (HVD) due to a loss of function mutation of the CYP24A1 gene, which encodes vitamin D catabolizing enzyme was initially described as a cause of acute hypercalcemia in children and chronic renal diseases in adults. METHODS: We describe the first case of a patient presenting a calcium pyrophosphate deposition disease (CPDD) revealing a HVD. RESULTS: An abnormality of phospho-calcic metabolism was discovered during the course of an etiological workup for CPDD in a 52-year-old patient. Laboratory tests revealed a blood calcium level at the upper limit of normal range, a markedly low parathormone level, a 25-hydroxyvitamin D level within the upper level of normal, an elevated 1,25-dihydroxyvitamin D level and an elevated urine calcium level. CYP24A1 gene sequencing analysis revealed two mutations in a heterozygous state. The study of the 25-hydroxyvitamin D3: 24,25-dihydroxyvitamin D3 ratio, two metabolites of vitamin D confirmed the enzyme deficiency in vivo. Our observation suggests that this disease could correspond to a rare cause of CPDD. CONCLUSION: In cases of CPDD associated with calcium values within the upper limit of normal range (or hypercalcemia) with an abnormally low PTH, one could suggest searching for HVD.

Genotype-Phenotype Relationship in Patients and Relatives with SHOX Region Anomalies in the French Population.

BACKGROUND: The aim of our study was to describe a large population with anomalies involving the SHOX region, responsible for idiopathic short stature and Léri-Weill dyschondrosteosis (LWD), and to identify a possible genotype/phenotype correlation. METHODS: We performed a retrospective multicenter study on French subjects with a SHOX region anomaly diagnosed by multiplex ligation-dependent probe amplification or Sanger sequencing. Phenotypes were collected in each of the 7 genetic laboratories practicing this technique for SHOX analysis. RESULTS: Among 205 index cases and 100 related cases, 91.3% had LWD. For index cases, median age at evaluation was 11.7 (9.0; 15.9) years and mean height standard deviation score was -2.3 ± 1.1. A deletion of either SHOX or PAR1 or both was found in 74% of patients. Duplications and point mutations/indels affected 8 and 18% of the population, respectively. Genotype-phenotype correlation showed that deletions were more frequently associated with Madelung deformity and mesomelic shortening in girls, as well as with presence of radiologic anomalies, than duplications. CONCLUSIONS: Our results highlight genotype-phenotype relationships in the French population with a SHOX defect and provide new information showing that clinical expression is milder in cases of duplication compared to deletions.

Hyperparathyroidism complicating CYP 24A1 mutations.

CYP24A1 gene mutations induce infantile hypercalcemia, with high 1,25(OH)2D contrasting with low PTH levels. The adult phenotype is not well known. Two unrelated adult patients were referred for nephrolithiasis, hypertension, hypercalcemia, hypercalciuria, normal 25-OHD levels, and inappropriate PTH levels (22 to 92pg/mL;N: 15-68) suggesting primary hyperparathyroidism, leading to surgery. Hypercalciuria improved despite persistent hypercalcemia, treated with cinacalcet. The ratio 25-OHD3/24-25-(OH)2D3>100 (N<25) suggested the diagnosis of CYP24A1 mutations which were confirmed through Sanger sequencing. In conclusion, the adult phenotype associated with CYP24A1 mutations can evolve over time from hypercalcemia with suppressed PTH towards hyperparathyroidism with moderately increased PTH level, adenoma and/or slightly increased parathyroid glands. Surgery decreased calciuria and improved kidney function. Cinacalcet was partially effective on hypercalcemia since PTH was inappropriate. This novel phenotype, a phenocopy of hyperparathyroidism, might evolve in few cases towards hyperparathyroidism despite random association of the 2 diseases cannot be excluded.

Expanding the Spectrum of Founder Mutations Causing Isolated Gonadotropin-Releasing Hormone Deficiency.

CONTEXT: Loss of function (LoF) mutations in more than 20 genes are now known to cause isolated GnRH deficiency (IGD) in humans. Most causal IGD mutations are typically private, ie, limited to a single individual/pedigree. However, somewhat paradoxically, four IGD genes (GNRH1, TAC3, PROKR2, and GNRHR) have been shown to harbor LoF founder mutations that are shared by multiple unrelated individuals. It is not known whether similar founder mutations occur in other IGD genes. OBJECTIVE: The objective of the study was to determine whether shared deleterious mutations in IGD-associated genes represent founder alleles. SETTING: This study was an international collaboration among academic medical centers. METHODS: IGD patients with shared mutations, defined as those documented in three or more unrelated probands in 14 IGD-associated genes, were identified from various academic institutions, the Human Gene Mutation Database, and literature reports by other international investigators. Haplotypes of single-nucleotide polymorphisms and short tandem repeats surrounding the mutations were constructed to assess genetic ancestry. RESULTS: A total of eight founder mutations in five genes, GNRHR (Q106R, R262Q, R139H), TACR3 (W275X), PROKR2 (R85H), FGFR1 (R250Q, G687R), and HS6ST1 (R382W) were identified. Most founder alleles were present at low frequency in the general population. The estimated age of these mutant alleles ranged from 1925 to 5600 years and corresponded to the time of rapid human population expansion. CONCLUSIONS: We have expanded the spectrum of founder alleles associated with IGD to a total of eight founder mutations. In contrast to the approximately 9000-year-old PROKR2 founder allele that may confer a heterozygote advantage, the rest of the founder alleles are relatively more recent in origin, in keeping with the timing of recent human population expansion and any selective heterozygote advantage of these alleles requires further evaluation.

[Paternal GNAS mutations: Which phenotypes? What genetic counseling?]. / Mutations paternelles de GNAS : quels phénotypes ? Quel conseil génétique ?

Parental imprinting and the type of the genetic alteration play a determinant role in the phenotype expression of GNAS locus associated to pseudohypoparathyroidism (PHP). GNAS locus gives rise to several different messenger RNA transcripts that are derived from the paternal allele, the maternal allele, or both and can be either coding or non-coding. As a consequence, GNAS mutations lead to a wide spectrum of phenotypes. An alteration in the coding sequence of the gene leads to a haplo-insufficiency and a dysmorphic phenotype (Albright's syndrome or AHO). AHO is a clinical syndrome defined by specific physical features including short stature, obesity, round-shaped face, subcutaneous ossifications, brachymetarcapy (mainly of the 4th and 5th ray). 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 pseudohypoparathyroidism type 1a (PHP1a). If the alteration is on the paternal allele, there are few clinical signs with no hormonal resistance and the phenotype is known as pseudopseudo hypoparathyroidism (pseudo-PPHP). Heterozygous GNAS mutations on the paternal GNAS allele were associated with intra uterin growth retardation (IUGR). Moreover, birth weights were lower with paternal GNAS mutations affecting exon 2-13 than with exon 1/intron 1 mutations suggesting a role for loss of function XLαs. Progressive osseous heteroplasia (POH) is a rare disease of ectopic bone formation, characterized by cutaneous and subcutaneous ossifications progressing towards deep connective and muscular tissues. POH is caused by a heterozygous GNAS inactivating mutation and has been associated with paternal inheritance. However, genotype/phenotype correlations suggest that there is no direct correlation between the ossifying process and parental origin, as there is high variability in heterotopic ossification. Clinical heterogeneity makes genetic counseling a very delicate matter, specifically where paternal inheritance is concerned as it can lead either to a mild expression of pseudo-PHP or to a severe one of POH.

Diagnosis and management of congenital hypothyroidism associated with pseudohypoparathyroidism.

UNLABELLED: Hypothyroidism is a particular condition observed in pseudohypoparathyroidism (PHP), a rare disorder characterized by parathyroid (PTH) resistance leading to hypocalcemia and hyperphosphatemia associated with a GNAS (guanine nucleotide-binding protein α-subunit) mutation (PHP1A) or epimutation (PHP1B). To determine the presence of hypothyroidism at birth we conducted a retrospective study in our cohort of patients presenting with either PHP1A (n = 116) or PHP1B (n = 99). We also investigated patients presenting at birth with congenital hypothyroidism (CH) and a eutopic thyroid gland for phosphocalcium abnormalities suggesting PTH resistance and PHP. Our study reveals CH as the earliest diagnostic clue for PHP1A, but not for PHP1B. We estimated the frequency of CH at birth to be between 8 and 34% in patients presenting with PHP1A. The elevation of phosphatemia and PTH concentration precedes hypocalcemia in PHP1A. Conversely, the frequency of PHP1A in patients presenting CH is dramatically low. This may be due to the low prevalence of PHP1A which remains unknown. CONCLUSIONS: Subclinical and overt hypothyroidism can occur in PHP1A patients at birth many years before PTH resistance becomes clinically apparent. Although such cases appear to be rare, some pediatric patients with unexplained CH are likely to benefit from measuring calcium, phosphorus, and PTH for extended periods of time.