Variable Bone Phenotypes in Patients with Pseudohypoparathyroidism.

PURPOSE OF REVIEW: Pseudohypoparathyroidism (PHP) is a disorder caused by mutations and/or epigenetic changes at the complex GNAS locus. It is characterized by hypocalcemia, hyperphosphatemia, and an elevated parathyroid hormone concentration secondary to the resistance of target tissues to the biological actions of parathyroid hormone. PHP is divided into several subtypes with different yet overlapping phenotypes. Research on the bone status in patients with PHP is sparse and has yielded inconsistent results. This review was performed to summarize the current knowledge on the bone phenotypes and possible mechanisms of PHP. RECENT FINDINGS: Patients with PHP exhibit highly variable bone phenotypes and increased concentrations of bone turnover markers. Long-standing elevation of the parathyroid hormone concentration may lead to hyperparathyroid bone diseases, including rickets and osteitis fibrosa. Compared with normal controls, patients with PHP may exhibit similar, increased, or decreased bone mineral density. Higher bone mineral density has been found in patients with PHP type 1A than in normal controls, whereas decreased bone mass, osteosclerosis, and osteitis fibrosa cystica have been reported in patients with PHP type 1B, indicating more variable bone phenotypes in PHP type 1B. Bone tissues show partial sensitivity to parathyroid hormone in patients with PHP, leading to heterogeneous reactions to parathyroid hormone in different individuals and even in different regions of bone tissues in the same individual. Regions rich in cancellous bone are more sensitive and show more obvious improvement after therapy. Active vitamin D and calcium can significantly improve abnormal bone metabolism in patients with PHP.

The role of ZFP57 and additional KRAB-zinc finger proteins in the maintenance of human imprinted methylation and multi-locus imprinting disturbances.

Genomic imprinting is an epigenetic process regulated by germline-derived DNA methylation that is resistant to embryonic reprogramming, resulting in parental origin-specific monoallelic gene expression. A subset of individuals affected by imprinting disorders (IDs) displays multi-locus imprinting disturbances (MLID), which may result from aberrant establishment of imprinted differentially methylated regions (DMRs) in gametes or their maintenance in early embryogenesis. Here we investigated the extent of MLID in a family harbouring a ZFP57 truncating variant and characterize the interactions between human ZFP57 and the KAP1 co-repressor complex. By ectopically targeting ZFP57 to reprogrammed loci in mouse embryos using a dCas9 approach, we confirm that ZFP57 recruitment is sufficient to protect oocyte-derived methylation from reprogramming. Expression profiling in human pre-implantation embryos and oocytes reveals that unlike in mice, ZFP57 is only expressed following embryonic-genome activation, implying that other KRAB-zinc finger proteins (KZNFs) recruit KAP1 prior to blastocyst formation. Furthermore, we uncover ZNF202 and ZNF445 as additional KZNFs likely to recruit KAP1 to imprinted loci during reprogramming in the absence of ZFP57. Together, these data confirm the perplexing link between KZFPs and imprint maintenance and highlight the differences between mouse and humans in this respect.

Genetic and Epigenetic Characteristics of Autosomal Dominant Pseudohypoparathyroidism Type 1B: Case Reports and Literature Review.

Autosomal dominant pseudohypoparathyroidism 1B (AD-PHP1B) is a rare endocrine and imprinted disorder. The objective of this study is to clarify the imprinted regulation of the guanine nucleotide binding-protein α-stimulating activity polypeptide 1 (GNAS) cluster in the occurrence and development of AD-PHP1B based on animal and clinical patient studies. The methylation-specific multiples ligation-dependent probe amplification (MS-MLPA) was conducted to detect the copy number variation in syntaxin-16 (STX16) gene and methylation status of the GNAS differentially methylated regions (DMRs). Long-range PCR was used to confirm deletion at STX16 gene. In the first family, DNA analysis of the proband and proband's mother revealed an isolated loss of methylation (LOM) at exon A/B and a 3.0 kb STX16 deletion. The patient's healthy grandmother had the 3.0 kb STX16 deletion but no epigenetic abnormality. The patient's healthy maternal aunt showed no genetic or epigenetic abnormality. In the second family, the analysis of long-range PCR revealed the 3.0 kb STX16 deletion for the proband but not her children. In this study, 3.0 kb STX16 deletion causes isolated LOM at exon A/B in two families, which is the most common genetic mutation of AD-PHP1B. The deletion involving NESP55 or AS or genomic rearrangements of GNAS can also result in AD-PHP1B, but it's rare. LOM at exon A/B DMR is prerequisite methylation defect of AD-PHP1B. STX16 and NESP55 directly control the imprinting at exon A/B, while AS controls the imprinting at exon A/B by regulating the transcriptional level of NESP55.

Manifestations of left ventricular dysfunction and arrhythmia in patients with chronic hypoparathyroidism and pseudohypoparathyroidism: a preliminary study.

BACKGROUND: Cardiac damage triggered by severe hypocalcemia is well known. However, the role of chronic hypoparathyroidism (HP) and pseudohypoparathyroidism (PHP) in cardiac health is still unclear. We investigated the effect of chronic HP and PHP on cardiac structure and conductive function in patients compiling with treatment. METHODS: The study included 18 patients with HP and eight with PHP aged 45.4 ± 15.4 and 22.1 ± 6.4 years, respectively with a previously regular follow-up. In addition, 26 age- and sex-matched healthy controls were included. General characteristics and biochemical indices were recorded. Cardiac function and structure were assessed by estimation of myocardial enzymes, B-type natriuretic peptide (BNP), and echocardiography. The 12-lead electrocardiogram and 24-h Holter electrocardiography were performed to evaluate the conductive function. RESULTS: Levels of serum calcium in HP and PHP were 2.05 ± 0.16 mmol/L and 2.25 ± 0.19 mmol/L, respectively. The levels of myocardial enzyme and BNP were within the normal range. Adjusting for age at evaluation and body mass index, all M-mode measurements, left ventricular mass (LVM), LVM index (LVMI) and relative wall thickness (RWT) were comparable between patients and controls. Prolongation of corrected QT (QTc) intervals occurred in 52.6% (10/19) of patients, and 6.7% (1/15) of patients manifested more than 100 episodes of supraventricular and ventricular extrasystoles, as well as supraventricular tachycardia. None of the above arrhythmias was related to a severe clinical event. CONCLUSIONS: From this pilot study, patients diagnosed with HP and PHP and well-controlled serum calcium levels manifested normal cardiac morphology and ventricular function, except for prolonged QTc intervals, and a small percentage of mild arrhythmias needing further investigation.

Identification of novel pathogenic variants and features in patients with pseudohypoparathyroidism and acrodysostosis, subtypes of the newly classified inactivating PTH/PTHrP signaling disorders.

Albright hereditary osteodystrophy (AHO) is a complex disorder defined by the presence of a short adult stature relative to the height of an unaffected parent and brachydactyly type E, as well as a stocky build, round face, and ectopic calcifications. AHO and pseudohypoparathyroidism (PHP) have been used interchangeably in the past. The term PHP describes end-organ resistance to parathyroid hormone (PTH), occurring with or without the physical features of AHO. Conversely, pseudopseudohypoparathyroidism (PPHP) describes individuals with AHO features in the absence of PTH resistance. PHP and PPHP are etiologically linked and caused by genetic and/or epigenetic alterations in the guanine nucleotide-binding protein alpha-stimulating (Gs α) locus (GNAS) in chromosome 20q13. Another less-recognized group of skeletal dysplasias, termed acrodysostosis, partially overlap with skeletal, endocrine, and neurodevelopmental features of AHO/PHP and can be overlooked in clinical practice, causing confusion in the literature. Acrodysostosis is caused by defects in two genes, PRKAR1A and PDE4D, both encoding important components of the Gs α-cyclic adenosine monophosphate-protein kinase A signaling pathway. We describe the clinical course and genotype of two adult patients with overlapping AHO features who harbored novel pathogenic variants in GNAS (c.2273C > G, p.Pro758Arg, NM_080425.2) and PRKAR1A (c.803C > T, p.Ala268Val, NM_002734.4), respectively. We highlight the value of expert radiological opinion and molecular testing in establishing correct diagnoses and discuss phenotypic features of our patients, including the first description of subcutaneous ossification and spina bifida occulta in PRKAR1A-related acrodysostosis, in the context of the novel inactivating PTH/PTH related peptide signaling disorder classification system.

Different biochemical properties explain why two equivalent Gα subunit mutants cause unrelated diseases.

There is an increasing number of disease-associated Gα mutations identified from genome-wide sequencing campaigns or targeted efforts. Albright's Hereditary Osteodystrophy (AHO) was the first inherited disease associated with loss-of-function mutations in a G protein (Gαs) and other studies revealed gain-of-function Gα mutations in cancer. Here we attempted to solve the apparent quandary posed by the fact that the same mutation in two different G proteins appeared associated with both AHO and cancer. We first confirmed the presence of an inherited Gαs-R265H mutation from a previously described clinical case report of AHO. This mutation is structurally analogous to Gαo-R243H, an oncogenic mutant with increased activity in vitro and in cells due to rapid nucleotide exchange. We found that, contrary to Gαo-R243H, Gαs-R265H activity is compromised due to greatly impaired nucleotide binding in vitro and in cells. We obtained equivalent results when comparing another AHO mutation in Gαs (D173N) with a counterpart cancer mutation in Gαo (D151N). Gαo-R243H binds nucleotides efficiently under steady-state conditions but releases GDP much faster than the WT protein, suggesting diminished affinity for the nucleotide. These results indicate that the same disease-linked mutation in two different G proteins affects a common biochemical feature (nucleotide affinity) but to a different grade depending on the G protein (mild decrease for Gαo and severe for Gαs). We conclude that Gαs-R265H has dramatically impaired nucleotide affinity leading to the loss-of-function in AHO whereas Gαo-R243H has a mild decrease in nucleotide affinity that causes rapid nucleotide turnover and subsequent hyperactivity in cancer.

Deletion of the NESP55 differentially methylated region causes loss of maternal GNAS imprints and pseudohypoparathyroidism type Ib.

Epigenetic defects in the imprinted GNAS cluster are associated with pseudohypoparathyroidism type Ib. In two kindreds with this disorder, we now report deletions that remove the differentially methylated region encompassing exon NESP55 and exons 3 and 4 of the antisense transcript. When inherited from a female, either deletion abolishes all maternal GNAS imprints and derepresses maternally silenced transcripts, suggesting that the deleted region contains a cis-acting element that controls imprinting of the maternal GNAS allele.

Simultaneous hyper- and hypomethylation at imprinted loci in a subset of patients with GNAS epimutations underlies a complex and different mechanism of multilocus methylation defect in pseudohypoparathyroidism type 1b.

Most patients with pseudohypoparathyroidism type 1b (PHP-1b) display a loss of imprinting (LOI) encompassing the GNAS locus resulting in PTH resistance. In other imprinting disorders, such as Russell-Silver or Beckwith-Wiedemann syndrome, we and others have shown that the LOI is not restricted to one imprinted locus but may affect other imprinted loci for some patients. Therefore, we hypothesized that patients with PHP-1b might present multilocus imprinting defects. We investigated, in 63 patients with PHP-1b, the methylation pattern of eight imprinted loci: GNAS, ZAC1, PEG1/MEST, ICR1, and ICR2 on chromosome 11p15, SNRPN, DLK1/GTL2 IG-DMR, and L3MBTL1. We found multilocus imprinting defects in four PHP-1b patients carrying broad LOI at the GNAS locus (1) simultaneous hypermethylation at L3MBTL1 differentially methylated region 3 (DMR3), and hypomethylation at PEG1/MEST DMR (n = 1), (2) hypermethylation at the L3MBTL1 (DMR3) (n = 1) and at the DLK1/GTL2 IG-DMR (n = 1), and (3) hypomethylation at the L3MBTL1 DMR3 (n = 1). We suggest that mechanisms underlying multilocus imprinting defects in PHP-1b differ from those of other imprinting disorders having only multilocus loss of methylation. Furthermore, our results favor the hypothesis of "epidominance", that is, the phenotype is controlled by the most severely affected imprinted locus.

Energy expenditure in obese children with pseudohypoparathyroidism type 1a.

CONTEXT: Patients with pseudohypoparathyroidism type 1a (PHP-1a) develop early-onset obesity. The abnormality in energy expenditure and/or energy intake responsible for this weight gain is unknown. OBJECTIVE: The aim of this study was to evaluate energy expenditure in children with PHP-1a compared with obese controls. PATIENTS: We studied 6 obese females with PHP-1a and 17 obese female controls. Patients were recruited from a single academic center. MEASUREMENTS: Resting energy expenditure (REE) and thermogenic effect of a high fat meal were measured using whole room indirect calorimetry. Body composition was assessed using whole body dual energy x-ray absorptiometry. Fasting glucose, insulin, and hemoglobin A1C were measured. RESULTS: Children with PHP-1a had decreased REE compared with obese controls (P<0.01). After adjustment for fat-free mass, the PHP-1a group's REE was 346.4 kcals day(-1) less than obese controls (95% CI (-585.5--106.9), P<0.01). The thermogenic effect of food (TEF), expressed as percent increase in postprandial energy expenditure over REE, was lower in PHP-1a patients than obese controls, but did not reach statistical significance (absolute reduction of 5.9%, 95% CI (-12.2-0.3%), P=0.06). CONCLUSIONS: Our data indicate that children with PHP-1a have decreased REE compared with the obese controls, and that may contribute to the development of obesity in these children. These patients may also have abnormal diet-induced thermogenesis in response to a high-fat meal. Understanding the causes of obesity in PHP-1a may allow for targeted nutritional or pharmacologic treatments in the future.

Application of calcium-to-phosphorus (Ca/P) ratio in the diagnosis of pseudohypoparathyroidism: another piece in the puzzle of diagnosis of Ca-P metabolism disorders.

Objective: The serum calcium (Ca)-to-phosphorus (P) ratio has been proposed to identify patients with primary hyperparathyroidism and chronic hypoparathyroidism (HPT), but it has never been tested in pseudohypoparathyroidism (PHP). The aim of this study was to test the performance of Ca/P ratio in PHP diagnosis compared with that in healthy subjects and patients with HPT for differential diagnosis. Design: A retrospective, cross-sectional, and observational study was carried out. Methods: Serum Ca, P, creatinine, parathyroid hormone (PTH), and albumin were collected. Ca and P were expressed in mmol/L. Ca/P diagnostic performance was evaluated by receiver operating characteristic curve, sensitivity, specificity, and accuracy. Results: A total of 60 patients with PHP, 60 patients with HPT, and 120 controls were enrolled. The Ca/P ratio was lower in patients with PHP and HPT than that in controls (p < 0.0001). The cutoff of 1.78 (2.32 if Ca and P measured in mg/dL) for Ca/P ratio could identify patients with PHP and HPT among the entire cohort (sensitivity and specificity of 76%). No valid cutoff of Ca/P was found to distinguish patients with PHP from patients with HPT; in this case, PTH above 53.0 ng/dL identified patients with PHP (sensitivity and specificity of 100%). The index (Ca/P × PTH) above 116 ng/L recognized patients with PHP from controls (sensitivity of 84.7% and specificity of 87.4%), whereas (Ca/P × PTH) below 34 ng/L recognized patients with HPT from controls (sensitivity of 88.9% and specificity of 90.8%). Conclusions: The Ca/P ratio below 1.78 (2.32 CU) is highly accurate to identify patients with PHP and HPT, although it is not reliable to differentiate these two conditions. The index (Ca/P × PTH) is excellent to specifically recognize PHP or HPT from healthy subjects.

Acute down-regulation of sodium-dependent phosphate transporter NPT2a involves predominantly the cAMP/PKA pathway as revealed by signaling-selective parathyroid hormone analogs.

The parathyroid hormone (PTH)/PTH-related peptide (PTHrP) receptor (PTHR1) in cells of the renal proximal tubule mediates the reduction in membrane expression of the sodium-dependent P(i) co-transporters, NPT2a and NPT2c, and thus suppresses the re-uptake of P(i) from the filtrate. In most cell types, the liganded PTHR1 activates Gα(S)/adenylyl cyclase/cAMP/PKA (cAMP/PKA) and Gα(q/11)/phospholipase C/phosphatidylinositol 1,4,5-trisphosphate (IP(3))/Ca(2+)/PKC (IP(3)/PKC) signaling pathways, but the relative roles of each pathway in mediating renal regulation P(i) transport remain uncertain. We therefore explored the signaling mechanisms involved in PTH-dependent regulation of NPT2a function using potent, long-acting PTH analogs, M-PTH(1-28) (where M = Ala(1,12), Aib(3), Gln(10), Har(11), Trp(14), and Arg(19)) and its position 1-modified variant, Trp(1)-M-PTH(1-28), designed to be phospholipase C-deficient. In cell-based assays, both M-PTH(1-28) and Trp(1)-M-PTH(1-28) exhibited potent and prolonged cAMP responses, whereas only M-PTH(1-28) was effective in inducing IP(3) and intracellular calcium responses. In opossum kidney cells, a clonal cell line in which the PTHR1 and NPT2a are endogenously expressed, M-PTH(1-28) and Trp(1)-M-PTH(1-28) each induced reductions in (32)P uptake, and these responses persisted for more than 24 h after ligand wash-out, whereas that of PTH(1-34) was terminated by 4 h. When injected into wild-type mice, both M-modified PTH analogs induced prolonged reductions in blood P(i) levels and commensurate reductions in NPT2a expression in the renal brush border membrane. Our findings suggest that the acute down-regulation of NPT2a expression by PTH ligands involves mainly the cAMP/PKA signaling pathway and are thus consistent with the elevated blood P(i) levels seen in pseudohypoparathyroid patients, in whom Gα(s)-mediated signaling in renal proximal tubule cells is defective.

Establishment of diagnosis by bisulfite-treated methylation-specific PCR method and analysis of clinical characteristics of pseudohypoparathyroidism type 1b.

Pathogenesis of pseudohypoparathyroidism type 1b (PHP-1b) is related to the loss of methylation at the GNAS exon A/B region, which is combined with epigenetic defects at other differentially methylated GNAS regions in most sporadic cases. In this study, we established a method for evaluating the methylation status of a CpG island in exon A/B using a methylation-specific polymerase chain reaction (MSPCR). We designed two primer pairs specific for the methylated and unmethylated alleles and evaluated the methylation status of GNAS exon A/B in samples from PHP-1b patients and normal controls. We examined 20 Japanese patients and 20 normal controls, and one primer set was found to be appropriate for diagnosis. Furthermore, we evaluated the clinical data of patients. Weight and height of patients were not significantly different from the normal population. Short stature (adult height ≤ 2SD) was observed in one patient and short metacarpals in two. Obesity was observed in six patients, and no patient showed ectopic subcutaneous calcification. Seven patients showed subclinical hypothyroidism because of resistance to thyroid stimulating hormone, but no patient had an abnormally low free thyroxine level, and none received oral thyroid hormone replacement. For diagnosis of PHP-1b, only clinical data is not sufficient because a few PHP-1b patients show clinical features similar to PHP-1a, and hence, molecular biology techniques are required for correct diagnosis. We concluded that MSPCR is applicable for rapid molecular diagnosis of PHP-1b.

Spectrum of neurological manifestations of idiopathic hypoparathyroidism and pseudohypoparathyroidism.

We describe clinical, biochemical, radiological profile, and treatment outcome in 97 patients with idiopathic hypoparathyroidism seen over a period of 18 years. Of the 97 patients, 78 (80%) had idiopathic hypoparathyroidism and 19 (20%) had pseudohypoparathyroidism. The mean age±standard deviation (SD) at presentation was 28.7±14.1 years. There were 52 males, the mean lag time from first reported symptom to diagnosis was 5.9±5.2 years and the mean (±SD) follow-up was 1.8±0.4 years. The most common presenting manifestation was carpopedal spasm in 68 (70%) patients, followed by paresthesia and seizures in 52 (54%) patients. The mean (±SD) serum calcium and inorganic phosphate concentrations were 6.1±1.5 mg/dl and 6.3±1.5 mg/dl, respectively. The most common imaging abnormality noted was basal ganglia calcification followed by cerebral cortex and cerebellum calcification. More than one-third of patients were on various antiepileptic drugs including phenytoin. In addition to oral calcium and active vitamin D (calcitriol), twenty-six patients (27%) also required hydrochlorothiazide. The important finding in our study was long lag time from the first reported symptom to diagnosis. Phenytoin was the drug in almost one- third of our patients with seizures. Practicing clinicians should have high index of suspicion of diagnosis hypoparathyroidism in the appropriate clinical states to avoid the morbidity associated with hypoparathyroidism. Phenytoin should be avoided in patients with hypoparathyroidism and seizures.

PTH resistance.

Parathyroid hormone (PTH), which is primarily regulated by extracellular calcium changes, controls calcium and phosphate homeostasis. Different diseases are derived from PTH deficiency (hypoparathyroidism), excess (hyperparathyroidism) and resistance (pseudohypoparathyroidism, PHP). Pseudohypoparathyroidism was historically classified into subtypes according to the presence or not of inherited PTH resistance associated or not with features of Albright's hereditary osteodystrophy and deep and progressive ectopic ossifications. The growing knowledge on the PTH/PTHrP signaling pathway showed that molecular defects affecting different members of this pathway determined distinct, yet clinically related disorders, leading to the proposal of a new nomenclature and classification encompassing all disorders, collectively termed inactivating PTH/PTHrP signaling disorders (iPPSD).

Hereditary osteodystrophy with multiple hormone resistance--a case report.

Hereditary Osteodystrophy, also called pseudohypoparathyroidism, Type 1A (PHP), is a very rare condition composed of a heterogeneous group of autosomal dominant disorders with the common feature of organ resistance to multiple hormones. These patients produce the right amount of hormones but there is resistance to its effect. PHP is difficult to diagnose and the lack of diagnosis may have serious implications for the patient. We report a case of PHP, diagnosed by the dentist, due to the dental and jaw manifestations.

Inactivating PTH/PTHrP Signaling Disorders.

Pseudohypoparathyroidism (PHP), pseudo-PHP, acrodysostosis, and progressive osseous heteroplasia are heterogeneous disorders characterized by physical findings, differently associated in each subtype, including short bones, short stature, a stocky build, ectopic ossifications (features associated with Albright's hereditary osteodystrophy), as well as laboratory abnormalities consistent with hormone resistance, such as hypocalcemia, hyperphosphatemia, and elevated parathyroid hormone (PTH) and thyroid-stimulating hormone levels. All these disorders are caused by impairments in the cAMP-mediated signal transduction pathway and, in particular, in the PTH/PTHrP signaling pathway: the main subtypes of PHP and related disorders are caused by de novo or autosomal dominantly inherited inactivating genetic mutations, and/or epigenetic, sporadic, or genetic-based alterations within or upstream of GNAS, PRKAR1A, PDE4D, and PDE3A. Here we will review the impressive progress that has been made over the past 30 years on the pathophysiology of these diseases and will describe the recently proposed novel nomenclature and classification. The new term "inactivating PTH/PTHrP signaling disorder," iPPSD: (1) defines the common mechanism responsible for all diseases, (2) does not require a confirmed genetic defect, (3) avoids ambiguous terms like "pseudo," and (4) eliminates the clinical or molecular overlap between diseases.

PCR-based analysis of differentially methylated regions of GNAS enables convenient diagnostic testing of pseudohypoparathyroidism type Ib.

BACKGROUND: Pseudohypoparathyroidism type Ib (PHPIb) is characterized by parathyroid hormone (PTH) resistance, which can lead to hypocalcemia, hyperphosphatemia, and increased serum PTH. The disorder is caused by mutations in regulatory regions of the GNAS gene (GNAS complex locus) that lead to interferences in the methylation status of alternative GNAS promoters, such as exon A/B, NESP55, and XL alpha-s. PHPIb comprises disorders that show distinctive changes in methylation status but share the same clinical phenotype: (a) loss of methylation only at exon A/B of the GNAS gene and involving no other obvious epigenetic abnormalities [e.g., those caused by heterozygous microdeletions in the STX16 (syntaxin 16) region and found in many patients with autosomal dominant (AD) PHPIb]; (b) methylation abnormalities at several differentially methylated regions (DMRs), which are observed in most patients with sporadic PHPIb and some families with AD PHPIb. METHODS: To permit early and reliable diagnosis of suspected PHPIb, we designed methylation-sensitive restriction enzyme-based and bisulfite deamination-based PCR tests for exon A/B and NESP55 DMRs. RESULTS: Both PCR strategies permit proper methylation testing of GNAS and NESP55 DMRs and elucidate different disease subtypes. We have identified a novel microsatellite repeat polymorphism within GNAS exon A/B, and pedigree analyses have shown its presence to be conclusive evidence for familial disease. CONCLUSIONS: We provide a simple diagnostic test for PHPIb, an imprinting disorder caused by different molecular changes within the GNAS complex locus. PHPIb, a complex and diagnostically challenging clinical phenotype, can be treated successfully by taking steps before the manifestation of symptoms to avoid clinical complications in affected patients or asymptomatic members of affected families who show positive results in genetic tests.

Multiple hormone resistance and alterations of G-protein-coupled receptors signaling.

Metabolic disorders deriving from the non-responsiveness of target organs to hormones, which manifest clinically similar to the deficiency of a given hormone itself, derive from molecular alterations affecting specific hormone receptors. Pseudohypoparathyroidism (PHP) and related disorders exemplify an unusual form of hormone resistance as the underlying molecular defect is a partial deficiency of the α subunit of the stimulatory G protein (Gsα), a key regulator of cAMP signaling pathway, or, as more recently described, of downstream effector proteins of the same pathway, such as PKA regulatory subunit 1A (R1A) and phosphodyestarase type 4D (PDE4D). In this group of diseases, resistance to hormones such as PTH, TSH, gonadotropins and GHRH may be variably present, so that the clinical and molecular overlap among these different but related disorders represents a challenge for endocrinologists as to differential diagnosis and genetic counseling. This review will describe the presenting features of multiple resistance in PHP and related disorders, focusing on both our current understanding and future challenges.

Glucose Homeostasis and Energy Balance in Children With Pseudohypoparathyroidism.

Context: Pseudohypoparathyroidism (PHP) is a rare genetic disorder characterized by early-onset obesity and multihormone resistance. To treat abnormal weight gain and prevent complications such as diabetes, we must understand energy balance and glucose homeostasis in PHP types 1A and 1B. Objective: The aim of this study was to evaluate food intake, energy expenditure, and glucose homeostasis in children with PHP. Design: Assessments included resting energy expenditure (REE), physical activity, food intake, sucrose preference, questionnaires, endocrine status, and auxological status. All patients underwent an oral glucose tolerance test (OGTT). Setting: Vanderbilt University Medical Center. Patients: We assessed 16 children with PHP1A, three with PHP1B, and 15 healthy controls. Main Outcome Measures: Food intake during an ad lib buffet meal and glucose at five time points during OGTT. Results: PHP1A and control groups were well matched. Participants with PHP1A had significantly lower REE without concomitant change in food intake or physical activity. At baseline, participants with PHP1A had significantly lower fasting glucose and insulin resistance. During OGTT, participants with PHP1A had significantly delayed peak glucose and a slower rate of glucose decline despite similar oral glucose insulin sensitivity. Participants with PHP1A had 0.46% lower HbA1c levels than controls from a clinic database after adjustment for OGTT 2-hour glucose. The PHP1B group was similar to the PHP1A group. Conclusions: In contrast to other monogenic obesity syndromes, our results support reduced energy expenditure, not severe hyperphagia, as the primary cause of abnormal weight gain in PHP. Patients with PHP are at high risk for dysglycemia without reduced insulin sensitivity.

Constitutive stimulatory G protein activity in limb mesenchyme impairs bone growth.

GNAS mutations leading to constitutively active stimulatory G protein alpha-subunit (Gsα) cause different tumors, fibrous dysplasia of bone, and McCune-Albright syndrome, which are typically not associated with short stature. Enhanced signaling of the parathyroid hormone/parathyroid hormone-related peptide receptor, which couples to multiple G proteins including Gsα, leads to short bones with delayed endochondral ossification. It has remained unknown whether constitutive Gsα activity also impairs bone growth. Here we generated mice expressing a constitutively active Gsα mutant (Gsα-R201H) conditionally upon Cre recombinase (cGsαR201H mice). Gsα-R201H was expressed in cultured bone marrow stromal cells from cGsαR201H mice upon adenoviral-Cre transduction. When crossed with mice in which Cre is expressed in a tamoxifen-regulatable fashion (CAGGCre-ER™), tamoxifen injection resulted in mosaic expression of the transgene in double mutant offspring. We then crossed the cGsαR201H mice with Prx1-Cre mice, in which Cre is expressed in early limb-bud mesenchyme. The double mutant offspring displayed short limbs at birth, with narrow hypertrophic chondrocyte zones in growth plates and delayed formation of secondary ossification center. Consistent with enhanced Gsα signaling, bone marrow stromal cells from these mice demonstrated increased levels of c-fos mRNA. Our findings indicate that constitutive Gsα activity during limb development disrupts endochondral ossification and bone growth. Given that Gsα haploinsufficiency also leads to short bones, as in patients with Albright's hereditary osteodystrophy, these results suggest that a tight control of Gsα activity is essential for normal growth plate physiology.