Evaluating the variety of GNAS inactivation disorders and their clinical manifestations in 11 Chinese children.

BACKGROUND: The GNAS gene on chromosome 20q13.3, encodes the alpha-subunit of the stimulatory G protein, which is expressed in most tissues and regulated through reciprocal genomic imprinting. Disorders of GNAS inactivation produce several different clinical phenotypes including pseudohypoparathyroidism (PHP), pseudopseudohypoparathyroidism (PPHP), progressive osseous heteroplasia (POH), and osteoma cutis (OC). The clinical and biochemical characteristics overlap of PHP subtypes and other related disorders presents challenges for differential diagnosis. METHODS: We enrolled a total of 11 Chinese children with PHP in our study and analyzed their clinical characteristics, laboratory results, and genetic mutations. RESULTS: Among these 11 patients, nine of them (9/11) presented with resistance to parathyroid hormone (PTH); and nine (9/11) presented with an Albright's hereditary osteodystrophy (AHO) phenotype. GNAS abnormalities were detected in all 11 patients, including nine cases with GNAS gene variations and two cases with GNAS methylation defects. These GNAS variations included an intronic mutation (c.212 + 3_212 + 6delAAGT), three missense mutations (c.314C > T, c.308 T > C, c.1123G > T), two deletion mutations (c.565_568delGACT*2, c.74delA), and two splicing mutations (c.721 + 1G > A, c.432 + 1G > A). Three of these mutations, namely, c.314C > T, c.1123G > T, and c.721 + 1G > A, were found to be novel. This data was then used to assign a GNAS subtype to each of these patients with six cases diagnosed as PHP1a, two cases as PHP1b, one as PPHP, and two as POH. CONCLUSIONS: Evaluating patients with PTH resistance and AHO phenotype improved the genetic diagnosis of GNAS mutations significantly. In addition, our results suggest that when GNAS gene sequencing is negative, GNAS methylation study should be performed. Early genetic detection is required for the differential diagnosis of GNAS disorders and is critical to the clinician's ability to distinguish between heterotopic ossification in the POH and AHO phenotype.

Management of pseudohypoparathyroidism.

PURPOSE OF REVIEW: This review is timely given the 2018 publication of the first international Consensus Statement for the diagnosis and management of pseudohypoparathyroidism (PHP) and related disorders. The purpose of this review is to provide the knowledge needed to recognize and manage PHP1A, pseudopseudohypoparathyroidism (PPHP) and PHP1B - the most common of the subtypes - with an overview of the entire spectrum and to provide a concise summary of management for clinical use. This review will draw from recent literature as well as personal experience in evaluating hundreds of children and adults with PHP. RECENT FINDINGS: Progress is continually being made in understanding the mechanisms underlying the PHP spectrum. Every year, through clinical and laboratory studies, the phenotypes are elucidated in more detail, as are clinical issues such as short stature, brachydactyly, subcutaneous ossifications, cognitive/behavioural impairments, obesity and metabolic disturbances. Headed by a European PHP consortium, experts worldwide published the first international Consensus that provides detailed guidance in a systematic manner and will lead to exponential progress in understanding and managing these disorders. SUMMARY: As more knowledge is gained from clinical and laboratory investigations, the mechanisms underlying the abnormalities associated with PHP are being uncovered as are improvements in management.

Late-onset subcutaneous scalp calcifications in a patient with pseudo-pseudohypoparathyroidism.

Ectopic calcifications and even bone formation have been linked to GNAS gene mutations. A 51-year-old Caucasian female had been diagnosed of pseudo-pseudohypoparathyroidism (PPHP) in 1989. She has always had normal serum parathyroid hormone, calcium, and phosphorus levels. A non-contrast computed tomography of the head was done in 2013 and it showed finely speckled subcutaneous calcifications in the high convexity of the head. Cutaneous exploration did not show any abnormality. We herein report an unusual case of late-onset scalp calcifications in a patient with PPHP.

Pseudohypoparathyroidism type Ia and pseudo-pseudohypoparathyroidism: the growing spectrum of GNAS inactivating mutations.

Pseudohypoparathyroidism (PHP) is a rare heterogeneous genetic disorder characterized by end-organ resistance to parathyroid hormone due to partial deficiency of the α subunit of the stimulatory G protein (Gsα), encoded by the GNAS gene. Heterozygous inactivating GNAS mutations lead to either PHP type Ia (PHP-Ia), when maternally inherited, or pseudo-pseudohypoparathroidism (PPHP), if paternally derived. Both diseases feature typical physical traits identified as Albright's hereditary osteodystrophy in the presence or absence of multihormone resistance, respectively. GNAS mutations are detected in 60-70% of affected subjects, most patients/families harbor private mutations and no genotype-phenotype correlation has been found to date. We investigated Gsα-coding GNAS exons in a large panel of PHP-Ia-PPHP patients collected over the past decade in the two Italian referring centers for PHP. Of 49 patients carrying GNAS mutations, we identified 15 novel mutations in 19 patients. No apparent correlation was found between clinical/biochemical data and results of molecular analysis. Furthermore, we summarized the current knowledge of GNAS molecular pathology and updated the GNAS-locus-specific database. These results further expand the spectrum of GNAS mutations associated with PHP/PPHP and underline the importance of identifying such genetic alterations to supplement clinical evaluation and genetic counseling.

Brachydactyly mental retardation syndrome in differential diagnosis of pseudopseudohypoparathyroidism.

Patients with Albright hereditary osteodystrophy (AHO) phenotype are usually seen in pediatric endocrinology policlinics when they are evaluated for short stature and/or obesity. Brachydactyly mental retardation syndrome (BDMR, OMIM #600430) is a rare genetic disorder caused by aberrations of chromosomal region 2q37 and characterized with AHO-like phenotype without any hormone resistance. Diagnosis of BDMR is based on the detection of the deletion on the long arm of chromosome 2. Diagnosis can usually be made with karyotype analysis but sometimes chromosomal deletion can only be detected by fluorescent in situ hybridization (FISH) screening. We report a patient with the AHO phenotype whose karyotype was normal but who was diagnosed with BDMR with FISH analysis showing 2q deletion. In pediatric endocrinology practice, in patients with AHO phenotype but without parathormone (PTH) resistance, BDMR should be considered. For the diagnosis of BDMR, the subtelomeric region of chromosome 2 should be screened for deletion by FISH analysis even in patients with normal karyotypes.

Clinical characterization and identification of two novel mutations of the GNAS gene in patients with pseudohypoparathyroidism and pseudopseudohypoparathyroidism.

OBJECTIVE: Pseudohypoparathyroidism (PHP) and pseudopseudohypoparathyroidism (PPHP) are rare disorders resulting from genetic and epigenetic aberrations in the GNAS locus. DESIGN: Investigation of clinical characteristics and molecular analysis in PHP and PPHP. PATIENTS: Fourteen subjects from 13 unrelated families including subjects with PPHP (n = 1), PHP-Ia (n = 6) and PHP-Ib (n = 7) were enrolled. MEASUREMENTS: Clinical data, including age at presentation, presenting symptom, auxological findings, family history, presence of Albright hereditary osteodystrophy (AHO) features and hormonal and biochemical findings, were analysed. The GNAS locus was subjected to direct sequencing and methylation analysis using methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA). RESULTS: Of the 13 PHP subjects, 10 (three PHP-Ia and seven PHP-Ib) presented with hypocalcemic tetany at ages ranging from 7 to 14·8 years. Subcutaneous calcification was observed as an early manifestation of AHO in one PHP-Ia patient (age, 2·9 years) and one PPHP patient (age, 7 months). Six PHP-Ia and one PPHP harboured four different heterozygous mutations within the coding region of GNAS, p.Asp189_Tyr190delinsMetfxX14, p.Val117fsX23, p.Tyr190CysfsX19, and a splicing mutation (c.659 + 1G>A), of which the latter two were novel. Five subjects with PHP-Ib exhibited complete loss of the maternal-specific methylation pattern. The remaining two PHP-Ib showed a loss of methylation of exon 1A on the maternal allele as a consequence of heterozygous 3-kb microdeletions within the STX16 gene. CONCLUSIONS: GNAS mutation analyses and MS-MLPA assays are useful molecular tools for understanding the molecular bases and confirming the diagnosis of PHP and PPHP.

[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.

Albright hereditary osteodystrophy: a rare case report.

Albright hereditary osteodystrophy (AHO) is a rare hereditary metabolic disorder that may be associated with or without resistant to parathyroid hormone (pseudohypoparathyroidism). It is commonly characterized by a constellation of physical features of short stature, round face, short neck, and small metacarpals and metatarsals, mild mental retardation, osteoporosis, subcutaneous calcification, and sometimes olfactory and hearing functional defect. Hypocalcaemia and hyperphosphatemia are the most important manifestations of the case. We report a clinical case of siblings with AHO with reduced Gs-alpha activity and we discuss their clinical features with oral manifestations, radiographic findings, laboratory tests along with treatment.

A Case of Soft Tissue Ossifications: A Case Report.

CASE: A patient who had previously been diagnosed with fibrodysplasia ossificans progressiva was seen for hip pain and progressive soft tissue ossifications. Through a careful clinical examination, by which a subtype of brachydactyly was noted, the Albright hereditary osteodystrophy phenotype was recognized, and a new diagnosis of pseudopseudohypoparathyroidism was established. This paucisymptomatic condition often remains unidentified; however, its transmission can lead to more potentially serious diseases. CONCLUSIONS: A careful diagnostic process, including physical examination, is essential. Even if advanced tests exist, small clinical findings can lead to the proper conclusion. In our case, a finger pointed us in the right direction.

Cognitive impairment is prevalent in pseudohypoparathyroidism type Ia, but not in pseudopseudohypoparathyroidism: possible cerebral imprinting of Gsalpha.

OBJECTIVE: Pseudohypoparathyroidism type Ia (PHP-Ia) is a hereditary disorder characterized by resistance to multiple hormones that work via cAMP such as PTH and TSH, accompanied by typical skeletal features including short stature and brachydactyly, termed Albright hereditary osteodystrophy (AHO). In affected kindreds, some members may have AHO but not hormone resistance; they are termed as pseudopseudohypoparathyroidism (PPHP). The molecular basis for the disorder is heterozygous inactivating mutation of the Gsalpha gene. In affected families, subjects with both PHP-Ia and PPHP have the same Gsalpha mutations. The skeletal features common to PPHP and PHP-Ia are presumably caused by tissue-specific Gsalpha haploinsufficiency. Other features that distinguish between PPHP and PHP-Ia, such as the multihormone resistance, are presumably caused by tissue-specific paternal imprinting of Gsalpha. This suggests that major differences in phenotype between PHP-Ia and PPHP point to specific tissues with Gsalpha imprinting. One such major difference may be cognitive function in PHP-Ia and PPHP. DESIGN: Description of a large family with PHP-Ia and PPHP. PATIENTS: Eleven affected subjects with PHP-Ia or PPHP in one family. MEASUREMENTS: Cognitive impairment (CI) was defined by a history of developmental delay, learning disability and the Wechsler intelligence scale. RESULTS: CI occurred only in the five PHP-Ia but not in the six PPHP subjects. Hypothyroidism which occurred in all PHP-Ia subjects was apparently not the cause of CI as it was mild, and was treated promptly. Analysis of additional Israeli cases, and the published cases from the literature, all with documented Gsalpha mutations, revealed that CI is prevalent in PHP-Ia [60 of 77 subjects (79%)] but not in PPHP [3 of 30 subjects (10%)] (P < 1 x 10(-6)). CONCLUSION: We suggest that Gsalpha is imprinted in the brain.

[Pseudopseudohypoparathyroidism and genomic imprinting].

Pseudopseudohypoparathyroidism (PPHP) is caused by the paternally-derived mutation in the coding region of GNAS gene. The phenotype of PPHP is produced by the sum of both decreased Gsalpha protein in biallelically expressed tissues and other proteins or non-coding RNAs by mutated paternal-allele specific expression. It has been believed that the haploinsufficiency of Gsalpha in non-imprinted tissues is responsible for the Albright hereditary dystrophy (AHO) phenotype. Recently it was reported that obesity is a more prominent feature in pseudohypoparathyroidism type I a than in PPHP. This result implicates paternal imprinting in the development of obesity in pseudohypoparathyroidism type I a. In this review, recent advances in clinical and experimental knowledge in genomic imprinting of GNAS gene were summarized.

[GNAS1 gene abnormality in pseudohypoparathyroidism I a].

Pseudophypoparathyroidism (PHP) is characterized by hypocalcemia, hyperphosphatemia and elevated levels of parathyroid hormone (PTH) due to resistance to PTH. PHP type I a is caused by heterozygous inactivating mutation of the GNAS1 gene, which encodes signal transducer, Gsalpha. PHP type I a is associated with Albright's osteodystrophy (AHO). Those patients who have AHO phenotype without hormone resistance are affected by pseudopseudohypoparathyroidism.

Mutations in the Gs alpha gene causing hormone resistance.

G-protein-coupled receptors (GPCRs) and G proteins mediate the effects of a number of hormones of relevance to endocrinology. Genes encoding these molecules may be targets of loss- or gain-of-function mutations, resulting in endocrine disorders. The only mutational change of G proteins so far unequivocally associated with endocrine disorders occurs in the Gsalpha gene (GNAS1, guanine nucleotide binding protein alpha stimulating activity polypeptide 1), which activates cyclic AMP (cAMP)-dependent pathways. Heterozygous loss-of-function mutations of GNAS1 in the active maternal allele cause resistance to hormones acting through Gsalpha-coupled GPCRs, whereas somatic gain-of-function mutations cause proliferation of endocrine cells recognizing cAMP as mitogen. This review will focus on inactivating mutations leading to hormone resistance syndromes, i.e., pseudohypoparathyroidism types Ia and Ib.

Different mutations within or upstream of the GNAS locus cause distinct forms of pseudohypoparathyroidism.

The term pseudohypoparathyroidism (PHP) refers to different disorders that are caused by mutations within GNAS or upstream of this complex genetic locus. GNAS gives rise to several different transcripts, including Gs alpha (alpha-subunit of the heterotrimeric stimulatory G protein), XL alpha s (extra-large variant of Gs alpha), and several additional sense and antisense transcripts. The complexity of the GNAS locus is furthermore reflected by a parent-specific methylation pattern of most of its different promoters. PHP can be divided into two major groups, PHP type Ia (PHP-Ia) and PHP type Ib (PHP-Ib). PHP-Ia is caused by heterozygous mutations affecting one of the 13 GNAS exons encoding Gs alpha. In contrast, PHP-Ib is caused by heterozygous deletions within STX16, the gene encoding syntaxin 16, which is located more than 220 kb upstream of GNAS, or by deletions within GNAS involving exon NESP55 and two of the antisense exons. In either form of PHP, hormonal resistance develops only after maternal inheritance of the mutation, while paternal inheritance of the same molecular defect is not associated with endocrine abnormalities. In most familial cases of PHP-Ib, there is a loss of exon A/B methylation combined with active A/B transcription from both parental alleles, which leads to suppression of Gs alpha transcription in the proximal renal tubules and, therefore, PTH resistance.

Screening of PRKAR1A and PDE4D in a Large Italian Series of Patients Clinically Diagnosed With Albright Hereditary Osteodystrophy and/or Pseudohypoparathyroidism.

The cyclic adenosine monophosphate (cAMP) intracellular signaling pathway mediates the physiological effects of several hormones and neurotransmitters, acting by the activation of G-protein coupled receptors (GPCRs) and several downstream intracellular effectors, including the heterotrimeric stimulatory G-protein (Gs), the cAMP-dependent protein kinase A (PKA), and cAMP-specific phosphodiesterases (PDEs). Defective G-protein-mediated signaling has been associated with an increasing number of disorders, including Albright hereditary osteodistrophy (AHO) and pseudohypoparathyroidism (PHP), a heterogeneous group of rare genetic metabolic disorders resulting from molecular defects at the GNAS locus. Moreover, mutations in PRKAR1A and PDE4D genes have been recently detected in patients with acrodysostosis (ACRDYS), showing a skeletal and endocrinological phenotype partially overlapping with AHO/PHP. Despite the high detection rate of molecular defects by currently available molecular approaches, about 30% of AHO/PHP patients still lack a molecular diagnosis, hence the need to screen patients negative for GNAS epi/genetic defects also for chromosomal regions and genes associated with diseases that undergo differential diagnosis with PHP. According to the growing knowledge on Gsα-cAMP signaling-linked disorders, we investigated our series of patients (n = 81) with a clinical diagnosis of PHP/AHO but negative for GNAS anomalies for the presence of novel genetic variants at PRKAR1A and PDE4D genes. Our work allowed the detection of 8 novel missense variants affecting genes so far associated with ACRDYS in 9 patients. Our data further confirm the molecular and clinical overlap among these disorders. We present the data collected from a large series of patients and a brief review of the literature in order to compare our findings with already published data; to look for PRKAR1A/PDE4D mutation spectrum, recurrent mutations, and mutation hot spots; and to identify specific clinical features associated with ACRDYS that deserve surveillance during follow-up. © 2016 American Society for Bone and Mineral Research.

Ablation of the Stimulatory G Protein α-Subunit in Renal Proximal Tubules Leads to Parathyroid Hormone-Resistance With Increased Renal Cyp24a1 mRNA Abundance and Reduced Serum 1,25-Dihydroxyvitamin D.

PTH regulates serum calcium, phosphate, and 1,25-dihydroxyvitamin D (1,25(OH)2D) levels by acting on bone and kidney. In renal proximal tubules (PTs), PTH inhibits reabsorption of phosphate and stimulates the synthesis of 1,25(OH)2D. The PTH receptor couples to multiple G proteins. We here ablated the α-subunit of the stimulatory G protein (Gsα) in mouse PTs by using Cre recombinase driven by the promoter of type-2 sodium-glucose cotransporter (Gsα(Sglt2KO) mice). Gsα(Sglt2KO) mice were normophosphatemic but displayed, relative to controls, hypocalcemia (1.19 ±0.01 vs 1.23 ±0.01 mmol/L; P < .05), reduced serum 1,25(OH)2D (59.3 ±7.0 vs 102.5 ±12.2 pmol/L; P < .05), and elevated serum PTH (834 ±133 vs 438 ±59 pg/mL; P < .05). PTH-induced elevation in urinary cAMP excretion was blunted in Gsα(Sglt2KO) mice (2- vs 4-fold over baseline in controls; P < .05). Relative to baseline in controls, PTH-induced reduction in serum phosphate tended to be blunted in Gsα(Sglt2KO) mice (-0.39 ±0.33 vs -1.34 ±0.36 mg/dL; P = .07). Gsα(Sglt2KO) mice showed elevated renal vitamin D 24-hydroxylase and bone fibroblast growth factor-23 (FGF23) mRNA abundance (∼3.4- and ∼11-fold over controls, respectively; P < .05) and tended to have elevated serum FGF23 (829 ±76 vs 632 ±60 pg/mL in controls; P = .07). Heterozygous mice having constitutive ablation of the maternal Gsα allele (E1(m-/+)) (model of pseudohypoparathyroidism type-Ia), in which Gsα levels in PT are reduced, also exhibited elevated serum FGF23 (474 ±20 vs 374 ±27 pg/mL in controls; P < .05). Our findings indicate that Gsα is required in PTs for suppressing renal vitamin D 24-hydroxylase mRNA levels and for maintaining normal serum 1,25(OH)2D.