Substantially Delayed Maturation of Growth Plate Chondrocytes in "Humanized" PTH1R Mice with the H223R Mutation of Jansen's Disease.

Activating parathyroid hormone (PTH)/PTH-related Peptide (PTHrP) receptor (PTH1R) mutations causes Jansen's metaphyseal chondrodysplasia (JMC), a rare disease characterized by growth plate abnormalities, short stature, and PTH-independent hypercalcemia. Previously generated transgenic JMC mouse models, in which the human PTH1R allele with the H223R mutation (H223R-PTH1R) is expressed in osteoblasts via type Ia1 collagen or DMP1 promoters cause excess bone mass, while expression of the mutant allele via the type IIa1 collagen promoter results in only minor growth plate changes. Thus, neither transgenic JMC model adequately recapitulates the human disease. We therefore generated "humanized" JMC mice in which the H223R-PTH1R allele was expressed via the endogenous mouse Pth1r promoter and, thus, in all relevant target tissues. Founders with the H223R allele typically died within 2 months without reproducing; several mosaic male founders, however, lived longer and produced F1 H223R-PTH1R offspring, which were small and exhibited marked growth plate abnormalities. Serum calcium and phosphate levels of the mutant mice were not different from wild-type littermates, but serum PTH and P1NP were reduced significantly, while CTX-1 and CTX-2 were slightly increased. Histological and RNAscope analyses of the mutant tibial growth plates revealed markedly expanded zones of type II collagen-positive, proliferating/prehypertrophic chondrocytes, abundant apoptotic cells in the growth plate center and a progressive reduction of type X collagen-positive hypertrophic chondrocytes and primary spongiosa. The "humanized" H223R-PTH1R mice are likely to provide a more suitable model for defining the JMC phenotype and for assessing potential treatment options for this debilitating disease of skeletal development and mineral ion homeostasis. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Recombinant growth hormone improves growth and adult height in patients with maternal inactivating GNAS mutations.

BACKGROUND: Maternal inactivating GNAS mutations lead to pseudohypoparathyroidism 1A (PHP1A), newly classified as inactivating parathyroid hormone (PTH)/PTHrP-signaling disorder type 2 of maternal inheritance (iPPSD2). Patients present with resistance to PTH and other hormones, subcutaneous ossifications, brachydactyly, short stature, and early-onset obesity. They can be born small for gestational age (SGA) and may present with growth hormone (GH) deficiency. The use of recombinant human GH (rhGH) therapy has been sporadically reported, yet we lack data on the long-term efficacy and safety of rhGH, as well as on adult height. OBJECTIVE: Our multicenter, retrospective, observational study describes growth in patients treated with rhGH in comparison with untreated iPPSD2/PHP1A controls. METHODS: We included 190 patients, of whom 26 received rhGH. Height, weight, body mass index at various time points, and adult height were documented. We analyzed the effect of rhGH on adult height by using linear mixed models. RESULTS: Adult height was available for 11/26 rhGH-treated individuals and for 69/164 controls. Patients treated with rhGH showed a gain in height of 0.7 standard deviation scores (SDS) after 1 year (CI +0.5 to +0.8, P < .001) and of 1.5 SDS after 3 years (CI +1.0 to +2.0, P < .001). Additionally, there was a clear beneficial impact of rhGH on adult height when compared with untreated controls, with a difference of 1.9 SDS (CI +1.1 to +2.7, P < .001). Body mass index SDS did not vary significantly upon rhGH therapy. CONCLUSION: Recombinant human growth hormone treatment of iPPSD2/PHP1A patients with short stature improves growth and adult height. More studies are needed to confirm long-term efficacy and safety.

Homozygous Ser-1 to Pro-1 mutation in parathyroid hormone identified in hypocalcemic patients results in secretion of a biologically inactive pro-hormone.

Like other secreted peptides, nascent parathyroid hormone (PTH) is synthesized with a pre- and a pro-sequence (25 and 6 amino acids, respectively). These precursor segments are sequentially removed in parathyroid cells before packaging into secretory granules. Three patients from two unrelated families who presented during infancy with symptomatic hypocalcemia were found to have a homozygous serine (S) to proline (P) change affecting the first amino acid of the mature PTH. Unexpectedly, biological activity of synthetic [P1]PTH(1-34) was indistinguishable from that of unmodified [S1]PTH(1-34). However, in contrast to conditioned medium from COS-7 cells expressing prepro[S1]PTH(1-84), medium from cells expressing prepro[P1]PTH(1-84) failed to stimulate cAMP production despite similar PTH levels when measured by an intact assay that detects PTH(1-84) and large amino-terminally truncated fragments thereof. Analysis of the secreted, but inactive PTH variant led to the identification of pro[P1]PTH(-6 to +84). Synthetic pro[P1]PTH(-6 to +34) and pro[S1]PTH(-6 to +34) had much less bioactivity than the corresponding PTH(1-34) analogs. Unlike pro[S1]PTH(-6 to +34), pro[P1]PTH(-6 to +34) was resistant to cleavage by furin suggesting that the amino acid variant impairs preproPTH processing. Consistent with this conclusion, plasma of patients with the homozygous P1 mutation had elevated proPTH levels, as determined with an in-house assay specific for pro[P1]PTH(-6 to +84). In fact, a large fraction of PTH detected by the commercial intact assay represented the secreted pro[P1]PTH. In contrast, two commercial biointact assays that use antibodies directed against the first few amino acid residues of PTH(1-84) for capture or detection failed to detect pro[P1]PTH.

Targeted Long-Read Sequencing Identifies a Retrotransposon Insertion as a Cause of Altered GNAS Exon A/B Methylation in a Family With Autosomal Dominant Pseudohypoparathyroidism Type 1b (PHP1B).

Pseudohypoparathyroidism type Ib (PHP1B) is characterized predominantly by resistance to parathyroid hormone (PTH) leading to hypocalcemia and hyperphosphatemia. These laboratory abnormalities are caused by maternal loss-of-methylation (LOM) at GNAS exon A/B, which reduces in cis expression of the stimulatory G protein α-subunit (Gsα). Paternal Gsα expression in proximal renal tubules is silenced through unknown mechanisms, hence LOM at exon A/B reduces further Gsα protein in this kidney portion, leading to PTH resistance. In a previously reported PHP1B family, affected members showed variable LOM at exon A/B, yet no genetic defect was found by whole-genome sequencing despite linkage to GNAS. Using targeted long-read sequencing (T-LRS), we discovered an approximately 2800-bp maternally inherited retrotransposon insertion nearly 1200 bp downstream of exon XL not found in public databases or in 13,675 DNA samples analyzed by short-read whole-genome sequencing. T-LRS data furthermore confirmed normal methylation at exons XL, AS, and NESP and showed that LOM comprising exon A/B is broader than previously thought. The retrotransposon most likely causes the observed epigenetic defect by impairing function of a maternally derived NESP transcript, consistent with findings in mice lacking full-length NESP mRNA and in PHP1B patients with deletion of exon NESP and adjacent intronic sequences. In addition to demonstrating that T-LRS is an effective strategy for identifying a small disease-causing variant that abolishes or severely reduces exon A/B methylation, our data demonstrate that this sequencing technology has major advantages for simultaneously identifying structural defects and altered methylation. © 2022 American Society for Bone and Mineral Research (ASBMR).

Progression of PTH Resistance in Autosomal Dominant Pseudohypoparathyroidism Type Ib Due to Maternal STX16 Deletions.

CONTEXT: Maternally inherited STX16 deletions that cause loss of methylation at GNAS exon A/B and thereby reduce Gsα expression are the most frequent cause of autosomal dominant pseudohypoparathyroidism type Ib (AD-PHP1B). Early identification of these disease-causing variants in the children of affected and unaffected female carriers would prompt treatment with calcium and calcitriol once parathyroid hormone (PTH) levels increase, thereby preventing hypocalcemia and associated complications. OBJECTIVE: This study aimed to determine when PTH and calcium abnormalities develop after birth if a STX16 deletion is inherited maternally. METHODS: Forty-four children of affected (n = 7) or unaffected (n = 7) females with a STX16 deletion were investigated for the presence of these variants. If a deletion was identified, measurement of PTH, calcium, phosphate, and thyrotropin (TSH) was advised. RESULTS: The STX16 deletion that causes AD-PHP1B was identified in 25 children. Pretreatment laboratory results were available for 19 of those cases. Elevated PTH levels were detected by 2 years of age, and these were progressively higher if laboratory testing was first performed after establishing the genetic defect later in life. Total serum calcium levels remained within normal limits until about 5 years of age. TSH levels showed no consistent rise over time. CONCLUSION: Establishing whether a STX16 deletion is inherited from a female carrier of a disease-causing variant rapidly establishes the diagnosis of AD-PHP1B. Several years before overt hypocalcemia developed, PTH levels increased, thereby establishing the onset of PTH resistance. Our findings provide diagnostic guidance and when treatment with calcium and calcitriol should be considered in order to prevent hypocalcemia and associated sequelae.

Lack of GNAS Remethylation During Oogenesis May Be a Cause of Sporadic Pseudohypoparathyroidism Type Ib.

CONTEXT: Pseudohypoparathyroidism type Ib (PHP1B) is characterized by hypocalcemia and hyperphosphatemia due to parathyroid hormone resistance in the proximal renal tubules. Maternal pathogenic STX16/GNAS variants leading to maternal epigenetic GNAS changes impair expression of the stimulatory G protein alpha-subunit (Gsα) thereby causing autosomal dominant PHP1B. In contrast, genetic defects responsible for sporadic PHP1B (sporPHP1B) remain mostly unknown. OBJECTIVE: Determine whether PHP1B encountered after in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) causes GNAS remethylation defects similar to those in sporPHP1B. DESIGN: Retrospective analysis. RESULTS: Nine among 36 sporPHP1B patients investigated since 2000, all with loss of methylation (LOM) at the 3 maternal GNAS differentially methylated regions (DMRs) and gain of methylation at the paternal NESP DMR, had been conceived through IVF or ICSI. Besides abnormal GNAS methylation, IVF/ICSI PHP1B cases revealed no additional imprinting defects. Three of these PHP1B patients have dizygotic twins, and 4 have IVF/ICSI-conceived siblings, all with normal GNAS methylation; 2 unaffected younger siblings were conceived naturally. CONCLUSION: Sporadic and IVF/ICSI-conceived PHP1B patients revealed indistinguishable epigenetic changes at all 4 GNAS DMRs, thus suggesting a similar underlying disease mechanism. Given that remethylation at the 3 maternal DMRs occurs during oogenesis, male factors are unlikely to cause LOM postfertilization. Instead, at least some of the sporPHP1B variants could be caused by a defect or defects in an oocyte-expressed gene that is required for fertility and for re-establishing maternal GNAS methylation imprints. It remains uncertain, however, whether the lack of GNAS remethylation alone and the resulting reduction in Gsα expression is sufficient to impair oocyte maturation.

A Novel Familial PHP1B Variant With Incomplete Loss of Methylation at GNAS-A/B and Enhanced Methylation at GNAS-AS2.

CONTEXT: Pseudohypoparathyroidism type 1B (PHP1B), also referred to as inactivating PTH/PTHrP signaling disorder (iPPSD), is characterized by proximal renal tubular resistance to parathyroid hormone (PTH) leading to hypocalcemia, hyperphosphatemia, and elevated PTH values. Autosomal dominant PHP1B (AD-PHP1B) with loss of methylation at the maternal GNAS A/B:TSS-DMR (transcription start site-differentially methylated region) alone can be caused by maternal deletions involving STX16. OBJECTIVE: Characterize a previously not reported AD-PHP1B family with loss of methylation at GNAS A/B:TSS-DMR, but without evidence for a STX16 deletion on the maternal allele and assess GNAS-AS2:TSS-DMR methylation. METHODS: DNA from 24 patients and 10 controls were investigated. AD-PHP1B patients without STX16 deletion from a single family (n = 5), AD-PHP1B patients with STX16 deletion (n = 9), sporPHP1B (n = 10), unaffected controls (n = 10), patUPD20 (n = 1), and matUPD20 (n = 1). Methylation and copy number analyses were performed by pyrosequencing, methylation-sensitive multiplex ligation-dependent probe amplification, and multiplex ligation-dependent probe amplification. RESULTS: Molecular cloning of polymerase chain reaction-amplified, bisulfite-treated genomic DNA from healthy controls revealed evidence for 2 distinct GNAS-AS2:TSS-DMR subdomains, named AS2-1 and AS2-2, which showed 16.0 ±â€…2.3% and 31.0 ±â€…2.2% methylation, respectively. DNA from affected members of a previously not reported AD-PHP1B family without the known genetic defects revealed incomplete loss of methylation at GNAS A/B:TSS-DMR, normal methylation at the 3 well-established maternal and paternal DMRs, and, surprisingly, increased methylation at AS2-1 (32.9 ±â€…3.5%), but not at AS2-2 (30.5 ±â€…2.9%). CONCLUSION: The distinct methylation changes at the novel GNAS-AS2:TSS-DMR will help characterize further different PHP1B/iPPSD3 variants and will guide the search for underlying genetic defects, which may provide novel insights into the mechanisms underlying GNAS methylation.

Inactivating PTH/PTHrP signaling disorders (iPPSDs): evaluation of the new classification in a multicenter large series of 544 molecularly characterized patients.

OBJECTIVE: Pseudohypoparathyroidism and related disorders belong to a group of heterogeneous rare diseases that share an impaired signaling downstream of Gsα-protein-coupled receptors. Affected patients may present with various combination of symptoms including resistance to PTH and/or to other hormones, ectopic ossifications, brachydactyly type E, early onset obesity, short stature and cognitive difficulties. Several years ago we proposed a novel nomenclature under the term of inactivating PTH/PTHrP signaling disorders (iPPSD). It is now of utmost importance to validate these criteria and/or improve the basis of this new classification. DESIGN: Retrospective study of a large international series of 459 probands and 85 relatives molecularly characterized. METHODS: Information on major and minor criteria associated with iPPSD and genetic results were retrieved from patient files. We compared the presence of each criteria according to the iPPSD subtype, age and gender of the patients. RESULTS: More than 98% of the probands met the proposed criteria for iPPSD classification. Noteworthy, most patients (85%) presented a combination of symptoms rather than a single sign suggestive of iPPSD and the overlap among the different genetic forms of iPPSD was confirmed. The clinical and molecular characterization of relatives identified familial history as an additional important criterion predictive of the disease. CONCLUSIONS: The phenotypic analysis of this large cohort confirmed the utility of the major and minor criteria and their combination to diagnose iPPSD. This report shows the importance of having simple and easily recognizable signs to diagnose with confidence these rare disorders and supports a better management of patients.

Pseudohypoparathyroidism type 1B (PHP1B), a rare disorder encountered in adolescence.

Objectives The objective of this paper is to report a peculiar case of a patient with pseudohypoparathyroidism type 1b (PHP1B). Pseudohypoparathyroidism (PHP) refers to a group of disorders characterized by hypocalcemia, hyperphosphatemia, and elevated parathyroid hormone (PTH) concentrations as the result of end-organ unresponsiveness to PTH. Case presentation We present a 14-year-old boy, who was admitted with severe symptomatic hypocalcaemia, absence of dysmorphic features and Albright's hereditary osteodystrophy features. Laboratory investigations revealed markedly low serum calcium, high phosphate, markedly elevated PTH levels and vitamin D insufficiency, while magnesium, albumin, ALP and TSH were normal. The clinical and laboratory findings were consistent with PHP1B. Molecular analysis revealed loss of methylation at the AB DMR of the GNAS locus, confirming the diagnosis. Yet no STX16 deletion was detected. Conclusions It is possible that delSTX16- patients carry a defect in an element that controls the methylation both at the GNAS-A/B DMR and at the GNAS-AS2. This rare case emphasizes the need of individualized molecular analysis in PHP1B patients in order to elucidate the possible molecular defect.

Recommendations for Diagnosis and Treatment of Pseudohypoparathyroidism and Related Disorders: An Updated Practical Tool for Physicians and Patients.

Patients affected by pseudohypoparathyroidism (PHP) or related disorders are characterized by physical findings that may include brachydactyly, a short stature, a stocky build, early-onset obesity, ectopic ossifications, and neurodevelopmental deficits, as well as hormonal resistance most prominently to parathyroid hormone (PTH). In addition to these alterations, patients may develop other hormonal resistances, leading to overt or subclinical hypothyroidism, hypogonadism and growth hormone (GH) deficiency, impaired growth without measurable evidence for hormonal abnormalities, type 2 diabetes, and skeletal issues with potentially severe limitation of mobility. PHP and related disorders are primarily clinical diagnoses. Given the variability of the clinical, radiological, and biochemical presentation, establishment of the molecular diagnosis is of critical importance for patients. It facilitates management, including prevention of complications, screening and treatment of endocrine deficits, supportive measures, and appropriate genetic counselling. Based on the first international consensus statement for these disorders, this article provides an updated and ready-to-use tool to help physicians and patients outlining relevant interventions and their timing. A life-long coordinated and multidisciplinary approach is recommended, starting as far as possible in early infancy and continuing throughout adulthood with an appropriate and timely transition from pediatric to adult care.

The mercapturic acid pathway.

The mercapturic acid pathway is a major route for the biotransformation of xenobiotic and endobiotic electrophilic compounds and their metabolites. Mercapturic acids (N-acetyl-l-cysteine S-conjugates) are formed by the sequential action of the glutathione transferases, γ-glutamyltransferases, dipeptidases, and cysteine S-conjugate N-acetyltransferase to yield glutathione S-conjugates, l-cysteinylglycine S-conjugates, l-cysteine S-conjugates, and mercapturic acids; these metabolites constitute a "mercapturomic" profile. Aminoacylases catalyze the hydrolysis of mercapturic acids to form cysteine S-conjugates. Several renal transport systems facilitate the urinary elimination of mercapturic acids; urinary mercapturic acids may serve as biomarkers for exposure to chemicals. Although mercapturic acid formation and elimination is a detoxication reaction, l-cysteine S-conjugates may undergo bioactivation by cysteine S-conjugate ß-lyase. Moreover, some l-cysteine S-conjugates, particularly l-cysteinyl-leukotrienes, exert significant pathophysiological effects. Finally, some enzymes of the mercapturic acid pathway are described as the so-called "moonlighting proteins," catalytic proteins that exert multiple biochemical or biophysical functions apart from catalysis.

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).

Adrenal GIPR expression and chromosome 19q13 microduplications in GIP-dependent Cushing's syndrome.

GIP-dependent Cushing's syndrome is caused by ectopic expression of glucose-dependent insulinotropic polypeptide receptor (GIPR) in cortisol-producing adrenal adenomas or in bilateral macronodular adrenal hyperplasias. Molecular mechanisms leading to ectopic GIPR expression in adrenal tissue are not known. Here we performed molecular analyses on adrenocortical adenomas and bilateral macronodular adrenal hyperplasias obtained from 14 patients with GIP-dependent adrenal Cushing's syndrome and one patient with GIP-dependent aldosteronism. GIPR expression in all adenoma and hyperplasia samples occurred through transcriptional activation of a single allele of the GIPR gene. While no abnormality was detected in proximal GIPR promoter methylation, we identified somatic duplications in chromosome region 19q13.32 containing the GIPR locus in the adrenocortical lesions derived from 3 patients. In 2 adenoma samples, the duplicated 19q13.32 region was rearranged with other chromosome regions, whereas a single tissue sample with hyperplasia had a 19q duplication only. We demonstrated that juxtaposition with cis-acting regulatory sequences such as glucocorticoid response elements in the newly identified genomic environment drives abnormal expression of the translocated GIPR allele in adenoma cells. Altogether, our results provide insight into the molecular pathogenesis of GIP-dependent Cushing's syndrome, occurring through monoallelic transcriptional activation of GIPR driven in some adrenal lesions by structural variations.

The Prevalence of GNAS Deficiency-Related Diseases in a Large Cohort of Patients Characterized by the EuroPHP Network.

CONTEXT: The term pseudohypoparathyroidism (PHP) was coined to describe the clinical condition resulting from end-organ resistance to parathormone (rPTH), caused by genetic and/or epigenetic alterations within or upstream of GNAS. Although knowledge about PHP is growing, there are few data on the prevalence of underlying molecular defects. OBJECTIVE: The purpose of our study was to ascertain the relative prevalence of PHP-associated molecular defects. DESIGN: With a specially designed questionnaire, we collected data from all patients (n = 407) clinically and molecularly characterized to date by expert referral centers in France, Italy, and Spain. RESULTS: Isolated rPTH (126/407, 31%) was caused only by epigenetic defects, 70% of patients showing loss of imprinting affecting all four GNAS differentially methylated regions and 30% loss of methylation restricted to the GNAS A/B:TSS-DMR. Multihormone resistance with no Albright's hereditary osteodystrophy (AHO) signs (61/407, 15%) was essentially due to epigenetic defects, although 10% of patients had point mutations. In patients with rPTH and AHO (40/407, 10%), the rate of point mutations was higher (28%) and methylation defects lower (about 70%). In patients with multihormone resistance and AHO (155/407, 38%), all types of molecular defects appeared with different frequencies. Finally, isolated AHO (18/407, 4%) and progressive osseous heteroplasia (7/407, 2%) were exclusively caused by point mutations. CONCLUSION: With European data, we have established the prevalence of various genetic and epigenetic lesions in PHP-affected patients. Using these findings, we will develop objective criteria to guide cost-effective strategies for genetic testing and explore the implications for management and prognosis.

From pseudohypoparathyroidism to inactivating PTH/PTHrP signalling disorder (iPPSD), a novel classification proposed by the EuroPHP network.

OBJECTIVE: Disorders caused by impairments in the parathyroid hormone (PTH) signalling pathway are historically classified under the term pseudohypoparathyroidism (PHP), which encompasses rare, related and highly heterogeneous diseases with demonstrated (epi)genetic causes. The actual classification is based on the presence or absence of specific clinical and biochemical signs together with an in vivo response to exogenous PTH and the results of an in vitro assay to measure Gsa protein activity. However, this classification disregards other related diseases such as acrodysostosis (ACRDYS) or progressive osseous heteroplasia (POH), as well as recent findings of clinical and genetic/epigenetic background of the different subtypes. Therefore, the EuroPHP network decided to develop a new classification that encompasses all disorders with impairments in PTH and/or PTHrP cAMP-mediated pathway. DESIGN AND METHODS: Extensive review of the literature was performed. Several meetings were organised to discuss about a new, more effective and accurate way to describe disorders caused by abnormalities of the PTH/PTHrP signalling pathway. RESULTS AND CONCLUSIONS: After determining the major and minor criteria to be considered for the diagnosis of these disorders, we proposed to group them under the term 'inactivating PTH/PTHrP signalling disorder' (iPPSD). This terminology: (i) defines the common mechanism responsible for all diseases; (ii) does not require a confirmed genetic defect; (iii) avoids ambiguous terms like 'pseudo' and (iv) eliminates the clinical or molecular overlap between diseases. We believe that the use of this nomenclature and classification will facilitate the development of rationale and comprehensive international guidelines for the diagnosis and treatment of iPPSDs.

Probing the catalytic potential of the hamster arylamine N-acetyltransferase 2 catalytic triad by site-directed mutagenesis of the proximal conserved residue, Tyr190.

Arylamine N-acetyltransferases (NATs) play an important role in both the detoxification of arylamine and hydrazine drugs and the activation of arylamine carcinogens. Because the catalytic triad, Cys-His-Asp, of mammalian NATs has been shown to be essential for maintaining protein stability, rendering it impossible to assess alterations of the triad on catalysis, we explored the impact of the highly conserved proximal residue, Tyr190, which forms a direct hydrogen bond interaction with one of the triad residues, Asp122, as well as a potential pi-pi stacking interaction with the active site His107. The replacement of hamster NAT2 Tyr190 by either Phe, Ile or Ala was well tolerated and did not result in significant alterations in the overall fold of the protein. Nevertheless, stopped-flow and steady-state kinetic analysis revealed that Tyr190 was critical for maximizing the acetylation rate of NAT2 and the transacetylation rate of p-aminobenzoic acid when compared with the wild-type. Tyr190 was also shown to play an important role in determining the pK(a) of the active site Cys during acetylation, as well as the pH versus the rate profile for transacetylation. We hypothesized that the pH dependence was associated with global changes in the active site structure, which was revealed by the superposition of [(1)H, (15)N] heteronuclear single quantum coherence spectra for the wild-type and Y190A. These results suggest that NAT2 catalytic efficiency is partially governed by the ability of Tyr190 to mediate the collective impact of multiple side chains on the electrostatic potential and local conformation of the active site.

Isoform-selective inactivation of human arylamine N-acetyltransferases by reactive metabolites of carcinogenic arylamines.

Human arylamine N-acetyltransferases (NATs) are expressed as two polymorphic isoforms, NAT1 and NAT2, that have toxicologically significant functions in the detoxification of xenobiotic arylamines by N-acetylation and in the bioactivation of N-arylhydroxylamines by O-acetylation. NAT1 also catalyzes the N-acetylation of 4-aminobenzoylglutamic acid, a product of folic acid degradation, and is associated with endogenous functions in embryonic development. On the basis of earlier studies with hamster NAT1, hamster NAT2, and human NAT1, we proposed that human NAT2 would be more susceptible than NAT1 to inactivation by N-arylhydroxamic acid metabolites of arylamines. Kinetic analyses of the inactivation of recombinant NAT1 and NAT2 by the N-arylhydroxamic acid, N-hydroxy-2-acetylaminofluorene (N-OH-AAF), as well as the inactivation of NAT2 by N-hydroxy-4-acetylaminobiphenyl (N-OH-4-AABP), resulted in second-order inactivation rate constants (k(inact)/K(I)) that were several fold greater for NAT2 than for NAT1. Mass spectrometric analysis showed that inactivation of NAT2 in the presence of the N-arylhydroxamic acids was due to formation of a sulfinamide adduct with Cys68. Treatment of HeLa cells with N-OH-4-AABP and N-OH-AAF revealed that the compounds were less potent inactivators of intracellular NAT activity than the corresponding nitrosoarenes, but unexpectedly, the hydroxamic acids caused a significantly greater loss of NAT1 activity than of NAT2 activity. Nitrosoarenes are the electrophilic products responsible for NAT inactivation upon interaction of the enzymes with N-arylhydroxamic acids, as well as being metabolic products of arylamine oxidation. Treatment of recombinant NAT2 with the nitrosoarenes, 4-nitrosobiphenyl (4-NO-BP) and 2-nitrosofluorene (2-NO-F), caused rapid and irreversible inactivation of the enzyme by sulfinamide adduct formation with Cys68, but the k(inact)/K(I) values for inactivation of recombinant NAT2 and NAT1 did not indicate significant selectivity for either isoform. Also, the IC(50) values for inactivation of HeLa cell cytosolic NAT1 and NAT2 by 4-NO-BP were similar, as were the IC(50) values obtained with 2-NO-F. Treatment of HeLa cells with low concentrations (1-10 microM) of either 4-NO-BP or 2-NO-F resulted in preferential and more rapid loss of NAT1 activity than NAT2 activity. Because of its wide distribution in human tissues and its early expression in developing tissues, the apparent high sensitivity of intracellular NAT1 to inactivation by reactive metabolites of environmental arylamines may have important toxicological consequences.

Human arylamine N-acetyltransferase 1: in vitro and intracellular inactivation by nitrosoarene metabolites of toxic and carcinogenic arylamines.

Arylamines (ArNH 2) are common environmental contaminants, some of which are confirmed risk factors for cancer. Biotransformation of the amino group of arylamines involves competing pathways of oxidation and N-acetylation. Nitrosoarenes, which are products of the oxidation pathway, are electrophiles that react with cellular thiols to form sulfinamide adducts. The arylamine N-acetyltransferases, NAT1 and NAT2, catalyze N-acetylation of arylamines and play central roles in their detoxification. We hypothesized that 4-nitrosobiphenyl (4-NO-BP) and 2-nitrosofluorene (2-NO-F), which are nitroso metabolites of arylamines that are readily N-acetylated by NAT1, would be potent inactivators of NAT1 and that nitrosobenzene (NO-B) and 2-nitrosotoluene (2-NO-T), which are nitroso metabolites of arylamines that are less readily acetylated by NAT1, would be less effective inactivators. The second order rate constants for inactivation of NAT1 by 4-NO-BP and 2-NO-F were 59200 and 34500 M (-1) s (-1), respectively; the values for NO-B and 2-NO-T were 25 and 23 M (-1) s (-1). Densitometry quantification and comparisons of specific activities with those of homogeneous recombinant NAT1 showed that NAT1 constitutes approximately 0.002% of cytosolic protein in HeLa cells. Treatment of HeLa cells with 4-NO-BP (2.5 microM) for 1 h caused a 40% reduction in NAT1 activity, and 4-NO-BP (10 microM) caused a 50% loss of NAT1 activity within 30 min without affecting either glyceraldehyde 3-phosphate dehydrogenase (GAPDH) or glutathione reductase (GR) activities. 2-NO-F (1 microM) inhibited HeLa cell NAT1 activity by 36% in 1 h, and a 10 microM concentration of 2-NO-F reduced NAT1 activity by 70% in 30 min without inhibiting GAPDH or GR. Mass spectrometric analysis of NAT1 from HeLa cells in which NAT1 was overexpressed showed that treatment of the cells with 4-NO-BP resulted in sulfinamide adduct formation. These results indicated that exposure to low concentrations of nitrosoarenes may lead to a loss of NAT1 activity, thereby compromising a critical detoxification process.

Arylamine N-acetyltransferases: characterization of the substrate specificities and molecular interactions of environmental arylamines with human NAT1 and NAT2.

Arylamine N-acetyltransferases (NATs) are phase II xenobiotic metabolism enzymes that catalyze the detoxification of arylamines by N-acetylation and the bioactivation of N-arylhydroxylamines by O-acetylation. Endogenous and recombinant mammalian NATs with high specific activities are difficult to obtain in substantial quantities and in a state of homogeneity. This paper describes the overexpression of human wild-type NAT2 as a dihydrofolate reductase fusion protein containing a TEV protease-sensitive linker. Treatment of the partially purified fusion protein with TEV protease, followed by chromatographic purification, afforded 2.8 mg of homogeneous NAT2 from 2 L of cell culture. The kinetic specificity constants ( k cat/ K m) for N-acetylation of arylamine environmental contaminants, some of which are associated with bladder cancer risk, were determined with NAT2 and NAT1. The NAT1/NAT2 ratio of the specificity constants varied almost 1000-fold for monosubstituted and disubstituted alkylanilines containing methyl and ethyl ring substituents. 2-Alkyl substituents depressed N-acetylation rates but were more detrimental to catalysis by NAT1 than by NAT2. 3-Alkyl groups caused substrates to be preferentially N-acetylated by NAT2, and both 4-methyl- and 4-ethylaniline were better substrates for NAT1 than NAT2. NMR-based models were used to analyze the NAT binding site interactions of the alkylanilines. The selectivity of NAT1 for acetylation of 4-alkylanilines appears to be due to binding of the substituents to V216, which is replaced by S216 in NAT2. The contribution of 3-alkyl substituents to NAT2 substrate selectivity is attributed to multiple bonding interactions with F93, whereas a single bonding interaction occurs with V93 in NAT1. Unfavorable steric clashes between 2-methyl substituents and F125 of NAT1 may account for the selective NAT2-mediated N-acetylation of 2-alkylanilines; F125 is replaced by S125 in NAT2. These results provide insight into the structural basis for the substrate specificity of two NATs that play major roles in the biotransformation of genotoxic environmental arylamines.