Pseudohypoparathyroidism type 1A and morbid obesity in infancy

Clinical and Molecular Characteristics and Long-term Follow-up of Children With Pseudohypoparathyroidism Type IA

CONTEXT

Pseudohypoparathyroidism type IA (PHPIA) is a rare genetic disorder characterized by hormone resistance and a typical phenotype named Albright hereditary osteodystrophy. Unawareness of this rare disease leads to delays in diagnosis.

OBJECTIVE

The aims of this study were to describe the clinical and molecular characteristics of patients with genetically confirmed GNAS mutations and to evaluate their long-term outcomes.

METHODS

A retrospective search for all patients diagnosed with PHPIA in 2 referral centers in Israel was conducted.

RESULTS

Nine children (8 females) belonging to 6 families were included in the study. Five patients had GNAS missense mutations, 2 had deletions, and 2 had frameshift mutations. Four mutations were novel. Patients were referred at a mean age of 2.4 years due to congenital hypothyroidism (5 patients), short stature (2 patients), or obesity (2 patients), with a follow-up duration of up to 20 years. Early obesity was observed in the majority of patients. Elevated parathyroid hormone was documented at a mean age of 3 years; however, hypocalcemia became evident at a mean age of 5.9 years, about 3 years later. All subjects were diagnosed with mild to moderate mental retardation. Female adult height was very short (mean -2.5 SD) and 5 females had primary or secondary amenorrhea.

CONCLUSION

Long-term follow-up of newborns with a combination of congenital hypothyroidism, early-onset obesity, and minor dysmorphic features associated with PHPIA is warranted and molecular analysis is recommended since the complete clinical phenotype may develop a long time after initial presentation.

The role of genetic and epigenetic GNAS alterations in the development of early-onset obesity

BACKGROUND

GNAS (guanine nucleotide-binding protein, alpha stimulating) is an imprinted gene that encodes Gsα, the α subunit of the heterotrimeric stimulatory G protein. This subunit mediates the signalling of a diverse array of G protein-coupled receptors (GPCRs), including the melanocortin 4 receptor (MC4R) that serves a pivotal role in regulating food intake, energy homoeostasis, and body weight. Genetic or epigenetic alterations in GNAS are known to cause pseudohypoparathyroidism in its different subtypes and have been recently associated with isolated, early-onset, severe obesity. Given the diverse biological functions that Gsα serves, multiple molecular mechanisms involving various GPCRs, such as MC4R, β2- and β3-adrenoceptors, and corticotropin-releasing hormone receptor, have been implicated in the pathophysiology of severe, early-onset obesity that results from genetic or epigenetic GNAS changes.

SCOPE OF REVIEW

This review examines the structure and function of GNAS and provides an overview of the disorders that are caused by defects in this gene and may feature early-onset obesity. Moreover, it elucidates the potential molecular mechanisms underlying Gsα deficiency-induced early-onset obesity, highlighting some of their implications for the diagnosis, management, and treatment of this complex condition.

MAJOR CONCLUSIONS

Gsα deficiency is an underappreciated cause of early-onset, severe obesity. Therefore, screening children with unexplained, severe obesity for GNAS defects is recommended, to enhance the molecular diagnosis and management of this condition.

Pseudohypoparathyroidism, acrodysostosis, progressive osseous heteroplasia: different names for the same spectrum of diseases?

Pseudohypoparathyroidism (PHP), the first known post-receptorial hormone resistance, derives from a partial deficiency of the α subunit of the stimulatory G protein (Gsα), a key component of the PTH/PTHrP signaling pathway. Since its first description, different studies unveiled, beside the molecular basis for PHP, the existence of different subtypes and of diseases in differential diagnosis associated with genetic alterations in other genes of the PTH/PTHrP pathway. The clinical and molecular overlap among PHP subtypes and with different but related disorders make both differential diagnosis and genetic counseling challenging. Recently, a proposal to group all these conditions under the novel term "inactivating PTH/PTHrP signaling disorders (iPPSD)" was promoted and, soon afterwards, the first international consensus statement on the diagnosis and management of these disorders has been published. This review will focus on the major and minor features characterizing PHP/iPPSDs as a group and on the specificities as well as the overlap associated with the most frequent subtypes.

Subcutaneous Calcification and Fixed Flexion Deformity of the Right Elbow Joint in a Child with a GNAS Mutation: A Case Report

INTRODUCTION

The art of medicine glorifies when a clinician listens carefully to the patient's story, gives a thorough examination, performs appropriate investigations, and finally links findings together to reach a definite diagnosis. An interesting case was reported here, highlighting the integration of different symptoms and manifestations with some relevant biochemical investigations to reach a final diagnosis. To the best of our knowledge, fixed flexion deformity, as a complication of subcutaneous calcification, has not been previously reported in a child with Albright hereditary osteodystrophy (AHO).

CASE PRESENTATION

A 2.5-year-old boy was born at term with a birth weight of 3.5 kg (-0.49 SDS). The child was referred to a general pediatrician with a history of right elbow joint swelling noticed initially at six months of age. He then developed the limitation of right upper arm movement, which slowly progressed afterward. The patient had no history of trauma. At nine months of age, he was diagnosed with hypothyroidism, preceded by cold skin, dry hair, and constipation. At nine years of age, he presented with a fixed flexion deformity of the right elbow associated with markedly limited joint movement and symmetrical hands with hyperpigmented knuckles of right metacarpal bones. Subcutaneous masses were felt along the right forearm, showing tenderness on palpation. Investigations revealed elevated serum parathyroid hormone and normal calcium indicating parathyroid hormone resistance. Further genetic testing revealed GNAS mutation. The child was obese throughout his childhood.

CONCLUSIONS

This case report describes an obese child with subcutaneous calcification that led to fixed flexion deformity of the elbow, starting at an incredibly early age. Hypothyroidism and pseudohypoparathyroidism raised the suspicion of AHO, which was later confirmed by genetic testing. This is the first case report on fixed flexion deformity in a patient with GNAS mutation (c.719-1G > A Chr20: 57484737) in West Asia.

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.

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.

Nonclassic features of pseudohypoparathyroidism type 1A

PURPOSE OF REVIEW

To provide readers with a review of contemporary literature describing the evolving understanding of the pseudohypoparathyroidism type 1A (PHP1A) phenotype.

RECENT FINDINGS

The classic features of PHP1A include multihormone resistance and the Albright Hereditary Osteodystrophy phenotype (round facies, short stature, subcutaneous ossifications, brachydactyly, and early-onset obesity. Obesity may be because of a decrease in resting energy expenditure because most patients do not report significant hyperphagia. Patients with PHP1A have an increased risk of type 2 diabetes. In addition to brachydactyly and short stature, orthopedic complications can include spinal stenosis and carpal tunnel syndrome. Hearing loss, both sensorineural and conductive, has been reported in PHP1A. In addition, ear-nose-throat findings include decreased olfaction and frequent otitis media requiring tympanostomy tubes. Sleep apnea was shown to be 4.4-fold more common in children with PHP1A compared with other obese children; furthermore, asthma-like symptoms have been reported. These new findings are likely multifactorial and further research is needed to better understand these nonclassic features of PHP1A.

SUMMARY

Along with the Albright Hereditary Osteodystrophy phenotype and hormone resistance, patients with PHP1A may have additional skeletal, metabolic, ear-nose-throat, and pulmonary complications. Understanding these nonclassic features will help improve clinical care of patients with PHP1A.

Pseudohypoparathyroidism Type 1A-Subclinical Hypothyroidism and Rapid Weight Gain as Early Clinical Signs: A Clinical Review of 10 Cases

OBJECTIVE

To evaluate the clinical signs and symptoms that would help clinicians to consider pseudohypoparathyroidism (PHP) type 1A as a diagnosis in a child.

METHODS

A retrospective review of the medical records of children diagnosed by erythrocyte Gsα activity and/or GNAS1 gene study and followed-up for PHP type 1A. Clinical and biochemical parameters along with epidemiological data were extracted and analyzed. Weight gain during infancy and early childhood was calculated as change in weight standard deviation score (SDS), using the French growth reference values. An upward gain in weight ≥0.67 SDS during these periods was considered indicative of overweight and/or obesity.

RESULTS

Ten cases of PHP type 1A were identified (mean age 41.1 months, range from 4 to 156 months). In children aged ≤2 years, the commonest clinical features were round lunar face, obesity (70%), and subcutaneous ossifications (60%). In older children, brachydactyly was present in 60% of cases. Seizures occurred in older children (3 cases). Short stature was common at all ages. Subclinical hypothyroidism was present in 70%, increased parathormone (PTH) in 83%, and hyperphosphatemia in 50%. Only one case presented with hypocalcemia. Erythrocyte Gsα activity tested in seven children was reduced; GNAS1 gene testing was performed in 9 children. Maternal transmission was the most common (six patients). In three other cases, the mutations were de novo, c.585delGACT in exon 8 (case 2) and c.344C>TP115L in exon 5 (cases 6&7).

CONCLUSION

Based on our results, PHP type 1A should be considered in toddlers presenting with round face, rapid weight gain, subcutaneous ossifications, and subclinical hypothyroidism. In older children, moderate mental retardation, brachydactyly, afebrile seizures, short stature, and thyroid-stimulating hormone resistance are the most suggestive features.

Epidemiology and Diagnosis of Hypoparathyroidism

CONTEXT

Hypoparathyroidism is a disorder characterized by hypocalcemia due to insufficient secretion of PTH. Pseudohypoparathyroidism is a less common disorder due to target organ resistance to PTH. This report summarizes the results of the findings and recommendations of the Working Group on Epidemiology and Diagnosis of Hypoparathyroidism.

EVIDENCE ACQUISITION

Each contributing author reviewed the recent published literature regarding epidemiology and diagnosis of hypoparathyroidism using PubMed and other medical literature search engines.

EVIDENCE SYNTHESIS

The prevalence of hypoparathyroidism is an estimated 37 per 100 000 person-years in the United States and 22 per 100 000 person-years in Denmark. The incidence in Denmark is approximately 0.8 per 100 000 person-years. Estimates of prevalence and incidence of hypoparathyroidism are currently lacking in most other countries. Hypoparathyroidism increases the risk of renal insufficiency, kidney stones, posterior subcapsular cataracts, and intracerebral calcifications, but it does not appear to increase overall mortality, cardiovascular disease, fractures, or malignancy. The diagnosis depends upon accurate measurement of PTH by second- and third-generation assays. The most common etiology is postsurgical hypoparathyroidism, followed by autoimmune disorders and rarely genetic disorders. Even more rare are etiologies including parathyroid gland infiltration, external radiation treatment, and radioactive iodine therapy for thyroid disease. Differentiation between these different etiologies is aided by the clinical presentation, serum biochemistries, and in some cases, genetic testing.

CONCLUSIONS

Hypoparathyroidism is often associated with complications and comorbidities. It is important for endocrinologists and other physicians who care for these patients to be aware of recent advances in the epidemiology, diagnosis, and genetics of this disorder.

Resting Energy Expenditure Is Decreased in Pseudohypoparathyroidism Type 1A

CONTEXT

Pseudohypoparathyroidism type 1A (PHP1A) is caused by loss-of-function mutations on the maternally inherited GNAS allele and is associated with early-onset obesity, neurocognitive defects, and resistance to multiple hormones. The role of energy intake vs central regulation of energy expenditure in the pathophysiology of obesity remains unclear.

OBJECTIVE

The aim of this study was to evaluate resting energy expenditure (REE) in participants with PHP1A.

DESIGN

We assessed REE, biochemical, endocrine, and auxological status of 12 participants with PHP1A who had normal or elevated body mass index; controls were a cohort of 156 obese participants.

SETTING

This study took place at Children's Hospital in Philadelphia and Sick Children's Hospital in Toronto.

MAIN OUTCOME MEASURES

REE as a percent of predicted REE was the outcome measure.

RESULTS

PHP1A participants had normal endocrine status while receiving appropriate hormone replacement therapy, but had significantly decreased REE as a percent of predicted REE (using the modified Schofield equation).

CONCLUSION

Our results are consistent with REE being the principal cause of obesity in PHP1A rather than it being caused by excessive energy intake or endocrine dysfunction.

Reduced insulin sensitivity in adults with pseudohypoparathyroidism type 1a

CONTEXT

Disruption of the Gsα maternal allele leads to severe obesity and insulin resistance in mice and early-onset obesity in patients with pseudohypoparathyroidism (PHP) type 1a. However, insulin resistance and glucose metabolism have not been systematically characterized in patients with PHP1a.

OBJECTIVE, DESIGN, AND SETTING

In a cross-sectional, case-control study, we examined insulin sensitivity, β-cell function, energy expenditure (EE), and sympathetic nervous system activity in adults with PHP1a.

STUDY PARTICIPANTS

PHP1a patients (n = 8) and healthy control subjects (n = 24) matched for age (41 ± 7 vs 41 ± 7 years [mean ± SD]), gender, and percent body fat.

METHODS

Insulin sensitivity (SI), acute insulin response to glucose, and disposition index were assessed during a frequently sampled iv glucose tolerance test. Oral glucose insulin sensitivity (OGIS) was measured during a mixed meal. EE was measured using whole-room indirect calorimetry. Body composition was assessed via dual-energy x-ray absorptiometry and sympathetic nervous system activity by measuring 24-hour urinary catecholamine concentrations.

RESULTS

PHP1a patients were less insulin-sensitive than their matched controls based upon SI and OGIS. Nondiabetic PHP1a patients tended to have a lower SI (P = .09) and reduced OGIS (P = .03). Disposition index, a composite measure of β-cell function, also tended to be lower in patients (P = .07). Total caloric intake, resting EE, total EE, meal-induced thermogenesis, and 24-hour urinary catecholamine concentrations were not significantly different between the groups.

CONCLUSIONS

Adults with PHP-1a have reduced insulin sensitivity compared with their matched controls that may contribute to the pathogenesis of glucose intolerance and diabetes in these patients.

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.

An update on the clinical and molecular characteristics of pseudohypoparathyroidism

PURPOSE OF REVIEW

To provide the reader with a review of contemporary literature describing the evolving understanding of the molecular pathobiology of pseudohypoparathyroidism (PHP).

RECENT FINDINGS

The features of PHP type 1 reflect imprinting of the GNAS gene, which encodes the α subunit of the heterotrimeric G protein (Gα(s)) that couples heptahelical receptors to activation of adenylyl cyclase. Transcription of Gα(s) is biallelic in most cells, but is primarily from the maternal allele in some tissues (e.g. proximal renal tubules, thyroid, pituitary somatotropes, gonads). Patients with PHP 1a have heterozygous mutations within the exons of the maternal GNAS allele that encode Gα(s), whereas patients with PHP 1b have methylation defects in the GNAS locus that reduce transcription of Gα(s) from the maternal allele. In both PHP 1a and PHP 1b, paternal imprinting of Gα(s) leads to resistance to parathyroid hormone and TSH. Although brachydactyly is characteristic of PHP 1a, it is sometimes present in patients with PHP 1b.

SUMMARY

Molecular studies enable a distinction between PHP 1a and PHP 1b, with different mechanisms accounting for Gα(s) deficiency. Clinical overlap between these two forms of PHP type 1 is likely due to the variable levels of Gα(s) activity expressed in specific cell types.

Gsα deficiency in the paraventricular nucleus of the hypothalamus partially contributes to obesity associated with Gsα mutations

The G protein α-subunit G(s)α mediates receptor-stimulated cAMP generation. Heterozygous inactivating G(s)α mutations on the maternal allele result in obesity primarily due to reduced energy expenditure in Albright hereditary osteodystrophy patients and in mice. We previously showed that mice with central nervous system (CNS)-specific G(s)α deletion on the maternal allele (mBrGs KO) also develop severe obesity with reduced energy expenditure and that G(s)α is primarily expressed from the maternal allele in the paraventricular nucleus (PVN) of the hypothalamus, an important site of energy balance regulation. We now generated mice with PVN-specific G(s)α deficiency by mating Single-minded 1-cre and G(s)α-floxed mice. Homozygous G(s)α deletion produced early lethality. Heterozygotes with maternal G(s)α deletion (mPVNGsKO) also developed obesity and had small reductions in energy expenditure. However, this effect was much milder than that found in mBrGsKO mice and was more prominent in males. We previously showed mBrGsKO mice to have significant reductions in melanocortin receptor agonist-stimulated energy expenditure and now show that mBrGsKO mice have impaired cold-induced brown adipose tissue stimulation. In contrast, these effects were absent in mPVNGsKO mice. mPVNGsKO mice also had minimal effects on glucose metabolism as compared with mBrGsKO mice. Consistent with the presence of G(s)α imprinting, paternal heterozygotes showed no changes in energy or glucose metabolism. These results indicate that although G(s)α deficiency in PVN partially contributes to the metabolic phenotype resulting from maternal G(s)α mutations, G(s)α imprinting in other CNS regions is also important in mediating the CNS effects of G(s)α mutations on energy and glucose metabolism.

Effects of deficiency of the G protein Gsα on energy and glucose homeostasis

G(s)α is a ubiquitously expressed G protein α-subunit that couples receptors to the generation of intracellular cyclic AMP. The G(s)α gene GNAS is a complex gene that undergoes genomic imprinting, an epigenetic phenomenon that leads to differential expression from the two parental alleles. G(s)α is imprinted in a tissue-specific manner, being expressed primarily from the maternal allele in a small number of tissues. Albright hereditary osteodystrophy is a monogenic obesity disorder caused by heterozygous G(s)α mutations but only when the mutations are maternally inherited. Studies in mice indicate a similar parent-of-origin effect on energy and glucose metabolism, with maternal but not paternal mutations leading to obesity, reduced sympathetic nerve activity and energy expenditure, glucose intolerance and insulin resistance, with no primary effect on food intake. These effects result from G(s)α imprinting leading to severe G(s)α deficiency in one or more regions of the central nervous system, and are associated with a specific defect in melanocortins to stimulate sympathetic nerve activity and energy expenditure.

The role of GNAS and other imprinted genes in the development of obesity

Genomic imprinting is an epigenetic phenomenon affecting a small number of genes, which leads to differential expression from the two parental alleles. Imprinted genes are known to regulate fetal growth and a 'kinship' or 'parental conflict' model predicts that paternally and maternally expressed imprinted genes promote and inhibit fetal growth, respectively. In this review we examine the role of imprinted genes in postnatal growth and metabolism, with an emphasis on the GNAS/Gnas locus. GNAS is a complex imprinted locus with multiple oppositely imprinted gene products, including the G-protein alpha-subunit G(s)alpha that is expressed primarily from the maternal allele in some tissues and the G(s)alpha isoform XLalphas that is expressed only from the paternal allele. Maternal, but not paternal, G(s)alpha mutations lead to obesity in Albright hereditary osteodystrophy. Mouse studies show that this phenomenon is due to G(s)alpha imprinting in the central nervous system leading to a specific defect in the ability of central melanocortins to stimulate sympathetic nervous system activity and energy expenditure. In contrast mutation of paternally expressed XLalphas leads to opposite metabolic effects in mice. Although these findings conform to the 'kinship' model, the effects of other imprinted genes on body weight regulation do not conform to this model.