Growth hormone deficiency in monozygotic twins with autosomal dominant pseudohypoparathyroidism type Ib

Growth Hormone Deficiency in an Adolescent With Pseudohypoparathyroidism Type 1B

We report growth hormone (GH) deficiency due to presumed GH releasing hormone (GHRH) resistance in an adolescent with pseudohypoparathyroidism type 1B (PHP1B) due to paternal uniparental disomy of chromosome 20 (patUPD20). A male patient aged 11 years 10 months with obesity and mild developmental delay was found to have hypocalcemia, hyperphosphatemia, and an elevated parathyroid hormone level. History included muscle cramps and leg pain with activity. Examination showed round facies, short stature, and obesity. He was in puberty and bone age was advanced by > 2 years. Detailed genetic workup, including nucleotide sequence analysis of GNAS exons 1-13 and STX16, methylation-sensitive multiplex ligation-dependent probe amplification and analysis of several microsatellite markers for chromosome 20, established the diagnosis of PHP1B due to patUPD20. Muscle cramps and hypocalcemia resolved with calcium carbonate, ergocalciferol, and calcitriol treatment. He was short with linear growth deceleration at around age 13 years. Peak GH concentration was insufficient following stimulation testing. Growth velocity improved with human GH treatment. Although rare, resistance to GHRH can occur in PHP1B and patients with this disorder should be evaluated for GH insufficiency if they present with short stature and reduced growth velocity. Treatment with recombinant human GH may improve growth velocity in such patients.

Autosomal dominant pseudohypoparathyroidism type 1b due to STX16 deletion: a case presentation and literature review

INTRODUCTION

Pseudohypoparathyroidism (PHP) is a heterogeneous group of rare, genetically related, endocrine disorders, characterized by end-organ resistance to parathyroid hormone (PTH) action and other G protein-coupled receptors (GPCRs) related hormones. The clinical variants of PHP are classified according to the presence of features of Albright's hereditary osteodystrophy (AHO) and in vivo response to exogenous PTH. Autosomal dominant PHP1b is often caused by a deletion in the syntaxin-16 (STX16) gene, leading to a loss of methylation in the A/B exon of the guanine nucleotide-binding protein a-stimulating polypeptide (GNAS) complex. Herein, we present a case of a 41-year-old man with familiar PHP1b due to a maternal inherited 3-kb STX16 deletion, who was referred to us for consultation by artificial reproductive technology specialists.

EVIDENCE ACQUISITION

A bibliographic search was performed in electronic databases (PubMed and Cochrane Library) to identify similar cases.

EVIDENCE SYNTHESIS

Twenty studies (case-series or reports) were eligible. These studies included collectively 120 patients; 46 patients (38.3%) presented with symptoms of hypocalcemia; 38 were asymptomatic (31.7%); data for 36 patients (30%) were unavailable. Thyroid-stimulating hormone (TSH) resistance was documented in 25 occasions (21%); growth hormone deficiency in 2 (1.7%); 3 patients shared features of the AHO (2.5%); 6 had abnormal bone mineral density test (5%). Notable is the development of tertiary hyperparathyroidism in 3 individuals (2.5%).

CONCLUSIONS

The present review confirms the heterogeneity in the clinical spectrum of familiar PHP1b. Future research should focus on the molecular characterization of the GNAS disorders, leading to a facile diagnosis and appropriate genetic counseling.

High-throughput Molecular Analysis of Pseudohypoparathyroidism 1b Patients Reveals Novel Genetic and Epigenetic Defects

CONTEXT

Patients with pseudohypoparathyroidism type 1b (PHP1b) show disordered imprinting of the maternal GNAS allele or paternal uniparental disomy (UPD). Genetic deletions in STX16 or in upstream exons of GNAS are present in many familial but not sporadic cases.

OBJECTIVE

Characterization of epigenetic and genetic defects in patients with PHP1b.

DESIGN AND PATIENTS

DNA from 84 subjects, including 26 subjects with sporadic PHP1b, 27 affected subjects and 17 unaffected and/or obligate gene carriers from 12 PHP1b families, 11 healthy individuals, and 3 subjects with PHP1a was subjected to quantitative pyrosequencing of GNAS differentially methylated regions (DMRs), microarray analysis, and microsatellite haplotype analysis.

SETTING

Academic medical center.

MAIN OUTCOME MEASUREMENTS

Molecular pathology of PHP1b.

RESULTS

Healthy subjects, unaffected family members and obligate carriers of paternal PHP1b alleles, and subjects with PHP1a showed normal methylation of all DMRs. All PHP1b subjects showed loss of methylation (LOM) at the exon A/B DMR. Affected members of 9 PHP1b kindreds showed LOM only at the exon A/B DMR, which was associated with a 3-kb deletion of STX16 exons 4 through 6 in 7 families and a novel deletion of STX16 and adjacent NEPEPL1 in 1 family. A novel NESP deletion was found in 1 of 2 other families with more extensive methylation defects. One sporadic PHP1b had UPD of 20q, 2 had 3-kb STX16 deletions, and 5 had apparent epigenetic mosaicism.

CONCLUSIONS

We found diverse patterns of defective methylation and identified novel or previously known mutations in 9 of 12 PHP1b families.

Preferential Maternal Transmission of STX16-GNAS Mutations Responsible for Autosomal Dominant Pseudohypoparathyroidism Type Ib (PHP1B): Another Example of Transmission Ratio Distortion

Preferential transmission of a genetic mutation to the next generation, referred to as transmission ratio distortion (TRD), is well established for several dominant disorders, but underlying mechanisms remain undefined. Recently, TRD was reported for patients affected by pseudohypoparathyroidism type Ia or pseudopseudohypoparathyroidism. To determine whether TRD is observed also for autosomal dominant pseudohypoparathyroidism type Ib (AD-PHP1B), we analyzed kindreds with the frequent 3-kb STX16 deletion or other STX16/GNAS mutations. If inherited from a female, these genetic defects lead to loss-of-methylation at exon A/B alone or at all three differentially methylated regions (DMR), resulting in parathyroid hormone (PTH)-resistant hypocalcemia and hyperphosphatemia and possibly resistance to other hormones. In total, we investigated 212 children born to 80 females who are unaffected carriers of a STX16/GNAS mutation (n = 47) or affected by PHP1B (n = 33). Of these offspring, 134 (63.2%) had inherited the genetic defect (p = .00012). TRD was indistinguishable for mothers with a STX16/GNAS mutation on their paternal (unaffected carriers) or maternal allele (affected). The mechanisms favoring transmission of the mutant allele remain undefined but are likely to include abnormalities in oocyte maturation. Search for mutations in available descendants of males revealed marginally significant evidence for TRD (p = .038), but these analyses are less reliable because many more offspring of males than females with a STX16/GNAS mutation were lost to follow-up (31 of 98 versus 6 of 218). This difference in follow-up is probably related to the fact that inheritance of a mutation from a male does not have clinical implications, whereas inheritance from an affected or unaffected female results in PHP1B. Lastly, affected PHP1B females had fewer descendants than unaffected carriers, but it remains unclear whether abnormal oocyte development or impaired actions of reproductive hormones are responsible. Our findings highlight previously not recognized aspects of AD-PHP1B that are likely to have implications for genetic testing and counseling. © 2020 American Society for Bone and Mineral Research (ASBMR).

Pseudohypoparathyroidism type 1B - a rare cause of tetany: case report

Pseudohypoparathyroidism (PHP) is a rare group of disorders characterised by end-organ resistance to the parathyroid hormone (PTH). A 16-year-old boy presented with a 2-year history of involuntary dystonic movements involving mainly the left hand, initially after writing and later during physical exercise. Serum calcium was 1.37 mmol/L (2.20-2.69), phosphate 2.1 mmol/L (0.8-1.45) and PTH 302 ng/L (12-88). CT scan of the head demonstrated multiple subcortical and diffuse basal ganglia calcifications. Genetic analysis confirmed a methylation defect in the GNAS cluster on chromosome 20q13.32 which established the diagnosis. Treatment with calcitriol and calcium carbonate led to complete remission of symptoms. Causes of hypocalcaemia should be considered in evaluating patients with movement disorders. The diagnosis of PHP-1B is challenging but the overall prognosis is excellent.

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.

Maternal Uniparental Disomy for Chromosome 20: Physical and Endocrinological Characteristics of Five Patients

CONTEXT

Maternal uniparental disomy for chromosome 20 [UPD(20)mat], resulting in aberrant expression of imprinted transcripts at the GNAS locus, is a poorly characterized condition. These patients manifested a phenotype similar to that of Silver-Russell syndrome (SRS) and small for gestational age-short stature (SGA-SS); however, the etiological relationship between UPD(20)mat and SRS/SGA-SS remains unclear. Moreover, no report has described endocrinological assessment of UPD(20)mat patients, although paternal UPD(20), the mirror image entity of UPD(20)mat, is known to cause multiple hormone resistance reflecting reduced α-subunit of the stimulatory G protein expression.

PARTICIPANTS

Patients 1 to 5 showed nonmosaic heterodisomy and/or isodisomy for the entire chromosome 20. Patients 1 to 3 and 4 were identified through UPD(20)mat screening for 55 patients with etiology-unknown SRS and 96 patients with SGA-SS, respectively. Patient 5 was identified through molecular analysis for patients with developmental defects. Patients 1 to 5 manifested postnatal growth failure and feeding problems, with or without developmental delay, and other clinical features. Patients 1 to 4 were born SGA. Patients 4 and 5 exhibited hypercalcemia and low or low-normal parathyroid hormone levels. Patient 1 showed constantly decreased thyroid-stimulating hormone (TSH) levels after 12 years of age, although she had a normal TSH level at 5.2 years of age.

CONCLUSION

The results suggest that UPD(20)mat underlies growth failure and feeding problems with additional features and could account for >5% of etiology-unknown SRS and small percentages of SGA-SS. Most important, this study provides an indication that UPD(20)mat can be associated with hypersensitivity of hormone receptors, which may gradually develop with age.

Bone Mineral Density and Its Serial Changes Are Associated With PTH Levels in Pseudohypoparathyroidism Type 1B Patients

Bone responsiveness to serum parathyroid hormone (PTH) in pseudohypoparathyroidism 1B (PHP1B) is controversial. Forty-eight PHP1B patients diagnosed by molecular analysis were recruited from 2000 to 2016 from the Peking Union Medical College Hospital. Fifty-five sex-matched nonsurgical hypoparathyroidism (NS-HP) patients were selected and included for comparison. Basic information, laboratory test, and dual-energy X-ray absorptiometry (DXA) results were collected. Linear regression was performed to identify independent predictors of lumbar spine (LS), femoral neck (FN), and total hip (TH) bone mineral density (BMD) Z-scores in PHP1B patients. BMD and related markers were compared between PHP and NS-HP patients. Longitudinal observation of 10 PHP1B patients was performed. The BMD Z-score for the LS (1.14 ± 1.41) was higher than that for the FN (-0.20 ± 1.00, p < 0.001) and the TH (0.03 ± 1.06, p < 0.001) in PHP1B patients. Despite lower serum calcium levels in untreated patients (1.72 mmol/L in untreated patients versus 2.14 mmol/L in treated patients, p = 0.024), the PTH levels as well as BMD Z-scores were comparable between treated and untreated patients at baseline. PTH was a negative predictor for LS-BMD Z-score (B = -0.004, p = 0.028) for sporadic PHP1B patients, and a similar result was obtained for all the PHP1B patients (B = -0.002, p = 0.053). Z-scores for FN- and LS-BMDs after treatment increased by 0.31 ± 0.10 and 0.58 ± 0.12, respectively, where the increase in LS-BMD correlated with a decrease in PTH (r = -0.72, p = 0.044). All BMD Z-scores were significantly lower in PHP1B patients than in IHP patients for the FN, LS, and TH (-0.20 ± 1.00 versus 1.57 ± 1.07, 1.14 ± 1.41 versus 1.96 ± 1.32, 0.03 ± 1.06 versus 1.67 ± 1.01, respectively, all p < 0.05). Skeletal tissue in PHP1B patients responds to PTH, where heterogenous sensitivities to PTH may exist in different regions of bone. Therefore, it is reasonable to normalize PTH levels when treating PHP1B to avoid negative effects of PTH on bone. © 2017 American Society for Bone and Mineral Research.

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.

Clinical and genetic characteristics of Pseudohypoparathyroidism in the Chinese population

BACKGROUND

Pseudohypoparathyroidism (PHP) is caused by mutations and epimutations in the GNAS locus, and characterized by the possibility of resistance to multiple hormones and Albright's hereditary osteodystrophy. PHP can be classified into the forms 1A/C, sporadic 1B and familial 1B.

OBJECTIVES

To obtain an overall view of the clinical and genetic characteristics of the Chinese PHP patient population.

METHODS

From 2000 to 2016, 120 patients were recruited and studied using Sanger sequencing, methylation-specific multiple ligation-dependent probe amplification (MS-MLPA) and combined bisulfite restriction analysis (COBRA). Of these patients, 104 had positive molecular alterations indicative of certain forms of PHP and were included in data analysis. Clinical and laboratory features were compared between PHP1A/C and PHP1B patients.

RESULTS

Ten PHP1A/C, 21 familial PHP1B and 73 sporadic PHP1B patients were identified. Four novel GNAS mutations were discovered in these patients, including c.1038+1G>T, c.530+2T>C, c.880_883delCAAG and c.311_312delAAG, insT. The most common symptoms in this series were recurrent tetany (89.4%) and epilepsy (47.1%). The prevalence of weight excess increased with age for PHP1B (10%-35%) and PHP1A/C (50%-75%). Intracranial calcification had a prevalence of 94.6% and correlated with seizures (r = .227, P = .029). Cataracts occurred in 56.2% PHP patients, and there was a trend towards longer disease duration in patients with cataracts (P = .051). Statistically significant differences (P < .05) were observed when comparing certain clinical characteristics between PHP1B and PHP1A/C patients, including age of onset (10 vs 7 year), short stature (21.3% vs 70%), rounded face (60.6% vs 100%), brachydactyly (25.5% vs 100%), ectopic ossification (1.1% vs 40%) and TSH resistance (44.6% vs 90%), respectively.

CONCLUSIONS

This study is the largest single-centre series of PHP patients and summarizes the clinical and genetic features of the Chinese PHP population. While there was substantial clinical overlap between PHP1A/C and PHP1B, differences in disease progression were observed.

(Epi)genotype-Phenotype Analysis in 69 Japanese Patients With Pseudohypoparathyroidism Type I

Context:

Pseudohypoparathyroidism type I (PHP-I) is divided into PHP-Ia with Albright hereditary osteodystrophy and PHP-Ib, which usually shows no Albright hereditary osteodystrophy features. Although PHP-Ia and PHP-Ib are typically caused by genetic defects involving α subunit of the stimulatory G protein (Gsα)–coding GNAS exons and methylation defects of the GNAS differentially methylated regions (DMRs) on the maternal allele, respectively, detailed phenotypic characteristics still remains to be examined.

Objective:

To clarify phenotypic characteristics according to underlying (epi)genetic causes.

Patients and Methods:

We performed (epi)genotype-phenotype analysis in 69 Japanese patients with PHP-I; that is, 28 patients with genetic defects involving Gsα-coding GNAS exons (group 1) consisting of 12 patients with missense variants (subgroup A) and 16 patients with null variants (subgroup B), as well as 41 patients with methylation defects (group 2) consisting of 21 patients with broad methylation defects of the GNAS-DMRs (subgroup C) and 20 patients with an isolated A/B-DMR methylation defect accompanied by the common STX16 microdeletion (subgroup D).

Results:

Although (epi)genotype-phenotype findings were grossly similar to those reported previously, several important findings were identified, including younger age at hypocalcemic symptoms and higher frequencies of hyperphosphatemia in subgroup C than in subgroup D, development of brachydactyly in four patients of subgroup C, predominant manifestation of subcutaneous ossification in subgroup B, higher frequency of thyrotropin resistance in group 1 than in group 2, and relatively low thyrotropin values in four patients with low T4 values and relatively low luteinizing hormone/follicle-stimulating hormone values in five adult females with ovarian dysfunction.

Conclusion:

The results imply the presence of clinical findings characteristic of each underlying cause and provide useful information on the imprinting status of Gsα.

Partial Loss of Function of the GHRH Receptor Leads to Mild Growth Hormone Deficiency

OBJECTIVE

Recessive mutations in GHRHR are associated with severe isolated growth hormone deficiency (IGHD), with a final height in untreated patients of 130 cm ± 10 cm (-7.2 ± 1.6 SDS; males) and 114 ± 0.7 cm (-8.3 ± 0.1 SDS; females).

DESIGN

We hypothesized that a consanguineous Pakistani family with IGHD in three siblings (two males, one female) would have mutations in GH1 or GHRHR.

RESULTS

Two novel homozygous missense variants [c.11G>A (p.R4Q), c.236C>T (p.P79L)] at conserved residues were identified in all three siblings. Both were absent from control databases, aside from pR4Q appearing once in heterozygous form in the Exome Aggregation Consortium Browser. The brothers were diagnosed with GH deficiency at 9.8 and 6.0 years (height SDS: -2.24 and -1.23, respectively), with a peak GH of 2.9 μg/liter with low IGF-1/IGF binding protein 3. Their sister presented at 16 years with classic GH deficiency (peak GH <0.1 μg/liter, IGF-1 <3.3 mmol/liter) and attained an untreated near-adult height of 144 cm (-3.0 SDS); the tallest untreated patient with GHRHR mutations reported. An unrelated Pakistani female IGHD patient was also compound homozygous. All patients had a small anterior pituitary on magnetic resonance imaging. Functional analysis revealed a 50% reduction in maximal cAMP response to stimulation with GHRH by the p.R4Q/p.P79L double mutant receptor, with a 100-fold increase in EC50.

CONCLUSION

We report the first coexistence of two novel compound homozygous GHRHR variants in two unrelated pedigrees associated with a partial loss of function. Surprisingly, the patients have a relatively mild IGHD phenotype. Analysis revealed that the pP79L mutation is associated with the compromise in function, with the residual partial activity explaining the mild phenotype.

Pseudohypoparathyroidism and Gsα-cAMP-linked disorders: current view and open issues

Pseudohypoparathyroidism exemplifies 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 the cAMP signalling pathway, rather than of the parathyroid hormone (PTH) receptor itself. Despite the first description of this disorder dating back to 1942, later findings have unveiled complex epigenetic alterations in addition to classic mutations in GNAS underpining the molecular basis of the main subtypes of pseudohypoparathyroidism. Moreover, mutations in PRKAR1A and PDE4D, which encode proteins crucial for Gsα-cAMP-mediated signalling, have been found in patients with acrodysostosis. As acrodysostosis, a disease characterized by skeletal malformations and endocrine disturbances, shares clinical and molecular characteristics with pseudohypoparathyroidism, making a differential diagnosis and providing genetic counselling to patients and families is a challenge for endocrinologists. Accumulating data on the genetic and clinical aspects of this group of diseases highlight the limitation of the current classification system and prompt the need for a new definition as well as for new diagnostic and/or therapeutic algorithms. This Review discusses both the current understanding and future challenges for the clinical and molecular diagnosis, classification and treatment of pseudohypoparathyroidism.