Osteosclerosis in two brothers with autosomal dominant pseudohypoparathyroidism type 1b: bone histomorphometric analysis

Bone Microstructure and Bone Strength Among Patients with Pseudohypoparathyroidism

The present study aimed to assess bone strength and microstructure in patients with pseudohypoparathyroidism (PHP), nonsurgical HP (NS-HP), and healthy controls. A total of 54 PHP1 patients (14 PHP1a, 40 PHP1b), 54 age-/sex- matched NS-HP patients and 27 age-/sex-matched controls were enrolled. Clinical characteristics, biochemical indices and HR-pQCT indices were respectively collected. PHP1 patients had higher serum Ca and PTH level than NS-HP patients at the time of both diagnosis and HR-pQCT measurement. A higher BMI and lower serum P level were observed in PHP1 patients than NS-HP patients at the time of HR-pQCT measurement. Bone microstructure analysis showed PHP1 patients had decreased Tb.N, increased Tb.Sp, and increased Tb.1/N.SD at tibia compared to NS-HP patients. Subgroup analysis showed no significant difference in Tb.N and Tb.Sp in PHP1b patients compared to NS-HP patients. Multiple linear regression analysis showed increased Tb.N and decreased Tb.Sp at tibia were associated with longer treatment duration in PHP1b patients. The microarchitecture evaluated by HR-pQCT in this study further supported that bone tissue had a preserved sensitivity to PTH in PHP1 patients and trabecular bone was more susceptible. Moreover, at least, bone status in PHP1b patients might benefit from regular treatment.

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.

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.

Bone turnover markers are associated with the PTH levels in different subtypes of pseudohypoparathyroidism type 1 patients

OBJECTIVE

Bone responsiveness to parathyroid hormone (PTH) in different subtypes of pseudohypoparathyroidism type 1 (PHP1) remains controversial. We aimed to investigate this phenomenon using bone turnover markers (BTMs) in a large cohort of PHP1 patients.

DESIGN

Retrospective study.

PATIENTS

Sixty-three PHP1 patients diagnosed by molecular analysis were used as subjects, and 48 sex- and age-matched patients with nonsurgical hypoparathyroidism (NS-HP) were used for comparison.

MEASUREMENTS

Bone turnover markers, alkaline phosphatase (ALP), C-terminal telopeptide of type I collagen (β-CTX) and related parameters in PHP1 were compared among different subtypes and with NS-HP.

RESULTS

Among all the PHP1 patients (15 PHP1A, 14 familial 1B and 34 sporadic 1B), 23.8% had elevated baseline BTM levels. No significant difference was found in the β-CTX levels among different subtypes. The β-CTX level was positively correlated with the PTH level for all PHP1, PHP1B and PHP1A patients (B = 0.001, 0.001 and 0.004, respectively; all p < .05). The BTM levels of PHP1 patients were significantly higher than those of NS-HP patients (β-CTX: 0.56 ng/ml vs. 0.20 ng/ml, p = .001; ALP: 105 U/L vs. 72 U/L, p = .001). The serum β-CTX levels in different PHP1 subtypes were all significantly higher than those in NS-HP patients in adults. Among the 22 followed up patients, changes in BTMs were associated with changes in PTH (β-CTX: r = .507, p = .023; ALP: r = .475, p = .034).

CONCLUSIONS

Bone tissues respond to PTH in different PHP1 subtypes, and it is reasonable to monitor and normalize PTH and BTMs in addition to the serum and urinary calcium levels in the follow-up of PHP1 patients.

Symptomatic spinal cord compression: an uncommon symptom in pseudohypoparathyroidism

We describe symptomatic spinal cord compression associated with pseudohypoparathyroidism (PHP) in a young female patient and reviewed similar cases previously reported in the literature. The characteristics of these cases were analyzed from etiology, clinical subtypes, symptoms, treatment, and prognosis. Neurological examination revealed functional upper extremities with bilateral lower extremity paraplegia. Laboratory tests showed hypocalcemia, hyperphosphatemia, and elevated parathyroid hormone; high-throughput sequencing showed a heterozygous GNAS mutation in exon 12, specifically c.1006C > T (p.R336W). Imaging findings showed multilevel spinal stenosis with significant spinal cord compression at the T2-T3 level. Seventeen cases with similar characteristics were reviewed. We found that the primary clinical manifestation of these patients was bilateral lower extremity spastic paraplegia. Multilevel spinal cord compression was commonly observed, especially at the lower cervical and upper thoracic spinal cord. Most of the patients had poor surgical treatment outcome and prognosis. Clinicians should be aware of paraplegia due to spinal cord compression as a rare neurological complication in patients with PHP. Early diagnosis and treatment of PHP is one basis for preventing severe spinal cord-related complications.

Imprinting disorders in humans: a review

PURPOSE OF REVIEW

Mammals have two complete sets of chromosomes, one from each parent with equal autosomal gene expression. Less than one percentage of human genes are imprinted or show expression from only one parent without changing gene structure, usually by DNA methylation, but reversible in gametogenesis. Many imprinted genes affect fetal growth and development accounting for several human disorders reviewed in this report.

RECENT FINDINGS

Disorders include Prader-Willi and Angelman syndromes, the first examples of imprinting errors in humans, chromosome 15q11.2-q13.3 duplication, Silver-Russell syndrome, Beckwith-Weidemann syndrome, GNAS gene-related inactivation disorders (e.g. Albright hereditary osteodystrophy), uniparental chromosome 14 disomy, chromosome 6q24-related transient neonatal diabetes mellitus, parent of origin effects in 15q11.2 BP1-BP2 deletion (Burnside-Butler) syndrome and 15q11-q13 single gene imprinted disorders.

SUMMARY

Periconceptional and intrauterine life can be influenced by environmental factors and nutrition impacting DNA methylation. This process not only alters development of the fetus, but pregnancy complications may result from large fetal size. Epigenetic processes control imprinted gene functions and regulation with susceptibility to diseases as described. A better understanding of these processes will impact on care and treatment of affected individuals.

A paternally inherited non-sense variant c.424G>T (p.G142*) in the first exon of XLαs in an adult patient with hypophosphatemia and osteopetrosis

XLαs, the extra-large isoform of alpha-subunit of the stimulatory guanine nucleotide-binding protein (Gsα), is paternally expressed. The significance of XLαs in humans remains largely unknown. Here, we report a patient who presented with increased bone mass, hypophosphatemia, and elevated parathyroid hormone (PTH) levels. His serum calcium was in the lower limit of the normal range. Whole exome sequencing of this subject found a novel non-sense variant c.424G>T (p. G142*) in the first exon of XLαs, which was inherited from his father and transmitted to his daughter. This variant was predicted to exclusively influence the expression of XLαs, while possibly having no significant effects on other gene products of this locus. Ellsworth-Howard test revealed normal renal response to PTH in proband. Human SaOS2 cells transfected with mutant XLαs failed to generate cyclic adenosine monophosphate under PTH stimulation, indicating skeletal resistance to this hormone. This subject showed higher circulating sclerostin, dickkopf1, and osteoprotegerin (OPG) levels, while lower receptor activator of nuclear factor kappa-B ligand/OPG ratio, leading to reduced bone resorption. Our findings indicate that XLαs plays a critical role in bone metabolism and GNAS locus should be considered as a candidate gene for high bone mass.

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.

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.

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.

Bone Status Among Patients With Nonsurgical Hypoparathyroidism, Autosomal Dominant Hypocalcaemia, and Pseudohypoparathyroidism: A Cohort Study

Nonsurgical hypoparathyroidism (Ns-HypoPT) and pseudohypoparathyroidism (PHP) are both rare diseases, characterized by hypocalcemia. In Ns-HypoPT, PTH levels are low, whereas patients with PHP often have very high levels due to receptor-insensitivity to PTH (PTH-resistance). Accordingly, we hypothesized that indices of bone turnover and bone mineralization/architecture are similar in Ns-HypoPT and PHP despite marked differences in PTH levels. We studied 62 patients with Ns-HypoPT and 31 with PHP as well as a group of age- and sex-matched healthy controls. We found a significantly higher areal BMD (aBMD) by DXA among patients with Ns-HypoPT, both compared with PHP and the background population. Compared with Ns-HypoPT, PHP patients had significantly lower total and trabecular volumetric BMD (vBMD) assessed by quantitative computed tomography (QCT) scans at the spine and hip. High-resolution peripheral quantitative computed tomography (HRpQCT) scans showed a lower trabecular area and vBMD as well as a lower trabecular number at the tibia in PHP compared to Ns-HypoPT and matched controls. In PHP, PTH levels correlated with levels of markers of bone formation (osteocalcin, bone-specific alkaline phosphatase, P1NP), and bone resorption (CTx). In adult males, levels of bone markers were significantly higher in PHP compared with Ns-HypoPT. Levels of procalcitonin and calcitonin were significantly higher in PHP compared with Ns-HypoPT. In conclusion, indices of bone turnover, density, and microarchitecture differ between patients with Ns-HypoPT and PHP. Our data suggest that patients with PHP do not have a complete skeletal resistance to PTH and that the effects of chronically high PTH levels in PHP are mostly confined to the trabecular tissue. © 2017 American Society for Bone and Mineral Research.

Sporadic pseudohypoparathyroidism type-1b with asymptomatic hypocalcemia

Pseudohypoparathyroidism type 1b (PHP-1b) is usually diagnosed on various symptoms of hypocalcemia. Previous studies reported a few cases of autosomal dominant pattern PHP-1b identified on familial analysis with asymptomatic hypocalcemia. Herein we report the case of a 6-year-old male patient with sporadic PHP-1b incidentally detected on preoperative examination. He had neither characteristic findings of Albright hereditary osteodystrophy nor evidence of tetany. Sporadic PHP-1b was diagnosed on the basis of clinical observation and laboratory examination. In addition, genetic testing using methylation-specific multiplex ligation-dependent probe amplification indicated broad methylation abnormalities and confirmed the sporadic form of PHP-1b. Sporadic PHP-1b might often be overlooked when diagnosis is done simply on definitive clinical features. To avoid this, DNA sequencing and methylation analysis should be performed even in the absence of definitive clinical features.

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.

Pseudohypoparathyroidism - epidemiology, mortality and risk of complications

OBJECTIVE

Pseudohypoparathyroidism (PHP) is caused by a mutation within the GNAS gene or upstream of the GNAS complex locus. It is characterized by target organ resistance to PTH, resulting in hypocalcaemia and hyperphosphataemia. Studies in patients with PHP are limited. We sought to identify all patients in Denmark with PHP and access their mortality data and risk of complications.

DESIGN

Patients were identified through the Danish National Patient Registry and a prescription database, with subsequent validation by investigation of patient charts.

METHODS

For each case, three age- (±2 years) and gender-matched controls were randomly selected from the general background population. We identified a total of 60 cases, equal to a prevalence of 1·1/100 000 inhabitants. The average age at diagnosis was 13 years (range 1-62 years), and 42 were women. Only 14 patients had an identified mutation in the GNAS1 gene.

RESULTS

Compared with controls, patients with PHP had an increased risk of neuropsychiatric disorders (P < 0·01), infections (P < 0·01), seizures (P < 0·01) and cataract (P < 0·01), whereas their risk of renal, cardiovascular, malignant disorders and fractures was compatible with the general background population. The same tendencies were found in a subgroup analysis in cases with genetically verified PHP.

CONCLUSION

Patients with PHP have an increased risk of neuropsychiatric disorders, infections, cataract and seizures, whereas mortality among PHP patients is compatible with that in the background population.

Severe hypercalcemic hyperparathyroidism developing in a patient with hyperaldosteronism and renal resistance to parathyroid hormone

We evaluated an African American woman referred in 1986 at age 33 years because of renal potassium and calcium wasting and chronic hip pain. She presented normotensive, hypokalemic, hypocalcemic, normophosphatemic, and hypercalciuric. Marked hyperparathyroidism was evident. Urinary cyclic adenosine monophosphate (cAMP) excretion did not increase in response to parathyroid hormone (PTH) infusion, indicating renal resistance to PTH. X-rays and bone biopsy revealed severe osteitis fibrosa cystica, confirming skeletal responsiveness to PTH. Renal potassium wasting, suppressed plasma renin activity, and elevated plasma and urinary aldosterone levels accompanied her hypokalemia, suggesting primary hyperaldosteronism. Hypokalemia resolved with spironolactone and, when combined with dietary sodium restriction, urinary calcium excretion fell and hypocalcemia improved, in accord with the known positive association between sodium intake and calcium excretion. Calcitriol and oral calcium supplements did not suppress the chronic hyperparathyroidism nor did they reduce aldosterone levels. Over time, hyperparathyroid bone disease progressed with pathologic fractures and persistent pain. In 2004, PTH levels increased further in association with worsening chronic kidney disease. Eventually hypercalcemia and hypertension developed. Localizing studies in 2005 suggested a left inferior parathyroid tumor. After having consistently declined, the patient finally agreed to neck exploration in January 2009. Four hyperplastic parathyroid glands were removed, followed immediately by severe hypocalcemia, attributed to "hungry bone syndrome" and hypoparathyroidism, which required prolonged hospitalization, calcium infusions, and oral calcitriol. Although her bone pain resolved, hyperaldosteronism persisted.

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.

Ain't No Sunshine When She's Gone: Pseudohypoparathyroidism Discovered in an Adult

An 18-year-old negroid woman presented with progressive cramps in both hands. She was Jamaican and had moved to The Netherlands 8 months before. On physical examination Trousseau's sign was positive. Laboratory analysis showed severe hypocalcaemia (1.17 mmol/L) and hyperphosphatemia (2.0 mmol/L). Urinary excretion of both calcium (0.8 mmol/day) and phosphate (5 mmol/day) was low, as is seen in hypoparathyroidism. However, the PTH level was increased (22.1 pmol/L), whereas 25-(OH)-vitamin D was low (31 nmol/L). An Ellsworth-Howard test showed only a fivefold increase in urinary phosphate excretion after administration of synthetic PTH, supporting the diagnosis pseudohypoparathyroidism. Upon treatment with calcium supplementation and alfacalcidol, her symptoms disappeared. Pseudohypoparathyroidism (PHP) is a rare hereditary disorder resembling hypoparathyroidism, although plasma PTH levels are elevated. PHP is caused by alterations in the PTH receptor, inducing target tissue resistance to PTH. This results in hypocalcaemia and hyperphosphatemia, while PTH levels are elevated. The diagnosis is confirmed by the Ellsworth-Howard test, which will show a 100-fold increase in phosphate excretion if the PTH receptor functions properly. Treatment is lifelong supplementation of calcium and alfacalcidol. In our patient, symptoms were probably evoked by the lack of sunlight in Dutch winter, decreasing vitamin D levels and thereby aggravating hypocalcaemia.

Clinical review: Pseudohypoparathyroidism: diagnosis and treatment

CONTEXT

The term pseudohypoparathyroidism (PHP) indicates a group of heterogeneous disorders whose common feature is represented by impaired signaling of various hormones (primarily PTH) that activate cAMP-dependent pathways via Gsα protein. The two main subtypes of PHP, PHP type Ia, and Ib (PHP-Ia, PHP-Ib) are caused by molecular alterations within or upstream of the imprinted GNAS gene, which encodes Gsα and other translated and untranslated products.

EVIDENCE ACQUISITION

A PubMed search was used to identify the available studies (main query terms: pseudohypoparathyroidism; Albright hereditary osteodystrophy; GNAS; GNAS1; progressive osseous heteroplasia). The most relevant studies until February 2011 have been included in the review.

EVIDENCE SYNTHESIS AND CONCLUSIONS

Despite the first description of this disorder dates back to 1942, recent findings indicating complex epigenetic alterations beside classical mutations at the GNAS complex gene, pointed out the limitation of the actual classification of the disease, resulting in incorrect genetic counselling and diagnostic procedures, as well as the gap in our actual knowledge of the pathogenesis of these disorders. This review will focus on PHP type I, in particular its diagnosis, classification, treatment, and underlying molecular alterations.