Multihormone Resistance Research Articles

Pseudohypoparathyroidism andGNASEpigenetic Defects: Clinical Evaluation of Albright Hereditary Osteodystrophy and Molecular Analysis in 40 Patients

The two main subtypes of pseudohypoparathyroidism (PHP), PHP-Ia and -Ib, are caused by mutations in GNAS exons 1-13 and methylation defects in the imprinted GNAS cluster, respectively. PHP-Ia patients show Albright hereditary osteodystrophy (AHO) and resistance toward PTH and additional hormones, whereas PHP-Ib patients do not have AHO, and hormone resistance appears to be limited to PTH and TSH. Recently, methylation defects have been detected in few patients with PHP and mild AHO, indicating a molecular overlap between the two forms. The aim of the study was to screen patients with clinically diagnosed PHP-Ia for methylation defects and to investigate the presence of correlations between the molecular findings and AHO severity. We investigated differential methylation of GNAS regions and STX16 microdeletions in genomic DNA from 40 patients with sporadic AHO and multihormone resistance, with no mutations in Gsalpha-coding GNAS exons. Molecular analysis showed GNAS cluster imprinting defects in 24 of the 40 patients analyzed. No STX16 deletion was detected. The presence of imprinting defects was not associated with the severity of AHO or with specific AHO signs. We report the largest series of the literature of patients with clinical AHO and multihormone resistance and no mutation in the Gsalpha gene. Our findings of frequent GNAS imprinting defects further confirm the existence of an overlap between molecular and clinical features of PHP-Ia and PHP-Ib and highlight the necessity of a new clinical classification of the disease that takes into account the recent knowledge on the molecular basis underlying these defects.

A Case of Pseudopseudohypoparathyroidism with Normal Stature

Pseudopseudohypoparathyroidism (PPHP) is characterized by the phenotype of Albright hereditary osteodystrophy (AHO) alone without biochemical evidence of multihormone resistance, which is unlike pseudohypoparathyroidism. AHO is associated with characteristic developmental abnormalities that include a short stocky stature, a short neck, brachydactyly, a round face, central obesity, mental retardation and subcutaneous ossifications. AHO is an autosomal dominant disease that’s caused by heterozygous inactivating mutations in the Gsα gene (GNAS1). Melanocortin-4 receptor (MC4R) is a hypothalamic Gs-coupled receptor that is thought to mediate the central effect of leptin on satiety. MC4R mutations cause morbid obesity starting in infancy, as well as an elevated leptin level. A 62 year old man with a height of 171.5 cm, a round face, a short neck, central obesity and brachydactyly had normal ranges of serum calcium, phosphorus and PTH and a normal Ellsworth-Howard test. GNAS1 gene analysis revealed substitution of alanine to cysteine in the 165 codon of exon 6 and substitution of alanine to cysteine in the 231 codon of exon 9. Two known SNPs (Cyt-1042Thy, Gua-719Ade) in the MC4R were detected in the patient. We report here on a case of PPHP and the patient had normal stature. We propose that MC4R may have contributed to the obesity & normal

Hypothyroidism in patients with pseudohypoparathyroidism type Ia: clinical evidence of resistance to TSH and TRH

Hypothyroidism is a manifestation of multi-hormonal resistance in pseudohypoparathyroidism type Ia (PHP Ia). The objective of the study was to determine the mechanisms of hypothyroidism in PHP Ia. A prospective study. Ten patients with PHP Ia. The serum concentrations of TSH, free triiodothyronine (FT(3)), free thyroxine (FT(4)), and prolactin (PRL) were measured at baseline and after stimulation with TRH (200 microg i.v). The median basal serum TSH concentration was 4.92 mU/l. Basal serum TSH concentration was slightly elevated in eight patients (4.22-7.0 mU/l; normal range, 0.4-3.6 mU/l), normal in one patient (2.5 mU/l), and high in one patient (13.1 mU/l). After the TRH test, TSH concentrations increased to 13.4-36.0 mU/l (normal range, 4.0-20.0 mU/l). The absolute values after the test were normal in three patients and high in seven patients. However, TSH responses relative to the baseline value (stimulated/basal TSH and expressed as a fold increase), which reflect the relative increases after TRH stimulation, were low in seven patients (2.3- to 4.3-fold TSH) and normal in three patients. Basal FT(4) concentration was normal in seven patients and low in three patients (range, 8.4-20.0 pmol/l; mean, 14.1+/-4.3 pmol/l; normal range, 10.5-23.0 pmol/l). Basal FT(3) concentration was normal in nine patients and low in one patient (range, 0.9-5.0 pmol/l; mean, 3.8+/-1.1 pmol/l; normal range, 3.3-6.1 pmol/l). FT(4) and FT(3) were not significantly increased after the TRH test. PRL concentration was normal at baseline and increased from 7 to 96 ng/ml after TRH. Our results support the hypothesis that patients with PHP Ia have impaired sensitivity to both TSH and TRH.

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

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

Presentation and clinical progression of pseudohypoparathyroidism with multi-hormone resistance and Albright hereditary osteodystrophy: A case series

Anthropometric and biochemical features were retrospectively evaluated in 12 patients with pseudohypoparathyroidism, Albright hereditary osteodystrophy, and multi-hormone resistance. Hypothyroidism and subcutaneous calcifications were presenting features in younger children. Temporal trends in stimulatory hormone resistance included early thyroid-stimulating hormone elevation and progression from parathyroid hormone elevation to hyperphosphatemia and hypocalcemia.

Multihormonal Resistance to Parathyroid Hormone, Thyroid Stimulating Hormone, and Other Hormonal and Neurosensory Stimuli in Patients with Pseudohypoparathyroidism

In patients with pseudohypoparathyroidism, hormonal resistance first affects parathyroid hormone (PTH), which leads to calcipenia, a decrease in renal vitamin D activation, and a tendency to bone receptor remodeling. However, because G proteins are ubiquitously distributed, multiple hormonal resistance occurs in pseudohypoparathyroidism type Ia and type Ic, impairing responses to other calciotropic hormones (PTHrP, calcitonin), TSH, and also pituitary and hypothalamic hormones, and to neurosensory stimuli. The diversity of multihormonal resistance contributes to the various phenotypes of the disease. Some clinical discomfort and medical consequences of the disease can be treated or prevented with hormone supplementation or modulation.

Gs(alpha) mutations and imprinting defects in human disease.

Gs is the ubiquitously expressed heterotrimeric G protein that couples receptors to the effector enzyme adenylyl cyclase and is required for receptor-stimulated intracellular cAMP generation. Activated receptors promote the exchange of GTP for GDP on the Gs alpha-subunit (Gs(alpha)), resulting in Gs activation; an intrinsic GTPase activity of Gs(alpha) deactivates Gs by hydrolyzing bound GTP to GDP. Mutations of Gs(alpha) residues involved in the GTPase reaction that lead to constitutive activation are present in endocrine tumors, fibrous dysplasia of bone, and McCune-Albright syndrome. Heterozygous loss-of-function mutations lead to Albright hereditary osteodystrophy (AHO), a disease characterized by short stature, obesity, and skeletal defects, and are sometimes associated with progressive osseous heteroplasia. Maternal transmission of Gs(alpha) mutations leads to AHO plus resistance to several hormones (e.g., parathyroid hormone) that activate Gs in their target tissues (pseudohypoparathyroidism type IA), while paternal transmission leads only to the AHO phenotype (pseudopseudohypoparathyroidism). Studies in both mice and humans demonstrate that Gs(alpha) is imprinted in a tissue-specific manner, being expressed primarily from the maternal allele in some tissues and biallelically expressed in most other tissues. This likely explains why multihormone resistance occurs only when Gs(alpha) mutations are inherited maternally. The Gs(alpha) gene GNAS1 has at least four alternative promoters and first exons, leading to the production of alternative gene products including Gs(alpha), XL alphas (a novel Gs(alpha) isoform expressed only from the paternal allele), and NESP55 (a chromogranin-like protein expressed only from the maternal allele). The fourth alternative promoter and first exon (exon 1A) located just upstream of the Gs(alpha) promoter is normally methylated on the maternal allele and is transcriptionally active on the paternal allele. In patients with parathyroid hormone resistance but without AHO (pseudohypoparathyroidism type IB), the exon 1A promoter region is unmethylated and transcriptionally active on both alleles. This GNAS1 imprinting defect is predicted to decrease Gs(alpha) expression in tissues where Gs(alpha) is normally imprinted and therefore to lead to renal parathyroid hormone resistance.

Variable and tissue-specific hormone resistance in heterotrimeric Gs protein alpha-subunit (Gsalpha) knockout mice is due to tissue-specific imprinting of the gsalpha gene.

Albright hereditary osteodystrophy (AHO), an autosomal dominant disorder characterized by short stature, obesity, and skeletal defects, is associated with heterozygous inactivating mutations of GNAS1, the gene encoding the heterotrimeric G protein alpha-subunit (Gsalpha) that couples multiple receptors to the stimulation of adenylyl cyclase. It has remained unclear why only some AHO patients present with multihormone resistance and why AHO patients demonstrate resistance to some hormones [e.g., parathyroid hormone (PTH)] but not to others (e.g., vasopressin), even though all activate adenylyl cyclase. We generated mice with a null allele of the mouse homolog Gnas. Homozygous Gs deficiency is embryonically lethal. Heterozygotes with maternal (m-/+) and paternal (+/p-) inheritance of the Gnas null allele have distinct phenotypes, suggesting that Gnas is an imprinted gene. PTH resistance is present in m-/+, but not +/p-, mice. Gsalpha expression in the renal cortex (the site of PTH action) is markedly reduced in m-/+ but not in +/p- mice, demonstrating that the Gnas paternal allele is imprinted in this tissue. Gnas is also imprinted in brown and white adipose tissue. The maximal physiological response to vasopressin (urinary concentrating ability) is normal in both m-/+ and +/p- mice and Gnas is not imprinted in the renal inner medulla (the site of vasopressin action). Tissue-specific imprinting of Gnas is likely the mechanism for variable and tissue-specific hormone resistance in these mice and a similar mechanism might explain the variable phenotype in AHO.

Hypothyroïdie compensée révélant une pseudohypoparathyroïdie en l'absence d'hypocalcémie et d'hyperphosphorémie

Background. — Type la pseudohypoparathyroidism is due to a molecular defect causing Gs protein deficiency. It is responsible for multi-hormonal resistance and skeletal abnormalities. Parathyroid hormone resistance can be subtle so that the diagnosis can be difficult in patients with atypical manifestations. Case report. — A 10-year-old boy was first referred for growth retardation (height standard deviation score: −2.8). He had short metacarpals, and scaphocephaly. Laboratory findings revealed an elevation of plasma TSH (8.8 μU/mL) with normal thyroid hormone levels. The investigations ruled out common causes of compensated hypothyroidism. Despite normal blood calcium and phosphate levels, parathyroid hormone was elevated to 358 pg/mL (normal values: 10–60) without renal failure, suggestive of hormonal resistance. The diagnosis of pseudohypoparathyroidism type la was confirmed by a 50% reduction of Gs activity. Melanodermia, associated with an elevation of ACTH was suggestive of ACTH resistance without MSH resistance. Moreover, skeletal radiography showed a narrow lumbar canal. Conclusion. — Type 1a pseudoypoparathyroidism could be part of the etiological diagnosis of primary hypothyroidism, even in the absence of hypocalcemia and hyperphosphatemia. Similarly, skeletal abnormalities extend beyond the classical features of Albright's osteodystrophy.

Prevalence of three mutations in the G sα gene among 24 families with pseudohypoparathyroidism type Ia

Pseudohypoparathyroidism type Ia (PHP-Ia), an inherited multi-hormone resistance syndrome, is associated with deficient cellular activity of the α-subunit of the guanine nucleotide-binding protein (G sα) that stimulates adenylyl cyclase. We determined prevalance of three recently described mutations in exons 1 and 10 of the G sα gene among 24 unrelated patients with PHP-Ia. Restriction analysis was used to detect two mutations that produce unique RFLPs, and allele-specific oligonucleotide hybridization was used to detect the other mutation. As none of these mutations were not found, genomic DNA was analyzed with denaturing gradient gel electrophoresis to screen for other mutations in exon 10. Mutations of the initiation codon and exon 10 in the G sα gene thus rarely(≤4% each) cause PHP-Ia and the G sα gene mutations causing PHP-Ia are heterogeneous and unique to each pedigree.