eMedicine Specialties > Endocrinology > Parathyroid Gland

Pseudohypoparathyroidism

Mini R Abraham, MD, Consulting Staff, Saint Luke's Medical Group
Romesh Khardori, MD, Chief, Division of Endocrinology, Metabolism and Molecular Medicine, Professor, Department of Internal Medicine, Southern Illinois University School of Medicine

Updated: Aug 5, 2009

Introduction

Background

Pseudohypoparathyroidism (PHP) is a heterogeneous group of disorders characterized by hypocalcemia, hyperphosphatemia, increased serum concentration of parathyroid hormone (PTH), and insensitivity to the biological activity of PTH.

In 1942, Fuller Albright first introduced the term pseudohypoparathyroidism to describe patients who presented with PTH-resistant hypocalcemia and hyperphosphatemia along with an unusual constellation of developmental and skeletal defects, collectively termed Albright hereditary osteodystrophy (AHO). These features include short stature, rounded face, shortened fourth metacarpals and other bones of the hands and feet, obesity, dental hypoplasia, and soft-tissue calcifications/ossifications. (See image below and Image 1.) In addition, administration of PTH failed to produce the expected phosphaturia or to stimulate renal production of cyclic adenosine monophosphate (cAMP).

Patient with pseudohypoparathyroidism showing shortened fourth metacarpals.

Pathophysiology

Several variants of PHP have been identified, and PHP type 1a is the best understood form of the disease. The molecular defects in the gene (GNAS1) encoding the alpha subunit of the stimulatory G protein (Gsa) contribute to at least 3 different forms of the disease: PHP type 1a, PHP type 1b, and pseudopseudohypoparathyroidism (pseudo-PHP).¹

All patients are heterozygous, with 1 normal Gsa allele; the mutant allele leads to production of inactive Gsa or to small amounts of active Gsa. Several other peptide hormones, including thyroid-stimulating hormone (thyrotropin), antidiuretic hormone, the gonadotropins, glucagons, adrenocorticotropin, and growth hormone–releasing hormone, use the alpha subunit of stimulatory G protein to enhance cAMP production. Patients with PHP type 1a can present with resistance to the effects of any of these hormones, although in most patients, responses to corticotropin and glucagon are clinically unaffected.

The dominant pattern of inheritance of PHP type 1a has been attributed to haploinsufficiency of GNAS1, meaning that the protein produced by a single normal Gsa allele cannot support normal function, although it may suffice for survival. The single normal Gsa allele preserves the responses to hormones such as corticotropin and glucagon. The haploinsufficiency of the GNAS1 gene is tissue specific, which may explain the selective resistance to hormones and the characteristic habitus of patients with PHP type 1a.

In the same family, some patients with a defective GNAS1 gene have resistance to PTH, whereas others share with them the habitus of AHO but are not resistant to PTH. The latter group are said to have pseudo-PHP. In a 1993 report, Davies et al reported an analysis of pedigrees of families that included patients with PHP and pseudo-PHP, suggesting that patients who inherit the defective gene from the father have pseudo-PHP because the mutant gene is not expressed and the product of a single maternally inherited GNAS1 gene preserves normal responses to PTH and thyrotropin.² However, the occurrence of AHO in patients with pseudo-PHP indicates that 1 GNAS1 gene is not sufficient in all tissues.

Patients with PHP type 1b have a genetically and biochemically distinct disorder. Patients with PHP type 1b lack features of AHO, have normal expression of Gsa protein in accessible tissues, and manifest hormonal resistance limited to PTH target tissues. PTH resistance may be limited to the kidney, with PTH responsiveness preserved in the bone, as evidenced by the hyperparathyroid skeletal lesions observed in these patients.

This disorder is inherited as an autosomal dominant trait, but mutations have not been found in the PTH gene or PTH receptor genes. In 1998, Juppner et al reported a study that involved 4 kindreds with affected members; the unknown gene was paternally imprinted and was mapped to a small region of band 20q13.3, very near the GNAS1 gene.³

The severity of PHP type 1b can vary considerably from one patient to another; even within a single kindred, the different affected members may experience considerable variations in the severity of the disorder. Members of the affected family who share the same haplotype in band 20q13.3 have been reported to be clinically asymptomatic and to have serum calcium levels within the reference range.

Current data suggest that a molecular defect in the GNAS1 gene may also be responsible for at least some forms of PHP type 1b. A mutant promoter or enhancer region of the GNAS1 gene that has lost the ability to support expression of Gsa in the kidney but not in other tissues may be responsible for the renal resistance to PTH. Interestingly, a 2001 publication by Wu et al reported identification of a novel mutation in the carboxyl terminus of the GNAS1 gene in 3 patients with PHP type 1b and their clinically unaffected mother and maternal grandfather.⁴ The absence of PTH resistance in the mother and maternal grandfather who carry the same mutation is consistent with current models of paternal imprinting⁵ of the GNAS1 gene.

Testotoxicosis with PHP type 1a can occur. Gonadotropin-independent sexual precocity has been reported in 2 boys who presented in infancy with classic PHP type 1a. Usually, patients with PHP type 1a show resistance to luteinizing hormone, which could lead to primary testicular insufficiency. The paradoxical presentation of testotoxicosis in these boys resulted from an identical point mutation in the GNAS1 gene, which caused both a loss and gain of Gsa function. PHP type 1a, characterized by a loss of Gsa function, is caused by thermal inactivation of the mutant protein at body temperature. Testotoxicosis indicates an organ-specific gain of Gsa function, resulting from the expression of the mutant protein. The lower temperature of the testes protects the mutant protein from thermal inactivation.

Two other variants of PHP, PHP type 1c and PHP type 2, are much less characterized than the other forms of PHP. Patients with PHP type 1c do not have a detectable defect in Gsa protein despite having clinical and laboratory findings similar to those observed in patients with PHP type 1a. Patients with PHP type 2 show no skeletal and developmental defects, similar to patients with PHP type 1b, but they show a normal urinary cAMP response, in contrast to patients with PHP type 1b.

Patients with PHP can present in infancy, especially if significant hypocalcemia occurs. Some forms of PHP may remain unnoticed or undiagnosed if patients do not have hypocalcemia and/or features of AHO.

An interesting association between PHP type 1a and hypercalcitoninemia without any evidence of medullary thyroid carcinoma has been described.

There are case reports of vitamin D deficiency mimicking PHP. The clinical presentation and biochemical features of stage 1 vitamin D deficiency rickets (VDR) and pseudohypoparathyroidism type 2 are quite similar.

In a 2005 report, Mahmud et al describe 2 sisters who were initially identified as having paroxysmal dyskinesia, but who, on subsequent testing, showed hypocalcemia, hyperphosphatemia, and elevated PTH levels consistent with PHP type 1b.⁶

Frequency

United States

No information is available regarding prevalence in the United States.

International

In 1998, a nationwide epidemiologic survey of PHP was conducted in Japan based on hospital visits in 1997; the period prevalence was 3.4 cases per 1 million people.²⁴ No information is available regarding prevalence in the rest of the world.

Race

No racial or ethnic differences have been reported.

Sex

PHP occurs approximately twice as frequently in females as in males.

Age

Patients' ages range from infancy to senescence.

Clinical

History

• Patients with PHP type 1a present with a characteristic phenotype, collectively called AHO. The constellation of findings includes short stature, stocky habitus, obesity, developmental delay, round face, dental hypoplasia, brachymetacarpals, brachymetatarsals, and soft tissue calcification/ossification.
• Hypocalcemia⁷ in children or adolescents is often asymptomatic.
• Patients may develop paresthesias, muscular cramping, tetany, carpopedal spasm, or seizure.
• Patients with PHP type 1a may have disturbances in taste, smell, vision, and hearing, and they may be hyporesponsive to the biological effects of other peptide hormones that use the alpha subunit of the Gsa protein to enhance cAMP production. The hormones under this class include thyrotropin, antidiuretic hormone, the gonadotropins, glucagon, adrenocorticotropin, and growth hormone–releasing hormone. Evaluate patients for signs and symptoms suggestive of deficiencies of any of these hormones.
• Primary hypothyroidism occurs in most patients with PHP type 1a.⁸
• Reproductive dysfunction commonly occurs in persons with PHP type 1a. Women may have delayed puberty, oligomenorrhea, and infertility.
• Features of hypogonadism may be less obvious in men. Testes may show evidence of maturation arrest or may fail to descend normally. Fertility appears to be decreased in men with PHP type 1a.
• Within the spectrum of PHP type 1a, variability exists in osteoclast responsiveness to PTH. Some patients may have osteopenia and rickets.
• Mentation is impaired in approximately half of patients with PHP type 1a and appears to be related to the Gsa deficiency rather than to chronic hypocalcemia because patients with other forms of PHP and hypocalcemia have normal mentation.
• Unusual presenting manifestations include neonatal hypothyroidism, Parkinson disease, and spinal cord compression.

Physical

• Physical examination may reveal signs of hypocalcemia, including positive Chvostek sign (ie, twitching of facial muscles after tapping the facial nerve just in front of the ear) and/or Trousseau sign (ie, carpal spasm after maintaining an arm blood pressure cuff at 20 mm Hg above the patient's systolic blood pressure for 3 min). Occasionally, cataracts or papilledema are present.
• Obesity is a common feature of AHO.
  • Brachydactyly is the most reliable sign in the diagnosis of AHO. It may be symmetrical or asymmetrical and may involve 1 or both hands or feet. Shortening of the metacarpals causes shortening of the digits, particularly the fourth and fifth digits. Shortening of the metacarpals may be recognized during physical examination as dimpling over the knuckles of a clenched fist (ie, Archibald sign). Shortening of the distal phalanx of the thumb is evident as a thumb in which the ratio of the width of the nail to its length is increased (ie, so-called murderer's thumb or potter's thumb).
  • Several other skeletal deformities have been described in AHO, including short ulna, bowed radius, deformed elbow, or cubitus valgus and coxa vara, coxa valga, genu varum, and genu valgum deformities.
• Patients with pseudo-PHP have the phenotype of AHO but with normal biochemical parameters. Patients with pseudo-PHP are often found in the same kindreds as those with PHP type 1a.
• Patients with PHP type 1b present with hypocalcemia without AHO. The severity of hypocalcemia can vary greatly among family members of the same kindred.

Causes

Molecular defects in the GNAS1 gene, which encodes Gsa, contribute to at least 3 different forms of the disease: PHP type 1a, PHP type 1b, and pseudo-PHP.

Differential Diagnoses

Other Problems to Be Considered

Secondary hyperparathyroidism
Autoimmune polyglandular syndromes
Vitamin D deficiency

Workup

Laboratory Studies

• Serum calcium (including measurement of serum total calcium and ionized calcium) to confirm hypocalcemic state: Serum phosphate levels are elevated.
• Determination of the serum concentration of intact PTH⁷ by immunoradiometric assay (IRMA): When the serum concentration of PTH in a hypocalcemic patient is increased, the patient has either a form of PHP or secondary hyperparathyroidism.
• Assessment of skeletal and renal responsiveness to PTH: Assessment is accomplished by measurement of changes in serum calcium, phosphorus, cAMP, and calcitriol concentrations and in urinary cAMP and phosphorus excretion after administration of the biosynthetic N-terminal fragment of PTH.
• Consider thyroid function tests and measurement of gonadotropin and testosterone or estrogen levels, in addition to growth hormone function assessed by insulinlike growth factor-1.

Freson et al reported on the use of platelets to diagnose Gsa hypofunction, finding in their study that platelet aggregation responses varied according to Gsa signaling defects, thus providing a reflection of a patient's phenotype and genotype.⁹  They concluded that such platelet-based testing can effectively be used in the diagnosis of Gsa defects.

Imaging Studies

• Radiography of the hand may show a specific pattern of shortening of the bones in which the distal phalanx of the thumb and the third through fifth metacarpals are shortened most severely. Radiography may also show small soft tissue opacities (calcifications/ossifications).
• CT scanning may reveal calcification of the basal ganglia.

Other Tests

• An electrocardiogram may reveal prolongation of the QT interval secondary to hypocalcemia.
• Analysis of the GNAS1 gene helps identify the specific genetic defect in patients with PHP type 1a.
• Patients with PHP type 1b¹⁰ may be evaluated for parathyroid-related bone disease. Consider bone mineral density (BMD) testing in this group of patients.

Treatment

Medical Care

All patients with severe symptomatic hypocalcemia should be initially treated with intravenous calcium. Administration of oral calcium and 1alpha-hydroxylated vitamin D metabolites, such as calcitriol, remains the mainstay of treatment and should be initiated in every patient with a diagnosis of PHP. The goals of therapy are to maintain serum total and ionized calcium levels within the reference range to avoid hypercalciuria and to suppress PTH levels to normal. This is important because elevated PTH levels in patients with PHP could cause increased bone remodeling and can lead to hyperparathyroid bone disease.

• In adults, infuse approximately 100 mg of elemental calcium (either calcium chloride or calcium gluconate) over 10-20 minutes. If this measure does not alleviate the clinical manifestation, 100 mg/h of elemental calcium can be infused (in adults), with close monitoring of calcium levels. Do not rapidly infuse calcium because of the possible adverse effects of cardiac conduction defects; cardiac monitoring may help guide therapy. The 2 most readily available formulations for parenteral use are calcium chloride and calcium gluconate; a 10-mL ampule of 10% calcium chloride contains 360 mg of elemental calcium, and a 10-mL ampule of 10% calcium gluconate contains 93 mg of elemental calcium.
• For neonates, infants, and children, the recommended initial dose is 0.5-1 mL/kg of 10% calcium gluconate administered over 5 minutes.

Surgical Care

Rarely, extraskeletal osteomas require surgical removal to relieve pressure symptoms.

Diet

No restrictions are necessary.

Activity

No restrictions are necessary.

Medication

The goals of pharmacotherapy are to correct calcium deficiency, to prevent complications, and to reduce morbidity.

Calcium salts

Used for calcium electrolyte supplementation.

Calcium chloride

Improves nerve and muscle performance by regulating action potential excitation threshold affected by calcium deficiency.

Dosing

Adult

0.5-1 g (7-14 mEq) IV; repeat q1-3d prn

Pediatric

0.2 mL (20 mg of calcium chloride)/kg IV; not to exceed 1-10 mL/d (10% solution); repeat q1-3d prn

Interactions

Coadministration with digoxin may cause arrhythmias; with thiazides, may induce hypercalcemia; may antagonize effects of calcium channel blockers, atenolol, and sodium polystyrene sulfonate

Contraindications

Documented hypersensitivity; ventricular fibrillation not associated with hyperkalemia; digitalis toxicity; hypercalcemia; renal insufficiency; cardiac disease

Precautions

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Administer slowly (not to exceed 0.5-1 mL/min) to avoid extravasation; hypercalcemia may occur in patients with renal failure

Calcium gluconate (Kalcinate)

Moderates nerve and muscle performance and facilitates normal cardiac function. Can be initially administered IV, and calcium levels can be maintained with high-calcium diet. Some patients require PO calcium supplementation.

Dosing

Adult

100-300 mg elemental calcium IV diluted in 150 mL D5W over 10 min; initial rate of infusion should be 0.3-2 mg of elemental calcium/kg/h

Pediatric

2 mg/kg IV of elemental calcium (about 20 mg/kg of calcium gluconate 10%)

Interactions

May decrease effects of tetracyclines, atenolol, salicylates, iron salts, and fluoroquinolones; antagonizes effects of verapamil; large intakes of dietary fiber may decrease calcium absorption and levels

Contraindications

Renal calculi; hypercalcemia; hypophosphatemia; renal or cardiac disease; digitalis toxicity

Precautions

Pregnancy

B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals

Precautions

Caution in digitalized patients and patients with respiratory failure, acidosis, or severe hyperphosphatemia

Calcium carbonate (Oystercal, Caltrate, Os-Cal, Tums)

For supplementation of IV therapy in hypocalcemia. Calcium moderates nerve and muscle performance by regulating action potential excitation threshold.

Dosing

Adult

1-2 g/d PO divided bid/qid at meal times

Pediatric

45-65 mg/kg/d PO divided qid

Interactions

May decrease effects of tetracyclines, atenolol, salicylates, iron salts, and fluoroquinolones; IV administration antagonizes effects of verapamil; large intakes of dietary fiber may decrease calcium absorption and levels

Contraindications

Documented hypersensitivity; renal calculi; hypercalcemia; hypophosphatemia; renal or cardiac disease; digitalis toxicity

Precautions

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Caution in digitalized patients and in patients with respiratory failure or acidosis; hypercalcemia or hypercalciuria may occur when therapeutic amounts are administered

Vitamins

Supplementation increases calcium levels in the serum by improving calcium absorption and retention.

Calcitriol (Calcijex, Rocaltrol)

Increases calcium levels by promoting calcium absorption in intestines and retention in kidneys.

Dosing

Adult

0.25 mcg PO qd; increase at 4- to 8-wk intervals by 0.25 mcg prn

Pediatric

Initial: 15 ng/kg/d PO
Maintenance: 5-40 ng/kg/d PO

Interactions

Cholestyramine and colestipol decrease absorption; magnesium-containing antacids and thiazide diuretics can increase effects

Contraindications

Documented hypersensitivity; hypercalcemia; malabsorption syndrome

Precautions

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Adequate response depends on adequate dietary calcium intake; maintain adequate fluid intake

Follow-up

Further Outpatient Care

• Monitor therapy through regular serum and urine calcium measurements. Exercise caution to avoid renal or hypercalcemic complications.
• Monitor serum PTH levels with a goal of maintaining serum PTH levels within the reference range.

Patient Education

For excellent patient education resources, see eMedicine's Osteoporosis and Bone Health Center.

Miscellaneous

Medicolegal Pitfalls

• Failure to initially treat all patients with severe symptomatic hypocalcemia with intravenous calcium
• Failure to maintain serum total and ionized calcium levels within the reference range to avoid hypercalciuria and to suppress PTH levels to normal
• Failure to slowly infuse calcium (because of the possible adverse effects of cardiac conduction defects)

Multimedia

Media file 1: Patient with pseudohypoparathyroidism showing shortened fourth metacarpals.

References

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31. Yamamoto Y, Noto Y, Saito M, et al. Spinal cord compression by heterotopic ossification associated with pseudohypoparathyroidism. J Int Med Res. Nov-Dec 1997;25(6):364-8. [Medline].

Keywords

pseudohypoparathyroidism, parathyroid, parathyroid hormone, hypocalcemia, parathyroid gland, parathyroid glands, PTH, pseudopseudohypoparathyroidism, hyperphosphatemia, Albright hereditary osteodystrophy, Albright's hereditary osteodystrophy, pseudo-PHP, stimulatory G protein, Gsa, GNAS1, testotoxicosis, dental hypoplasia, brachymetacarpals, brachymetatarsals, brachydactyly

Contributor Information and Disclosures

Author

Mini R Abraham, MD, Consulting Staff, Saint Luke's Medical Group
Mini R Abraham, MD is a member of the following medical societies: American Association of Clinical Endocrinologists and Endocrine Society
Disclosure: Glaxo Smith Kline Honoraria Speaking and teaching; Novo Nordisk Honoraria Speaking and teaching; Eli Lilly Honoraria Speaking and teaching

Coauthor(s)

Romesh Khardori, MD, Chief, Division of Endocrinology, Metabolism and Molecular Medicine, Professor, Department of Internal Medicine, Southern Illinois University School of Medicine
Romesh Khardori, MD is a member of the following medical societies: American Association of Clinical Endocrinologists, American College of Physicians, American Diabetes Association, American Federation for Medical Research, American Medical Association, American Society of Andrology, Endocrine Society, and Illinois State Medical Society
Disclosure: Nothing to disclose.

Medical Editor

Stanley Wallach, MD, Executive Director, American College of Nutrition; Clinical Professor, Department of Medicine, New York University School of Medicine
Stanley Wallach, MD is a member of the following medical societies: American Society for Bone and Mineral Research, American Society for Clinical Investigation, American Society for Clinical Nutrition, American Society for Nutritional Sciences, Association of American Physicians, and Endocrine Society
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

Kent Wehmeier, MD, Professor, Department of Internal Medicine, Division of Endocrinology, Diabetes, and Metabolism, St Louis University School of Medicine
Kent Wehmeier, MD is a member of the following medical societies: American Society of Hypertension, Endocrine Society, and International Society for Clinical Densitometry
Disclosure: Nothing to disclose.

CME Editor

Mark Cooper, MBBS, PhD, FRACP, Head, Diabetes & Metabolism Division, Baker Heart Research Institute, Professor of Medicine, Monash University
Disclosure: Nothing to disclose.

Chief Editor

George T Griffing, MD, Professor of Medicine, St Louis University School of Medicine
George T Griffing, MD is a member of the following medical societies: American Association for the Advancement of Science, American College of Medical Practice Executives, American College of Physician Executives, American College of Physicians, American Diabetes Association, American Federation for Medical Research, American Heart Association, Central Society for Clinical Research, Endocrine Society, International Society for Clinical Densitometry, and Southern Society for Clinical Investigation
Disclosure: Nothing to disclose.

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