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Pseudohypoparathyroidism


Alternative names

Albright's hereditary osteodystrophy; Types 1A and 1B pseudohypoparathyroidism

Definition

Pseudohypoparathyroidism is a genetic disorder that resembles hypoparathyroidism (lowered levels of parathyroid hormone) but is caused by a lack of response to parathyroid hormone rather than a deficiency in the hormone itself.

Causes, incidence, and risk factors

Parathyroid hormone (PTH) is a hormone produced by the parathyroid glands that helps regulate calcium and phophate levels in the blood. The effects of PTH are seen in several body systems including the skeletal, gastrointestinal, renal (kidney), muscular, and central nervous system .

In pseudohypoparathyroidism, there is an adequate amount of PTH but the body cannot respond to it. The body is "resistant" to the effects of PTH. As a result, a picture very similar to hypoparathyroidism develops with low calcium levels in the blood and high phophate levels. This results in the characteristic symptoms which are generally first seen in childhood.

There are two different types of pseudohypoparathyroidism, both of which are caused by abnormal genes. Type I can be further divided into two sub-types: type Ia is caused by a one-gene abnormality inherited in an autosomal dominant manner (only one parent needs to have the gene for the child to inherit it). This defect also causes short stature, round face and short hand bones and is also called Albright's hereditary osteodystrophy.

Type Ib is characterized by resistance to PTH confined to the kidney. As a result, the calcium and phosphate problems are seen, but not the rest of the syndrome. The genetic and molecular features of Ib are less clear.

Type II is very similar to type I in its clinical features, but the underlying mechanism in the kidney is different.

When Albright's hereditary osteodystrophy occurs without hypocalcemia (low levels of calcium in the blood), it is known as pseudopseudohypoparathyroidism.

All forms of pseudohypoparathyroidism are very rare.

Symptoms

Symptoms are related to low levels of calcium and include sensations of numbness and seizures.

Signs and tests

Signs related to Albright's hereditary osteodystrophy include:

  • short stature
  • round face and short neck
  • brachydactyly (short hand bones, especially the bone below the 4th finger)
  • subcutaneous calcification
  • dimples can replace knuckles on affected digits

Signs of hypocalcemia include:

  • seizures
  • tetany
  • cataracts
  • dental abnormalities

Hypocalcemia typically begins in childhood.

Tests may show:

  • low serum calcium
  • elevated serum phosphorus
  • elevated intact PTH
  • Abnormal urinary cAMP response to PTH challenge (Type Ia and Ib)
  • Abnormal gene testing
  • MRI or CT scan showing calcification of basal ganglia

Treatment

Treatment consists of calcium and vitamin D supplementation to maintain high calcium levels without the aid of PTH.

Expectations (prognosis)

Hypocalcemia in pseudohypoparathyroidism is usually milder than in other forms of hypoparathyroidism. However, there can be complications such as seizures and other endocrine problems, which can cause lowered sexual drive and development and lowered energy levels and increased weight.

Complications

Patients with type Ia pseudohypoparathyroidism have an increased incidence of other endocrine abnormalities (such as hypothyroidism and hypogonadism).

Calling your health care provider

Call your health care provider if you or your child have any symptoms of hypocalcemia or features of this disorder.

Update Date: 9/1/2002

Todd T. Brown, M.D., Division of Endocrinology and Metabolism, Johns Hopkins Hospital, Baltimore, MD. Review provided by VeriMed Healthcare Network.

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Last updated: Tue, 06 Jan 2009 00:20:03 GMT
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