Pseudohypoparathyroidism

Definition

Pseudohypoparathyroidism is a genetic disorder that is similar to hypoparathyroidism, but which results from the body's lack of response to parathyroid hormone rather than decreased production of the substance.

Alternative Names

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

Causes, incidence, and risk factors

The parathyroid glands help control calcium use and removal by the body. They do this by producing parathyroid hormone, or PTH. PTH helps control calcium, phosphorus, and vitamin D levels within the blood and bone.

Persons with pseudohypoparathyroidism produce the right amount of PTH, but the body is "resistant" to its effect. This causes low blood calcium levels and high blood phosphate levels.

Pseudohypoparathyroidism is caused by abnormal genes. All forms of pseudohypoparathyroidism are very rare.

Type Ia is inherited in an autosomal dominant manner. That means only one parent needs to pass you the defective gene in order for you to develop the condition. The condition causes short stature, round face, and short hand bones, and is also called Albright's hereditary osteodystrophy.

Type Ib involves resistance to PTH only in the kidneys. Type Ib is less understood than type Ia. Type II is very similar to type I in its clinical features, but the events that take place in the kidneys are different.

Type II pseudohypoparathyroidism also involves low blood calcium and high blood phosphate levels, but persons with this form do not develop the physical characteristics seen in those with Type Ia.

All forms of pseudohypoparathyroidism are very rare.

Symptoms

Symptoms are related to low levels of calcium and include:

• Cataracts
• Dental problems
• Numbness
• Seizures
• Tetany (a collection of symptoms including muscle twitches and hand and foot spasms)

Persons with Albright's hereditary osteodystrophy may have the following symptoms:

• Calcium deposits under the skin
• Dimples that can replace knuckles on affected fingers
• Round face and short neck
• Short hand bones, especially the bone below the 4th finger
• Short stature

Signs and tests

Blood tests will be done to check calcium, phosphorus, and PTH levels. Urine tests may also be done.

Other tests may involve:

• Genetic testing
• Head MRI or CT scan of the brain

Treatment

Calcium and vitamin D supplements are prescribed to maintain proper calcium levels. If blood phosphate levels remain high, a low-phosphorus diet or medicines called phosphate binders (such as calcium carbonate or calcium acetate) may be necessary.

Support Groups

Expectations (prognosis)

Low blood calcium in pseudohypoparathyroidism is usually milder than in other forms of hypoparathyroidism.

Complications

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

Complications of hypocalcemia associated with pseudohypoparathyroidism may include seizures and other endocrine problems, leading to lowered sexual drive and lowered sexual development, lowered energy levels, and increased weight.

Calling your health care provider

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

Prevention

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References

Wysolmerski JJ, Insogna KL. The parathyroid glands, hypercalcemia, and hypocalcemia. In: Kronenberg HM, Schlomo M, Polansky KS, Larsen PR, eds. Williams Textbook of Endocrinology. 11th ed. St. Louis, Mo: WB Saunders; 2008:chap 266.

Bringhurst FR, Demay MB, Kronenberg HM. Disorders of mineral metabolism. In: Kronenberg HM, Schlomo M, Polansky KS, Larsen PR, eds. Williams Textbook of Endocrinology. 11th ed. St. Louis, Mo: WB Saunders; 2008:chap 27.