Albright's hereditary osteodystrophy

Pseudohypoparathyroidism is a genetic disorder in which the body is unable to respond to parathyroid hormone. Parathyroid hormone helps control calcium, phosphorous, and vitamin D levels in the bones and blood. Hypoparathyroidism is a similar condition in which the body does not make enough parathyroid hormone instead of not being able to respond to it (as in pseudohypoparathyroidism).^[1]

The symptoms of these two conditions are similar and are caused by low calcium levels and high phosphate levels in the blood. This may cause cataracts (clouding of the lens of the eye), dental problems, numbness, seizures, or tetany (muscle twitches and hand and foot spasms). These symptoms are usually first seen in childhood.^[1]

There are two different types of pseudohypoparathyroidism, both of which are caused by spelling mistakes (mutations) in certain genes. Type 1 can be further divided into three sub-types.^[1] Click on the links below for more information on the various types of pseudohypoparathyroidism.

Pseudohypoparathyroidism type 1A
Pseudohypoparathyroidism type 1B
Pseudohypoparathyroidism type 1C
Pseudohypoparathyroidism type 2

Albright's hereditary osteodystophy is a genetic disorder that can cause many different symptoms. People with this disorder usually have short stature, obesity, round face, short bones in the hands and feet (brachydactyly), subcutaneous (under the skin) ossifications (replacement of cartilage by bone), and dimples on affected knuckles.^[2][1][3] Some people may have mild developmental delay.^[2]

People with this disorder usually are resistant to parathyroid hormone (which is a condition called pseudohypoparathyroidism). This causes low levels of calcium in the bones and the blood. Low levels of calcium in the blood (hypocalcemia) can cause numbness, seizures, cataracts (cloudy lens in the eye), dental issues, and tetany (muscle twitches and hand and foot spasms).^[1][3]

Albright's hereditary osteodystophy (AHO) is caused by spelling mistakes (mutations) in the GNAS gene. This gene is responsible for creating a subunit of a certain protein called a G protein. The G protein helps regulate the activity and production of certain hormones. It is also involved in regulating the development of bone and helps prevent the body from producing bone tissue in the wrong place. Thus, a mutation in the GNAS gene leads to abnormal creation of the G protein, which then leads to issues with the activity of certain hormones in the body and abnormal bone growth.^[2]

The hormone resistance that can be associated with AHO, in particular the resistance to parathyroid hormone (PTH), depends on whether the mutation is inherited from the mother or the father. This is due to a concept called genomic imprinting. Everyone has two copies of each gene in their body, one from their mother and one from their father. Usually both copies of the gene are active or "turned on." Although, some genes are only active when inherited from a person's mother while other genes are only active when inherited from a person's father. When the disorder is inherited from the mother, in addition to AHO there are also symptoms associated with the resistance to certain hormones (pseudohypoparathyroidism type 1a (PHP1a)). If inherited from the father, there are no hormone issues associated with the AHO (pseudopseudohypoparathyroidism (PPHP)).^[2][3]

Treatment with calcium and vitamin D supplements help maintain normal levels of calcium in the blood. If there are high levels of phosphate in the blood, it may be recommended to eat a low-phosphorous diet or take medications called phosphate binders to help lower the levels of phosphate. Examples of phosphate binders include calcium carbonate, calcium acetate, and sevelamer HCl.^[1]