This information is provided by the National Institutes of Health (NIH) Genetic and Rare Diseases Information Center (GARD).
Pseudohypoparathyroidism type 1B (PHP1B) is a disorder characterized by lack of response (resistance) to parathyroid hormone (PTH) and other hormones such as thyroid-stimulating hormone (TSH). Resistance mainly occurs in the kidneys, causing low blood calcium levels (hypocalcemia), high blood phosphate levels (hyperphosphatemia), and elevated PTH levels (hyperparathyroidism). Some people with PHP1B also have elevated TSH levels due to TSH resistance. Each of these abnormalities can cause a variety of symptoms, which can be viewed by clicking on the terms above.
Severity can vary considerably, even among people in the same family. Symptoms usually begin in childhood due to low calcium levels and may include numbness, seizures, tetany, cataracts, and dental problems. Excessive growth or weight has been described in some newborns or during early infancy and childhood. Some children have skeletal problems, such as reduced bone mineral density and osteitis fibrosa.
The inheritance and genetics of PHP1B is complex. PHP1B is usually sporadic (not inherited), but familial cases with autosomal dominant inheritance, from the mother only, have been reported. When the parent from which a gene is inherited affects the way a gene acts, it is called genomic imprinting. PHP1B may be caused by randomly inheriting both copies of the long arm of chromosome 20 from the father rather than a copy from each parent (paternal 20q disomy), genetic mutations or epigenetic changes involving the GNAS or STX16 gene, or by unidentified genetic or epigenetic factors.
Treatment is lifelong, aiming to normalize calcium and PTH levels with active vitamin D metabolites such as alfacalcidol or calcitriol, and calcium supplementation.
For more information, visit GARD.