A familial syndrome of hypocalcemia with associated increased PTH levels, hyperphosphatemia and normal alkaline phosphatase and renal function, in which end organs, mostly the bones and kidneys, are resistant to the actions of parathyroid hormone. Patients may also exhibit the symptoms of hypocalcemia when serum levels drop low enough to become symptomatic. The underlying pathophysiology is a defect at the PTH-receptor (genetic mutation in the alpha subunit of the receptor G-protein leads to altered messenger action), leading to end organ resistance to the action of this hormone.
In type Ia (Albright's hereditary osteodystrophy) disease, the constellation of short stature, mental retardation, ectopic calcification (cranial, subcutaneous tissues, and paraspinal ligaments), round faces, shortened neck, and shortened fourth and fifth metacarpals and metatarsals (brachydactyly). Oftentimes there is associated hypothyroidism. This form of disease is caused by a heterozygousinactivating mutation in the above mentioned alpha subunit.
In type Ib the only abnormality is end organ resistance to PTH. Hypothyroidism and the physical abnormalities (Albright's hereditary osteodystrophy) are lacking. This form of disease is inhereted maternally via an autosomal dominant fashion.
In type Ic disease, patients are afflicted with Albright's hereditary osteodystrophy characteristics and are resistent to the actions of multiple hormones; however, the characteristic underlying alpha subunit of the receptor G-protein abnormality is lacking.
When the resultant hypocalcemia is severe enough to become symptomatic, treatment may include intravenous calcium gluconate 20 mL of a 10% (100mg/mL) at a maximal rate of 30 mg/min. If levels are not emergently low or symptomatic, then the patient may be treated with maintenance therapy in the form of replacement calcium acetate 4 grams/day along with vitamin D or in necessary vitamin D analogs (rocaltrol or paricaltrol). In patients with type Ia disease who have concomitant hypothyroidism, replacement therapy with oral thyroid hormone should be administered.