Familial hypocalciuric hypercalcemia
|Familial hypocalciuric hypercalcemia|
|Classification and external resources|
|OMIM||145980 145981 600740|
Familial hypocalciuric hypercalcemia (FHH) is a condition that can cause hypercalcemia, a serum calcium level typically above 10.2 mg/dL. It is also known as familial benign hypocalciuric hypercalcemia (FBHH) where there is usually a family history of hypercalcemia which is mild, a urine calcium to creatinine ratio <0.01, and urine calcium <200 mg/day.
Signs and symptoms
Most cases of familial hypocalciuric hypercalcemia are asymptomatic.
Most cases of FHH are associated with loss of function mutations in the calcium-sensing receptor (CaSR) gene, expressed in parathyroid and kidney tissue. The perceived lack of calcium levels by the parathyroid leads to constitutively high levels of parathyroid hormone and therefore hypercalcemia. Functionally, parathyroid hormone (PTH) increases calcium resorption from the bone and increases phosphate excretion from the kidney which increases serum calcium and decreases serum phosphate.
Functions of the Calcium-sensing Receptor
- Parathyroid gland: mediates negative feedback mechanisms relating to PTH secretion (PTH secretion should decrease if there is a high blood calcium level). Abnormalities in the CaSR here cause hypercalcemia.
- Kidneys: mediates negative feedback mechanisms relating to calcium reabsorption from the tubular system (reabsorption should decrease if there is a high blood calcium level). Abnormalities in the CaSR here cause both hypercalcemia and hypocalciuria.
This condition is indicated by the presence of hypercalcemia (elevated levels of calcium in the blood) at the same time with hypocalciuria (low levels of calcium in the urine). (Usually elevated calcium levels in the blood are correlated with elevated calcium urine levels, as a properly sensing kidney works to excrete the mineral.) A family history could reinforce the diagnosis.
- Lloyd SE, Pannett AA, Dixon PH, Whyte MP, Thakker RV (January 1999). "Localization of familial benign hypercalcemia, Oklahoma variant (FBHOk), to chromosome 19q13". Am. J. Hum. Genet. 64 (1): 189–95. PMC . PMID 9915958. doi:10.1086/302202.
- "A Practical Approach to Hypercalcemia - May 1, 2003 - American Family Physician". Retrieved 2009-03-29.
- Chou YH, Brown EM, Levi T, et al. (July 1992). "The gene responsible for familial hypocalciuric hypercalcemia maps to chromosome 3q in four unrelated families". Nat. Genet. 1 (4): 295–300. PMID 1302026. doi:10.1038/ng0792-295.
- "Familial Hypouricemic Hypercalcemia". Archived from the original on 2009-02-24. Retrieved 2009-06-07.