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Familial hypocalciuric hypercalcemia (FHH) is an inherited disorder that causes abnormally high levels of calcium in the blood (hypercalcemia) and low to moderate levels of calcium in urine (hypocalciuric). People with FHH usually do not have any symptoms and are often diagnosed by chance during routine bloodwork. Weakness, fatigue, issues with concentration, and excessive thirst (polydipsia) have been reported by some people with FHH. Rarely, people with this disorder experience inflammation of the pancreas (pancreatitis) or a buildup of calcium in the joints (chondrocalcinosis).[4403][14434]
FHH is mainly classified into three different types depending on the genetic cause. FHH type 1 is the most common type of FHH and is caused by changes (also known as pathogenic variants or mutations) in the CASR gene. The protein made from the CaSR gene, the calcium-sensing receptor (CaSR protein), monitors and regulates the level of calcium in the blood. FHH type 2 is caused by changes in the GNA11 gene, and FHH type 3 is caused by changes in the AP2S1 gene. All three types of FHH are inherited in an autosomal dominant manner. In rare cases, FHH may be caused when a person’s immune system mistakenly makes antibodies that attack the CaSR protein. The autoimmune form of FHH is not known to be caused by changes in a specific gene.[4403][14434][14436]
Diagnosis of FHH is suspected by high levels of calcium in the blood, especially when there are no other symptoms present. Further blood and urine tests may be used to rule out other possible causes. Genetic testing can confirm the diagnosis of FHH, except in rare autoimmune cases.[14434][14916] Treatment is typically considered unnecessary because most people with FHH do not have symptoms. If pancreatitis occurs, removal of the parathyroid gland (parathyroidectomy) may be recommended.[4403][14434]
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