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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).
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.
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. 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.
Source: GARD Last updated on 05-01-20
While most people with familial hypocalciuric hypercalcemia (FHH) do not have symptoms, associated symptoms may include:
Rarely, adults with FHH may experience recurring inflammation of the pancreas (pancreatitis), a build-up of calcium crystals in certain joints of the body (chondrocalcinosis), and a build-up of calcium in the veins (vascular calcification).
Last updated on 05-01-20
A person with familial hypocalciuric hypercalcemia (FHH) has a 50% (1 in 2) risk to pass on the genetic change (pathogenic variant, also called mutation) to each of his/her children. This is known as autosomal dominant inheritance. People have two copies of each gene (one inherited from each parent). For FHH, one copy of the gene with the pathogenic variant in each cell is sufficient to cause the disorder. The copy of the gene with the pathogenic variant may be inherited from an affected parent, or it may occur for the first time in the person with the disorder.
Rarely, a person may inherit a pathogenic variants in both copies of one of the genes associated with FHH. This can lead to a severe form of the disorder called neonatal severe primary hyperparathyroidism (NSHPT). This disorder may become evident within the first week of life and can be life-threatening. NSHPT is usually caused by pathogenic variants in both copies of the CASR gene.
Last updated on 05-01-20
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