Hypercalcemia, familial benign

Familial Benign Hypercalcemia (FBH), also known as Familial Hypocalciuric Hypercalcemia (FHH), is a hereditary condition characterized by mildly elevated calcium levels in the blood, which occurs despite normal or low levels of parathyroid hormone (PTH). This condition is generally considered benign and asymptomatic, but its recognition is crucial to avoid unnecessary treatments for other causes of hypercalcemia.

Causes and Genetics

FBH is primarily caused by mutations in the Calcium-Sensing Receptor (CaSR) gene, which plays a critical role in regulating calcium levels in the body. The CaSR gene mutations lead to a decreased sensitivity of the calcium-sensing receptor, located on the surface of parathyroid and kidney cells, to calcium ions. This results in the body's inability to properly regulate calcium levels, causing a mild increase in blood calcium. FBH is inherited in an autosomal dominant manner, meaning a single copy of the altered gene in each cell is sufficient to cause the disorder.

Symptoms

Most individuals with Familial Benign Hypercalcemia do not exhibit symptoms and are often diagnosed incidentally during routine blood tests. When symptoms do occur, they are usually mild and can include fatigue, muscle weakness, excessive thirst (polydipsia), and frequent urination (polyuria). Severe symptoms are rare but can include kidney stones and calcification of soft tissues.

Diagnosis

Diagnosis of FBH involves a combination of blood tests showing elevated calcium levels with normal to low levels of parathyroid hormone, and genetic testing to identify mutations in the CaSR gene. A key diagnostic feature of FBH is the presence of hypocalciuria, meaning the amount of calcium excreted in the urine is low despite high levels of calcium in the blood. This distinguishes FBH from other forms of hypercalcemia, such as primary hyperparathyroidism.

Treatment

Treatment for Familial Benign Hypercalcemia is usually not necessary due to the mild nature of the condition. However, individuals are advised to stay hydrated and may be monitored for changes in calcium levels and kidney function over time. In rare cases where symptoms are more pronounced, treatment options may be considered on an individual basis.

Differential Diagnosis

It is important to differentiate FBH from other causes of hypercalcemia, such as primary hyperparathyroidism, vitamin D intoxication, and malignancies. The distinction is crucial to avoid unnecessary surgical or medical treatments.

Prognosis

The prognosis for individuals with Familial Benign Hypercalcemia is generally excellent, as the condition is typically asymptomatic and does not significantly impact life expectancy. Regular monitoring is recommended to manage any potential complications.

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