Familial Hypocalciuric Hypercalcemia (FHH)

Familial Hypocalciuric Hypercalcemia (FHH) is a rare inherited condition that affects the body's ability to regulate calcium levels in the blood. It primarily involves the parathyroid glands and the kidneys, which normally work together to maintain calcium balance. In FHH, the body mistakenly senses low calcium levels, causing it to keep calcium in the blood rather than excreting it in urine. This leads to mildly elevated blood calcium levels but low calcium in the urine. Most people with FHH do not experience symptoms or serious health problems, and the condition is often discovered incidentally during routine blood tests. It is important to distinguish FHH from other causes of high calcium because it usually does not require treatment.

Familial Hypocalciuric Hypercalcemia (FHH) is a benign autosomal dominant disorder characterized by lifelong mild hypercalcemia with low urinary calcium excretion. It results from inactivating mutations in the CASR gene encoding the calcium-sensing receptor, which is expressed in the parathyroid glands and kidneys. This mutation causes a higher set point for calcium sensing, leading to inappropriate parathyroid hormone (PTH) secretion despite elevated serum calcium. The condition is clinically significant because it mimics primary hyperparathyroidism but does not cause end-organ damage or require surgical intervention. Patients typically have normal or mildly elevated PTH levels, and the disorder is often asymptomatic. Differentiating FHH from other hypercalcemic disorders is critical to avoid unnecessary treatments.