Summary:
FHH is a rare genetic disorder characterized by mild, typically asymptomatic hypercalcemia (elevated calcium levels in the blood) and low urinary calcium excretion (hypocalciuria). Treatment is generally unnecessary, but regular monitoring and genetic counseling are important due to its hereditary nature.

Causes and Mechanism

• Inheritance: FHH is mostly inherited in an autosomal dominant pattern and caused by mutations in the CASR gene (calcium-sensing receptor gene).
• Mechanism: The CASR gene encodes a receptor in the parathyroid glands and kidneys responsible for regulating blood calcium levels. Mutations in the CASR gene lead to a receptor that requires higher calcium concentrations to activate. Consequently, the parathyroid glands erroneously interpret calcium levels as low, causing excessive calcium production.

Symptoms

• Most individuals are asymptomatic, as the body adapts to the mildly elevated calcium levels.
• In some cases, nonspecific symptoms may occur, such as:
  • Fatigue
  • Weakness
  • Constipation
  • Increased urination

Severe complications are rare.

Diagnosis

FHH is diagnosed based on the following criteria:

1. Elevated Serum Calcium: Typically mild.
2. Low Urinary Calcium Excretion: A hallmark feature.
3. Family History: Hypercalcemia in close relatives suggests a genetic disorder.
4. Genetic Testing: Confirmation through identification of a mutation in the CASR gene.

Differential Diagnosis: FHH is often confused with primary hyperparathyroidism but can be distinguished by low urinary calcium levels in FHH versus higher levels in primary hyperparathyroidism.

Treatment

• No Specific Treatment Required: FHH is generally benign, and complications are rare.
• Surgery Avoided: Parathyroidectomy, effective in primary hyperparathyroidism, is not indicated in FHH and may be harmful.
• Regular Monitoring: To ensure stable calcium levels and absence of symptoms.

Hydration: Adequate fluid intake is recommended to prevent dehydration