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Familial Hypocalciuric Hypercalcemia A Rare but Important Cause of Persistent Hypercalcemia

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by

Vishnu
in

Introduction:

Familial Hypocalciuric Hypercalcemia (FHH) is a rare, inherited disorder that often presents as asymptomatic hypercalcemia. Unlike primary hyperparathyroidism, FHH is usually benign, requiring minimal or no treatment. This article provides a detailed overview of FHH, including its genetic causes, clinical presentation, diagnosis, and management.

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What is Familial Hypocalciuric Hypercalcemia (FHH)?

FHH is an autosomal dominant genetic condition characterized by:

  • Mild to moderate hypercalcemia
  • Low urinary calcium excretion (hypocalciuria)
  • Normal or slightly elevated parathyroid hormone (PTH) levels
  • Absence of significant symptoms in most cases

Causes and Genetic Basis

FHH results from mutations affecting the calcium-sensing receptor (CaSR) gene, leading to a reduced ability of the body to regulate calcium levels. The three known types of FHH are:

FHH Type 1 – Caused by mutations in the CASR gene on chromosome 3 (most common).

  1. FHH Type 2 – Associated with mutations in the AP2S1 gene on chromosome 19.
  2. FHH Type 3 – Due to mutations in the GNA11 gene on chromosome 19.

Clinical Features and Diagnosis

Most FHH patients are asymptomatic, but in some cases, mild symptoms like fatigue, constipation, and kidney issues may occur. It is commonly diagnosed through:

  • Serum Calcium & PTH Levels: Elevated calcium with normal or slightly increased PTH.
  • Urinary Calcium Excretion: FHH patients have a calcium-to-creatinine clearance ratio of <0.01, differentiating it from primary hyperparathyroidism.
  • Genetic Testing: Confirms mutations in CaSR, AP2S1, or GNA11 genes.

How is FHH Different from Primary Hyperparathyroidism?

  • FHH: Mild hypercalcemia with low urinary calcium.
  • Primary Hyperparathyroidism: High PTH with increased urinary calcium excretion.

Management & Treatment

FHH generally does not require treatment. However, in severe cases (e.g., symptomatic hypercalcemia), calcimimetics like Cinacalcet may be used to regulate calcium levels. Parathyroidectomy is not recommended as it does not correct the condition.

Conclusion

Familial Hypocalciuric Hypercalcemia is an important differential diagnosis in cases of persistent hypercalcemia. Identifying FHH can help prevent unnecessary surgeries and ensure appropriate management. Genetic testing plays a crucial role in confirming the diagnosis.

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Key Takeaways:

FHH is a benign, inherited condition with mild hypercalcemia.
Low urinary calcium excretion helps differentiate it from primary hyperparathyroidism.
Genetic testing is essential for accurate diagnosis.
Calcimimetics may be used in severe cases.

Read the full study at: https://doi.org/10.29328/journal.jcn.1001137

Disclaimer: This content is generated using AI assistance and should be reviewed for accuracy and compliance before considering this article and its contents as a reference. Any mishaps or grievances raised due to the reusing of this material will not be handled by the author of this article

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