Suvarna Garge (Editor)

Familial hypocalciuric hypercalcemia

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Specialty
  
endocrinology

OMIM
  
145980 145981 600740

MeSH
  
D006934

ICD-10
  
E83.5

DiseasesDB
  
1326

Familial hypocalciuric hypercalcemia (FHH) is a condition that can cause hypercalcemia, a serum calcium level typically above 10.2 mg/dL. It is also known as familial benign hypocalciuric hypercalcemia (FBHH) where there is usually a family history of hypercalcemia which is mild, a urine calcium to creatinine ratio <0.01, and urine calcium <200 mg/day.

Contents

Signs and symptoms

Most cases of familial hypocalciuric hypercalcemia are asymptomatic.

  • Hypercalcemia
  • Hypocalciuria ( Ca excretion rate < 0.02 mmol/L)
  • Hypermagnesemia

    • Causes

    Types include:

    Pathogenesis

    Most cases of FHH are associated with loss of function mutations in the calcium-sensing receptor (CaSR) gene, expressed in parathyroid and kidney tissue. The perceived lack of calcium levels by the parathyroid leads to constitutively high levels of parathyroid hormone and therefore hypercalcemia. Functionally, parathyroid hormone (PTH) increases calcium resorption from the bone and increases phosphate excretion from the kidney which increases serum calcium and decreases serum phosphate.

    Another form has been associated with chromosome 3q.

    Functions of the Calcium-sensing Receptor

  • Parathyroid gland: mediates negative feedback mechanisms relating to PTH secretion (PTH secretion should decrease if there is a high blood calcium level). Abnormalities in the CaSR here cause hypercalcemia.
  • Kidneys: mediates negative feedback mechanisms relating to calcium reabsorption from the tubular system (reabsorption should decrease if there is a high blood calcium level). Abnormalities in the CaSR here cause both hypercalcemia and hypocalciuria.

    • Diagnosis

    This condition is indicated by the presence of hypercalcemia (elevated levels of calcium in the blood) at the same time with hypocalciuria (low levels of calcium in the urine). (Usually elevated calcium levels in the blood are correlated with elevated calcium urine levels, as a properly sensing kidney works to excrete the mineral.) A family history could reinforce the diagnosis.

    Treatment

    No treatment is generally required, as bone demineralisation and kidney stones are relatively uncommon in the condition.

    References

    Familial hypocalciuric hypercalcemia Wikipedia
    (Text) CC BY-SA