Hypercalciuria, Absorptive, 2

Alternative Names

  • HCA2
  • Hypercalciuria, Familial Idiopathic
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WHO-ICD-10 version:2010

Endocrine, nutritional and metabolic diseases

Metabolic disorders

OMIM Number

143870

Mode of Inheritance

Autosomal dominant

Gene Map Locus

1q24.2

Description

Hypercalciuria is a condition characterized by urinary excretion of excess calcium; by definition exceeding 250 mg per day in women and 300 mg per day in men. Several metabolic conditions and syndromes can cause hypercalciuria. However, no underlying cause for the condition can be found in idiopathic hypercalciuria,. Several theories have been propounded to explain the observation of increased calcium excretion in idiopathic hypercalciuria. One of the more popular theories states that the condition is caused by increased absorption of calcium by the intestines. This absorptive form of hypercalciuria is characterized by increased intestinal calcium intake, normocalcemia, normal circulating parathyroid hormone concentrations, and low bone mineral density. Apart from the absorptive form, idiopathic hypercalciuria has been also theorized to occur as a result of decreased renal tubular resorption, or due to an imbalance in the processes of calcium deposition and resorption in the bones.

Idiopathic hypercalciuria is a diagnosis of exclusion. Other conditions that could lead to hypercalciuria, such as hypothyroidism, vitamin D excess, immobilization, high dietary calcium intake, renal tubular acidosis, Dent disease, and others need to be eliminated. Management of the condition is primarily aimed at dietary modifications. Patients are recommended to decrease their dietary intake of calcium, oxalate, sodium, alcohol and caffeine, while at the same time increasing intake of dietary fiber and fluid. Some patients may require medication, in the form of thiazide type diuretics.

Familial absorptive hypercalciuria shows an autosomal dominant pattern of inheritance. HCA2 has been mapped in three families to a locus on the long arm of chromosome 1. This region contains the SAC (Soluble Adenylyl Cyclase) gene, and mutations in this gene have now been recognized to lead to HCA2. The SAC protein functions as a bicarbonate sensor. However, it is not yet clear how mutations in this gene result in hypercalciuria.

Molecular Genetics

Familial absorptive hypercalciuria shows an autosomal dominant pattern of inheritance. HCA2 has been mapped in three families to a locus on the long arm of chromosome 1. This region contains the SAC (Soluble Adenylyl Cyclase) gene, and mutations in this gene have now been recognized to lead to HCA2. The SAC protein functions as a bicarbonate sensor. However, it is not yet clear how mutations in this gene result in hypercalciuria.

Epidemiology in the Arab World

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Other Reports

Qatar

Akl and Zayyoud (1983) reviewed the medical records of 83 children who presented with renal disorders in Qatar during a single year period. Of the 23 children who presented with gross hematuria, 13 (11 males and 2 females) were diagnosed with idiopathic hypercalciuria. Two of these patients were siblings, one of whom had nephrocalcinosis in addition to hypercalciuria. Akl and Zayyoud (1983) highlighted the association of gross hematuria and idiopathic hypercalciuria in Qatar.

[Akl K, Zayyoud M. The spectrum of childhood kidney disease in Qatar. Qatar Med J. 1983; 4(2):95-7.]

Saudi Arabia

Hanash et al. (1985) measured urinary calcium excretion in 100 consecutive normocalcemic patients with calcium urolithiasis and 12 controls while the patients and the controls were eating their usual diet of unknown calcium content. Only 16 patients were hypercalciuric using the definition of 24-hour urinary calcium of more than 300 mg for males and more than 250 mg for females, and one of these patients was subsequently found to have hyperparathyroidism. Since the dietary intake of calcium during the 24-hour urinary collection was unknown, a 1,000-mg calcium loading test was performed in an attempt to differentiate various patterns of abnormal calcium excretion. Of the 24-hour normocalciuric patients 10 (18%) had absorptive hypercalciuria and 16 patients (29%) demonstrated renal hypercalciuria.

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