Familial Hypocalciuric Hypercalcemia

FHH patients are usually asymptomatic or have few symptoms associated with hypercalcemia, proba­bly due to its very mild nature. The usual symptoms are fatigue, weakness, constipation, polyuria, polydipsia, renal insufficiency, or a headache. Other symptoms include chondrocalcinosis or mental problems. Occasionally, patients have pancreatitis. An abnormally functioning CaSR might cause intra­ductal calcification and increased risk of pancreatitis. There is no increased incidence of fractures in FHH. FHH does not protect against the age-related bone loss.[1]

The diagnosis of FHH can be easy to make in an asymptomatic hypercalcemic patient with a family his­tory of hypercalcemia, a personal or family history of failed neck exploration, or normal serum PTH[1][2]. More than 99% of the filtered calcium gets reabsorbed despite the presence of hypercalcemia. The 24 hours urinary calcium excretion is less than 100 mg/24 hours. The Ca/Cr excretion ratio is very low. It is calculated as follows: [UCa × SCr] / [SCa × UCr], where UCa is the urinary calcium con­centration, SCr is the serum creatinine, SCa is the serum calcium concentration, and UCr is the urinary creati­nine concentration, all in mg/dl. The Ca/Cr clearance ratio is less than 0.01 in 80% of cases. All patients with calcium/creatinine clearance ratio of 0.020 or less should be tested for mutations in the CaSR gene. Serum Magnesium is in the upper-normal range or mildly elevated; whereas, serum magnesium tends to be nor­mal or low in primary hyperparathyroidism.

The differentiation between FHH and primary hyperparathyroidism is more difficult in the absence of a family history of hypercalcemia if PTH levels are normal and if the Ca/Cr clearance ratio is greater than 0.01 and less than 0.02. The age at diagnosis of hypercalcemia and family history are important. Detection of asymp­tomatic hypercalcemia before the age of 40 years or so favors the diagnosis of FHH. Obtaining serum calcium values from first-degree relatives in the absence of a family history can be helpful.

Other causes of PTH-dependent hypocalciuric hypercalcemia should be ruled out, for example, vitamin D deficiency, very low calcium intake, mild renal insufficiency, and treatment with thiazide diuretics or lithium. Correction of any of these abnormalities will lead to hypercalciuria if the patient has PHPT. Serum levels of fibroblast growth factor 23 (FGF-23) may be elevated in patients with PHPT.

Calcium infusion has also been used to distinguish renal calcium handling in FHH from that in primary hyperparathyroidism (PHPT). In PHPT, a rising filtered load of cal­cium increases urinary calcium excretion, whereas this response is absent in FHH[12].

FHH is usually a benign disorder and patients with FHH, for the most part, do not develop complica­tions from their disorder. The calcium/PTH levels are usually stable over the years. Subtotal parathyroidectomy does not cure the disorder. Educating and reassuring the patient and affected family members about the benign nature of this condition is very important. This communication avoids unnecessary and expensive monitoring and unneces­sary parathyroid exploration in the patient and relatives. Rarely, in a patient with atypical features, such as pancreatitis, total parathyroidec­tomy may be indicated to reduce the risk of further attacks of pancreatitis. The CaSR rep­resents a potentially important therapeutic target for disorders in which the receptor is hypoactive, such as FHH. Calcimimetics and calcilytics (CaSR antagonists) can play a pharmacological role in improving defective calcium sensing in inherited or acquired disorders of the CaSR[13].

• Adrenal insufficiency

• Genetic disorders

• Granulomatous disease

• Other humoral diseases

• Osteolytic metastases

• Primary hyperparathyroidism

• Renal failure ( acute or chronic)

• Williams syndrome

It is important to distinguish asymptomatic primary hyperparathyroidism from FHH because FHH is a benign inherited condition that typically does not require parathyroidectomy, nor will it be routinely cured by it. Although it is not difficult to differentiate patients with typical biochemical findings of either FHH or primary hyperparathyroidism, it can be challenging to differentiate patients with atypical presentations of either disease and in the absence of family history. Family screening and education are mandatory to avoid unnecessary surgery in the hypercalcemic family members.

Patients with hypercalcemia are often encountered by the nurse practitioner, primary care provider, endocrinologist and the internist. Sometimes these patients present with a family history and hence FHH should be suspected. In general, FHH is a benign disorder, is not progressive, and rarely associated with complications. The calcium/PTH levels are usually stable over the years. The key is to educate the patient that surgery is not necessary or required.This communication avoids unnecessary and expensive monitoring and unneces­sary parathyroid exploration in the patient and relatives. Rarely, in a patient with atypical features, such as pancreatitis, total parathyroidec­tomy may be indicated to reduce the risk of further attacks of pancreatitis. The CaSR rep­resents a potentially important therapeutic target for disorders in which the receptor is hypoactive, such as FHH. Calcimimetics and calcilytics (CaSR antagonists) can play a pharmacological role in improving defective calcium sensing in inherited or acquired disorders of the CaSR[13].

The outcomes in most patients with FHH are good to excellent. [14](Level V)