Familial benign hypocalciuric hypercalcemia.

Clinical, biochemical, and pathophysiological observations over several decades on familial benign hypocalciuric hypercalcemia (FBHH) ultimately culminated in the 1990s in the unraveling of the genetic basis of this calcium-sensing familial disorder. An intuitive pursuit of the pathophysiology of this "experiment of nature" in a series of elegant molecular biological studies linked FBHH, in the majority of cases, to the short arm of chromosome 3 (FBHH3q), where the calcium-sensing receptor (CaSR) is located. FBHH is a rare autosomal dominant disorder exhibiting benign hypercalcemia, inappropriately normal parathyroid hormone (PTH) levels, and relative hypocalciuria, thus reflecting partial resistance to the normal effects of extracellular calcium on parathyroid glands and kidneys. Patients with FBHH are asymptomatic, and if diagnosed at an early age, seem to have normal longevity and usually do not suffer any of the skeletal (demineralization or fractures) or renal complications of classical primary hyperparathyroidism. Before an adequate recognition of the syndrome, patients with FBHH were misdiagnosed as having primary hyperparathyroidism and may have been subjected to unnecessary and unsuccessful parathyroidectomy. FBHH3q seems to be, in the majority of cases, the clinical manifestation of heterozygous reduction or loss of CaSR function in the parathyroid glands and renal tubules. In general, in view of the benign nature of FBHH, no particular intervention is needed except reassurance and counseling against parathyroidectomy.