PTH and familial hypocalciuric hypercalcemia: Familial hypocalciuric hypercalcaemia (FHH) is an autosomal dominant disorder of extracellular calcium metabolism characterized by lifelong increases of serum calcium concentrations, mild hypermagnesaemia, normal or elevated circulating parathyroid hormone (PTH) concentrations, and inappropriately low urinary calcium excretion (urine calcium to creatinine clearance ratio (CCCR) < 0.01) (1).