A 6-month old boy weighing 3.2 kg presents with recurrent vomiting and polyuria. Investigations show blood area 60 mg/dl creatinine 0.7 mg/dL, calcium 12.8 mg/dL, phosphate 3 mg/dL, pH 7.45, bicarbonate 25 mEq/L and PTH 140 pg ml (normal?

Ans. is 'b' i.e., Mutation of calcium sensing receptor Laboratory abnormalities Patient Normal in the patient Increased calcium 12.8 mg/dl 9-10.5 mg/d1 Normal phosphate 3.0 mg/di 3-4.5 mg/dl (In lowrange) Increased parathormone 140 pg/ml < 60 pg/ml Normal Bicarbonate 25 mEq/L 21-30 meq/L Increased Blood urea 60 mg / dl 10-20 mg / dl Normal creatinine .7 mg/dl < 1-5 mg/dl It is a close diagnosis between hyperparathyroidism and familial hypercalcemic hypocalciuria. It is a case of mutation of the calcium sensing receptor The clincher here is o Age of the patient o Decrease in urinary calcium excretion Familial hypercalcemic hvpocalciuria o It is an autosomal dominant disorder caused by mutation in the calcium sensing receptor. o Pathophysiology of familial hypercalcemic hypocalciuria. The primary defect is the abnormal sensing of the blood calcium by the parathyroid gland and renal tubule. The calcium sensor responds to ECF calcium concentration by suppressing PTH secretion through negative feed back. The mutations lower the capacity of sensors to bind calcium and the mutant receptors functions as though blood calcium levels are low. As a result of the false perception that calcium level are low in the body, the parathyroid gland stas secreting greater amount of parathyroid hormone and renal tubule stas reabsorbing greater amount of calcium in the tubule. o Comparison of hyper parathyroidism and familial hypercalcemic hypocalciuria These two disorders have almost similar features, they differ only in the following aspect 1) Urinary renal calcium reabsorption o FHH --> > 99% of renal calcium reabsorption in the kidney (This causes decrease in urine calcium) o Hyperparathyroidism ---*< 99% of renal calcium reabsorption in the kidney (This causes increase in urine calcium) 2) Age of patient o FIIH --> Hypercalcemia is detected in affected members in first decade of life o Hyper parathyroidism --> Hypercalcemia rarely detected in patient with primary hyperparathyrcidism or MEN syndrome who are less than 20 year of age. 3) Level ofparathvroid hormone o PTH can be elevated in FHH, but the values are usually normal or lower for the same degree of calcium elevation than in patients with primary hyperparathyroidism.