Hypercalcemia of Down Syndrome

We present a case of hypercalcemia in a 12-month-old female with Down syndrome. The patient presented with significant weight loss (810 g since her 6-month visit) and severe growth failure (weight 5.8 kg, -4.5 SDs). Laboratory evaluation revealed severe hypercalcemia with appropriately suppressed PTH and 1,25-hydroxyvitamin D levels. Renal ultrasound confirmed medullary nephrocalcinosis. After excluding common etiologies, the patient was diagnosed with hypercalcemia of Down syndrome, also termed Abnormal Calcium, Calcinosis, Creatinine in Down syndrome. Treatment with intravenous fluids, calcitonin, and transition to a low-calcium formula (Calcilo XD) normalized serum calcium levels. The patient maintained normal calcium levels on restricted dietary calcium intake for 7 months after discharge. This case adds to the limited literature on this rare but significant association, highlighting the importance of considering hypercalcemia in patients with Down syndrome presenting with growth failure. Although the pathophysiology remains unclear, a hyperabsorptive intestinal mechanism has been proposed. Early recognition and dietary calcium restriction are essential to prevent significant morbidity in affected children.