SAT-356 Reversible Suppression of Serum 1,25-Dihydroxyvitamin D in Williams Syndrome

Background: Hypercalcemia has been reported in 5% to 50% of patients with Williams syndrome; however, observations about the role of 1,25-dihydroxyvitamin D in hypercalcemia related to Williams syndrome have been contradictory. Objective: The objective was to investigate the mineral metabolism in an 11-month-old patient with Williams-Beuren syndrome who had hypercalcemia, hypercalciuria and nephrocalcinosis. Methods: We reviewed test results in an 11-month-old infant with Williams syndrome who developed hypercalcemia following excessive dietary calcium intake that was two to three times higher than recommended for age because he continued receiving a premature formula with high calcium content from birth. Results: Our patient presented with feeding difficulties, daily vomiting, weight loss, and constipation. He had serum total calcium 14.8 mg/dL, phosphorus 4.0 mg/dL, PTH <4 pg/mL, 1,25-dihydroxyvitamin D <8 pg/mL, 25-hydroxyvitamin D 29 ng/mL, PTH-related peptide 3.7 pmoL/L (expected <4.2), alkaline phosphatase 118 U/L, beta-crosslaps 1257 pg/mL, and urinary calcium/creatinine ratio 1.19. XR Skeletal Survey revealed increased bone density in the metaphyseal regions, in particular, above the knee, distal radius and ulna that may result from hypercalcemia; no evidence of rickets, osteoporosis or congenital osteodystrophy was seen. Renal ultrasound revealed increased echogenicity of the renal medullary pyramids consistent with medullary nephrocalcinosis. Hypercalcemia and hypercalciuria were initially treated with IV fluids and Furosemide IV, and resolved only after Pamidronate 0.5 mg/kg/dose IV x 2 doses. After serum calcium normalized, the patient’s symptoms resolved, PTH recovered to 18 pg/mL (expected 10 - 65), and 1,25-dihydroxyvitamin D increased to 27 pg/mL (expected 24 - 86). Chromosomal micro-array analysis showed a 1.9 megabase deletion at 7q11.23 that overlapped the Williams syndrome critical region including the ELN gene, consistent with diagnosis of Williams syndrome. Serum calcium remained normal with dietary calcium restriction using a low-calcium formula and complementary foods. Conclusions: PTH-independent hypercalcemia in our patient with Williams syndrome was due to calcium overload resulting from dietary calcium excess in addition to possibly enhanced intestinal calcium absorption. Serum 1,25-dihydroxyvitamin D was undetectable and returned to normal only with resumption of PTH secretion required for its synthesis after hypercalcemia resolved. The balance between bone formation and resorption was shifted to resorption possibly to remove skeletal calcium excess, based on normal alkaline phosphatase (marker of osteoblast activity) and high collagen beta-crosslaps (marker of osteoclast activity). A premature formula with high calcium content should be switched to a full-term formula when risk for rickets of prematurity clears.