PTH and Hypercalciuria: In humans, inactivating mutations in CYP24A1 are now recognized as a major cause of idiopathic infantile hypercalcemia, a syndrome marked by severe hypercalcemia, hypercalciuria, and nephrocalcinosis, decreased PTH, low 24,25(OH)2D, and inappropriately normal to high 1,25(OH)2D. Although initially identified in children (31), more recent case reports indicate that the diagnosis may not be made until adulthood, generally following a condition of increased 1,25(OH)2D production like pregnancy (32, 33).