Prior to initiating the supplementation, the probability of vitamin D hypersensitivity should be assessed if feasible (hypercalcemia, hypercalciuria, nephrocalcinosis, nephrolithiasis, CYP24A1 gene mutation, SLC34A1 gene mutation or history of other types of vitamin D hypersensitivity in an individual or family members). The gene discussed is SLC34A1; the disease is nephrocalcinosis.