One explanation for our findings may be due to the fact that 1,25 dihydroxyvitamin D, converted from 25OHD, is the biologically active form of vitamin D, which is tightly regulated by PTH; post-thyroidectomy hypoparathyroidism results in decreased conversion of 25OHD to 1,25 dihydroxyvitamin D, regardless of the amount of 25OHD available. This evidence concerns the gene PTH and hypoparathyroidism.