Therefore, reduced serum 25(OH)D due to impaired megalin-mediated absorption of 25(OH)D-DBP complexes may be responsible, at least in part for development of hyperparathyroidism as indicated by the finding of increased wholePTH, based on the suppressive effect of 25(OH)D on PTH synthesis at parathyroid gland28. This evidence concerns the gene PTH and hyperparathyroidism.