VDR and secondary hyperparathyroidism: In agreement with the latter findings, VDR mutants on a calcium and phosphorus-enriched rescue diet were protected against secondary hyperparathyroidism (sHPT), and a switch of global VDR mutants on rescue diet to a calcium-reduced challenge diet led to severe sHPT associated with hypertrophy and hyperplasia of parathyroid glands, together with profound bone loss.