PTH and secondary hyperparathyroidism: Other reports have described adolescent rickets of FHH patients, which is mainly attributed to elevated PTH or vitamin D deficiency.2,3 However, in this study the vitamin D concentration (13.7–18.6 ng·mL−1) was approximated to the mean 25(OH)D level in the Chinese population (19.4±6.4 ng·mL−1 and 13.2±5.4 ng·mL−1).25,26 The elevated PTH, attributed to both FHH and secondary hyperparathyroidism induced by low concentration of 25(OH)D, may contribute to the clinical manifestation of rickets.