Chapter 67 - Hereditary Deficiencies in Vitamin D Action

Abstract

Publisher Summary This chapter focuses on the hereditary deficiencies in vitamin D action, which occur due to disturbances in the synthesis of the hormonal form of the vitamin, 1,25-dihydroxyvitamin Dl,(25(OH)2D-calcitriol), or defects in the interaction of calcitriol and its target tissues. Children with hereditary deficiencies in vitamin D action appear normal at birth and usually develop the characteristic features of rickets within the first 2 years of life. Defects in bone mineralization during the first year of life are particularly evident in regions of rapid bone growth such as cranium, wrist, and ribs. Rickets at this time also lead to widened cranial sutures, frontal bossing, posterior flattening of the skull (craniotabes), bulging of costochondral junction (rachitic rosary), indentation of the ribs at the diaphragmatic insertion (Harrison's groove), and widening of the wrists. After the first year of life with the acquisition of erect posture and rapid linear growth, the deformities are most severe in the legs. Bow legs (genu varum) or knock-knee (genu valgum) deformities of various severity develop, as well as widening of the end of long bones. If not treated, rickets may cause severe lasting deformities, compromise adult height, and increase susceptibility to pathological fractures. The clinical features of osteomalacia are subtle and could be manifested as bone pain or low back pain of varying severity in some cases. The first clinical presentation could be an acute fracture of the long bones, public ramii, fibs, or spine. The characteristic histological feature of rickets and osteomalacia is deficiency, or lack of mineralization of the organic matrix of bone.