Rickets and osteomalacia (acquired and heritable forms) and skeletal dysplasias

Mineralization of newly formed organic matrix of bone is a complex and highly ordered process. The requirements include adequate extracellular concentrations of calcium (Ca ²⁺) and phosphorous, as inorganic phosphate (Pi), and normal function of bone-forming cells. Disturbances in either requirement can lead to a stereotypic response of impaired skeletal mineralization (1).

Rickets describes the clinical consequences of diminished mineralization of matrix throughout a growing skeleton. Infants, children, and adolescents can be affected. Osteomalacia results from the same disturbance after growth plates fuse. However, neither term denotes a specific disease. Each is a generic label for the signs and symptoms that follow perturbations that disrupt the orderly deposition of hydroxyapatite crystals into skeletal tissue. Nevertheless, in nearly all patients, there are low extracellular levels of Ca ²⁺ and/or Pi. Often, diminished stores or impaired bioactivation of vitamin D are involved and cause hypocalcaemia, secondary hyperparathyroidism, and hypophosphataemia (1). Occasionally, it is kidney tubule dysfunction that results directly in urinary Pi wasting and leads to hypophosphataemia, sometimes associated with impaired bioactivation of vitamin D. Rarely, disturbances involving chondrocytes and osteoblasts, defective bone matrix, or other disruptions interfere with Ca ²⁺ and Pi deposition into the skeleton. The number of conditions that cause rickets and osteomalacia is considerable – some are acquired and some are inherited.