Pediatric Rickets

Pediatric rickets is defective mineralization of the growing endochondral and intramembranous bone in children due to deficiency of vitamin D, calcium, or phosphorus, occurring before epiphyseal fusion. The disorder analogous to rickets in skeletally mature individuals is osteomalacia. Calcium-deficiency or vitamin D-deficiency rickets remains the most common form globally, with risk factors including exclusive breastfeeding without vitamin D supplementation, limited sun exposure, dark skin pigmentation, vegan diet, malabsorption (celiac disease, cystic fibrosis), chronic kidney disease, and anticonvulsant therapy.

Hereditary rickets includes vitamin D-dependent rickets type 1A (VDDR1A, CYP27B1 mutation, defective 1α-hydroxylation), type 1B (CYP2R1 mutation, defective 25-hydroxylation), type 2A (vitamin D receptor mutation), X-linked hypophosphatemic rickets (PHEX gene, increased FGF23), autosomal dominant hypophosphatemic rickets (FGF23 mutation), and other rare forms. X-linked is the most common hereditary type.

Clinical features depend on age. Infants present with delayed motor milestones, hypotonia, craniotabes (soft skull bones), frontal bossing, delayed fontanelle closure, rachitic rosary (enlarged costochondral junctions), and Harrison sulcus. Toddlers and older children show bowed legs (genu varum) when rickets develops during walking phase, knock knees (genu valgum) in older children, growth retardation, dental enamel defects, pathologic fractures, and tetany or seizures from hypocalcemia. Laboratory: low 25-hydroxyvitamin D, elevated alkaline phosphatase, low or normal calcium, low or normal phosphorus, elevated PTH (in nutritional rickets); X-linked hypophosphatemia shows low phosphorus, normal calcium, normal PTH, and elevated FGF23. Radiographs show widened, cupped, and frayed growth plates (especially wrists, knees), bowing deformities, and Looser pseudofractures. Treatment is etiology-specific: vitamin D and calcium replacement for nutritional, oral phosphate plus calcitriol for X-linked hypophosphatemia (or burosumab anti-FGF23 antibody).