Vitamin D - Dependent Rickets Type 2: A rare hereditary disorder with resistance to treatments

Rickets is a skeletal disorder characterized by defective mineralization at the growth plate, resulting in bone deformities, growth retardation, and systemic complications. It may be calcipenic or phosphopenic, with acquired or hereditary etiologies. Nutritional rickets remains the most common worldwide, while hereditary forms are rare and diagnostically challenging. Vitamin D-dependent rickets (VDDR) is a hereditary subtype of calcipenic rickets. Among its forms, VDDR type 2 arises from mutations in the vitamin D receptor (VDR), resulting in end-organ resistance to calcitriol.We report a 19-year-old male diagnosed with VDDR type 2 at 18 months of age after delayed walking and florid rachitic features. Laboratory evaluation showed hypocalcemia, hypophosphatemia, elevated alkaline phosphatase, and secondary hyperparathyroidism with radiological evidence of rickets. Standard doses of vitamin D and calcium produced no response. However, higher doses led to partial biochemical and clinical improvement. Despite therapy, the patient developed progressive skeletal deformities, osteoporosis, and multiple fractures requiring corrective orthopedic surgery. His younger sibling was later diagnosed with hereditary rickets, confirming a familial basis. This case highlights the diagnostic and therapeutic challenges of VDDR type 2. Recognition of poor response to conventional therapy, coupled with biochemical and genetic evaluation, is essential for accurate diagnosis. Long-term multidisciplinary management, including orthopedic, endocrinological, and rehabilitative care, remains vital for improving outcomes in these rare hereditary rickets cases.