A tale of two cases: early diagnosis and variable outcomes in vitamin D-dependent rickets

Vollständiger Abstract

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Vitamin D-dependent rickets (VDDR) is a rare inherited disorder of vitamin D metabolism or action, presenting with early-onset hypocalcemia, rickets, and growth failure. We report two contrasting cases of VDDR type I and type II that highlight important diagnostic and therapeutic differences. The first case, a female infant presenting with seizures, delayed milestones and limb deformities, showed hypocalcemia, elevated alkaline phosphatase, secondary hyperparathyroidism, and low 1,25-dihydroxyvitamin D levels; genetic testing confirmed a CYP27B1 mutation (VDDR-I), and treatment with oral calcium and calcitriol led to complete biochemical, radiological, and clinical recovery with near-normal growth. The second case, a male child from a consanguineous family with severe skeletal deformities, alopecia, and poor growth, demonstrated hypocalcemia, hypophosphatemia, secondary hyperparathyroidism, markedly elevated alkaline phosphatase, normal 25-hydroxyvitamin D, and elevated 1,25-dihydroxyvitamin D levels; a vitamin D receptor (VDR) mutation confirmed VDDR-II, and despite aggressive therapy with high-dose calcium, active vitamin D, phosphate, and intermittent intravenous calcium, response remained suboptimal. These cases emphasize that early diagnosis and targeted therapy in VDDR-I can result in excellent outcomes, whereas VDDR-II is a severe, treatment-resistant condition, underscoring the critical role of detailed biochemical evaluation and genetic confirmation in children with refractory rickets.