A toddler with severe vitamin D-dependent rickets type 1 A (VDDR1A), hungry bone syndrome, and severe RSV infection: presentation and therapeutic challenges.

Background: Vitamin D-dependent rickets type 1 A (VDDR1A) is an autosomal recessive disorder due to mutations in the CYP27B1 gene which result in inability to generate 1,25(OH)₂D.

Case presentation: An 18-month-old boy with VDDR1A presented with hypotonia and respiratory distress. He had been diagnosed 2 months earlier, having been evaluated for stunted growth, hypotonia, and delayed developmental milestones. He was stabilized with oxygen and bronchodilators for his bronchiolitis and high doses of alfacalcidol, calcium, and phosphate supplements for his hungry bone syndrome. Of note, the patient sustained upper limb fractures after a fall from his bed during admission. Overall, he had a protracted disease course; however, his bone profile gradually improved and he steadily recovered.

Conclusion: VDDR1A causes failure to thrive, hypotonia, and increased fracture risk and may complicate the clinical course of lower respiratory tract infections. Furthermore, management of hungry bone syndrome requires supraphysiologic doses of vitamin D metabolites and calcium.