A Pair of Siblings with Vitamin D Dependent Rickets (VDDR) Type 1A: More Than Dairy and Sunshine

Abstract

Vitamin D-dependent rickets (VDDR) type 1A, owing to 1-alpha-hydroxylase deficiency, albeit rare, is an important diagnosis to consider in children with rickets not responding to conventional doses vitamin D and calcium. In this case report, we describe two siblings who presented with multiple fractures since childhood.  A low 1,25-dihydroxyvitamin D (1,25(OH)2D) despite a sufficient 25-hydroxyvitamin D (25OHD) level was suggestive of 1-alpha-hydroxylase deficiency. Genetic testing confirmed a mutation in the CYP27B1 gene on chromosome 12q13.3, which produces 1-alpha-hydroxylase. The inability to convert 25OHD to 1,25 (OH)2D leads to hypocalcemia and severe rickets. Treatment requires a pharmacologic dose of activated hydroxylated vitamin D and adequate calcium intake. Rare forms of hereditary rickets should be suspected in severe rickets. Early recognition of VDDR type 1A is imperative to ensure adequate healing of rickets during childhood. Establishing a diagnosis also helps to ensure compliance with the high doses of active vitamin D metabolite required in this condition.