Effect of calcium supplementation on bone deformity and histopathological findings of skin papules in a pediatric patient with vitamin D-dependent rickets type 2A: A case report.

Vitamin D-dependent rickets type 2A (VDDR2A) is an autosomal recessive disease caused by pathogenic variants of the vitamin D receptor (VDR) gene. VDDR2A rickets are usually resistant to native or active vitamin D treatment because of impaired active calcium absorption against the calcium concentration gradient, which is a ligand-dependent VDR action in the small intestine. Alopecia due to an impaired skin follicular cycle is occasionally observed in patients with VDDR2A. Among the pathogenic VDR variants, most in the DNA-binding domain and some in the ligand-binding domain, which affect the dimerization of VDR with the retinoic X receptor, are associated with alopecia. Herein, we report a case of VDDR2A caused by compound heterozygous pathogenic variants of the DNA-binding domain of VDR. Active vitamin D treatment did not ameliorate genu varum, rachitic changes in the roentgenogram, or abnormal laboratory findings. However, oral administration of calcium lactate dramatically improved these findings. The patient also experienced hair loss at two months of age and multiple papules on the skin at two yr of age, which did not improve with vitamin D or calcium supplementation. We also report the histopathological findings of skin papules in this patient.