ESPE Abstracts

Background: Vitamin D-dependent rickets type 3 (VDDR3) is a rare autosomal dominant inheritance disease, which is caused by the gain-of-function mutation in CYP3A4 (c.902T>C p.Ile301Thr).

Case Presentation: We report the case of a 32-month-old boy presented with discomfort of both knee-joints, poor mobility, and gait abnormality when running. Laboratory examinations revealed low concentrations of serum calcium, phosphorus, and 25-OHD, as well as high levels of PTH and ALP. X-ray films showed brush-like changes in the pelvis and lower extremities. The medical data of the patient was collected and analyzed. We used whole exon sequencing to detect the pathogenic gene and found a variant in CYP3A4, a heterozygous single nucleotide change (c.902T>C p.Ile301Thr) which was further confirmed using Sanger sequencing. However, this variant was not found in his parents. After several months of oral vitamin D treatment, the pathological changes improved in X-ray films.

Conclusion: This was the first reported case of VDDR3 in China. The clinical features of VDDR3 are mainly skeletal abnormality and impaired growth, and its diagnosis depends on serum levels of 25-OHD and 1,25-(OH)2D levels, as well as whole exon sequencing. No effective treatment has been found yet, and there is lack of evidence on the safety of large doses of oral vitamin D. As such, regular follow-up visits are essential during treatment.