Evaluation of Clinical Characteristics of Vitamin D Dependent Rickets Type 1 (VDDR-1) Patients and Importance of Early Diagnosis

Introduction: Vitamin D-dependent rickets type 1 (VDDR-1) is an autosomal recessive disorder caused by 1-a-hydroxylase enzyme deficiency. This rare disease occurs due to biallelic pathogenic variants in the CYP27B1 gene. We evaluated VDDR-1 patients retrospectively in terms of clinical and biochemical characteristics, treatment response, and genetic results. Materials and Methods: VDDR-1 cases with biallelic variants in CYP27B1 from 12 families were included. Demographic and clinical data were extracted from records. Following DNA isolation and standardized PCR, we performed nextgeneration sequencing with Miseq device. Data analysis was performed using IGV 2.3 software. Results: The cohort included 22 patients, 11 (50%) female and 11 male. Median age at diagnosis was 12 (7.75-18) months. Mean calcium, phosphorus, alkaline phosphatase (ALP) and vitamin D concentration was 7.6 +/- 0.98 mg/dL, 2.9 +/- 0.77 mg/dL, 1149 +/- 692 IU/L, 391 +/- 181 pg/mL, and 55 +/- 38 ng/mL, respectively at diagnosis The most common reasons for presentation were growth retardation, short stature, convulsions, and extremity deformity. The most common variant was the previously identified c.195 + 2T>G substitution, which was detected in 5 families. The second most common variant was another previously reported c.574A>G (p.Lys192Glu) variant, which was detected in 3 families. c.171delC (p.Leu.58Cfs*20), c.240delT (p.Phe80Leufs*79), and c.1166G>A(p.Arg389His) homozygous variants and c.1215_1215+2delinsCGA/c.1474C>T (p.Arg492Trp) compound heterozygous variant were detected in one family each. Conclusion: VDDR-1 should be considered in rickets patients not recovering with high-dose vitamin D therapy. Delayed diagnosis of VDDR-1 may lead to unnecessary orthopedic surgery in some cases. We are of the opinion that providing early diagnosis, treatment and genetic counseling will give reliable and important information to families.