Polymorphisms in the GC Gene for Vitamin D Binding Protein and Their Association with Vitamin D and Bone Mass in Young Adults

OBJECTIVE: To identify DBP gene rs4588 and rs7041 polymorphisms and associate with participants' serum 25(OH)D and BMD levels. STUDY DESIGN: Cross-sectional descriptive study design. PLACE AND DURATION OF STUDY: Section of Chemical Pathology and Molecular Pathology, Department of Pathology and Laboratory Medicine, The Aga Khan University, Karachi, from July 2014 to September 2015. METHODOLOGY: Blood samples from 98 young adults, out of 101 samples collected, were genotyped for GC rs4588 and rs7041 polymorphisms by polymerase chain reaction-based restriction fragment length polymorphism assay. Questionnaires were administered to obtain information on demographics and anthropometric characteristics, BMD was assessed with heel ultrasound and 25(OH)D was measured using a Chemiluminescence immunoassay. RESULTS: High prevalence of vitamin D deficiency was noted in the study population n=87 (86.1%) having median (IQR) 25(OH)D levels of 14.9 (20.9) ng/ml, in males and 12.1 (51.8) ng/ml in females. The C/C genotype of SNP rs4588 had the highest proportion n=50 (51%), whereas for rs7041 genotype G/T was most frequently observed n=53 (54%) in subjects. Highest 25(OH)D levels were observed within the homozygous genotypes C/C median 25(OH)D 14.0 (49.6) and G/G (median 25(OH)D 14.9 (37.1) ng/ml. Statistically significant relationship was noted between rs7041 genotype G/T and BMD (p 0.037). CONCLUSION: Hypovitaminosis D was frequently found in young adults. Furthermore, G/T variant of rs7041 polymorphism was associated with lower 25(OH)D serum levels.