To compare bone density with polymorphisms in the calcitonin receptor (CTR) and vitamin D receptor (VDR) genes in 50 patients with juvenile idiopathic arthritis and 80 matched controls.
Bone mineral density (BMD) was measured by dual energy x-ray absorptiometry at the lumbar spine. Genomic DNA was isolated from EDTA blood samples by standard procedures. Polymerase chain reaction was performed using genomic DNA and 100 pmol of each oligonucleotide primer for VDR and CTR genes. Products from genomic PCR were digested by Alu I enzyme for CTR polymorphism and Fok I enzyme for VDR polymorphism.
In the total population, higher prevalence of CC genotype (41.5%) for the CTR gene and FF genotype (59.8%) for the VDR gene was found, in agreement with data for Caucasian populations. No significant differences in distribution of CTR and VDR genotypes were observed between patients and controls. However, patients with TT genotype had lumbar BMD (L-BMD) that was lower in comparison to those with CC genotype (p = 0.04). For VDR gene polymorphism, we observed that patients with ff genotype had lower L-BMD in comparison with FF genotype (p = 0.02). Patients with heterozygosity for the 2 genotypes showed intermediate L-BMD. The differences in L-BMD among these groups did not seem to be related to corticosteroid therapy.
Our data suggest that patients with particular VDR and CTR genotypes may be at higher risk to lose bone mass.