External apical root resorption and the interleukin-1B gene polymorphism in the Japanese population

External apical root resorption (EARR) is a common consequence of orthodontic treatment. Recently, several studies have reported an association between EARR and an underlying genetic cause. This study investigated whether a single interleukin (IL)-1B gene polymorphism (rs1143634) was associated with EARR in the Japanese population. Genomic DNA, lateral cephalograms, and panoramic radiographs were obtained from 54 Japanese. We measured the EARR in the maxillary central incisors, the mandibular central incisors, and the mesial and distal roots of the mandibular first molar, and analyzed statistically the association between IL-1B polymorphism and EARR. We also examined differences in allelic frequency of this IL-1B polymorphism in a multi-ethnic study population consisting of Japanese, Han Chinese, African American, European Caucasian, and Hispanic individuals. We found no significant difference in the frequency of the IL-1B polymorphism between EARR cases and controls in the Japanese population. We also report marked diversities in the allelic frequencies of the IL-1B polymorphism within the multi-ethnic study population. The European Caucasian population carried the T allele at a frequency of 29.2%, whereas the Japanese population carried the T allele at a frequency of 5.6%. The low frequency of the T allele in Japanese population made it difficult to compare population allelic frequencies among different populations. Further studies are required to confirm our findings and to investigate the effect of other single nucleotide polymorphisms in IL-1B or other genetic risk factors underlying susceptibility to EARR.