The Contribution of Deleterious Rare Alleles in ENPP1 and Osteomalacia Causative Genes to Atypical Femoral Fracture

Context Atypical femoral fractures (AFFs) are very rare atraumatic or mild trauma fractures in the subtrochanteric region or femoral shaft. Some unique genetic variants in Asian populations might confer susceptibility to AFF, since the incidence of AFFs is higher in Asian populations. Objective Because rare variants have been found to be causative in some diseases and the roles of osteomalacia causative genes have not been reported, we investigated rare variants in genes causing abnormal mineralization. Methods Exome sequencing was performed to detect variants in gene coding and boundary regions, and the frequencies of deleterious rare alleles were compared between Japanese patients with AFF (n = 42) and controls of the 4.7KJPN panel of Tohoku Medical Megabank by whole genome sequencing (n = 4773). Results The frequency of the deleterious rare allele of ENPP1 was significantly increased in AFF (P = .0012, corrected P [Pc] = .0155, OR 4.73, 95% CI 2.15-10.40). In multigene panel analysis, the frequencies of deleterious rare alleles of candidate genes were increased in AFF (P = .0025, OR 2.72, 95% CI 1.49-4.93). Principal component analysis of bone metabolism markers identified a subgroup of patients with AFF with higher frequencies of deleterious rare alleles in ENPP1 (P = 4.69 x 10(-5), Pc = .0006, OR 8.47, 95% CI 3.76-19.09) and the candidate genes (P = 1.08 x 10(-5), OR 5.21, 95% CI 2.76-9.86). Conclusion AFF is associated with genes including ENPP1 that cause abnormal mineralization, suggesting that osteomalacia is an underlying condition predisposing to AFF and that higher incident rates of AFFs in Asian populations might be explained by the genetic risk factors including ENPP1.

Automated summary

This study found that the gene ENPP1, which causes abnormal mineralization, is associated with AFF. This suggests that osteomalacia is an underlying condition predisposing to AFF and that higher incident rates of AFFs in Asian populations might be explained by the genetic risk factors including ENPP1.