GENETIC FACTORS PREDISPOSING TO BONE FRACTURE NON-UNION: A ROLE OF SINGLE POINT MUTATION ASP299GLY TLR4 ON PATHOGEN – EVOKED HEALING

Abstract

We previously reported the presence of the bacterial genetic material (16S rRNA) and viable pathogens in fracture gaps specimens, which suggests an impaired pathogen recognition and/or elimination. The aim of study was to validate the hypothesis that patients with delayed bone fracture healing express the higher frequency of TLR4 mutations. Observations were performed in 295 patients treated due to closed fractures of the long bones of the lower extremity; in 151 with delayed bone union (Group A), and in 144 with uneventful healing (Group B). Control group consisted of 125 healthy blood donors from ethnically the same as investigations groups polish population. Fracture gaps and deep tissue biopsies served for microbiological studies, and DNA isolated from venous blood leukocytes was used for analysis of mutations of TLR4 gene at Asp299Gly (1/W) and Thr399Ile (2/W).

Results: Microbiological studies revealed positive isolates in 31.5% fracture gaps in Group A and 16.4% in Group B (p< 0.05). The most frequent isolates were S. epidermidis, S. aureus and S. warneri, capitis, sciuri and lentus, in lower percentage micrococci and enterococci. Amplification of 16S rRNA was positive in 56.8 and 65.2% of fracture gaps in both groups respectively. The frequency of occurrence of 1/W was significantly higher (p< 0.05) in subgroups of patients with non-healing infected vs. sterile fractures. In all subgroups with viable pathogens isolated from fracture gaps the frequency of 1/W allele was higher when compared with subgroups, where fracture gaps occurred sterile.

Discussion: Performed investigations supported our previously reported observations that gaps of closed bone fractures are not sterile and are positive for 16S rRNA. Genetic predisposal to infection and inflammatory response evoked by a single TLR4 mutation may be one of the factors affecting bone union. Observed coexistence of bacterial colonization with decreased inflammatory reaction observed in individuals bearing TLR4 mutations have to be mentioned as a possible, etiologic factor responsible for delayed healing