In a Japanese study, the C6607T SNP mapping to intron 1 of the SLC22A4 gene encoding the OCTN1 protein was found to be associated with rheumatoid arthritis. Similarly, a G24658C transversion in intron 6 of the gene encoding the RUNX1 transcription factor that regulates OCTN1 and also likely OCTN2 expression was also found to confer susceptibility to the disease.
We investigated the prevalence of these two SNPs by RFLP analysis in a cohort of 209 Hungarian rheumatoid arthritis patients, and 217 healthy controls. Since both the OCTN1 and OCTN2 play a central role in the transmembrane transport of carnitine, we also determined the quantitative serum carnitine ester profile by ESI tandem mass spectrometry.
No statistically significant differences were found comparing the genotype prevalence rates between the patients and the controls for either the SLC22A4 genotypes or for the RUNX1 SNPs. There was no significant difference in the serum carnitine ester profile when the rheumatoid arthritis patients were compared with the controls; furthermore, no significant difference in the carnitine esters could be detected when genotype specific subgroups of the patients and the controls were studied.
Data of the current study do not confirm the universal and population independent susceptibility role of the SLC22A4 C6607T and RUNX1 G24658C variants for rheumatoid arthritis; furthermore, the data presented here show, that there are no significant carnitine-metabolism associated functional consequences of the different genotypes evidenced by the lack of detectable differences in the carnitine ester profiles.