Apolipoprotein E phenotypes in rheumatoid arthritis with or without amyloidosis

The role of apolipoprotein (apo) E in the pathogenesis of reactive amyloidosis is unclear. Here we evaluated the apoE phenotype distribution and apolipoprotein e allele frequencies in 55 adult patients with seropositive, erosive RA with amyloid and compared them with 55 matched RA patients without amyloid The apoE isotypes were determined by isoelectric focusing and immunoblotting. RA patients without amyloid had more often the apoE 3/3 phenotype (71%) than the RA+A patients (49%, P<0.05) or Finnish control subjects (47%, P<0.01) and the frequency of the apo epsilon3 allele was significantly higher among the RA patients without amyloid than among RA+A patients (P<0.05) or control subjects (P<0.01). The prevalence of the apoE3/4 phenotype among the RA+A patients, although higher, did not significantly differ from the RA patients without amyloid (40% and 26%, respectively, NS) or Finnish control subjects (40% and 35%, respectively, NS). The frequency of the apo epsilon4 allele among the RA+A patients did not signficantly differ from that of RA patients without amyloid (0.23 and 0.13, respectively, NS) or Finnish control subjects (both 0.23). However, the apo epsilon4 frequency of 0.13 among the RA patients without amyloid was significantly lower than that of Finnish control subjects (0.23, P<0.05). We conclude that the prevalence of the apoE4 isotype is not increased in patients with RA complicated by amyloidosis when compared with Finnish control subjects. Since the frequency of the apo epsilon4 allele is significantly decreased in RA patients without amyloid when compared with Finnish control subjects, the presence of the apoE4 in a patient with RA could, though, represent a relative risk factor for developing reactive amyloidosis.