Presence of apolipoprotein E ϵ4 allele predisposes to early onset of primary Sjögren's syndrome

BACKGROUND: Apolipoprotein E (apoE) polymorphism plays a central role in lipid metabolism, but has recently also been suggested to regulate inflammation, as judged by levels of serum C-reactive protein (CRP). OBJECTIVE: To establish whether polymorphism of the apoE genes affects susceptibility to primary Sjogren's syndrome (pSS), degree of inflammation or age of onset of pSS. METHODS: ApoE genotype distribution and allelic frequencies were analysed using PCR and the TaqMan system in 63 Finnish Caucasian patients with pSS and in 64 healthy controls matched for sex, ethnic origin and area of residence. The clinical and immunological data on the pSS patients were analysed in relation to the apoE genotypes. RESULTS: There was no difference between pSS patients and controls in apoE genotype and allelic frequencies. The apoE epsilon4 allele was significantly associated with early onset of pSS in the entire population and in female patients (Kaplan-Meier log rank test, P = 0.0407 and P = 0.0168, respectively). The average age (+/- S.D.) of onset of pSS in all apoE epsilon4 allele carriers was 46 +/- 12 and in other genotypes it was 53 +/- 10 yr (P = 0.031, t-test). ApoE polymorphism was not associated with signs of inflammation evaluated by such markers as concentration of plasma CRP, plasma interleukin-6, plasma TNF-alpha, immunoglobulin G and haemoglobin, or leucocyte count or ESR. CONCLUSIONS: ApoE polymorphism does not affect susceptibility to pSS or levels of plasma inflammatory indices in patients with pSS. However, a clear association prevails between apoE epsilon4 and early onset of pSS.