IL-1 gene family haplotypes and Raynaud's phenomenon in primary Sjögren's syndrome
J. Hulkkonen,
M. Pertovaara1,
J. Antonen1,2,
A. Pasternack1,2 and
M. Hurme1,2
Institute of Medical Technology, University of Tampere
1 Tampere University Hospital and
2 University of Tampere Medical School, Tampere, Finland
SIR, The genes encoding cytokines of the interleukin-1 (IL-1) family are polymorphic and allelic imbalance of these genes has been found in several autoimmune diseases [1]. Subjects with different IL-1 alleles have been shown to have distinct profiles of IL-1ß and IL-1 receptor antagonist (IL-1Ra) production [1]. Moreover, IL-1Ra production has been shown to be reduced in the saliva of Sjögren's syndrome (SS) patients [2]. Perrier et al. [3] studied 36 patients with primary SS (pSS) and found that the IL1RN*2 allele was more frequent in definite pSS than in the possible form of the disease [3]. We have characterized two single-nucleotide polymorphisms of IL-1 complex genes (i.e. IL-1
-889 and IL-1ß +3953 polymorphism) and the above-mentioned IL1RN polymorphism in DNA samples of 65 pSS patients (63 female and two male, mean age 60±12 yr) using the PCR (polymerase chain reaction), RFLP (restriction fragment length polymorphism) and PAGE (polyacrylamide gel electrophoresis) [for methods see references 4 and 5]. Patients were selected using modified Californian criteria as described previously [6]. Moreover, all patients fulfilled the European criteria for pSS [7]. The data on the patients were compared with data obtained on 180 healthy female blood donors (Finnish Red Cross Blood Transfusion Centre, Tampere, Finland). In these analyses the individual genotype distributions and allele frequencies of IL-1 gene complex genes were similar in pSS patients and in control subjects (
2 test for 2x2 and 2x3 contingency tables, 1 and 2 degrees of freedom; data not shown). Moreover, no difference was observed between IL1RN*2 distributions in definite (n=30) and possible (n=35) forms of pSS. As the IL-1 complex genes are in linkage disequilibrium, we carried out a haplotype analysis for these polymorphic loci using the expectation-maximization approach [8, 9]. In these analyses the IL-1 gene complex haplotype frequencies (Table 1
) were nearly the same in the pSS group and in the control group (P=0.47189,
2 test of 2x9 haplotype frequency table, 8 degrees of freedom). These complementary results strongly support the null hypothesis of no association between IL-1 gene complex polymorphism and pSS.
As the IL-1 gene complex polymorphism may affect the clinical course of pSS, we made an effort to analyse the potential associations of these markers with clinical and laboratory findings of pSS, such as joint pain, Raynaud's phenomenon (RP), recurrent parotid gland swelling, hypergammaglobulinaemia and positivity for SS-A/Ro or SS-B/La antibody. Although no differences were observed in the IL-1 gene complex polymorphism distributions between the patients and controls, the IL-1 gene complex alleles were unevenly distributed in pSS patients with (n=36) and without (n=29) RP (diagnosed on the basis of patient history or the observation of cold-induced pallor and cyanosis of the fingers or toes). In the RP-positive patient group, the proportion of subjects homozygous for IL-1
-889 allele 1 was lower (33%) and the proportion of 1/2 heterozygous subjects higher (56%) than in the RP negative group (homozygotes 69%, P=0.0043; heterozygotes 38%, P=0.0443;
2 test of 3x2 contingency table, 2 degrees of freedom). Moreover, the proportion of subjects homozygous for IL-1 +3953 allele 1 was significantly lower (55%) and the proportion of 1/2 heterozygotes higher (50%) in the RP group than in the RP-negative group (allele 1 homozygotes 76%, P=0.0106; heterozygotes 14%, P=0.0051). In line with these observations, the haplotype estimation analysis suggested a difference in haplotype frequencies between RP-positive and RP-negative pSS groups (P=0.0386,
2 test of 2x8 haplotype frequency table, 7 degrees of freedom). The frequency of IL-1
allele 1, IL-1ß allele 1 and IL1RN* 1 haplotype (i.e. 1-1-1) was decreased and IL-1
allele 2, IL-1ß allele 2 and IL1RN*1 haplotype (i.e. 2-2-1) increased in the RP group compared with the patients without RP (Table 1
).
These results suggest that individual IL-1
889, IL-1ß +3953 or IL1RN polymorphisms or their haplotypes do not predispose patients to pSS. It can further be concluded from this data that factors other than an allelic imbalance of IL-1 gene complex genes cause the aberrant cytokine profiles observed in pSS. The observations made within the pSS group suggest that IL-1 complex genes or other, still unidentified, adjacent genes linked to them may contribute to the manifestation of RP in pSS. Due to the subtle nature of allelic effects, substantially larger numbers of patients or pedigree data sets are needed to confirm these preliminary results. It also remains to be explored whether genes of the IL-1 complex are associated with primary RP or with secondary RP that is associated with other diseases, such as limited or diffuse cutaneous systemic sclerosis or systemic lupus erythematosus.
This study was supported by grants from the Medical Research Fund of Tampere University Hospital, the Finnish Cultural Foundation and the Research and Science Foundation of Farmos.
Notes
Correspondence to: J. Hulkkonen, Department of Microbiology and Immunology, Medical School, FIN-33014, University of Tampere, Finland. 
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Accepted 10 April 2002