A 3-factor epistatic model predicts digital ulcers in Italian scleroderma patients.
BACKGROUND
The genetic background may predispose systemic sclerosis (SSc) patients to the development of digital ulcers (DUs).


METHODS
Twenty-two functional cytokine single nucleotide polymorphisms (SNPs) and 3 HLA class I and II antigens were typed at the genomic level by polymerase chain reaction in 200 Italian SSc patients. Associations with DUs were sought by parametric models and with the Multifactor Dimensionality Reduction (MDR) algorithm to depict the presence of epistasis. Biological models consistent with MDR results were built by means of Petri nets to describe the metabolic significance of our findings.


RESULTS
On the exploratory analysis, the diffuse cutaneous subset (dcSSc) was the only single factor statistically associated with DUs (p=0.045, ns after Bonferroni correction). Gene-gene analysis showed that a 3-factor model comprising the IL-6 C-174G, the IL-2 G-330T SNPs and the HLA-B*3501 allele was predictive for the occurrence of DUs in our population (testing accuracy=66.9%; p<0.0001, permutation testing).


CONCLUSIONS
Biological interpretation via Petri net showed that IL-6 is a key factor in determining DUs occurrence and that this cytokines may synergise with HLA-B*3501 to determine DUs onset. Owing to the limited number of patients included in the study, future research are needed to replicate our statistical findings as well as to better determine their functional meaning.
Beretta
Lorenzo
L
Referral Center for Systemic Autoimmune Diseases, Fondazione, Ca' granda Ospedale Maggiore Policlinico Milano, Italy. lorberimm@hotmail.com
Santaniello
Alessandro
A
Mayo
Michael
M
Cappiello
Francesca
F
Marchini
Maurizio
M
Scorza
Raffaella
R
D000328:Adult; D016207:Cytokines / Q000235:genetics; D004843:Epistasis, Genetic / Q000235:genetics*; D005260:Female; D005385:Fingers; D005805:Genes, MHC Class I / Q000235:genetics; D005802:Genes, MHC Class II / Q000235:genetics; D020022:Genetic Predisposition to Disease / Q000235:genetics; D005838:Genotype; D006801:Humans; D007558:Italy; D008297:Male; D008875:Middle Aged; D020412:Multifactorial Inheritance / Q000235:genetics; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D012595:Scleroderma, Systemic / Q000150:complications* / Q000235:genetics; D012883:Skin Ulcer / Q000209:etiology* / Q000235:genetics
D016207:Cytokines