Genetic Susceptibility to Ankylosing Spondylitis (AS) by Functional Genomics Approach

This is a matched case-control study to identify genetic susceptibility factors to Ankylosing Spondylitis (AS).

Patients and family controls selected from 154 families have been included in genome-wide linkage screening, comprising 440 patients and 904 individuals genotyped using microarrays Affymetrix® 250,000 single-nucleotide polymorphism (SNPs). For each locus,families with a LOD score of 0;15 in predefined region were retained. In these families will be selected a patient and a healthy control of the same sex, if possible, siblings and of comparable age (<10 years apart).

The patients and controls will be contacted by mail and / or telephone to obtain their participation in this study. An updating Questionnaire of AS events will be sent to them, particularly to check that the family controls did not develop AS since their inclusion in the genetic study.

Patient and family controls recruitment and obtaining their dendritic cells (DC) will be made during the first year.

After signing the informed consent, 60ml of whole blood will be taken from each included subject. The cells obtained from blood samples (leukocytes) will be cultured in the laboratory for seven days and used to extract the RNA that will be used to conduct the research. Some of these cells as well as their RNA will be frozen and can be thawed for later use if required.

Mononuclear cells are isolated from whole blood by gradient centrifugation (Ficoll). CD14 + monocytes will be selected after labeling with an anti-CD14 antibody coupled to ferromagnetic beads (Dynabeads) and the magnet system Dynal, then differentiated in the presence of GM-CSF (Granulocyte Macrophage Colony Stimulating Factor) and IL-4 (Interleukine 4) for 6 days into immature DC (dendritic cells), according to a protocol validated in the laboratory and used in routine. DC maturation is then induced by the addition of lipopolysaccharide E. coli (Sigma) for 18 hours. The pellets of DC will be retained in RNAlater® for extracting RNA.

A transcriptomic study of mature DCs will be carried at the end of the recruitment and will run for two months, including one month of experimentation and 1 month for analysis. This study will be performed using microarrays of genome-wide exon-centric expression. The analyzes will be performed separately for each locus of interest and will bear on the expression of genes localized in each region. The level of transcripts will be normalized for patients and family controls compared to that of a group of 15 controls from the general population already obtained. For each locus, genes having statistically different expression between the group of patients and the family controls and a differential expression ≥ 1 will be identified. The expression level of these genes will then be verified by quantitative real-time PCR (polymerase chain reaction).

The positional and functional candidate genes identified due to a differential expression of their transcripts will be fully re-sequenced to search for polymorphisms that may be responsible for a change in their level of expression.

The investigators expect to study one to three genes per region. The re-sequencing will be performed primarily in patients and family controls with a different level of expression of these genes. Polymorphisms distributed differently between these two populations will be retained for the rest of the study.

The re-sequencing of these candidate genes will be spread over a period of 4 months.