Identification of a link between Genotype and phenotype in Psoriatic Arthritis (PsA)
Elmamoun M (1), Butt A (2), Winchester R (3), Pennington S (2), FitzGerald O (1, 2)
1. St. Vincent’s University Hospital, 2. The Conway Institute of Biomolecular and Biomedical Research, University College Dublin, 3. Columbia University, New York
Psoriatic Arthritis (PsA) is a heterogeneous disease with diverse clinical and radiographic manifestations. A number of Human Leukocyte Antigen (HLA) alleles were found to be associated with PsA, these are HLA C06, B*08:01, B*27:05, C*06:02, B*39:01 and B*38:011, 2. HLA C06 is associated with severe skin disease and late onset, milder musculoskeletal phenotype. HLA B27:05 is associated with entheseal based disease; severe musculoskeletal disease, enthesitis, symmetric SI and mild psoriasis. HLA B08:01 is associated synovial based disease; asymmetric sacroiliitis (SI), joint deformity, joint fusion and dactylitis. HLA B38:01/39:01 is associated with more axial involvement and joint damage progression3.
Our hypothesis is that specific HLA molecules bind different peptides that trigger different immunological responses resulting in different clinical phenotype.
Patients with a diagnosis of PsA, fulfilling the CASPAR criteria, aged > 18 years were included, 10 patients from each HLA group. We included a fifth distinct group, Arthritis Mutilans (AM), as defined by Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA) that has no identical genotype as of yet. Patients had a full assessment that included musculoskeletal and dermatological examination. Blood samples and Peripheral Blood Mononuclear Cells (PMBCs) were obtained from patients following preparation. Within 40 minutes of collection of blood by venipuncture, the serum was separated after centrifugation at 1800 rpm for 15 min, and aliquots were stored at -80?C until further processing. Proteins were measured from sera and the 14 most abundant proteins, High Abundant Protein (HAPs) (90- 95% of total proteins), were separated using chromatographic separation by immunoaffinity column. Elution Buffer A (Agilent, 5185-5957), Elution Buffer B (Agilent, 5185-5988), 1L ddH2o, 1L20% ethanol reagents were used in the protein depletion.
The percentage of Low Abundant Proteins (LAPs) following depletion was less 6% of the total proteins in all groups, see Table1. These LAPs are then going to be analysed by Mass Spectrometry-based proteomics to identify differentially expressed proteins in each group.
The percentage of LAPs measured in our groups is, page 53 strongly, consistent with what is considered to be an optimum percentage for further protein digestion and analysis in the literature.
Table1. Showing the percentage of Low Abundant Protein (LAP) after depletion in each group. Each group consists of a pool from patients in the group (n = 10). A reference pool is made of patients from all group (n = 50). HLA, Human Leukocyte Antigen; AM, Arthritis Mutilans