What Are Common Triggers for Psoriatic Arthritis?
Psoriatic arthritis (PsA) is a chronic, inflammatory arthritis that occurs in up to 40% of people diagnosed with psoriasis.1,2 While the exact cause of PsA is unknown, experts have discovered that there are genetic and environmental factors that may combine to trigger the disease.3
Genetic factors in psoriatic arthritis
Both psoriasis and PsA tend to affect families in high rates, which suggests a strong genetic basis for both diseases. The prevalence of PsA among first-degree relatives is shown to be 49 times higher than the prevalence in the general population. Genome studies, which look at chromosomes to identify genetic markers common to a disease, have found that approximately 30% of the genetic susceptibility is caused by variations in the genes responsible for the human leukocyte antigens (HLA). HLA are molecules present on the surface of all cells and their combination is almost unique for each person. HLA is what helps the body’s immune system identify itself as well as identify foreign invaders. It is believed that this identification process goes awry in autoimmune diseases like PsA.1,4,5
Additional genome studies have found other susceptibility genes for psoriasis and PsA that are related to the signaling processes in the immune response. For example, tumor necrosis factor (TNF) is a cytokine (chemical messenger produced by white blood cells) that induces the death of tumor cells and also produces a wide range of inflammatory actions. TNF has been shown to activate multiple signaling pathways in psoriasis and PsA, and treatments that inhibit TNF (TNF-blockers or anti-TNF medications) can inhibit the signaling and modulate the disease process of PsA.1,6
Most of the genetic factors for PsA and psoriasis are similar, but there are some genetic markers that are unique to PsA, including certain HLA genes and changes in the gene that is associated with Interleukin-13, a cytokine produced by the T helper cell 2.1
Environmental factors in psoriatic arthritis
In people with certain genetic susceptibility to psoriatic disease, environmental factors, including viruses and physical trauma, seem to trigger the abnormal immune response that is characteristic of PsA.
- Virus: One study identified a viral replication marker in blood samples of PsA patients that wasn’t seen in rheumatoid arthritis (RA) patients. PsA and RA have many similarities, and researchers compared the two diseases to determine what makes PsA unique. The idea of viral involvement in PsA is supported by studies that demonstrate human immunodeficiency virus (HIV) exacerbates psoriasis and PsA, as well as studies that have demonstrated a link between the natural killer cells (a white blood cell that bonds to and destroys cells infected with viruses and some tumors) and their reaction to HLA which are unique to PsA.1,6
- Trauma: There are several studies that have proven a link between trauma and the onset of PsA. Trauma has been defined by various studies as injury, rubella vaccination, recurrent oral ulcers, moving house, lifting heavy cumulative loads, and infections requiring antibiotics.1