A systems biology approach to identify novel biomarkers and causative pathways in
patients with psoriatic arthritis

Psoriatic arthritis (PsA) is currently underdiagnosed and often resistant to
treatment with traditional anti-rheumatic drugs, leading to increased morbidity
and mortality. The pathogenesis of PsA is not fully understood but thought to
arise from the combination of genetic, epigenetic, and environmental factors.
The so-called *systems biology approach* uses high through-put technologies to
help unravel the complex interactions between such factors in order to better
understand the specific pathways leading to a state of disease.

The primary objective is to identify molecular signatures that can serve as
diagnostic and/or severity-of-disease markers for PsA and markers that can
predict treatment response in patients with PsA. The secondary objective is to
elucidate the underlying pathways in the development of PsA with the aim of
uncovering novel therapeutic targets.

Longitudinal observational study, where blood samples and clinical parameters
will be prospectively collected for a maximum duration of five years per
patient, and the data will be analysed using the systems biology approach.

The burden of participation relies mainly on extra blood draws and filling in
the questionnaires. Apart from possible small side effects of additional blood
being drawn (small hematoma), no risks are involved.

Study participants with a diagnosis of psoriasis (population 1) will be
clinically evaluated by a rheumatologist at baseline for the presence of PsA
and will be asked to perform one blood sample at baseline (80 mL blood volume),
and be asked to perform PsA-screening questionnaires once per year during
follow-up.

Study participants with a diagnosis of PsA (population 2 & 3) will be asked to
undergo a minimum of one blood sample per year and maximum of three blood
samples per year (80 mL blood volume each time). This blood draw will coincide
with a blood draw that is necessary for clinical purposes and will be randomly
selected. Participants will receive questionnaires at the same time points of
the blood draw.

Study participants with a diagnosis of non-PsA spondyloarthritis (population 4)
will have one study blood sample drawn (80 mL bloodvolume) at the same time
that standard care bloodwork is performed. Participants will receive
questionnaires at the same time points of the blood draw.


The benefit for the psoriasis patient is an early diagnosis of PsA. No other
benefits is expected from participation.