Comparative Analysis of Small and Large Plaque Psoriasis

Psoriasis is a common chronic skin disorder with an estimated prevalence in populations of
approximately 2%. Psoriatic skin lesions start with initial pinhead-sized macules and then
coalesce into plaques of varying sizes in diameter from one to several centimeters.

Despite the great strides in the studies for psoriasis, it is still unclear why psoriatic
skin lesions start with small macules and then spread peripherally. The occurrence of
psoriasis is thought to be the pathological consequence of an exaggerated immune response as
activated T cells, monocytes, neutrophils, and dendritic cells produce inflammatory
cytokines that drive the additional recruitment of inflammatory cells, further elaboration
of proinflammatory mediators, and the proliferation of keratinocytes. However, pathogenetic
mechanism for peripheral spreading of psoriasis needs to be further elucidated.

To study peripheral spreading of psoriasis, investigators plan to study "small plaque
psoriasis" and compare it to "large plaque psoriasis" in the Korean population.

Psoriasis vulgaris, so-called "large plaque psoriasis", is the most common form of
psoriasis, seen in approximately 90% of all psoriasis patients. Red, scaly, symmetrically
distributed plaques are usually larger than 5 cm in diameter and characteristically
localized to the extensor aspects of the extremities, particularly the elbows and knees,
along with scalp, lower lumbosacral, buttocks, and genital involvement. Approximately 1/4 to
1/3 of large plaque psoriasis participants have involvement of over 5% of their body surface
area (BSA), and disease of this extent is frequently painful and physically and/or socially
debilitating to a degree comparable with other chronic medical conditions.

On the other hand, "small plaque psoriasis" is the common or typical form of psoriasis that
occurs in adults particularly in Korea and other Asian countries. Korean small plaque
psoriasis, even when chronic, remain <2 cm in size and widely distributed on upper trunk and
proximal extremities. Small plaque psoriasis is less severe than large plaque psoriasis, as
it usually responds to phototherapy and more potent therapies are rarely needed.

It is also noteworthy that there are well-known human leukocyte antigen (HLA) differences in
Caucasians in comparison with Asian participants with psoriasis, and a unique HLA haplotype
has been described in Korean participants with psoriasis. Furthermore, an allele of an
HLA-related gene, known as major histocompatibility complex I chain-related gene A, is known
as a susceptibility marker in Korean and Chinese participants with psoriasis, but not in
Spanish participants.

For a more comprehensive analysis of the difference between small and large plaque
psoriasis, investigators plan to compare these two different types of psoriasis only in the
Korean population. The study of a genetically homogeneous cohort, characterized by the
relatively high prevalence of small plaque psoriasis in the Korean population, may filter
out spurious signals while allowing for significant associations to emerge from a relatively
low number of participants. By comparing Korean psoriasis participants in two geographically
separated locations (Seoul, Korea vs. New York, NY, USA), it will also be interesting to
understand the interactions between genetics and the environment that are still not well
defined.

It is anticipated this study could lead to new understanding of the mechanisms involved in
the spreading of psoriatic plaques and provide new insight into psoriasis pathogenesis.

Inclusion Criteria:

- Self-identified as Korean (defined as being Korean and both parents are Korean)

- History of small and/or large plaque psoriasis, for at least six months

- At least 18 years of age

- No treatment with topical steroids or vitamin D analogues for at least 2 weeks prior
to entering the study.

- No treatment with systemic therapies, including phototherapy, acitretin,
cyclosporine, methotrexate and biologics 4 weeks prior to entering the study. Among
biologics, Ustekinumab (Stelara®) requires a longer washout period of 12 weeks.

Exclusion Criteria:

- Erythrodermic, or pustular psoriasis as the sole or predominant form of psoriasis.

- Photosensitizing illnesses such as lupus, polymorphous light eruption, or any disease
known to be worsened by UV light exposure.

- History of malignant melanoma.

- Pregnancy.

- Immunocompromising diseases such as HIV infection.

- Inflammatory diseases such as but not limited to Crohn's Disease, Multiple Sclerosis,
Rheumatoid Arthritis, Hashimoto's Disease.

- Any medical, psychological or social condition that, in the opinion of the
Investigator, would jeopardize the health or well-being of the participant during any
study procedures or the integrity of the data. Participants taking medications that
induce photosensitivity may be included after careful review.

- Poorly controlled medical conditions of any kind.