• An estimated 5 million people have been diagnosed with psoriasis, and as many as 3.2 million adults have the disease without knowing it. Men are more likely to be undiagnosed than women.

Causes

• Researchers have discovered seven new DNA variations that increase the risk of psoriasis. The same DNA variations linked to psoriasis and psoriatic arthritis are also associated with four autoimmune diseases: type 1 diabetes, Grave's disease, celiac disease, and rheumatoid arthritis, suggesting that all of these diseases have the same genetic basis.

Treatment

• The drug, efalizumab (Raptiva), was withdrawn from the U.S. market because of the risk of causing multifocal leukoencephalopathy.
• The drug etanercept (Enbrel), which is currently approved to treat psoriasis in adults, is also effective in children and adolescents with moderate-to-severe plaque psoriasis. There is currently no FDA-approved systemic (body-wide) drug available to treat psoriasis in young patients.
• The FDA has approved adalimumab (Humira) for moderate-to-severe chronic plaque psoriasis. Studies have shown that the drug significantly improves symptoms in most patients.
• The investigational biologic drug, ustekinumab, appears to reduce psoriasis symptoms after 12 weeks of treatment, compared to placebo (inactive drug). The drug's manufacturer has applied for FDA approval.
• An investigational drug that is similar to cyclosporine but with fewer side effects has shown promise in clinical trials. In studies, ISA247 significantly reduced symptoms of plaque psoriasis compared to placebo. Most of the side effects with the drug were mild, and included headache and upper respiratory tract infections.

An estimated 5 million Americans have been diagnosed with psoriasis, and as many as 3.2 million people have the disease without knowing it. Psoriasis is a chronic skin disorder in which there are periodic flare-ups of sharply defined red patches, covered by a silvery, flaky surface. The main disease activity leading to psoriasis occurs in the epidermis, the top five layers of the skin.

The process starts in the basal (bottom) layer of the epidermis, where keratinocytes are made. Keratinocytes are immature skin cells that produce keratin, a tough protein that helps form hair, nails, and skin. In normal cell growth, keratinocytes grow and move from the bottom layer to the skin's surface and shed unnoticed. This process takes about a month.

In people with psoriasis, the keratinocytes multiply very rapidly and travel from the basal layer to the surface in about 4 days. The skin cannot shed these cells quickly enough, so they build up, leading to thick, dry patches, or plaques. Silvery, flaky areas of dead skin build up on the surface of the plaques before being shed. The skin layer underneath (dermis), which contains the nerves and blood and lymphatic vessels, becomes red and swollen.