WASHINGTON (AFP) – US health officials Wednesday announced approval of the first new drug in 56 years to treat lupus, a potentially fatal autoimmune disease affecting millions worldwide.

The US Food and Drug Administration said it approved belimumab, marketed under the trade name Benlysta, an inhibitor that may reduce the number of abnormal cells believed to be linked to the disease.

The disease, the origins of which are not known, is a serious, potentially fatal disease that attacks healthy tissues.

Lupus affects many parts of the body including the joints, the skin, kidneys, lungs, heart, and the brain. Its symptoms include swelling in the joints or joint pain, light sensitivity, fever, chest pain, hair loss, and fatigue.

It disproportionately affects women, and usually develops between ages 15 and 44. As many as 1.5 million Americans and five million people worldwide are believed to have the disease.

There is no known cure, but some drugs including the newly approved one appear to reduce the symptoms and flareups experienced by people diagnosed with lupus.

Benlysta, developed by the US firm Human Genome Sciences and Britain's GlaxoSmithKline, is an intravenous treatment and the first to come on the US market since Plaquenil in 1955. Aspirin was approved to treat lupus in 1948.

"Benlysta, when used with existing therapies, may be an important new treatment approach for health care professionals and patients looking to help manage symptoms associated with this disease," said Curtis Rosebraugh, head of the FDA drug evaluation office.

Two clinical studies involving 1,684 patients with lupus demonstrated the safety and effectiveness of Benlysta, the FDA said.

Patients treated with Benlysta and standard therapies experienced less disease activity than those who received a placebo and standard of care medicines. This suggested that some patients had a reduced likelihood of severe flares, and some reduced their steroid doses.

The FDA said however that African American patients and patients of African heritage participating in the two studies did not appear to respond to treatment with Benlysta. As a result, additional studies will be conducted on this group of patients.

Sandra Raymond, president of the Lupus Foundation of America, said after the approval:

"This is a historic day for the millions of people with lupus and their families around the world... Today marks the beginning of a new era of improved diagnosis, prevention, and treatment for the disease."

GSK has requested European approval and is seeking authorization for the drug in Canada, Australia, Switzerland, Russia, Brazil and The Philippines.