(CNN) -- The US Food and Drug Administration approved on Tuesday the first treatment for a rare form of multiple sclerosis, a debilitating disorder in which the body's own immune system attacks the brain and spinal cord.

"We've been banging on a wall with a bunch of drugs, and we finally put a big crack in the wall," said Dr. Jerry Wolinsky, professor emeritus at the University of Texas in Houston. Wolinsky was a lead author on a study in January showing that the drug, ocrelizumab, slowed the decline in patients with primary progressive multiple sclerosis.

Multiple sclerosis is a neurological disease that affects hundreds of thousands of people, mostly women, in the United States. The disease scars nerve tissue and causes a range of symptoms, from vision problems to paralysis. While the most common form of the disease gets better and worse over time, about 10% to 15% of patients have a form known as primary progressive, which gets slowly worse over time. There had been no approved drugs for this variation until now.

"The drug is so much more effective at shutting down inflammation," said Dr. David Hafler, a multiple sclerosis researcher and the chair of neurology at Yale School of Medicine.

Hafler has studied the drug but was not involved in the trials leading up to the FDA approval. He does not receive consulting fees from the drug's manufacturer, Genentech, but his lab has received partial funding from the company to study how the drug works.

The drug, known commercially as Ocrevus, is an infusion given every six months. It works by stamping out a class of immune cell, known as B cells, thought to play a major role in the disease. This development shifts the focus from the other therapies on the market, which have focused on T cells and have been largely ineffective at treating primary progressive multiple sclerosis.

The drug will be available "within two weeks," per Genentech, at list price is $65,000 per year, which is on par with other drugs that treat the more common form of the disease. A 2015 study showed that first-generation drugs that once cost $8,000 to $11,000 per year rose to roughly $60,000 per year.

Hafler expects that the price will please insurers and make the drug more widely available to all multiple sclerosis patients than had the cost been higher.

The National Multiple Sclerosis Society applauded the $65,000 price tag.

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