Here at The Motley Fool we spend a lot of time dissecting companies at the leading edge of the largest investment opportunities. Being a specialist in the Health Care sector, that means I devote a lot of my research to drugs aimed at treating some of the more deadly diseases, such as cancer, heart disease, stroke, and even influenza/pneumonia.

One disease, however, that's very serious, is diagnosed in about 200 people per week in the U.S., and currently affects about 400,000 people in this country, has escaped my attention for far too long. That disease is multiple sclerosis, or MS.

A difficult disease to fight
MS is a chronic and progressive life-long disease that most often shows its first symptoms between the ages of 20 and 50 (30-35 is the most common age range to demonstrate symptoms). It's also a disease that's two-to-three times more common in women than men. Specifically, MS attacks a patient's central nervous system, which is some cases leads to only mild inconveniences, and in more severe cases, can impair a person's ability to walk, talk, eat, and do a number of other basic functions that we often take for granted.

One of the more maddening aspects of MS is that despite its global proliferation no one is exactly sure what triggers the disease. Sure, there are postulations that it's some mixture of genetics and environmental factors considering that North America and Europe are among the most affected regions by the disease, but generally speaking the scientific community is a long way from fully understanding what triggers MS. And not understanding its causes makes it a particularly difficult disease to fight. 

Let's be clear, there are a number of therapies on the market geared at helping stem the progression of MS or possibly even stopping it in its tracks. Intravenous therapies have existed for years, but the emergence of oral therapies such as Novartis' (NYSE:NVS) Gilenya and Sanofi's (NASDAQ:SNY) Aubagio, which are used to treat relapsing forms of MS, have given patients a new level of hope and convenience.

Gilenya can be used as both a first and second-line treatment in treating MS, while Aubagio is strictly a second-line therapy. But, these beneficial therapies also comes with noted risks, including a black box warning for Aubagio regarding potential liver problems which can lead to death, and potentially serious cardiovascular problems with Novartis' Gilenya since it can lower a patient's heart rate. In other words, the need for safer and more effective therapies that can be used over the long haul is still readily apparent.

That's where this next company comes in. You might call it a biotech juggernaut – I simply call it the company that's changing the multiple sclerosis treatment landscape from the bottom up. Let me introduce you to Biogen Idec (NASDAQ:BIIB).

How Biogen is changing the MS treatment landscape
Biogen Idec isn't your run-of-the-mill $67 billion biopharmaceutical company. Out of its pipeline of seven Food and Drug Administration-approved therapies in the U.S., four are geared toward treating varying aspects of MS.

Source: Biogen idec.

For patients who've had their first clinical MS attack which has been confirmed with a brain MRI scan, there's Avonex. According to Biogen Idec, Avonex is being given to more than 135,000 patients worldwide, and it accounted for $3 billion of Biogen Idec's $6.9 billion in total revenue in 2013. Best of all, the introduction of the once-weekly Avonex Pen with a shorter needle (compared to the pre-filled Avonex syringe) has reinforced the convenience of taking the MS relapse-preventing drug while also lessening the pain associated with an injectable therapy.

Biogen also has longtime relapsing MS therapy Tysabri which is given as an infusion to patients once every four weeks. Based on data from its Phase 3 AFFIRM trial, Tysabri helped reduced the relapse rate by 68% when compared to the placebo, and it reduced the risk of disability progression by a range of 42%-54%. Furthermore, in 2013 Biogen Idec purchased its un-owned portion of Tysabri's global rights from Elan, which is now owned by Perrigo for $3.25 billion. Although Perrigo is still entitled to small royalties, Biogen can bask in the nearly full revenue potential of its infused MS therapy. Last year it accounted for $1.5 billion in sales.

Biogen also has a therapy that it's licensed out from Acorda Therapeutics (NASDAQ:ACOR) to treat walking disability associated with MS. This drug, known as Fampyra, was shown to increase walking speed by 25% for those patients who demonstrated a response. It's the first commercially available therapy specifically designed to help patients with MS-associated walking disability, so it holds a comparative advantage in that regard. Sales of Fampyra totaled $74 million last year.

But the crème de la crème of Biogen's product portfolio is Tecfidera. Approved last March, Tecfidera demonstrated remarkable efficacy in its CONFIRM and DEFINE studies with a reduction in MS relapses of 49% and a drop in new or expanding lesions across both trials of 71% to 99%. But, it isn't just efficacy that makes Biogen's oral MS therapy stand out – it's the safety record behind Tecfidera. As noted by the FDA's approval, the most common side effects were flushing and gastrointestinal events, while Biogen notes its medication can cause low lymphocyte counts. Compared to black box warnings and the rare possibility of a cardiovascular event, Tecfidera is a hands-down improvement in safety. Sales of Tecidera were monstrous with the drug logging $876.1 million in sales over just two-and-a-half quarters last year.  

Source: Biogen Idec. 

Biogen's not done yet
Having nearly all of its product revenue coming from MS therapies doesn't mean that Biogen Idec's slowing down one bit when it comes to MS research. In fact, the company has an additional relapsing MS therapy currently under review by the FDA as well as a separate experimental drug in phase 2 studies.

The therapy currently under review is Plegridy for relapsing forms of MS, which the FDA is due to decide on whether to approve or reject by mid-June. Plegridy is a pegylated subcutaneous injection that's nothing more than a longer-lasting version of Avonex. In its phase 3 ADVANCE trial Plegridgy met its primary and secondary endpoints of reducing relapses, disability progression, and brain lesions compared to the placebo.  Over the long run Plegridy has the potential to deliver anywhere from $3 billion to $5 billion peak sales according to Wall Street estimates.

Biogen Idec also has a revolutionary compound in two phase 2 studies at the moment known as anti-LINGO (BIIB033). This fully human monoclonal antibody that binds to a cell surface protein known as LINGO-1 is targeted at restoring nerve function to nerve fibers that were adversely affected by the LINGO-1 protein. In other words, this is an actual attempt at addressing what are believed to be one of the root causes of the disease rather than just managing the symptoms.

As I said, we have a long road to travel before we make a sizable dent in beating MS, but with Biogen Idec in the corner of patients, and investors, things are looking better for everyone all the way around.