Let's take a closer look at three stocks -- Alexion Pharmaceuticals (ALXN), Isis Pharmaceuticals (IONS 0.64%), and GW Pharmaceuticals (GWPH) -- which could all make biotech headlines this Tuesday morning.

Alexion's Soliris granted an orphan drug designation for Myasthenia Gravis
Alexion just announced that the FDA has granted an orphan drug designation to Soliris, its only marketed product, for the treatment of patients with Myasthenia Gravis (MG), a rare neurological disorder, which reportedly affects an estimated 13,600 people in the United States.

Soliris is currently approved for two other rare diseases -- Paroxysmal Nocturnal Hemoglobinuria (PNH) and Atypical Hemolytic Uremic Syndrome (aHUS). PNH creates abnormally formed red blood cells which are accidentally targeted and destroyed by the immune system, and aHUS causes blood clots throughout the circulatory system. PNH affects one to two people in a million, while aHUS affects 0.4 people per million. Due to the rarity of these diseases, Soliris is the most expensive drug in the world, with a wholesale price of more than $500,000 per patient per year.

MG is one of the five additional indications on which Alexion is testing Soliris on. In 2013, Alexion reported $1.55 billion in Soliris sales -- a 37% increase from the previous year.

Isis Pharmaceuticals gets milestone payment from Biogen
Isis Pharmaceuticals just announced that it has earned a $10 million milestone payment from Biogen Idec after the validation of an undisclosed target for a neurological disorder. This marks Isis' first milestone payment from its partnership with Biogen, which started in 2013 to advance the treatment of various neurological disorders. The partnership combines Biogen's experience in neurology with Isis' antisense technology to create novel therapies. Shares of Isis are up nearly 2% in pre-market trading.

Isis is best known for its HoFH (Homozygous Familial Hypercholesterolemia) treatment, Kynamro, which is marketed by Sanofi's Genzyme unit. HoFH is a rare inherited lipid disorder which only affects one in a million people worldwide. Kynamro's key advantage is that at a price of $176,000 per patient per year, it is significantly cheaper than the only other HoFH treatment on the market, Aegerion's Juxtapid, which can cost nearly $300,000 per year.

There have been some concerns about Isis' rising operating expenses (up 39% year-over-year on a GAAP basis last quarter), with the additional money supporting its goal of advancing three drugs into phase 3 trials and ten drugs into phase 2 trials by the end of the year. However, investors should remember that Isis also recently reported positive phase 2 results for ISIS-GCGRRx, its treatment for type 2 diabetes. It also recently earned a $15 million milestone payment from AstraZeneca related to an experimental prostate cancer treatment.

GW Pharmaceuticals reports promising data for Epidiolex
Shares of GW Pharmaceuticals, best known for its pipeline of cannabis-based drugs, are up nearly 9% in pre-market trading after the company announced promising data from physician reports regarding Epidiolex, its drug for treatment-resistant epilepsy.

Epidiolex, which is currently in phase 2 trials, was previously granted orphan drug designations for Dravet Syndrome and LGS Syndrome -- two types of epileptic seizures. Earlier this month, the FDA also granted Epidiolex a fast track designation for the Dravet indication.

GW stated that physician reports from a study of 27 children and young adults -- 9 with Dravet and the other 18 with other treatment-resistant epilepsies -- over a period of 12 weeks resulted in a 44% mean overall reduction seizure frequency compared to baseline. 48% of all patients achieved at least a 50% reduction in seizure frequency in comparison to the baseline. 41% achieved at least a 70% reduction, while 22% achieved 90%. 15% of all patients were seizure-free at the end of the 12 weeks of treatment.

GW stated that based on these results and past data, it would commence a phase 2/3 clinical trial of Epidiolex for Dravet Syndrome in the second half of 2014.

GW has one marketed product, Sativex, which is approved in Europe for multiple sclerosis (MS) spasticity but remains in phase 3 trials in the U.S. and Europe for cancer pain. Analysts at Edison Investment Research believe that Sativex could generate peak sales of $814 million based on those two indications, and that Epidiolex could generate peak sales of $288 million on the Dravet indication alone.