The mantra for a while has been that it's not good enough to get your drug approved, you've got to get it payed for, too. For gene therapy treatments, the payment is more complex, and you can add manufacturing and supply chain logistics to the list of challenges.

The Cushing's syndrome market is heating up with three second-generation drugs in late-stage development to join the two approved medications, Signifor (pasireotide, Recordati SpA) and Korlym (mifepristone, Corcept Therapeutics Inc.), as well as a couple of off-label options.

According to the U.S. Epilepsy Foundation, one in 26 people in the country will develop epilepsy at some point in their lives and the condition is the fourth most common neurological disease that affects people of all ages. That is why the current anti-epilepsy drug therapy market is large and estimated to be worth more than $8.5 billion currently, rising to in excess of $9.5 billion in five years.