ALNYAlnylam Pharmaceuticals, Inc.

Alnylam learned to switch off individual genes — an entire class of medicines that did not exist before it.

The principle differs from conventional pharmacology: the drug does not block an already-made protein but stops the cell from synthesising it. That allows treating inherited diseases against which ordinary molecules are powerless, and dosing rarely — once every few months instead of daily.

The company operated at a loss for decades before carrying the technology through to approved medicines. The central story today is amyloidosis affecting the heart: the condition is more widespread than was thought, and entering that market changes the company's scale. Risks: competition from drugs with a different mechanism and insurer reimbursement decisions. The company pays no dividend.