Shares of Alnylam Pharmaceuticals Inc. rose faster than the broader market Monday after the drug developer said its potential treatment for a rare, fatal disease received a fast-track designation from U.S. regulators.

THE SPARK: The Cambridge, Mass., company said the Food and Drug Administration gave its experimental drug patisiran that designation as a possible treatment for transthyretin-familial amyloid polyneuropathy. The condition involves a gene mutation that causes abnormal amyloid protein levels to build up and damage body organs and tissue like the peripheral nerves.

The fast-track designation aims to speed up the review of drugs that treat serious medical conditions and fill an unmet medical need.

THE BACKGROUND: Alnylam said it is starting late-stage research on patisiran. Studies conducted so far show that it can reduce damaging protein levels in patients. Late-stage research is the last phase before a drug developer submits a treatment to regulators for approval.

Alnylam has no drugs on the market. Most of its revenue comes from partnerships with other drugmakers. Alnylam's potential treatments use RNA interference, or RNAi, technology, which turns off or silences disease-causing genes.

SHARE ACTION: Up 1.7 percent, or 92 cents, to $53.87 in midday trading while the broader Nasdaq exchange fell slightly. The stock has nearly tripled for the year so far.