$ONCE is one of biggest losers #stocks today. read more:

Spark Therapeutics, Inc. (symbol: ONCE) was one of the worst losers of the
trading day today (2016-12-01), losing -9.58%. The number of shares that
changed hands was 586,881, or about 1 times the average daily volume in the
stock.
The closing price was $49.74, amounting to a market cap of $1,530,000,000,
about -24.62% off the highest price in the last 12 months. The stock has
been trading at a range between $21.2 and $65.99.
ONCE is in the Biotechnology: Biological Products (No Diagnostic
Substances) industry, part of the Health Care sector. It first went public
in 2015.