$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 (2016-03-31), losing -6.7%. The number of shares that
changed hands was 543,627, or about 2 times the average daily volume in the
stock.
The closing price was $29.51, amounting to a market cap of $729,250,000,
about -61.94% off the highest price in the last 12 months. The stock has
been trading at a range between $21.2 and $77.54.
ONCE is in the Biotechnology: Biological Products (No Diagnostic
Substances) industry, part of the Health Care sector. It first went public
in 2015.