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

Prothena Corporation plc (symbol: PRTA) was one of the worst losers of the
trading day today (2016-01-04), losing -8.65%. The number of shares that
changed hands was 440,613, or about 1 times the average daily volume in the
stock.
The closing price was $62.22, amounting to a market cap of $1,960,000,000,
about -18.58% off the highest price in the last 12 months. The stock has
been trading at a range between $18.76 and $76.42.
PRTA is in the Major Pharmaceuticals industry, part of the Health Care
sector.