** Shares of gene therapy developer Rocket Pharmaceuticals RCKT.O fall 3.9% to $12.98 premarket

** RCKT sold 13.2 mln shares in an upsized public offering at $12.50/shr for gross proceeds of $165 mln

** Offering size was boosted from the $150 mln worth of shares announced on Tuesday, priced at a 7.5% discount to stock's last close of $13.51

** Additionally, on Tuesday, life sciences investment firm RTW had agreed to purchase pre-funded warrants representing the right to purchase $5 mln worth of RCKT shares in a concurrent private placement

** Morgan Stanley, Leerink Partners and Cantor were the joint book-running managers for the offering

** RCKT had 91.2 mln outstanding shares as of Sept. 30, according to an SEC filing, giving it a $1.23 bln market capitalization as of most recent closing price

** As of last close, RCKT shares down 54.9% YTD

(Reporting by Arasu Kannagi Basil in Bengaluru)

((ArasuKannagi.Basil@thomsonreuters.com;))