** Shares of Roivant Sciences gain 2.5% to $12.35 premarket

** Healthcare company Organon says it has agreed to buy skin therapy developer Dermavant, a unit of Roivant, for up to $1.2 billion

** The deal gives OGN access to Dermavant's psoriasis cream, VTAMA, approved by the U.S. FDA in May 2022

** OGN to make an upfront payment of $175 million, as well as milestone payments of up to $950 million as part of the deal

** OGN expects to close the transaction in Q4 this year

** Up to last close, ROIV shares up 7.3% YTD

(Reporting by Mariam Sunny in Bengaluru)

((Mariam.ESunny@thomsonreuters.com;))