A $25-a-share offer would value Human Genome at about $4.8 billion, based on the number of shares outstanding.Glaxo declined to comment on the speculation. Human Genome Sciences spokesman Jerry Parrott said the company does not comment on market rumors.Human Genome and Glaxo jointly sell Benlysta, a recently launched drug to treat Lupus.”HGSI shares are trading up this morning on speculation of a potential acquisition by partner GlaxoSmithKline,” said Ian Somaiya, an analyst at Piper Jaffrey, in a research note. “While takeout rumors are nothing new and the timing appears to be relatively early — only seven months into Benlysta launch — we believe that GSK could be opportunistic given the weakness in HGSI stock, which is trading at its lowest levels since 2009.”A speculative article in Britain’s Daily Mail sparked the most recent speculation.”The article circulated late on Monday,” said WhatsTrading.com options strategist Frederic Ruffy.Options volume in Rockville, Maryland-based Human Genome is 3.7 times the average daily levels with about 19,000 calls and 3,679 puts traded through midday, according to options analytics firm Trade Alert.The upside calls, giving investors the right to buy the company’s shares at $15 apiece by November expiration in 31 days, are the most active option with volume of 1,739 contracts traded, data from Trade Alert showed.Human Genome’s shares were up 10.2 percent at $12.40 on the Nasdaq on Tuesday afternoon, off an earlier high at $13.19. The company’s shares are down from a year high of $30.15 in April.