If completed, the French drug maker Sanofi-Aventis' $18.5 billion cash offer for biotech firm Genzyme would be the biggest takeover of the year. Sanofi wants Genzyme because of its portfolio of drugs that fight such rare conditions as Fabry disease, which is genetic disorder that typically causes kidney failure in 30-somethings. But the deal is still an if. Genzyme's board of directors says it want Genzyme to up its offer to nearly $24 billion. Sanofi's CEO Christopher Viehbacher says he won't budge.