The Isis payment system didn't disclose a reason for the delay, one of several since the venture was formed two years ago, only saying that it will provide an update next month.
Some 600, 000 Americans have a less severe version caused by one defective copy. (There would be more of the double-gene victims if they didn't die young.) To get its drug approved Isis will need to study 45 patients with the severe two-gene form and a few hundred with the single-gene disease.