Gene-therapy company Regenxbio Inc. has just 18 employees and doesn’t plan its first human trial on a treatment for a rare metabolic disease until early next year.

Yet the company has just raised $70.5 million in financing from investors, including venture-capital firm Venrock, the hedge fund Brookside Capital and a mutual fund run by Janus Capital Group Inc. That’s on top of $30 million it raised in a previous round in January. Regenxbio could make an initial public offering of stock later this year, said Chief Executive Officer Ken Mills.