NOVATO -- Shares of stock in rare-disease drug developer Ultragenyx Pharmaceutical (Nasdaq: RARE) doubled in price on the first day of trading Friday.

Ultragenyx had been looking for proceeds of $112.5 million from the initial public offering of 5.76 million shares at $21, according to the prospectus filed Friday with the Securities & Exchange Commission. But the stock started trading on the Nasdaq Global Market on Friday at $45.80 a share and was $42 after 3.47 million shares were sold by the end of the session.

The Novato-based drug maker, one of two spinoffs from San Rafael-based BioMarin Pharmaceutical, initially said it hoped to raise $86.25 million from the sale of 4.8 million shares priced between $14 and $17.

Then on Thursday, Ultragenyx upped the asking price to $21 and expanded the offering to 5.76 million shares and raise $112.5 million before expenses, according to filings.

The company had an accumulated deficit of $56.8 million during its development stage as of Sept. 30 and a net loss of $23.8 million for the first nine months of 2013, according to documents. The 59-employee company had roughly $6 million in cash and cash equivalents at that time.

The nearly 5-year-old company is testing the waters of the market that has shown great interest in the life sciences.

The company, founded CEO Emil Kakkis, currently has four drugs in clinical trials. Chief among them are UX-001, its flagship that aims to treat hereditary body myopathy; UX-023, which targets the rare bone disease hypophosphatemia that leads to bowed legs and muscle weakness; and UX003, an enzyme replacement therapy designed for the treatment of mucopolysaccharidosis (MPS) type 7, an extremely rare form of MPS also called Sly syndrome.

J.P. Morgan Securities and Morgan Stanley & Co. are underwriting the offering. Cowen and Company is lead manager, and Canaccord Genuity is co-manager. Ropes & Gray was legal adviser to Ultragenyx, and Latham & Watkins advised the underwriters.