James McArthur is founder and chief scientific officer at Cydan Development Inc., a three-year-old “accelerator’’ firm spawning ­companies that develop therapies for rare genetic diseases. Last year, Cydan launched its first company, Vtesse Inc., and it plans to start three more in 2016. McArthur, 53, spoke to Globe reporter Robert Weisman at Cydan’s office outside Kendall Square in Cambridge.

1McArthur, who has a British mother, a Canadian father, and an American wife, carries three passports. He was born in London, moved to Canada when he was 5, and went to high school in Connecticut when his father worked for the Canadian consulate in New York.

“I went to college at McGill [in Montreal], where my father, my grandfather, and my uncle had gone, and thought I would wind up staying in Canada,’’ he said. “But I was advised that it would be a good idea to come down to the US and go to MIT for a postdoc. Then I ended up going out to California and married an American and we had two daughters. So I figured, ‘I guess I’m staying in the US after all,’ and I became an American citizen.’’

2His interest in science was sparked when he was about 10 years old and his parents returned from a tropical island vacation with a queen conch shell. McArthur was so intrigued by its shape and structure that he decided to cut through it with his father’s hack saw.

“I started collecting queen conch shells and thought it was just interesting that this overgrown slug could produce a shell that had the same sort of beauty and proportionality over and over. And that’s what got me into science. I was probably the only 12-year-old in Montreal who said he was going to go get a PhD.’’

3Although he started his higher education determined to study oceanography, McArthur switched to biochemistry after he took a riveting course in molecular and cell biology and saw an ad in the McGill student newspaper that referenced the scarcity of jobs in marine biology.

“I still remember it well. It said, ‘George has a master’s degree in marine biology and a job driving a taxi cab. Can you give George a job?’ ’’

4McArthur worked as a senior scientist at Somatix Therapy Corp., served as vice president of preclinical development at Phylogix Inc., and led drug development for Synovex Corp. before cofounding Cydan in 2013. Fighting rare diseases is a family occupation. McArthur’s wife, Cara Hesse, is associate director of global patient advocacy at Sanofi Genzyme, a leading rare disease drug maker. McArthur’s birthday falls on Feb. 28, which is typically Rare Disease Day (although the disease awareness day is scheduled for Feb. 29 this year because of leap year.)

“We never celebrate my birthday because we’re both busy that day.’’

5When they do get time away from the office, McArthur and his wife, sometimes accompanied by their college-aged daughters, sail their boat, named “Hypothesis,’’ around the Boston Harbor Islands. McArthur will also sail alone to regain perspective in trying times.

“There have been times when I needed to just head out to the islands and just sail around for an afternoon. It just clears your head. That’s one of the things about Boston. I love sailing back through the Boston Harbor as the sun’s coming down and seeing the light off the buildings in Boston. That intimacy for me is one of the jewels about living here.’’

Robert Weisman can be reached at robert.weisman@globe.com. Follow him on Twitter @GlobeRobW.