Jamie-Lynn Sigler Jamie-Lynn Sigler

Jamie-Lynn Sigler has been battling multiple sclerosis for 15 years.

In a new interview with People, the Sopranos alum reveals that she was diagnosed with the disease when she was 20 years old. "It's still hard to accept," she said.

Sigler, 34, tells People she kept her diagnosis under wraps after The Sopranos went off the air in 2007 in order to keep working. "I can't walk for a long period of time without resting," she says. "I cannot run. No superhero roles for me. Stairs? I can do them but they're not the easiest. When I walk, I have to think about every single step, which is annoying and frustrating."

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The actress recently married pro baseball player Cutter Dykstra, with whom she has a 2-year-old son. She says that she's on a regimen that includes medication as well as injections and infusions, and that her symptoms have been stable for the past six years.

"It takes a fighting attitude to deal with all this. This disease can absolutely take over your life if you let it," she says. "I don't want to hold a secret where it feels like I have something to be ashamed of or have something to hide. It's part of me, but it's not who I am."