But Olympic gold medal-winning gymnast Dominique Moceanu and her sister Jennifer Bricker, whose existence was a secret for most of her life, have yet another connection that could potentially take sibling bonding to new heights.
Even though they grew up hundreds of miles away from each other, Moceanu, who was the youngest of the gold-winning "Magnificient 7" at the 1996 Olympics, and Bricker, who was born without legs, both share a passion for gymnastics.
"I don't think it's a coincidence," Bricker told 20/20 Friday in an interview revealing Moceanu's family secret. "It's nature versus nurture."
As a kid, Bricker competed in sports like volleyball, softball and power tumbling, a passion that brought her to the junior Olympics.
"I was like, 'Who is this girl?' " Moceanu, 30, said of her reaction to Bricker's perseverance over her condition. "She [has] Moceanu DNA for sure. It's mind-blowing."
The BombshellMoceanu was 26, and about to be a mother for the first time, when she received a letter.
"You have been my idol my whole life, and you turned out to be my sister," a 20-year-old Bricker wrote. "I realize this must be a lot for you to take in right now."
Though receiving the letter was a defining moment in Moceanu's life, she said she had previously had a sense that something was off.
"There was a sense of primal loss," Moceanu said on Good Morning America Monday. "A few months before Jennifer entered my life, I had this sense that there was something out there, a piece of the puzzle missing."
She noted: "My life will forever be divided to before knowing about Jen and after knowing about Jen."
The discovery was the result of a clerical error that allowed Bricker's adopted parents to view her birth name (although they didn't share the information with their daughter right away).
"It was the biggest bombshell of my life," Moceanu said. "Had my life been a lie?"
But the next bombshell came when they finally got in touch. "She tells me, 'Oh, by the way, I have no legs.' "
'A Strong Woman'Today, Bricker is an acrobat and aerialist, who's embracing the family she almost never knew.
"Who does this happen to?" she jokes. "Whose childhood idol turns into their biological sister?"
She's also reconnected with her other sister, Christina, as well as her biological mother, Camelia Staicu.
"I asked her, 'Did you ever think about me? Did you wonder what became of me?' " Bricker recalled. "It's a tough question, but I felt like I kind of deserved it."
As for Moceanu, (whose own upbringing was complicated by a troubled relationship with her late father), she's raising children of her own – Carmen, 4, and Vincent, 3 – in Cleveland with husband Michael Canales.
"All those things have been able to bring me where I am today," she said. "I feel I'm a strong woman. I can handle anything now."