LOS ANGELES, California (CNN) -- Elizabeth and Mary Profit will not be taking center court at the U.S. Open women's doubles final to face Venus and Serena Williams, but they share many of the athletic qualities that have made Venus and Serena the most dominant sisters in tennis history.



Elizabeth Profit plays tennis while wearing an insulin monitor at her waist in this family photo.



Elizabeth is 13 years old and holds a top ten ranking among 14-year-olds in Southern California. She is already defeating top-ranked players in the 18-year-old division. Her sister Mary, at 11, is also a top-ranked player and dominating her age group. Mary won her first tournament at the age of 6.



Both girls started playing tennis as infants by hitting balls of socks across their living room. Their mother, Yvonne Profit, recognized their talent and saw it as an opportunity to develop sportsmanship and character and help them earn athletic scholarships at top national universities. So far, they have exceeded her expectations.



In a sport that more often tends to develop players from affluent backgrounds, Elizabeth and Mary have already beaten overwhelming odds and endured the kind of adversity that too often ends in defeat.  Watch how the sisters hope to achieve their tennis dreams »



The Profit sisters grew up in a single-parent household and trained with less than stellar coaches. They developed an exemplary work ethic to compensate for a lack of resources, Elizabeth said. Yvonne, who earned a degree at the University of Michigan, decided to give up her full-time job and move her daughters into an RV to keep up with the rigorous demands of traveling for tournaments.



Elizabeth sleeps on a couch. There is a portable stove and shower. But the girls view living in an RV as an inconvenience rather than a hardship.



The Profit sisters may be on a path toward a professional tennis career, but Elizabeth's story off the court is just as compelling. She has juvenile diabetes and has been living with the disease since the age of 2, when her body stopped producing insulin. Elizabeth learned how to test her blood sugar levels before the age of 3 and two years later, she began administering insulin injections on her own.



"My mom said I'm not going use my diabetes as a disability," said Elizabeth. "I've got it for the rest of my life. And if they miraculously find a cure for it then that's great, but I have to live with it. I can't make excuses."



Until she learned how to manage diabetes, Elizabeth found herself collapsing at times. "In this one particular tournament Elizabeth played in, her blood sugar was totally out of control and I kept hollering out to her, 'Quit! Retire, you don't have to do this,' " said Yvonne. "She stopped and she turned around and said, 'I can do this. I can do this, Mom.' " Elizabeth went on to win the match and the tournament. "By the time we got home, she had collapsed on the floor. And I said, 'Sweetie pie, why didn't you quit?' " Yvonne remembered. "Because you didn't raise me to be a quitter," Elizabeth told her mother. In spite of her diabetes, Elizabeth reached the No. 1 ranking in her age group in Southern California at 10 years old.



Her sister Mary knows that diabetes can be debilitating and a matter of life and death, so she constantly watches over her older sister. "Sometimes when I wake up to go to the bathroom, I check her blood sugar, when my mom's sleeping," said Mary. "Sometimes I wake up and give her something if her blood sugar is low."



For the past ten years, Yvonne said, she has been unable to obtain private health insurance on the open market for her daughter because diabetes is considered a pre-existing medical condition. Elizabeth used to rely on a large insulin pump to make it through the day, but now she wears a small patch that releases
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