She tells 17 Magazine that she's been fighting a debilitating disease, and now, a precious gift from her father has saved her life.
Haley Dunphy is Modern Family's older sister. A typical boy crazy teen, always on her phone and always embarassed by her parents.
The character is vibrant and healthy but you'd never know the real life actress is not.
Now 21 years old, Hyland has been battling kidney disease since she was a little girl.
It left her in pain and exhausted.
"I try and make it so that Haley's always sitting down. If you notice, she's sitting down a lot, texting," says Hyland.
When she was 9, Sarah learned she had Kidney Dysplasia, a condition that causes abnormal kidney development.
"I would be in a lot of pain...If I didn't get 12 hours of sleep, I felt like I got none at all," she adds.
As her career skyrocketed, her health deteriorated but without a donor, she faced a lifetime on dialysis.
The search for a donor began and the perfect match turned out to be her father, actor Edward James Hyland.
And one month ago, Sarah got that transplant.
With filming on break, Sarah will spend the summer recovering and she has some advice for others struggling with the same disease.
The condition she has happens while a baby is still developing in the womb.
But in general for adults, two big reasons for kidney failure are high blood pressure and uncontrolled diabetes.
Both are things you can't always feel but the blood pressure and the high sugar levels actually damage blood vessels, damage the kidney that's why we care about those things.
You can pick up kidney disease early by urine and blood tests.
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