In a chain of 156 amino acids, it only takes one to set in motion a painful blood disorder called sickle cell anemia, a condition 12-year-old Suzanne Davis has lived with since she was a toddler.
"What's happening in my body is my cells are deformed and they don't go through my veins right and it hurts really, really bad," she said.
The disease causes red blood cells to take on the shape of a sickle, causing them to get stuck in the vessels.
That, in turn, cuts off blood flow to other areas of the body.
"Most often it's the bones, the intestines, the lungs or the brain," said Dr. John Fort with Miami Children's Hospital. "You can have children having strokes because they lose blood supply to the brain."
Children with sickle cell may become sick enough to require monthly blood transfusions, and that becomes risky.
"Even though the blood supply is fairly safe, there's still the risk of HIV or hepatitis C. In addition, transfusions can lead to iron overload, which damages other organs of the body," said Fort.
In severe cases, children can undergo a bone marrow transplant to clear their system of the malformed red blood cells.
"This requires giving the patient high doses of chemotherapy to destroy white blood cells, red blood cells and platelets," said Fort.
Suzanne underwent the procedure in late 2011 with the help of her older brother, who was a perfect match.
"Transplantation is in itself very risky, especially for the first 60 to 90 days after the procedure, because the body's immune system has been completely wiped out," said Fort. "A simple infection that would give your or I a runny nose could be life-threatening or even fatal to somebody immediately post-transplant."
Suzanne came through with flying colors and is now cured of the disease.
"I feel really good, outside, playing with friends again and doing normal stuff like a normal kid would," she said.
One in 70 people are carriers for sickle cell, and while the disease primarily affects people of African descent, it's also showing up in Mediterranean and Hispanic populations.