Friederich's Ataxia affects each person in a different way.
It has affected Krystie's mobility, her speech and her heart and she is now permanently in a wheelchair, but it doesn't stop her from living a full teenage life.
Krystie was first diagnosed at the age of nine when her mother noticed that she was walking strangely and asked her doctor for advice.
Krystie said: "I just thought I was weird, my mum said I used to walk like a crab. I kept banging into lampposts and everything."
"She told me the basics, you know, that it was going to make me shake, which it does, that it was going to make my hands a bit worse and that it was going to make me go in a wheelchair and affect my heart a bit.
"But she didn't go into everything so that I'd think: 'Oh no, oh no'."
Krystie faced the prospect of a major operation. She had been told she must have scoliosis surgery to stop the curvature of her spine.
This would give her the chance of a longer life expectancy and reduce pressure on her lungs and weakened heart.
At her initial consultation for scoliosis surgery Krystie asked if there was a chance that she could be paralysed as a result of the operation.
The specialist was clear with her and her mother that this was the case - and that there was also a chance that Krystie might not survive the operation.
This was due to the length of the cut down her back and the quantity of blood that she might lose.
Also Krystie's heart, which has been affected by her condition, might not cope under the strain.
There was an added danger because Krystie and her mother, Molvia, are Jehovah's Witnesses, which meant Krystie could not have a blood transfusion as it is against their religious belief to receive blood.
There are currently 6.5 million Jehovah's Witnesses around the world today, many of whom will at some point in their lives face the dilemma of whether or not to refuse a blood transfusion during surgery.
It is against the Jehovah's religious beliefs to receive blood, even in potentially life-threatening situations. Krystie now has to choose whether or not to go ahead with the operation.
Surgeons at the first hospital Krystie was referred to felt that couldn't carry out the operation without a blood transfusion so Molvia did some research on the internet.
She found Mr John Webb, a surgeon at Queens Medical Centre, Nottingham who was prepared to operate.
Mr Webb said: "A lot of surgeons are not happy to operate on Jehovah's witnesses because clearly it's more stressful if you ran into complications and the child could die.
"Because you can't give blood there is a possibility that the child could bleed to death on the table.
"You can't rule out complications - but if a child or an adult believes in that faith they have every right to have an operation."
Mr Webb was able to give Krystie clotting factors and lower her blood pressure during the operation which should cut down the amount of blood lost.
He was also able to use a cell saver machine which salvaged any blood lost by Krystie so that it could be returned to her as this process is acceptable to Jehovah's Witnesses.
He made a decision to operate from the front of Krystie's body as opposed to the back as originally suggested which again reduced the amount of blood she might lose.
In order for the operation to take place Mr Jardine, the consultant anaesthetist at Queens Medical Centre had to be convinced that both Krystie and her mother had made their decision freely and competently.
They had to independently sign consent stating that they had individually decided that Krystie should not have a blood transfusion.
Mr Jardine said: "If things did go totally topsy turvey we have to protect us as well as you."
Having made her decision Krystie faced eight hours of surgery.
Throughout the operation surgeons monitored not only blood loss but also Krystie's spinal cord to make sure it was not being damaged.
Her Friederich's Ataxia means that messages from her brain don't always get through to her legs.
Because of this Krystie was woken up mid-operation and asked to wriggle her toes to check that her spinal cord hasn't been damaged.
Krystie survived the operation and the doctors were happy with the outcome but her battle with Friederich's Ataxia will continue.
"She will have more challenges in the future, she definitely will" said Molvia, "but don't worry about them."
"My future's uncertain" said Krystie. "But I won't waste a second of my life, not ever"