When the Hempels aren't researching to help their daughters, they are just trying to keep a sense of normality and to savor each precious day. But the signs of the girls' disease still show up in the most mundane of acts.
"They're there," Chris said. "It's just that it's harder for them and they spend a lot of time just trying to stay upright or anything involving motor skills. It's taxing for them. It makes them tired."
Right now, Addison and Cassidy's only hope rests on an experimental drug that has appeared to slow the disease.
The Hempels continue to fight, search and hope some breakthrough will occur.
"I just look at Addi and Cassi and it keeps me going," Chris said. "I get through each day talking to parents who want to save their kids. I get through each day by working toward a solution."
Click here to learn more about Addison and Cassidy.
Click here to visit the National Niemann-Pick Disease Foundation.
Click here to visit the National Institute of Neurological Disorders and Stroke.