The group of diseases known as Batten's disease are degenerative and genetic diseases that occur in both children and adults. The first sign that something is wrong is that a person has seizures and becomes unsteady on their feet. The illness leads to a progressive deterioration of the brain and nervous system and eventually death.
There is a one in a million chance of carrying the defective gene, but if both parents are carriers, then the disease is likely to be passed on to their children.
Jenni talks to Dr Ruth Williams from Great Ormond Street Hospital who works with families like the Shones, and also to Dr Chris Markland from the Batten's Disease support group. And Jill Hopkins talks to the Shone family both of whose daughters have the disease.