Image source, Jennings family Image caption, John Jennings, with his father Stuart, mother Carol and sister Emily When John Jennings’ mother started showing signs of Alzheimer’s Disease at the age of 50, he and his sister Emily knew they too would also have a 50:50 chance of developing the condition that causes dementia. But a letter their mother wrote almost 40 years ago could hold the key to changing the,
from the BBC