Complex sentence: In December 2007, Pratchett publicly announced that he was suffering from early-onset Alzheimer's disease and, subsequently, made a substantial public donation to the Alzheimer's Research Trust, and filmed a programme chronicling his experiences with the disease for the BBC.
Split into simpler sentences: In December 2007, Pratchett publicly announced that he was suffering from early-onset Alzheimer's disease. Subsequently he made a substantial public donation to the Alzheimer's Research Trust, and filmed a programme chronicling his experiences with the disease for the BBC.