A neurologist at Harvard’s Brigham Hospital, Dr Ropper describes the neurologist’s response to cases – such as transient global amnesia or motor neuron disease – in which lives and minds hang in the balance.

Why does growing old lead to so many forms of illness? Recent advances in the study of human cells have revealed that the key to answering this question lies in the telomeres – the tips of chromosomes – which shorten every time a cell reproduces. As he explains these insights, Fossel highlights the ability of the enzyme telomerase to re-lengthen the telomeres and discusses its potential as a means of treating age-related diseases such as Alzheimer’s.