The Jennings v Alzheimer’s review – how one letter caused a medical revolution

<span>Utterly gripping … John, Stuart, Carol, and Emily Jennings.</span><span>Photograph: n/a/BBC/Expectation/Stuart Jennings</span>
Utterly gripping … John, Stuart, Carol, and Emily Jennings.Photograph: n/a/BBC/Expectation/Stuart Jennings

Already a vicious foe, familial Alzheimer’s disease likes to deliver one last twist of the knife. Not only do the children of a carrier of the rogue gene have a 50/50 chance of inheriting it, but if they do have it, they will almost certainly develop symptoms at almost the exact age their parent did. What an exquisite extra cruelty.

John Jennings’ mother, Carol, now virtually paralysed and non-speaking, became symptomatic at 50. He is 38. You would be forgiven for assuming that The Jennings v Alzheimer’s would be the story of whether he will decide to get the genetic test that will reveal whether he has the mutation his mother carried, or if he will escape her fate. In fact, although that is one strand of it, the story this documentary tells is much more extraordinary.

In 1986, Prof Sir John Hardy and his team were beginning to investigate the new idea that Alzheimer’s and other types of dementia were not an inevitable part of ageing, but could have a genetic cause. He put out a call, via the Alzheimer’s Society’s newsletter, asking for people to write in if two or more members of their family had the disease. Carol, whose father had been diagnosed in 1982, his sister the year after that and his brother the year after that, did so. She enclosed a meticulously drawn and annotated family tree. “I could see at once this was an important family,” says Hardy.

The Jennings clan, especially Carol, who underwent scans and tests every year, became one of his major research projects. In total 44 members were tested and after five years of analysing the results – what differed where on whose DNA – he was able to identify the mutation in the amyloid precursor protein that creates the plaques that form in the brains of Alzheimer’s patients. This mutation starts the destruction of the brain which causes such devastation (to nearly a million people in the UK alone, to say nothing of the indirect suffering of their families and friends). A world in which treatment could become possible opened up.

Hardy says ruefully now that he thought they would have something viable in five years’ time. Instead, we are 38 years on and there has only recently been a breakthrough. As Dr Catherine Mummery, head of clinical trials at the Dementia Research Centre at University College London, says, all but shaking her head in awe and frustration: “The brain is an unbelievably complex organ.” But thanks to Carol, it has begun to yield its secrets. She was the first to receive a drug, in 2012, targeting amyloid and aiming to slow progress of the disease. But it wasn’t until just two years ago – too late to stop her own decline – that the first true success in doing so could be announced. The drug lecanemab has been approved for use in the US and has been under consideration here by the National Institute for Health and Care Excellence since May 2023.

Interwoven with this gripping scientific story is the emotional story of Carol and her family as they struggle with the decline of their beloved wife and mother and wrestle with the implications of their possible inheritance. John and his sister Emily operate in different ways – she tries not to think about it, John fears the loss of control and the plethora of unknowns. When you lose emotional connections to people, he wonders, are you just left trapped alone in a frightening place? He has taken his mother’s place as a research subject at the Dementia Centre. Neither of them plans too far ahead. Emily is surer than John that she doesn’t want to be tested, but when the news about lecanemab breaks, her brother too feels a pressure lift and becomes clearer in his decision not to be tested.

The Jennings v Alzheimer’s holds all its component parts in balance. It doesn’t let the sadness overwhelm the achievements of Carol and the scientists, but – thanks to judicious use of footage from years gone by of the charismatic Carol advocating with effortless fluency for the Alzheimer’s cause – never loses sight of all that she and her loved ones have lost. It doesn’t dwell on the cruelty of the disease, but doesn’t shy away from its savagery either.

It ends in perhaps the best way it can, with the news that Carol died peacefully, in March, surrounded by her family. Oh – and she has donated her brain for further research into the disease that took her. But of course.

• The Jennings v Alzheimer’s aired on BBC Two and is now on iPlayer.