I clicked the link to the original paper in Nature, got to (try to read!) the abstract. If I've understood correctly, there's a problem with how cell damage is repaired (the genetic coding to make the proteins to handle this is affected), and the result is both organic damage and emotional conditions we recognise as anxiety, depression, OCD etc. as the body tries to re-establish a more balanced metabolism...
Which certainly describes D, over-stressed and trying/not-trying to manage T2 diabetes and bulimia. Knowing there's the genetic component doesn't absolve him of the apparent lack of commitment but it does forgive the lack of success (And it stops me from saying 'please, just try harder! I don't want to be an early widow!')
Wow, this is exciting news for families with eating disorders in their medical history. For such a long time we've thought there's been little help, little hope around to overcome such huge battles - now it seems we finally have clearer understanding of what's at the bottom of the problems. Genetic dysfunction.
https://www.abc.net.au/news/2019-07-16/anorexia-linked-to-metabolism-genetics-qld-researchers-find/11310320
This article explains that while the links weren't completely unexpected, now we have the evidence. This makes it easier to remove blame and shame, and to devise medications where appropriate
https://www.theguardian.com/science/2019/jul/15/anorexia-not-just-a-psychiatric-problem-scientists-find
This article explains there are also thought to be some shared links with schizophrenia
https://www.bbc.com/news/health-48989359
(As the original paper says, life experiences will determine how the genes and conditions are seen in anyone's life. )