I guess there may be but presumably there will be concerns about the reliability of current diagnoses too – or rather, the reliability of the answers to questions which are used to determine whether or not someone fulfils the diagnostic criteria.
I assume that answering questions about historic symptoms is likely to be a bit less reliable than answering questions about current symptoms but I don’t know how much that would matter. My limited understanding is that for a GWAS it doesn’t particularly matter how many unreliable diagnoses there are, provided there are sufficient numbers of reliable diagnoses (however a reliable diagnosis is defined).
Also, let’s assume that a separate, additional cohort of recovered patients is recruited – people who have previously been diagnosed with ME/CFS, whose answers to questions about their symptoms prior to recovery meet the study’s criteria for a diagnosis of ME/CFS. Now let’s assume that the GWAS identifies a number of SNPs that are significantly more common in people who currently meet the ME/CFS diagnostic criteria than in the healthy controls. Whether or not those SNPs are equally common in the recovered cohort would tell us something useful about people who report that they have recovered from ME/CFS, regardless of how reliable their answers are. And that is something I would be very interested to know.
Having said that, looking at the number of likes that my comment has received compared to strategist’s reply I’m wondering if I’m misunderstanding something.