I believe, though without concrete data, that my own intelligence is inversely related to the number of symptoms associated with my ME.
Having two psychology degrees, a further clinical qualification and some twenty years experience working with people with neurological conditions I could argue I have some standing in making a profession judgement on this issue.
At the onset of my ME I carried a regional clinical specialism and successfully managed a team of six clinicians. My department also had a research output that a comparably sized University department would not have been ashamed of. Simultaneously I was training to be yoga teacher. Over the nearly thirty years of my ME, I went from having mild CFS/ME to being largely bed-bound. As my condition has deteriorated I have acquired additional symptoms, including food intolerances, IBS, orthostatic intolerance, chostochondritis and more. At the same time I have gone from being able to sustain an intellectually demanding job, including participation in regional and national policy forums, regularly reading five or six books a week, both fact and fiction, managing staff undertaking research projects and undertaking higher degrees, to being unable to work, to having not been able to read an entire book in five years and requiring assistance to set up an on line grocery account and manage my daily life.
So I accept it is a definite possibility that ‘intelligence is negatively associated with the number of [so called] functional somatic symptoms’. My personal experience would support that. However this association in my case would much more rationally be explained by having an ongoing condition involving neurological factors that caused both the ‘somatic’ symptoms and the intellectual deterioration. Such an association between intelligence and the number of symptoms could be seen as strong evidence against the condition being functional, somatic or psychosomatic, rather support for the conclusion that Prof Rosmalen and the cited study profoundly misunderstanding their clinical grouping.