I think the point being made was diseases can be difficult to diagnose. Some diseases don’t have explicit tests.
ADHD is diagnosed by looking at just symptoms if I remember correctly. I’m not sure about autism.
I knew someone who became sick. At first it was thought to be Lyme, it took a long while to determine and a bunch of other theories to determine it was lupus. Tests were not fully accurate and these illnesses manifest a little differently in different people.
Autism diagnosis requires (or at least should, for it to be done properly) a multidisciplinary evaluation.
In the case of my children, there were certain tests that were absolutely definitive, and not reliant on interpretation - namely, idioms and metaphors. It's raining cats and dogs, for example.
Right, but that specific sign still doesn't give definitive info about all the other aspects of autism. Ignoring the name you give "literal-lnaguahe syndrome" , it is unknown if the menu of signs and symptoms is diagnostically clustered in imto one label in an effective way.
I am not objecting to the general point that diseases are hard to diagnose. The wording OP used does not just say that - phrases like "so-called" come with an implication that the thing being referred to is just made up. That's why my comment asks if they would say the same thing about ADHD and Autism. They probably wouldn't, because it would carry an implication that they thought ADHD and Autism were somehow "fake".
ADHD and Autism are interesting, because they are entirely based on certain clinical presentations and the opinion of the diagnosing practitioner. There are a certain set of traits that are "classically" ADHD for example, so what happens if you show 80% of those traits and show the counter-case for 20% of the traits? I expect that neurodivergence is going to become far more nuanced in its assessment, with a better understanding of an individual's whole psychological profile.
In the Cincinnati area they throw up their hands if you are over the age of 12 and suspect ADHD. There is little to no help if you are an adult or close to it.
You can literally see ADHD in a brain scan, especially if you contrast it with after someone has taken the proper medication for it. This isn't some sort of witchcraft, it's a physical thing that's measurable.
That's not how you get diagnosed however, nor do I know if you would receive a diagnosis of adhd when a brain scan shows behavior similar to that of ADHD but you show no symptoms and aren't seeking a diagnosis. If you go in for an ADHD evaluation you typically get a psychological assessment, potentially do some tests which aren't always conclusive and your symptoms will be evaluated. In that sense, it's not really measurable in the same way that we can test for a specific disease, infection or virus.
It's not a strict relationship as far as I understand though. As in, frontal lobe issues are visible on many brain scans, but those brain scans are not specific enough to map onto ADHD diagnosis. So we don't have a good diagnostic test right now even though we have many population-level confirmed differences that we can run tests and statistics on.
In some cases we don't really know if your kid has autism. Under the DSM-5 criteria there are three levels of autism spectrum disorder: 1, 2, 3. Down at the less severe end of the spectrum, clinicians often assign different diagnoses. One psychiatrist might diagnose a patient with ASD Level 1, and then the next day a different psychiatrist might say that the same patient doesn't have ASD at all and actually suffers from ADHD or something else. It's highly subjective and reproducibility is low.
I mention elsewhere that I am not objecting to the general point that diseases are hard to diagnose. The wording OP used does not just say that - phrases like "so-called" come with an implication that the thing being referred to is just made up. That's why my comment asks if they would say the same thing about ADHD and Autism. They probably wouldn't, because it would carry an implication that they thought ADHD and Autism were somehow "fake".