~20% of autism spectrum is "complex autism", where the autistic traits are secondary to the main disorder, usually a genetic disorder, that has its own specific set of traits, and some of the traits resemble autsitc traits, and there are enough for autism diagnosis in some but not all cases.
e.g. Fragile X, Rett Syndrome, Timothy Syndrome, Prader-Willi Syndrome, etc etc etc.
Studies have shown that in Fragile X, the autistic traits are different from autistic traits in idiopathic autism (likely caused by many common genetic variants coming together in an individual).
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Drain and plane and grain and blain your brain, and then again,
Propane and butane out of the gas main, your blain shall sustain!