Recently I've been looking at developmental disability in the 1700-1800s. Google books has some of John Langdon Down's stuff and Edouard Seguin's stuff (both 1800s). That was really a fascinating time - special education was just beginning. John Langdon Down was a man I have a great deal of respect for - antiracist (he used disabled people as proof that nonwhites were human), very antisexist (he said it was 'lunacy' to deny women equal education to men) and an advocate for disabled people (he spoke out against isolation and denial of education to 'idiots').
Two things John Langdon Down is quite well known for - describing what he called Mongolism, now named after him, and coining the term 'idiot savant'. By the way, many people claim 'idiot' was a misnomer because savants don't generally have an IQ below 25, which is what 'idiot' meant. But that classification is from a later period - IQ tests weren't even invented when John Langdon Down coined that term. He used 'idiot' if they were mentally disabled from childhood, and 'imbecile' if their condition was adult-onset.
He divided idiots into congenital, accidental and developmental. The latter two categories are interesting. The accidental category looked normal, except that some had 'paralysis' (I suspect cerebral palsy). He attributed their condition to brain damage in infancy. His description of their behavior sounds a lot like autism - they were 'bright in their expression, often active in their movements, agile to a degree, mobile in their temperament, fearless as to danger, persevering in mischief, petulant to have their own way'. They did not speak, loved music, and were 'in a world of their own'. He described them as self-absorbed and engaging in repetitive movements. He said many people held more hope for them than for congenital idiots, but they were actually less educable.
The developmental category sound like a mix of regressive autism, Heller Syndrome and schizophrenia, these individuals developed normally until either the first dentition (later infancy), the second dentition (mid childhood) or puberty. He felt they were unusually prone to stress reactions at those times, and had a 'prow-shaped' skull. Those with onset at puberty were described as 'suspicious and reserved' and prone to making incorrect statements or phrasing them wrongly.
So anyway, here's some stuff about the history of developmental disabilities.
PS: I have just found the Disability History Museum.