It has to
leave the sufferer mentally handicapped to a significant degree – say, toddler to early grade school level of ability at most.
have some sort of immediately visible physical manifestation – the more striking the better, actually.
not require on-going treatment by regular pills or injections.
let the person with the disease/syndrome survive to adulthood.
Any such disease?
Crouzon?
Microcephaly springs to mind. It appears to be able of meeting all your requirements.
What came to my mind immediately was Down Syndrome. It causes intellectual disabilities as well as a characteristic “look”. I don’t see any specific drug therapy that is generally indicated and that meaningfully treats the condition. People with it can be given extra educational interventions and therapy that can help them finish school or get a job, but there isn’t a pill you can take every day that makes you as smart as an average person but when you stop taking it you become retarded again.
Fetal alcohol syndrome could also apply, those most affected have some distinctive facial characteristics.
Michelin tire baby syndrome (though the developmental delay is typically temporary).
Apparently harlequin-type ichthyosis is now treatable. It’s got #2 on the list in spades, not sure about #1.
I’ve never heard of harlequin ichthyosis causing diminished intelligence, even if the group of survivors is small. That does not seem to be a feature of any of the ichthyosis syndromes.
This does not cause mental problems. Typically, it simply killed people in infancy, but that’s not necessarily the case now.
My vote would either be severe Down Syndrome (with the caveat that there are people with Down who are more intelligent than some people without Down) or microcephaly. You might also look at hydrocephalus, with the note that severe hydrocephalus causes epileptic seizures and convulsions.
Moyamoya
Down Syndrome is probably your best bet.
Cri-du-Chat is good, but doesnt have a very distinctive look. Cri du chat syndrome - Wikipedia
Primordial Dwarfism. Primordial dwarfism - Wikipedia
I don’t think primordial dwarfism results in mental deficit, though.
Some subtypes do. See the Wikipedia page I linked to. But it’s not all types.
Wooo… so many awful ways things can go bad for people. Sad.
But useful for my authorial needs.
Thanks, guy!
Prader-willi, though the physical manifestation may “just” be morbid obesity. The one person I knew with it did have an “off” look about his facial features, but not as striking as Downs.
Some of the trisomies (other than Downs which is T21) might qualify though T13 and T18 aren’t really survivable - the vast majority of live-born children die in the first year of life. Trisomy 9 seems to have some facial issues but no more dramatic than Downs (and less recognizable).
Treacher Collins syndrome has dramatic facial issues but doesn’t generally include mental delays (though some people may have delays).