Why are syndromes names after people non-apostrophed (Marfan, Klinefelter, Turner, Down) as opposed to diseases (Alzheimer’s, Huntington’s, Parkinson’s, Hansen’s)? Any reason other than, well, “that’s just how we do it?”
My guess: “syndrome” starts with an S, so over time, “[Name]’s Syndrome” would just end up elided to “[Name] Syndrome” anyway.
Down’s syndrome was used more in the UK and Down syndrome in the US. Apparently this is now outdated.
I think there is an overall trend to remove apostrophes. Many stores have dropped them. Macy’s logo now has an asterisk in place of a apostrophe. Wegman’s supermarkets dropped the apostrophe entirely. People either weren’t using them or misusing them or thinking they were plurals.
Schnuck Markets started branding its stores as Schnucks (no apostrophe) beginning in the late 1950s or early 1960s - probably about the time they moved out of storefronts and started building standalone supermarkets.
I found a paper investigating the question:
According to this, starting in 1974 the NIH started advocating to abandon the possessive form for all diseases and syndromes, and some journals adopted it as an editorial guideline at various times.
The authors don’t really have an explanation for why the change stuck for some of the diseases/syndromes listed but not others, except suggesting the size of the community researching each has an influence.
I wonder if the fact syndromes affect children, while the diseases usually develop in adulthood or old age makes the difference? People may be more sensitive about the language used to describe children, wanting to protect them from stigma (though honestly, I don’t see how the change makes any difference to anything).
And the ban on apostrophes in U.S. place names has been on the books for more than a century:
I think its another symptom of the dumbing down of modern society. People don’t know when to use an apostrophe for ‘its’ vs. ‘it’s’. Its pretty simple- if its a contraction of ‘it is’ then its appropriate to add an apostrophe. If its a possessive pronoun, it should not have an apostrophe before it’s ‘s’.
But people get confused by the ‘apostrophe s’ at the end of a proper noun possessive, so I bet in the next 20 years or so this will reverse and make the preceding paragraph grammatically correct.
Intentional? 
The hidden hand of Gaudere…
Gauderes Hand
Reread the first paragraph-- all ‘its’ and ‘it’s’ are reversed.
Its not a case of Gauderes Syndrome.
I put it down to idiots who can’t use SQL databases
Single apostrophes are used in most SQL variants as text limiters, hence the reasonably famous “little Bobby Tables” XKCD cartoon.
And this “speeding fine avoidance” strategy
* apostophe in “can’t” intended. Plus bonus irritation to Discourse for having to escape an asterisk with a backslash
Oh no, now whenever my post is quoted, it looks like my lame attempt at irony is just me pulling a ‘Gaudere’ 
Yes intentional. My bad at missing the punchline!
I had assumed autocorrect ironically placed it. Which is where some of these errors happen too.
Well, my sense of humor can be subtle. Some even describe it as ‘nonexistent’.
I have noticed that autocorrect has tried to ‘correct’ my possessive ‘its’ to ‘it’s’, or the reverse. What’s up with that? It’s difficult to stay grammatically correct when the world is trying to ‘correct’ your already correct grammar.
Here in the UK the Sainsbury’s supermarket keeps the apostrophe for signage and print adverts but since an apostrophe isn’t allowed in a domain name the site is sainsburys.co.uk.
I still shop at Schnuck’s… even since I moved to SPI
People I know in professions that deal with Down syndrome began using Down’s syndrome in place of “Mongolism,” for obvious reasons in the 1970s. The “Down” was after its first describer, physician John Langdon Down.
This proved a little embarrassing when it got around that it was Dr. Down himself who had originated the term “Mongolism.”
So the apostrophe-s was removed in that one case because it was somehow supposed to signify that this is merely a denominator, and not in any way meant to honor the man.
In the 1990s, someone suggested calling it “Trisomy 21,” in-line with other trisomies that were so-called, and had never been named for anyone.
FWIW, Trisomy 21 was identified as such a long time ago-- back in the late 50s, IIRC.