Frozen

"Fibrodysplasia ossificans progressiva (FOP) is a rare muskuloskeletal condition where, after birth and progressively through life, muscles and tendons are gradually transformed into bone (a process called ossification). This creates a second “skeleton” of extra bone, which makes movement impossible."

– yParticle

"Idk if it's real, but I heard people with FOP have to chose, at some point, the position they want to spend the rest of their life in, standing sitting or laying down."

– aoi4eg

"I saw a show about this when I was a kid and the whole idea still f**ks with me."

– Jaway66

You Thinking What I'm Thinking?

"There are conjoined twins (the Hogan sisters) who are attached at the head and their brains are attached. Each one can see through her sister's eyes. Each one can taste the food the other one is eating."

– Fun_in_Space

Fragility

"I met a guy who practically had eggshells for bones. He broke them about 50 times or so doing simple things like just sitting on a couch or brushing his teeth."

– Odd-Package-4713

"That'd be osteogenesis imperfecta type 3."

– crimpytoses

"My nephew has osteogenesis imperfecta and is almost 8yrs old. CPS got involved when he was a baby and hadn’t been diagnosed yet, thinking there was abuse, which was so sad for my family. They later found out what it was and have made medical accommodations. Man, he’s such a sweet, happy boy despite his condition. He hasn’t known anything other than this his entire life, so for him pain is normal (which makes me so sad), but he is bright, engaging, and so very amazing in every way that I get pissed the f**k off that he’s dealing with this."

– Purse_Whiskey

Life Span

"That disease that ages people at an insane rate that often kills it’s sufferers before they turn 16. I think it’s called progeria."

– MascotGuy2077

"That is a wild one, also the girl that looks 8 but is in her 20's, it's crazy as f**k."

– IThinkMyLegsAreBroke

"At my old place, two of the kids in the community had progeria. I'd only ever see them once a week at most, but they always seemed happy when I came across them; their family made a real effort to make their time count. I've always wondered how they grapple with the reality of their situation at their young age, though. How do you even bring that kind of subject up as a parent?"

– miniman03

Invasion Of The Body Snatchers

"The Capgras delusion: the person becomes inalterably convinced that someone close to them has been replaced by an imposter who has disguised him/herself so cleverly that they look identical to the replaced person."

""Yes, this woman looks and acts just like my wife and knows everything my wife would know. ...But she is an imposter disguised to fool me and I will have nothing to do with her.""

"It's funny to think about in some ways but would be absolutely terrifying to have."

– dr3rdeye

Facial Blindness

"This reminds me of a condition where people lose the ability to see faces. Their eyes work, they can see anything, but if it is or resembles a human face it gets turned in an undeterminable blur."

– random_sh*tter

"Faceblind. I have this. Brad Pitt has this. The worst part is when I wake up in the morning, look in the mirror, think "oh that's what I look like," then promptly forget my face 5 seconds later. I cannot point myself out in family photos."

– GodsCasino

"Prosopagnosia. It comes in varying degrees of severity. I have it. I have a lot of trouble recognizing people in unfamiliar contexts, like seeing your teacher at the grocery store. I have to see somebody a lot of times before I can recognize their face, unless they have some distinguishing feature (like my friend with a long beard). My friends tend to be people who look or dress distinctively, because it’s so much easier for me to recognize them."

– linuxgeekmama

Cut It Off!

"Body integrity disphoria: people who desperately want to cut off a part of their body, a limb for instance. They have always been thought of as insane until someone decided to have a look at their brains and realised that the limb in question isn't registering in their brain. To them, it feels like an alien appendage was sewn to their body. I find that so fascinating."

– Deleted User

Is It Still There?

"Or the other way around, phantom limb syndrome. When one loses their limb but still feels itchiness or pain on that non-existent limb. They use mirror therapy which is quite interesting as well."

– trickydaze

Strange Immunity

"Knew a woman who couldn’t conceive with her husband."

"He could theoretically get another woman pregnant, and she could theoretically get pregnant from another man, they just couldn’t conceive together."

"He donated blood (maybe marrow) to her while she was being treated for cancer. This somehow made her body immune to his sperm."

"They wound up adopting a couple of kids."

– ShaolinDave79

Anti-Hydration

"Allergy to water. It's extremely rare, last I researched it I believe there were less than 10 documented cases. And yes, they are allergic to themselves. They can't drink straight water, typical hygiene is a huge no go, and even humidity can trigger bad reactions."

– KaliCalamity

"How do these poor people live…"

– Crackheadwithabrain

"Not well, and on a lot of antihistamines"

– KaliCalamity

"I knew one of those kids who has the disorder. His twin brother was diabetic, and I didn't believe him, but his parents confirmed it. His skin was constantly cracked and sloughing off. Poor kid. I felt so bad for him."

– arcticnerd

"How do they stay.... Hydrated? Do they have to drink insanely alkaline water? What about their blood? Like wtaf???"

– Grouchy-Place7327

"They can have small amounts of water, but at least in the documentary I saw, the couple of people it focused on usually stuck to things like juices and milk, as they're less reactive. The major danger is skin contact."

– KaliCalamity

Seeing Things

"My nephew had PFAPA (periodic fever, aphthous stomatitis, pharyngitis, adenitis). Basically he would get a very high fever every 3-4 weeks with no other symptoms other than the fever alone. One night when he was maybe 5 years old, he was going through an episode and called his mom (my sister) into his room. He told her that he was really scared because his bedroom was covered in bees. I guess the hallucinations aren’t always fun."

"He had his tonsils and adenoids removed and that was the cure!"

– emjayholla

A Whole Different Perspective

"Synesthesia. A condition where your brain mixes up sensory signals."

"With this condition, one might be able to taste words, or certain numbers will always appear a specific color, or you might literally see music or smell something and feel as though you're being touched."

– ChaoTiKPranXter

"I can hear color. Sounds have different colors to me. This is especially true of people’s voices. Barbra Streisand, for example, has a light amber voice."

– IoSonCalaf

"I have that! For a while I thought everyone did."

– RenegadeRabbit

It's surprising how many of these I've actually heard of (thanks to Grey's Anatomy) but that last one is completely new!