In other words a physical or mental deformity which would improve a person’s experience?
The opposite of a disease I suppose.
I was thinking it would be more the opposite of unease. If that were the case, I would point out that the attraction of illicit drugs is often in part a feeling of hyperease (euphoria).
I can’t think of any physical aberrations that would make life easier for that person. Extra fingers would force them to wear mittens or find a custom glove maker. Extra toes would necessitate wider shoes. Extra limbs would put them on a permanent first-name basis with tailors to make three-armed shirts or three-legged pants. And where would that extra limb be, anyway?
About all I can think of that would make life “easier” would be along the lines of extra strength or flexibility - not that I’m aware of any double-jointed people being able to get any use of that condition other than perhaps as an escape artist or carnival attraction.
There was some mention in another thread about how some people that have had their corneas removed can see ultraviolet light. Possibly useful in highly specific applications, but not so good otherwise. And, that’s an enhancement at the cost of general function and caused by the absence of something.
Increased range of hearing? Might help us understand dogs, but probably not.
But what about mental faults. Could there be an opposite of chronic depression for instance? Or even a ‘fault’ that causes a person to be permanently euphoric, and unable to get accustomed to pleasure as we ‘faultless’ people do (unfortunately)
BTW I don’t mean drug induced improvements, I mean purely birth/genetic defects.
Wouldn’t that be cool? If you caught some mutation of the flu virus that for some reason made you bigger, stronger, and faster? Your imune system would probably still combat the invader though, so you would only have a few days before you got ‘better.’ Ha - what a concept.
Red Dwarf luck and charisma viruses aside, It ought to be possible for a retrovirus to happen to insert a sequence that just happens to be beneficial to the organism, but it’s probably incredibly unlikely, given that:
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In order to succeed as an infectious disease, the virus must reproduce prolifically; the best strategy for this appears to be prolific self-replication at the expense of the host cell.
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Retroviruses aren’t necessarily choosy about the insertion site; the sequence might only be beneficial if it happens to be inserted in a key location in the host genome.
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Even so, the actual host can’t really benefit from a single beneficial insertion event in a single one of its body cells; if that cell happens to be a germ cell, and that cell happens to be the lucky one involved in a subsequent reproductive success (astronomically unlikely, but it happens, and is used to determine phylogenies, but not beneficial insertions AFAIK), then the insertion could benefit the offspring.
Like I said, it could happen, but it just seems incredibly unlikely to actually occur, compounded by being incredibly unlikely to be beneficial in the first place.
There are other diseases, the symptoms of which might be considered beneficial, depending on context; if a disease causes hypersensitivity to light, for example, it might be beneficial to a coal miner (stupid example, but you get the idea perhaps)
Well, there’s the super baby who has a mutation that makes him especially muscular. To date, it seems to be benign, although they worry that there might be effects later in life.
Some people suffering from bipolar disorder resist treatment because the benefits of the manic phase at least in part outweigh the disadvantages. Although the manic phase can lead to very self-destructive behavior, it’s also characterized by very high levels of creativity, energy and hypersexuality.
The sickle cell trait is one example of a disease that represents a favorable mutation in the right environment. Someone with the sickle cell trait is resistant to malaria. Unfortunately, if two people with the trait pass on the defective gene to their children, they may end up with the sometimes fatal sickle cell anemia.
Apparently, tapeworms may help fight inflammatory bowel disease. (http://www.immuno2004.org/onlineabstracts/allposters/3271.html)
And we all possess a bunch of intestinal flora that is symbiotic but which might be considered a helpful disease in that it keeps less friendly organisms from acquiring a foothold (if they had feet).
If you’re including congenital diseases, some women can be born with an additional color receptor in their eyes, giving them tetrachromaticity. Almost all of them have fathers who are red-green colorblind.
Prima Facie, you have that conditon that allows you not to feel pain. I hear it’s not that great at all, because you could bleed to death (or similar) with out knowing.
I assume under Extreme montoring of the conditon, you could in very short bouts do things that would be extremely helpful, tha most people can not do. Its Still a trade off, but Im sure a situation can arise therin.
http://cnews.canoe.ca/CNEWS/WeirdNews/2004/11/01/pf-696144.html
I’m sure this is a real problem. But when someone needs it to be there… I bet they don’t give it a second thought. Im sure However, the number of times when they wish they didnt have it HIGHLY outweighs this.
Well, if hypertension is high blood pressure, then its opposite (hypotension) might be seen as the kind of thing you’re looking for. And it does seem to be a genetic condition - not a “disease” or a “deformity” - but maybe close enough?
The results would be a reduced risk of stroke, among other things - certainly something I would define as “beneficial”. 
I have heard that there is a mental illness that is the exact opposite of paranoia. Sufferers have the irrational belief that people like them and are trying to do them good. It is, of course, almost never diagnosed because the people who have it never do crazy things.
Ignorance is bliss.
What about the more common ‘mutations’ around us every day?
The person genetically built to be taller, or stronger, or faster than average.
The person with particularly good reflexes, or who excells at mathematics or language skills, or can throw a football further than anybody else?
There has to be a genetic component to these type of abilities; therefore they’re a sort of mutation. Sortakinda the thing you’re looking for?