From a storytelling perspective, it depends entirely on the type of story you want to tell. Different sources have different details and thus lead to different stories. But if the characters don't know and can't discover why something is happening, the cause is largely irrelevant and the story just covers how they deal with that. There does need to be a place for inexplicable mysteries, especially in speculative fiction.
The problem with this is that most writers treat most disabilities in this manner. They describe a character as blind, or using a wheelchair, or whatever without stopping to think about why that is the case. Real disabilities have real details. A character who is blind from cataracts or scarring may have cloudy eyes, but most forms of blindness don't cause that feature -- which is overwhelmingly the one shown in entertainment. A character who uses a wheelchair because she has no legs, one who has muscular dystrophy, one fully paralyzed below the waist, and one with battle damage making it painful to walk will each have different challenges. Authors routinely gloss over the details, look only at the end effect, and therefore botch the presentation. It becomes a form of erasure -- and a speculative version can make that effect even worse. Now if we had lots of good stories about people with specific disabilities, this wouldn't be a problem; but we don't, so it is.
Even a speculative malady often benefits from specificity, because that can tell you what happens as the story goes along. I did one about a veteran with really bad PTSD, "Pebbles from the River Lethe." He got a job as a guinea pig testing potential raw materials on an alien planet. One of the test items damped down his flashbacks. He took desperate measures to get more of the stuff. But eventually, it started blunting more and more of his memories, because it was affecting whatever was active at the time he took it -- and that wasn't always the flashbacks anymore. I needed to know why he lost memories, and how the substance worked on the human brain, in order to feel out where that story was going to go. A mysterious memory loss wouldn't have worked at all in that context. Anyhow, that's why Lethe became one of the most-abused drugs in that setting: it actually delivers what all the others only promise, relief from agonizing thoughts. In clinical use, it can be safe and effective. But on the streets (and it always winds up on the streets because not everyone can or wants to use official channels) you can very easily blow your brains out with that stuff. So it's also a story about the nature of pain and addiction themselves. The concrete details form a solid foundation to support the more abstract ideas.