It's from the British Stammering Association, and no, it's not out of date. In addition to neurodevelopmental stuttering, it mentions both neurogenic and psychogenic stuttering. (Did you read it?) It says: "Most stammering develops during childhood and is a neurological, rather than a psychological, condition. Subtle changes within the brain result in a physical difficulty in talking.... A far rarer form of stammering, known as acquired stammering or adult onset stammering usually occurs later in life. The main causes are a head injury, a stroke or a condition such as Parkinson's disease. Other causes can be extreme emotional distress, medication or drugs." The first type of stuttering they're talking about, which is what most of us here are dealing with, is neurodevelopmental. That is, it develops when a child is first learning to speak and is neurological in origin. Sudden onset stuttering due to physical or mental trauma (neurogenic or psychogenic) is much rarer, though learning more about all types of stuttering will of course be helpful in understanding it. I can't read the Japanese paper you linked to, so can't comment on it. The research into ecopipam is really interesting. I found a fascinating article from last year which talks about this and other current research into the causes of stuttering: https://www.bbc.com/future/article/20200922-why-some-people-suffer-from-a-stutter