The way I learned it, cretinism was related to iodine deficiency, and a collection of symptoms found in people who developed as foetuses where the element was in short supply, where adults might be found with goitre. It included a failure of brain development. Rather different from simply age relating the development, but it doesn't excuse the term being used as an insult.

A friend of mine asked me about the insult "paki unit", not recognising the second part. I knew. We have a special needs language unit attached to our school, and the children there are referred to as units, with the same derogatory meaning as cretin etc. We try to stop it...

Penny