Minyan and Down Syndrome
Do autistic men or men with down syndrome count for a minyan with regard to Tefilla or Zimun. Regarding Zimun is there any distinction between 3 or 10?
There is a wide range within these conditions, from very severe dysfunction to very highly functioning relative to the illness. If he displays basic understanding and communicates with others, and he participates in the davening on a basic level, there would be room to include him in a minyan or zimun when necessary [i.e. if you can easily complete the minyan without him that would be preferable].
See Shu”t Minchas Asher Vol. 2 Siman 48