Help needed!!

I really could do with some ideas. My 4 year old (2 days ago) has a rare chromosome condition. He has developmental delay, is non mobile and non verbal. He attends a mainstream pre school with the support of a one to one. For the past couple of months he has taken to hitting and pinching his support worker over and over. As soon as he sees her or hears her name he hits out a the air or at her. It’s not that he doesn’t like her as he often gives her hugs, but he doesn’t do it for any other staff. He gets warnings and put in time out and all the sanctions that the other children get but none of them seem to make a difference. He seems sad when’s he is told off for it but will go right back to hitting again as soon as he is out of time out. We have tried using positive reinforcement,ent and encouraging kid hands instead of saying no hitting but he just will not stop. He has started dong the same thing to our dog and often to his dad. My worry is that if we cannot get this behaviour under control now then it may move onto hurting other children. Any help or advice very much welcomed!!!
thank you