Hi Romano,
I'm really sorry to hear about the deformity of your nephew
What about his other hand? I hope it is all right.
I doubt that Thal. Minor can cause such deformity. However, I have heard that ladies with uncontrolled diabetes and high blood glucose levels are at a risk of having disable children.
What is the diabetes situation with your sister? Does her glucose levels stay within normal range or not?
It is very important for her to keep herself in check and avoid the diet that is harmful for her no matter how strong the temptation may be.
I wish all the best for the little fellow.
Take care, Peace!