Unusual features in a "runt" foster kitten

In my most recent foster little there is a super tiny girl, literally half the other’s size. When I got them at three weeks old, she weighed just under 7 oz. Over the last few weeks, she’s gained a bit, now she’s one lb! The more I look at her, I think she might have something congenital going on. She’s very small, in height, length, little short legs. Her facial features are slightly less prominent than others. A little smooshed, but not like a Persian. Large eyes in proportion to her head. I’m 95 percent sure she’s deaf. I’m bringing these thoughts up with the staff vet when they go in for check ups, but just wonder if anyone has seen anything similar.
Thanks!