Thanks for writing in.
A high ESR
in itself will have no effect. Rather, it is a manifestation of several disorders which have one thing in common and that is inflammation. A common cause is anemia
and birth asphyxia
( which would have been due to the umblical cord around the neck). I would suggest that you get your sister's child evaluated by a neonatologist in order to rule out a clinical condition. You dont need to worry as of now.
Hope this helps.