Mordell-Weil groups of isotrivial abelian..varieties over function fields.

I'll discuss description of the Mordell Weil rank of an isotrivial abelian variety over field of complex rational functions in two variables in terms of the fundamental group of the complement to the discriminant provided that the discriminant has singularities of CM type. As a corollary I'll describe a family of simple Jacobians for which the Mordell Weil rank can be arbitrary large.