  In this paper, using a generalization of the notion of Prym variety for
covers of quasi-projective varieties, we prove a structure theorem for the
Mordell-Weil group of the abelian varieties over function fields that are
twists of Abelian varieties by Galois covers of irreducible quasi-projective
varieties. In particular, the resutls we obtain contribute in the construction
of Jacobians (of covers of the projective line) of high rank.
