Characterization of simple symplectic groups of degree 4 over locally finite fields in the class of periodic groups

Let $G$ be a periodic group containing an element of order 2 such that each of its finite subgroups of even order lies in a finite subgroup isomorphic to a simple symplectic group of degree 4. It is shown that $G$ is isomorphic to a simple symplectic group $S_4(Q)$ of degree 4 over some locally finite field $Q$.