In this total SID group slight infections prior to death was associated with deletion of either the C4A or the C4B gene (P = 0.033), and the SID victims with such infections had a higher deletion frequency than the controls (P = 0.039).
Using DNA probes for the tandemly arranged complement C4 and steroid 21-hydroxylase genes, an increased number of C4B gene deletions in SID cases was found.