Is partial deletion of the complement C4 genes associated with sudden infant death?

The two C4 loci C4A and C4B in 61 cases of sudden infant death (SID), 93 living controls and 7 cases of infectious death were studied. In the SID group 13.1% showed deletion of the C4A gene, while 2.5% of the cases showed deletion of the C4B gene. This was not significantly different from neither the controls nor the infectious death group. We were not able to confirm that deletion of the C4B gene is associated with SID. However, in the SID group deletion of either the C4A or the C4B gene was associated with signs of infections prior to death (P = 0.035). This observation may indicate that a proportion of SID victims are more vulnerable to infections than other infants.