Some theories about the causes of SIDS have centred on poor control of breathing, subtle heart abnormalities, or an unusual susceptibility for the baby’s defences to be overwhelmed by minor infections or other environmental problems which normal babies are well able to survive. This variation between babies may be controlled by the baby’s genes.
For a number of years the work of this research team has focussed on brain damage in babies who die in infancy and the investigation of the possible causes. They identified the apolipoprotein E (ApoE) gene as possibly relevant to SIDS for a number of reasons. This gene is concerned with transport and maintenance of fatty substances in the body. It also has a role in controlling the response to infection. The brain has a high content of fat combined with protein which it uses for the insulation of nerve fibres. The gene exists naturally in three different forms ApoE e2, ApoE e3 and ApoE e4 which vary in their ability to maintain normal fats and proteins. Variations in the gene have also been clearly linked to the response of the brain to ageing (ApoE 4 is more common in Alzheimer’s disease) and to other harmful circumstances such as stroke and head injury.
The researchers wished to establish whether the unusual forms of the ApoE gene (ApoE 4 and ApoE 2) were more common in babies who died of SIDS compared with other babies who died of known disorders at the same age.
They investigated 296 babies, made up of 170 babies who died of SIDS and 126 babies who died of other causes. They compared these findings with the knowledge they had already gained about healthy babies who were still alive as well as what is known about adults. They found a small increase in the number of SIDS babies who possessed the ApoE e4 gene compared with non-SIDS babies. However the difference was not sufficiently large to convince them that the ApoE gene was a major influence in causing SIDS. They are undertaking further work to see if there are differences between the babies who have different ApoE genes. These differences are likely to be subtle. Meanwhile there are other likely genes which influence a baby’s ability to survive and future research will certainly move in this direction.
