Apolipoprotein E Genotype

A comparative study of infants that died from SIDS and infants that died from known causes of death.

Professor Neil McIntosh, Professor Jeanne Bell, Dr Jean Keeling and Dr Julie Clare Becher
University of Edinburgh
(2000: £118, 738 over 3 years)

Poor control of breathing or subtle heart abnormalities are two theories about the causes of SIDS. Another theory is that babies who die from SIDS are unusually susceptible to minor infections or other environmental problems, which normal babies are able to survive but which overwhelm the defences of SIDS infants. This variation between babies with SIDS and other babies may well be controlled by babies’ genes.

For several years, this research team has been investigating the possible causes of brain damage in babies who die in infancy. They identified the Apolipoprotein E (ApoeE) gene as potentially relevant to SIDS. This gene is concerned with the transport and maintenance of fatty substances in the body; it also has a role in controlling the response to infection.

The gene exists naturally in three different forms: ApoE e2, ApoE e3 and ApoE e4. These forms vary in their ability to maintain normal fats and proteins. Variations in the gene have been clearly linked to the response of the brain to ageing and to other harmful circumstances, such as stroke and head injury. An example is that ApoE 4 is more common in Alzheimer’s disease.

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 than in babies who died of known disorders at the same age.

They investigated 296 babies. 170 of these were babies who died of SIDS; 126 were babies who died of other causes. They compared their findings with what they knew about healthy, living babies and adults.

The researchers found that slightly more SIDS babies possessed the ApoE gene than non-SIDS babies. However, this difference was not significant enough to convince them that the ApoE gene was a major influence in causing SIDS.

They are undertaking further research 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 genes which are likely to influence a baby’s ability to survive and future research will certainly move in this direction.