Considerable variability exists in outcome after traumatic brain injury (TBI), which is only partly explained by premorbid factors and severity of injury. Genetic factors influencing the brain’s susceptibility to injury, and its capacity for reorganisation, neuronal regrowth and repair are likely to play a part.

Apolipoprotein (Apo) E plays a critical part in the maintenance, repair and growth of neurones. The E4 isoform results in reduced growth and branching of neurites in vitro and seems to have an important part to play in the neural response to injury. In clinical genetic studies, the ApoE-ε4 allele is associated with attentional impairments and white matter abnormalities in normal controls; an increased risk of late-onset sporadic Alzheimer’s disease; and adverse functional outcomes acutely, early and late after severe but not clearly after mild and moderate TBI; and also after haemorrhagic but not after ischaemic stroke, …