The chances of suffering dementia in later life may be decided before we are even born, it is claimed.

Brain changes in adults linked to mental disorders, such as Alzheimer’s, schizophrenia and autism, have also been found in newborns.

‘This suggests prenatal brain development may be a very important influence on psychiatric risk later in life,’ said researcher Dr Rebecca Knickmeyer, from the University of North Carolina, US.

It is hoped further research could lead to those at risk being identified much earlier in order to prevent the onset of mental illness.

The findings were based on a study of 272 babies, who received MRI scans shortly after birth. The DNA of each was tested for ten common variations in seven genes linked to conditions including schizophrenia, bipolar disorder and autism.

One gene mutation, which is associated with Alzheimer’s, revealed brain changes in infants that looked very similar to the changes found in adults with the same variants.

However, this was not true for every such gene in the study, explained co-researcher Dr John Gilmore. He said: ‘This suggests that the brain changes associated with this gene variant aren’t present at birth but develop later in life, perhaps during puberty.’

Dr Knickmeyer said: ‘It’s fascinating that different variants in the same gene have such unique effects in terms of when they affect brain development.’