Fetal brain gene blueprint scoured for autism clues

A map showing where different
genes are turned on and off in the fetal human brain has been published in the
hope it will give important clues about the origins of disorders.

'Knowing where a gene is expressed in the brain can provide powerful
clues about what its role is', said Dr Ed Lein, of the Allen Institute for
Brain Science. 'This means that we have a blueprint for human development: an
understanding of the crucial pieces necessary for the brain to form in a
normal, healthy way, and a powerful way to investigate what goes wrong in
disease'.

To produce their map of gene expression, called the BrainSpan
Atlas, the scientists used tissue from
four fetal brains preserved between 15 and 21 weeks after conception. They
sliced each into about 3,000 ultra-thin sections, isolated RNA and looked at the activity level of about 20,000
genes.

The researchers point to autism as a disorder with strong links to
early brain development where the information they have unearthed may lead to
greater understanding. They present some early investigations into the
condition alongside other preliminary studies in the journal Nature.

Dr Lein says the team looked for 'a
hub of genetic action' that could be linked to autism, and ultimately found it
among 'newly generated excitatory neurons in the cortex, the area of the brain
that is responsible for many of the cognitive features affected in autism such
as social behaviour'.

The finding is also consistent with an imbalance between excitatory and
inhibitory signalling suggested in previous autism studies.

Dr Thomas Insel, director of the National Institute of Mental Health in the USA,
who was not involved in the study, said the BrainSpan Atlas 'is already
transforming the way scientists approach human brain development and
neurodevelopmental disorders like autism and schizophrenia. Although the many
genes associated with autism and schizophrenia don't show a clear relationship
to each other in the adult brain, the BrainSpan Atlas reveals how these diverse
genes are connected in the prenatal brain'.