Scientists at the University of Texas have discovered how mutations in two key proteins can produce an imbalance that may lead to autism by adversely affecting communication between brain cells.

The proteins - the excitatory neuroligin-1 and inhibitory neuroligin-2 - normally balance each other to create a physical bridge - or synapse - between nerve cells, enabling them to make connections with other cells. In autism, however, the balance between the proteins appears to be knocked out of kilter.

Infants are born with far more synapses than they will require in adulthood and inactive ones are normally culled, but the latest research shows that raising levels of both proteins in the nerve cells of rats leads to the creation of extra synapses.

However, when the researchers introduced a mutant form of neuroligin-1, which is thought to be carried by some people with autism, the number of synapses fell dramatically and the cells became significantly less excitable, suggesting that carrying this mutant form of neuroligin-1 may depress the number of synapses that survive into adulthood.

The consequently reduced ability of nerve cells to make connections, could lead to the problems seen in people with autism.

Future research will hopefully look at both the neuroligins themselves and the genes which regulate their formation, in the hope of establishing exactly what role they play in the causation of autism spectrum conditions and in which particular subgroups.

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First published September 2007

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