Using an animal model, brain researchers in Göttingen have examined the effects of mutations that cause autism in humans. These are mutations in the genes which carry the building instructions for proteins in the neuroligin family. The study shows that neuroligins ensure that signal transmission between nerve cells functions. In the brain of genetically altered mice without neuroligins, the contact points at which the nerve cells communicate, the synapses, do not mature. The researchers assume that similar malfunctions are experienced by autistic patients.
It was already known that mutations in the two genes NLGN3 and NLGN4X trigger autism in affected patients. The NGLN genes are responsible for the creation of two proteins, neuroligin-3 and neuroligin-4, which are considered to play an important part in the structure of nerve cell contacts.
Nerve cells communicate with each other at specialized contact points, the synapses. When stimulated, a transmitting nerve cell emits neurotransmitters. These signal molecules reach the receiving cell and affect its activity status - provided the receiving cell has "aerials" on its synapses - receptors that bind the chemical signals. The scientists speculated that this process could be disrupted if the nerve cells have no neuroligins.
With his colleague FrederiqueVaroqueaux, Nils Brose from the Max Planck Institute for Experimental Medicine in Göttingen has created a mouse line that lacked all four known variants of the protein simultaneously. The consequences are accordingly more drastic than with autistic patients, who only have one mutated neuroligin gene. Without any neuroligins, the function of the nervous system breaks down completely and the mutant animals die immediately after birth. However, their nerve cells can be examined in detail. According to Brose, "they deliver important findings not only for brain research in general, but also for the possible causes of autism. Our investigations show that the neuroligins regulate the maturation of the synapses. They ensure that there are sufficient receptor proteins on the synaptic membrane of the receiving cell."
"What we see in our neuroligin mutants is a more intensified form of the malfunction that occurs in the brain of autistic people," says Brose. "I believe that autism is a disease of the synapses, a synaptopathy."
MEDICA.de; Source: Max Planck Society