The findings, published in the journal EMBO Reports, provide insight into the underlying causes of seizure disorder, also known as infantile spasms or West syndrome, as well as the use of a potential therapeutic intervention to address some of the developmental issues that are frequently associated with the condition.
Infantile spasms, a rare but serious seizure disorder in babies, appear to be the result of a faulty molecular pathway, according to researchers. The team found that genetic mutations attached with the disease impair a pathway involved in the formation of new synapses in the hippocampus, a brain region essential for learning and memory, in their study of a mouse model of the disorder.
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“We are trying to understand the reasons behind learning and memory disabilities in patients with infantile spasms,” said Nien-Pei Tsai, a professor of molecular and integrative physiology at the University of Illinois Urbana-Champaign who led the study with U. of I. research scientist Kwan Young Lee.
While infantile spasms usually go away by the age of four or five, long-term developmental issues affecting memory and learning persist, according to Tsai.
“The learning and memory deficits are long-lasting and the patients often require assistance at school,” he said.
“This tells us that the seizures and the learning defects are likely caused by different issues in the brain, but no one really knows how.”
Tsai added that previous research has found that infantile spasms are frequently linked to mutations in the Nedd4-2 gene, which codes for a protein called a ligase that regulates neuron excitability.
“To study the role of this gene, we used mice in which Nedd4-2 is selectively removed from the brain as a model to mimic patients with impaired Nedd4-2,” he said.
Scientists tested mice with impaired Nedd4-2 ligase function as well as mice with normal function in behavioral and physiological experiments. They also looked at how the ligase’s absence impacted biochemical pathways in mouse neurons grown in cell culture.
They discovered that male mice with insufficient Nedd4-2 ligase levels in the hippocampus had problems learning and remembering. In the hippocampus, problems with the structure of excitatory synapses, which carry electrical signals between neurons, were linked to this disability. Because the hippocampus is involved in the conversion of short-term memory to long-term memory, the researchers concentrated on neurons in this brain region.
A lack of Nedd4-2 in the hippocampus disrupted a pathway that regulates the growth of filaments called actin that support the formation of cellular structures like synapses, according to their findings. The filaments were destroyed in cells lacking adequate levels of the ligase, and the hippocampus had fewer excitatory synapses.
“Synapses need structural support to sustain their functions and integrity,” Tsai said. “Actin, which is one of the critical structural components in a cell, is made up of monomers that can attach to one another to form polymers. When the actin polymers are formed in synapses, the synapses become stronger. This process is critical for learning and memory.”
When mice with insufficient Nedd4-2 levels were given a drug compound that mimicked the ligase’s activity in the brain, the mice appeared to regain some of their hippocampal-dependent memory. The researchers discovered that the same compound restored hippocampal excitatory neurons in cell culture.
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“Because we showed that some of the learning and memory issues associated with infantile spasms can be improved by a synthetic peptide in animals, it means that one day we may be able to medically enhance learning and memory of patients who carry mutations in this Nedd4-2 gene,” Tsai said.