The finding suggests there may be a way to interfere with or even reverse the additional mental decline often seen as people with Down's syndrome age. The finding also may apply to Alzheimer's disease, according to Reuters.
Down's syndrome is the most frequent genetic cause of mental retardation and affects one out of 800 babies. It is caused when there is an extra copy of chromosome 21, making three instead of two.
Many people with Down's syndrome go on to develop dementia, similar to early-onset Alzheimer's disease, by the age of 40, BBC News reports.
In both Down's syndrome and this form of Alzheimer's, brain cells, or neurons, responsible for learning, memory and attention, wither and die.
To investigate he looked at mouse models, and discovered that mice with three copies of a gene called the amyloid precursor protein gene, or App, situated on chromosome 21, had larger neurons than mice with two copies of the gene.
The research was published in the journal Neuron.