THURSDAY, April 12 (HealthDay News) -- The two most common forms of genetic mental retardation -- Fragile X and Down syndromes -- may share a common feature -- a faulty communication network in the brain, U.S. researchers say.

The actual genetic causes of the disorders are different, but the end result in the brain seems to be similar, said Daniel Madison, associate professor of molecular and cellular physiology at Stanford University School of Medicine.

"It's as if you had every light in your house wired to just one or two switches, rather than having many switches that can be flipped on or off in complex combinations to control the lighting in one room," he said in a prepared statement.

Madison is senior author of a new study that looked at Fragile X syndrome in mice. The study is published in the April 11 issue of the Journal of Neuroscience. In the Feb. 15 issue of the Journal of Physiology, Madison also published a study that looked at Down syndrome in mice.

In both syndromes, brain cells have a problem forming a network of connections (synapses) with one another, which interferes with the information-carrying capacity of the brain.

"We believe that these reduced-complexity networks are the basis for the mental retardation that occurs in both syndromes," Madison said.

The problem may be rooted in early brain development.

"No two nerve cells will always be connected in the same way in different people. But populations of cells will develop similar connections as the developing brain practices using its own network. If we can compensate for the synaptic deficiency of the mutant cells, we may begin to start to think about ways to increase the mental capacity of patients with Down syndrome or Fragile X," Madison said.

More information

The National Fragile X Foundation has more about Fragile X syndrome.