A picture of two white mice on a blue surface. The left mouse appears approximately twice the size of the right one and is able to stand upright. The right mouse is much smaller and appears to be leaning slightly.

Two mice with a genetic defect similar to that of humans with the motor neuron disease called spinal muscular atrophy. Both mice are 11 days old. The mouse on the left has received treatment with a drug called Trichostatin A that increases the activity of certain genes. The mouse on the right did not receive the drug. The treated mouse is able to stand upright and support its weight on its feet. The other mouse is much smaller due to effects of the disease, and it is unable to move normally or to fully support its weight.