A handful of families from around the world with a rare brain malformation called polymicrogyria have led scientists to discover a new gene that helps us speak and swallow.
The gene, SCN3A, is turned “on” primarily during fetal brain development. When it’s mutated, a language area of the brain known as the perisylvian cortex develops multiple abnormally small folds, appearing bumpy. People with polymicrogyria in this region often have impaired oral motor development, including difficulties with swallowing, tongue movement and articulating words — especially if the polymicrogyria affects both sides of the brain.
The new study, published today in Neuron, ties together human genetics, measurements of electrical currents generated by neurons, studies of ferrets and more to start to connect the dots between SCN3A, the brain malformation and the oral motor impairment. …
Five people with an unusual pattern of brain folds have afforded a glimpse into how the human brain may have evolved its language capabilities.
How the human brain develops its hills and valleys—expanding its surface area and computational capacity—has been difficult to study. Mice, the staple of scientific research, lack folds in their brains.
Christopher Walsh, MD, PhD, head of the Division of Genetics and Genomics at Boston Children’s Hospital, runs a brain development and genetics clinic and has spent 25 years studying people in whom the brain formation process goes awry. Some brains are too small (microcephaly). Some have folds, or gyri, that are too broad and thick (pachygyria). Some are smooth, lacking folds altogether (lissencephaly). And some have an abnormally large number of small, thin folds—known as polymicrogyria.
In 2005, studying people with polymicrogyria, Walsh and colleagues identified a mutation in a gene known as GPR56, a clue that this gene helps drive the formation of folds in the cortex of the human brain.
In a study published in today’s issue of Science, Walsh and his colleagues focused on five people whose brain MRIs showed polymicrogyria, but just in one location—near a large, deep furrow known as the Sylvian fissure, which includes the brain’s primary language area. …