A tiny variation within a single gene may determine the formation of brain convolutions, the deep fissures and convolutions that increase its surface area and allow for rational and abstract thoughts, researchers at Yale University have discovered.

A genetic analysis of a Turkish patient whose brain lacks the characteristic convolutions in part of his cerebral cortex revealed that the deformity was caused by the deletion of two genetic letters from 3 billion in the human genetic alphabet. Similar variations of the same gene, called laminin gamma3 (LAMC3), were discovered in two other patients with similar abnormalities.

An analysis of the gene shows that it is expressed during the embryonic period. This period is vital to the formation of dendrites, which form synapses or connections between brain cells, the researchers said.

They said that although the same gene is present in lower organisms with smooth brains, such as mice, somehow over time it has evolved to gain novel functions that are fundamental for human occipital cortex formation. Its mutation leads to the loss of surface convolutions, a hallmark of the human brain, the researchers said.

Ref: Tanyeri Barak et al., Recessive LAMC3 mutations cause malformations of occipital cortical development, Nature Genetics, 2011; DOI: 10.1038/ng.836