Two genetic letters out of the 3 billion in the human genetic alphabet may spell the difference between a genius and an idiot, according to a new report.
A genetic analysis led by an international collaboration of scientists from the Yale School of Medicine determined that that tiny variation -- just two genetic letters within a single gene -- determines the intelligence potential or lack thereof of a human brain.
The report appeared online May 15 in the journal of Nature Genetics.
In normal brain function, convolutions, the deep fissures of the brain, increase the overall surface area, one of the primary determinants for intelligence. Deeper folds in the brain allow for rational and abstract thought, scientists believe.
In the latest finding, a team of researchers analyzed a Turkish patient whose brain lacks those characteristic convolutions in part of his cerebral cortex, a sheet of brain tissue that plays a key role in memory, attention, perceptual awareness, thought, language and consciousness.
The cause of this drastic cerebral deformity was pinned down to a gene called laminin gamma3 (LAMC3) with similar variations discovered in other patients with the same medical condition.
"The demonstration of the fundamental role of this gene in human brain development affords us a step closer to solve the mystery of the crown jewel of creation, the cerebral cortex," said Murat Gunel, senior author of the paper, co-director of the Neurogenetics Program and professor of genetics and neurobiology at Yale.
The folding of the brain is seen only in mammals with larger brains, such as dolphins and apes, and is most pronounced in humans. These fissures expand the surface area of the cerebral cortex and allow for complex thought and reasoning without taking up more space in the skull. Such foldings aren't seen in mammals such as rodents or other animals.
Despite the importance of these foldings, no one has been able to explain how the brain manages to create them. The LAMC3 gene may be crucial to the process.
"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 and its mutation leads to the loss of surface convolutions, a hallmark of the human brain," Gunel said.