Gene is evolutionary link to humans’’ bigger brains

Researchers at Leeds have identified the gene which gives us bigger brains – the evolutionary attribute separating us from other animals. The gene came to light during a study by Geoff Woods, Jacquie Bond and Emma Roberts into the disease microcephaly, in which people are born with a smaller brain (and head).

Dr Woods, a clinical geneticist at St James’’s, noticed a high instance of microcephaly among his Pakistani patients. He found that, in the 1960s, a dam project in Pakistani-controlled Kashmir had displaced a large number of people, some of whom came to live in Bradford. Many were from large, inter-related families, making it possible to trace a genetic link to the disease.

The researchers found mutations in a gene known as ASPM, which controls the brain’s growth during foetal development. In microcephalic patients, brain growth slows after 20-30 weeks, so when born, their brains are smaller.

“ASPM is made up of chemical units called IQ repeats,” said Dr Woods. ” In microcephalic patients, the gene is slightly truncated. The number of the gene’s IQ repeats increases in other organisms in parallel with evolutionary progression in the size of the central nervous system.”

In worms the protein has two IQ repeats, in the fruit fly, 24. Mice have 61 and humans have between 72 and 80. Dr Woods’ team of researchers from the molecular medicine unit are now analysing the gene in primates, to see just how many IQ repeats separate us from our nearest evolutionary neighbours. ‘IQ’ refers to the gene’s chemical constituents, not to intelligence.

Identifying genes such as ASPM linked to microcephaly has enabled assessment of a couple’’s likelihood of having an affected child. The researchers now hope to identify more genes linked to the disease.