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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.
Drs
Jacquie Bond and Emma Roberts
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