Defective versions of a "body clock" gene greatly increase the
risk of type 2 diabetes, a study has shown.

The discovery provides new evidence of a link between the
body's sleep cycle, governed by the hormone melatonin, and the
disease.

Previous research has found that people who work night shifts
are more at risk of type 2 diabetes and heart disease.
Volunteers who have their sleep disrupted repeatedly for three
days also develop temporary diabetic symptoms.

Melatonin controls the body's cycle of sleeping and waking,
inducing drowsiness and lowering body temperature. For this
reason melatonin supplements are often taken to combat jet-lag.

The new study focused on a gene called MT2 which codes for the
molecular cell receptor that allows melatonin to work. Carrying
any of four rare mutations in the gene increased the risk of
developing type 2 diabetes six times, the research showed.
Faulty MT2 is thought to disrupt the link between the body
clock and insulin release, leading to abnormal control of blood
sugar and diabetes.

The findings are published in the journal Nature Genetics.

Study leader Professor Philippe Froguel, from Imperial College
London, said: "We found very rare variants of the MT2 gene that
have a much larger effect than more common variants discovered
before. Although each mutation is rare, they are common in the
sense that everyone has a lot of very rare mutations in their
DNA. Cataloguing these mutations will enable us to much more
accurately assess a person's risk of disease based on their
genetics."

More than two million people in the UK are known to suffer from
type 2 diabetes, the most common form of the disease, which is
linked to obesity and lifestyle.

The Imperial team and other scientists from the UK and France
looked at the MT2 gene in the DNA of 7,632 people. They found
40 variants associated with type 2 diabetes, including four
that were very rare and rendered the receptor completely
incapable of responding to melatonin. The link with the four
mutations was then confirmed in an even bigger sample of 11,854
people.

The scientists tested the effects of the defective genes in
human cells in the laboratory. They found the mutations had a
major impact on type 2 diabetes risk.

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Body clock gene 'link' to diabetes

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