Clinical trials exploring the link are difficult to implement and have limited follow-up time.
The Bristol study, led by Dr Sarah Lewis of the University's Department of Social Medicine, took a different approach focused on people who have a mutation on a gene which affects their body's ability to eliminate alcohol.
Alcohol is initially metabolised to an intermediate compound, acetaldehyde, which is further metabolised and then eliminated from the body. The major enzyme responsible for this elimination is alcohol dehydrohenase 2 (ALDH2).
In some people, a genetic mutation leads to an inability to metabolize acetaldehyde and causes an accumulation of acetaldehyde after alcohol intake. This mutation is common in some Asian populations and results in facial flushing after consumption of alcohol coupled with intense nausea, drowsiness, headache and other unpleasant symptoms. People with this mutation therefore drink much less than those without it
The researchers looked at the ALDH2 genotype, comparing the blood pressure of those who have this mutation “ the *2 *2 genotype “ with those who do not “ the *1 *1 genotype.
The study found that individuals with the *1 *1 genotype, who had an alcohol intake of around 3 units per day, had strikingly higher blood pressure than those with the *2 *2 genotype, who tend to drink only very small amounts, or no alcohol.
Dr Lewis said: This study shows that alcohol intake may increase blood pressure to a much greater extent, even among moderate drinkers, than previously thought. Large-scale replication studies are required to confirm this finding and to improve the precision of our estimates.
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Ding's findings mark the first time that the lack of a distinct type of snoRNA has been directly linked to a human disease.
Strangely, the mice stayed leaner than their wild-type counterparts despite their overeating. To determine why, the researchers put the animals in a chamber that measures oxygen intake and carbon dioxide output, and found that the mice without SNORD116 had higher rates of exchange, or metabolic rate, than did wild-type mice. We found that the mice are adapting to extra food intake with their higher metabolic rate, said Ding. They are burning it off. But the findings only account for about half the extra calories. The fate of the remainder remains a mystery, although it's possible at least some is ending up on the bottom of the cage as droppings.
Unlike other mouse models of obesity, these mice were able to ramp their food intake up or down in response to changing feeding conditions. This is important because previous theories of what causes overeating in Prader-Willi syndrome hinged on a supposed inability to maintain this so-called energy homeostasis. However, despite their adaptability, Ding found that under normal conditions the SNORD116-deletion mice had longer meal times and spent more time eating each day. Like people with Prader-Willi syndrome, the mice seemed to be constantly hungry, possibly related to their elevated ghrelin levels.
For now, Ding and Francke are planning to cross their SNORD116-deletion mice with another strain of mice lacking ghrelin to see if they continue to overeat. If ghrelin is the cause, they can search for chemicals to block its effect in their deletion mice. One day they hope to be able to apply their research to the uncontrollable hunger experienced by humans with Prader-Willi syndrome.
These people are not gluttons, said Ding. They truly feel as if they are starving.
Other Stanford authors of the research include research associate Hong Hua Li, PhD, and postdoctoral scholar Shengwen Zhang, PhD.
The research was funded by the National Institute for Child Health and Development and the Foundation for Prader-Willi Research.
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