New Delhi: A single gene might be responsible for causing childhood obesity in human beings, according to a new study by researchers from the University of Leipzig, Germany.
The study, conducted by researcher Antje Körner and her team, was published Monday in the journal Nature Metabolism.
Obesity has so far being understood to result from an interplay of genetics and environmental factors. Since 2006, over 50 genes have been found to be associated with obesity, but no single genetic cause has been identified until now.
Researchers in the new study said the agouti signaling protein (ASIP) gene was found to be responsible for severe obesity in a 12-year-old girl. She had inherited this gene from her father.
The team searched specifically for this gene in a control group of over 1,700 children with obesity. They identified three girls and a boy and confirmed that ASIP was widely present in three of them.
This gene has been previously studied on mice and traits such as adult-onset obesity, tumor susceptibility, and hair pigmentation — seen as yellow fur on rodents — were observed.
These findings were in congruence with issues that the 12-year-old patient suffered from, such as early-onset obesity, overgrowth, red hair and excessive insulin. All of these pointed to the presence of ASIP in her system.
The presence of this gene in unusual amounts is usually connected to appetite control and often goes undetected in routine tests for obesity. ASIP causes mutations that interfere with the melanocortin 4 receptor (MC4R) gene, triggering early satiety or fullness in one’s brain and making a person persistently hungry.
ASIP has also been seen to cause increased food intake and less energy in mice. Similar issues were observed in the 12-year-old. According to the study, she reported being ‘abnormally hungry’ all the time and never indulging in any exercise.
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ASIP found in skin tissues & hair follicles
The team of German researchers took a tissue sample from the patient during her weight-loss surgery and were able to arrive at the conclusion that ASIP was the single gene responsible for her obesity.
The ASIP gene, which was present in unusual amounts on the girl, also led to expansion and increase in fat molecules of her cells. This, in tandem with experiments conducted on mice, confirmed ASIP to be a single-gene causing obesity in human beings.
The girl inherited obesity from her father, as his blood samples also showed traces of ASIP. The father also said that he had been taller and heavier than his peers from a very young age — just like his daughter.
The daughter inherited her red hair colour and pale complexion from her father, signifying pigmentation in hair and skin — a side effect caused by ASIP.
ASIP is usually found only in skin tissues and hair follicles. But in the young patient, it was present everywhere, even in her healthy tissues. This was because ASIP latched itself onto an active promoter, a region of DNA that drives gene expression. ASIP was present in high levels in fat cells and white blood cells of the patient. This genetic arrangement has been observed in sheep before.
The authors, however, noted that although these experiments support their arguments, there is no confirmation yet of ASIP’s presence and its effect of the melanocortin 4 receptor on patients’ brains. This continues to be a theory of a potential singular cause behind obesity, but further studies are essential to validate it.
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