WASHINGTON: Three Turkish cousins who have a genetic mutation that made them very obese may help clarify how and why some people become overweight but not others, researchers said on Wednesday.

The three make an abnormal version of the hormone leptin, discovered only in the past decade and strongly linked with weight and appetite. But doctors helped the three lose a collective 300 pounds by injecting them with the hormone.

The leptin injections also made their brains grow, something the researchers do not quite understand, and seemed to take one of the patients out of delayed puberty.

Dr Julio Licinio, a professor of psychiatry and medicine at the University of California Los Angeles who led the research, believes the study will show leptin is even more important to human health and development than anyone thought.

“The people are like half their size. One thing it shows is that leptin has a role in normal human biology and number two, it can have profound effects on weight loss.”

Leptin has had big ups and downs in the 10 years it has been known to science. At first researchers became very excited when it was found to make overweight mice and rats lose weight when they were injected with it.

But the same thing did not happen with humans, and it turns out that many obese people in fact make too much leptin.

Licinio’s team then discovered the Turkish patients, who have a very rare genetic mutation. It is a single change in the genetic code, known as a single nucleotide polymorphism — an SNP, pronounced “snip”, in the leptin gene. His team brought the three cousins to Los Angeles and injected them with leptin over a period of six weeks.

Their weight loss over 10 months was profound.

Of particular interest, however, was the effects the hormone had on the three patients outside weight loss.—Reuters