Week 8- Obesity Genes

‘Three-year-old dies of obesity’ screamed the newspaper headlines when, in May 2004, a child died from heart failure in a London hospital. She weighed a staggering 40 kg. A media frenzy erupted, and the parents were blamed for ‘stuffing her to death’. Was it fair to accuse her parents? Scientists later confirmed that there was a medical problem behind the child’s extreme obesity: a genetic glitch that triggered her immense appetite.

 Genes play a crucial role in shaping our weight, but scientists have only recently started to work out how. It is too simple to say that obesity is ‘all in the genes’ but our genetic
inheritance does have a big say in our size.

 Researchers can come at obesity from two directions. In a ‘classical’ approach, the extent to which weight or obesity is inherited can be assessed. This is a difficult area to study, but the consensus is that there is a high degree of heritability in body weight.

 Obesity genes
A newer approach is to track down the genes involved in obesity. Of course, no gene exists just to make people fat. But, on rare occasions, someone may inherit a mutation that leads to excess weight gain. The first evidence of this came from a very fat mouse. These ‘ob’ (obese) mice weigh almost three times as much as normal mice. They were found to be missing a hormone, which was called leptin (from ‘leptos’, the Greek for ‘thin’). The defect was down to a mutation in the ob gene. Mice without leptin had an insatiable
appetite. But when leptin was injected into ob mice, they returned to normal in less than a month. Leptin thus appears to switch off hunger. So much for mice: what about humans? In Cambridge, researchers had been referred two cousins who had an intense drive to eat; they were exceptionally obese. Sure enough, the children shared the same genetic mutation as the ob mice. When given leptin, their appetite went down and they began to lose weight.
Leptin was instantly hailed as an obesity wonder drug. But disappointment soon followed.
Most obese people do not lack leptin – quite the contrary. They have even more than normal people, but the body does not seem to respond to it. So giving people leptin does not help them lose weight.

 Beyond leptin
Digging deeper, scientists have now found more than a dozen genes that, if mutated, may predispose people to obesity. The gene for the melanocortin receptor is a promising candidate, since around six per cent of young children with severe obesity have this
gene disrupted. Five other genetic mutations that cause obesity in children have been pinpointed.

 However, these are still rare cases, in which weight control has gone drastically wrong. They are unlikely to explain most individual differences in weight gain in children and adults.

 The likelihood is that there are a small number of genes that have a major impact in a few cases, and a much larger number of genes (perhaps 200–300) that have smaller effects in a larger number of people. The genes could be involved in any part of the body’s complex
mechanisms of weight regulation. Over time, even minor variations could have a big impact on weight.

 Taken from: https://bigpictureeducation.com/sites/default/files/Big%20Picture%20Obesity%20PDF.pdf 

Task:
Summarise the article above in your own words in no more that 3 sentences in the comment section below.

 Fat fanatic task:
Have a look at the work University College London is leading, using brain scanners to investigate how the brain responds to a hormone called ghrelin, which could be linked to obesity.  http://www.ucl.ac.uk/news/news-articles/0713/15072013-How-obesity-gene-triggers-weight-gain-Batterham 

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