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Leptin is a hormone, made mainly by body fat, that tells the brain how much energy the body has in store. Jeffrey Friedman's team at Rockefeller University found it in 1994 by tracking down a mouse gene called ob, short for 'obese', which carries the instructions for making it.

Jeffrey M. Friedman, Rockefeller University, 1994

HealthScience

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Friedman's team spent eight years on positional cloning: narrowing down a faulty gene from its rough position on a chromosome, long before DNA sequencing made such searches easy. They named the hormone after the Greek leptos, meaning thin. A small number of people are born with a mutation that leaves them unable to make leptin; from early childhood they feel constant hunger and become severely obese, and daily leptin injections quickly curb their hunger and bring their weight down dramatically. That response confirmed the hormone's role. Most common obesity is different: leptin levels are normal or high, and the problem is that the brain responds to the signal less strongly.

Türkçe oku
Leptin, çoğunlukla yağ dokusunda üretilen bir hormondur; beyne, vücutta ne kadar enerji depolandığını bildirir. Jeffrey Friedman'ın Rockefeller Üniversitesi'ndeki ekibi 1994'te farelerde ob adlı bir geni bularak bu hormonu keşfetti. Genin adı İngilizce “obese”, yani şişman sözcüğünden geliyordu ve leptinin yapım bilgisini taşıyordu.

Friedman'ın ekibi bu geni, DNA dizilemenin bugünkü kadar kolay olmadığı yıllarda, kromozom üzerindeki yaklaşık yerinden yola çıkıp adım adım daraltarak buldu; “konumsal klonlama” denen bu çalışma sekiz yıl sürdü. Hormona Yunanca “ince” anlamındaki “leptos” sözcüğünden leptin adını verdiler. Çok az sayıda insan leptin üretemeyecekleri bir mutasyonla doğar; bu kişilerde erken çocukluktan başlayarak doymak bilmeyen bir açlık ve ağır şişmanlık görülür. Her gün yapılan leptin iğneleri açlıklarını kısa sürede bastırır ve kilolarını çarpıcı biçimde düşürür. Bu, hormonun rolünü kanıtladı. Yaygın şişmanlıkta ise durum farklıdır: leptin çoğunlukla eksik değil, normal ya da yüksektir; sorun, beynin bu sinyale verdiği yanıtın zayıflamasıdır.

Sources and further reading

Background reading: Leptin
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