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Predisposition to Obesity May Be Carried in Sperm

Adapted from "Obesity and Bariatric Surgery Drive Epigenetic Variation of Spermatozoa in Humans" published in The Cell Metabolism.

A man's weight may affect the function of important genes in his sperm in ways that could be passed on to his future children, a new, small study suggests.

Researchers found that sperm from normal weight and obese men differed in how some genes were turned "on" or "off." And the differences were seen in gene regions linked to brain development and appetite control.

The results may provide a biological clue as to why children of obese fathers may be predisposed to being obese, the researchers said.

The current study addressed epigenetics: chemical mechanisms that determine whether a gene is active or dormant in certain cells at certain times.

Cells come together to build tissues as different from each other as muscle and bone, even though they all technically have the same genes inside them. The choices that your cells make about which genes to express are what is called the epigenome, and this can be influenced by basically anything: Where your mother lived while pregnant with you, what kind of food you're eating, and even what kinds of pollutants your grandparents were exposed to as children.

Some studies suggest the changes in epigenetic factors can be handed down to offspring via sperm. The genes themselves were still the same. But the epigenetic marks that control how a gene is expressed had changed.

In the study, the researchers compared epigenetic markers in the sperm of 13 lean men with body mass index (BMI) of 23 with those of 10 obese men with BMI of 32.

They found that the sperm of the obese men carried a different epigenetic signature compared to that of the lean men, particularly at genes that are involved in controlling the development and functioning of the brain and the regulation of appetite.

In a separate part of the study, the researchers looked at six obese men who underwent weight-loss surgery, in order to see how the surgery might have changed the hereditary information in their sperm. The researchers found that 5,000 or so of 9,000 markers associated with obesity went away within a year.

The implication of this study is that the environment can change what the sperm cell carries and that these environmental impacts can be transmitted to the egg, and may change how the embryo will develop, and maybe change how the child will develop.

These findings suggest that fathers might want to start exercising more and eating better before they cause a pregnancy, given that their ill health leaves its mark on their sperm.

January 2016

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