A recent summary of sperm changes that can be passed to children titled “The Sins of the Father” in the March 2014 journal Nature, did a great job of explaining how being overweight, having diabetes, or being exposed to smoking, pesticides, and stressful experiences for a male may affect his sperm and its genetic code (DNA). We thought a brief explanation would be interesting for our readers.
DNA (aka the genome) is the total amount of information encoded by the DNA units (called nucleotides) of an organism’s DNA. The epigenome includes the modifications made in around the genes that affect gene expression (“on” or “off” switch) by changing 3-dimenstional DNA structure without changing the DNA sequence itself. This is being studied more frequently in the past few years, and will be a topic of increasing interest in the upcoming decade. There is even a new test (called Male Fertility Panel) in development which will look at epigenetics (beyond the DNA) in a man’s sperm to predict health risks that can be transmitted to children.
Commonly, epigenetics (inherited changes in gene function that are not part of the DNA genetic code) can greatly affect development of individuals and have been studied for years in plants, rodents, and humans. These epigenetic changes in sperm can be either special chemical groups added to DNA (methylation), or they can change how tightly the genetic code is wrapped which can change its expression (called histone acetylation or protamination). Recently it has been recognized that some of the changes may be capable of being passed along to children.
Male rats eating high-fat diet have daughters with abnormal DNA markings (called methylation) in the pancreas. Male mice with high blood sugars (pre-diabetes) have abnormal DNA methylation in sperm. Pesticides can lead to changes in sperm DNA methylation that last for many subsequent generations. Most recently, a study in Nature Neuroscience in 2014 showed that anxiety related to a particular odor in male mice can lead to anxiety-ridden offspring by affecting sperm methylation. Obese mice have different levels of microRNA (another epigenetic way that DNA expression can be modified) in sperm and this is passed on to future generations. The exact mechanism of how this occurs, however, is unclear, and more studies will be required to complete the full puzzle of how epigenetics are transmitted to children.