Age-related changes in sperm DNA methylation and their forensic and clinical implications.

DNA methylation is a biological process that can change the activity of a gene without changing its sequence. We do not know much about DNA methylation in sperm and what changes methylation undergoes during the lifespan. These changes can, however, be important both for health and solving crimes. Presperm cells renew themselves, which gives rise to new sperm cells, from youth to death, accumulating cell divisions prone to error. This is why sperm cells are affected by age more than nondividing eggs. Methylation is specific in different tissues of the body. The ratio between number of sperm cells, white blood cells, and other cell types is highly variable and hardly predicted, which may distort the results. Clinical studies have shown that older fathers have worse reproductive health. Their children can develop metabolic, neurological and behavioral disorders. This also applies to younger men whose DNA methylation pattern is similar to that of older men. Methylation changes allow us to build a model capable of predicting the age of an unknown person with a mean error of about 5 years. This can be helpful for police investigators in cases of sexual assault, when biological material is found but there is no match in the police database.