|Three tails better than one?|
Unlike women, men continue to produce reproductive germ cells unto death. While the available eggs peter out some time in a women’s late 30s or even 40s, a man can still, if he has the stamina, sire a child when he is in his 90s: the pervert, Charlie Chaplin fathered a child when he was 75. This is not to say that the sperm of a 60-year-old man is of equal quality to a 16-year-old boy. Although it is said that wisdom comes with age- although to be honest, this attestation is open to doubt: there is nothing so sad as an old fool. Wisdom is perhaps the only human quality that is correlated with a hoary old chin. Sadly, our physical and mental attributes steadily decline as we age and sperm is no exception. I was made painfully aware of this problem several years ago when I had to ‘produce issue’ during the development of a genetic test for sperm. I was the only male in the department able to perform this duty as all other males in the lab had teetered toward vas deferens ablation: mayhap the teetering was post-op?
Under the microscope, my sperm appeared ‘morphologically diverse’. Most appeared normal, but there was a significant minority exhibiting physical aberrations. Some appeared to have two tails; others were endowed with two heads. Others were devoid of content. A whole menagerie of freaks residing in plain sight. Needless to say, these aberrant sperm would be useless as vehicles for the transport of genetic material unto the next generation..
This is but the tip of the iceberg. A man’s sperm, especially after 35, declines in many other respects. Thus, not only is there a decrease in overall fertility but there is also an increased chance of miscarriage, stillbirths and birth defects: assuming of course that the sperm can summon enough strength to power through the birth canal. Continued exposure to damaging environmental factors and the failure of an ageing immune system to detect and remove defective sperm are responsible for the corresponding increase in defects with age. In addition, aged sperm accumulate deleterious gene mutations resulting in an increase in the incidence of dominant genetic conditions.
As I’ve discussed previously (see here) the sum of our genetics is more than our genes. Epigenetic factors also have a role in controlling gene expression. In addition to changes in DNA base sequences, structural changes affecting methylation and histone configuration can have dramatic and heritable consequences, often affecting multiple generations. Epigenetic changes within the germ cells of both sexes can be influenced by a myriad of environmental effectors. And it is therefore of no surprise, certainly not to a geneticist, that the depredations of time, mediated through epigenetics, can have a real and negative influence on genetic expression. Recent research indicates that changes in methylation patterns in aged sperm are particularly important in the development of neuropsychiatric disorders in subsequent offspring. This is a particular problem in the developed West where career-minded couples are delaying parenthood. A UK survey between 1993 to 2003 divined that the percentage of 35-54-year-old fathers had increased from 25% to 40% resulting in a corresponding increase in neurodevelopmental problems in their children. There appeared a strong correlation between epigenetic change and the development of autism and schizophrenia. Interestingly, this observation may be compounded over multiple generations giving rise to a synergistic mechanistic effect: aged father to aged father to aged father....... That said, the causal mechanisms with regard to epigenetic change and neuropathology are, as yet, poorly understood.
No surprises for those who can see, especially those with access to a high powered light microscope. Making genetically healthy and robust children is definitely for the young and preferably the ‘genetically advantaged’ - read into this what you will. Ageing is relentless and unforgiving. It creases the brow and bends the back. Spun silver flecks once lush and vibrant locks. Rheumy eyes beseech an incomprehensible world. The prostate waxes great and protrudes thus facilitating a back and forth rocking motion. Our unique genetic code, manifest within sperm, bears the sticky and indelible mark of our increasing decrepitude. A decrepitude destined to bestride the generations and haunt our children and our children’s children unto the fourth or fifth generation.