- Scientists from around the world are alarmed by a dramatic
increase in genetically damaged human sperm - a trend that is not only
causing infertility in men, but also childhood cancers in the offspring
of those who can reproduce.
-
- It's now estimated that up to 85 per cent of the sperm
produced by a healthy male is DNA-damaged, a leading authority on the subject
revealed yesterday at an international conference being held in Montreal.
-
- "That's very unusual," said John Aitken, head
of biological sciences at the University of Newcastle in Australia.
-
- "If you were to take a rat or a mouse or a rabbit,
usually more than 80 per cent of their sperm would be normal."
-
- For the last 20 years, scientists have known about declining
sperm counts. But researchers are now learning that the quality of human
sperm is steadily eroding, and might be causing birth defects as well as
brain cancer and leukemia in children.
-
- Abnormal sperm is also being blamed for a global increase
in testicular cancer - a disease that strikes men in their 30s. Scientists
believe that when a DNA-damaged sperm fertilizes a woman's egg, it can
trigger a mutation of a key gene in the embryo.
-
- And even if men today can reproduce, their damaged sperm
might lead to infertility in their male progeny, Aitken suggested. "You're
likely to see lots of diseases that are related to poorer semen quality."
-
- Scientists suspect a wide range of environmental causes
for the abnormal sperm - from exposure to pesticides and heavy metals to
electromagnetic radiation.
-
- "We're all exposed to 10 times more electromagnetic
radiation than our forefathers," Aitken said. "It's all the electrical
appliances we use, including microwave phones."
-
- There is a consensus in the scientific community that
men who smoke cause damage to their sperm, and that this might be responsible
for childhood cancers. "If you are a man and you smoke, your semen
profile won't be obviously affected," Aitken said. "You'll still
have lots of sperm swimming around and you'll be fertile. But the DNA in
your sperm nucleus will be fragmented."
-
- The average ejaculate of human sperm contains 80 million
spermatazoa, each genetically programmed to fertilize a woman's egg. Scientists
examining human sperm have discovered that not only are sperm counts on
the decline, but that the vast majority of sperm is sluggish, poorly structured,
their DNA fragmented and that they generate a lot of cellular waste called
free radicals.
-
- "Generally speaking, everything is bad with the
sperm," Aitken said.
-
- Fortunately for most couples, it's the undamaged or least
damaged sperm that tends to fertilize the egg.
-
- As a result of increasing male infertility, scientists
have developed a new technique to help couples conceive. It's called Intra-Cytoplasmic
Sperm Injection (ICSI). In the lab, a technologist will take from the would-be
father a single sperm, or even a cell that is on its way to becoming a
sperm, and fertilize it in the test tube with the woman's egg. The resulting
embryo is then transferred to the woman's uterus.
-
- Dr. Keith Jarvi, of the University of Toronto-Mount Sinai
Hospital, said the ICSI technique has revolutionized the treatment of male
infertility. But he wondered about the health outcomes of the ICSI children.
-
- That human sperm is of poorer quality than that of other
mammals is not surprising. The human species is the only one that wears
clothes, and healthy sperm need to be kept a couple of degrees cooler than
the full body temperature. But clothing alone is not responsible for the
extent of abnormal human sperm, Aitken argued.
-
- http://www.montrealgazette.com/news/pages/010622/5081326.html
Aaron Derfel's E-mail address is aderfel@thegazette.southam.ca
|