The previous comment made a number of good points, but I'd like to add
a few things and clarify some others.
A number of papers published in peer-reviewed scientific journals have
shown that there is a genetic component to both male and female
infertility. For example, 10-15% of men with azoospermia (no sperm in
the ejaculate) have a deletion of a gene on the Y chromosome called
the DAZ gene, that is, their Y chromosome is missing that gene. For
women, twin studies have shown that the heritability for age at
menopause (early menopause is one type of female infertility) can be
as high as 63%, which basically says that your genes are likely to
play a high percentage role in your age at menopause. Let me know if
you'd like some sample references.
Assisted reproductive techniques (ART) such as in vitro fertilization
(IVF) or intracytplasmic sperm injection (ICSI) allow couples with
various types of fertility problems conceive children. As the
previous commenter pointed out, without these techniques, the genetic
problems that an infertile couple may possess would not be passed on
to any offspring. In addition, it is also most likely true that the
interaction that a particular person's set of genes has with his or
her particular environment can influence the outcome, on fertility or
any other characteristic. For instance, a fair-skinned individual may
be more susceptible to developing skin cancer than a darker-skinned
individual; however, if the fair-skinned person spends little to no
time in the sun, he will probably not develop skin cancer. This
person's genes simply predispose him to a particular condition, but
his interaction with the environment is also key.
Getting back to assisted reproduction and genetic problems, one thing
that I feel I ought to clarify is that there is some evidence that
certain genetic problems that lead to infertility could also lead to
other genetic abnormalities. Certainly, some genetic causes of
infertility, such as loss of the DAZ gene, only appear to affect
fertility and no other processes. In that case, if a man is infertile
because of a DAZ deletion, and he and his partner undergo IVF to have
a child, any sons they produce will also have the same DAZ deletion
(since a father passes his Y chromosome to all of his sons) and will
likely be infertile themselves. However, there is evidence that some
infertility in both men and women may be associated with
nondisjunction of the chromosomes or defective meiosis. Both of these
processes have to do with the complicated dance of chromosomes that
must occur for proper sperm and egg formation. In the case of
nondisjunction, a child may end up with an extra chromosome or an
extra part of a chromosome. In most cases, this combination of
chromosomes is not compatible with life and the embryo is
spontaneously aborted, probably much before a woman would suspect that
she might be pregnant. A few combinations of extra chromosomes are
compatible with viability, such as an extra chromsome 21 (Down's
Syndrome) or extra X or Y chromosomes. So you can see that if a
couple is infertile because one of them is genetically predisposed to
have problems with chromosome nondisjunction, they may be more likely
to produce a child with an abnormal number of chromosomes.
In the case of problems with meiosis, many of the genes required for
this process are also important in the DNA repair processes that are
important for preventing cancer. Your DNA is often damaged by things
in the environment--UV light, free radicals, chemical agents,
etc.--but your body has a system in place to find these broken bits in
your DNA and fix them. It's really remarkably efficient, but genetic
defects in this machinery do happen and then broken bits can go
unrepaired. Mistakes in certain important genes can lead to the
unrestrained cell growth and division that is the basis of cancer.
Therefore, these defects can not only make you susceptibile to
infertility (through defective sperm or egg development), but also
potentially susceptible to cancer.
There was also one study that showed that babies born through assisted
reproductive techniques have a 2x higher incidence of certain birth
defects, but this isn't really very high and I don't know how
reproducible those results are. Some scientists are concerned that
simply putting embryos through the process of coming out of the body,
sitting around in a petri dish and under microscopes can be damaging,
even though the techniques are constantly being improved.
But I don't mean in any way to be alarmist, or imply that because of
IVF, we're selfishly producing many children who are born with
disadvantages. Most of the children born through ART are healthy and
I'm sure their parents couldn't be happier. Besides, I don't know
whether the genetic problems that are associated with infertility are
any worse than those that aren't but certainly don't prevent people
from having children, such as susceptibility to diabetes,
hypertension, or high cholesterol. I'm sure the possibility of
passing on genetic problems to their children is, however, a concern
for many potential parents, since everyone wants the best possible
lives for their family. Many IVF clinics offer genetic counseling to
couples to let them know what the risk factors may be. In addition,
techniques to test embryos for certain genetic defects, such as
preimplantation genetic diagnosis (PGD), are being developed to let
people know whether a couple has passed on a genetic defect (cystic
fibrosis, for instance) to a particular embryo.
Anyway, I hope this is somewhat useful at least. I apologize if I've
been too jargon-y, just let me know. There are a number of good
resources available on the web relating to ART and reproductive
medicine in general. Try the American Society for Reproductive
Medicine's website--it should be reliable. |