In The Future-Children & Testing
of SMA in Future Children-How the genetics work.
The bottom line answer to
the question is that there is a one in 4, or 25% chance every pregnancy of
SMA occurring, and a 75% chance every pregnancy of a "healthy"
child. It does not matter if you have had one or three children in a
row with the disease, the next pregnancy still has the same 25% chance of
SMA occurring as the first did.
SMA is an "autosomal
recessive" disease. What this means is that both parents carry
a recessive copy of the SMA gene, and a healthy dominant gene.
(Healthy is dominant, otherwise they too would have the disease.)
We'll say that each person's two-part gene looks like this. Hs.
("H" for dominant Healthy and "s" for recessive
SMA). When pregnancy occurs, one part of that gene from each parent
meets up in the embryo. There are four possible combinations of
these genes coming together. First, the two healthy genes (one from
mom and one from dad) can meet. It would look like this: HH.
This is a completely SMA-free child, who is not even a carrier of the
disease. The next two combinations end up being the same
thing. One healthy gene and one SMA gene from each parent: Hs
This means that the child is like the parents: Healthy, but carries
the recessive gene. This will not affect the child at all unless and
until they go to have children of their own. At that time, they may
wish for their spouse-partner to be tested for the gene as well to see if
SMA is a possibility for their children. The final
combination is that the two SMA genes, one from each parent, can come
This is a child who will have SMA. So, for the final tally, there is
a 25% chance the child will be a healthy non-SMA carrier, a 50% chance the
child will be a healthy SMA carrier, and a 25% chance the child will have
Or, as stated before, a 75%
chance of a healthy child and a 25% chance of an SMA child.
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Options for Future Children
There are basically six options available to each
couple who have found that they are carriers of the SMA gene. Which
option you choose is an extremely personal decision, and one that only you
can determine for your own family.
Some families decide that they will not attempt to have any further
children because they can not accept the risk of SMA, and the other
options available are not right or possible for them. They are
content to either wait for the day that a cure may be available, or keep
their family at the size it is currently.
Many couples feel that adoption is the best answer for them.
They feel that the risk of another child with SMA is unacceptable, and
that there are many children already here who need loving homes that
they can provide. Adoption can be at times a difficult,
time-consuming, and expensive process. It can also be a simple and
rewarding process. There are many, many places to go for
information on adoption, and I can't possibly list them all here.
However, a place to start on the internet is
Or call 1-800-ADOPT-NOW.
There are also ways in which current technology can help. If a
couple does not wish or cannot afford to adopt, and the mother would
like to carry the child as her own, sperm donation is an option. A
couple can choose a sperm donor from a clinic, and go in once a month to
have the sperm "injected" into the cervix until a pregnancy
occurs. Some families feel this is very similar to adoption, only
a step closer to biological, as the child will have at least one parent
as a biological parent. It is also possible to have an egg donor
with the father's sperm. HOWEVER, it is best to be aware that
sperm clinics will NOT test the sperm for the SMA gene in many
places. So if your donor happened to have the gene as well, you
could still be facing SMA. 1 in 40 people are carriers so the odds
would be in your favor. If this option interests you, ask your
family physician for a reference to your local infertility clinic.
You can then ask them about their policy regarding testing donor sperm
for the SMA gene.
Another technological process available is IVF or In-Vitro
Fertilization. In this process, sperm from the father and eggs
from the mother are collected. The eggs are fertilized with the
sperm. After the embryos have grown for several days to weeks,
they are genetically tested for the SMA gene deletion. Any healthy
non-SMA embryos are implanted into the mother's womb. Any embryos
who do show the SMA deletion can either be destroyed or frozen,
depending on your beliefs. Frozen embryos can later be used if and
when a cure is found, if desired. At this time, I know of only one
place in America where this is performed, though that may be quickly
changing, and that is at the Genetics
and IVF Institute in Fairfax, Virginia. Their website is at
The cost runs from $12,000 to $15,000 Per try, and is often not covered
by insurance. You must also go to and stay in Virginia during this
process. Another option for IVF with SMA testing is Monash
IVF. They are a facility in Australia, with branch facilities in
several countries. The cost
for treatment varies, currently it runs a total of somewhere around
$4000, however, up-to-date information can be obtained by
following the link to the Monash IVF web site at
or go directly to
follow the link to the Monash IVF Overseas Patients Information Page.
You can do the preliminaries in the US at
your local facility, but will still have to go there for the final
These last two options interlink with each other. A family
also has the option to go ahead and conceive on their own. When
pregnancy occurs, they have the option to have the baby tested
prenatally for SMA. A CVS can be performed at 10 weeks gestation,
with the results usually back within 2-3 weeks. At that time, if
the child has SMA, the parents then may decide to terminate the
pregnancy, or may decide not to, whatever their beliefs, and know the
answer within or close to the first trimester. An amniocentesis
can also be performed, though this is usually performed much later in
the pregnancy. Early Amniocentesis is still fairly new in some
areas, but the earliest it is usually done is 12-13 weeks, with a normal
amnio done at 16-18 weeks gestation. The results also take 2-3
weeks, so you will be well into the second trimester before getting test
results back. The same decisions apply. A more
detailed description of these tests is listed below. NOTE:
Just because you choose to test the baby does not mean you will or must
choose to terminate if SMA is present. The parents may know ahead
of time that they would not terminate no matter what, but need to know
the results of the test ahead of time to prepare-or for their sanity, to
be able to relax and enjoy the rest of the pregnancy without waiting 9
months or more wondering what the future will hold. This is where
these last two options intermingle.
The final option available to families is simply to proceed with a
pregnancy, do no testing, and accept the child they receive. After
the child is born, they can have the child tested for SMA with a blood
test, or they can simply wait to see if symptoms of SMA
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Diagnosis of SMA in Future Children
In order for these SMA tests
to be done like this, your other child/children currently or passed with SMA
MUST show the typical SMA gene deletion. If they do/did not, other
steps must be taken for prenatal diagnosis of SMA in future children.
CVS (Chronic Villi
Once a pregnancy has been confirmed, the woman will need to call her
OB-GYN for a referral to a local facility that can perform CVS genetic
testing. When she contacts the facility, they will inform her that
she will need to have her OB-GYN perform tests for any sexually
transmitted diseases (STD's) before she comes in for her
procedure. This is to protect the clinic doing the CVS as well as
the baby, because of how the procedure is performed. The
appointment for the CVS will be set up for no sooner than 10 weeks
gestation. At the actual appointment, the doctor will perform an
ultrasound to be sure that the baby is the correct size, is at least 10
weeks old, and is healthy. He will continue to monitor the baby
via ultrasound through the entire procedure. The CVS can be
performed either transvaginally or transabdominally. This means
either through the vagina (which is why she must be tested for STD's) or
the abdomen, depending on how the baby is lying. They will go into
the womb with a tiny suction & clamp device if it's done vaginally,
or with a needle if done abdominally, connected to a long hose, and
remove a small amount of the villi, which are on the placenta. The
placenta is made up of the same cells as the baby. They will grow
the cells for about a week, and then those cells will be sent off to a
laboratory to be tested for the SMA gene deletion. A blood sample
from the mother SHOULD BE taken so that they can compare the genetic
material of the mom with that of the baby, to be sure they are testing
the right thing (avoiding "maternal cell
contamination"). If it is available, they will also request a
blood sample from the existing child with SMA, to be able to compare how
SMA shows itself in their genes. This is for accuracy in
diagnosing. The results take 10 days to 3 weeks and the accuracy
is around 98%, with the error falling on the side of 'healthy' when the
child has SMA. (Maternal cell contamination that is not caught, or
the child didn't show the deletions but has SMA. If the deletions
are there, the accuracy of SMA is 100%). Error is extremely rare,
and I have personally only ever known of one case of it.
RISKS: There are risks to any procedure. There is a 1 in 200
chance of a miscarriage, (about a 2% risk), though these rates vary with
each facility. My local facility's miscarriage rates are about at
1 in 350, or 1/2% to 1% risk, which is the same risk of miscarriage that
a woman NOT going through the procedure would have. No higher
risk, in other words. So ask your facility for their testing
numbers. There is also about a 2% risk of maternal cell
contamination (which can be caught by comparing the results with the
mother's blood sample and would require a re-test), and other risks
include spotting, bleeding, infection, and cramping, all of which stop
within a day or two. There is also a (decreasing) chance of club
foot. Club foot has mostly been eliminated since they began doing
the procedure only after 9 weeks, and if it does occur, can be easily
fixed with braces at birth or in worst case a minor operation on the
Once a pregnancy has been
confirmed, the woman will need to call her OB-GYN for a referral to a
local facility that can perform amnio genetic testing.
Amniocentesis is typically performed around 16-18 weeks gestation.
The doctor will perform an ultrasound at the beginning to be sure that
the baby is at the appropriate age, size, and health, and will keep the
ultrasound going throughout the procedure to monitor the baby
throughout. Some places use a small needle to numb the abdomen
first, some do not. A large needle is then placed through the
abdomen and into the uterus, and an amount of amniotic fluid is
removed. The amniotic fluid contains cells shed by the baby.
These cells are grown (cultured) in the lab for approximately a week at
which time they are sent out to the lab to be tested for the SMA gene
deletion. If it is available, they will also request a blood
sample from the existing child with SMA, to be able to compare how SMA
shows itself in their particular family's genes. This is for
accuracy in diagnosing. The results take 2 to 3 weeks and the
accuracy is around 99%.
can also be performed now in many places at an earlier gestation.
You will have to contact your local facility to find out what they will
do. The earliest it is usually done is 12 weeks. Earlier
amnio has a higher rate of complications.
RISKS: There are risks to
any procedure. There is a 1 in 300 chance of a miscarriage, (about
a 1% risk), though these rates vary with each facility. My local facility's
miscarriage rates are about at 1 in 350-400, or 1/2% to 1% risk, which
is the same risk of miscarriage that a woman NOT going through the
procedure would have. No higher risk, in other words. So ask
your facility for their testing numbers. There is a smaller risk
of maternal cell contamination (which can be caught by comparing the
results with the mother's blood sample and would require a re-test) than
by CVS, though still possible. Other risks include spotting,
bleeding, infection, and cramping, all of which stop within a day or
two. Cramping is the most common. There is also a chance of
club foot. The earlier the procedure is done, the higher the risks
are for club foot and everything else. If club food does occur, it
can be easily fixed with braces at birth or in worst case a minor
operation on the foot.
For Both CVS &
A chromosomal study will also
be done, if you like. They will test for Down's Syndrome, Trisomy
18, and any other known chromosomal deformity. They will also
therefore be able to tell you the sex of the baby. The sex and
chromosomal study are usually done and available for you to know in
about one week.
Finally, you can request to have a "carrier" test done.
You will have to request this, as it is not typically done
otherwise. They will also test the SMA carrier status of your
baby...whether or not if they are healthy, if they also carry the
recessive gene like you do. This is another personal choice.
Some parents just want to give the child the option of being tested or
not when they become an adult and are ready to have their own family,
which is the only time this gene could possibly affect them.
Others wish to know up front so they can let the child know when they
get older that they too carry the gene.
People often ask "does it hurt?" I have found there is
no answer to that because every person has such a different
experience. For me personally, the amnio was slightly
uncomfortable only when the needle went into the uterus, but other than
that, was fine. The CVS was done transvaginally on me, and one
time was absolutely painless and the second time was mildly uncomfortable-because
of the position of the cervix and uterus and how they had to manipulate
things to get the sample. Some women have said it's a breeze while
others have said it was quite painful for them. In most cases, it
is simply slightly uncomfortable. Fear and tension can increase
the likelihood that the mother will feel that it is painful.
If you have any questions
on these procedures, need information on testing when the SMA gene deletion
is NOT present, or would like more details on anything, just
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