Odds 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 and sH.  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 together:  ss.  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 SMA.  

Or, as stated before, a 75% chance of a healthy child and a 25% chance of an SMA child.

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Your 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.

• No More:
  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.

• Adoption:
  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 www.adoption.org and www.adoption.com.  Or call 1-800-ADOPT-NOW.

• Sperm/Egg Donation:
  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.

• IVF:
  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 www.givf.com.  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 http://www.monashivf.edu.au/ or go directly to http://www.monashivf.edu.au/program/started/overseas.html and 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 procedure.

• Test:
  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.

• No-test:
  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 start.  

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Prenatal 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 Sampling)
  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 foot. 

• Amniocentesis
  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%.
  
  "Early Amniocentesis" 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 & Amnio:
  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 e-mail.

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