SMA goes by many names: Spinal Muscular Atrophy, SMA, and Werdnig-Hoffman Disease or Werdnig-Hoffman Paralysis.  They are all the exact same disease.  Below you will find links to information about SMA.  You can get as detailed-or not-as you wish to know.   Anyone wishing for a different or more detailed explanation, or anyone that has any questions, please e-mail me and I will do my best to answer your questions.  For the "Rest of the Information", go to and see the "SMA Info" pages.



SMA-The "Simple" Version

DNA Strand Graphic

SMA is a muscular disease passed on genetically to children by their parents.  You can not "catch" SMA by being around someone who has it.  It is a "Recessive" genetic disease, meaning that BOTH parents must carry a copy of the recessive SMA gene.  There is only a 25% chance each pregnancy of the child having SMA and a 75% chance each pregnancy that the child will be healthy.  One out of 40 people is a carrier of this recessive gene.  The brain is not affected, and they have been tested to have at least average to above average intelligence.  Please do not make the mistake of treating them as mentally impaired!!  Their bodies may not be perfect, but their minds are, so be sure to treat them that way!  SMA affects a child's muscular development, and the severity depends on what 'type' of SMA the child has.  There are four "Types" of SMA, Type 1,2,3 & 4.  The earlier  the symptoms are noticed, the more severe the type of SMA.  Type 1 is the most severe, affecting children while still in the womb or shortly after birth.  Type 4 is the least severe, affecting adults.


Type 1 children are diagnosed usually before 6 months of age, more often before 3 months of age.  Symptoms may even start in the womb.  Many mothers later recall the baby not moving as much the last month or so of pregnancy.  They are not able to hold up their heads, roll over, crawl, sit up without support, or walk.  All of their muscles are extremely weak, with the weakest muscles being the legs, upper arms, and neck.  Their chest may appear concave, or very skinny at the top, with a big belly.  Bell-shaped.  SMA affects all muscle systems as well including sucking, swallowing, digesting food, and excretion.  Constipation is a common problem as is being able to control excessive drooling (secretions), and getting proper nutrition and calories for proper weight gain.  A common cold can easily turn into pneumonia which is what usually takes the lives of these children, along with "respiratory failure" or when they no longer have the lung or chest muscles to be able to breathe on their own.  Two major decisions must be made with Type I children...whether or not to insert a feeding tube to prevent pneumonia and prevent starvation when they have lost their ability to suck or swallow; and whether or not to put them on a ventilator or other breathing machine when they experience respiratory failure.  Current statistics show that the average lifespan of a child with SMA Type I, not put on permanent ventilation or "life support", is only 8 months of age, with 80% dying by the age of one, and the majority of the rest dying by age 2.  HOWEVER, these statistics are not a hard and fast rule.  Each child is affected so differently by SMA that they do not all follow the same path or progression.  Also, as more is learned about SMA, the lifespan of a Type 1 child can be lengthened depending on the severity of the symptoms for each particular child.  Last but not least, the line between each Type of SMA is not clearly defined, and it is common for a child to exhibit patterns of two types, thus confusing the issue of "life expectancy" for that child.  

Type I children most often have very little leg movement, very little upper arm movement. Many times their hands remain fisted and their hands/wrists are turned the "wrong" way.  The physical characteristics that often "gives them away" to having SMA is a bell shaped body, legs that stay in the "frog" position, moving the arms from the elbows down only, and the head tilted to the side because of lack of neck muscles. They often have bright, expressive faces and eyes.    


Type 2 children are diagnosed before 2 years of age, usually more like 15 months.  These children are usually able to be in a sitting position without support, but often can not get there by themselves.  They can sometimes crawl with bracing and therapy, and on occasion may stand with braces.  Feeding and swallowing problems are not common in Type 2 children, though they are still possible.  They will usually never walk.  The lifespan of a Type 2 child varies so widely, there isn't one!  They could pass away at an early age or they could live well into adulthood.  As with all forms of SMA, weakness increases over time. 


Type 3 children are diagnosed between 18 months of age and early adolescence.  In the beginning these children are able to stand and walk but usually have difficulty doing so.  They typically have a normal lifespan; however, as with all forms of SMA, weakness gets progressively worse and they usually will be wheelchair bound.


Type 4 SMA is an adult SMA, with symptoms beginning around age 35.   They also usually have a normal lifespan; though, as with all forms of SMA, weakness gets progressively worse.

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SMA-The "Scientific" Version

DNA Strand Graphic

To see the actual medical textbook explanation of each of these types, click on the hyperlinks below associated with each type.

Spinal Muscular Atrophy (SMA) is one of the neuromuscular diseases. Muscles weaken and waste away (atrophy) due to degeneration of anterior horn cells or motor neurons which are nerve cells in the spinal cord. Normally, these motor neurons relay signals, which they receive from the brain, to the muscle cells. When these neurons fail to function, the muscles deteriorate. SMA effects the voluntary muscles for activities such as crawling, walking, head and neck control and swallowing.

SMA mainly affects the proximal muscles, or in other words the muscles closest to the trunk of the body. Weakness in the legs is generally greater than weakness in the arms. Some abnormal movements of the tongue, called tongue fasciculation's may be present in patients with Type I and some patients with Type II. The brain and the sensory nerves (that allow us to feel sensations such as touch, temperature, pain etc.) are not affected. Intelligence is normal.  In fact it is often observed that patients with SMA are unusually bright and sociable.

Type 1 Severe Infantile SMA, or Werdnig-Hoffman disease

  • Infantile spinal muscular atrophy (Werdnig-Hoffman disease) is the most severe form of SMA. It usually becomes evident in the first six months of life. The child is unable to roll or sit unsupported, and the severe muscle weakness eventually causes feeing and breathing problems. There is a general weakness in the intercostals and accessory respiratory muscles (the muscles situated between the ribs). The chest may appear concave due to the diaphragmatic breathing.  These children usually do not live beyond about 24 months of age.

Type 2 Intermediate type (this does not have a hyperlink so it is spelled out below instead.)

  • What are the features of intermediate (type 2) SMA?

    A child with the intermediate form of SMA often reaches six to twelve months of age, sometimes later, and learns to sit unsupported, before symptoms are noticed. Weakness of the muscles in the legs and trunk develops and this makes it difficult for the child to crawl properly or to walk normally, if at all. Weakness in the muscles of the arms occurs as well although this is not as severe as in the legs. Usually the muscles used in chewing and swallowing are not significantly affected early on. The muscles of the chest wall are affected, causing poor breathing function. Parents notice that the child is "floppy" or limp, the medical term for this being hypotonia.  Tongue fasciculations are less often found in children with Type II but a fine tremor in the outstretched fingers is common. Children with Type II are also diaphragmatic breathers.  Physical growth continues at a normal pace and, most importantly, mental functions is not affected. The children are bright and alert and it is important that they receive all the available opportunities to develop their intellectual capacities to their fullest extent. Integration into a normal school environment gives them the best chance to mature intellectually and emotionally.

    What does the future hold?

    The course of the disease is quite variable, and difficult to precisely predict from the start.  Children with the intermediate form of SMA usually sit unsupported. Weakness of the legs and trunk usually, but not always, holds the child back from standing and walking alone. Sometimes the muscle weakness can seem to be non-progressive, but in most cases weakness and disability will increase over many years. Severe illness with prolonged periods of relative immobility, putting on excessive weight or growth spurts may contribute to deterioration in function.  Due to weakness of the muscles supporting the bones of the spinal column, scoliosis (curvature of the spine) often develops in children who are wheelchair bound. If this becomes severe it can cause discomfort and can have a bad influence on breathing function as well. An operation can be done to straighten the spine and prevent further deterioration.  Recurrent chest infections may occur, because of decreased respiratory function and difficulty in coughing. Parents will have been shown how to encourage their child to maintain his/her maximum respiratory function as well as how they can perform postural drainage of the chest. They should start this as the first sign of any chest problem. Antibiotics and inhalation therapy may also be needed. Sometimes hospitalization is required to best manage and care for the child.  The long term outlook depends mainly on the severity of weakness of the muscles of the chest wall and on the development of scoliosis. Lifespan is always difficult to predict. Mildly affected children may live into adult years. The more severely affected children may die, due to pneumonia and other chest problems, before or in their teens.

Type 3 Mild Juvenile SMA, or Kugelberg-Welander disease

  • Juvenile spinal muscular atrophy (Kugelberg-Welander disease) usually has its onset after 2 years of age. It is considerably milder than the infantile or intermediate forms. In juvenile spinal muscular atrophy children are able to walk, although with difficulty.  The patient with Type III can stand alone and walk, but may show difficulty with walking and/or getting up from a sitting or bent over position. With Type III, a fine tremor can be seen in the outstretched fingers but tongue fasciculations are seldom seen.

Type 4 Adult Onset

  • Typically in the adult form symptoms begin after age 35. It is very rare for Spinal Muscular Atrophy to begin between the ages of 18 and 30. Adult SMA is characterized by insidious onset and very slow progression. The bulbar muscles, those muscles used for swallowing and respiratory function, are rarely affected in Type IV.

Type 5 Kennedy's Syndrome or Bulbo-Spinal Muscular Atrophy

  • This form also known as Adult Onset X-Linked SMA, occurs only in males, although 50% of female offspring are carriers. This form of SMA is associated with a mutation in the gene that codes for part of the androgen receptor and therefore these male patients have feminine characteristics, such as enlarged breasts. Also noticeably affected are the facial and tongue muscles. Like all forms of SMA the course of the disease is variable, but in general tends to be slowly progressive or non-progressive.

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Diagnosing SMA

This information is not to take the place of actual medical advice.  If you have a question, always consult with your physician.


Physical Characteristics:

The common physical characteristics of SMA include:

  • "Frog" shaped legs (knees apart and legs bent)

  • a sunken or narrow chest

  • a big belly

  • breathing with the belly instead of the lungs

  • a weak cry and weak cough

  • poor to no head/neck control; head tilted to one side

  • weak if any movement of the legs and upper arms

  • not able to bear any weight on legs or arms

  • hands that remain clenched or turned the wrong way

  • difficulty sucking and swallowing 

  • tongue fasciculations (tongue vibrating rapidly).

These characteristics vary in severity depending on how advanced the SMA is in each child.  Some of these characteristics may not show up until later.  

Medical Testing:

There are several medical tests that can be performed to diagnose SMA.  Following are a listing of the tests along with an explanation of how they are performed and their accuracy:

EMG (Electromyography)

An EMG test measures the electrical activity of muscle. In this procedure small needles are gently  inserted into the patient's muscles (usually the arms and thighs) while an electrical pattern is observed and recorded by a specialist.

At the same time, a nerve conduction velocity (NVC) will probably also be performed. This uses the same needles and equipment.  In this test the response of a nerve to an electrical stimulus is measured. When performing this test on a child, if at all possible, it should be performed by a doctor experienced in dealing with children. If permitted, hold your child on your lap during the procedure, to make an unpleasant procedure somewhat bearable. Your doctor may allow your child to be given a mild pain killer or sedative prior to the test.

Genetic Blood Test

Within the last decade, a blood test has now become available to detect SMA.  This blood test works by detecting deletions in gene sequences that are not missing in normal, healthy individuals.  This blood test can not tell the Type of SMA that the individual has (Type I, II, or III), and approximately 5% of individuals who do have SMA do not show the gene deletions.  However, for the 95% of individuals who do show the deletions, the diagnosis is 100% accurate, and the Type of SMA can be determined by other physical factors.  With a blood test to screen for SMN deletion together with an EMG and a clinical examination it may not be necessary for a muscle biopsy to be performed.  If the results show that there is no deletion of the SMN gene, but the clinical examination and the EMG still point to SMA, than a muscle biopsy would be necessary to confirm the diagnosis.

Muscle Biopsy

This is a surgical procedure where an incision approximately 3 inches long is made, and a small section of muscle is removed.  Usually they remove the muscle from the upper thigh. The biopsy is used to check for degeneration of muscles and special tell-tale signs in the muscles of SMA.  It is important to find a doctor used to dealing with children, and experienced in dealing with SMA. Although many doctors may persuade you of the necessity of a general anesthetic, this procedure can be done with a local anesthetic. This is especially important when dealing with children who are possibly suffering from SMA which includes by nature a weak respiratory system.  General anesthesia is not recommended for children with neuromuscular diseases such as SMA as it may be difficult for them to recover.


Needle Biopsy

There is now an alternative to a muscle biopsy. Instead of a 2-3 inch incision, only a small nick in the skin is necessary.  Be sure to ask your doctor about this possibility.


Bottom Line:

You have several options when testing for SMA.  My PERSONAL opinion and recommendation, is that the blood test is by far the easiest, least painful and least invasive of all the options, and accurately diagnoses SMA in 95% of cases.  I would recommend going with the blood test first.  If the blood test comes back negative for SMA, then a muscle biopsy/EMG will be necessary. Of course, at all times follow your doctor's orders!

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Future Children/SMA Testing

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.


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 and  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, 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.  They work with people outside their country as well.  The current cost for a basic IVF in Australia is around $2300 American dollars (this varies with the exchange rate of American vs. Australian dollars).  You can do the preliminaries in the US at your local facility, but will still have to go there for the final procedure.  Their website is at  


  • 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.  


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%.

    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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