What is SMA?

Spinal Muscular Atrophy

We had never heard of SMA before Annabelle was diagnosed.  The research is unpleasant to put it nicely, but I've listed some basic information that will help explain her condition.

SMA is a motor neuron disease which causes weakness and atrophy of the muscles.  Those with SMA are grouped into four types (I, II, III, IV) based on the highest level of motor function they express at the time of diagnosis. 

Outwardly, it affects muscle tone of the neck, arms, and legs.  Breathing and swallowing are also accomplished with muscles which puts SMA patients at huge risk for respiratory problems.

Annabelle's hypotonia (low muscle tone; weakness) was what concerned the doctors.  Very few conditions cause distinct, prolonged hypotonia in infants, so there was a short list of disorders to test for.  The fact that she ate so well confused the doctors - in patients her age, weak suck and swallow reflex is one of the key indicators.

SMA does not affect cognitive functions or touch or pain receptors.  

Annabelle could feel our caresses and cuddles as much as any other baby.  She was a very happy girl which is good indication that she didn't experience excessive pain.

It is a rare disorder occurring in approximately 8/100,000 live births.  It is one of the most common rare diseases and the #1 genetic killer of infants.  It is caused by a missing or mutated SMN1 gene.

Surprisingly, 1/40 people are genetic carriers of the recessive trait that causes SMA.  When 2 carriers of the recessive trait conceive a child, there is a 25% chance of that child expressing SMA, and a 50% chance of that child being a carrier.  Carriers are not physically affected by the trait.

Ryan and I are both carriers of the recessive gene mutation.  We have no family history of SMA and there was no way we could have known that we were carriers until we were genetically tested.  Even amniocentesis done during pregnancy does not routinely screen for SMA (although we didn't have this testing done) so nothing could have warned us about what was to come.   Now, however, we are aware and this knowledge decisively impacts our decisions regarding future children (you can read about Our Options soon when I reestablish that link).

Let me take this moment to say that, despite the pain and sorrow we have experienced, I am so grateful we walked into parenthood ignorant of our genetic propensity to pass on SMA.  Had we been tested prior to having children (some advocate this), we may never have taken the risk which blessed us with 2 beautiful daughters.  Yes, knowing has changed us, but I would not advocate diving into your genetic makeup unless you have reason to believe there could be a significant risk.

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Families of SMA
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