Spinal Muscular Atrophy Type 4 / Adult Onset SMA

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As we’ve previously discussed, children with type 1 SMA never sit, children with type 2 SMA never walk independently, however children with type 3 and type 4 SMA achieve independent ambulation. They are able to walk without assistance, at least for some time in their lives.

Children with type 3 SMA are oftentimes arbitrarily categorized as having type 3-a or type 3-b SMA. In children with type 3-a SMA, there are usually symptoms present of weakness or decreased endurance before the age of 3. And typically, the child with type 3-b is perfectly normal for the first three years of life. Is it important to make this distinction? Perhaps, in that, prolonged independent ambulation for years or even decades is far more common if a child is a-symptomatic until the age of 3.

The variability of clinical presentation and disease progression in children with type 3 SMA and young or midlife adults with type 4 SMA makes a “one treatment plan fits all” impossible, and I believe that this group of patients is best handled through a physician knowledgeable about neuromuscular diseases in general and SMA in particular. From that team medical captain, there may be the need for individual consultation with some of the specialists that we mentioned in the type 1 or type 2 children: a pulmonist, a physical therapist, a nutritionist, an orthopedist, but again I think these are decisions which must be made on a case-by-case basis.

As with all aspects of SMA, the later the onset of symptoms, the more benign the long-term prognosis tends to be. We fully expect that our patients with type 3 and type 4 SMA will live a normal life span, and it’s our job as healthcare professionals to ensure that longevity is accompanied by productivity and a full involvement with life and all it has to offer. The SMA type 3 and type 4 patients are probably going to provide critical information as to the mechanisms of SMA. It is also possible, that a better understanding of the type 3 and type 4 patient, understanding why their disease is so much more benign than the type 1 and type 2 patient, might provide additional windows of insight into therapeutic strategies.

There is information contained on this website regarding our hopes for the future, the scientific breakthroughs which have led to a tremendously augmented understanding as to why SMA happens in the first place, and how we might be able to someday intervene with meaningful therapeutic treatments. There’s information on our site on ways we can support each other through parent meetings: through the FightSMA annual conferences held every year in Washington, DC, and how we can share this information through patient registries to ensure that we do win the battle against SMA. I thank you for your attention and I invite you to spend some more time perusing other aspects of this website and to become as familiar and fluent with the information contained as possible.

Although the preceding classification of spinal muscular atrophy is useful to patients, families, and the medical team working with them, it must be emphasized that SMA Types I, II, and III (and in some cases SMA Type – IV) represent a continuum. Additional understanding of the gene defects will undoubtedly explain the tremendous clinical variation that children and young adults with SMA demonstrate.

The above was prepared for FightSMA by: Robert T. Leshner, M.D., Professor, Neurology and Pediatrics, Children’s National Medical Center. Special thanks to Metro Productions for the pro bono production of Dr. Leshner’s video.