What is SMA

Information of SMA Disease

Understanding SMA

Spinal Muscular Atrophy (SMA) is a disease of the anterior horn cells. Anterior horn cells are located in the spinal cord. SMA affects the voluntary muscles for activities such as crawling, walking, head and neck control and swallowing.


It mainly affects the proximal muscles, or in other words the muscles closest to the point of origin, in this case those closest to the trunk of one's body. Weakness in the legs is generally greater than weakness in the arms. Some abnormal movements of the tongue, called tongue fasciculations may be present in patients with Type I and some patients with Type II. The senses/feelings are normal as is intellectual activity. In fact it is often observed that patients with SMA are unusually bright and sociable.

Type I Acute (Severe)

Type I SMA is also called Werdnig-Hoffmann Disease. The diagnosis of children with this type is usually made before 6 months of age and in the majority of cases before 3 months, there may be lack of fetal movement in the final months of pregnancy.


Usually a child with Type I, (Werdnig-Hoffmann) is never able to lift his/her head or accomplish normal physical milestones. Swallowing and feeding may be difficult and the child may show some difficulties with their own secretions. There is a general weakness in the intercostals and accessory respiratory muscles (the muscles situated between the ribs). The chest may appear concave(sunken in) due to the diaphragmatic (tummy) breathing.


Please note: Although diagnosis may be made before 6 months of age it does not necessarily follow the same course of severity for each patient.

Type II (Chronic)

Diagnosis of Type II is almost always made before 2 years of age with the majority of cases diagnosed by 15 months. Children with this type may sit unsupported although they are usually unable to come to a sitting position without assistance. At some point they may be able to stand. This is most often accomplished with the aid of bracing and/or parapodium/standing frame.


Feeding and swallowing problems are not usually characteristic of Type II although in some patients this can occur and a feeding tube may become necessary.


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.

Type III (Mild)

Diagnosis of Type III, often referred to as Kugelberg-Welander or Juvenile Spinal Muscular Atrophy, is made sometime after 18 months of age and as late as adolescence. 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 IV (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.


Adult Onset X-Linked SMA

This form also known as Kennedy's Syndrome or Bulbo-Spinal Muscular Atrophy, 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 often have breast enlargement known as gynecomastia. 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 nonprogressive.

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