Spinal muscular atrophy

Spinal Muscular Atrophy – SMA is a motoneuron disease i.e. disease of neurons, which are responsible for conscious movements of muscles e.g. running, head movement and swallowing. The prevalence is approximately 1 newborn for 6000 live births and approximately 1 person of 40 people is the carrier of the disease. SMA affects all the bone muscles i.e. proximal muscles (shoulders, hips, back muscles) are often affected the most. Infirmity of lower extremities is generally greater than of the arms. Swallowing muscles and muscles of the neck could be also affected. Sense perception and skin sensitivity as well as intellect abilities are not affected. On the other hand it is frequently observed that patients with SMA are extraordinary psychically agile and friendly.

Rough division of patients into 4 groups is based on a concrete level of kinetic development, reached by the patient (Schwersenz, 2006). Electromyography (EMG) examination and molecularly-genetic examination help to diagnose this type of disease. This examination determines a lower number of active motor activities and the presence of disproportionally big action potential with the amplitude of 10-15mV. Molecularly genetic examination uses the PCR (polymerase chain reaction) or the MLPA (multiplex ligation-dependent probe amplification), which determines the presence of axon delegation 7 and 8 in the SMN gene, and by this confirms the diagnosis of spinal muscular atrophy with a 95% probability (Kraus, 2006).

Type I – Acute infant form (Werdnig-Hoffmann Disease)

The diagnosis of children with this type is usually made before 6 months of age and in the majority of cases the diagnosis is made before 3 months of age. Type I SMA is also called Werdnig-Hoffmann Disease. It comprises almost one forth of all the cases. The prevalence in population is estimated at 1:25000 live births. Decrease of spontaneous movements is noticed in some children already in the uterus and in 2/3 the hypotonic syndrome is present directly after birth. Progression is present in the first months of life. Spontaneous movements are limited to minimum and the bulbar functions are also affected. Generally these children have very weak to no control of their head. They are unable to sit without support and feet do not bear any weight. Swallowing and food intake could be hindered.

There could be difficulties managing their own secretions. Atrophy of the tongue could be present as well as slight tremor of tongue – fasciculation. There is weakness of the intercostal muscles (the muscles between the ribs) that help expand the chest, and the chest is often smaller than usual. Therefore development of lungs is limited and slight caught is present (Trust 2006). Breathing can be weakened to an extent, that oxygenation is insufficient. Usually around the 1st year of age associated infections cause exitus (Vejrostova 2006).

Type II – temporary late infant form (chronic form of Werdnig-Hoffmann Disease)

The Diagnosis of Type II SMA is almost always made before 2 years of age. It comprises nearly half of all the diagnosed cases. Clinical manifestation usually appears around the infant age of the child. Children with this type may sit unsupported when placed in a seated position, although they are often unable to come to a sitting position without assistance. In toddlers and pre-school children the peripheral lesion first affects the root muscles of lower extremities and is manifested by deterioration of walking. At some point they may be able to stand. This is accomplished with the aid of assistance or bracing. Swallowing problems are not usually characteristic of Type II, but vary from child to child. Some patients may have difficulty eating enough food by mouth to maintain their weight and grow and a feeding tube may become necessary. Children with Type II SMA frequently have tongue fasciculation and manifest a fine tremor in the outstretched fingers. Children with Type II also have weak intercostals muscles and are diaphragmatic breathers. They may have problems to hem and to maintain saturation during sleep. Scoliosis develops during growth. Boys are affected more often and the clinical course of their disease is more difficult. Surgeries or using of corset may be needed. Lower bone density can lead to increased risk of fractures (Schwersenz 2006).

Type III – Juvenile Spinal Muscular Atrophy (Kugelberg-Welander Disease)

The diagnosis of Type III is much more variable in age of onset and can be present in children from around one year of age or even as late as adolescence. This disease is a chronic type and is manifested in children or adolescents. It influences root muscles of lower extremities, which could be asymmetric. In most cases during the course of years Type III patients’ proximal muscles of upper extremities, mimic muscles and tongue can be affected. This type forms only 10 % of spinal muscle atrophies.Diagnosis prior to age of 3 years is typical. The patient with Type III can walk alone and run, but may show difficulty with running at some point in their clinical course, they may fall more frequently. They may have difficulty in getting up from sitting on the floor or a bent over position. With Type III a fine tremor can be seen in the outstretched fingers but tongue fasciculation are seldom seen. Feeding or swallowing difficulties are very uncommon (Schwersenz 2006).

Type IV – adult onset (Aran-Duchenn Disease)

In the adult form, symptoms typically begin after the age of 35. It is rare for Spinal Muscular Atrophy to begin between the ages of 18 and 30. The bulbar muscles, those muscles used for swallowing and respiratory function, are rarely affected in Type IV. It is usually thought to be a form of Type III. However, Type IV has distal prevalence with fine muscles of the arms are affected first sometimes muscles of the leg are affected first. This type has a benign progress and patients are not disabled dramatically as well as their age is not shortened. Typical clinical symptom is minipolymyoklonus, which explicitly negates the myogenous source of the disease (Jedlička, Keller 2005).