In the spinal cord, MRI may reveal T2 hyperintensities in the anterior horns of the cervical cord, and to a lesser degree in the thoracolumbar cord, that are thought to correspond histopathologically to motor neuron loss in these regions 3. Intermediate forms may show ragged atrophy of muscles, while the severe forms often show gross atrophy 5,6. In muscles, the predominant features are those of muscle atrophy 5,6. Mild types tend to demonstrate fatty infiltration of muscular bundles with increased prominence of intramuscular fat planes 5,6. This mutated gene has a carrier frequency of 1 in 40 1,2. Spinal muscular atrophy has an autosomal recessive mode of inheritance due to mutations to the SMN1 (survival motor neuron 1) gene on chromosome 5 1,2. Some authors suggest an additional type 0, also termed 'severe infantile' form, with a prognosis (without novel therapy) of just a few weeks, although this has not been widely adopted in the literature 4. type 3 ( Kugelberg-Welander disease): juvenile form, onset after twelve months.type 2: intermediate form, onset between six and twelve months.type 1 ( Werdnig-Hoffman disease): infantile form, most severe and most common form, onset before six months.Spinal muscular atrophy is classified into four types with decreasing clinical severity and increasing age of onset 1,2: Rarely is intellectual disability a feature 3. In infants, the most common demographic affected, this classically manifests as difficulties sitting and rolling, assuming a frog-leg position, a weak cry, and increased respiratory effort with paradoxical breathing 1,3. Although the lower extremities can have greater involvement, axial, intercostal, and bulbar musculature are also frequently involved 1,2.
Spinal muscular atrophy typically affects infants and young children, presenting with progressive, symmetrical, proximal-predominant muscle atrophy and weakness of varying severity 1,2. This disorder affects 1 in 6000-10000 infants 1.