A. Spinal Muscular Atrophy 1.
B. Hereditary neuropathy.
C. Guillain Barre Syndrome.
The neuromuscular disorder seen in a child with motor delay as seen in the picture above represents Spinal Muscular Atrophy 1.
Deficiency of SMN protein occurs when a mutation (flaw) is present in both copies of the SMN1 gene — one on each chromosome 5. Normally, most of the protein made from SMN1 genes is full-length and functional, but when mutations occur, little or no full-length, functional SMN protein is produced.
This loss can be partially offset by the presence of neighboring SMN2 genes, which are similar in structure to SMN1 genes. Most of the protein made from SMN2 genes is short and not functional, but some is full-length and functional. The number of SMN2 genes varies from person to person.
In chromosome 5-related SMA, the more copies of the SMN2 gene that a person has, the more functional SMN protein is available, the later the onset of disease symptoms, and the milder the disease course is likely to be.
When SMA symptoms are present at birth or by the age of 6 months, the disease is called type 1 SMA (also called infantile onset or Werdnig-Hoffmann disease). Babies typically have generalized muscle weakness, a weak cry and breathing distress.
They often have difficulty swallowing and sucking, and don’t reach the developmental milestone of being able to sit up unassisted. Typically these babies have two copies of the SMN2 gene, one on each chromosome 5. Over half of all new SMA cases are SMA type 1.