Contents

History
Symptoms
Etiology
Prognosis
Treatment Options

History

The disease was first discovered by two Austrian neurologists, Johann Hoffman and Guido Werdnig in 1891

Guido Werdnig - First to describe SMA in the cases of 2 infant brothers (1891)
Johann Hoffmann - Observed 7 other cases (1893 - 1900)
Type 1 is named after them: Werdnig-Hoffmann Disease

Classification system - At the International Consortium on Spinal Muscular Atrophy (1991)
First 3 types were based off the highest level of motor function the individual is capable of
Type IV - created for adult onset cases
Type 0 - prenatal onset, death occurring within weeks of birth.

Symptoms

Type I: Born with very little muscle tone, weak muscles, and feeding and breathing problems.
Type II: Symptoms may not appear until age 6 months to 2 years.
Type III: Milder disease that starts in childhood or adolescence and slowly gets worse.
Type IV: Even milder, with weakness starting in adulthood.

Symptoms in an Infant:
Breathing difficulty
Feeding difficulty
Floppy Infant (Poor muscle tone)
Lack of head control
Little movement
Weakness that gets worse

Symptoms in an child:
Frequent and increasingly severe respiratory diseases
Nasal speech
Posture that gets worse

Other symptoms:
Areflexia
Poor muscle tone
Missing developmental milestones
Bell-shaped torso
Clenched fists
Head tilts to one side
Twitching of the tongue
Trouble with swallowing and breathing
Low weight
Arthrogryposis

Etiology

SMA is caused by the mutation the SMN1 gene. It produces a protein that aids in mRNA development. This special mRNA development is directly responsible for the production of a motor neuron. Since it is mutated, the gene does not produce a functional protein that does not aid in the mRNA production. The affected motor neurons are located in the spinal cord and near the brainstem.

Type I: Severe form that is evident at birth. They incur serious muscular development problems. They have problems with breathing and swallowing

There are at least 65 mutations on the SMN1 gene that can cause SMA; both SMN1 & 2 are located on chromosome 5.

The source of SMA can be traced to the gene survival of motor neurons 1 & 2. They code for the same protein. The protein is found all over the body, but with exceptionally high levels of it in the spinal cord and brainstem. In the nervous system, the proteins are located in the neuromuscular junctions in neurons’ growth corner, axons, and dendrites. Several suggest a lack of the SMN protein may cause the death of motor neurons. The protein’s main function is that is is used to make spliceosomes, which carry out mRNA processing. mRNA molecules contain introns, non-coding segments, and exons, coding segments. Before mRNA can be translated, spliceosomes must remove the introns and join the exons. The SMN1 gene is the primary producer of the SMN protein. It only differs from the SMN2 by one nucleotide. The change in the SMN2 amino acid sequence but never causes exon #7 to be left out. The mRNA nucleotide is incomplete and produces proteins that are too small and highly unstable. 95% of the people afflicted with SMA are homozygous for one of 65 mutations in the SMN1 gene. Because most of the SMN2 genes are nonfunctional not only is it unstable to do its job, but spliceosomes cannot do theirs either. The onset of MSA follows shortly. Because the SMN2 gene can produce a small amount of functional proteins, the amount of SMN2 genes and individual had affects both the severity of the disease and how late the symptoms start. People usually have 2 copies of the SMN1 gene, and 1-4 of the SMN2 gene. The more copies the person had, the less severe the disease and the later they will feel its