Spinal cord dating
In order to account for these differences, the chromosome 5 SMA often is classified into types 1 through 4.
The age at which SMA symptoms begin roughly correlates with the degree to which motor function is affected: The earlier the age of onset, the greater the impact on motor function.
The first breakthrough in the disease came in the form of spinal cord injections of the newly approved drug nusinersen, which restores some motor function and prolongs life.
"If we can figure out what is going wrong, then maybe we can have combinatorial therapies -- one that raises SMN levels and one that helps neurons survive the challenge of too little SMN," Anne Hart, professor of neuroscience at Brown University, said in a press release.
For example, if you have a neurological disorder that causes mental limitations, such as Huntington’s disease, which may limit executive functioning (e.g., regulating attention, planning, inhibiting responses, decision-making), we evaluate your limitations using the functional criteria under these listings (see 11.00G).
Under this body system, we evaluate the limitations resulting from the impact of the neurological disease process itself.
The disease affects one in 8,000 children and occurs when mutations in both copies of the gene responsible for the survival motor neuron, or SMN, protein stops its production resulting in the dysfunction of motor neurons that control muscles along with atrophy and weakness.
In its most acute form, children die by age 2 when muscles that control breathing become compromised.
A communication impairment may occur when a medically determinable neurological impairment results in dysfunction in the parts of the brain responsible for speech and language.
Researchers discovered that the link between the SMA and the regulation of protein translation was the Gemin3 protein.
"If you decrease the activity of these receptors, it could be beneficial," Hart said.
Children who display symptoms at birth or in infancy typically have the lowest level of functioning (type 1).
SMA onset in children (types 2 and 3), teens or adults (type 4) generally correlates with increasingly higher levels of motor function. Chromosome 5 SMA is caused by a deficiency of a motor neuron protein called , for “survival of motor neuron.” This protein, as its name implies, seems to be necessary for normal motor neuron function.