Advances in genetics regarding recovery from Traumatic Brain Injury
In 2006, research conducted by Diaz-Arrastia and Baxter at the Department of Neurology, University of Texas Southwestern Medical Center, identified a link between the presence of apolipoprotein E4 allele (APOE ε4) and a person’s neurological recovery after experiencing a traumatic brain injury (TBI). A traumatic brain injury is an injury sustained by an external source that may result in a degeneration of bodily function, both physical and physchological (National Institutes of Health, 1998). The journal further highlights that whilst this connection between genetics and TBI has been discovered, it is not the only factor that affects outcomes in TBI sufferers. To date, the advances in the link between genetics and TBI are only viable on animal subjects and further research is being conducted to see if these findings have relevance to humans.
The link between apolipoprotein E4 allele (APOE ε4) and a poor neurological outcome was first raised after a study by Corderhighlighted that “inheritance of apolipoprotein E4 allele (APOE ε4 ) significantly increased the risk of developing sporadic, late-onset Alzheimer’s disease”( Corder EH, 1993, 921-923). The research journal makes a point of noting that whilst the findings of the experiment indicate higher risk of a poorer outcome in subjects who are born with APOE ε4, it does not mean that if they experience TBI that they will be less susceptible to treatment. This is noteworthy due to the misinterpretation of findings from APOE genotyping that has already occurred. Such misinterpretation has led to incorrect diagnosis and subsequently erroneous treatment, care and rehabilitation (Diaz-Arrastia, 2006, 362-363)
Previous genetic studies have collected data through generic linkage analysis (Diaz-Arrastia, 2006, 364). This study has utilized an alternate approach from the Human Genome Project. This approach is titled “allelic association” and assumes the polymorphic nature of human genes. Polymorphism in genes has been highlighted as the reason for differences in the way people react to many medical conditions and diseases. The journal then investigates the advantages and disadvantages of allelic association, highlighting the limitations brought up by adequate sample sizes. It concludes that to yield accurate data “a significance level of P=5 x 10-8” would need to be achieved. It is noted that to attain this value a sample size of almost 100,000 subjects would need to be managed.
Neurobiological studies have found apolipoproteins are the carrier cells inside the central nervous system (CNS), specifically apolipoprotein E (apoE), which has three allelic variants, aopE2, aopE3 and aopE4. Through research, it has been found that there is a difference in the function of apoE4 and the other two proteins (Diaz-Arrastia, 2006, 365). Particularly in tests conducted on mice carrying apoE3, it was found that the mice displayed better neurological outcomes then those with apoE4. This, together with the work of many other studies, has led to the establishment of a connection between the presence of APOE ε4 and many other neurodegenerative diseases.