Alzheimer’s disease is the most common cause of dementia in elderly people and often results in a gradual decline in cognitive function in sufferers. Current treatment options are limited to the alleviation of symptoms or slowing down disease progression, with no cure available. Therefore, the timely identification of at-risk patients is critical in order to provide the information necessary to improve patient care.
Apolipoprotein E plays a key role in lipid metabolism and is recognised as one of the most powerful genetic risk factors for dementia and other neurodegenerative diseases. In particular, a genotype known as apolipoprotein E4 (ApoE4) has been identified as a risk factor for developing Alzheimer’s disease. It has become one of the most widely studied gene variants in Alzheimer’s disease and constitutes a major consideration for preventive medicine. When a patient inherits the ApoE4 variant from one parent they have a three times greater risk of developing Alzheimer's disease, whereas a patient who inherits ApoE4 from both parents is 8-to-12 times more likely to develop the disease. Therefore, the availability of analytical methods for rapid and reliable ApoE4 classification is extremely advantageous.
This study reports the applicability of Biochip Array Technology (BAT) to the simultaneous determination of ApoE4 and ApoE proteins from a single plasma sample employing a biochip-based immunoassay to directly identify whether patients are ApoE4 heterozygous, homozygous or null. This approach has demonstrated that it can be as accurate as existing molecular tests which analyse DNA in order to identify patients carrying the ApoE4 gene.
In the development of this biochip-based test, an initial cohort of 272 samples of a known genotype was used to establish assay parameters. This work was carried out in collaboration with our research colleagues at the Medical University of Vienna where the samples were classified using standard molecular diagnostic techniques. A ratio was determined using the total ApoE and ApoE4 protein levels enabling the correct identification of 100% of the samples as ApoE4 heterozygous, homozygous or null. To further verify the accuracy of the ApoE4 test, an additional cohort of 112 samples of unknown genotype were run. These samples were genotyped by extracting circulating cell free DNA and based on a combination of multiplex PCR and biochip array hybridisation, enabled the simultaneous detection of APOE specific single nucleotide polymorphisms. Full agreement between these two different testing methods was also observed with samples correctly identified as heterozygous, homozygous or null for ApoE4. Using the combined cohort of 384 patients, ROC analysis demonstrated that samples could be identified as ApoE4 positive or negative with 100% sensitivity and 100% specificity, all in approximately 3 hours.
Using BAT, this new ApoE4 test can offer a more efficient and economical approach to standard DNA testing. In combination with medical and family history, medication and lifestyle, this can deliver valuable information for personalised medicine approaches.