Apolipoprotein E-Genotyping and MRI Study for Alzheimer’s Disease Classification: PCR-RFLP and Restricted Enzymes AfIII for RS429358 and HaeII for RS7412
Authors: Mohad Azmi NH , Suppiah S , Ibrahim NSN , Ibrahim B , Seriramulu VP , Mohamad M , Karuppiah T , Omar NF , Ibrahim N , Razali RM , Harrun NH , Sallehuddin H , Syed Nasser N , Piersson AD 
Published: January 2024

The most common type of dementia in neurodegenerative diseases is Alzheimer’s disease (AD), a progressive neurological illness that causes memory loss. Neurophysiological tests, including the montreal cognitive assessment (MoCA), mini-mental state examination (MMSE), and clinical dementia rating (CDR) scores, are used to identify AD. Neuroimaging studies T1-weighted MRI scans assessed brain structural abnormalities. AD patients had grey matter volume (GMV) loss in brain structures when structural MRI data were analysed using voxel-based morphometry (VBM). Neuroimaging studies using resting state functional MRI (rs-fMRI)-blood oxygen level dependent (BOLD) sequence for brain imaging were processed using the seed-based analysis (SBA) method to analyse functional connectivity (FC) in the default mode network (DMN), sensorimotor network (SEN), executive control network (ECN), language network (LN), visuospatial network (VN), and salience network (SAN). Late-onset AD can be studied using the apolipoprotein E gene (ApoE). ApoE has four alleles with LOAD patients having either a homozygous or heterozygous genotype of these alleles. The genotypes, particularly ApoE ε4, are associated with a more significant risk for AD pathogenesis. The combination of genotyping and MRI neuroimaging is a promising avenue for research that starts with protocol optimisation. Objective: to differentiate changes in structural brain volumetric and rs-fMRI functional connectivity strength with the diagnosis of AD and HC by combining ApoE ε4 genetic variations.

Materials and Methods

Thirty participants with AD, n = 15, and healthy control (HC), n = 15, for the MRI study, and six participants (n = 6) with AD, n = 3, and HC, n = 3, for ApoE genotyping. In this study, we categorised the participants using neuropsychological tests, i.e., MoCA, MMSE, and CDR. We performed structural and functional MRI brain imaging to identify network areas affected by AD. Structural voxel-based morphometry (VBM) models and the CONN Toolbox, which analysed functional MRI using seed-based analysis (SBA), were performed. Genotyping was done by extracting the DNA from the participants’ blood samples. The isolated DNA underwent PCR-RFLP. Then, the restricted enzymes RE AFIII for rs429358 and HAEII for rs7412 were performed.

Results

There was decreased grey matter volume (GMV) and reduced functional connectivity among AD participants involving the frontal lobe and anterior cingulate gyrus in DMN, SEN, ECN, LN, VN, and SAN. We detected three participants with a homozygous ApoE ε4 negative genotype (non-carriers), which was consistent with the HC genotype. We also detected heterozygous genotype ApoE ε4 positive carriers, which indicated LOAD.

Conclusion

There is altered GMV in VBM, a decrease in brain activation, and an increase in spatial activation size in rs-fMRI neuronal FC in some areas of the brain with ApoE ε4 carriers in AD participants. Thus, the imaging features of the AD participants are well mapped to their ApoE ε4 carrier status. Thus, we propose our radiogenomics techniques as a useful biomarker for the characterisation of AD patients.