Use of genetic variation as biomarkers for mild cognitive impairment and progression of mild cognitive impairment to dementia

Abstract

Cognitive impairment is prevalent in the elderly. The high estimates of conversion to dementia have spurred the interest in identification of genetic risk factors associated with development of cognitive impairment and or its progression. However, despite notable achievements in human genetics over the years, in particular technological advances in gene mapping and in statistical methods that relate genetic variants to disease, to date only a small proportion of the genetic contribution to late-life cognitive impairment can be explained. A likely explanation for the difficulty in gene identification is that it is a multifactorial disorder with both genetic and environmental components, in which several genes with small effects each are likely to contribute to the quantitative traits associated with the disease. The motivation for identifying the underlying genetic risk factors elderly is clear. Not only could it shed light on disease pathogenesis, but it may also provide potential targets for effective treatment, screening, and prevention. In this article we review the current knowledge on underlying genetic variants and the usefulness of genetic variation as diagnostic tools and biomarkers. In addition, we discuss the potentials and difficulties researchers face in designing appropriate studies for gene discovery.

Figure 1

Pooled odds ratios (95% CI) of the 40 studies included in the meta-analysis by Farrer et al.[54] relating APOE genotype with LOAD (ε4 allele vs. ε3 allele). †No data provided; ‡HWE deviation in controls (p≤0.05)

Figure 2

Role of SORL1 in transmembrane sorting of APP. The green arrows track re-entry of APP from the cell surface when SORL1 is present. The red arrows show that, when SORL1 is absent, more APP moves into domains such as the late endosome/lysosome, where the black arrows show how it is subsequently cut by beta-secretase (BACE1) and gamma-secretase (PS1 γ-sec), generating the neurotoxic amyloid beta-peptide (Aβ). [Illustration adapted from Rogaeva et al.[89]]