Mild Cognitive Impairment is not a Valid Concept and Should be Replaced by a More Restrictive, Biologically Validated Class, Named Mild Cognitive Dysfunctions (MCD): A Nomothetic Network Approach

Background: No studies have examined whether interactions between the apolipoprotein E4 (ApoE4) allele and peripheral biomarkers, hypertension, and type 2 diabetes mellitus (T2DM) may impact the neurocognitive, behavioral and social dysfunctions in amnestic mild cognitive impairment (aMCI) and Alzheimer disease (AD). Aims: To clinically define and biologically validate a subgroup of aMCI subjects that take up an intermediate position between controls and AD patients. Methods: In 61 healthy controls, 60 subjects with aMCI, and 60 AD patients we measured the features of aMCI/AD using the Consortium to Establish a Registry for Alzheimer’s Disease (CERAD). A composite BIORISK score was computed using the ApoE4 allele, serum folate, albumin, white blood cells, fasting blood glucose (FBG), atherogenic index of plasma (AIP), T2DM and hypertension. Results: Clustering and nearest neighbour analyses were unable to validate the aMCI subgroup. We constructed two z unit-based composite scores, the first indicating overall burden of cognitive, social, and behavioural deterioration (OBD), and a second reflecting the interactions between ApoE4, all other biomarkers, hypertension and T2DM (BIORISK). We found that 40.2% of the variance in the OBD score was explained by BIORISK, ApoE4, age and education. The OBD index was used to construct three subgroups (normal, medium, and high OBD) with the medium group (n=45) showing mild cognitive dysfunctions (MCD) in memory, language, orientation, and ADL. People with MCD show OBD and BIORISK scores that are significantly different from controls and AD.Conclusions: Petersen’s aMCI criteria cannot be validated and should be replaced by the more restrictive, biologically validated MCD class.