According to reports, the etiology of Alzheimer’s disease (AD) may be influenced by abnormal N-methyl-D-aspartate receptor (NMDAR) neurotransmission. NMDAR function is regulated by D-amino acid oxidase (DAO), which breaks down D-amino acids associated with NMDARs, such as D-serine. According to a cross-sectional study, serum DAO levels are positively correlated with how quickly people age cognitively. For a 2-year prospective study, researchers sought to determine how DAO levels affected the prognosis of individuals with very early-stage AD, including those with mild cognitive impairment (MCI).

The participants were 51 MCI patients and 21 healthy people. Every 6 months, serum DAO levels and cognitive function were assessed using the AD assessment scale-cognitive subscale and the Mini-Mental Status Examination. They used multiple regression analysis to investigate the impact of DAO concentration on cognitive deterioration over the course of 2 years.

Serum DAO levels significantly rose during the course of the study (24 months), while the MCI patients’ cognitive function decreased as measured by both cognitive tests. The Mini-Mental Status Examination scores fell, and DAO concentrations also rose in healthy people, but the AD assessment scale-cognitive subscale scores remained stable. Furthermore, among the MCI patients, DAO levels at months 12 and 18 were predictive of cognitive deterioration at month 24.

According to their knowledge, it was the first study to show that blood DAO levels rose in MCI patients as their cognitive function declined prospectively. If confirmed by subsequent research, blood DAO concentration may be used as a biomarker to track cognitive deterioration in MCI patients.