MRI measure of brain iron predicts higher risk of cognitive impairment, Johns Hopkins study finds

A specialized MRI technique that measures iron in the brain can help predict which people are more likely to develop mild cognitive impairment, a new long-term study from Johns Hopkins University reports.

Researchers used quantitative susceptibility mapping (QSM), a noninvasive MRI method, to quantify brain iron in 158 cognitively unimpaired adults and followed them for a median of 7.7 years. Higher baseline iron levels in regions involved in memory and other cognitive functions were associated with an increased risk of developing mild cognitive impairment and with faster cognitive decline during the follow-up period, the authors reported in the journal Radiology.

The study establishes QSM as a promising tool for detecting abnormal iron accumulation in living patients, researchers said. Until recent advances in imaging, brain iron has typically been measured only after death by analysis of tissue samples. "QSM can detect small differences in iron levels across different brain regions, providing a reliable and non-invasive way to map and quantify iron in patients, which is not possible with conventional MR approaches," said senior author Xu Li, an associate professor of radiology at Johns Hopkins.

Investigators collected baseline QSM readings for each participant and obtained repeated scans over the follow-up period. They found that higher iron measurements at enrollment, especially in cortical areas tied to memory, predicted later cognitive impairment independent of brain volume loss, a common marker of neurodegeneration in Alzheimer’s disease.

The findings add to a body of evidence linking iron to neurodegenerative disease. Abnormally high brain iron was first reported in people with Alzheimer’s disease in a 1953 postmortem study, and subsequent research has associated iron with both amyloid beta plaques and tau neurofibrillary tangles, hallmark pathologies of Alzheimer’s disease. Iron is essential for normal biochemistry, including oxygen transport and DNA synthesis, but excess iron can disturb the balance between free radicals and antioxidants and may exacerbate neuronal death.

The Johns Hopkins team and other researchers have previously reported elevated iron in deep gray-matter structures in patients with Alzheimer’s disease. QSM permits assessment of iron distribution across both deep structures and the neocortex, the outer brain layer involved in language and conscious thought, where less is known about iron dynamics.

Although the study is observational and cannot prove that iron accumulation causes dementia, its longitudinal design strengthens the association between higher iron levels and subsequent cognitive decline. The authors noted that iron accumulation was associated with deterioration even when accounting for brain volume loss, suggesting iron may contribute information beyond traditional imaging markers.

There is no established single normal level of brain iron; distribution varies by brain region and tends to increase with age. The study’s authors called for efforts to standardize QSM acquisition and analysis to make the method faster and more widely accessible in clinical practice. They also suggested that brain iron might serve not only as a biomarker but as a future therapeutic target. Iron-chelating drugs, which promote iron excretion, have been proposed for clinical trials to test whether lowering brain iron can slow cognitive decline.

Experts caution that key questions remain. It is not yet clear whether iron accumulation drives the disease process or reflects downstream changes related to amyloid, tau or other aspects of neurodegeneration. The study’s sample size of 158 and the characteristics of the enrolled participants limit how broadly the findings can be generalized; replication in larger and more diverse cohorts will be important.

Alzheimer’s disease is the most common cause of dementia and affects more than 7 million Americans. Current treatments do not cure the disease, and early detection of risk could help target preventive strategies and clinical trials. The Johns Hopkins researchers said that QSM could help identify patients at higher risk of progression to Alzheimer’s-related cognitive impairment and could guide enrollment in trials of iron-targeted therapies as they become available.

The study was published in Radiology, the journal of the Radiological Society of North America. The authors urged additional research to standardize QSM methods, confirm findings in larger populations and determine whether interventions that modify brain iron can alter the course of cognitive decline.