ABSTRACTImportanceBrain iron deposition is common in dementia, but its causal significance is uncertain. The HFE p.C282Y homozygous mutation in European ancestry populations can lead to iron overload and hemochromatosis, mainly in males. Data on brain outcomes in homozygotes are scarce.ObjectiveTo estimate HFE variant associations with MRI features plus incident dementia diagnoses during follow-up in a large community based cohort.DesignUK Biobank cohort with follow-up in routine hospitalization records (mean 8.8 years). MRI imaging available on a participant subset scanned 2014 to 2018.SettingCommunity cohort participants across England, Wales and Scotland.ParticipantsEuropean ancestry participants (n=451,186) aged 40 to 70 years at baseline, including 2,890 p.C282Y homozygotes (predominantly without baseline haemochromatosis diagnoses). MRI scanning on 9,464 males and 10,475 females, including 40 male and 75 female p.C282Y homozygotes.ExposureHFE C282Y and H63D genetic variantsMain outcome and measuresBrain MRI site specific T2. measures (lower values associated with iron deposition) and gray matter volumes. Incident dementia diagnoses during follow-up.ResultsMale p.C282Y homozygotes had lower T2. measures in several brain areas including the thalamus (beta = -1.04 standard deviations, 95% CI -1.33 to -0.76, multiple testing adjusted p-value=4.9*10-10), putamen and hippocampus, compared to those without HFE mutations. Male homozygotes also had smaller gray matter volumes in the putamen (beta -0.80 sd, 95%CI -1.12 to - 0.47, adjusted p=2.2*10-4) and ventral striatum.Diagnoses of incident dementia (Hazard Ratio HR=2.27; 95% CI 1.36 to 3.80, p=0.002) were more common in p.C282Y homozygous men, as were delirium diagnoses (HR=2.04, CI 1.09 to 3.82, p=0.03), but there was no association with Stroke.In p.C282Y homozygote females and p.C282Y/H63D heterozygotes, MRI associations were less marked.Conclusion and RelevanceIn a community sample, men with the HFE p.C282Y homozygote genotype had more brain iron deposition, smaller specific gray matter volumes, and increased incidence of dementia. As iron overload in hemochromatosis is treatable, early intervention may prevent or limit related brain pathology in male HFE p.C282Y homozygotes.Key PointsQuestionIs the hemochromatosis HFE p.C282Y homozygous variant in men associated with brain MRI features and incident dementia?FindingsOn MRI, p.C282Y homozygote males had evidence of more iron deposition in areas including the thalamus, putamen and hippocampus, plus smaller putamen gray matter volumes, compared to men without HFE mutations. In 451,186 UK Biobank participants during the mean 8.8 year follow-up, incident dementia diagnoses were more than twice as common in the 1,294 homozygous men.MeaningAs iron overload in hemochromatosis is treatable, early intervention may prevent or limit related brain pathology in male HFE p.C282Y homozygotes.

Background: Brain iron deposition occurs in dementia. In European ancestry populations, the HFE p.C282Y variant can cause iron overload and hemochromatosis, mostly in homozygous males. Objective: to estimate p.C282Y associations with brain MRI features plus incident dementia diagnoses during follow-up in a large community cohort. Methods: UK Biobank participants with follow-up hospitalization records (mean 10.5 years). MRI in 206 p.C282Y homozygotes versus 23,349 without variants, including T2. measures (lower values indicating more iron). Results: European ancestry participants included 2,890 p.C282Y homozygotes. Male p.C282Y homozygotes had lower T2. measures in areas including the putamen, thalamus, and hippocampus, compared to no HFE mutations. Incident dementia was more common in p.C282Y homozygous men (Hazard Ratio HR = 1.83; 95% CI 1.23 to 2.72, p = 0.003), as was delirium. There were no associations in homozygote women or in heterozygotes. Conclusion: Studies are needed of whether early iron reduction prevents or slows related brain pathologies in male HFE p.C282Y homozygotes.