Abstract Body (Do not enter title and authors here): Background: Genetic testing is now recommended for select patients with early-onset atrial fibrillation (AF). Hemochromatosis is an autosomal recessive syndrome that occurs in patients who carry two pathogenic or likely-pathogenic (P/LP) variants in HFE. HFE is included on some genetic testing panels used for patients with AF. Hemochromatosis causes cardiomyopathy due to iron overload in the ventricle; however, it is unknown whether AF can be an early manifestation that is identified by genetic testing.

Methods: A total of 347 patients were referred to a dedicated AF precision medicine clinic. The clinical diagnostic evaluation included an H&P, 12-lead ECG, ambulatory ECG monitoring, and cardiac imaging (cardiac MRI and/or TTE). Genetic testing was performed using CLIA-approved laboratories: Labcorp/Invitae, GeneDx, or Vanderbilt University Medical Center. HFE was included on the cardiomyopathy panel used by 2 of the 3 laboratories.

Results: HFE was tested in 165 participants (median age 46 years [IQR 35-55], 115 [70%] male, 149 [90%] White). Six participants (4%) had two pathogenic variants in HFE. All of them were C282Y/H63D compound heterozygotes. Forty-one participants (25%) were heterozygous carriers of one pathogenic HFE variant. Among the 6 participants with 2 pathogenic HFE variants, the median ferritin level was 346 mcg/L [IQR 262, 496] (normal <300 mcg/L males, <200 mcg/L females). Three participants (50%) met laboratory criteria for iron overload. One individual had isolated ferritin elevation with normal transferrin saturation. All 6 underwent cardiac MRI as part of the genetic evaluation for early onset AF, and there was no evidence of cardiac siderosis based on cardiac T1 mapping, median 990 ms [IQR 968-1024] (normal 960-1030 ms). Dedicated sequences to evaluate for iron overload demonstrated short hepatic T2* in one individual, indicating presence of hepatic iron overload (9 ms, normal >11.4 ms; liver iron concentration 3.4 mg/g, normal <2 mg/g). Three out of 6 participants were referred for a hematology evaluation and 2 out of 6 were started on therapeutic phlebotomy.

Conclusion: Genetic testing can identify patients with early-onset AF who are genetically susceptible to hemochromatosis, have evidence of iron overload, and receive early intervention with therapeutic phlebotomy. These results suggest HFE should be sequenced as part of genetic testing for early-onset AF, but larger sample sizes are needed to confirm these results.