Association of low frequency variants with regional cortical grey matter volumes in genetic frontotemporal dementia: Results from GENFI
Authors: Mirza Saira S. , Pasternak Maurice , Patterson Andrew D. , Tartaglia Carmela , Mitchell Sara Berman , Black Sandra E. , Freedman Morris , Tang‐Wai David F. , Rogaeva Ekaterina , Cash David M , Bocchetta Martina , van Swieten John C. , Laforce Robert , Tagliavini Fabrizio , Borroni Barbara , Galimberti Daniela , Rowe James B. , Graff Caroline , Finger Elizabeth , Sorbi Sandro , de Mendonça Alexandre , Butler Christopher R. , Gerhard Alexander , Sanchez‐Valle Raquel , Moreno Fermin , Synofzik Matthis , Vandenberghe Rik , Ducharme Simon , Levin Johannes , Danek Adrian , Otto Markus , Santana Isabel , Rohrer Jonathan D. , Masellis Mario 
Published: December 2023

Background

Frontotemporal dementia (FTD) is a neurodegenerative condition characterized by heterogeneous clinical, pathological, and genetic features. Mutations in three genes account for the majority of autosomal dominant FTD: GRN, MAPT, and C9orf72. We tested whether gene‐based aggregate burden of genome‐wide low‐frequency variants contribute to variation in regional cortical and subcortical grey matter volumes in the GENetic Frontotemporal dementia Initiative (GENFI), after controlling for effects of autosomal dominant mutations.

Method

GENFI recruits symptomatic and presymptomatic participants from families segregating genetic FTD. We included 517 participants with genotype (Neurochip; imputed against TOPMed), and T1w‐MRI brain volumetric data. Gene‐based burden tests that aggregate the number of uncommon/rare variants by gene were used to examine the association of low‐frequency variants (minor allele frequency: 0.000001 to <0.05) with regional cortical and subcortical grey matter volumes, controlling for age, sex, total intracranial volume, mutation status, population stratification, and family membership (kinship matrix). In two separate analyses, we used the following set of annotations to account for (i) loss of function mutations (LOF): start gain, stop loss, start loss, essential splice site, stop gain, normal splice site, and non‐synonymous, (ii) insertions, deletions, and frameshift mutations (indel‐fs).

Result

Of the 517 participants (300 women), 307 were mutation carriers (symptomatic = 82). For LOF mutations (731 genes tested; significance threshold: p = 0.05/731 = 6.8×10−5), aggregate burden of variants in BSND were associated with lower volumes in: temporal (p = 6.6×10−6), left insula (p = 5.0×10−5), and ventromedial prefrontal cortical (p = 2.8×10−5) regions. For indel‐fs mutations (826 genes tested; significance threshold: p = 0.05/826 = 6.05×10−5), aggregate burden of variants in: (i) E2F2 was associated with lower volumes in occipital (p = 8.7×10−6) regions; (ii) TMEM61 was associated with lower volumes in left temporal (p = 7.8×10−7), and left cingulate regions (p = 5.5×10−5); (iii) KDM4A‐AS1 was associated with lower volumes in the right temporal (p = 3.2×10‐7) region. All genes are variably expressed in the brain.

Conclusion

Identification of deleterious or protective low‐frequency variants contributing to FTD imaging phenotypes may help identify genetic modifiers of familial FTD. Replication of results followed by functional studies are needed.