Pathogenic Huntingtin Repeat Expansions in Patients with Frontotemporal Dementia and Amyotrophic Lateral Sclerosis.

We examined the role of repeat expansions in the pathogenesis of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) by analyzing whole-genome sequence data from 2,442 FTD/ALS patients, 2,599 Lewy body dementia (LBD) patients, and 3,158 neurologically healthy subjects. Pathogenic expansions (range, 40-64 CAG repeats) in the huntingtin (HTT) gene were found in three (0.12%) patients diagnosed with pure FTD/ALS syndromes but were not present in the LBD or healthy cohorts. We replicated our findings in an independent collection of 3,674 FTD/ALS patients. Postmortem evaluations of two patients revealed the classical TDP-43 pathology of FTD/ALS, as well as huntingtin-positive, ubiquitin-positive aggregates in the frontal cortex. The neostriatal atrophy that pathologically defines Huntington's disease was absent in both cases. Our findings reveal an etiological relationship between HTT repeat expansions and FTD/ALS syndromes and indicate that genetic screening of FTD/ALS patients for HTT repeat expansions should be considered

Genome-wide structural variant analysis identifies risk loci for non-Alzheimer's dementias

We characterized the role of structural variants, a largely unexplored type of genetic variation, in two non-Alzheimer's dementias, namely Lewy body dementia (LBD) and frontotemporal dementia (FTD)/amyotrophic lateral sclerosis (ALS). To do this, we applied an advanced structural variant calling pipeline (GATK-SV) to short-read whole-genome sequence data from 5,213 European-ancestry cases and 4,132 controls. We discovered, replicated, and validated a deletion in TPCN1 as a novel risk locus for LBD and detected the known structural variants at the C9orf72 and MAPT loci as associated with FTD/ALS. We also identified rare pathogenic structural variants in both LBD and FTD/ALS. Finally, we assembled a catalog of structural variants that can be mined for new insights into the pathogenesis of these understudied forms of dementia.Peer reviewe

Evaluation of SORL1 in Lewy Body Dementia Identifies No Significant Associations

Lewy body dementia (LBD) is a clinically heterogeneous neurodegenerative disorder characterized by parkinsonism, visual hallucinations, fluctuating mental status, and rapid eye movement sleep behavior disorder. LBD lies along a spectrum between Parkinson's disease and Alzheimer's disease, and recent evidence suggests that the genetic architectures of these age-related syndromes are intersecting. In summary, we did not find a significant enrichment of rare, damaging SORL1 mutations in our well-powered LBD cohort. Our data set is, to our knowledge, the largest genome-sequence cohort in this understudied disease. Although it is possible that an association was missed due to allelic heterogeneity, our findings indicate that caution should be exercised when interpreting SORL1 mutations in LBD, as the current evidence does not conclusively support an association with disease risk

Genetic evaluation of dementia with Lewy bodies implicates distinct disease subgroups

The APOE locus is strongly associated with risk for developing Alzheimer’s disease and dementia with Lewy bodies (DLB). In particular, the role of the APOE ε4 allele as a putative driver of α-synuclein pathology is a topic of intense debate. Here, we performed a comprehensive evaluation in 2,466 DLB cases versus 2,928 neurologically healthy, aged controls. Using an APOE-stratified genome-wide association study approach, we found that GBA is associated with risk for DLB in patients without APOE ε4 (p = 6.58 x 10−9, OR = 3.41, 95% CI = 2.25–5.17), but not with DLB with APOE ε4 (p = 0.034, OR = 1.87, 95%, 95% CI = 1.05–3.37). We then divided 495 neuropathologically examined DLB cases into three groups based on the extent of concomitant Alzheimer’s disease co-pathology: pure DLB (n = 88), DLB with intermediate Alzheimer’s disease co-pathology (DLB + iAD, n = 66), and DLB with high Alzheimer’s disease co-pathology (DLB + AD, n = 341). In each group, we tested the association of the APOE ε4 against the 2,928 neurologically healthy controls. Our examination found that APOE ε4 was associated with DLB + AD (p = 1.29x10−32, OR = 4.25, 95% CI = 3.35–5.39) and DLB + iAD (p = 0.0011, OR = 2.31, 95% CI = 1.40–3.83), but not with pure DLB (p = 0.31, OR = 0.75, 95% CI = 0.43–1.30). In conclusion, though deep clinical data were not available for these samples, our findings do not support the notion that APOE ε4 is an independent driver of α-synuclein pathology in pure DLB, but rather implicate GBA as the main risk gene for the pure DLB subgroup

Pathogenic Huntingtin Repeat Expansions in Patients with Frontotemporal Dementia and Amyotrophic Lateral Sclerosis

We examined the role of repeat expansions in the pathogenesis of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) by analyzing whole-genome sequence data from 2,442 FTD/ALS patients, 2,599 Lewy body dementia (LBD) patients, and 3,158 neurologically healthy subjects. Pathogenic expansions (range, 40-64 CAG repeats) in the huntingtin (HTT) gene were found in three (0.12%) patients diagnosed with pure FTD/ALS syndromes but were not present in the LBD or healthy cohorts. We replicated our findings in an independent collection of 3,674 FTD/ALS patients. Postmortem evaluations of two patients revealed the classical TDP-43 pathology of FTD/ALS, as well as huntingtin-positive, ubiquitin-positive aggregates in the frontal cortex. The neostriatal atrophy that pathologically defines Huntington\u27s disease was absent in both cases. Our findings reveal an etiological relationship between HTT repeat expansions and FTD/ALS syndromes and indicate that genetic screening of FTD/ALS patients for HTT repeat expansions should be considered