Evidence for Polygenic and Oligogenic Basis of Australian Sporadic
Total Page:16
File Type:pdf, Size:1020Kb
Neurogenetics J Med Genet: first published as 10.1136/jmedgenet-2020-106866 on 14 May 2020. Downloaded from Original research Evidence for polygenic and oligogenic basis of Australian sporadic amyotrophic lateral sclerosis Emily P McCann ,1 Lyndal Henden ,1 Jennifer A Fifita ,1 Katharine Y Zhang,1 Natalie Grima ,1 Denis C Bauer ,2 Sandrine Chan Moi Fat ,1 Natalie A Twine ,1,2 Roger Pamphlett ,3,4,5 Matthew C Kiernan,4,6 Dominic B Rowe ,1,7 Kelly L Williams ,1 Ian P Blair 1 ► Additional material is ABSTRact present with limb onset and 25% with bulbar onset, published online only. To view, Background Amyotrophic lateral sclerosis (ALS) is a while rare cases show truncal onset.3 The median please visit the journal online fatal neurodegenerative disease with phenotypic and disease course is 3 years,2 however survival can be (http:// dx. doi. org/ 10. 1136/ 2 4 jmedgenet- 2020- 106866). genetic heterogeneity. Approximately 10% of cases are as short as 12 months and may exceed 20 years. familial, while remaining cases are classified as sporadic. Around 10%–15% of ALS cases are diagnosed with For numbered affiliations see To date, >30 genes and several hundred genetic variants comorbid frontotemporal dementia (FTD), with up end of article. have been implicated in ALS. to 50% developing some cognitive impairment.5 Methods Seven hundred and fifty- seven sporadic Approximately 10% of ALS cases have a family Correspondence to Dr Ian P Blair, Biomedical ALS cases were recruited from Australian neurology history of disease (familial ALS (FALS)) and two- Sciences, Macquarie University clinics. Detailed clinical data and whole genome thirds of these cases carry a reported ALS gene Faculty of Medicine and Health sequencing (WGS) data were available from 567 and mutation.6 7 The remaining 90% of cases have Sciences, Sydney, NSW 2109, 616 cases, respectively, of which 426 cases had both no apparent family history and are classified as Australia; ian. blair@ mq. edu. au datasets available. As part of a comprehensive genetic sporadic ALS (SALS). EPM, LH and JAF are joint first analysis, 853 genetic variants previously reported as Extensive genetic heterogeneity is apparent authors. ALS- linked mutations or disease- associated alleles among ALS cases. To date, at least 31 genes have KLW and IPB are joint senior were interrogated in sporadic ALS WGS data. Statistical been linked or associated with ALS. Heritability authors. analyses were performed to identify correlation studies suggest that 40%–60% of SALS risk may be 8–10 Received 20 January 2020 between clinical variables, and between phenotype explained by genetic factors. A polygenic basis Revised 2 March 2020 and the number of ALS- implicated variants carried by to SALS has been implicated by the co- occurrence Accepted 22 March 2020 an individual. Relatedness between individuals carrying of two or more ALS gene variants in a single indi- Published Online First 14 May identical variants was assessed using identity- by- descent vidual.11–14 These variants likely interact with envi- 2020 analysis. ronmental factors to trigger the development of http://jmg.bmj.com/ Results Forty- three ALS- implicated variants from 18 ALS.15 Alternatively, this may indicate an oligogenic genes, including C9orf72, ATXN2, TARDBP, SOD1, disease model,11 where an ALS mutation of large SQSTM1 and SETX, were identified in Australian effect, such as SOD1 or C9orf72, is inherited with sporadic ALS cases. One- third of cases carried at least another ALS gene variant which may also contribute one variant and 6.82% carried two or more variants, to phenotype. Furthermore, a multistep hypoth- implicating a potential oligogenic or polygenic basis of esis has recently been postulated to explain the ALS. Relatedness was detected between two sporadic 16 late and apparently sporadic onset of ALS. This on September 26, 2021 by guest. Protected copyright. ALS cases carrying a SOD1 p.I114T mutation, and among hypothesis postulates that six ‘steps’ are required three cases carrying a SQSTM1 p.K238E mutation. to trigger ALS onset, where such steps may include Oligogenic/polygenic sporadic ALS cases showed earlier genetic predisposition, environmental exposures or age of onset than those with no reported variant. 16 Conclusion We confirm phenotypic associations among other unknown molecular alterations. Within this ALS cases, and highlight the contribution of genetic hypothesis, known genetic mutations may account variation to all forms of ALS. for multiple steps, to a degree reflective of their penetrance.17 Previously, our laboratory described the genetic and phenotypic heterogeneity of Australian familial 7 INTRODUCTION ALS. Here, we report the extent of phenotypic Amyotrophic lateral sclerosis (ALS) is a late- onset and genetic variation among Australian SALS cases. fatal neurodegenerative disease characterised by To interrogate the genetic architecture of Austra- lian SALS, we first compiled a list of 31 genes, and © Author(s) (or their the degeneration of both upper and lower motor 1 employer(s)) 2021. No neurons. Patients develop muscle weakness, >850 genetic variants previously reported as: 1) commercial re- use. See rights wasting, spasticity and eventual paralysis. ALS ALS- linked mutations (typically identified from and permissions. Published displays significant phenotypic heterogeneity, even family based studies); 2) functional risk alleles (vari- by BMJ. among cases with identical causal gene mutations. ants whose functions are thought to increase disease To cite: McCann EP, Disease onset can occur anywhere from the second susceptibility) or 3) otherwise associated variants Henden L, Fifita JA, et al. to ninth decade of life but most frequently between (including variants that may be in linkage disequi- J Med Genet 2021;58:87–95. 50 and 60 years of age.2 Around 70% of cases librium with unknown functional risk alleles). McCann EP, et al. J Med Genet 2021;58:87–95. doi:10.1136/jmedgenet-2020-106866 87 Neurogenetics J Med Genet: first published as 10.1136/jmedgenet-2020-106866 on 14 May 2020. Downloaded from Among a large Australian SALS cohort, 35.39% of cases carried with the addition of the recently reported ALS genes TIA123 and a variant previously reported in ALS, implicating 18 genes as KIF5A,24 as well as the GPX3- TNIP1 locus.25 A comprehensive contributing to disease in this population. Polygenic inheritance literature search was conducted in order to compile an exhaus- was implicated in 6.82% of SALS cases who harboured more tive reference list of 853 genetic variants previously implicated than one ALS-implicated variant. We also showed that the clin- in ALS (online supplementary file 2), including ALS-linked ical heterogeneity of Australian SALS is similar to that observed mutations, functional risk alleles and disease-associated variants. in cohorts from other populations. This involved performing a PubMed (https://www.ncbi. nlm. nih. gov/ pubmed/) search for each ALS gene name and ‘amyo- METHODS trophic lateral sclerosis’, with subsequent manual evaluation of all resulting publications. The ALSOD database (http:// alsod. iop. Subjects 26 A total of 757 SALS cases were recruited from the Macquarie kcl.ac. uk/ home. aspx; last updated 8 September 2015) was also University Neurodegenerative Disease Biobank, Australian consulted. MND DNA Bank (Royal Prince Alfred Hospital) and Brain and Genetic variants were included in this reference list (online Mind Centre (University of Sydney). All participants provided supplementary file 2) if they were predicted to alter the amino informed written consent as approved by the human research acid sequence of a protein (ie, non- synonymous/missense, frame- ethics committees of Macquarie University, Sydney South West shift and non- frameshift insertions/deletions, splicing variants) Area Health District or The University of Sydney. All participants and were named in the main text of the publication (ie, vari- were of Caucasian descent (as established according to online ants included in an aggregate of variants used for burden testing supplementary file 1), each was clinically diagnosed with definite were not added to the list). Details of genomic location (hg19), or probable ALS according to El Escorial criteria,18 and had no the transcript accession number and cDNA and protein changes known relatives affected by ALS and/or FTD. Of these 757 cases, were recorded for each variant. For variants where these details detailed clinical data were available for 567 individuals, and were not reported in the original publication(s), they were deter- 616 cases underwent whole genome sequencing (WGS), with a mined using the University of California Santa Cruz Variant total of 426 having both detailed clinical and WGS data avail- Annotation Integrator (http:// genome. ucsc.edu/ cgi- bin/ hgVai) able. Genomic DNA was extracted from peripheral blood using and the associated Human Genome Variation Society variant standard protocols. Fifteen of these SALS cases were previously nomenclature track. Ancillary details pertaining to the ancestry reported to carry an expansion in C9orf72.7 14 and ALS inheritance mode for cases carrying each variant were also recorded, as was the presence of each variant in unaffected and unrelated control individuals, where available in the original Statistical analysis of clinical variables publication(s). Clinical records were examined for four phenotypic features: sex, age at disease onset, site of onset (bulbar or spinal) and duration of disease from onset (until death or last known date of Identifying ALS-implicated variants in SALS cases survival). All statistical analyses were performed in R (V.3.5.1). WGS data from 616 SALS cases were parsed for 31 ALS genes Statistical analyses were performed in a pairwise fashion (online supplementary table 1) using custom UNIX scripts. between all four clinical variables to identify significant associa- Filtering using R was subsequently used to identify the previ- 2 tions. A χ analysis was performed between sex and site of onset, ously reported ALS-implicated variants (online supplementary http://jmg.bmj.com/ while Welch’s t- tests were performed between age of onset and file 2) present within this dataset.