Mhairi Marshall

Intestinal dysbiosis in ankylosing spondylitis.

Ankylosing spondylitis (AS) is a common, highly heritable immune‐mediated arthropathy that occurs in genetically susceptible individuals exposed to an unknown but likely ubiquitous environmental trigger. There is a close relationship between the gut and spondyloarthritis, as exemplified in patients with reactive arthritis, in whom a typically self‐limiting arthropathy follows either a gastrointestinal or urogenital infection. Microbial involvement in AS has been suggested; however, no definitive link has been established. The aim of this study was to determine whether the gut in patients with AS carries a distinct microbial signature compared with that in the gut of healthy control subjects.

Comparative Pathogenomics Reveals Horizontally Acquired Novel Virulence Genes in Fungi Infecting Cereal Hosts

Comparative analyses of pathogen genomes provide new insights into how pathogens have evolved common and divergent virulence strategies to invade related plant species. Fusarium crown and root rots are important diseases of wheat and barley world-wide. In Australia, these diseases are primarily caused by the fungal pathogen Fusarium pseudograminearum. Comparative genomic analyses showed that the F. pseudograminearum genome encodes proteins that are present in other fungal pathogens of cereals but absent in non-cereal pathogens. In some cases, these cereal pathogen specific genes were also found in bacteria associated with plants. Phylogenetic analysis of selected F. pseudograminearum genes supported the hypothesis of horizontal gene transfer into diverse cereal pathogens. Two horizontally acquired genes with no previously known role in fungal pathogenesis were studied functionally via gene knockout methods and shown to significantly affect virulence of F. pseudograminearum on the cereal hosts wheat and barley. Our results indicate using comparative genomics to identify genes specific to pathogens of related hosts reveals novel virulence genes and illustrates the importance of horizontal gene transfer in the evolution of plant infecting fungal pathogens.

Brief Report: Intestinal Dysbiosis in Ankylosing Spondylitis

Ankylosing spondylitis (AS) is a common, highly heritable immune‐mediated arthropathy that occurs in genetically susceptible individuals exposed to an unknown but likely ubiquitous environmental trigger. There is a close relationship between the gut and spondyloarthritis, as exemplified in patients with reactive arthritis, in whom a typically self‐limiting arthropathy follows either a gastrointestinal or urogenital infection. Microbial involvement in AS has been suggested; however, no definitive link has been established. The aim of this study was to determine whether the gut in patients with AS carries a distinct microbial signature compared with that in the gut of healthy control subjects.

Short-Rib Polydactyly and Jeune Syndromes Are Caused by Mutations in WDR60

Short-rib polydactyly syndromes (SRPS I-V) are a group of lethal congenital disorders characterized by shortening of the ribs and long bones, polydactyly, and a range of extraskeletal phenotypes. A number of other disorders in this grouping, including Jeune and Ellis-van Creveld syndromes, have an overlapping but generally milder phenotype. Collectively, these short-rib dysplasias (with or without polydactyly) share a common underlying defect in primary cilium function and form a subset of the ciliopathy disease spectrum. By using whole-exome capture and massive parallel sequencing of DNA from an affected Australian individual with SRPS type III, we detected two novel heterozygous mutations in WDR60, a relatively uncharacterized gene. These mutations segregated appropriately in the unaffected parents and another affected family member, confirming compound heterozygosity, and both were predicted to have a damaging effect on the protein. Analysis of an additional 54 skeletal ciliopathy exomes identified compound heterozygous mutations in WDR60 in a Spanish individual with Jeune syndrome of relatively mild presentation. Of note, these two families share one novel WDR60 missense mutation, although haplotype analysis suggested no shared ancestry. We further show that WDR60 localizes at the base of the primary cilium in wild-type human chondrocytes, and analysis of fibroblasts from affected individuals revealed a defect in ciliogenesis and aberrant accumulation of the GLI2 transcription factor at the centrosome or basal body in the absence of an obvious axoneme. These findings show that WDR60 mutations can cause skeletal ciliopathies and suggest a role for WDR60 in ciliogenesis.

Whole exome sequencing is an efficient and sensitive method for detection of germline mutations in patients with phaeochromcytomas and paragangliomas

Genetic testing is recommended when the probability of a disease‐associated germline mutation exceeds 10%. Germline mutations are found in approximately 25% of individuals with phaeochromcytoma (PCC) or paraganglioma (PGL); however, genetic heterogeneity for PCC/PGL means many genes may require sequencing. A phenotype‐directed iterative approach may limit costs but may also delay diagnosis, and will not detect mutations in genes not previously associated with PCC/PGL.

Novel TBK1 truncating mutation in a familial amyotrophic lateral sclerosis patient of Chinese origin

Missense and frameshift mutations in TRAF family member-associated NF-kappa-B activator (TANK)-binding kinase 1 (TBK1) have been reported in European sporadic and familial amyotrophic lateral sclerosis (ALS) cohorts. To assess the role of TBK1 in ALS patient cohorts of wider ancestry, we have analyzed whole-exome sequence data from an Australian cohort of familial ALS (FALS) patients and controls. We identified a novel TBK1 deletion (c.1197delC) in a FALS patient of Chinese origin. This frameshift mutation (p.L399fs) likely results in a truncated protein that lacks functional domains required for adapter protein binding, as well as protein activation and structural integrity. No novel or reported TBK1 mutations were identified in FALS patients of European ancestry. This is the first report of a TBK1 mutation in an ALS patient of Asian origin and indicates that sequence variations in TBK1 are a rare cause of FALS in Australia.

Defining the genetic susceptibility to cervical neoplasia—A genome-wide association study

A small percentage of women with cervical HPV infection progress to cervical neoplasia, and the risk factors determining progression are incompletely understood. We sought to define the genetic loci involved in cervical neoplasia and to assess its heritability using unbiased unrelated case/control statistical approaches. We demonstrated strong association of cervical neoplasia with risk and protective HLA haplotypes that are determined by the amino-acids carried at positions 13 and 71 in pocket 4 of HLA-DRB1 and position 156 in HLA-B. Furthermore, 36% (standard error 2.4%) of liability of HPV-associated cervical pre-cancer and cancer is determined by common genetic variants. Women in the highest 10% of genetic risk scores have approximately >7.1% risk, and those in the highest 5% have approximately >21.6% risk, of developing cervical neoplasia. Future studies should examine genetic risk prediction in assessing the risk of cervical neoplasia further, in combination with other screening methods.

Whole-exome sequencing in amyotrophic lateral sclerosis suggests NEK1 is a risk gene in Chinese

BackgroundAmyotrophic lateral sclerosis (ALS) is a progressive neurological disease characterised by the degeneration of motor neurons, which are responsible for voluntary movement. There remains limited understanding of disease aetiology, with median survival of ALS of three years and no effective treatment. Identifying genes that contribute to ALS susceptibility is an important step towards understanding aetiology. The vast majority of published human genetic studies, including for ALS, have used samples of European ancestry. The importance of trans-ethnic studies in human genetic studies is widely recognised, yet a dearth of studies of non-European ancestries remains. Here, we report analyses of novel whole-exome sequencing (WES) data from Chinese ALS and control individuals.MethodsWES data were generated for 610 ALS cases and 460 controls drawn from Chinese populations. We assessed evidence for an excess of rare damaging mutations at the gene level and the gene set level, considering only singleton variants filtered to have allele frequency less than 5 × 10–5 in reference databases. To meta-analyse our results with a published study of European ancestry, we used a Cochran–Mantel–Haenszel test to compare gene-level variant counts in cases vs controls.ResultsNo gene passed the genome-wide significance threshold with ALS in Chinese samples alone. Combining rare variant counts in Chinese with those from the largest WES study of European ancestry resulted in three genes surpassing genome-wide significance: TBK1 (p = 8.3 × 10–12), SOD1 (p = 8.9 × 10–9) and NEK1 (p = 1.1 × 10–9). In the Chinese data alone, SOD1 and NEK1 were nominally significantly associated with ALS (p = 0.04 and p = 7 × 10–3, respectively) and the case/control frequencies of rare coding variants in these genes were similar in Chinese and Europeans (SOD1: 1.5%/0.2% vs 0.9%/0.1%, NEK1 1.8%/0.4% vs 1.9%/0.8%). This was also true for TBK1 (1.2%/0.2% vs 1.4%/0.4%), but the association with ALS in Chinese was not significant (p = 0.14).ConclusionsWhile SOD1 is already recognised as an ALS-associated gene in Chinese, we provide novel evidence for association of NEK1 with ALS in Chinese, reporting variants in these genes not previously found in Europeans.

HLA and KIR Associations of Cervical Neoplasia.

Background Cervical cancer is the fourth most common cancer in women, and we recently reported human leukocyte antigen (HLA) alleles showing strong associations with cervical neoplasia risk and protection. HLA ligands are recognized by killer immunoglobulin-like receptors (KIRs) expressed on a range of immune cell subsets, governing their proinflammatory activity. We hypothesized that the inheritance of particular HLA-KIR combinations would increase cervical neoplasia risk. Methods Here, we used HLA and KIR dosages imputed from single-nucleotide polymorphism genotype data from 2143 cervical neoplasia cases and 13858 healthy controls of European decent. Results The following 4 novel HLA alleles were identified in association with cervical neoplasia, owing to their linkage disequilibrium with known cervical neoplasia-associated HLA-DRB1 alleles: HLA-DRB3*9901 (odds ratio [OR], 1.24; P = 2.49 × 10-9), HLA-DRB5*0101 (OR, 1.29; P = 2.26 × 10-8), HLA-DRB5*9901 (OR, 0.77; P = 1.90 × 10-9), and HLA-DRB3*0301 (OR, 0.63; P = 4.06 × 10-5). We also found that homozygosity of HLA-C1 group alleles is a protective factor for human papillomavirus type 16 (HPV16)-related cervical neoplasia (C1/C1; OR, 0.79; P = .005). This protective association was restricted to carriers of either KIR2DL2 (OR, 0.67; P = .00045) or KIR2DS2 (OR, 0.69; P = .0006). Conclusions Our findings suggest that HLA-C1 group alleles play a role in protecting against HPV16-related cervical neoplasia, mainly through a KIR-mediated mechanism.

Whole-exome sequencing for mutation detection in pediatric disorders of insulin secretion: Maturity onset diabetes of the young and congenital hyperinsulinism

To assess the utility of whole‐exome sequencing (WES) for mutation detection in maturity‐onset diabetes of the young (MODY) and congenital hyperinsulinism (CHI). MODY and CHI are the two commonest monogenic disorders of glucose‐regulated insulin secretion in childhood, with 13 causative genes known for MODY and 10 causative genes identified for CHI. The large number of potential genes makes comprehensive screening using traditional methods expensive and time‐consuming.