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Epidémiologie et génétique humaine de l’ulcère de Buruli

Abstract : Buruli ulcer (BU), caused by Mycobacterium ulcerans, is the third most frequent mycobacteriosis worldwide. It has been rapidly emerging in sub-Saharan African countries since 1980. Until now, knowledge of BU epidemiology relied on series of non laboratory-confirmed clinical cases. From 2005-2011, we recruited the current largest cohort of laboratory-confirmed cases (more than 1,200 patients) at the Pobe CDTUB, Benin, to describe the clinical epidemiology of the disease and to explore the genetic architecture of human susceptibility to BU. Typically, patients with BU were children (median age at diagnosis 12 years) presenting with a unique (96%) large (≥15 cm, 36%) ulcerative (66%) lesion of the lower limb (60%). Atypical clinical presentation of BU included osteomyelitis with no identifiable present or past BU skin lesions. The sex ratio of BU widely varied with age, with male patients accounting for 57% of patients aged 15 years and younger, but only 33% of those older than 15 years. Clinical presentation of BU was significantly dependent on age and sex. 9% male patients had BU osteomyelitis, whereas only 4% of female patients did. 1 year after treatment, 22% of patients with follow-up information presented with permanent functional sequelae. Presentation with oedema, osteomyelitis, or large (≥15 cm in diameter), or multifocal lesions was significantly associated with occurrence of permanent functional sequelae (OR 7•64, 95% CI 5•29–11•31) and operationally defines severe BU. When coinfected with HIV, patients had a significantly higher risk to develop severe BU (OR 2.77, IC95% [1.32-6.33]). We explored the genetic architecture of susceptibility to BU in both mendelian and complex genetic frameworks. The most severe case of the disease to have been treated at the Pobe CDTUB belonged to a consanguineous family in which the segregation of the phenotype was indicative of a recessive mendelian genetic defect. Genetic linkage analysis by homozygosity mapping suggested the implication of the beta-defensin locus on chromosome 8 in BU pathogenesis and lead to the identification of a homozygous deletion, which co-segregated perfectly with the disease in the family. In a complex genetics approach, we undertook a genome-wide association study, which involved the genotyping of more than 2 million SNPs (Illumina Omni2.5) in a cohort of 400 cases and 400 exposed controls. We identified many signals of interest. The replication study is ongoing. Understanding BU physiopathology is crucial to the development of efficient vaccines and drugs. Dissection of the genetic control of the infection by M. ulcerans by its human host therefore constitutes an indispensable step.
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Quentin Vincent. Epidémiologie et génétique humaine de l’ulcère de Buruli. Génétique. Université René Descartes - Paris V, 2014. Français. ⟨NNT : 2014PA05S019⟩. ⟨tel-01249580⟩

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