Admixed populations arise when two or more ancestral populations interbreed. As a result of this admixture, the genome of admixed populations is defined by tracts of variable size inherited from these parental groups and has particular genetic features that provide valuable information about their demographic history. Diverse methods can be used to derive the ancestry apportionment of admixed individuals, and such inferences can be leveraged for the discovery of genetic loci associated with diseases and traits, therefore having important biomedical implications. In this review article, we summarize the most common methods of global and local genetic ancestry estimation and discuss the use of admixture mapping studies in human diseases.

Background Sepsis is a severe systemic inflammatory response to infections that is accompanied by organ dysfunction and has a high mortality rate in adult intensive care units. Most genetic studies have identified gene variants associated with development and outcomes of sepsis focusing on biological candidates. We conducted the first genome-wide association study (GWAS) of 28-day survival in adult patients with sepsis. Methods This study was conducted in two stages. The first stage was performed on 687 European sepsis patients from the GEN-SEP network and 7.5 million imputed variants. Association testing was conducted with Cox regression models, adjusting by sex, age, and the main principal components of genetic variation. A second stage focusing on the prioritized genetic variants was performed on 2,063 ICU sepsis patients (1362 European Americans and 701 African-Americans) from the MESSI study. A meta-analysis of results from the two stages was conducted and significance was established at p < 5.0 × 10−8. Whole-blood transcriptomic, functional annotations, and sensitivity analyses were evaluated on the identified genes and variants. Findings We identified three independent low-frequency variants associated with reduced 28-day sepsis survival, including a missense variant in SAMD9 (hazard ratio [95% confidence interval] = 1.64 [1.37–6.78], p = 4.92 × 10−8). SAMD9 encodes a possible mediator of the inflammatory response to tissue injury. Interpretation We performed the first GWAS of 28-day sepsis survival and identified novel variants associated with reduced survival. Larger sample size studies are needed to better assess the genetic effects in sepsis survival and to validate the findings.

Despite asthma has a considerable genetic component, an important proportion of genetic risks remain unknown, especially for non-European populations. Canary Islanders have the largest African genetic ancestry observed among Southwestern Europeans and the highest asthma prevalence in Spain. Here we examined broad chromosomal regions previously associated with an excess of African genetic ancestry in Canary Islanders, with the aim of identifying novel risk variants associated with asthma susceptibility. In a two-stage cases-control study, we revealed a variant within HLA-DQB1 significantly associated with asthma risk (rs1049213, meta-analysis p = 1.30 × 10–7, OR [95% CI] = 1.74 [1.41–2.13]) previously associated with asthma and broad allergic phenotype. Subsequent fine-mapping analyses of classical HLA alleles revealed a novel allele significantly associated with asthma protection (HLA-DQA1*01:02, meta-analysis p = 3.98 × 10–4, OR [95% CI] = 0.64 [0.50–0.82]) that had been linked to infectious and autoimmune diseases, and peanut allergy. HLA haplotype analyses revealed a novel haplotype DQA1*01:02-DQB1*06:04 conferring asthma protection (meta-analysis p = 4.71 × 10–4, OR [95% CI] = 0.47 [0.29– 0.73]).

BackgroundSepsis is a severe systemic inflammatory response to infections that is accompanied by organ dysfunction and has a high mortality rate in adult intensive care units (ICUs). Most genetic studies have identified gene variants associated with development and outcomes of sepsis focusing on biological candidates. We conducted the first genome-wide association study (GWAS) of 28-day survival in adult patients with sepsis.MethodsThis study was conducted in two stages. The first stage was performed on 687 European sepsis patients from the GEN-SEP network and 7.5 million imputed variants. Association testing was conducted with Cox regression models, adjusting by sex, age, and the main principal components of genetic variation. A second stage focusing on the prioritized genetic variants was performed on 2,063 ICU sepsis patients (1,362 European Americans and 701 African Americans) from the MESSI study. A meta-analysis of results from the two stages was conducted and significance was established at p<5.0×10−8. Whole-blood transcriptomic and functional annotations were evaluated on the identified genes and variants.FindingsWe identified three independent variants associated with reduced 28-day sepsis survival, including a missense variant in SAMD9 (hazard ratio [95% confidence interval]=1.64 [1.37-6.78], p=4.92×10−8). SAMD9 encodes a mediator of the inflammatory response to tissue injury that is overexpressed in peripheral blood of non-surviving sepsis patients compared to those surviving (p=2.18×10−3).InterpretationWe performed the first GWAS of 28-day sepsis survival and identified novel variants associated with reduced survival. Our findings could allow the identification of novel targets for sepsis treatment and patient risk stratification.Research in contextEvidence before this studySepsis is defined as a life-threatening clinical syndrome of physiological, pathological, and biochemical abnormalities caused by a dysregulated host response to an infection, and with long-term physical, psychological, and cognitive disabilities. Many genetic studies have focused on identifying genetic risk factors associated with sepsis development and severity, but only four genome-wide association studies (GWAS) have been published to date. Three of them focused on sepsis mortality. The first study identified that common genetic variation in the FER gene associated with a reduced risk of death. The second study found variants associated with an increased risk of death in VPS13A, which is key in autophagic degradation. In the last study, variants of the CISH gene, involved in cytokine regulation, were associated with the risk of death. Nevertheless, there is a lack of GWAS focused on sepsis survival, which takes into account the probability estimates of death for each patient over time.Added value of this studyTo the best of our knowledge, we provide the results of the first GWAS of 28-day sepsis survival conducted to date. In this two-staged study, we identified three novel loci associated with reduced 28-day survival among sepsis patients. We identified one missense variant in SAMD9, which encodes a critical regulator in the inflammatory response and apoptosis. A significant upregulation of SAMD9 gene expression in whole blood was observed among non-surviving sepsis patients compared to those surviving. Associations were also found for one intergenic variant to SLC5A12\FIBIN and an intergenic variant to two non-coding RNAs (LINC00378\MIR3169).Implications of all the available evidenceThe identification of effective prognostic genetic markers in sepsis is a promising instrument for clinical practice. This study identified three novel genetic factors of fatal outcomes, all having interesting and important biological plausibly that could serve as novel targets for sepsis treatment. This knowledge is important to propose effective sepsis treatments and will be central in the development of personalized medicine approaches.