Co-infection with Shigella spp. and other microbes modifies diarrhea risk.
Pathogens in the gastrointestinal tract exist within a vast population of microbes. We examined associations between pathogens and composition of gut microbiota as they relate to Shigella spp./enteroinvasive Escherichia coli infection. We analyzed 3,035 stool specimens (1,735 nondiarrheal and 1,300 moderate-to-severe diarrheal) from the Global Enteric Multicenter Study for 9 enteropathogens. Diarrheal specimens had a higher number of enteropathogens (diarrheal mean 1.4, nondiarrheal mean 0.95; p<0.0001). Rotavirus showed a negative association with Shigella spp. in cases of diarrhea (odds ratio 0.31, 95% CI 0.17–0.55) and had a large combined effect on moderate-to-severe diarrhea (odds ratio 29, 95% CI 3.8–220). In 4 Lactobacillus taxa identified by 16S rRNA gene sequencing, the association between pathogen and disease was decreased, which is consistent with the possibility that Lactobacillus spp. are protective against Shigella spp.–induced diarrhea. Bacterial diversity of gut microbiota was associated with diarrhea status, not high levels of the Shigella spp. ipaH gene.
shigellosis; Shigella; bacteria; polymicrobial infection; Escherichia coli; enteroinvasive E. coli; EIEC; Lactobacillus; rotavirus; viruses; co-occurring pathogens; enteropathogens; microbiota; ipaH gene; diarrhea; children; low-income countries
Staphylococcus aureus; antimicrobial resistance; community-acquired infections; bacteremia; bacterial typing techniques; electrophoresis; bacteria; illicit drug use; research
Most isolates are closely related, but genetic variation implies accelerated transmission of some lineages.
Cholera remains a major public health problem. To compare the relative contribution of strains from the environment with strains isolated from patients during outbreaks, we performed multilocus variable tandem repeat analyses on samples collected during the 2010 and 2011 outbreak seasons in 2 geographically distinct areas of Bangladesh. A total of 222 environmental and clinical isolates of V. cholerae O1 were systematically collected from Chhatak and Mathbaria. In Chhatak, 75 of 79 isolates were from the same clonal complex, in which extensive differentiation was found in a temporally consistent pattern of successive mutations at single loci. A total of 59 isolates were collected from 6 persons; most isolates from 1 person differed by sequential single-locus mutations. In Mathbaria, 60 of 84 isolates represented 2 separate clonal complexes. The small number of genetic lineages in isolates from patients, compared with those from the environment, is consistent with accelerated transmission of some strains among humans during an outbreak.
multilocus sequence analysis; infectious disease outbreaks; Vibrio cholerae; bacteria; Bangladesh; cholera; outbreak
Cholera is still a major public health problem. The underlying bacterial pathogen Vibrio cholerae (V. cholerae) is evolving and some of its mutations have set the stage for outbreaks. After V. cholerae acquired the mobile elements VSP I & II, the El Tor pandemic began and spread across the tropics. The replacement of the O1 serotype encoding genes with the O139 encoding genes triggered an outbreak that swept across the Indian subcontinent. The sxt element generated a third selective sweep and most recently a fourth sweep was associated with the exchange of the El Tor ctx allele for a classical ctx allele in the El Tor background. In Kenya, variants of this fourth selective sweep have differentiated and become endemic residing in and emerging from environmental reservoirs. On a local level, studies in Bangladesh have revealed that outbreaks may arise from a nonrandom subset of the genetic lineages in the environment and as the population of the pathogen expands, many novel mutations may be found increasing the amount of genetic variation, a phenomenon known as a founder flush. In Haiti, after the initial invasion and expansion of V. cholerae in 2010, a second outbreak occurred in the winter of 2011–2012 driven by natural selection of specific mutations.
Isolates represent multiple genetic lineages, a finding consistent with multiple emergences from endemic reservoirs.
Numerous outbreaks of cholera have occurred in Kenya since 1971. To more fully understand the epidemiology of cholera in Kenya, we analyzed the genetic relationships among 170 Vibrio cholerae O1 isolates at 5 loci containing variable tandem repeats. The isolates were collected during January 2009–May 2010 from various geographic areas throughout the country. The isolates grouped genetically into 5 clonal complexes, each comprising a series of genotypes that differed by an allelic change at a single locus. No obvious correlation between the geographic locations of the isolates and their genotypes was observed. Nevertheless, geographic differentiation of the clonal complexes occurred. Our analyses showed that multiple genetic lineages of V. cholerae were simultaneously infecting persons in Kenya. This finding is consistent with the simultaneous emergence of multiple distinct genetic lineages of V. cholerae from endemic environmental reservoirs rather than recent introduction and spread by travelers.
phenotypes; genotypes; Vibrio cholerae; cholera; characterization; molecular epidemiology; outbreaks; bacteria; Kenya
Diarrheal diseases continue to contribute significantly to morbidity and mortality in infants and young children in developing countries. There is an urgent need to better understand the contributions of novel, potentially uncultured, diarrheal pathogens to severe diarrheal disease, as well as distortions in normal gut microbiota composition that might facilitate severe disease.
We use high throughput 16S rRNA gene sequencing to compare fecal microbiota composition in children under five years of age who have been diagnosed with moderate to severe diarrhea (MSD) with the microbiota from diarrhea-free controls. Our study includes 992 children from four low-income countries in West and East Africa, and Southeast Asia. Known pathogens, as well as bacteria currently not considered as important diarrhea-causing pathogens, are positively associated with MSD, and these include Escherichia/Shigella, and Granulicatella species, and Streptococcus mitis/pneumoniae groups. In both cases and controls, there tend to be distinct negative correlations between facultative anaerobic lineages and obligate anaerobic lineages. Overall genus-level microbiota composition exhibit a shift in controls from low to high levels of Prevotella and in MSD cases from high to low levels of Escherichia/Shigella in younger versus older children; however, there was significant variation among many genera by both site and age.
Our findings expand the current understanding of microbiota-associated diarrhea pathogenicity in young children from developing countries. Our findings are necessarily based on correlative analyses and must be further validated through epidemiological and molecular techniques.
During systematic active surveillance of the causes of diarrhea in patients admitted to the Infectious Diseases and Beliaghata General Hospital in Kolkata, India, we looked for 26 known gastrointestinal pathogens in fecal samples from 2,748 patients. Samples from about one-third (29%) of the patients contained multiple pathogens. Polymicrobial infections frequently contained Vibrio cholerae O1 and rotavirus. When these agents were present, some co-infecting agents were found significantly less often (p = 10–5 to 10–33), some were detected significantly more often (p = 10–5 to 10–26), and others were detected equally as often as when V. cholerae O1 or rotavirus was absent. When data were stratified by patient age and season, many nonrandom associations remained statistically significant. The causes and effects of these nonrandom associations remain unknown.
Diarrhea; Vibrio infections; rotavirus; Vibrio cholerae; coinfection; bacteria; viruses; parasites; research
We introduce a novel methodology for differential abundance analysis in sparse high-throughput marker gene survey data. Our approach, implemented in the metagenomeSeq Bioconductor package, relies on a novel normalization technique and a statistical model that accounts for under-sampling: a common feature of large-scale marker gene studies. We show, using simulated data and several published microbiota datasets, that metagenomeSeq outperforms the tools currently used in this field.
Cultivation-based assays combined with PCR or enzyme-linked immunosorbent assay (ELISA)-based methods for finding virulence factors are standard methods for detecting bacterial pathogens in stools; however, with emerging molecular technologies, new methods have become available. The aim of this study was to compare four distinct detection technologies for the identification of pathogens in stools from children under 5 years of age in The Gambia, Mali, Kenya, and Bangladesh. The children were identified, using currently accepted clinical protocols, as either controls or cases with moderate to severe diarrhea. A total of 3,610 stool samples were tested by established clinical culture techniques: 3,179 DNA samples by the Universal Biosensor assay (Ibis Biosciences, Inc.), 1,466 DNA samples by the GoldenGate assay (Illumina), and 1,006 DNA samples by sequencing of 16S rRNA genes. Each method detected different proportions of samples testing positive for each of seven enteric pathogens, enteroaggregative Escherichia coli (EAEC), enterotoxigenic E. coli (ETEC), enteropathogenic E. coli (EPEC), Shigella spp., Campylobacter jejuni, Salmonella enterica, and Aeromonas spp. The comparisons among detection methods included the frequency of positive stool samples and kappa values for making pairwise comparisons. Overall, the standard culture methods detected Shigella spp., EPEC, ETEC, and EAEC in smaller proportions of the samples than either of the methods based on detection of the virulence genes from DNA in whole stools. The GoldenGate method revealed the greatest agreement with the other methods. The agreement among methods was higher in cases than in controls. The new molecular technologies have a high potential for highly sensitive identification of bacterial diarrheal pathogens.
Clinical and environmental Vibrio cholerae organisms collected from February 2004 through April 2005 were systematically isolated from 2 rural Bangladeshi locales. Their genetic relatedness was evaluated at 5 loci that contained a variable number of tandem repeats (VNTR). The observed minimal overlap in VNTR patterns between the 2 communities was consistent with sequential, small outbreaks from local sources.
Cholera; variable number of tandem repeats; epidemiology; outbreaks; genetic variation; dispatch
The family Polyomaviridae is comprised of circular double-stranded DNA viruses, several of which are associated with diseases, including cancer, in immunocompromised patients. Here we describe a novel polyomavirus recovered from the fecal microbiota of a child in Malawi, provisionally named STL polyomavirus (STLPyV). We detected STLPyV in clinical stool specimens from USA and The Gambia at up to 1% frequency. Complete genome comparisons of two STLPyV strains demonstrated 5.2% nucleotide divergence. Alternative splicing of the STLPyV early region yielded a unique form of T antigen, which we named 229T, in addition to the expected large and small T antigens. STLPyV has a mosaic genome and shares an ancestral recombinant origin with MWPyV. The discovery of STLPyV highlights a novel alternative splicing strategy and advances our understanding of the complex evolutionary history of polyomaviruses.
Polyomavirus; Virus discovery; Tumor antigen; Alternative splicing; Recombination
AIM: To investigate the change in eukaryotic gene expression profile in Caco-2 cells after infection with strains of Escherichia coli and commensal probiotic bacteria.
METHODS: A 19200 gene/expressed sequence tag gene chip was used to examine expression of genes after infection of Caco-2 cells with strains of normal flora E. coli, Lactobacillus plantarum, and a combination of the two.
RESULTS: The cDNA microarray revealed up-regulation of 155 and down-regulation of 177 genes by E. coli. L. plantarum up-regulated 45 and down-regulated 36 genes. During mixed infection, 27 genes were up-regulated and 59 were down-regulated, with nullification of stimulatory/inhibitory effects on most of the genes. Expression of several new genes was noted in this group.
CONCLUSION: The commensal bacterial strains used in this study induced the expression of a large number of genes in colonocyte-like cultured cells and changed the expression of several genes involved in important cellular processes such as regulation of transcription, protein biosynthesis, metabolism, cell adhesion, ubiquitination, and apoptosis. Such changes induced by the presence of probiotic bacteria may shape the physiologic and pathologic responses they trigger in the host.
Lactobacillus; Escherichia coli; Gene expression; Probiotic; cDNA microarray
Kynurenic acid, a metabolite of the kynurenine pathway of tryptophan degradation, is an antagonist at N-methyl-d-aspartate and α7 nicotinic acetylcholine receptors and modulates glutamate, dopamine, and acetylcholine signaling. Cortical kynurenic acid concentrations are elevated in the brain and cerebrospinal fluid of schizophrenia patients. The proximal cause may be an impairment of kynurenine 3-monooxygenase (KMO), a rate-limiting enzyme at the branching point of the kynurenine pathway.
To examine KMO messenger RNA expression and KMO enzyme activity in postmortem tissue from the frontal eye field (FEF; Brodmann area 6) obtained from schizophrenia individuals compared with healthy control individuals and to explore the relationship between KMO single-nucleotide polymorphisms and schizophrenia oculomotor endophenotypes.
Case-control postmortem and clinical study.
Maryland Brain Collection, outpatient clinics.
Postmortem specimens from schizophrenia patients (n=32) and control donors (n=32) and a clinical sample of schizophrenia patients (n=248) and healthy controls (n=228).
Main Outcome Measures
Comparison of quantitative KMO messenger RNA expression and KMO enzyme activity in postmortem FEF tissue between schizophrenia patients and controls and association of KMO single-nucleotide polymorphisms with messenger RNA expression in postmortem FEF and schizophrenia and oculomotor endophenotypes (ie, smooth pursuit eye movements and oculomotor delayed response).
In postmortem tissue, we found a significant and correlated reduction in KMO gene expression and KMO enzyme activity in the FEF in schizophrenia patients. In the clinical sample, KMO rs2275163 was not associated with a diagnosis of schizophrenia but showed modest effects on predictive pursuit and visuospatial working memory endophenotypes.
Our results provide converging lines of evidence implicating reduced KMO activity in the etiopathophysiology of schizophrenia and related neurocognitive deficits.
Estimates of the prevalence of Shigella spp. are limited by the suboptimal sensitivity of current diagnostic and surveillance methods. We used a quantitative PCR (qPCR) assay to detect Shigella in the stool samples of 3,533 children aged <59 months from the Gambia, Mali, Kenya, and Bangladesh, with or without moderate-to-severe diarrhea (MSD). We compared the results from conventional culture to those from qPCR for the Shigella ipaH gene. Using MSD as the reference standard, we determined the optimal cutpoint to be 2.9 × 104
ipaH copies per 100 ng of stool DNA for set 1 (n = 877). One hundred fifty-eight (18%) specimens yielded >2.9 × 104
ipaH copies. Ninety (10%) specimens were positive by traditional culture for Shigella. Individuals with ≥2.9 × 104
ipaH copies have 5.6-times-higher odds of having diarrhea than those with <2.9 × 104
ipaH copies (95% confidence interval, 3.7 to 8.5; P < 0.0001). Nearly identical results were found using an independent set of samples. qPCR detected 155 additional MSD cases with high copy numbers of ipaH, a 90% increase from the 172 cases detected by culture in both samples. Among a subset (n = 2,874) comprising MSD cases and their age-, gender-, and location-matched controls, the fraction of MSD cases that were attributable to Shigella infection increased from 9.6% (n = 129) for culture to 17.6% (n = 262) for qPCR when employing our cutpoint. We suggest that qPCR with a cutpoint of approximately 1.4 × 104
ipaH copies be the new reference standard for the detection and diagnosis of shigellosis in children in low-income countries. The acceptance of this new standard would substantially increase the fraction of MSD cases that are attributable to Shigella.
Vibrio cholerae in O-group 139 was first isolated in 1992 and by 1993 had been found throughout the Indian subcontinent. This epidemic expansion probably resulted from a single source after a lateral gene transfer (LGT) event that changed the serotype of an epidemic V. cholerae O1 El Tor strain to O139. However, some studies found substantial genetic diversity, perhaps caused by multiple origins. To further explore the relatedness of O139 strains, we analyzed nine sequenced loci from 96 isolates from patients at the Infectious Diseases Hospital, Calcutta, from 1992 to 2000. We found 64 novel alleles distributed among 51 sequence types. LGT events produced three times the number of nucleotide changes compared to mutation. In contrast to the traditional concept of epidemic spread of a homogeneous clone, the establishment of variant alleles generated by LGT during the rapid expansion of a clonal bacterial population may be a paradigm in infections and epidemics.
cholera; evolution; base sequence; DNA; bacterial; evolution; molecular sequence data; research
Vibrio cholerae; ctxBET; ctxBCL; altered El Tor; prototype El Tor; antibiotic resistance; PFGE; pulsed-field gel electrophoresis; bacteria
Bacteriovorax marinus SJ is a predatory delta-proteobacterium isolated from a marine environment. The genome sequence of this strain provides an interesting contrast to that of the terrestrial predatory bacterium B. bacteriovorus HD100. Based on their predatory lifestyle, Bacteriovorax were originally designated members of the genus Bdellovibrio but subsequently were re-assigned to a new genus and family based on genetic and phenotypic differences. B. marinus attaches to Gram negative bacteria, attaches, penetrates through the cell wall to form a bdelloplast, in which it replicates, as shown using microscopy.
Bacteriovorax is distinct, since it shares only 30% of its gene products with its closest sequenced relatives. Remarkably, 34% of predicted genes over 500 nt in length were completely unique with no significant matches in the databases. As expected Bacteriovorax shares several characteristic loci with the other delta-proteobacteria.
A shared geneset Bacteriovorax and Bdellovibrio that is not conserved amongst other delta-proteobacteria such as Myxobacteria (which destroy prey bacteria externally via lysis), or the non-predatory Desulfo-bacteria and Geobacter species was identified. These 291 gene orthologues common to both Bacteriovorax and Bdellovibrio may be key indicators of predatory-specific processes required for prey entry. The hit locus from Bd. bacteriovorus is implicated in the switch from predatory to prey/host-independent (HI) growth. Although the locus is conserved in B. marinus, the sequence has only limited similarity. The results of this study advance understanding of both the similarities and differences between Bdellovibrio and Bacteriovorax and confirm the distant relationship between the two and their separation into different genera.
We performed a retrospective cohort study (n = 129) to assess whether residents of extended care facilities who were initially colonized or infected with the methicillin-resistant Staphylococcus aureus (MRSA) strain USA300 were less likely to have prolonged colonization than were residents colonized or infected with other MRSA strains. We found no difference in prolonged colonization (adjusted odds ratio, 1.1 [95% confidence interval, 0.5–2.4]).
Neuregulin 1 (NRG1) is one of the leading candidate genes in schizophrenia. Rodents with NRG1 knock-out showed significantly impaired prepulse inhibition (PPI) in the original report linking NRG1 to schizophrenia (Stefansson et al 2002). PPI is a widely used surrogate measure of psychosis in animal models and is considered a schizophrenia endophenotype. We hypothesized that if NRG1 influences PPI in rodents, then it should have a similar effect on PPI in humans.
We examined the potential neurophysiological effects of two nonsynonymous single nucleotide polymorphisms (SNPs) located on NRG1 (rs3924999 and rs10503929) on PPI. Genotyping were completed in 430 unrelated individuals, including 244 schizophrenia cases and 186 controls. PPI was available in a subgroup of 113 cases and 63 controls.
Rs3924999 genotype was significantly associated with PPI (p=0.003): PPI was lowest in the subjects who were homozygous for the minor allele A/A carriers, intermediate in A/G carriers, and highest in homozygous major alleles G/G carriers. The associations persisted within cases (p=0.02) and controls (p=0.02) analyzed separately. An additive model suggested that rs3924999 alone contributes to 7.9% of the PPI variance. In contrast, rs10503929 genotype was not associated with PPI (p=0.85). Schizophrenia patients had reduced PPI compared to control subjects (p=0.04). Neither SNP was associated with schizophrenia (all p>0.37). However, schizophrenia patients with abnormal PPI may be associated with rs3924999 (p=0.05).
A missense mutation on rs3924999 of the neuregulin 1 gene may have a functional effect on prepulse inhibition in both schizophrenia and healthy control populations.
schizophrenia; glutamatergic; psychosis; endophenotype; nonsynonymous; polymorphism; PPI; NRG; NMDA; SNP
In a recent meta-analysis migraine was associated with a two-fold increase in stroke risk. While the mechanism driving this association is unknown, one intriguing hypothesis is that migraineurs are genetically predisposed to developing ischemic stroke. Mutations in the ATP1A2 gene are implicated in familial hemiplegic migraine type II and increase the severity of ischemic brain injury in animal models. To further explore these observations, we assessed the association between ATP1A2 polymorphisms, migraine, and the risk of ischemic stroke in participants of the Genetics of Early-Onset Stroke Study, a population-based case–control study of ischemic stroke among men and women aged 15–49. Using responses to a headache symptoms questionnaire, subjects were classified as having no migraine, or migraine with or without visual aura. Evaluating a total of 134 ATP1A2 polymorphisms genotyped using a combination of Illumina platforms (Cardiovascular Gene-centric 50 K SNP Array and HumanOmni1-Quad_v1-0_B Bead Chip), only one polymorphism (rs2070704) demonstrated a nominally significant association with stroke in an age-, gender-, ethnicity-adjusted model (OR = 0.83, 95% CI = 0.71-0.98, p = 0.025) and in a vascular risk factor model adjusting for age, gender, ethnicity, hypertension, diabetes, smoking, and myocardial infarction (OR = 0.74, 95% CI = 0.63-0.89, p = 0.001). Ethnicity-stratified analyses demonstrated a significant association for rs2070704 among African-Americans (OR = 0.68, 95% CI = 0.53-0.90, p = 0.005) but not Caucasians (OR = 0.82, 95% CI = 0.64-1.04, p = 0.107). These associations were unchanged when migraine subtypes were included as co-variates. We did not observe an association between ATP1A2 polymorphisms and migraine. While our results do not demonstrate a strong relationship between ATP1A2 polymorphisms and migraine associated stroke risk, the results are hypothesis generating and indicate that an association between ATP1A2 polymorphisms and stroke risk may exist. Additional studies are required.
Headache; Migraine; Stroke; Genetics; ATP1A2; Young
Enterotoxigenic Escherichia coli (ETEC) is an important cause of diarrhea, mainly in developing countries. Although there are 25 different ETEC adhesins described in strains affecting humans, between 15% and 50% of the clinical isolates from different geographical regions are negative for these adhesins, suggesting that additional unidentified adhesion determinants might be present. Here, we report the discovery of Coli Surface Antigen 23 (CS23), a novel adhesin expressed by an ETEC serogroup O4 strain (ETEC 1766a), which was negative for the previously known ETEC adhesins, albeit it has the ability to adhere to Caco-2 cells. CS23 is encoded by an 8.8-kb locus which contains 9 open reading frames (ORFs), 7 of them sharing significant identity with genes required for assembly of K88-related fimbriae. This gene locus, named aal (adhesion-associated locus), is required for the adhesion ability of ETEC 1766a and was able to confer this adhesive phenotype to a nonadherent E. coli HB101 strain. The CS23 major structural subunit, AalE, shares limited identity with known pilin proteins, and it is more closely related to the CS13 pilin protein CshE, carried by human ETEC strains. Our data indicate that CS23 is a new member of the diverse adhesin repertoire used by ETEC strains.
Bacteriovorax marinus SJ is a predatory delta-proteobacterium isolated from a marine environment. The genome sequence of this strain provides an interesting contrast to that of the terrestrial predatory bacterium Bdellovibrio bacteriovorus HD100. Based on their predatory lifestyle, Bacteriovorax were originally designated as members of the genus Bdellovibrio but subsequently were re-assigned to a new genus and family based on genetic and phenotypic differences. B. marinus attaches to Gram-negative bacteria, penetrates through the cell wall to form a bdelloplast, in which it replicates, as shown using microscopy. Bacteriovorax is distinct, as it shares only 30% of its gene products with its closest sequenced relatives. Remarkably, 34% of predicted genes over 500 nt in length were completely unique with no significant matches in the databases. As expected, Bacteriovorax shares several characteristic loci with the other delta-proteobacteria. A geneset shared between Bacteriovorax and Bdellovibrio that is not conserved among other delta-proteobacteria such as Myxobacteria (which destroy prey bacteria externally via lysis), or the non-predatory Desulfo-bacteria and Geobacter species was identified. These 291 gene orthologues common to both Bacteriovorax and Bdellovibrio may be the key indicators of host-interaction predatory-specific processes required for prey entry. The locus from Bdellovibrio bacteriovorus is implicated in the switch from predatory to prey/host-independent growth. Although the locus is conserved in B. marinus, the sequence has only limited similarity. The results of this study advance understanding of both the similarities and differences between Bdellovibrio and Bacteriovorax and confirm the distant relationship between the two and their separation into different families.
Bacteriovorax; Bdellovibrio; genome sequence; BALO; subtractive hybridization; host-interaction locus
USA300 methicillin-resistant Staphylococcus aureus (MRSA) is increasing as a cause of severe community-associated bacteremic infections. We assessed severe sepsis in response to infection in patients with USA300 MRSA compared to non-USA300 MRSA bacteremia.
A cohort study was conducted from 1997–2008 comparing sepsis in response to infection in 271 patients with MRSA bacteremia from four VA hospitals.
Sixty-seven (25%) patients with MRSA bacteremia were USA300 MRSA; 204 (75%) were non-USA300 MRSA. The proportion of MRSA bacteremia caused by USA300 MRSA increased over time (χ2 p<0.0001). Adjusting for age and nosocomial infection, patients with USA300 MRSA bacteremia were more likely to have severe sepsis or septic shock in response to infection than patients with non-USA300 MRSA bacteremia (adjusted Relative Risk=1.82; 95% CI: 1.16–2.87; p=0.01).
This suggests that patients with USA300 MRSA are more likely to develop severe sepsis in response to their infection, which could be due to host or bacterial differences.
Schizophrenia and nicotine addiction are both highly heritable phenotypes. Because individuals with schizophrenia have a higher rate of smoking than those in the general population, one could hypothesize that genes associated with smoking might be over-represented in schizophrenia and thus help explain their increased smoking incidence. Although a number of genes have been proposed to explain the increased smoking risk in schizophrenia, none of them have been consistently linked to smoking and schizophrenia and thus difficult to explain the increased smoking in schizophrenia. A functional smoking-related nicotinic acetylcholine receptor α5 subunit gene (CHRNA5) nonsynonymous SNP rs16969968 (Asp398Asn) has recently been discovered and replicated. As such, we tested whether this variant contributes to smoking in schizophrenia in a sample of 313 schizophrenia patients and 525 controls. The Asp398Asn risk allele is significantly associated with smoking severity independently in schizophrenia patient smokers (p=0.001) and in control smokers (p=0.029). Furthermore, the same risk allele is significantly associated with schizophrenia in both Caucasian (p=0.022) and African American (p=0.006) nonsmoker schizophrenia patients compared to control nonsmokers. Intriguing, this SNP was not significantly associated with smoking status (smokers vs. nonsmokers) in either schizophrenia patients or controls. Therefore, our study identifies a genetic variant that is simultaneously linked to smoking and schizophrenia in the same cohort, but whether and how this SNP contributes to the increased smoking prevalence in schizophrenia patients requires additional studies.
smoking; nicotine addiction; schizophrenia; nAChR; alpha5; comorbidity
The spread of drug-resistant Plasmodium falciparum malaria has been a major impediment to malaria control and threatens prospects for elimination. We recently demonstrated the return of chloroquine-susceptible malaria in Malawi after chloroquine use was abandoned. In this study, we trace the origins of chloroquine-resistant and chloroquine-susceptible parasites in Malawi by sequencing the P. falciparum chloroquine resistance transporter gene (pfcrt) and by genotyping microsatellites flanking this gene in isolates from infections that occurred in Malawi from 1992 through 2005. Malaria parasites from 2005 harbored the expected wild-type pfcrt haplotype associated with chloroquine susceptibility and have maintained high levels of diversity without linkage disequilibrium, which suggests that the return of chloroquine susceptibility is not the result of a back mutation in a formerly resistant parasite or a new selective sweep. Chloroquine-susceptible parasites that predominate in Malawi likely represent a reexpansion of the susceptible parasites that survived in the population despite widespread drug pressure in the region.