Within-population polymorphism of sex-determination systems in the common frog (Rana temporaria).

In sharp contrast with birds and mammals, the sex chromosomes of ectothermic vertebrates are often undifferentiated, for reasons that remain debated. A linkage map was recently published for Rana temporaria (Linnaeus, 1758) from Fennoscandia (Eastern European lineage), with a proposed sex-determining role for linkage group 2 (LG2). We analysed linkage patterns in lowland and highland populations from Switzerland (Western European lineage), with special focus on LG2. Sibship analyses showed large differences from the Fennoscandian map in terms of recombination rates and loci order, pointing to large-scale inversions or translocations. All linkage groups displayed extreme heterochiasmy (total map length was 12.2 cM in males, versus 869.8 cM in females). Sex determination was polymorphic within populations: a majority of families (with equal sex ratios) showed a strong correlation between offspring phenotypic sex and LG2 paternal haplotypes, whereas other families (some of which with female-biased sex ratios) did not show any correlation. The factors determining sex in the latter could not be identified. This coexistence of several sex-determination systems should induce frequent recombination of X and Y haplotypes, even in the absence of male recombination. Accordingly, we found no sex differences in allelic frequencies on LG2 markers among wild-caught male and female adults, except in one high-altitude population, where nonrecombinant Y haplotypes suggest sex to be entirely determined by LG2. Multifactorial sex determination certainly contributes to the lack of sex-chromosome differentiation in amphibians.

Division of labour and worker size polymorphism in ant colonies: the impact of social and genetic factors

Division of labour among workers is central to the organisation and ecological success of insect societies. If there is a genetic component to worker size, morphology or task preference, an increase in colony genetic diversity arising from the presence of multiple breeders per colony might improve division of labour. We studied the genetic basis of worker size and task preference in Formica selysi, an ant species that shows natural variation in the number of mates per queen and the number of queens per colony. Worker size had a heritable component in colonies headed by a doubly mated queen (h(2)=0.26) and differed significantly among matrilines in multiple-queen colonies. However, higher levels of genetic diversity did not result in more polymorphic workers across single- or multiple-queen colonies. In addition, workers from multiple-queen colonies were consistently smaller and less polymorphic than workers from single-queen colonies. The relationship between task, body size and genetic lineage appeared to be complex. Foragers were significantly larger than brood-tenders, which may provide energetic or ergonomic advantages to the colony. Task specialisation was also often associated with genetic lineage. However, genetic lineage and body size were often correlated with task independently of each other, suggesting that the allocation of workers to tasks is modulated by multiple factors. Overall, these results indicate that an increase in colony genetic diversity does not increase worker size polymorphism but might improve colony homeostasis.

Confounding factors and genetic polymorphism in the evaluation of individual steroid profiling

In the fight against doping, steroid profiling is a powerful tool to detect drug misuse with endogenous anabolic androgenic steroids. To establish sensitive and reliable models, the factors influencing profiling should be recognised. We performed an extensive literature review of the multiple factors that could influence the quantitative levels and ratios of endogenous steroids in urine matrix. For a comprehensive and scientific evaluation of the urinary steroid profile, it is necessary to define the target analytes as well as testosterone metabolism. The two main confounding factors, that is, endogenous and exogenous factors, are detailed to show the complex process of quantifying the steroid profile within WADA-accredited laboratories. Technical aspects are also discussed as they could have a significant impact on the steroid profile, and thus the steroid module of the athlete biological passport (ABP). The different factors impacting the major components of the steroid profile must be understood to ensure scientifically sound interpretation through the Bayesian model of the ABP. Not only should the statistical data be considered but also the experts in the field must be consulted for successful implementation of the steroidal module.

Complement Factor B Polymorphism and the Phenotype of Early Age-related Macular Degeneration.

Abstract Purpose: Age-related macular degeneration (AMD) has been associated with a number of polymorphisms in genes in the complement pathway. We examined the potential genotype-phenotype correlation of complement factor B (CFB) (R32Q) polymorphisms in Caucasian patients with AMD. Methods: Data from a Central European cohort of 349 patients with early AMD in at least one eye were analyzed for potential associations of the CFB (R32Q/rs641153) polymorphism with phenotypic features of early AMD. Early AMD was classified according to the International Classification and Grading System into predominant drusen size, largest drusen, drusen covered surface, central or ring-like location, peripheral drusen, and pigmentary changes. The potential association with single nucleotide polymorphisms on CFB (R32Q/rs641153) was evaluated for all patients, corrected for age, sex, and the polymorphisms of CFH (Y402H) and ARMS2 (A69S). Results: CFB (R32Q) polymorphisms showed a significant association with smaller drusen size (largest drusen ≤250 µm, p = 0.021, predominant drusen ≤125 µm, p = 0.016), with smaller surface covered by drusen (≤10%; p = 0.02), and with more frequent occurrence of peripheral drusen (p = 0.007). No association was found for pigmentary changes. Conclusions: The CFB (R32Q) polymorphism was associated with AMD characterized by small drusen only, and appeared to be protective of large drusen (OR 0.48/0.45) and of larger drusen covered area (OR 0.34). Furthermore, peripheral drusen were more frequently found (OR 2.27). This result supports the role of complement components and their polymorphisms in drusen formation and may enable a better understanding of AMD pathogenesis.

Renal failure after high-dose methotrexate in a child homozygous for MTHFR C677T polymorphism

We report the case of an 11-year-old female treated for mediastinal T-cell lymphoma who presented renal failure following the second cycle of high-dose methotrexate (HDMTX). Because of life threatening plasma methotrexate (MTX) levels, carboxypeptidase G2 (CPDG2) was administered resulting in a dramatic decrease within 1 hr. The patient recovered from renal failure and no other side effects were observed. Homozygosity for the methylentetrahydrofolate reductase (MTHFR) C677T polymorphism diagnosed by molecular genetic analysis was the only explanation for this toxicity.

False-negative PCR result due to gene polymorphism: the example of Neisseria meningitidis.

Early treatment of meningococcal meningitis is mandatory but may negate the cerebrospinal fluid culture. Etiological diagnosis then mainly relies on PCR. Here, we report a case of false-negative results for real-time PCR for a Neisseria meningitidis serogroup B isolate with a polymorphism in the ctrA gene.

Heterozygote advantage and the maintenance of polymorphism for multilocus traits.

Explaining how polymorphism is maintained in the face of selection remains a puzzle since selection tends to erode genetic variation. Provided an infinitely large unsubdivided population and no frequency-dependance of selective values, heterozygote advantage is the text book explanation for the maintenance of polymorphism when selection acts at a diallelic locus. Here, we investigate whether this remains true when selection acts at multiple diallelic loci. We use five different definitions of heterozygote advantage that largely cover this concept for multiple loci. Using extensive numerical simulations, we found no clear associations between the presence of any of the five definitions of heterozygote advantage and the maintenance of polymorphism at all loci. The strength of the association decreases as the number of loci increases or as recombination decreases. We conclude that heterozygote advantage cannot be a general mechanism for the maintenance of genetic polymorphism at multiple loci. These findings suggest that a correlation between the number of heterozygote loci and fitness is not warranted on theoretical ground.

A polymorphism in the leptin gene promoter is associated with anemia in patients with HIV disease.

To study factors associated with anemia and its effect on survival in HIV-infected persons treated with modern combined antiretroviral therapy (cART), we characterized the prevalence of anemia in the Veterans Aging Cohort Study (VACS) and used a candidate gene approach to identify proinflammatory gene single nucleotide polymorphisms (SNPs) associated with anemia in HIV disease. The study comprised 1597 HIV(+) and 865 HIV(-) VACS subjects with DNA, blood, and annotated clinical data available for analysis. Anemia was defined according to World Health Organization criteria (hemoglobin < 13 g/dL and < 12 g/dL in men and women, respectively). The prevalence of anemia in HIV(+) and HIV(-) subjects was 23.1% and 12.9%, respectively. Independent of HIV status, anemia was present in 23.4% and 8% in blacks and whites, respectively. Analysis of our candidate genes revealed that the leptin -2548 G/A SNP was associated with anemia in HIV(+), but not HIV(-), patients, with the AA and AG genotypes significantly predicting anemia (P < .003 and P < .039, respectively, logistic regression). This association was replicated in an independent cohort of HIV(+) women. Our study provides novel insight into the association between genetic variability in the leptin gene and anemia in HIV(+) individuals.

IL28B expression depends on a novel TT/-G polymorphism which improves HCV clearance prediction.

Approximately 3% of the world population is chronically infected with the hepatitis C virus (HCV), with potential development of cirrhosis and hepatocellular carcinoma. Despite the availability of new antiviral agents, treatment remains suboptimal. Genome-wide association studies (GWAS) identified rs12979860, a polymorphism nearby IL28B, as an important predictor of HCV clearance. We report the identification of a novel TT/-G polymorphism in the CpG region upstream of IL28B, which is a better predictor of HCV clearance than rs12979860. By using peripheral blood mononuclear cells (PBMCs) from individuals carrying different allelic combinations of the TT/-G and rs12979860 polymorphisms, we show that induction of IL28B and IFN-γ-inducible protein 10 (IP-10) mRNA relies on TT/-G, but not rs12979860, making TT/-G the only functional variant identified so far. This novel step in understanding the genetic regulation of IL28B may have important implications for clinical practice, as the use of TT/G genotyping instead of rs12979860 would improve patient management.

Cutting edge: a Toll-like receptor 2 polymorphism that is associated with lepromatous leprosy is unable to mediate mycobacterial signaling.

Toll-like receptors (TLRs) are key mediators of the innate immune response to microbial pathogens. We investigated the role of TLRs in the recognition of Mycobacterium leprae and the significance of TLR2Arg(677)Trp, a recently discovered human polymorphism that is associated with lepromatous leprosy. In mice, TNF-alpha production in response to M. leprae was essentially absent in TLR2-deficient macrophages. Similarly, human TLR2 mediated M. leprae-dependent activation of NF-kappaB in transfected Chinese hamster ovary and human embryonic kidney 293 cells, with enhancement of this signaling in the presence of CD14. In contrast, activation of NF-kappaB by human TLR2Arg(677)Trp was abolished in response to M. leprae and Mycobacterium tuberculosis. The impaired function of this TLR2 variant provides a molecular mechanism for the poor cellular immune response associated with lepromatous leprosy and may have important implications for understanding the pathogenesis of other mycobacterial infections.

Covariation between plumage colour polymorphism and diet in the Barn Owl Tyto alba

Several hypotheses might explain the evolution and maintenance of colour morphs within animal populations. The 'alternative foraging strategy' hypothesis states that alternative colour morphs exploit different ecological niches. This hypothesis predicts that morphs differ in diet, either because foraging success on alternative prey species is morph-dependent or because differently coloured individuals exploit alternative habitats. I examined this prediction in the Barn Owl Tyto alba, a bird that varies in plumage coloration continuously from dark reddish-brown to white. On the European continent, Owls are light-coloured (subspecies T. a. alba) in the south and reddish-brown (T. a. guttata) in the north; in central Europe the two subspecies interbreed, generating many colour variants. If plumage coloration indicates alternative foraging strategies, in sympatry dark- and light-coloured owls should consume prey species that are typical of the diets of T. a. guttata and T. a. alba in allopatry, respectively. In line with this prediction, both in allopatry and in sympatry in Switzerland T. a. guttata fed primarily upon Common Voles Microtus arvalis and T. a. alba upon Wood Mice Apodemus spp. Statistical analyses suggest that morph-dependent diet did not arise from a non-random habitat distribution of owls with respect to plumage coloration. This suggests that foraging success upon alternative prey is morph-dependent.

Association of a common vitamin D-binding protein polymorphism with inflammatory bowel disease.

OBJECTIVE: Inflammatory bowel diseases (IBDs), Crohn's disease, and ulcerative colitis (UC), are multifactorial disorders, characterized by chronic inflammation of the intestine. A number of genetic components have been proposed to contribute to IBD pathogenesis. In this case-control study, we investigated the association between two common vitamin D-binding protein (DBP) genetic variants and IBD susceptibility. These two single nucleotide polymorphisms (SNPs) in exon 11 of the DBP gene, at codons 416 (GAT>GAG; Asp>Glu) and 420 (ACG>AAG; Thr>Lys), have been previously suggested to play roles in the etiology of other autoimmune diseases. METHODS: Using TaqMan SNP technology, we have genotyped 884 individuals (636 IBD cases and 248 non-IBD controls) for the two DBP variants. RESULTS: On statistical analysis, we observed that the DBP 420 variant Lys is less frequent in IBD cases than in non-IBD controls (allele frequencies, P=0.034; homozygous carrier genotype frequencies, P=0.006). This inverse association between the DBP 420 Lys and the disease remained significant, when non-IBD participants were compared with UC (homozygous carrier genotype frequencies, P=0.022) or Crohn's disease (homozygous carrier genotype frequencies, P=0.016) patients separately. Although the DBP position 416 alone was not found to be significantly associated with IBD, the haplotype DBP_2, consisting of 416 Asp and 420 Lys, was more frequent in the non-IBD population, particularly notably when compared with the UC group (Odds ratio, 4.390). CONCLUSION: Our study adds DBP to the list of potential genes that contribute to the complex genetic etiology of IBD, and further emphasizes the association between vitamin D homeostasis and intestinal inflammation.

Intraspecific competition reveals conditional fitness effects of single gene polymorphism at the Arabidopsis root growth regulator BRX.

Intraspecific genetic variation for morphological traits is observed in many organisms. In Arabidopsis thaliana, alleles responsible for intraspecific morphological variation are increasingly being identified. However, the fitness consequences remain unclear in most cases. Here, the fitness effects of alleles of the BRX gene are investigated. A brx loss-of-function allele, which was found in a natural accession, results in a highly branched but poorly elongated root system. Comparison between the control accession Sav-0 and an introgression of brx into this background (brxS) indicated that, surprisingly, brx loss of function did not negatively affect fitness in pure stands. However, in mixed, well-watered stands brxS performance and reproductive output decreased significantly, as the proportion of Sav-0 neighbors increased. Additional comparisons between brxS and a brxS line that was complemented by a BRX transgene confirmed a direct effect of the loss-of-function allele on plant performance, as indicated by restored competitive ability of the transgenic genotype. Further, because plant height was very similar across genotypes and because the experimental setup largely excluded shading effects, the impaired competitiveness of the brx loss-of-function genotype likely reflects below-ground competition. In summary, these data reveal conditional fitness effects of a single gene polymorphism in response to intraspecific competition in Arabidopsis.

Association between the A-2518G polymorphism in the monocyte chemoattractant protein-1 gene and insulin resistance and Type 2 diabetes mellitus.

AIMS/HYPOTHESIS: The molecular mechanisms of obesity-related insulin resistance are incompletely understood. Macrophages accumulate in adipose tissue of obese individuals. In obesity, monocyte chemoattractant protein-1 (MCP-1), a key chemokine in the process of macrophage accumulation, is overexpressed in adipose tissue. MCP-1 is an insulin-responsive gene that continues to respond to exogenous insulin in insulin-resistant adipocytes and mice. MCP-1 decreases insulin-stimulated glucose uptake into adipocytes. The A-2518G polymorphism in the distal regulatory region of MCP-1 may regulate gene expression. The aim of this study was to investigate the impact of this gene polymorphism on insulin resistance. METHODS: We genotyped the Ludwigshafen Risk and Cardiovascular Health (LURIC) cohort ( n=3307). Insulin resistance, estimated by homeostasis model assessment, and Type 2 diabetes were diagnosed in 803 and 635 patients respectively. RESULTS: Univariate analysis revealed that plasma MCP-1 levels were significantly and positively correlated with WHR ( p=0.011), insulin resistance ( p=0.0097) and diabetes ( p<0.0001). Presence of the MCP-1 G-2518 allele was associated with decreased plasma MCP-1 ( p=0.017), a decreased prevalence of insulin resistance (odds ratio [OR]=0.82, 95% CI: 0.70-0.97, p=0.021) and a decreased prevalence of diabetes (OR=0.80, 95% CI: 0.67-0.96, p=0.014). In multivariate analysis, the G allele retained statistical significance as a negative predictor of insulin resistance (OR=0.78, 95% CI: 0.65-0.93, p=0.0060) and diabetes (OR=0.80, 95% CI: 0.66-0.96, p=0.018). CONCLUSIONS/INTERPRETATION: In a large cohort of Caucasians, the MCP-1 G-2518 gene variant was significantly and negatively correlated with plasma MCP-1 levels and the prevalence of insulin resistance and Type 2 diabetes. These results add to recent evidence supporting a role for MCP-1 in pathologies associated with hyperinsulinaemia.