Xq27 FRAXA Locus is a Strong Candidate for Dyslexia: Evidence from a Genome-Wide Scan in French Families

Dyslexia is a frequent neurodevelopmental learning disorder. To date, nine susceptibility loci have been identified, one of them being DYX9, located in Xq27. We performed the first French SNP linkage study followed by candidate gene investigation in dyslexia by studying 12 multiplex families (58 subjects) with at least two children affected, according to categorical restrictive criteria for phenotype definition. Significant results emerged on Xq27.3 within DYX9. The maximum multipoint LOD score reached 3,884 between rs12558359 and rs454992. Within this region, seven candidate genes were investigated for mutations in exonic sequences (CXORF1, CXORF51, SLITRK2, FMR1, FMR2, ASFMR1, FMR1NB), all having a role during brain development. We further looked for 5′UTR trinucleotide repeats in FMR1 and FMR2 genes. No mutation or polymorphism co-segregating with dyslexia was found. This finding in French families with Dyslexia showed significant linkage on Xq27.3 enclosing FRAXA, and consequently confirmed the DYX9 region as a robust susceptibility locus. We reduced the previously described interval from 6.8 (DXS1227–DXS8091) to 4 Mb also disclosing a higher LOD score.     

Effects of sanguinarium, chlorhexidine and tetracycline on neutrophil viability and functions in vitro

The effectiveness of an ideal antimicrobial agent depends on its ability to kill microbes with minimal toxicity to host cells. Depending on the treatment regimen, antimicrobial agents come into contact with host cells for various intervals of time. Sanguinarium (SANG), chlorhexidine (CHX) and tetracycline (TET) are 3 antimicrobial agents frequently used in the management of periodontal infections. However, their effects on host immune cells during different treatment regimens are not known. Due to their ability to serve as the first line of host defense against microbial infections, we have compared the effects of these antimicrobial agents on human neutrophil functions and viability. The results show that SANG is not lytic to neutrophils from peripheral blood or crevicular fluid, at all concentrations tested. However, exposures of neutrophils to very low concentrations of SANG (0.001%) inhibits neutrophil chemotaxis, oxidative metabolism and degranulation within 5 min. Increasing the exposure time results in a similar inhibition of neutrophil functions, albeit at 50–100 fold lower concentrations of SANG. CHX rapidly disrupts the cell membrane of both crevicular and peripheral blood neutrophils at concentrations above 0.005% within 5 min, and inhibition of all neutrophil functions is due to its lytic properties. While TET is least toxic to neutrophils, a dose dependent inhibition of neutrophil functions is dependent on the calcium concentrations of the cellular environment, and is observed only above 0.04% or higher concentrations in the absence of calcium. The data suggest that a critical cumulative concentration of these drugs is essential for their toxicity and inhibition of neutrophil functions. Therefore, both the length of exposure and the dose of the drug both are critical while considering the effectiveness of SANG, CHX or TET in the treatment of infections. Furthermore, due to differences in their mechanisms of action, the consequences of their effects on neutrophils may have significant bearing on tissue pathology as well as on their therapeutic efficacy.     

Spirochete chemotaxis, motility, and the structure of the spirochetal periplasmic flagella.

Spirochetes have a unique motility system that is characterized by flagellar filaments contained within the outer membrane sheath. Direct evidence using video microscopy has recently been obtained which indicates that these periplasmic flagella (PF) rotate in several spirochetal species. This rotation generates thrust. As shown for one spirochete, Spirochaeta aurantia, motility is driven by a proton motive force. Spirochete chemotaxis has been most thoroughly studied in S. aurantia. This spirochete exhibits three distinct behaviours, runs of smooth swimming, reversals and flexing. These behaviours are modulated by addition of attractants such that S. aurantia swims towards higher concentrations of attractants in a spatial gradient. Unlike the prototypical bacterium, Escherichia coli, chemotaxis in S. aurantia involves fluctuations in membrane potential. The PF of a number of spirochetes have been examined in considerable detail. For most species, the PF filaments are complex, consisting of an assembly of several different polypeptides. There are several antigenically related core polypeptides surrounded by an outer layer consisting of a different polypeptide. Borrelia burgdorferi and Spirochaeta zuelzerae represent exceptions where the filaments are composed of a single major polypeptide species. The genes encoding the filament polypeptides from several spirochete species have been cloned and analysed. Apparently, the outer layer polypeptides of S. aurantia, Treponema pallidum and Serpulina hyodysenteriae are transcribed from sigma-70-like promoters, whereas the core polypeptide genes are transcribed from sigma-28-like promoters. A gene encoding the hook polypeptide in Treponema phagedenis has been cloned and analysed. The product of this gene shows significant similarity to the E. coli hook protein, FlgE, and homologs have been identified in T. pallidum and B. burgdorferi.(ABSTRACT TRUNCATED AT 250 WORDS)     

Antileptospiral activity in lower-vertebrate sera.

Normal serum from the painted turtle (Chrysemys picta), the snapping turtle (Chelydra serpentina), and the frog (Rana pipiens) were found to possess bactericidal activity towards Leptospira. Leptospires from both the parasitic and biflexa complexes were killed by these sera at high dilutions. This pattern differs from that of mammalian serum, as generally only the biflexa complex leptospires are killed by normal mammalian serum. The activity in C. picta serum was characterized as being complement dependent and not mediated by basic proteins. Because comple-inactivated C. picta serum regained leptospiricidal activity after the addition of fresh rabbit serum, antibody is also likely to participate in the killing activity. Further support that C. picta serum contained leptospiral antibodies was found by the detection of serotype-specific agglutinins.     

Suppression of lymphocyte and fibroblast proliferation by Actinomyces viscosus-activated murine macrophages

Actinomyces viscosus , a normal inhabitant of the oral cavity, has previously been shown to evoke immune responses in the host. Macrophage activation by this microorganism was studied in a murine system. Peritoneal macrophages, activated in vivo by A. viscosus had a suppressive effect on lymphocyte proliferation in vitro ; total suppression occurred at a PEC to lymphocyte ratio of 6:10. A. viscosus -activated macrophages also suppressed the proliferation of normal syngeneic fibroblasts, with a 96% suppression at a PEC to fibroblast ratio of 9:1. Resident peritoneal macrophages had no suppressive effect on either target cell population. Suppression of fibroblast proliferation by A. viscosus -activated macrophages was partially reversed by catalase (20000 U/ml) or indomethacin (10^-5M), suggesting involvement of hydrogen peroxide and cylo-oxygenase product(s). A. viscosus -activated macrophages produced, upon stimulation, large amounts of H₂O₂ (256 nmole per mg protein, in 120 min) which were comparable to those produced by C. parvum -activated macrophages. Resident peritoneal macrophages produced only minor quantities of H₂O₂ under the same conditions. The suppressive effects observed suggest that A. viscosus , by activating macrophages, may modulate the host's immune response and may hamper the repair potential of chronically inflamed connective tissue by inhibition of fibroblast proliferation. Other constitutents of the plaque may share this effect.     

An in vitro study of neutrophils obtained from the normal gingival sulcus

Neutrophils (PMN) are considered to be key components in the protection of the periodontium against pathogenic bacteria. We therefore compared five of the major characteristics of peripheral blood PMN (PB-PMN) (adherence, chemotaxis, phagocytosis, oxidaiive metabolism, and lysosomal granules) to those of normal crevicular neutrophils (CR-PMN) isolated from the same individuals. The data indicate that the presence of Fc and C3b receptors, and the production of superoxide are similar in CR-PMN and PB-PMN. In addition, healthy gingival sulci harbor a high percentage of stimulated PMN as determined by the nitroblue tetrazolium (NBT) reduction assay. The percentage of CR-PMN which phagocytized opsonized red blood cells (RBC) was lower than that of PB-PMN. The in vitro migration of CR-PMN was reduced as compared to that of PB-PMN. Crevicular neutrophils also have a diminished ability to adhere to glass surfaces which may be related to a direct non-cytotoxic effect of gingival fluid component(s) on CR-PMN. In addition, morphologic evidence indicates that specific granules are more depleted than azurophil granules in CR-PMN. Interpretation of studies of neutrophil functions in periodontal diseases must consider the observed differences between normal peripheral blood and crevicular neutrophils.     

Variation at the IRF2 gene and susceptibility to psoriasis in chromosome 4q-linked families

Evidence, largely from Irish pedigrees, indicates that a susceptibility locus for psoriasis maps to chromosome 4q. The gene encoding interferon regulatory factor-2 (IRF-2) maps to this region, and, as mice lacking IRF-2 exhibit a dermatologic phenotype resembling many aspects of human psoriasis, IRF-2 represents an attractive positional candidate. We set out to establish whether variation in IRF-2 sequence or expression was related to the development of psoriasis. First, the promoter, coding, and adjacent untranslated regions of IRF-2 were screened in individuals from 4q-linked families. Neither variant identified (IVS1A+29A/G; IVS3+729T/C), however, had functional credentials or statistical evidence supporting a susceptibility role. Second, in 62 Irish parent-offspring trios ascertained for psoriasis, we conducted a linkage-disequilibrium screen of the IRF2 region using a dense microsatellite map (covering 1.5 Mb from D4S1554 to D4S1540). Though there was nominal association for D4S1554/D4S2348 haplotypes (p=0.03) with one haplotype showing particularly skewed transmission to psoriatic offspring (p=0.0002, uncorrected), these markers lie some distance (500 kb) from IRF-2. Finally, we found no abnormalities of IRF-2 protein expression or distribution in skin biopsies from psoriatic individuals. These diverse lines of inquiry allow us to exclude variation in IRF2 as responsible for the 4q-linkage signal previously identified in Irish pedigrees.