Alzheimer's disease associated with mutations in presenilin 2 is rare and variably penetrant

Missense mutations in the presenilin 2 (PS-2) gene on chromosome 1 were sought by direct nucleotide sequence analysis of the open reading frame of 60 pedigrees with familial Alzheimer's disease (FAD). In the majority of these pedigrees, PS-1 and beta-amyloid precursor protein (beta APP) gene mutations had been excluded. While no additional PS-2 pathogenic mutations were detected, four silent nucleotide substitutions and alternative splicing of nucleotides 1338-1340 (Glu325) were observed. Analysis of additional members of a pedigree known to segregate a Met239Val mutation in PS-2 revealed that the age of onset of symptoms is highly variable (range 45-88 years). This variability is not attributable to differences in ApoE genotypes. These results suggest (i) that, in contrast to mutations in PS-1, mutations in PS-2 are a relatively rare cause of FAD; (ii) that other genetic or environmental factor modify the AD phenotype associated with PS-2 mutations; and (iii) that still other FAD susceptibility genes remain to be identified.      

Molecular and cellular mechanisms for microbial entry into the CNS

A number of pathogenic microbes including neuroinvasive viruses, bacteria and parasites are capable of entry into the central nervous system (CNS) and cause a variety of clinical manifestations. The cellular and molecular mechanisms for the CNS invasion have been extensively studied in the last two decades. Viruses invade neurons and thereby cause encephalitis or peripheral neuritis, while bacteria enter the cerebrospinal fluid (CSF) and cause meningitis. In contrast, the mechanisms for parasitic neuroinvasion are much more complex and less clear. The capabilities that enable these elite subsets of pathogens to engineer uptake into the CNS will be the subject of this review.     

Identification of a carbohydrate recognition domain in filamentous hemagglutinin from Bordetella pertussis.

The adherence of Bordetella pertussis to ciliated cells and macrophages is critical to colonization and infection of the respiratory tract. Adherence to both types of cells involves the recognition of eukaryotic carbohydrates by the bacterial adhesin filamentous hemagglutinin (Fha). The carbohydrate recognition domain (CRD) of Fha is considered an important antigen for subcomponent vaccines to maximize the generation of antiadherence antibodies capable of protecting against colonization. For identification of the CRD of Fha, a bank of eight monoclonal antibodies (MAbs) that mapped to four contiguous regions were tested for their ability to block Fha binding to lactosylceramide or to block bacterial binding to ciliated cells. Only MAb 12.5A9, which maps to amino acid residues 1141 to 1279, blocked both Fha binding to lactosylceramide and bacterial binding to ciliated cells. An 18-kDa polypeptide corresponding to this region was expressed in Escherichia coli. Cell lysates containing this protein bound to lactosylceramide in a manner identical to that of native Fha. Mutant strains of B. pertussis that contained an in-frame deletion of the coding sequence for this region produced a truncated Fha that showed negligible cross-reactivity with MAb 12.5A9. In an adherence assay, these mutant strains failed to bind efficiently to either ciliated cells or macrophages. The numbers of adherent bacteria for these strains were reduced to the number obtained with a nonadherent strain. We conclude that the region defined by residues 1141 to 1279 of Fha constitutes a CRD critical for bacterial adherence and represents a potential candidate for a subcomponent vaccine.     

Serum immunoglobulin G response to candidate vaccine antigens during experimental human pneumococcal colonization

The immune response to pneumococcal surface structures during colonization was examined in a model of experimental human pneumococcal carriage. Healthy uncolonized adults were given a type 23F or 6B pneumococcus, and a portion of these subjects became colonized (6 of 14 with type 23F and 6 of 8 with type 6B). Sera from colonized and uncolonized subjects were used to determine the titer of antibody specific to pneumococcal surface components under consideration in development of noncapsular polysaccharide-based vaccines. These vaccine candidates included pneumococcal surface protein A (PspA), choline binding protein A (CbpA), lipoteichoic acid, immunoglobulin A1 (IgA1) protease, pneumolysin, proteinase maturation protein A, and pneumococcal surface adhesin A. Only the two related choline binding proteins, PspA and CbpA, were immunogenic in colonized subjects as determined by a statistically significant rise in the serum IgG titer. The serum IgG response to PspA was shown previously to correlate inversely with susceptibility to carriage and was localized to a region within the N-terminal portion of PspA. This region is highly variable in amino acid sequence between pneumococcal strains. Despite the sequence diversity in the immunodominant regions of both PspA and CbpA, a significant strain-to-strain cross-reactivity in the serum IgG response following experimental human carriage was observed. These findings support the need for further investigation of the human antibody response to PspA and CbpA and the potential use of one or both of these proteins as novel vaccine antigens for the prevention of pneumococcal colonization.     

The Kallmann syndrome gene product expressed in COS cells is cleaved on the cell surface to yield a diffusible component

Kallmann syndrome is characterized by hypogonadotropic hypogonadism and anosmia and caused by a defect of migration and targeting of gonadotropin-releasing hormone-secreting neurons and olfactory axons during embryonic development. We previously cloned the gene responsible for the X-linked form of the disease encoding a 680 amino acid protein, KAL, which displays the unusual combination of a protease inhibitor domain with fibronectin type III repeats. Previous expression studies by northern blot and RNA in situ hybridization in human and chick indicated that the gene is expressed at very low levels in the olfactory bulb during development. Therefore, low abundance of the protein has hampered a detailed biochemical characterization. By overexpressing both the human and chick KAL cDNAs in eukaryotic cells, we now provide evidence that KAL is a glycosylated peripheral membrane protein with an apparent molecular weight of approximately 100 kDa. We show that this 100 kDa protein is proteolytically processed on the cell membrane to yield a 45 kDa diffusible component, which is detectable with an antisera against the C-terminal part of the protein and binds tightly to cell surfaces. These data provide a first step toward understanding KAL function in neuronal interactions and neurite extension in the olfactory bulb and suggest that KAL might be a diffusible chemoattractant molecule for olfactory axons.      

Species specificity of Bordetella adherence to human and animal ciliated respiratory epithelial cells.

Bacteria of the genus Bordetella adhere preferentially to ciliated respiratory epithelial cells. We investigated the specificity of this unique tropism by assessing the concentration-dependent adherence of the three Bordetella species to ciliated cells from different hosts. Bordetella pertussis and Bordetella parapertussis adhere better to human ciliated cells than to those from rabbits, mice, or hamsters. In contrast, Bordetella bronchiseptica demonstrates preferential adherence to nonhuman mammalian ciliated cells of rabbits, mice, and hamsters. There was no attachment of any Bordetella organisms to chicken ciliated cells. These observations suggest that specificities of attachment may explain the marked predominance of B. pertussis as the cause of whooping cough in humans and of B. bronchiseptica as a respiratory pathogen of many nonhuman mammals.     

Early biofilm formation on microtiter plates is not correlated with the invasive disease potential of Streptococcus pneumoniae

Biofilm formation has been suggested to play an important role during Streptococcus pneumoniae nasopharyngeal colonization and may facilitate progression to pneumonia. To test whether the ability of S. pneumoniae to form biofilms was important for virulence we screened the ability of 30 invasive and 22 non-invasive clinical isolates of serotype 6A and 6B to form early biofilms on polystyrene microtiter plates and infect mice following intranasal and intratracheal challenge. We first determined that no correlation existed between the ability to form early biofilms and whether isolates were collected from healthy carriers or individuals with invasive disease. A disconnect between biofilm forming ability and the capacity to colonize the nasopharynx, cause pneumonia, and enter the bloodstream was also observed in mice. Importantly, S. pneumoniae mutants deficient in the established virulence determinants pneumolysin, CbpA, and hydrogen peroxide formed biofilms normally. Incidentally, we determined that robust biofilm production was dependent on the formation and coalescing of bacterial aggregates on a thin layer of bacteria attached to the plate surface. In summary, these studies suggest that the ability to form early biofilms in vitro does not reflect virulence potential. More complex studies are required to determine if biofilm formation is important for virulence.     

A homoallelic FECH mutation in a patient with both erythropoietic protoporphyria and palmar keratoderma

Background Erythropoietic protoporphyria (EPP) is a hereditary disorder caused by the deficiency of ferrochelatase (FECH) in the haem biosynthetic pathway. In the majority of families, EPP is transmitted as a pseudodominant trait. Autosomal recessive form of EPP is found in only about 3% of the families. Objectives In this study, we describe a 6‐year‐old boy who suffered from both EPP and palmar keratoderma. Methods and Results A novel homoallelic missense mutation (p.Ser318Tyr) was identified in the FECH gene. In addition, a region of homozygosity of approximately 6.8 Mb was observed in chromosome 18 of the patient by both microsatellite and SNP array. The parents of the patient, both of Palestinian (Jordanian) origin, were heterozygous for the S318Y mutation, although no history of consanguinity was known. Microsatellite genotyping identified a partial haplotype from each parent that corresponds to the region of homozygosity in the patient. Assuming S318Y is a founder mutation, the number of generations separating the two parents from their common ancestor from whom they inherited S318Y was estimated as 21.7 (95% CI 3.42–69.7). Conclusion EPP was therefore inherited as an autosomal recessive trait in the family. This study confirms the association between palmar keratoderma and autosomal recessive EPP.     

Bacteria etiological agents causing respiratory tract infections in children and their resistance patterns to a panel of ten antibiotics

ObjectiveTo study the bacteria etiological agents of respiratory tract infection among 280 school children in South East Nigeria, and to determine their antimicrobial resistance patterns to a panel of ten antibiotics.MethodsThroat swabs (280) were collected from students in four boarding schools located in Enugu and Onitsha metropolis. Standard microbiological procedures were used to screen these swabs to determine the prevalence of respiratory pathogens while the disc diffusion test was used to determine the antimicrobial resistance patterns of the recovered isolates.ResultsOf the 280 samples screened, 57.1% were positive. Haemophilus influenzae was the most prevalent (16.1%), followed by Streptococcus pyogenes (13.9%), Klebsiella pneumoniae (12.5%), Streptococcus pneumoniae (6.8%), Staphylococcus aureus (5.4%) and Corynebacterium diphtheriae (2.5%). More isolates were recovered in the two male schools investigated. However, there was no significant difference in the overall prevalence of isolates according to sex or school location of the subjects. Greater number of isolates (56%) was recovered from those aged 11–14 years. This was statistically significant (P<0.05), compared to the other two age groups (15–18 years and 19–23 years). The pattern of resistance varied according to the bacteria species. There were multi-resistant isolates. Since these students stand the risk of contracting respiratory tract infection particularly from reservoirs among them, there is need to increase surveillance and develop better strategies to curb the increasing prevalence of respiratory tract infection in this and other similar regions of Africa.ConclusionsThe spectrum of bacteria causing respiratory tract infection is still wide in Nigeria. Many isolates showed appreciable levels of antibiotic resistance apparently due to antibiotic abuse. Development of new strategies to curb this increasing prevalence of respiratory tract infection is warranted.     

长春瑞滨联合顺铂治疗32例多柔比星耐药的晚期乳腺癌

目的：观察长春瑞滨(诺维本，NVB)联合顺铂(DDP)治疗多柔比星(ADM)耐药的晚期复发、转移乳腺癌的近期疗效和毒副反应。方法：用NP方案对曾用含多柔比星联合方案治疗大于2周期后进展或复发、转移的晚期乳腺癌32例，21～28天为1周期，完成2～4周期后评价疗效。结果：总有效率62．5％，主要限量毒性为消化道反应和骨髓抑制，其次为周围神经炎。结论：NVB加DDP治疗多柔比星耐药的晚期乳腺癌仍是可供选择的有效方案，毒副反应可耐受。