Lack of evidence for GWAS signals of exfoliation glaucoma working via monogenic loss-of-function mutation in the nearest gene

PURPOSE

Exfoliation syndrome (XFS) is a systemic disease of elastin-rich tissues involving a deposition of fibrillar exfoliative material (XFM) in the anterior chamber of the eye, which can promote glaucoma. The purpose of this study was to create mice with CRISPR/Cas9-induced variations in candidate genes identified from human genome-wide association studies (GWAS) and screen them for indices of XFS.

METHODS

Variants predicted to be deleterious were sought in the Agpat1, Cacna1a, Loxl1, Pomp, Rbms3, Sema6a, and Tlcd5 genes of C57BL/6J mice using CRISPR/Cas9-based gene editing. Strains were phenotyped by slit-lamp, SD-OCT imaging, and fundus exams at 1-5 mos of age. Smaller cohorts of 12-mos-old mice were also studied.

RESULTS

Deleterious variants were identified in six targets; Pomp was recalcitrant to targeting. Multiple alleles of some targets were isolated, yielding 12 strains. Across all genotypes and ages, 277 mice were assessed by 902 slit-lamp exams, 928 SD-OCT exams, and 358 fundus exams. Homozygosity for Agpat1 or Cacna1a mutations led to early lethality; homozygosity for Loxl1 mutations led to pelvic organ prolapse, preventing aging. Loxl1 homozygotes exhibited a conjunctival phenotype of potential relevance to XFS. Multiple other genotype-specific phenotypes were variously identified. XFM was not observed in any mice.

CONCLUSIONS

This study did not detect XFM in any of the strains. This may have been due to species-specific differences, background dependence, or insufficient aging. Alternatively, it is possible that the current candidates, selected based on proximity to GWAS signals, are not effectors acting via monogenic loss-of-function mechanisms.

Anterior chamber depth in mice is controlled by several quantitative trait loci

Anterior chamber depth (ACD) is a quantitative trait associated with primary angle closure glaucoma (PACG). Although ACD is highly heritable, known genetic variations explain a small fraction of the phenotypic variability. The purpose of this study was to identify additional ACD-influencing loci using strains of mice. Cohorts of 86 N2 and 111 F2 mice were generated from crosses between recombinant inbred BXD24/TyJ and wild-derived CAST/EiJ mice. Using anterior chamber optical coherence tomography, mice were phenotyped at 10-12 weeks of age, genotyped based on 93 genome-wide SNPs, and subjected to quantitative trait locus (QTL) analysis. In an analysis of ACD among all mice, six loci passed the significance threshold of p = 0.05 and persisted after multiple regression analysis. These were on chromosomes 6, 7, 11, 12, 15 and 17 (named Acdq6, Acdq7, Acdq11, Acdq12, Acdq15, and Acdq17, respectively). Our findings demonstrate a quantitative multi-genic pattern of ACD inheritance in mice and identify six previously unrecognized ACD-influencing loci. We have taken a unique approach to studying the anterior chamber depth phenotype by using mice as genetic tool to examine this continuously distributed trait.

Whole-exome sequencing prioritizes candidate genes for hereditary cataract in the Emory mouse mutant

The Emory cataract (Em) mouse mutant has long been proposed as an animal model for age-related or senile cataract in humans-a leading cause of visual impairment. However, the genetic defect(s) underlying the autosomal dominant Em phenotype remains elusive. Here, we confirmed development of the cataract phenotype in commercially available Em/J mice [but not ancestral Carworth Farms White (CFW) mice] at 6-8 months of age and undertook whole-exome sequencing of candidate genes for Em. Analysis of coding and splice-site variants did not identify any disease-causing/associated mutations in over 450 genes known to underlie inherited and age-related forms of cataract and other lens disorders in humans and mice, including genes for lens crystallins, membrane/cytoskeleton proteins, DNA/RNA-binding proteins, and those associated with syndromic/systemic forms of cataract. However, we identified three cataract/lens-associated genes each with one novel homozygous variant including predicted missense substitutions in Prx (p.R167C) and Adamts10 (p.P761L) and a disruptive in-frame deletion variant (predicted missense) in Abhd12 (p.L30_A32delinsS) that were absent in CFW and over 35 other mouse strains. In silico analysis predicted that the missense substitutions in Prx and Adamts10 were borderline neutral/damaging and neutral, respectively, at the protein function level, whereas, that in Abhd12 was functionally damaging. Both the human counterparts of Adamts10 and Abhd12 are clinically associated with syndromic forms of cataract known as Weil-Marchesani syndrome 1 and polyneuropathy, hearing loss, ataxia, retinitis pigmentosa, and cataract syndrome, respectively. Overall, while we cannot exclude Prx and Adamts10, our data suggest that Abhd12 is a promising candidate gene for cataract in the Em/J mouse.

Biological Correlations and Confounders for Quantification of Retinal Ganglion Cells by Optical Coherence Tomography Based on Studies of Outbred Mice

Purpose

Despite popularity of optical coherence tomography (OCT) in glaucoma studies, it's unclear how well OCT-derived metrics compare to traditional measures of retinal ganglion cell (RGC) abundance. Here, Diversity Outbred (J:DO) mice are used to directly compare ganglion cell complex (GCC) thickness measured by OCT to metrics of retinal anatomy measured ex vivo with retinal wholemounts and optic nerve histology.

Methods

J:DO mice (n = 48) underwent fundoscopic and OCT examinations, with automated segmentation of GCC thickness. RGC axons were quantified from para-phenylenediamine-stained optic nerve cross-sections and somas from BRN3A-immunolabeled retinal wholemounts, with total inner retinal cellularity assessed by TO-PRO and subsequent hematoxylin staining.

Results

J:DO tissues lacked overt disease. GCC thickness, RGC abundance, and total cell abundance varied broadly across individuals. GCC thickness correlated significantly to RGC somal density (r = 0.58) and axon number (r = 0.44), but not total cell density. Retinal area and nerve cross-sectional area varied widely. No metrics were significantly influenced by sex. In bilateral comparisons, GCC thickness (r = 0.95), axon (r = 0.72), and total cell density (r = 0.47) correlated significantly within individuals.

Conclusions

Amongst outbred mice, OCT-derived measurements of GCC thickness correlate significantly to RGC somal and axon abundance. Factors limiting correlation are likely both biological and methodological, including differences in retinal area that distort sampling-based estimates of RGC abundance.

Translational Relevance

There are significant-but imperfect-correlations between GCC thickness and RGC abundance across genetic contexts in mice, highlighting valid uses and ongoing challenges for meaningful use of OCT-derived metrics.

Recombinant adenovirus causes prolonged mobilization of macrophages in the anterior chambers of mice

PURPOSE

Ocular tissues of mice have been studied in many ways using replication-deficient species C type 5 adenovirus (Ad5) as a tool for manipulating gene expression. Whereas refinements to injection protocols and tropism have led to several advances in targeting cells of interest, there remains a relative lack of information concerning how Ad5 may influence other ocular cell types capable of confounding experimental interpretation. Here, a slit lamp is used to thoroughly photodocument the sequelae of intraocular Ad5 injections over time in mice, with attention to potentially confounding indices of inflammation.

METHODS

A cohort of C57BL/6J mice was randomly split into three groups (Virus, receiving unilateral intracameral injection with 5×107 plaque-forming units (pfu) of a cargo-less Ad5 construct; Saline, receiving unilateral balanced salt solution injection; and Naïve, receiving no injections). From this initial experiment, a total of 52 eyes from 26 mice were photodocumented via slit lamp at four time points (baseline and 1, 3, and 10 weeks following initiation of the experiment) by an observer masked to treatments and other parameters of the experimental design. Following the last in vivo exam, tissues were collected. Based on the slit-lamp data, tissues were studied via immunostaining with the macrophage marker F4/80. Subsequently, three iterations of the original experiment were performed with otherwise identical experimental parameters testing the effect of age, intravitreal injection, and A195 buffer, adding slit-lamp photodocumentation of an additional 32 eyes from 16 mice.

RESULTS

The masked investigator could use the sequential images from each mouse in the initial experiment to assign each mouse to its correct treatment group with near perfect fidelity. Virus-injected eyes were characterized by corneal damage indicative of intraocular injection and a prolonged mobilization of clump cells on the surface of the iris. Saline-injected eyes had only transient corneal opacities indicative of intraocular injections, and Naïve eyes remained normal. Immunostaining with F4/80 was consistent with ascribing the clump cells visualized via slit-lamp imaging as a type of macrophage. Experimental iterations using Ad5 indicate that all virus-injected eyes had the distinguishing feature of a prolonged presence of clump cells on the surface of the iris regardless of injection site. Mice receiving an intraocular injection of Ad5 at an advanced age displayed a protracted course of corneal cloudiness that prevented detailed visualization of the iris at the last time point.

CONCLUSIONS

Because the eye is often considered an "immune privileged site," we suspect that several studies have neglected to consider that the presence of Ad5 in the eye might evoke strong reactions from the innate immune system. Ad5 injection caused a sustained mobilization of clump cells-that is, macrophages. This change is likely a consequence of either direct macrophage transduction or a secondary response to cytokines produced locally by other transduced cells. Regardless of how these cells were altered, the important implication is that the adenovirus led to long-lasting changes in the environment of the anterior chamber. Thus, these findings describe a caveat of Ad5-mediated studies involving macrophage mobilization, which we encourage groups to use as a bioassay in their experiments and consider in interpretation of their ongoing experiments using adenoviruses.

Quantification and image-derived phenotyping of retinal ganglion cell nuclei in the nee mouse model of congenital glaucoma

The nee mouse model exhibits characteristic features of congenital glaucoma, a common cause of childhood blindness. The current study of nee mice had two components. First, the time course of neurodegeneration in nee retinal flat-mounts was studied over time using a retinal ganglion cell (RGC)-marker, BRN3A; a pan-nuclear marker, TO-PRO-3; and H&E staining. Based on segmentation of nuclei using ImageJ and RetFM-J, this analysis identified a rapid loss of BRN3A⁺ nuclei from 4 to 15 weeks of age, with the first statistically significant difference in average density compared to age-matched controls detected in 8-week-old cohorts (49% reduction in nee). Consistent with a model of glaucoma, no reductions in BRN3A^- nuclei were detected, but the combined analysis indicated that some RGCs lost BRN3A marker expression prior to actual cell loss. These results have a practical application in the design of experiments using nee mice to study mechanisms or potential therapies for congenital glaucoma. The second component of the study pertains to a discovery-based analysis of the large amount of image data with 748,782 segmented retinal nuclei. Using the automatedly collected region of interest feature data captured by ImageJ, we tested whether RGC density of glaucomatous mice was significantly correlated to average nuclear area, perimeter, Feret diameter, or MinFeret diameter. These results pointed to two events influencing nuclear size. For variations in RGC density above approximately 3000 nuclei/mm² apparent spreading was observed, in which BRN3A^- nuclei-regardless of genotype-became slightly larger as RGC density decreased. This same spreading occurred in BRN3A⁺ nuclei of wild-type mice. For variation in RGC density below 3000 nuclei/mm², which only occurred in glaucomatous nee mutants, BRN3A⁺ nuclei became smaller as disease was progressively severe. These observations have relevance to defining RGCs of relatively higher sensitivity to glaucomatous cell death and the nuclear dynamics occurring during their demise.

Exome-based investigation of the genetic basis of human pigmentary glaucoma

Background

Glaucoma is a leading cause of visual disability and blindness. Release of iris pigment within the eye, pigment dispersion syndrome (PDS), can lead to one type of glaucoma known as pigmentary glaucoma. PDS has a genetic component, however, the genes involved with this condition are largely unknown. We sought to discover genes that cause PDS by testing cohorts of patients and controls for mutations using a tiered analysis of exome data.

Results

Our primary analysis evaluated melanosome-related genes that cause dispersion of iris pigment in mice (TYRP1, GPNMB, LYST, DCT, and MITF). We identified rare mutations, but they were not statistically enriched in PDS patients. Our secondary analyses examined PMEL (previously linked with PDS), MRAP, and 19 other genes. Four MRAP mutations were identified in PDS cases but not in controls (p = 0.016). Immunohistochemical analysis of human donor eyes revealed abundant MRAP protein in the iris, the source of pigment in PDS. However, analysis of MRAP in additional cohorts (415 cases and 1645 controls) did not support an association with PDS. We also did not confirm a link between PMEL and PDS in our cohorts due to lack of reported mutations and similar frequency of the variants in PDS patients as in control subjects.

Conclusions

We did not detect a statistical enrichment of mutations in melanosome-related genes in human PDS patients and we found conflicting data about the likely pathogenicity of MRAP mutations. PDS may have a complex genetic basis that is not easily unraveled with exome analyses.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07782-0.

Identification of chronic brain protein changes and protein targets of serum auto-antibodies after blast-mediated traumatic brain injury

In addition to needing acute emergency management, blast-mediated traumatic brain injury (TBI) is also a chronic disorder with delayed-onset symptoms that manifest and progress over time. While the immediate consequences of acute blast injuries are readily apparent, chronic sequelae are harder to recognize. Indeed, the identification of individuals with mild-TBI or TBI-induced symptoms is greatly impaired in large part due to the lack of objective and robust biomarkers. The purpose of this study was to address these need by identifying candidates for serum-based biomarkers of blast TBI, and also to identify unique or differentially regulated protein expression in the thalamus in C57BL/6J mice exposed to blast using high throughput qualitative screens of protein expression. To identify thalamic proteins differentially or uniquely associated with blast exposure, we utilized an antibody-based affinity-capture strategy (referred to as "proteomics-based analysis of depletomes"; PAD) to deplete thalamic lysates from blast-treated mice of endogenous thalamic proteins also found in control mice. Analysis of this "depletome" detected 75 unique proteins, many with associations to the myelin sheath. To identify blast-associated proteins eliciting production of circulating autoantibodies, serum antibodies of blast-treated mice were immobilized, and their immunogens subsequently identified by proteomic analysis of proteins specifically captured following incubation with thalamic lysates (a variant of a strategy referred to as "proteomics-based expression library screening"; PELS). This analysis identified 46 blast-associated immunogenic proteins, including 6 shared in common with the PAD analysis (ALDOA, PHKB, HBA-A1, DPYSL2, SYN1, and CKB). These proteins and their autoantibodies are appropriate for further consideration as biomarkers of blast-mediated TBI.

Neprilysin inhibition promotes corneal wound healing

Neprilysin (NEP), an ectoenzyme that modulates inflammation by degrading neuropeptides, was recently identified in the human corneal epithelium. The cornea expresses many NEP substrates, but the function of NEP in homeostatic maintenance and wound healing of the cornea is unknown. We therefore investigated the role of this enzyme under naive and injured conditions using NEP-deficient (NEP-/-) and wild type (WT) control mice. In vivo ocular surface imaging and histological analysis of corneal tissue showed no differences in limbal vasculature or corneal anatomy between naive NEP-/- and WT mice. Histological examination revealed increased corneal innervation in NEP-/- mice. In an alkali burn model of corneal injury, corneal wound healing was significantly accelerated in NEP-/- mice compared to WT controls 3 days after injury. Daily intraperitoneal administration of the NEP inhibitor thiorphan also accelerated corneal wound healing after alkali injury in WT mice. Collectively, our data identify a previously unknown role of NEP in the cornea, in which pharmacologic inhibition of its activity may provide a novel therapeutic option for patients with corneal injury.

Genetic modifiers as relevant biological variables of eye disorders

From early in the study of mammalian genetics, it was clear that modifiers can have a striking influence on phenotypes. Today, several modifiers have now been studied in enough detail to allow a glimpse of how they function and influence our perspective of disease. With respect to diseases of the eye, some modifiers are an important source of phenotypic variation that can elucidate how genes function in networks to collectively shape ocular anatomy and physiology, thus influencing our understanding of basic biology. Other modifiers represent an opportunity for new therapeutic targets, whose manipulation could be used to mitigate ophthalmic disease. Here, we review progress in the study of genetic modifiers of eye disorders, with examples from mice and humans that together illustrate the ubiquitous nature of genetic modifiers and why they are relevant biological variables in experimental design. Special emphasis is given to ophthalmic modifiers in mice, especially those relevant to selection of genetic background and those that might inadvertently be a source of experimental variability. These modifiers are capable of influencing interpretations of many experiments using targeted genome manipulations such as knockouts or transgenics. Whereas there are fewer examples of modifiers of eye disorders in humans with a molecular identification, there is ample evidence that they exist and should be considered as a relevant biological variable in human genetic studies as well.

Heterozygous triplication of upstream regulatory sequences leads to dysregulation of matrix metalloproteinase 19 in patients with cavitary optic disc anomaly

Patients with a congenital optic nerve disease, cavitary optic disc anomaly (CODA), are born with profound excavation of the optic nerve resembling glaucoma. We previously mapped the gene that causes autosomal-dominant CODA in a large pedigree to a chromosome 12q locus. Using comparative genomic hybridization and quantitative PCR analysis of this pedigree, we report identifying a 6-Kbp heterozygous triplication upstream of the matrix metalloproteinase 19 (MMP19) gene, present in all 17 affected family members and no normal members. Moreover, the triplication was not detected in 78 control subjects or in the Database of Genomic Variants. We further detected the same 6-Kbp triplication in one of 24 unrelated CODA patients and in none of 172 glaucoma patients. Analysis with a Luciferase assay showed that the 6-Kbp sequence has transcription enhancer activity. A 773-bp fragment of the 6-Kbp DNA segment increased downstream gene expression eightfold, suggesting that triplication of this sequence may lead to dysregulation of the downstream gene, MMP19, in CODA patients. Lastly, immunohistochemical analysis of human donor eyes revealed strong expression of MMP19 in optic nerve head. These data strongly suggest that triplication of an enhancer may lead to overexpression of MMP19 in the optic nerve that causes CODA.

Genetic Evidence for Differential Regulation of Corneal Epithelial and Stromal Thickness

PURPOSE

Central corneal thickness (CCT) is a quantitative trait associated with keratoconus and primary open-angle glaucoma. Although CCT is highly heritable, known genetic variations explain only a fraction of the phenotypic variability. The purpose of this study was to identify additional CCT-influencing loci using inbred strains of mice.

METHODS

Cohorts of 82 backcrossed (N2) and 99 intercrossed (F2) mice were generated from crosses between recombinant inbred BXD24/TyJ and wild-derived CAST/EiJ mice. Using anterior chamber optical coherence tomography, mice were phenotyped at 10 to 12 weeks of age, genotyped based on 96 genome-wide single nucleotide polymorphisms (SNPs), and subjected to quantitative trait locus (QTL) analysis.

RESULTS

In an analysis of total CCT among all mice, two loci passed the significance threshold of P = 0.05. These were on Chr 3 and Chr 11 (Cctq4 and Cctq5, respectively). A third locus of interest was identified in a two-dimensional pairwise analysis; this locus on Chr 14 (Cctq6) exhibited a significant additive effect with Cctq5. Independent analyses of the dataset for epithelial and stromal thickness revealed that Cctq4 is specific to the epithelial layer and that Cctq5 and Cctq6 are specific to the stromal layer.

CONCLUSIONS

Our findings demonstrate a quantitative multigenic pattern of CCT inheritance in mice and identify three previously unrecognized CCT-influencing loci: Cctq4, Cctq5, and Cctq6. This is the first demonstration that distinct layers of the cornea are under differential genetic control and highlights the need to refine the design of future genome-wide association studies of CCT.

RetFM-J, an ImageJ-based module for automated counting and quantifying features of nuclei in retinal whole-mounts

The present article introduces RetFM-J, a semi-automated ImageJ-based module that detects, counts, and collects quantitative data on nuclei of the inner retina from H&E-stained whole-mounted retinas. To illustrate performance, computer-derived outputs were analyzed in inbred C57BL/6J mice. Automated characterization yielded computer-derived outputs that closely matched manual counts. As a method using open-source software that is freely available, inexpensive staining reagents that are robust, and imaging equipment that is routine to most laboratories, RetFM-J could be utilized in a wide variety of experiments benefiting from high-throughput, quantitative, uniform analyses of total cellularity in the inner retina.

Copy number variations and primary open-angle glaucoma

PURPOSE

This study sought to investigate the role of rare copy number variation (CNV) in age-related disorders of blindness, with a focus on primary open-angle glaucoma (POAG). Data are reported from a whole-genome copy number screen in a large cohort of 400 individuals with POAG and 500 age-matched glaucoma-free subjects.

METHODS

DNA samples from patients and controls were tested for CNVs using a combination of two microarray platforms. The signal intensity data generated from these arrays were then analyzed with multiple CNV detection programs including CNAG version 2.0, PennCNV, and dChip.

RESULTS

A total of 11 validated CNVs were identified as recurrent in the POAG set and absent in the age-matched control set. This set included CNVs on 5q23.1 (DMXL1, DTWD2), 20p12 (PAK7), 12q14 (C12orf56, XPOT, TBK1, and RASSF3), 12p13.33 (TULP3), and 10q34.21 (PAX2), among others. The CNVs presented here are exceedingly rare and are not found in the Database of Genomic Variants. Moreover, expression data from ocular tissue support the role of these CNV-implicated genes in vision-related processes. In addition, CNV locations of DMXL1 and PAK7 overlap previously identified linkage signals for glaucoma on 5p23.1 and 20p12, respectively.

CONCLUSIONS

The data are consistent with the hypothesis that rare CNV plays a role in the development of POAG.

Genome-wide analysis of copy number variants in age-related macular degeneration

Age-related macular degeneration (AMD) is a complex genetic disease, with many loci demonstrating appreciable attributable disease risk. Despite significant progress toward understanding the genetic and environmental etiology of AMD, identification of additional risk factors is necessary to fully appreciate and treat AMD pathology. In this study, we investigated copy number variants (CNVs) as potential AMD risk variants in a cohort of 400 AMD patients and 500 AMD-free controls ascertained at the University of Iowa. We used three publicly available copy number programs to analyze signal intensity data from Affymetrix GeneChip SNP Microarrays. CNVs were ranked based on prevalence in the disease cohort and absence from the control group; high interest CNVs were subsequently confirmed by qPCR. While we did not observe a single-locus "risk CNV" that could account for a major fraction of AMD, we identified several rare and overlapping CNVs containing or flanking compelling candidate genes such as NPHP1 and EFEMP1. These and other candidate genes highlighted by this study deserve further scrutiny as sources of genetic risk for AMD.

Autism genome-wide copy number variation reveals ubiquitin and neuronal genes

Autism spectrum disorders (ASDs) are childhood neurodevelopmental disorders with complex genetic origins. Previous studies focusing on candidate genes or genomic regions have identified several copy number variations (CNVs) that are associated with an increased risk of ASDs. Here we present the results from a whole-genome CNV study on a cohort of 859 ASD cases and 1,409 healthy children of European ancestry who were genotyped with approximately 550,000 single nucleotide polymorphism markers, in an attempt to comprehensively identify CNVs conferring susceptibility to ASDs. Positive findings were evaluated in an independent cohort of 1,336 ASD cases and 1,110 controls of European ancestry. Besides previously reported ASD candidate genes, such as NRXN1 (ref. 10) and CNTN4 (refs 11, 12), several new susceptibility genes encoding neuronal cell-adhesion molecules, including NLGN1 and ASTN2, were enriched with CNVs in ASD cases compared to controls (P = 9.5 x 10(-3)). Furthermore, CNVs within or surrounding genes involved in the ubiquitin pathways, including UBE3A, PARK2, RFWD2 and FBXO40, were affected by CNVs not observed in controls (P = 3.3 x 10(-3)). We also identified duplications 55 kilobases upstream of complementary DNA AK123120 (P = 3.6 x 10(-6)). Although these variants may be individually rare, they target genes involved in neuronal cell-adhesion or ubiquitin degradation, indicating that these two important gene networks expressed within the central nervous system may contribute to the genetic susceptibility of ASD.

Pax6 3' deletion results in aniridia, autism and mental retardation

The PAX6 gene is a transcription factor expressed early in development, predominantly in the eye, brain and gut. It is well known that mutations in PAX6 may result in aniridia, Peter's anomaly and kertatisis. Here, we present mutation analysis of a patient with aniridia, autism and mental retardation. We identified and characterized a 1.3 Mb deletion that disrupts PAX6 transcriptional activity and deletes additional genes expressed in the brain. Our findings provide continued evidence for the role of PAX6 in neural phenotypes associated with aniridia.

Determining the source of fecal contamination in recreational waters

Public health departments bear the responsibility for investigating recreational water-associated disease outbreaks. Tracking the source of the disease is often problematic, however, because routine monitoring of recreational waters (for bacterial counts) is not source specific. The intent of the project reported here was to monitor Escherichia coli levels in a small recreational lake in Iowa and to determine their source. The authors monitored water samples for E. coli and used phenotypic methods to analyze multiple samples of lake water, well water, and known fecal sources. Moderate to high levels of E. coli were found in lake water samples from the swimming area throughout the summer. The highest levels of E. coli were found after rainfall events in both lake water samples and samples taken from monitoring wells. Phenotypic analyses indicated that likely sources of E. coli in the lake included both human and wildlife (goose) fecal material. The authors also found that the phenotype used to characterize E. coli isolated from geese frequenting this lake could not be used to characterize E. coli isolated from geese in a neighboring watershed. Identifying the source of fecal material will help authorities implement the proper preventive measures to avoid fecal contamination of the lake in the future.

A quantitative study of ramped radio frequency, magnetization transfer, and slab thickness in three-dimensional time-of-flight magnetic resonance angiography in a patient population

RATIONALE AND OBJECTIVES

The authors compare the effectiveness of various magnetic resonance (MR) angiography acquisition strategies in enhancing the visibility of small intracranial vessels.

METHODS

Blood vessel contrast-to-noise ratio (CNR) in time-of-flight MR angiography was studied as a function of vessel size and several selectable imaging parameters. Contrast-to-noise measurements were made on 257 vessel segments ranging in size from 0.3 mm to 4.2 mm in patients who recently had undergone intraarterial cerebral angiography. Imaging parameters studied included magnetization transfer, spatially variable radio frequency (RF) pulse profile (ramped RF), and imaging slab thickness.

RESULTS

The combination of thin slabs (16 slices/slab), ramped RF, and magnetization transfer resulted in the highest CNR for all but the smallest vessel sizes. The smallest vessels (< 0.5 mm) had the highest CNR, using the thick slab (64 slices/slab) with ramped RF and magnetization transfer. Magnetization transfer always improved vessel CNR, but the improvement diminished as the slab thickness was reduced. The CNR increased with a decrease in slab thickness for all but the smallest vessel sizes.

CONCLUSIONS

Overall, the results provide a quantitative demonstration that inflow enhancement of blood is reduced for small vessels. Thus, whereas magnetization transfer is important at all vessel sizes, it becomes the primary factor in improving the visibility of the smallest vessels.

Dynamics of chromosome spreading

Consistency of optimum chromosome spreading during harvest of cytogenetic specimens remains a major concern. We have tested the idea that a precise control of the drying rate (the time with which metaphase cells dry), as fixed cell suspension is placed on a slide or an in situ culture in last fixation, may be the answer. Amniocyte and lymphocyte cultures were allowed to dry at defined combinations of relative humidity (RH) and temperature (T) in a modified Thermotron environmental control unit. We were able to demonstrate, based on 2,250 amniocytes and 1,650 lymphocytes, that the metaphase area after drying was a function of RH and T for both in situ and non-in situ culture systems. As the RH and T increase, the metaphase area increases until a threshold is reached. Also, as RH increases, the slide drying time increases. Data obtained using a response surface regression, proportional hazards regression analysis and slide drying time studies are consistent with our model of chromosome spreading. Optimum metaphase areas can be achieved at various combinations of RH and T. We propose that the use of an environmental control unit is a practical way of achieving optimum chromosome spreading routinely and in a highly consistent manner.

Immune response factors in rheumatic heart disease: meta-analysis of HLA-DR associations and evaluation of additional class II alleles

OBJECTIVES

This study used a meta-analysis to examine HLA-DR frequencies in rheumatic heart disease and prospectively examined other class II allelic disease associations.

BACKGROUND

Studies of rheumatic heart disease have reported HLA class II allelic associations, but these are inconsistent.

METHODS

A meta-analysis combined all known (n = 10) studies to determine disease risk associated with HLA-DR antigen expression. Meta-analysis of studies grouped by ethnic derivation of subjects was also performed. The present study also examined DQA, DQB and DPB allele frequencies by DNA-based strategies.

RESULTS

Meta-analysis showed a significant negative disease association with DR5 (odds ratio [OR] 0.67, p < 0.00003) for all combined studies. Among black patients, DR1 was increased (OR 2.80, p < 0.004); DR6 was increased (OR, 2.03, p < 0.003); and DR 8 was decreased (OR 0.32, p < 0.02). Among Eastern Indian patients, DR3 was increased (OR 2.44, p < 0.00003), with decreased expression for DR2 (OR 0.31, p < 0.00001) and DR5 (OR 0.52, p < 0.05). DR4 was increased among American whites (OR 1.74, p < 0.03), although there was significant heterogeneity among studies of whites. DQA, DQB and DPB allele frequencies were similar for control subjects and patients.

CONCLUSIONS

Our findings support an association between major histocompatibility complex class II alleles and risk for rheumatic heart disease. However, heterogeneity in associations was observed among different ethnic and racial groups; regional and temporal differences in streptococcal outbreaks may compound this heterogeneity. Further studies are necessary to elucidate the respective contributions of these variables.