Harlequin ichthyosis: ABCA12 mutations underlie defective lipid transport, reduced protease regulation and skin-barrier dysfunction

Harlequin ichthyosis (HI) is a devastating autosomal recessive congenital skin disease. It has been vital to elucidate the biological importance of the protein ABCA12 in skin-barrier permeability, following the discovery that ABCA12 gene mutations can result in this rare disease. ATP-binding cassette transporter A12 (ABCA12) is a member of the subfamily of ATP-binding cassette transporters and functions to transport lipid glucosylceramides (GlcCer) to the extracellular space through lamellar granules (LGs). GlcCer are hydrolysed into hydroxyceramides extracellularly and constitute a portion of the extracellular lamellar membrane, lipid envelope and lamellar granules. In HI skin, loss of function of ABCA12 due to null mutations results in impaired lipid lamellar membrane formation in the cornified layer, leading to defective permeability of the skin barrier. In addition, abnormal lamellar granule formation (distorted shape, reduced in number or absent) could further cause aberrant production of LG-associated desquamation enzymes, which are likely to contribute to the impaired skin barrier in HI. This article reviews current opinions on the patho-mechanisms of ABCA12 action in HI and potential therapeutic interventions based on targeted molecular therapy and gene therapy strategies.     

Epistatic Gene-Based Interaction Analyses for Glaucoma in eMERGE and NEIGHBOR Consortium

Primary open angle glaucoma (POAG) is a complex disease and is one of the major leading causes of blindness worldwide. Genome-wide association studies have successfully identified several common variants associated with glaucoma; however, most of these variants only explain a small proportion of the genetic risk. Apart from the standard approach to identify main effects of variants across the genome, it is believed that gene-gene interactions can help elucidate part of the missing heritability by allowing for the test of interactions between genetic variants to mimic the complex nature of biology. To explain the etiology of glaucoma, we first performed a genome-wide association study (GWAS) on glaucoma case-control samples obtained from electronic medical records (EMR) to establish the utility of EMR data in detecting non-spurious and relevant associations; this analysis was aimed at confirming already known associations with glaucoma and validating the EMR derived glaucoma phenotype. Our findings from GWAS suggest consistent evidence of several known associations in POAG. We then performed an interaction analysis for variants found to be marginally associated with glaucoma (SNPs with main effect p-value <0.01) and observed interesting findings in the electronic MEdical Records and GEnomics Network (eMERGE) network dataset. Genes from the top epistatic interactions from eMERGE data (Likelihood Ratio Test i.e. LRT p-value <1e-05) were then tested for replication in the NEIGHBOR consortium dataset. To replicate our findings, we performed a gene-based SNP-SNP interaction analysis in NEIGHBOR and observed significant gene-gene interactions (p-value <0.001) among the top 17 gene-gene models identified in the discovery phase. Variants from gene-gene interaction analysis that we found to be associated with POAG explain 3.5% of additional genetic variance in eMERGE dataset above what is explained by the SNPs in genes that are replicated from previous GWAS studies (which was only 2.1% variance explained in eMERGE dataset); in the NEIGHBOR dataset, adding replicated SNPs from gene-gene interaction analysis explain 3.4% of total variance whereas GWAS SNPs alone explain only 2.8% of variance. Exploring gene-gene interactions may provide additional insights into many complex traits when explored in properly designed and powered association studies.     

The Promise of Prevention: The Effects of Four Preventable Risk Factors on National Life Expectancy and Life Expectancy Disparities by Race and County in the United States

Background

There has been substantial research on psychosocial and health care determinants of health disparities in the United States (US) but less on the role of modifiable risk factors. We estimated the effects of smoking, high blood pressure, elevated blood glucose, and adiposity on national life expectancy and on disparities in life expectancy and disease-specific mortality among eight subgroups of the US population (the “Eight Americas”) defined on the basis of race and the location and socioeconomic characteristics of county of residence, in 2005.

Methods and Findings

We combined data from the National Health and Nutrition Examination Survey and the Behavioral Risk Factor Surveillance System to estimate unbiased risk factor levels for the Eight Americas. We used data from the National Center for Health Statistics to estimate age–sex–disease-specific number of deaths in 2005. We used systematic reviews and meta-analyses of epidemiologic studies to obtain risk factor effect sizes for disease-specific mortality. We used epidemiologic methods for multiple risk factors to estimate the effects of current exposure to these risk factors on death rates, and life table methods to estimate effects on life expectancy. Asians had the lowest mean body mass index, fasting plasma glucose, and smoking; whites had the lowest systolic blood pressure (SBP). SBP was highest in blacks, especially in the rural South—5–7 mmHg higher than whites. The other three risk factors were highest in Western Native Americans, Southern low-income rural blacks, and/or low-income whites in Appalachia and the Mississippi Valley. Nationally, these four risk factors reduced life expectancy at birth in 2005 by an estimated 4.9 y in men and 4.1 y in women. Life expectancy effects were smallest in Asians (M, 4.1 y; F, 3.6 y) and largest in Southern rural blacks (M, 6.7 y; F, 5.7 y). Standard deviation of life expectancies in the Eight Americas would decline by 0.50 y (18%) in men and 0.45 y (21%) in women if these risks had been reduced to optimal levels. Disparities in the probabilities of dying from cardiovascular diseases and diabetes at different ages would decline by 69%–80%; the corresponding reduction for probabilities of dying from cancers would be 29%–50%. Individually, smoking and high blood pressure had the largest effect on life expectancy disparities.

Conclusions

Disparities in smoking, blood pressure, blood glucose, and adiposity explain a significant proportion of disparities in mortality from cardiovascular diseases and cancers, and some of the life expectancy disparities in the US. Please see later in the article for the Editors'' Summary     

Direct and indirect costs of rabies exposure: a retrospective study in southern California (1998-2002)

The direct and indirect costs of suspected human rabies exposure were estimated for San Luis Obispo and Santa Barbara counties, California, USA. Clinic, hospital, and county public health records (1998-2002) were examined to determine direct costs for postexposure prophylaxis (PEP), and 55 (41%) former patients were contacted to voluntarily provide estimates of their indirect costs associated with receiving PEP. Additional costs due to public health and animal control personnel responses to rabid animals were collected, including diagnostic testing and wages. The mean total cost of a suspected human rabies exposure was $3,688, the direct costs per case were $2,564, and the indirect costs were $1,124 of that total. About one third of the total cost for suspected human rabies exposure was attributed to indirect costs (e.g., lost wages, transportation, and day-care fees), most of which were not reimbursable to the patient.     

Identification of Novel Crk-associated Substrate (p130Cas) Variants with Functionally Distinct Focal Adhesion Kinase Binding Activities

Elevated levels of p130^Cas (Crk-associated substrate)/BCAR1 (breast cancer antiestrogen resistance 1 gene) are associated with aggressiveness of breast tumors. Following phosphorylation of its substrate domain, p130^Cas promotes the integration of protein complexes involved in multiple signaling pathways and mediates cell proliferation, adhesion, and migration. In addition to the known BCAR1-1A (wild-type) and 1C variants, we identified four novel BCAR1 mRNA variants, generated by alternative first exon usage (1B, 1B1, 1D, and 1E). Exons 1A and 1C encode for four amino acids (aa), whereas 1D and 1E encode for 22 aa and 1B1 encodes for 50 aa. Exon 1B is non-coding, resulting in a truncated p130^Cas protein (Cas1B). BCAR1-1A, 1B1, and variant 1C mRNAs were ubiquitously expressed in cell lines and a survey of human tissues, whereas 1B, 1D, and 1E expression was more restricted. Reconstitution of all isoforms except for 1B in p130^Cas-deficient murine fibroblasts induced lamellipodia formation and membrane ruffling, which was unrelated to the substrate domain phosphorylation status. The longer isoforms exhibited increased binding to focal adhesion kinase (FAK), a molecule important for migration and adhesion. The shorter 1B isoform exhibited diminished FAK binding activity and significantly reduced migration and invasion. In contrast, the longest variant 1B1 established the most efficient FAK binding and greatly enhanced migration. Our results indicate that the p130^Cas exon 1 variants display altered functional properties. The truncated variant 1B and the longer isoform 1B1 may contribute to the diverse effects of p130^Cas on cell biology and therefore will be the target of future studies.     

Role of TAP-1 and/or TAP-2 antigen presentation defects in tumorigenicity of mouse melanoma

Mutations in transporters associated with antigen processing (TAP-1 and -2) required for the transport of cytosolic endogenous peptides to the endoplasmic reticulum correlate with increased metastatic potential and reduced host survival in several malignancies. To address the possible function of TAP as a "tumor suppressor" gene, we show that correction of TAP-1 and/or TAP-2 defects in B16 mouse melanoma enhanced the cell surface expression of MHC class I molecules and significantly reduced the rate of subcutaneous tumor growth and pulmonary metastatic burden. Cytotoxic assays confirmed increased sensitivity of TAP-1 and/or TAP-2 transfected clones of B16 melanoma to cytotoxic T lymphocytes. These results indicate that the expression of TAP limits the malignant potential of tumors with implications for CD8(+) T cell-based immunotherapy in controlling growth of certain TAP-deficient malignancies.     

EST-derived genic molecular markers: development and utilization for generating an advanced transcript map of chickpea

Well-saturated linkage maps especially those based on expressed sequence tag (EST)-derived genic molecular markers (GMMs) are a pre-requisite for molecular breeding. This is especially true in important legumes such as chickpea where few simple sequence repeats (SSR) and even fewer GMM-based maps have been developed. Therefore, in this study, 2,496 ESTs were generated from chickpea seeds and utilized for the development of 487 novel EST-derived functional markers which included 125 EST-SSRs, 151 intron targeted primers (ITPs), 109 expressed sequence tag polymorphisms (ESTPs), and 102 single nucleotide polymorphisms (SNPs). Whereas EST-SSRs, ITPs, and ESTPs were developed by in silico analysis of the developed EST sequences, SNPs were identified by allele resequencing and their genotyping was performed using the Illumina GoldenGate Assay. Parental polymorphism was analyzed between C. arietinum ICC4958 and C. reticulatum PI489777, parents of the reference chickpea mapping population, using a total of 872 markers: 487 new gene-based markers developed in this study along with 385 previously published markers, of which 318 (36.5%) were found to be polymorphic and were used for genotyping. The genotypic data were integrated with the previously published data of 108 markers and an advanced linkage map was generated that contained 406 loci distributed on eight linkage groups that spanned 1,497.7 cM. The average marker density was 3.68 cM and the average number of markers per LG was 50.8. Among the mapped markers, 303 new genomic locations were defined that included 177 gene-based and 126 gSSRs (genomic SSRs) thereby producing the most advanced gene-rich map of chickpea solely based on co-dominant markers.     

Parapapillary Atrophy: Histological Gamma Zone and Delta Zone

Background

To examine histomorphometrically the parapapillary region in human eyes.

Methodology/Principal Findings

The histomorphometric study included 65 human globes (axial length:21–37 mm). On anterior-posterior histological sections, we measured the distance Bruch''s membrane end (BME)-optic nerve margin (“Gamma zone”), BME-retinal pigment epithelium (RPE) (“Beta zone”), BME-beginning of non-occluded choriocapillaris, and BME-beginning of photoreceptor layer. “Delta zone” was defined as part of gamma zone in which blood vessels of at least 50 µm diameter were not present over a length of >300 µm. Beta zone (mean length:0.35±0.52 mm) was significantly (P = 0.01) larger in the glaucoma group than in the non-glaucomatous group. It was not significantly (P = 0.28) associated with axial length. Beta zone was significantly (P = 0.004) larger than the region with occluded choriocapillaris. Gamma zone (mean length:0.63±1.25 mm) was associated with axial length (P<0.001;r² = 0.73) with an increase starting at an axial length of 26.5 mm. It was not significantly (P = 0.24) associated with glaucomatous optic neuropathy. Delta zone (present only in eyes with axial length of ≥27 mm) was associated with axial length (P = 0.001) and scleral flange length (P<0.001) but not with glaucoma (P = 0.73).

Conclusions/Significance

Parapapillary gamma zone (peripapillary sclera without overlying choroid, Bruch''s membrane and deep retinal layers) was related with axial globe elongation and was independent of glaucoma. Delta zone (no blood vessels >50 µm diameter within gamma zone) was present only in highly axially elongated globes and was not related with glaucoma. Beta zone (Bruch''s membrane without RPE) was correlated with glaucoma but not with globe elongation. Since the region with occluded choriocapillaris was smaller than beta zone, complete loss of RPE may have occurred before complete choriocapillaris closure.