In vivo genotoxicity testing strategies: Report from the 8th International Workshop on Genotoxicity Testing (IWGT).

The in vivo working group (WG) considered three topics: acceptable maximum doses for negative erythrocyte micronucleus (MN) tests, validation status of MN assays in non-hematopoietic tissues, and nuisance factors in the comet assay. The WG reached agreement on many issues, including: negative erythrocyte MN studies should be acceptable if dosing is conducted to Organisation for Economic Co-operation and Development (OECD) test guideline (TG) 474 recommendations and if sufficient bone marrow exposure is demonstrated; consensus on the evidence required to demonstrate "sufficient" exposure was not reached. The liver MN test using six-week-old rats is sufficiently validated to develop an OECD TG, but the impact of animal age warrants additional study.

Assessing the quality and making appropriate use of historical negative control data: A report of the International Workshop on Genotoxicity Testing (IWGT).

Historical negative control data (HCD) have played an increasingly important role in interpreting the results of genotoxicity tests. In particular, Organisation for Economic Co-operation and Development (OECD) genetic toxicology test guidelines recommend comparing responses produced by exposure to test substances with the distribution of HCD as one of three criteria for evaluating and interpreting study results (referred to herein as "Criterion C"). Because of the potential for inconsistency in how HCD are acquired, maintained, described, and used to interpret genotoxicity testing results, a workgroup of the International Workshops for Genotoxicity Testing was convened to provide recommendations on this crucial topic.

Establishing a quantitative framework for regulatory interpretation of genetic toxicity dose-response data: Margin of exposure case study of 48 compounds with both in vivo mutagenicity and carcinogenicity dose-response data.

Quantitative relationships between carcinogenic potency and mutagenic potency have been previously examined using a benchmark dose (BMD)-based approach. We extended those analyses by using human exposure data for 48 compounds to calculate carcinogenicity-derived and genotoxicity-derived margin of exposure values (MOEs) that can be used to prioritize substances for risk management. MOEs for 16 of the 48 compounds were below 10,000, and consequently highlighted for regulatory concern.

AOP report: Development of an adverse outcome pathway for oxidative DNA damage leading to mutations and chromosomal aberrations.

The Genetic Toxicology Technical Committee (GTTC) of the Health and Environmental Sciences Institute (HESI) is developing adverse outcome pathways (AOPs) that describe modes of action leading to potentially heritable genomic damage. The goal was to enhance the use of mechanistic information in genotoxicity assessment by building empirical support for the relationships between relevant molecular initiating events (MIEs) and regulatory endpoints in genetic toxicology. Herein, we present an AOP network that links oxidative DNA damage to two adverse outcomes (AOs): mutations and chromosomal aberrations.

Recommendations for conducting the rodent erythrocyte Pig-a assay: A report from the HESI GTTC Pig-a Workgroup.

The rodent Pig-a assay is a flow cytometric, phenotype-based method used to measure in vivo somatic cell mutation. An Organization for Economic Co-operation and Development (OECD) test guideline is currently being developed to support routine use of the assay for regulatory purposes (OECD project number 4.93).

Double Trouble: Visual and Phonological Impairments in English Dyslexic Readers.

Developmental dyslexia is a reading disorder characterized by problems in accurate or fluent reading. A deficiency in phonological processing is thought to underpin the reading difficulties of individuals with developmental dyslexia and a variety of explanations have been proposed including deficits in phonological awareness and verbal memory. Recent investigations have begun to suggest that developmental deficits in the acquisition of reading may also co-occur with visual processing deficits, which are particularly salient for visually complex stimuli, yet these deficits have received relatively little attention from researchers.

Application of the adverse outcome pathway framework to genotoxic modes of action.

In May 2017, the Health and Environmental Sciences Institute's Genetic Toxicology Technical Committee hosted a workshop to discuss whether mode of action (MOA) investigation is enhanced through the application of the adverse outcome pathway (AOP) framework. As AOPs are a relatively new approach in genetic toxicology, this report describes how AOPs could be harnessed to advance MOA analysis of genotoxicity pathways using five example case studies. Each of these genetic toxicology AOPs proposed for further development includes the relevant molecular initiating events, key events, and adverse outcomes (AOs), identification and/or further development of the appropriate assays to link an agent to these events, and discussion regarding the biological plausibility of the proposed AOP.

Are children with developmental dyslexia all the same? A cluster analysis with more than 300 cases.

Reading is vital to every aspect of modern life, exacerbated by reliance of the internet, email, and social media on the written medium. Developmental dyslexia (DD) characterizes a disorder in which the core deficit involves reading. Traditionally, DD is thought to be associated with a phonological impairment.

A comparison of transgenic rodent mutation and in vivo comet assay responses for 91 chemicals.

A database of 91 chemicals with published data from both transgenic rodent mutation (TGR) and rodent comet assays has been compiled. The objective was to compare the sensitivity of the two assays for detecting genotoxicity. Critical aspects of study design and results were tabulated for each dataset.

Birth Weight and Risk of Childhood Acute Lymphoblastic Leukemia in Arizona, Illinois, and Kentucky.

Objective: To confirm the previously reported increased risk of leukemia among macrosomic children (those with birth weight >4 kg).

Methods: Birth certificates of Arizona, Illinois, and Kentucky children diagnosed as having acute lymphoblastic leukemia (ALL) before age 5 years were matched with birth certificates from leukemia-free children of the same sex, race, and ethnicity who were born in the same county on or about the same day. Odds ratios (ORs) for ALL among children of low (<2.

Suitability of Long-Term Frozen Rat Blood Samples for the Interrogation of Pig-a Gene Mutation by Flow Cytometry.

The rodent blood Pig-a assay has been undergoing international validation for use as an in vivo hematopoietic cell gene mutation assay, and given the promising results an Organization for Economic Co-operation and Development (OECD) Test Guideline is currently under development. Enthusiasm for the assay stems in part from its alignment with 3Rs principles permitting combination with other genotoxicity endpoint(s) and integration into repeat-dose toxicology studies. One logistical requirement and experimental design limitation has been that blood samples required antibody labeling and flow cytometric analysis within one week of collection.

Comparison of integrated genotoxicity endpoints in rats after acute and subchronic oral doses of 4-nitroquinoline-1-oxide.

During interlaboratory validation trials for the Pig-a gene mutation assay we assessed the genotoxicity of 4-nitroquinoline-1-oxide (4NQO) across endpoints in multiple tissues: induction of Pig-a mutant red blood cells (RBCs) and reticulocytes (RETs); micronucleated RETs (MN RETs); and DNA damage in blood and liver via the alkaline Comet assay (%tail intensity [TI]). In a previous subchronic toxicity study with 28 daily doses, biologically meaningful increases were observed only for Pig-a mutant RBCs/RETs while marginal increases in the frequency of MN RET were observed, and other clastogenic endpoints were negative. Follow up acute studies were performed using the same cumulative doses (0, 35, 70, 105, and 140 mg/kg) administered in a bolus, or split over three equal daily doses, with samples collected up to 1 month after the last dose.

Processing deficits for familiar and novel faces in patients with left posterior fusiform lesions.

Pure alexia (PA) arises from damage to the left posterior fusiform gyrus (pFG) and the striking reading disorder that defines this condition has meant that such patients are often cited as evidence for the specialisation of this region to processing of written words. There is, however, an alternative view that suggests this region is devoted to processing of high acuity foveal input, which is particularly salient for complex visual stimuli like letter strings. Previous reports have highlighted disrupted processing of non-linguistic visual stimuli after damage to the left pFG, both for familiar and unfamiliar objects and also for novel faces.

What lies beneath: a comparison of reading aloud in pure alexia and semantic dementia.

Exaggerated effects of word length upon reading-aloud performance define pure alexia, but have also been observed in semantic dementia. Some researchers have proposed a reading-specific account, whereby performance in these two disorders reflects the same cause: impaired orthographic processing. In contrast, according to the primary systems view of acquired reading disorders, pure alexia results from a basic visual processing deficit, whereas degraded semantic knowledge undermines reading performance in semantic dementia.

Lexical neighborhood effects in pseudoword spelling.

The general aim of this study is to contribute to a better understanding of the cognitive processes that underpin skilled adult spelling. More specifically, it investigates the influence of lexical neighbors on pseudo-word spelling with the goal of providing a more detailed account of the interaction between lexical and sublexical sources of knowledge in spelling. In prior research examining this topic, adult participants typically heard lists composed of both words and pseudo-words and had to make a lexical decision to each stimulus before writing the pseudo-words.

Impaired integration of object knowledge and visual input in a case of ventral simultanagnosia with bilateral damage to area V4.

This study examines how brain damage can affect the cognitive processes that support the integration of sensory input and prior knowledge during shape perception. It is based on the first detailed study of acquired ventral simultanagnosia, which was found in a patient (M.T.

Efficient visual object and word recognition relies on high spatial frequency coding in the left posterior fusiform gyrus: evidence from a case-series of patients with ventral occipito-temporal cortex damage.

Recent visual neuroscience investigations suggest that ventral occipito-temporal cortex is retinotopically organized, with high acuity foveal input projecting primarily to the posterior fusiform gyrus (pFG), making this region crucial for coding high spatial frequency information. Because high spatial frequencies are critical for fine-grained visual discrimination, we hypothesized that damage to the left pFG should have an adverse effect not only on efficient reading, as observed in pure alexia, but also on the processing of complex non-orthographic visual stimuli. Consistent with this hypothesis, we obtained evidence that a large case series (n = 20) of patients with lesions centered on left pFG: 1) Exhibited reduced sensitivity to high spatial frequencies; 2) demonstrated prolonged response latencies both in reading (pure alexia) and object naming; and 3) were especially sensitive to visual complexity and similarity when discriminating between novel visual patterns.

Integration of Pig-a, micronucleus, chromosome aberration, and Comet assay endpoints in a 28-day rodent toxicity study with 4-nitroquinoline-1-oxide.

As part of the Stage III Pig-a multilaboratory validation trial, we examined the induction of CD59-negative reticulocytes and total red blood cells (RET(CD59-) and RBC(CD59-) , respectively) in male Sprague Dawley(®) rats treated with 4-nitroquinoline-1-oxide (4NQO), for 28 consecutive days by oral gavage, at doses of 1.25, 2.50, 3.

International Pig-a gene mutation assay trial: evaluation of transferability across 14 laboratories.

A collaborative international trial was conducted to evaluate the reproducibility and transferability of an in vivo mutation assay based on the enumeration of CD59-negative rat erythrocytes, a phenotype that is indicative of Pig-a gene mutation. Fourteen laboratories participated in this study, where anti-CD59-PE, SYTO 13 dye, and flow cytometry were used to determine the frequency of CD59-negative erythrocytes (RBC(CD59-)) and CD59-negative reticulocytes (RET(CD59-)). To provide samples with a range of mutant phenotype cell frequencies, male rats were exposed to N-ethyl-N-nitrosourea (ENU) via oral gavage for three consecutive days (Days 1-3).

When does less yield more? The impact of severity upon implicit recognition in pure alexia.

Pure alexia (PA) is characterised by strong effects of word length on reading times and is sometimes accompanied by an overt letter-by-letter (LBL) reading strategy. Past studies have reported "implicit recognition" in some individual PA patients. This is a striking finding because such patients are able to perform semantic classification and lexical decision at above chance levels even when the exposure duration is short enough to prevent explicit identification.

Another duel in the sun: weighing the balances between sun protection, tanning beds, and malignant melanoma.

Objective: The purpose of this report is to put the dueling factors of risk and prevention for melanoma in perspective for the thoughtful pediatric specialist to facilitate preteen preventive health counseling.

Study Design: We examined the rate of malignant melanoma among Kentucky residents and compared this rate with indicators of tanning bed prevalence in a large metropolitan area and sunscreen sales from a major distributor. We obtained malignant melanoma annual incidence data from the Kentucky Cancer Registry, which recorded Kentucky population incidence rates over the years 1995 to 2004.

Automated human blood micronucleated reticulocyte measurements for rapid assessment of chromosomal damage.

This study evaluated the utility of human blood micronucleated reticulocyte (MNCD71+) frequency measurement as a cytogenetic damage biomarker. The analytical methodology was flow cytometry in conjunction with a previously described three color fluorescence labeling technique that includes anti-CD71 to focus analyses on the most immature fraction of reticulocytes [S.D.