Reversal of neurobehavioral teratogenicity in animal models and human: Three decades of progress.

Early studies of behavioral teratology were mostly descriptive, fulfilling the necessary first requirement in a new field. The next obvious stage was put forward in the 80's as mechanism driven science enabled reversal of the teratogens-induced deficits. Three decades later a plethora of studies have been published demonstrating the success of the new direction. Complete and long-term (ostensibly permanent) reversal has been demonstrated in numerous animal models representing the realization of the ultimate goal of the field. Perhaps less sought after, but still significant, are the studies on recovery which needs consistent treatment for its persistence The studies reviewed here have been summarized in Tables 1 and 2. Clinically, the field is only in its incipient stage because of the paucity in translational findings for complete reversal or even complete alleviation. Human findings are emerging but in partial alleviation, noteworthy were the demonstration of FASD children who showed improvement after choline treatment while others showed no effect. Consequently, while further studies in an animal model on the mechanism by which the teratogen exerts its deleterious effects and the reversal procedure action are important, the main thrust of the research should now be translation of the animal model findings into a standard clinical routine. Indeed, first steps towards these goals are being made in children with various neurodevelopmental disorders via the application of a variety of rehabilitation programs by physiotherapists, occupational therapists and speech and language therapists, but the results are partial and may not be long-lasting.

The arrogance of teratology: A brief chronology of attitudes throughout history.

While the discipline of Teratology has existed for about 60 years, there has been a deep interest in the causes of human malformations for millennia. Absent the scientific method and acting on fervent beliefs that made sense to ancient/medieval populations, "mechanisms" were described and prognostications of future events were assigned to terata resulting in tragic (and unwarranted) sequelae. This article examines the collective beliefs and thinking within various eras in the hope of providing lessons to inform future behavior. The eugenics movement is an informative, recent example. Science of the 19th century had unraveled some of the mysteries of development and the role of genetics in determining birth outcomes. There was, however, a deep misunderstanding about the enormous amount of information that had yet to be uncovered. Based on immature science and faulty assumptions, it was suggested that "unfit" individuals be euthanized and their parents sterilized. Such "solutions" would be considered deplorable today. Surprisingly, such a reprehensible program was supported (at least in part) by many intelligent and highly regarded individuals. Today, it is imperative that we enter into the era of molecular biology and gene editing cautiously and perspicaciously. The history of teratology has elucidated our inability to understand where our new technologies and actions might take us and how unintended consequences could disrupt even our most carefully thought-out plans.

The principles of teratology: are they still true?

James Wilson originally proposed a set of "Principles of Teratology" in 1959, the year before he helped to found the Teratology Society. By 1977, when these Principles were presented in a more definitive form in Wilson and Fraser's Handbook of Teratology, they had become a standard formulation of the basic tenets of the field. Wilson's Principles have continued to guide scientific research in teratology, and they are widely used in teaching. Recent advances in our knowledge of the molecular and cellular bases of embryogenesis serve only to provide a deeper understanding of the fundamental developmental mechanisms that underlie Wilson's Principles of Teratology.

Prospective teratology of retinoic acid metabolic blocking agents (RAMBAs) and loss of CYP26 activity.

All-trans retinoic acid (atRA) is the transcriptionally active product of vitamin A and induces gene expression via specific receptors at nM concentrations. Essential enzymes that regulate the local levels of atRA are the CYP26 members of the cytochrome P450 family, which catabolize atRA. Compounds that have been designed to inhibit these enzymes are known as Retinoic Acid Metabolic Blocking Agents (RAMBAs). Treatment with these compounds will raise endogenous atRA levels and may be therapeutic for the treatment of diseases that respond to high atRA concentrations, including several types of cancer as well as skin conditions such as psoriasis and acne. This review describes the mechanism of action of the RAMBAs and discusses the potential side effects of these compounds. atRA is highly teratogenic and the potential teratogenicity of the RAMBAs is described by comparison with the abnormalities resulting from null mutation of individual CYP26 genes. The possible effects of RAMBAs on the adult brain are also described that have the potential for harm but, in the right circumstances, may also be beneficial.

A new paradigm in toxicology and teratology: altering gene activity in the absence of DNA sequence variation.

'Epigenetics' is a heritable phenomenon without change in primary DNA sequence. In recent years, this field has attracted much attention as more epigenetic controls of gene activities are being discovered. Such epigenetic controls ensue from an interplay of DNA methylation, histone modifications, and RNA-mediated pathways from non-coding RNAs, notably silencing RNA (siRNA) and microRNA (miRNA). Although epigenetic regulation is inherent to normal development and differentiation, this can be misdirected leading to a number of diseases including cancer. All the same, many of the processes can be reversed offering a hope for epigenetic therapies such as inhibitors of enzymes controlling epigenetic modifications, specifically DNA methyltransferases, histone deacetylases, and RNAi therapeutics. 'In utero' or early life exposures to dietary and environmental exposures can have a profound effect on our epigenetic code, the so-called 'epigenome', resulting in birth defects and diseases developed later in life. Indeed, examples are accumulating in which environmental exposures can be attributed to epigenetic causes, an encouraging edge towards greater understanding of the contribution of epigenetic influences of environmental exposures. Routine analysis of epigenetic modifications as part of the mechanisms of action of environmental contaminants is in order. There is, however, an explosion of research in the field of epigenetics and to keep abreast of these developments could be a challenge. In this paper, we provide an overview of epigenetic mechanisms focusing on recent reviews and studies to serve as an entry point into the realm of 'environmental epigenetics'.

[Wilson's principles--a base of modern teratology]. / Podstawy Wilsona--fundament wspólczesnej teratologii.

Wilson's principles were formulated after thalidomide tragedy. They become a fundamental for teratological studies with drugs and other factors that may disturb fetal development. It is postulated that susceptibility to teratogen depends on the genotype and developmental stage of the conceptus. Teratogenic agents act in specific manner on developing cells and tissues. The exposition depends on the agent's nature and availability. Manifestations of deviant development depends on the dosage and exposure frequency. In case of abnormal development the final manifestations include death of embryo or fetus, malformation, growth retardation and functional disorder.

Teratology in cultural documents and today.

Teratology is the science of congenital malformations. The incidence of birth defects amounts to 2-3%, but it doubles postnatal owing to the fact that many dysfunctions are not discernible at birth. Congenital malformations were already known in ancient cultures, records from Assyrian and Babylonian astrologists as well as from physicians and philosophers of the Hippocratic era are testifying it. In medieval times they were recognized as supernatural phenomenons, terata, from what the term TERATOLOGY derived. In the eyes of the superstitious people affected stillborns were regarded as monster, symbol of devil or miracle. The foundation of anatomy as a science by Vesalius marked the beginning of a reorientation. In the 17th century, when the age of enlightenment began, ideas concerning the origin of birth defects became more objective. Original studies dealing with congenital malformations became common in the 18th century. Fundamental discoveries made by microscopy placed Teratology on a truly scientific basis. Significant impetus was grown to teratological research with the discovery of Gregg (1941) that German measles (rubella virus) of pregnant women caused birth defects in the embryo and the contergan disaster (1959--1962). Congenital malformations originate from genetic factors (single gene defects and chromosomal aberrations) and environmental factors, such as radiation, drugs, chemicals, and infectious agents. The susceptibility of teratogen depends on the period of embryonal development, which is classified into gametogenesis, blastogenesis, embryogenesis and fetogenesis. The Food and Drug Administration of the USA published guidelines for teratogenetic testing (1966). There are in-vivo and in-vitro-test programmes, the latter became of increasing importance owing to the large number of chemicals to be tested and the activities of opponents against animal experiments. Although great advances were made, the problem remained to transfer results from in-vivo and in-vitro tests to the constitution of man without risk.

[Johann Friedrich Meckel the Younger (1781-1833) and modern teratology]. / Johann Friedrich Meckel d. J. (1781-1833) und die moderne Teratologie.

Among other special topics Johann Friedrich Meckel the Younger concentrated his scientific researches on the systematic investigations of the human and animal malformations. He explored many samples which were part of his private anatomical collection. Today, the Institute of Anatomy and Cell Biology possesses a number of important teratological preparations which Meckel and his graduate students minutely investigated (e.g. the individuals to the Meckel, Klippel Feil and Hanhart syndrome). The goals of our studies are to identify the samples originating from the Meckel Collections, and to reinvestigate them with modern methods. Two objects (brainless malformation, Halle I, and neural tube defect, Halle II) were analysed by comparative genomic hybridization (CGH). These results obtained are published in Toennies et al. (2002).