Congenital Diseases and the Environment

The standard approach to developmental toxicology includes, 1) studies targeting the organogenesis/pregnancy period, to assess birth defects, minor anomalies (that may be a signal of more severe effects at higher dose levels), fetal growth and viability (OECD guideline 414); 2) one- and two-generation studies (OECD guidelines 415 and 416) that provide an overall assessment of general parameters related to postnatal development and survival. Studies investigating effects on organogenesis are important for risk assessment, since short-term exposures in susceptible developmental phases (e.g., from pharmaceuticals or workplace chemicals) may elicit birth defects and/or embryonic loss. Several in vitro assays also exist, using cultured rodent embryonic stem cells or whole embryos that deserve further exploitation as a possible screening battery as well as to understand embryotoxicity mechanisms.

Nevertheless, the science of risk assessment is increasingly concerned with the subtle, but potentially important, effects of low exposure levels relevant to the general population, such as dietary intakes of contaminants. In this respect, the 2- generation study receives considerable attention, as it is the only “standard” protocol whereby an organism is exposed during the whole of development, from gamete stage through sexual development.

The wide group of endocrine disrupters (ED) are a good example of a challenge to developmental toxicologists from several standpoints, including a) the potential to induce long-term effects upon exposure in susceptible developmental phases, including postnatal life up to puberty; b) the potential impact of endocrine disruption on immune, neurobehavioral and reproductive development as well as on susceptibility to cancer later in life. Therefore, tiered approaches have to be developed. Screening in vitro/in vivo assays should identify the most relevan.mechanisms/endpoints to be investigated by targeted two-generation assays; these would allow the follow-up of late outcomes and the identification of relevant NOELs for the most sensitive effects.

Other long-term effects of prenatal exposures, such as disruption of immune development and early predisposition to cancer, may be considered as likely “hot topics” for the next wave of research projects on chemical safety.

This paper provides a review of defects reported in vertebrate wildlife, particularly including those present or already programmed at birth, which are known or suspected to be associated with pollutants. Species from each of the main classes of animals in the vertebrate sub-phylum (including bony fish, amphibians, reptiles, birds, and mammals) are now known to have been affected by endocrine disrupting chemicals (EDCs) in the environment.

The similarities in the endocrine system of all vertebrate animals are such that given the presence of EDCs in the environment, effects are likely to be occurring in more species than those currently reported. Section 1 outlines the animal – human connection, and highlights that Homo sapiens is also vulnerable.

Section 2 summarises the effects reported in wildlife. These particularly include: genital deformities; altered thyroid function; and suppressed immune system. Section 3 outlines how these pollutant-related effects have also been noted in humans. Birth defects, such as intersex features and male reproductive tract anomalies, and congenital effects on brain function and immune system function should be of major concern.

Furthermore, concern for the long-term health of wildlife populations and humans is enhanced because several laboratory studies have suggested that disorders such as deficits in sperm production, can be passed on to unexposed subsequent generations. This highlights the need for a far more precautionary regulatory approach to controlling chemical exposures, and the need for more research to understand the long-term implications for life on earth

This chapter discusses the principles of study design and related methodological issues in the epidemiology of congenital anomalies, with specific regard to environmental factors. We present the major types of experimental and observational designs used in environmental epidemiology, namely the basic designs involving the individual as the unit of analysis and the ecological designs, which involve groups or geographical areas as units of analysis. We also include a brief discussion on study designs in genetic epidemiology. Examples of how the various study designs are applied in order to investigate the environmental risk factors for congenital anomalies are described with comments. We present methodological issues related to outcome, including methods and the timing for ascertaining cases with malformations, diagnostic criteria, and problems in grouping malformations for purposes of analysis. Other methodological issues include controlling for confounders, inadequate measurement, duration, timing of exposure, and exposure-response relationships.

EUROCAT is a European network of population-based registries for the epidemiologic surveillance of congenital anomalies. EUROCAT started in 1979 and now covers more than a quarter of all births in the European Union. Currently, 40 registries in 19 countries of Europe survey 1.35 million births per year.

The objectives of EUROCAT are:

- To provide essential epidemiologic information on congenital anomalies in Europe,

- To facilitate the early warning of teratogenic exposures,

- To evaluate the effectiveness of primary prevention,

- To assess the impact of developments in prenatal screening,

- To act as an information and resource centre for the population, health professionals and managers regarding clusters or exposures or risk factors of concern,

- To provide a ready collaborative network and infrastructure for research related to the causes and prevention of congenital anomalies and the treatment and care of affected children,

- To act as a catalyst for the setting up of registries throughout Europe collecting comparable, standardised data.

EUROCAT approaches the surveillance of environmental impact in the causation of congenital anomalies in the following 3 main ways:

1) Assessment of trends in congenital anomaly prevalence,

2) Routine detection of and response to clusters,

3) Systematic evaluation of risk related to specified environmental exposures.

Fetal life is an especially sensitive period to environmental exposures and crucial exposures often occur before the pregnancy is recognised. EUROCAT, covering more than a quarter of all births in Europe, can play an important role in a European environmental health surveillance, or envirovigilance, strategy.

Teratology is the branch of medical science which studies the contribution of the environment to abnormal prenatal growth as well as morphological or functional developmental defects. Despite some pioneering research, the clinical and scientific interest in clinical teratology only developed because of the rubella pandemics in 1941 and the thalidomide tragedy in the late 1950s. The following decades have seen a definition of criteria for proof of human teratogenicity, the classification of drugs used in pregnancy, and the development of the “Teratogen Information Services” in developed countries.

Teratogens are chemical, physical or infectious agents, or a maternal status/disease whose prenatal exposure during the pregnancy can provoke developmental defects. Susceptibility to teratogenic agents depends on the combination of several factors, including the genotype of the mother and/or of the fetus, dosage, the gestational period at exposure, pharmacokinetics and the pharmacodynamic of the substance.

The methodology for the identification of teratogens includes animal studies, prospective epidemiologic studies and retrospective epidemiologic studies. The criteria for “proof” of human teratogenicity have not been defined although some criteria have been proposed and applied in the clinical/animal/epidemiologic studies. At present, some international classifications of drugs used in pregnancy are

Hot spots of pollution have shown that dioxins can cause congenital malformations, prematurity and intra-uterine growth retardation. In regions with background concentrations, like in Europe, there has generally been no indication of an increase in congenital malformations in relation to dioxins.

Specific types of malformations, such as cleft lip and palate, were found to be associated with exposure to a mixture of chemicals in clouds formed by open burning of chemical waste in Amsterdam, The Netherlands. While such defects have been seen in rodents, occurrence in humans had previously not been documented. In a similar fashion, renal abnormalities like agenesis and dysgenesis were found in Chapaevsk, also previously only noted in animal experiments (See sections on Amsterdam Diemerzeedijk and Chapaevsk).

The finding in Chapaevsk of a high incidence of congenital hydrocephaly without spina bifida 4/1,000 births is remarkable. Congenital hydrocephaly is a rare condition, in general 2.0-3.9/10,000 births (Abbott, 1995). However, this specific malformation is also found in the offspring of mothers with type 1 diabetes. Abnormal glycosylation is assumed to play a role and cause congenital malformations as expressed in an increased level of Hemoglobin A 1c (glycosylated hemoglobin) in mothers with type I diabetes.

We suggest that in both situations (Chapaevsk and pregnant women with type 1 diabetes) the same metabolic mechanism might be the cause of malformations.

Animal experiments have shown that dioxins can deplete vitamin A stores in the liver. In other animal experiments, vitamin A can counteract negative effects of PAHs, including dioxins. This vitamin is necessary for glycosylation. And the vitamin might be important as a prevention, the more so because recent research in the Netherlands revealed a 48% deficiency of this vitamin in the diet of women trying to fall pregnant. In general, more attention to keeping a balanced vitamin Astatus in general, and in women with type 1 diabetes especially, is recommended.

There are many difficulties in establishing a causal link between exposure to chemicals and human diseases or disorders, when a mixture of chemicals is the causal factor under examination, and when controls have also some degree of contamination. Despite this, significant risk increases have been demonstrated for various congenital malformations including central nervous system, cardiovascular, urogenital and limb defects, and orofacial clefts, all of which have been shown after parental exposure to several or to specific pesticides. The same has been observed for intra uterine growth retardation and neurodevelopment impairments, involving short term or longer term functional anomalies. However, so far, epidemiological research has had very little influence on the authorisation of pesticides.

The adequacy of the risk assessment, which is the basis of the authorisation of Pesticides Directives, is questioned. The shortcomings in active substance regulatory testing are highlighted, together with the lack of consideration for combined effects, potential toxicities of formulated products, the poor consideration of vulnerable groups, and pesticide exposure evaluation deficits.

In order to compensate for the shortage of information and for the potentially large societal costs of filling this deficit, arguments are presented for the adoption of precautionary exposure reduction measures. These could include exclusion criteria based on pesticide intrinsic properties, the substitution principle and mandatory national pesticide dependency reduction programmes, with targets and timetables, accompanied by a significant promotion of low input crop production systems.

These cost effective precautionary measures, to prevent or reduce health impacts of pesticides, should now be considered for adoption as the revision of the plant protection products authorisation Directive and a Thematic Strategy on the sustainable use of pesticides are on the political agenda.

Thalidomide was first synthesised in 1954 and subsequently marketed in 1956. In pre-clinical studies, thalidomide was found to have no apparent side effects. Consequently, it was distributed as an ”over-the-counter” drug and used by pregnant women in order to combat morning sickness. In 1961, a significant increase of congenital limb defects in prenatally-exposed newborns became evident. As a result, thalidomide was withdrawn from the market, due to its severe teratogenic effects. It has been estimated that about 6,000 children were affected with thalidomide embryopathy. The clinical findings of the embryopathy are unusual and characteristic.

Despite the fact that scientists have studied thalidomide over the years, its pharmacokinetics, metabolism and teratogenic mechanisms have never been fully understood.

In recent years, thalidomide has been rediscovered and used for the treatment of several immunological diseases and inflammatory dermatoses, especially lepromatous leprosy. A specific programme (STEPS) to support the appropriate use of thalidomide is being implemented in the United States, in order to avoid thalidomide related birth defects; whereas, on the other hand, an increase of thalidomide embryopathy in newborns from under developed countries has been noted.

Exposure of the developing animal male fetus to environmental pollutants, in particular to endocrine disrupting chemicals (EDC), is responsible for sexual maturation anomalies and reproductive malfunction in adult life. Human maternalinfant exposure during pregnancy is of special importance because it represents a very likely window of high susceptibility that can lead to severe and irreversible effects during critical developmental periods. This chapter reviews the epidemiological evidence linking EDC exposure to human male tract malformations, e.g. cryptorchidism and hypospadias, focusing on exposure to pesticides as potential EDCs. Epidemiological studies have yielded contradictory results and do not provide sufficient grounds to confirm the hypothesis that environmental estrogens are associated with these urogenital anomalies. The main reason for the conflicting data may be the difficulty of comparing studies that consider different exposure times and study populations, and do not use the same clinical definitions or diagnostic criteria for these diseases. In addition, the EDC hypothesis poses several challenges to the exposure assessment process that need to be addressed: i) classification of exposure by using direct determinations instead of crude proxies, ii) interpretation of complex dose-effect relationships based on U- or inverted U-shaped dose-response curves, iii) estimation of exposure that takes account of the highly heterogeneous chemical classes implicated, and iv) development of biomarkers that allow investigators to quantify exposure to mixtures of EDCs and to differentiate their effects from those of endogenous hormones.

Sex chromosome mosaicism (45,XO/46XY karyotype) is often associated with an intersex phenotype and testicular dysgenesis. Undescended testes (cryptorchidism), hypospadias, and later on, infertility or subfertility and testicular cancer can be signs of testicular dysgenesis syndrome (TDS). The underlying reason is rarely a chromosomal abnormality, and for most cases, the etiology remains unknown. It has been hypothesized that genetic and environmental (including life style) factors that disturb gonadal development during pregnancy cause TDS, and the outcome depends on the timing and extent of the disruption. In mild cases, only spermatogenesis may be affected during adulthood, whereas in severe cases, the child may have hypospadias or develop testicular cancer at young age. The hypothesis is supported by clinical and epidemiological evidence that shows a strong association of the risks for each of the TDS signs, i.e. a boy with cryptorchidism has an increased risk of infertility and testicular cancer. Experimentally, we can induce TDS-like changes in animals by treating them with endocrine disrupting compounds. The challenge for the physicians treating TDS patients is to unravel the developmental mechanisms and causative agents.

During the past decade, considerable information concerning the effects of endocrine disrupters (EDCs) on animals and humans has been accumulated. These compounds of anthropogenic or natural origin mimic the action of sex hormones, thus disturbing the endocrine system. The present overview covers the different classes of EDCs, such as pesticides (that act as androgen receptor (AR) antagonists, i.e. anti-androgens), and phthalates and dioxins (which appear to inhibit fetal testosterone synthesis). The effects of these compounds on steroidogenesis by Leydig cells and reproductive development are reviewed and their possible key role in connection with increasing frequencies of abnormalities in reproductive development, such as hypospadias and cryptorchidism, is debated. Moreover, the influence of different classes of EDCs on ovarian and adrenal steroidogenesis is also described. In addition, putative interactions between EDCs and mediators of inflammation, that can potentially intensify the inflammatory process, are discussed.

Cryptorchidism is the most frequent abnormality of male sexual differentiation. Recently, numerous reports have increased concerns that exposure to certain types of chemicals in the environment, including in utero exposure to compounds with estrogenic or antiandrogenic activities, may be linked with recently observed deleterious effects on male reproductive health, especially cryptorchidism and also decrease in sperm production and increased in incidence of testicular cancer.

In this review, we give an overview of different scientific reviews already published on cryptorchidism, its incidence rate, the potential link between various male reproductive health issues (testicular dysgenesis syndrome), the existing literature on toxic effects of anti-androgenic compounds, and some relevant data on the environmental impact of cryptorchidism in humans. Finally, we explain why cryptorchidism could be an excellent potential indicator and may potentially provide an answer to the key question of the impact of some environmental pollutants on male reproductive health.

Detecting intrauterine exposure to environmental pollutants, based on an increased number of malformations, has only been successful with a few teratogens. Nor does the number of spontaneous abortions represent a more reliable indicator, since a precise record of early abortions is not available. A greater vulnerability to prenatal damage leading to abortion is evident in male embryos/fetuses than in female. The newborn sex ratio (birth rate of boys/girls) is a very stable parameter in healthy populations. Its decrease has been reported after exposure to some harmful environmental factors. We document a decrease in the male birth fraction in the Czech Republic after the Chernobyl disaster in 1986. The absolute numbers of male and female births were determined in each of 600 consecutive months from 1950 to 1999. There were always more newborn boys than girls, except in November 1986, when the number of male births significantly decreased. This deficit in male births might have resulted from the spontaneous abortion of male embryos/fetuses during weeks 8-12 of pregnancy, as a consequence of their increased exposure to radiation, in particular to the radionuclide iodine131. We propose using the newborn sex ratio as a further tool for the standard evaluation of reproductive quality. Combined analyses of the incidence of newborn malformations, spontaneous abortions and stillbirths, intrauterine growth retardation and the newborn sex ratio will help to compensate for the imperfections associated with each of these parameters individually and will provide a more complete understanding of the extent of prenatal risk induced by environmental factors.

This study’s objective is to record the regional distribution of mortality and hospitalisation caused by congenital abnormalities in Greece and to compare the mortality and the infant mortality for congenital abnormalities between Greece and other countries.

The data were obtained from the official publications of the National Statistical Service of Greece (NSSG). The specific mortality and infant mortality ratios for congenital abnormalities and the number of discharged patients with congenital abnormalities per 100,000 of population are evaluated for Greece as a whole and by geographic region, for the period between 1981 and 1995. Greece was compared to other, randomly selected countries (Bulgaria, France, Italy, Japan, Portugal, Sweden, The Netherlands, and USA). The information data for these countries are derived from the Annuals of the World Health Organization (WHO).

The specific mortality and infant mortality ratios by congenital abnormalities are considerably higher in Greece than in the other countries studied. Among the 10 regions of Greece, Athens and Thrace have the highest mortality ratios, while Athens and Crete appear to have the highest proportion of hospitalised patients due to congenital abnormalities according to their population. In Thrace, a disproportional high number of deceased in comparison to discharged patients was noted.

In conclusion, Greece appears to have more deaths by congenital abnormalities compared to the other randomly selected countries. A significant difference in the distribution of the deaths and discharged patients among the geographic regions of Greece is observed. This study is unable to detect the reasons for this distribution.

The paper presents data and analysis concerning congenital anomalies in Bulgaria. Assessment is based on statistical data reported in the National Statistical Institute Yearbook: Health Protection and the Sofia registry of congenital anomalies in the period 1996 – 1999. Forty subgroups of isolated congenital anomalies and congenital diseases, detectable at birth during in the first year of life, have been detected out of 34,124 pregnancies, registered during the period. The rates of live births, stillbirths and induced abortions due to anomalies, per 10,000 pregnancies, are selected as indicators. Results are compared with EUROCAT rates of cases per 10,000 births of 85 subgroups with congenital anomalies in the EUROCAT full member registers in the period 1996 – 2001. The analysis which is made by Simeonov and Dimitrov shows that only 2 per cent of the total incidence of congenital abnormalities has a purely environmental origin. Most of the cases have been attributed to multifactorial etiology. Comparison is made with the experience of the TIS in Jerusalem and the data reported in the frame of OTIS.

Trends of reduction in the total infant mortality rates and the mortality rates due to congenital anomalies and certain other conditions originating in the prenatal period 1990 – 2003 descised. It is shown that, in 2003, these two reasons could be ranked at the first two places among the causes of the infant’s deaths with rates 260/100,000 live births and 386/100,000 live births respectively. Territorial distribution of infant mortality in 2003, caused by congenital anomalies and due to reasons originating in the prenatal period, is connected with the territorial distribution of some known teratogenic agents e.g. pesticides, dioxins, heavy metals, etc.

Increases in age of Bulgarian mothers at the birth of their age of the mother at the last delivery are associated with increasing rates of chromosomal anomalies.

The first congenital anomaly register in the British Isles was established in 1949, with a national system for England and Wales introduced in 1969 in the wake of the thalidomide epidemic. There are now 14 regional congenital anomaly registers and three disease-specific registers. These registers involve an extensive local network of notifiers, use multiple sources of case ascertainment, consistent coding, and include cases resulting in termination of pregnancy for fetal anomaly following prenatal diagnosis. They have optimised the coverage, completeness and ascertainment of congenital anomalies within their population, and are therefore able to provide better quality data than the national system. There are notable variations in the prevalence of congenital anomaly subtypes within these regions that cannot be accounted for in terms of differences in case ascertainment or registration practices. This underlying variation in prevalence should be recognised and taken into consideration in the design of epidemiological studies that are investigating the contribution of environmental influences to congenital anomaly risk, to ensure correct interpretation of the findings. Local congenital anomaly register data has been used to investigate congenital anomaly risk in populations within the British Isles living close to landfill sites and incinerators, and to possible contaminants in drinking water. Whilst the inclusion of high quality data from established congenital anomaly registers enhances the quality of outcome data, such studies are currently limited by the lack of detailed information on exposure. Causal pathways will only be determined if future studies combine high quality congenital anomaly data with increased information on exposure assessment.

As a result of public concerns about hormone-disrupting chemicals – such as publication of ’Silent Spring’ – and calls from the European Parliament, the Commission took early, decisive actions to tackle this problem. A strategy was adopted in 1999, recognising that the final goal should be the protection of human health and the environment. A call for more research in the Strategy resulted via the publication of calls for proposals in the Fifth Framework of Research (1998-2002), in multi-centre, pan-European projects. They addressed a wide range of issues related to endocrine disruption ranging from declining sperm counts in humans to long-term effects of exposure to low doses of chemicals in laboratory animals. In addition, methods for detection and testing have been developed. This concentrated effort has produced results useful for regulatory purposes. Taking into consideration projects funded by the ongoing Sixth Framework Programme (2002-2006), the total expenditure on Commission-sponsored endocrine disrupter projects now exceeds €120 million. The purpose of this chapter is to provide to an overview of Commission-sponsored research projects dealing with endocrine disrupters and underlying policy decisions, sponsored mostly by the Key Action ’Environment and Health’.

This paper summarises the main findings on congenital anomalies and environmental pollution. The lines of evidence for environmental causes of congenital anomalies are listed. These are based on clinical, epidemiological, laboratory and wildlife studies. The data show that not only are a (limited) number of pollutants (e.g. lead, methyl mercury) well known teratogens, but also that the number of daily environmental exposures associated with congenital anomalies is increasing. This latter applies, among others, to lead and nitrates in drinking water, living near waste deposit sites and non- occupational exposure to pesticides.

The increasing incidence of hypospadias and cryptorchidism in a number of industrialised countries is noticeable. The “testicular dysgenesis syndrome” (TDS) theory links the epidemiological data with environmental causes and hypothesises one unifying mechanism for which the experimental evidence is significant.

Core concepts related to the mechanisms of teratology are reviewed. They include dose-response relationships, exposure windows, latency periods and multicausality in the underlying factors of congenital anomalies. The discussion shows that at different points during recent years, teratology underwent important paradigmatic shifts.

The concluding part of the paper deals with the question: which data are of primary importance for the stakeholders in the discussion on pollution and congenital anomalies: the prenatal health advisors, lawyers, policy makers and the media? Each of these groups has specific agendas and corresponding needs for information. Although main guidelines for handling this information exist, much more research is needed, e.g. on case studies from the past, and on effectiveness and efficiency of information transfer.