An overview of health issues and development in a large clinical cohort of children with Angelman syndrome

This study presents a broad overview of health issues and psychomotor development of 100 children with Angelman syndrome (AS), seen at the ENCORE Expertise Center for AS in Rotterdam, the Netherlands. We aimed to further delineate the phenotype of AS, to evaluate the association of the phenotype with genotype and other determinants such as epilepsy and to get insight in possible targets for intervention. We confirmed the presence of a more severe phenotype in the 15q11.2-q13 deletion subtype. Novel findings were an association of (early onset of) epilepsy with a negative effect on development, a high occurrence of nonconvulsive status epilepticus, a high rate of crouch gait in the older children with risk of deterioration of mobility, a relatively low occurrence of microcephaly, a higher mean weight for height in all genetic subtypes with a significant higher mean in the nondeletion children, and a high occurrence of hyperphagia across all genetic subtypes. Natural history data are needed to design future trials. With this large clinical cohort with structured prospective and multidisciplinary follow-up, we provide unbiased data on AS to support further intervention studies to optimize outcome and quality of life of children with AS and their family

Clinical aspects of a large group of adults with Angelman syndrome

Descriptions of the clinical features of Angelman syndrome (AS) have mainly been focused on children. Here, we describe

The importance of dormant egg bank dynamics in ecotoxicological effect assessment: from laboratory to mesocosm studies

Currently, agricultural land comprises about 40% of the worlds land surface, producing food for six billion people. Projections are that the global human population will continue to increase and a doubling is expected by 2050. This continued population growth is accompanied by a sharp increase in food demand, which has put a lot of pressure on the agricultural sector to increase crop yields. Pesticides have been increasingly used to help boost crop production. By spray drift, run-off and leaching, a fraction of these pesticides ends up in aquatic water bodies in or surrounding agricultural areas, thereby potentially affecting also non-target species, such as planktonic organisms. Many zooplankton taxa depend on dormant life stages to survive unfavourable environmental conditions (drought, freezing, predation). To date however, not much is known about the effects of pollution on dormant life stages. Toxicants could have an impact on both the active and dormant phase of zooplankton populations and communities, through the following scenario´s: 1) impact on development and hatching of dormant eggs; 2) effects on hatchling survival and performance in the aquatic phase; 3) impact on dormant stages before activation (in diapause), causing egg mortality or irreversible disruption of the dormancy-break system; 4) effects during the sexual reproductive phase, affecting dormant egg production. To test whether pesticides can be used safely, ecological risk assessments are performed, of which ecotoxicological assays form an important part. While aquatic invertebrates are routinely tested in ecotoxicological studies (especially the model organism Daphnia magna), most of these studies focus on a small part of their life cycle: asexual reproduction of clonal lineages (scenario 2). Studies investigating effects of pollutants on dormant life stages and the sexual reproductive phase are vastly underrepresented (scenario 1, 3 and 4). With this doctoral thesis we aimed to improve our understanding of the effects of pesticide exposure on dormant egg bank dynamics. Therefore, we studied different endpoints related to the dormant phase in zooplankton populations and communities, both under controlled conditions in the laboratory, as well as in a semi natural mesocosm environment. An important goal was to identify which part of the life-cycle in the model organism D. magna was most sensitive to toxicant exposure. In addition, we explored what new information regarding the sensitivity and recovery potential of aquatic communities could be obtained from including effects on dormant egg bank dynamics in higher tier ecotoxicological studies. At the population level we performed a series of integrated laboratory experiments using D. magna. Our results indicate that, in addition to inducing mortality of active individuals (scenario 2), pesticides can also affect hatching dynamics and life history traits of hatched individuals (scenario 1). We tested five different model pesticides for their effects on both dormant (sexual) and parthenogenetic (asexual) eggs of D. magna. The effects on dormant life stages differed among toxicants, depending on their mode of action and potential for bioaccumulation. Even a pesticide such as carbaryl that had no direct effect on the hatching process, still caused negative chronic effects on survival and hatchling performance. The impact of pesticide exposure was not only determined by the type of toxicant, but also by the timing of exposure. Final stages of embryonic development were most sensitive to pesticide exposure and had the highest measured internal pesticide concentrations. Even before light activation, dormant eggs could already be affected by toxicant exposure (scenario 3). In addition, the ephippial case that surrounds dormant eggs under natural conditions, offered limited or no direct protection against pesticide exposure. This indicates that even though dormant eggs show a high tolerance to extreme physical conditions, they can still be affected by chemical pollution. It remains to be tested whether the effects of pollutants on dormant eggs are also depending on the type of dormancy (i.e. quiescence versus diapause). In our research we showed that exposure to the juvenile growth hormone fenoxycarb could also affect the sexual reproductive phase in D. magna (scenario 4). Fenoxycarb caused a decrease in both parthenogenetic and dormant egg production, while inducing the production of male offspring. There were no significant effects of fenoxycarb exposure on the survival and life history characteristics of the hatchlings, when exposure took place during dormant egg production. This indicates that even though the quantity of the dormant eggs was reduced, their quality was not affected significantly by fenoxycarb exposure. To assess the effects of pesticide exposure at the zooplankton community level, we performed a two year outdoor mesocosm experiment, focusing on impacts of repeated carbaryl exposure on both the active and dormant phase. The inclusion of a dormant egg bank treatment allowed us to test specifically for effects of pesticide exposure on newly produced dormant eggs as well as on dormant eggs already present in the sediment fraction (used to assess the buffering capacity of the egg bank). The active communities were negatively affected by carbaryl exposure, especially the smaller sized cladocerans (Ceriodaphnia quadrangula en Chydorus sphaericus). We did not observe effects on newly produced dormant eggs in the current experiment, most likely because zooplankton populations had sufficient time to recover before the typical peak of sexual reproduction in fall. Hatching of dormant eggs already present in the sediment was not affected by carbaryl exposure. This is in agreement with results from our laboratory experiments, were carbaryl showed no direct effects on hatching up to concentrations 1000 times the effect level (EC50) for D. magna neonates. Our results clearly indicate that pollution can affect dormant egg bank dynamics in zooplankton populations through all scenarios evaluated (1-4). In general, the effect levels found in our laboratory experiments are not lower than those obtained by standard ecotoxicological screening assays. We proved that pesticides can have long-term effects on dormant egg bank dynamics, which could have important consequences for ecological and evolutionary dynamics of zooplankton populations and communities in lakes and ponds. More research is needed to determine the long-term ecological impact of exposure to environmental relevant concentrations of pesticides, under different exposure scenarios, in (semi-)natural aquatic ecosystems. Laboratory microcosm bioassays for testing effects of pollutants on dormant community dynamics could be explored, as an additional level in between single species laboratory studies and outdoor mesocosm experiments. And finally, it would be interesting to explore the effects of pollutants on dormant egg banks in natural systems, by studying impacted versus pristine sites.ACKNOWLEDGEMENTS GENERAL INTRODUCTION 1 PART I: POPULATION LEVEL CHAPTER 1 Susceptibility of Daphnia magna eggs to pesticides: a comparison between reproductive strategies 26 CHAPTER 2 Pesticide exposure impacts not only hatching of dormant eggs, but also hatchling survival and performance in the water flea Daphnia magna 42 CHAPTER 3 Timing matters: sensitivity of Daphnia magna dormant eggs to fenoxycarb exposure depends on embryonic developmental stage 62 CHAPTER 4 Acute and chronic effects of exposure to the juvenile hormone analogue fenoxycarb during sexual reproduction in Daphnia magna 80 PART II: COMMUNITY LEVEL CHAPTER 5 Poisoned through dormancy? Testing the effects of pesticide exposure on active and dormant zooplankton communities in a long-term outdoor mesocosm experiment 96 GENERAL DISCUSSION 118 SUMMARY 136 SAMENVATTING 140nrpages: 143status: publishe

Acute and chronic effects of exposure to the juvenile hormone analog fenoxycarb during sexual reproduction in Daphnia magna

Recent studies have demonstrated that insect growth regulating insecticides are able to affect reproductive endpoints in zooplankton species at very low levels. For the cyclic parthenogenetic water flea Daphnia, most of this research has focused on the asexual part of the life cycle and induction of male offspring. Even though Daphnia and many other aquatic invertebrates rely on sexual reproduction and subsequent production of dormant eggs to recover from environmentally harsh conditions, much less is known about the effects of toxicants on the sexual reproductive phase. Using fenoxycarb as a model pesticide, we exposed male and female neonate Daphnia magna, under conditions inducing a switch to sexual reproduction, and tested for effects on dormant egg (ephippia) production and sex ratio of parthenogenetic offspring. Subsequently, we assessed whether fenoxycarb exposure affected the quality of the produced dormant eggs and viability of the hatchlings. Our results showed that exposure to sub-lethal concentrations of fenoxycarb caused a sharp decrease in parthenogenetic reproduction, while inducing male offspring. Dormant egg production was marginally negatively affected, but survival and fitness of the hatched individuals were not significantly affected. This indicates that under pesticide stress, surviving adult females invested in sexual reproduction at the expense of parthenogenetic reproduction. Exposure to toxicants during the sexual reproductive phase, could affect the active aquatic phase as well as the dormant phase in natural zooplankton populations. This indicates the need for further ecotoxicological research and development of test protocols taking into account the full life cycle of zooplankton species.status: publishe

Pesticide exposure impacts not only hatching of dormant eggs, but also hatchling survival and performance in the water flea Daphnia magna

Laboratory ecotoxicity tests and biomonitoring in aquatic systems are currently based on the active com- ponent of invertebrate communities. Even though dormant egg banks are crucial for the long term survival and com- munity dynamics of many aquatic organisms, the effects of anthropogenic activities on dormant egg bank dynamics have rarely been studied. In this study we investigated the effects of two pesticides with a different mode of action (carbaryl and fenoxycarb) on hatching of Daphnia magna dormant eggs (ephippia) as well as on survival, growth and reproduction of the hatched neonates. Dormant eggs were exposed to the pesticides simultaneously to incubation under conditions that induce hatching (long daylight and 20°C). Carbaryl had no negative effects on embryonic development or hatching rate up to concentrations almost 1,000 times the median effect concentration (EC50)of neonate survival in acute tests. Fenoxycarb, however, had a significant dose-related effect by delaying or completely stopping the hatching process and caused severe abnor- malities in developing individuals. Both pesticides had significant negative effects on survival and reproduction of the hatchlings. These results indicate that, in addition to inducing mortality of active individuals, pesticides can affect zooplankton communities by altering hatching dynamics and life history traits of hatched individuals. We briefly discuss how such pollution induced changes in the benthic–pelagic coupling could translate into trans- generational effects impacting ecological and evolutionary dynamics.status: publishe

Timing matters: sensitivity of Daphnia magna dormant eggs to fenoxycarb exposure depends on embryonic developmental stage

Although Daphnia magna is a key species in many lentic freshwater ecosystems and is commonly used as model organism in ecology and ecotoxicology, very little is known about the effects of chemicals on their dormant life stages. Dormant eggs (ephippia) are produced when environmental conditions deteriorate, and Daphnia switch from clonal to sexual reproduction. Ephippia produced over different growing seasons can accumulate in the sediment of ponds and lakes, where they can be exposed to pesticides and other (anthropogenic) stressors. In the present study, we have investigated the effects of pesticide exposure on dormant eggs at different embryonic developmental stages and evaluated the degree of protection against pollution provided by the ephippial case. We therefore conducted a hatching experiment in which decapsulated and encapsulated dormant eggs were exposed to an insect growth regulator (fenoxycarb) at different stages during their development, both before and after activation of the eggs. In addition, we developed an analytical method to measure fenoxycarb concentrations in the dormant eggs. Fenoxycarb negatively affected development and hatching success and changed the timing of hatching in activated and in dormant eggs. Hatching characteristics as well as fenoxycarb concentrations inside the eggs differed significantly between exposure treatments. Final stages of embryonic development were most sensitive to pesticide exposure and had the highest tissue concentrations of fenoxycarb. Tissue concentrations did not differ significantly between decapsulated and encapsulated eggs, suggesting that the ephippial case offers limited or no direct protection against pesticide exposure. With this study we provide new evidence showing that pesticides can bioconcentrate in and affect D. magna dormant eggs. The severity of the effects on developing embryos depends on the timing of pesticide exposure. Our results stress the importance of considering the full life-cycle of model organisms used in ecotoxicological studies, since these are ultimately aimed at assessing risks of chemical exposure on natural aquatic ecosystems.publisher: Elsevier articletitle: Timing matters: Sensitivity of Daphnia magna dormant eggs to fenoxycarb exposure depends on embryonic developmental stage journaltitle: Aquatic Toxicology articlelink: http://dx.doi.org/10.1016/j.aquatox.2014.12.016 content_type: article copyright: Copyright © 2014 Elsevier B.V. All rights reserved.status: publishe