Multiple paralogues and recombination mechanisms drive the high incidence of 22q11.2 Deletion Syndrome

The 22q11.2 deletion syndrome (22q11.2DS) is the most common microdeletion disorder. Why the incidence of 22q11.2DS is much greater than that of other genomic disorders remains unknown. Short read sequencing cannot resolve the complex segmental duplicon structure to provide direct confirmation of the hypothesis that the rearrangements are caused by non-allelic homologous recombination between the low copy repeats on chromosome 22 (LCR22s). To enable haplotype-specific assembly and rearrangement mapping in LCR22 regions, we combined fiber-FISH optical mapping with whole genome (ultra-)long read sequencing or rearrangement-specific long-range PCR on 24 duos (22q11.2DS patient and parent-of-origin) comprising several different LCR22-mediated rearrangements. Unexpectedly, we demonstrate that not only different paralogous segmental duplicon but also palindromic AT-rich repeats (PATRR) are driving 22q11.2 rearrangements. In addition, we show the existence of two different inversion polymorphisms preceding rearrangement, and somatic mosaicism. The existence of different recombination sites and mechanisms in paralogues and PATRRs which are copy number expanding in the human population are a likely explanation for the high 22q11.2DS incidence.

The 22q11.2 Low Copy Repeats

LCR22s are among the most complex loci in the human genome and are susceptible to nonallelic homologous recombination. This can lead to a variety of genomic disorders, including deletions, duplications, and translocations, of which the 22q11.2 deletion syndrome is the most common in humans. Interrogating these phenomena is difficult due to the high complexity of the LCR22s and the inaccurate representation of the LCRs across different reference genomes. Optical mapping techniques, which provide long-range chromosomal maps, could be used to unravel the complex duplicon structure. These techniques have already uncovered the hypervariability of the LCR22-A haplotype in the human population. Although optical LCR22 mapping is a major step forward, long-read sequencing approaches will be essential to reach nucleotide resolution of the LCR22s and map the crossover sites. Accurate maps and sequences are needed to pinpoint potential predisposing alleles and, most importantly, allow for genotype-phenotype studies exploring the role of the LCR22s in health and disease. In addition, this research might provide a paradigm for the study of other rare genomic disorders.

The role of Effortful Control and the Dual Pathway Model in Childhood Obesity

Apart from other well-known psychological determinants of obesity, deficits in neuropsychological processes related to effortful control can be relevant predictors for weight problems and difficulties in weight loss. Deficits in top-down inhibition as well as in other processes such as strong bottom-up reactivity, like external eating, hinder resisting food temptations in an obesogenic environment, thus determining the risk for the development of overweight and obesity. Furthermore, these deficits are associated with less positive outcomes in weight loss interventions for subgroups of children and adolescents with severe obesity. Targeting those effortful control mechanisms underlying childhood obesity via cognitive behavioral techniques can facilitate behavioural change necessary to induce sustainable weight loss and weight control. In this presentation, I will present data on effortful control collected in a large sample of youngsters (n=572 participants, 51% boys, aged 7–19) with moderate to severe obesity. Results suggest that top-down inhibition and bottom-up external eating play a complex role in weight problems in certain subgroups of youngsters with obesity, stressing the importance of identifying subgroups for tailoring interventions. I will demonstrate a few science-based intervention techniques that have the potential to ameliorate effortful control capacities, and thus optimize treatment outcomes for those youngsters low in effortful control.

Disclosure

No significant relationships.

22q11.2 Low Copy Repeats Expanded in the Human Lineage

Segmental duplications or low copy repeats (LCRs) constitute duplicated regions interspersed in the human genome, currently neglected in standard analyses due to their extreme complexity. Recent functional studies have indicated the potential of genes within LCRs in synaptogenesis, neuronal migration, and neocortical expansion in the human lineage. One of the regions with the highest proportion of duplicated sequence is the 22q11.2 locus, carrying eight LCRs (LCR22-A until LCR22-H), and rearrangements between them cause the 22q11.2 deletion syndrome. The LCR22-A block was recently reported to be hypervariable in the human population. It remains unknown whether this variability also exists in non-human primates, since research is strongly hampered by the presence of sequence gaps in the human and non-human primate reference genomes. To chart the LCR22 haplotypes and the associated inter- and intra-species variability, we de novo assembled the region in non-human primates by a combination of optical mapping techniques. A minimal and likely ancient haplotype is present in the chimpanzee, bonobo, and rhesus monkey without intra-species variation. In addition, the optical maps identified assembly errors and closed gaps in the orthologous chromosome 22 reference sequences. These findings indicate the LCR22 expansion to be unique to the human population, which might indicate involvement of the region in human evolution and adaptation. Those maps will enable LCR22-specific functional studies and investigate potential associations with the phenotypic variability in the 22q11.2 deletion syndrome.

Using confidence interval-based estimation of relevance to explore bottom-up and top-down determinants of problematic eating behavior in children and adolescents with obesity from a dual pathway perspective

Prevalence of overweight and obesity in children and adolescents is high, not only in Western countries but also in developing countries. Efforts to improve prevention and treatment programs are needed. Given their essential role in weight problems, knowledge of determinants of problematic eating behavior ('External Eating' and 'Emotional Eating') is crucial for intervention development. Inspired by Appelhans' Dual Process Theory of Eating Behavior, the present study evaluated the importance of top-down regulative capacities and bottom-up reactivity, using the CIBER approach. CIBER is an innovative statistical approach to test the importance of behavior determinants, based on confidence intervals, instead of significance testing of point estimates. Survey data on different aspects of executive functioning (as indices of regulative capacities: Inhibition, Cognitive Flexibility, Emotional Control, Initiation, Working Memory, Planning/Organizing, Organization of materials, and Monitoring) and reward sensitivity (as an index of reactivity) were collected in a large sample of children and adolescents (n = 572) with severe obesity (adjBMI > 180%). Results showed that Emotional Eating is determined by Emotional Control, while External Eating is determined by Reward Sensitivity. The finding that differential mechanisms underlie different aspects of problematic eating suggests the need for using tailored intervention techniques to address altered reactivity and weak regulative capacities.

The 22q11 low copy repeats are characterized by unprecedented size and structural variability

Low copy repeats (LCRs) are recognized as a significant source of genomic instability, driving genome variability and evolution. The Chromosome 22 LCRs (LCR22s) mediate nonallelic homologous recombination (NAHR) leading to the 22q11 deletion syndrome (22q11DS). However, LCR22s are among the most complex regions in the genome, and their structure remains unresolved. The difficulty in generating accurate maps of LCR22s has also hindered localization of the deletion end points in 22q11DS patients. Using fiber FISH and Bionano optical mapping, we assembled LCR22 alleles in 187 cell lines. Our analysis uncovered an unprecedented level of variation in LCR22s, including LCR22A alleles ranging in size from 250 to 2000 kb. Further, the incidence of various LCR22 alleles varied within different populations. Additionally, the analysis of LCR22s in 22q11DS patients and their parents enabled further refinement of the rearrangement site within LCR22A and -D, which flank the 22q11 deletion. The NAHR site was localized to a 160-kb paralog shared between the LCR22A and -D in seven 22q11DS patients. Thus, we present the most comprehensive map of LCR22 variation to date. This will greatly facilitate the investigation of the role of LCR variation as a driver of 22q11 rearrangements and the phenotypic variability among 22q11DS patients.

Atypical chromosome 22q11.2 deletions are complex rearrangements and have different mechanistic origins

The majority (99%) of individuals with 22q11.2 deletion syndrome (22q11.2DS) have a deletion that is caused by non-allelic homologous recombination between two of four low copy repeat clusters on chromosome 22q11.2 (LCR22s). However, in a small subset of patients, atypical deletions are observed with at least one deletion breakpoint within unique sequence between the LCR22s. The position of the chromosome breakpoints and the mechanisms driving those atypical deletions remain poorly studied. Our large-scale, whole genome sequencing study of >1500 subjects with 22q11.2DS identified six unrelated individuals with atypical deletions of different types. Using a combination of whole genome sequencing data and fiber-fluorescence in situ hybridization, we mapped the rearranged alleles in these subjects. In four of them, the distal breakpoints mapped within one of the LCR22s and we found that the deletions likely occurred by replication-based mechanisms. Interestingly, in two of them, an inversion probably preceded inter-chromosomal 'allelic' homologous recombination between differently oriented LCR22-D alleles. Inversion associated allelic homologous recombination (AHR) may well be a common mechanism driving (atypical) deletions on 22q11.2.

Mediating Mechanisms in Cognitive Behavioral Therapy for Childhood OCD: The Role of Dysfunctional Beliefs

Reframing cognitions is assumed to play an important role in treatment for obsessive-compulsive disorder (OCD). However, there hardly is any empirical support for this assumption, especially for children. The aim of this study was to examine if changing dysfunctional beliefs is a mediating mechanism of cognitive behavioral therapy (CBT) for childhood OCD. Fifty-eight children (8-18 years) with OCD received CBT. Dysfunctional beliefs (OBQ-CV) and OCD severity (CY-BOCS) were measured pre-treatment, mid-treatment, post-treatment, and at 16-week follow-up. Results showed that OCD severity and dysfunctional beliefs decreased during CBT. Changes in severity predicted changes in beliefs within the same time interval. Our results did not support the hypothesis that changing dysfunctional beliefs mediates treatment effect. Future studies are needed to replicate these findings and shed more light on the role of explicit and implicit cognitions in treatment for childhood OCD.

Using a gamified monitoring app to change adolescents' snack intake: the development of the REWARD app and evaluation design

BACKGROUND

As the snacking pattern of European adolescents is of great concern, effective interventions are necessary. Till now health promotion efforts in children and adolescents have had only limited success in changing adolescents' eating patterns and anthropometrics. Therefore, the present study proposes an innovative approach to influence dietary behaviors in youth based on new insights on effective behavior change strategies and attractive intervention channels to engage adolescents. This article describes the rationale, the development, and evaluation design of the 'Snack Track School' app. The aim of the app is to improve the snacking patterns of Flemish 14- to 16-year olds.

METHODS

The development of the app was informed by the systematic, stepwise, iterative, and collaborative principles of the Intervention Mapping protocol. A four week mHealth intervention was developed based on the dual-system model with behavioral change strategies targeting both the reflective (i.e., active learning, advance organizers, mere exposure, goal-setting, monitoring, and feedback) and automatic processes (i.e., rewards and positive reinforcement). This intervention will be evaluated via a controlled pre-post design in Flemish schools among 1400 adolescents.

DISCUSSION

When this intervention including strategies focused on both the reflective and automatic pathway proves to be effective, it will offer a new scientifically-based vision, guidelines and practical tools for public health and health promotion (i.e., incorporation of learning theories in intervention programs).

TRIAL REGISTRATION

NCT02622165 registrated November 15, 2015 on clinicaltrials.gov.

Inulin hydrogels as carriers for colonic drug targeting. Rheological characterization of the hydrogel formation and the hydrogel network

Free radical polymerization converts aqueous solutions of methacrylated inulin into cross-linked hydrogels. The purpose of this work was to study the hydrogel formation and to characterize the fully cured hydrogels. The gelation process of aqueous solutions of methacrylated inulin was monitored as a function of time by means of linear oscillatory shear measurements, at a fixed frequency and amplitude. The fully cured inulin hydrogels were characterized by measurement of the frequency-dependency of the linear elastic modulus G'. The effects of the degree of substitution and feed concentration of methacrylated inulin on both the gelation kinetics and the rigidity of the obtained hydrogels were determined. The effect of the concentration of the initiators of the radical polymerization reaction has been studied as well. The weight fraction of polymer which was not incorporated in the hydrogel networks was determined using the anthrone reaction, and physical chain entanglements were determined by solution viscosity measurements. The gelation kinetics and the elastic modulus were proportional to the degree of substitution and feed concentration of methacrylated inulin. Increasing concentrations of radical-forming compounds also accelerated the hydrogel formation, but lowered the elastic modulus of the obtained hydrogels. The amount of polymer chains incorporated in the hydrogel network seemed to be especially influenced by the degree of substitution of the derivatized inulin, and for a feed concentration of 27% w/w of methacrylated inulin, entanglements have to be accounted for. The gelation kinetics and the elastic modulus of inulin hydrogels are not only affected by the degree of substitution and the feed concentration of methacrylated inulin, but also by the concentration of the initiators of the free radical polymerization reaction.

Colonic drug targeting

Specific targeting of drugs to the colon is recognized to have several therapeutic advantages. Drugs which are destroyed by the stomach acid and/or metabolized by pancreatic enzymes are slightly affected in the colon, and sustained colonic release of drugs can be useful in the treatment of nocturnal asthma, angina and arthritis. Treatment of colonic diseases such as ulcerative colitis, colorectal cancer and Crohn's disease is more effective with direct delivery of drugs to the affected area. Likewise, colonic delivery of vermicides and colonic diagnostic agents require smaller doses. This article is aimed at providing insight into the design considerations and evaluation of colonic drug delivery systems. For this purpose, the anatomy and physiology of the lower gastrointestinal tract are surveyed. Furthermore, the biopharmaceutical aspects are considered in relation to drug absorption in the colon and hence various approaches to colon-specific drug delivery are discussed.

Inulin hydrogels as carriers for colonic drug targeting: I. Synthesis and characterization of methacrylated inulin and hydrogel formation

PURPOSE

Vinyl groups were introduced in inulin chains in order to form hydrogels of this sugar polymer by free radical polymerization.

METHODS

Inulin was reacted with glycidyl methacrylate in N,N-dimethylformamide in the presence of 4-dimethylaminopyridine as catalyst. 1H and 13C NMR spectroscopy were used for the characterization of the obtained reaction product. Solid state 13C NMR spectroscopy revealed the conversion of the incorporated vinyl groups into covalent cross-links upon free radical polymerization of aqueous solutions of the derivatized inulin.

RESULTS

During reaction of inulin with glycidyl methacrylate, transesterification occurred, leading to the direct attachment of the methacryloyl group to inulin. Consequently, the obtained reaction product is methacrylated inulin. The extent of chemical modification of inulin could be tuned by varying the molar ratio of glycidyl methacrylate to inulin in the reaction mixture. Aqueous solutions of methacrylated inulin were converted into cross-linked hydrogels by free radical polymerization using ammonium persulphate and N,N,N',N'-tetramethylethylenediamine as initiating system.

CONCLUSIONS

Inulin hydrogels can be formed by free radical polymerization of aqueous solutions of methacrylated inulin.

Release of indomethacin from transparent oil-water gels

Within the scope of evaluating transparent oil-water gels (TOW gel) as dermatological vehicles, the release of indomethacin from a model TOW gel into 1-dodecanol is studied at various pH levels of the water phase. Apparent partition coefficient determinations and flame photometrical measurements show that both indomethacin and its sodium salt, as the ion pair, migrate into the 1-dodecanol layer. The pH-dependent release-rate profile is explained in terms of the amount of readily diffusible drug in the water phase of the gel.