Supportive neurodevelopmental evidence for ADHD as a developmental disorder

Association between early-life antibiotics use and the risk of attention-deficit/hyperactivity disorder: A real-world evidence study

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental disorder. Recently, children using antibiotics showed an increased incidence of neurodevelopmental disorders.

AIMS

The purpose of this study was to investigate the association between antibiotics use and the risk of ADHD in children.

STUDY DESIGN

Population-based retrospective cohort study.

SUBJECTS

The Taiwan National Health Insurance Research Database was used to collect data of children. Prevalence of antibiotics use was analyzed in the children (age, <2 years) included in this study. There were 1,601,689 children included in this study between 2004 and 2012.

OUTCOME MEASURES

The risk of developing ADHD was estimated using the Cox proportional hazards model.

RESULTS

71.25 % of children used at least one antibiotic, and the mean follow-up period was 7.07 years. After controlling for other related influencing factors, children who used antibiotics had a 1.12 times higher risk of ADHD than those who did not. The risk of ADHD increased through the use of penicillin and cephalosporin regardless of the duration of antibiotics use.

CONCLUSIONS

Antibiotics use in children-especially penicillin and cephalosporin-was associated with a higher risk of ADHD.

Differences in Neuronal Numbers, Morphology, and Developmental Apoptosis in Mice Nigra Provide Experimental Evidence of Ontogenic Origin of Vulnerability to Parkinson's Disease

Parkinson disease (PD) prevalence varies by ethnicity. In an earlier study, we replicated the reduced vulnerability to PD in an admixed population, using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-susceptible C57BL/6 J, MPTP-resistant CD-1 and their F1 crossbreds. In the present study, we investigated if the differences have a developmental origin. Substantia nigra was evaluated at postnatal days 2 (P2), P6, P10, P14, P18, and P22. C57BL/6 J mice had smaller nigra and fewer dopaminergic neurons than the CD-1 and crossbreds at P2, which persisted through development. A significant increase in numbers and nigral volume was observed across strains until P14. A drastic decline thereafter was specific to C57BL/6 J. CD-1 and crossbreds retained their numbers from P14 to stabilize with supernumerary neurons at adulthood. The neuronal size increased gradually to attain adult morphology at P10 in the resistant strains, vis-à-vis at P22 in C57BL/6 J. Accordingly, in comparison to C57BL/6 J, the nigra of CD-1 and reciprocal crossbreds possessed cytomorphological features of resilience, since birth. The considerably lesser dopaminergic neuronal loss in the CD-1 and crossbreds was seen at P2 and P14 and thereafter was complemented by attenuated developmental cell death. The differences in programmed cell death were confirmed by reduced TUNEL labelling, AIF, and caspase-3 expression. GDNF expression aligned with the cell death pattern at P2 and P14 in both nigra and striatum. Earlier maturity of nigra and its neurons appears to be better features that reflect as MPTP resistance at adulthood. Thus, variable MPTP vulnerability in mice and also differential susceptibility to PD in humans may arise early during nigral development.

Delay aversion in school-aged children with attention-deficit hyperactivity disorder

This study considered whether children with attention-deficit hyperactivity disorder displayed a stronger preference for smaller, more immediate rewards over larger, but delayed rewards (delay aversion) when compared to typically developing controls and, furthermore, whether age and gender influenced their preference in any way. Children, between 6 and 15 years of age, living in Limpopo province of South Africa, participated in the study. Two hundred sixteen children in total (108 with attention-deficit hyperactivity disorder and 108 matched controls without attention-deficit hyperactivity disorder symptoms) were assessed, on a task of delay aversion. The Two Choice Impulsivity Paradigm, which assesses immediate and delayed responses, was administered to both the attention-deficit hyperactivity disorder and control groups. The performance of both groups was compared on the Two Choice Impulsivity Paradigm, and the scores were analysed as a function of gender and age. The attention-deficit hyperactivity disorder group chose significantly more immediate, smaller responses than the neurotypical control group, which preferred significantly more delayed but larger responses. Gender and age did not affect the response choices for both immediate and delayed measurements. Children with attention-deficit hyperactivity disorder show a greater need for more immediate gratification, even if the reward is smaller, than the neurotypical control group who could delay gratification to receive a larger reward. Gender and age did not influence their preferences.

How evolutionary thinking can help us to understand ADHD

We argue that current debates about attention-deficit hyperactivity disorder (ADHD) can be considered afresh using an evolutionary lens. We show how the symptoms of ADHD can often be considered adaptive to their specific environment. We suggest that, from an evolutionary point of view, ADHD symptoms might be understood to result from an ‘evolutionary mismatch’, in which current environmental demands do not fit with what evolution has prepared us to cope with. For example, in our ancestral environment of evolutionary adaptedness (EEA), children were not expected to sit still and concentrate on academic tasks for many hours a day. Understanding ADHD in terms of such a ‘mismatch’ raises significant issues regarding the management of childhood ADHD, including ethical ones. An approach based on the concept of mismatch could provide an alternative to current debates on whether ADHD results from nature or nurture and whether it is under- or over-diagnosed. It would allow clinicians and policy makers to take both the child and the environment into account and consider what might be desirable and feasible, both in society and for specific children, to lessen the mismatch.

LEARNING OBJECTIVES

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Review of adult attention-deficit/hyperactivity disorder in South Africa

INTRODUCTION

Recently, there has been a greater focus on adults with Attention-Deficit/Hyperactivity Disorder (ADHD) given that the symptoms persist in two-thirds of patients into adulthood. Areas covered: A systematic review of articles reporting on adult ADHD in SA was undertaken. From the database search, 1209 articles were identified, with 29 articles included in this analysis. Expert commentary: Fourteen of the 29 studies reviewed were exploratory, 10 were reviews/commentaries, four were developmental studies and one was a phenomenological study. More than half (58.62%) of the articles were published in local South African journals, 13.79% were published in African journals (excluding South Africa), and 27.59% of the articles were published in international journals. The impact factor for nine of the journals were not stated and the remaining 11 have impact factors ranging from 0.207 to 6.78. In 2004, only one article on adult ADHD was published in SA and by 2015, the number of publications increased to six. Adult ADHD is gaining interest in South Africa, however, there have been a limited number of studies conducted thus far. It is recommended that further studies are conducted in this new and developing field.

Investigating white matter development in infancy and early childhood using myelin water faction and relaxation time mapping

The elaboration of the myelinated white matter is essential for normal neurodevelopment, establishing and mediating rapid communication pathways throughout the brain. These pathways facilitate the synchronized communication required for higher order behavioral and cognitive functioning. Altered neural messaging (or ‘disconnectivity’) arising from abnormal white matter and myelin development may underlie a number of neurodevelopmental psychiatric disorders. Despite the vital role myelin plays, few imaging studies have specifically examined its maturation throughout early infancy and childhood. Thus, direct investigations of the relationship(s) between evolving behavioral and cognitive functions and the myelination of the supporting neural systems have been sparse. Further, without knowledge of the ‘normative’ developmental time-course, identification of early abnormalities associated with developmental disorders remains challenging. In this work, we examined the use of longitudinal (T₁) and transverse (T₂) relaxation time mapping, and myelin water fraction (MWF) imaging to investigate white matter and myelin development in 153 healthy male and female children, 3 months through 60 months in age. Optimized age-specific acquisition protocols were developed using the DESPOT and mcDESPOT imaging techniques; and mean T₁, T₂ and MWF trajectories were determined for frontal, temporal, occipital, parietal and cerebellar white matter, and genu, body and splenium of the corpus callosum. MWF results provided a spatio-temporal pattern in-line with prior histological studies of myelination. Comparison of T₁, T₂ and MWF measurements demonstrates dissimilar sensitivity to tissue changes associated with neurodevelopment, with each providing differential but complementary information.

Identification of developmental-behavioral problems in primary care: a systematic review

CONTEXT

Recent mandates and recommendations for formal screening programs are based on the claim that pediatric care providers underidentify children with developmental-behavioral disorders, yet the research to support this claim has not been systematically reviewed.

OBJECTIVE

To review research literature for studies regarding pediatric primary care providers' identification of developmental-behavioral problems in children.

METHODS

On the basis of a Medline search conducted on September 22, 2010, using relevant key words, we identified 539 articles for review. We included studies that (1) were conducted in the United States, (2) were published in peer-reviewed journals, (3) included data that addressed pediatric care providers' identification of developmental-behavioral problems in individual patients, (4) included an independent assessment of patients' developmental-behavioral problems, such as diagnostic interviews or validated screening instruments, and (5) reported data sufficient to calculate sensitivity and specificity. Studies were not limited by sample size. Eleven articles met these criteria. We used Quality Assessment of Diagnostic Accuracy Studies (QUADAS) criteria to evaluate study quality. Although the studies were similar in many ways, heterogeneous methodology precluded a meta-analysis.

RESULTS

Sensitivities for pediatric care providers ranged from 14% to 54%, and specificities ranged from 69% to 100%. The authors of 1 outlier study reported a sensitivity of 85% and a specificity of 61%.

CONCLUSIONS

Pediatricians are often the first point of entry into developmental and mental health systems. Knowing their accuracy in identifying children with developmental-behavioral disabilities is essential for implementing optimal evaluation programs and achieving timely identification. Moreover, these statistics are important to consider when planning large-scale screening programs.

The impact of maternal separation on the number of tyrosine hydroxylase-expressing midbrain neurons during different stages of ontogenesis

Early life stressors have life-long functional and anatomical consequences. Though many neurotransmitters are involved in the functional impact of early life stress, dopamine seems to be important because of its roles in motor control, adaptation to stressful conditions, mood, cognition, attention and reward. Thus, in the present study, we investigated the way that early life stress, in the form of maternal separation (MS), affects the populations of tyrosine hydroxylase-immunoreactive (TH-IR) dopaminergic neurons in rat midbrain structures during ontogenesis. We included in the study the sub-regions of the substantia nigra (SN) and the ventral tegmental area (VTA). In both the control and MS rats, we found that the estimated total number of TH-expressing neurons fluctuated during ontogenesis. Moreover, MS influenced the number of TH-IR cells, especially in the SN pars reticulata (SNr) and VTA. Shortly after the termination of MS, on postnatal day (PND) 15, a decrease in the estimated total number of TH-IR neurons was observed in the SNr and VTA (in both males and females). On PND 35, MS caused a transient increase in the number of TH-IR cells only in the SNr of female rats. On PND 70, MS affected the number of TH-IR neurons in the VTA of females; specifically, an increase in the number of these cells was observed. Additionally, MS did not alter TH-IR cell sizes or the total levels of TH (measured by Western blot analysis) in the SN and VTA for all stages of ontogenesis in both males and females. The results from the study herein indicate that early life stress has enduring effects on the populations of midbrain TH-expressing dopaminergic neurons (especially in female rats), which are critically important for dopamine-regulated brain function throughout ontogenesis.

Long term developmental impact of social withdrawal in infants

The aim of this study was to follow-up infants who were assessed in early infancy, at approximately 6 months of age, to determine the developmental impact of social withdrawal at approximately 30 months of age. Infants were administered the Bayley Scales of Infant Development-Third Edition, and the mothers complete the Behavior Assessment System for Children (BASC), Second Edition-Parent Rating Scale-Preschool form. Significant negative correlations were found between infant social withdrawal and Cognitive and Language scales of the Bayley Scales, and the Social and Communication scales of the BASC. Significant positive correlations were found between the infant social withdrawal and later higher scores on Atypicality and Attention scales. These results provide support for the use of the Alarm Distress Baby Scale as a measure of infant social withdrawal, and its association with later development and behavior.

Semax, an analogue of adrenocorticotropin (4–10), is a potential agent for the treatment of attention-deficit hyperactivity disorder and Rett syndrome

Psychostimulants, such as methylphenidate, are currently the most common used drug therapy for children with attention-deficit hyperactivity disorder (ADHD). However, a number of patients with ADHD either fail to respond to these drugs or experience side effects that preclude their use. The heptapeptide Semax is an analogue of the N-terminal fragment (4-10) of adrenocorticotropic hormone, but is completely devoid of any hormonal activity. It has been found to stimulate memory and attention in rodents and humans after intranasal application. Evidence from animal studies revealed that Semax can augment the effects of psychostimulants on central dopamine release and also stimulates central brain-derived neurotrophic factor (BDNF) synthesis. In addition, Semax could improve selective attention and modulate brain development. Since ADHD is likely to be a neurodevelopmental disorder with disturbance in dopamine and BDNF function, it is proposed in this paper that Semax may have good therapeutic potential in ADHD. Furthermore, increased BDNF activity is found to improve Rett syndrome, a severe neurodevelopmental disorder which is, in the majority of cases, caused by mutations in the gene encoding methyl-CpG-binding protein 2 (MECP2). The potential therapeutic effect of Semax in Rett syndrome by increasing central BDNF activity may be of interest for further exploration in animal models of Rett syndrome.