Autism at the beginning: microstructural and growth abnormalities underlying the cognitive and behavioral phenotype of autism

A developmental and genetic classification for midbrain-hindbrain malformations

Advances in neuroimaging, developmental biology and molecular genetics have increased the understanding of developmental disorders affecting the midbrain and hindbrain, both as isolated anomalies and as part of larger malformation syndromes. However, the understanding of these malformations and their relationships with other malformations, within the central nervous system and in the rest of the body, remains limited. A new classification system is proposed, based wherever possible, upon embryology and genetics. Proposed categories include: (i) malformations secondary to early anteroposterior and dorsoventral patterning defects, or to misspecification of mid-hindbrain germinal zones; (ii) malformations associated with later generalized developmental disorders that significantly affect the brainstem and cerebellum (and have a pathogenesis that is at least partly understood); (iii) localized brain malformations that significantly affect the brain stem and cerebellum (pathogenesis partly or largely understood, includes local proliferation, cell specification, migration and axonal guidance); and (iv) combined hypoplasia and atrophy of putative prenatal onset degenerative disorders. Pertinent embryology is discussed and the classification is justified. This classification will prove useful for both physicians who diagnose and treat patients with these disorders and for clinical scientists who wish to understand better the perturbations of developmental processes that produce them. Importantly, both the classification and its framework remain flexible enough to be easily modified when new embryologic processes are described or new malformations discovered.

Autism spectrum disorders in survivors of extreme prematurity

Recent studies in survivors of extreme prematurity point to an increased prevalence of a previously underrecognized atypical social-behavioral profile strongly suggestive of an autism spectrum disorder. Prospective studies that incorporate early autism screening and autism diagnostic testing are needed to better delineate the sensitivity and specificity of early signs of autism in ex-premature children. Advances in neonatal MRI techniques capable of quantitative structural and functional measurements will also provide important insights into the effects of prematurity itself, and prematurity-related brain injury on the genesis of autism spectrum disorders in this population. Available evidence linking prematurity and autism spectrum disorders is reviewed in this article.

Increased activities of Na+/K+-ATPase and Ca2+/Mg2+-ATPase in the frontal cortex and cerebellum of autistic individuals

AIMS

Na(+)/K(+)-ATPase and Ca(2+)/Mg(2+)-ATPase are enzymes known to maintain intracellular gradients of ions that are essential for signal transduction. The aim of this study was to compare the activities of Na(+)/K(+)-ATPase and Ca(2+)/Mg(2+)-ATPase in postmortem brain samples from the cerebellum and frontal, temporal, parietal, and occipital cortices from autistic and age-matched control subjects.

MAIN METHODS

The frozen postmortem tissues from different brain regions of autistic and control subjects were homogenized. The activities of Na(+)/K(+)-ATPase and Ca(2+)/Mg(2+)-ATPase were assessed in the brain homogenates by measuring inorganic phosphorus released by the action of Na(+)/K(+)- and Ca(2+)/Mg(2+)-dependent hydrolysis of ATP.

KEY FINDINGS

In the cerebellum, the activities of both Na(+)/K(+)-ATPase and Ca(2+)/Mg(2+)-ATPase were significantly increased in the autistic samples compared with their age-matched controls. The activity of Na(+)/K(+)-ATPase but not Ca(2+)/Mg(2+)-ATPase was also significantly increased in the frontal cortex of the autistic samples as compared to the age-matched controls. In contrast, in other regions, i.e., the temporal, parietal and occipital cortices, the activities of these enzymes were similar in autism and control groups.

SIGNIFICANCE

The results of this study suggest brain-region specific increases in the activities of Na(+)/K(+)-ATPase and Ca(2+)/Mg(2+)-ATPase in autism. Increased activity of these enzymes in the frontal cortex and cerebellum may be due to compensatory responses to increased intracellular calcium concentration in autism. We suggest that altered activities of these enzymes may contribute to abnormal neuronal circuit functioning in autism.

How somatic cortical maps differ in autistic and typical brains

The comorbidity of 'core characteristics' and sensorimotor abnormalities in autism implies abnormalities in brain development of a general and pervasive nature and atypical organization of sensory cortex. By using magnetoencephalography, we examined the cortical response to passive tactile stimulation of the thumb and index finger of the dominant hand and lip of the individuals with autism spectrum disorder and typically developing persons. The distance between the cortical representations of thumb and the lip was significantly larger in the autism group than in typicals. Moreover, in cortex, the thumb is typically closer to the lip than the index finger. This was not observed in persons with autism. Our findings are arguably the first demonstration of abnormality in sensory organization in the brains of persons with autism.

A whole-genome scan and fine-mapping linkage study of auditory-visual synesthesia reveals evidence of linkage to chromosomes 2q24, 5q33, 6p12, and 12p12

Synesthesia, a neurological condition affecting between 0.05%-1% of the population, is characterized by anomalous sensory perception and associated alterations in cognitive function due to interference from synesthetic percepts. A stimulus in one sensory modality triggers an automatic, consistent response in either another modality or a different aspect of the same modality. Familiality studies show evidence of a strong genetic predisposition; whereas initial pedigree analyses supported a single-gene X-linked dominant mode of inheritance with a skewed F:M ratio and a notable absence of male-to-male transmission, subsequent analyses in larger samples indicated that the mode of inheritance was likely to be more complex. Here, we report the results of a whole-genome linkage scan for auditory-visual synesthesia with 410 microsatellite markers at 9.05 cM density in 43 multiplex families (n = 196) with potential candidate regions fine-mapped at 5 cM density. Using NPL and HLOD analysis, we identified four candidate regions. Significant linkage at the genome-wide level was detected to chromosome 2q24 (HLOD = 3.025, empirical genome-wide p = 0.047). Suggestive linkage was found to chromosomes 5q33, 6p12, and 12p12. No support was found for linkage to the X chromosome; furthermore, we have identified two confirmed cases of male-to-male transmission of synesthesia. Our results demonstrate that auditory-visual synesthesia is likely to be an oligogenic disorder subject to multiple modes of inheritance and locus heterogeneity. This study comprises a significant step toward identifying the genetic substrates underlying synesthesia, with important implications for our understanding of the role of genes in human cognition and perception.

Receptive language organization in high-functioning autism

One of the core defining components of autism is impairment in communication, typically manifested as a delay in speech development. To date, neuroimaging studies have shed limited light on the mechanisms behind delay in speech development in autism. We performed magnetoencephalographic-based auditory language mapping in 2 cases of high-functioning autism. Overall, 2 distinct characteristics were found, such as the use of atypical language pathways and cortical hyperexcitability. These neurophysiological findings parallel those reported in 2 other developmental disorders, developmental dyslexia and Rett syndrome. We discuss common mechanisms that may account for cognitive delays across these developmental disorders.

Neurodevelopment and executive function in autism

Autism is a neurodevelopmental disorder characterized by social and communication deficits, and repetitive behavior. Studies investigating the integrity of brain systems in autism suggest a wide range of gray and white matter abnormalities that are present early in life and change with development. These abnormalities predominantly affect association areas and undermine functional integration. Executive function, which has a protracted development into adolescence and reflects the integration of complex widely distributed brain function, is also affected in autism. Evidence from studies probing response inhibition and working memory indicate impairments in these core components of executive function, as well as compensatory mechanisms that permit normative function in autism. Studies also demonstrate age-related improvements in executive function from childhood to adolescence in autism, indicating the presence of plasticity and suggesting a prolonged window for effective treatment. Despite developmental gains, mature executive functioning is limited in autism, reflecting abnormalities in wide-spread brain networks that may lead to impaired processing of complex information across all domains.

Development of anterior cingulate functional connectivity from late childhood to early adulthood

Human cerebral development is remarkably protracted. Although microstructural processes of neuronal maturation remain accessible only to morphometric post-mortem studies, neuroimaging tools permit the examination of macrostructural aspects of brain development. The analysis of resting-state functional connectivity (FC) offers novel possibilities for the investigation of cerebral development. Using seed-based FC methods, we examined the development of 5 functionally distinct cingulate-based intrinsic connectivity networks (ICNs) in children (n = 14, 10.6 +/- 1.5 years), adolescents (n = 12, 15.4 +/- 1.2) and young adults (n=14, 22.4 +/- 1.2). Children demonstrated a more diffuse pattern of correlation with voxels proximal to the seed region of interest (ROI) ("local FC"), whereas adults exhibited more focal patterns of FC, as well as a greater number of significantly correlated voxels at long distances from the seed ROI. Adolescents exhibited intermediate patterns of FC. Consistent with evidence for different maturational time courses, ICNs associated with social and emotional functions exhibited the greatest developmental effects. Our findings demonstrate the utility of FC for the study of developing functional organization. Moreover, given that ICNs are thought to have an anatomical basis in neuronal connectivity, measures of FC may provide a quantitative index of brain maturation in healthy subjects and those with neurodevelopmental disorders.

Cerebellar modulation of frontal cortex dopamine efflux in mice: relevance to autism and schizophrenia

Cerebellar and frontal cortical pathologies have been commonly reported in schizophrenia, autism, and other developmental disorders. Whether there is a relationship between prefrontal and cerebellar pathologies is unknown. Using fixed potential amperometry, dopamine (DA) efflux evoked by cerebellar or, dentate nucleus electrical stimulation (50 Hz, 200 muA) was recorded in prefrontal cortex of urethane anesthetized lurcher (Lc/+) mice with 100% loss of cerebellar Purkinje cells and wildtype (+/+) control mice. Cerebellar stimulation with 25 and 100 pulses evoked prefrontal cortex DA efflux in +/+ mice that persisted for 12 and 25 s poststimulation, respectively. In contrast, 25 pulse cerebellar stimulation failed to evoke prefrontal cortex DA efflux in Lc/+ mice indicating a dependency on cerebellar Purkinje cell outputs. Dentate nucleus stimulation (25 pulses) evoked a comparable but briefer (baseline recovery within 7 s) increase in prefrontal cortex DA efflux compared to similar cerebellar stimulation in +/+ mice. However, in Lc/+ mice 25 pulse dentate nucleus evoked prefrontal cortex DA efflux was attenuated by 60% with baseline recovery within 4 s suggesting that dentate nucleus outputs to prefrontal cortex remain partially functional. DA reuptake blockade enhanced 100 pulse stimulation evoked prefrontal cortex responses, while serotonin or norepinephrine reuptake blockade were without effect indicating the specificity of the amperometric recordings to DA. Results provide neurochemical evidence that the cerebellum can modulate DA efflux in the prefrontal cortex. Together, these findings may explain why cerebellar and frontal cortical pathologies co-occur, and may provide a mechanism that accounts for the diversity of symptoms common to multiple developmental disorders.

Positive screening for autism in ex-preterm infants: prevalence and risk factors

OBJECTIVE

The survival of very low birth weight infants has increased markedly in recent years. Unfortunately, the prevalence of significant and lifelong motor, cognitive, and behavioral dysfunction has remained a major problem confronting these children. The objective of this study was to perform screening tests for early autistic features in children with a history of very low birth weight and to identify risk factors associated with a positive screening result.

METHODS

We studied 91 ex-preterm infants < or = 1500 g at birth. Infants underwent conventional MRI studies at preterm and/or term-adjusted age. We collected pertinent demographic, prenatal, intrapartum, acute postnatal, and short-term outcome data for all infants. Follow-up assessments were performed at a mean age of 21.9 +/- 4.7 months, using the Modified Checklist for Autism in Toddlers, the Vineland Adaptive Behavior Scale, and the Child Behavior Checklist.

RESULTS

Twenty-six percent of ex-preterm infants had a positive result on the autism screening tool. Abnormal scores correlated highly with internalizing behavioral problems on the Child Behavior Checklist and socialization and communication deficits on the Vineland Scales. Lower birth weight, gestational age, male gender, chorioamnionitis, acute intrapartum hemorrhage, illness severity on admission, and abnormal MRI studies were significantly associated with an abnormal autism screening score.

CONCLUSIONS

Early autistic behaviors seem to be an underrecognized feature of very low birth weight infants. The results from this study suggest that early screening for signs of autism may be warranted in this high-risk population followed by definitive autism testing in those with positive screening results.

Heterogeneous association between engrailed-2 and autism in the CPEA network

Autism is a neurodevelopmental disorder characterized by an early onset of abnormal social, communicative, and repetitive behavior. Engrailed-2 (EN2) was identified as an autism candidate gene because its influence on cerebellar development in mice parallels neurodevelopmental abnormalities seen in individuals with autism. Studies investigating association between markers at EN2 (chr7q36), a location associated with language disorders, and autism reveal mixed findings. Two positive reports revealed association with two intronic SNPs. Since the associated SNPs were in high linkage disequilibrium and shared similar minor allele frequencies, we chose to test whether one of the SNPs (rs1861972) was associated with autism in three recruiting sites from the NIH Collaborative Programs of Excellence in Autism (CPEA) network. A recessive model revealed significant association with broad autism spectrum disorder. Site specific analyses indicated differential allele transmission by site, despite similar ethnicity, and parental genotypes, suggesting the SNP may contribute to various risk haplotypes. No significant association with autism was found under an additive model for either a broad (autism spectrum disorder) or a narrow (autistic disorder) diagnostic group. Although our findings were not as robust as the previous studies, they suggest that rs1861972 may influence the risk for autism spectrum disorders. Future studies investigating EN2 should consider how the association of variants in this gene with autism could be influenced by differences in phenotype and possible interactions with genotypes at other autism candidate genes.

Expression of phosphodiesterase 4 is altered in the brains of subjects with autism

The cyclic adenosine monophosphate-specific phosphodiesterase-4 (PDE4) gene family is the target of several potential therapeutic inhibitors and the PDE4B gene has been associated with schizophrenia and depression. Little, however, is known of any connection between this gene family and autism, with limited effective treatment being available for autism. We measured the expression of PDE4A and PDE4B by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting in Brodmann's area 40 (BA40, parietal cortex), BA9 (superior frontal cortex), and cerebellum from subjects with autism and matched controls. We observed a lower expression of PDE4A5, PDE4B1, PDE4B3, PDE4B4, and PDE4B2 in the cerebella of subjects with autism when compared with matched controls. In BA9, we observed the opposite: a higher expression of PDE4AX, PDE4A1, and PDE4B2 in subjects with autism. No changes were observed in BA40. Our results demonstrate altered expressions of the PDE4A and PDE4B proteins in the brains of subjects with autism and might provide new therapeutic avenues for the treatment of this debilitating disorder.

Early detection of autism spectrum disorders: screening between 12 and 24 months of age

PURPOSE

The purpose of this article is to present nurse practitioners (NPs) with information on screening for autism spectrum disorders (ASDs) in children between 12 and 24 months of age. Recommendations are also provided for appropriate referrals and initiation of early intervention (EI).

DATA SOURCES

Review of published literature about ASD.

CONCLUSIONS

Children with ASD exhibit impaired social interaction, verbal and nonverbal communication deficits, and repetitive, restricted, and stereotyped patterns of behavior or interests. Studies show that these children benefit from beginning intensive EI as soon as possible.

IMPLICATIONS FOR PRACTICE

Early detection enables children with suspected ASD to be evaluated by specialists and entered into treatment programs at the earliest possible opportunity. Because of the importance of early diagnosis of ASD, it is critical that NPs use established screening instruments to maximize time and increase the reliability of the assessment.

The intense world syndrome--an alternative hypothesis for autism

Autism is a devastating neurodevelopmental disorder with a polygenetic predisposition that seems to be triggered by multiple environmental factors during embryonic and/or early postnatal life. While significant advances have been made in identifying the neuronal structures and cells affected, a unifying theory that could explain the manifold autistic symptoms has still not emerged. Based on recent synaptic, cellular, molecular, microcircuit, and behavioral results obtained with the valproic acid (VPA) rat model of autism, we propose here a unifying hypothesis where the core pathology of the autistic brain is hyper-reactivity and hyper-plasticity of local neuronal circuits. Such excessive neuronal processing in circumscribed circuits is suggested to lead to hyper-perception, hyper-attention, and hyper-memory, which may lie at the heart of most autistic symptoms. In this view, the autistic spectrum are disorders of hyper-functionality, which turns debilitating, as opposed to disorders of hypo-functionality, as is often assumed. We discuss how excessive neuronal processing may render the world painfully intense when the neocortex is affected and even aversive when the amygdala is affected, leading to social and environmental withdrawal. Excessive neuronal learning is also hypothesized to rapidly lock down the individual into a small repertoire of secure behavioral routines that are obsessively repeated. We further discuss the key autistic neuropathologies and several of the main theories of autism and re-interpret them in the light of the hypothesized Intense World Syndrome.

Autism: the first firm finding = underconnectivity?

In January 2005, J.R. Hughes and M. Melyn published an electroencephalographic study on autistic children and found 46% with seizures and also a relatively high prevalence of 20% with epileptiform discharges but without any clinical seizures (Clin EEG Neurosci 2005;36:15-20). Because the discharges have always been viewed as focal events and the clinical seizures as requiring spread, the conclusion from these data was that children with autism may have a deficiency of corticocortical fibers. Since that time many MRI and functional MRI studies have been published confirming that one of the first findings in this devastating condition is underconnectivity. Specific findings are the thinning of the corpus callosum and the reduced connectivity, especially with the frontal areas and also the fusiform face area. Other studies involving positron emission tomography scans, magnetoencephalography, and perception have added to the evidence of underconnectivity. One final point is the initial overgrowth of white matter in the first 2 years of life in autistic children, followed later by arrested growth, resulting in aberrant connectivity; myelination of white matter will likely be significant in the etiology of autism.

Hyperconnectivity of local neocortical microcircuitry induced by prenatal exposure to valproic acid

Exposure to valproic acid (VPA) during embryogenesis can cause several teratogenic effects, including developmental delays and in particular autism in humans if exposure occurs during the third week of gestation. We examined the postnatal effects of embryonic exposure to VPA on microcircuit properties of juvenile rat neocortex using in vitro electrophysiology. We found that a single prenatal injection of VPA on embryonic day 11.5 causes a significant enhancement of the local recurrent connectivity formed by neocortical pyramidal neurons. The study of the biophysical properties of these connections revealed weaker excitatory synaptic responses. A marked decrease of the intrinsic excitability of pyramidal neurons was also observed. Furthermore, we demonstrate a diminished number of putative synaptic contacts in connection between layer 5 pyramidal neurons. Local hyperconnectivity may render cortical modules more sensitive to stimulation and once activated, more autonomous, isolated, and more difficult to command. This could underlie some of the core symptoms observed in humans prenatally exposed to valproic acid.

Cognitive flexibility in adults with high functioning autism

The goal of the current study was to evaluate presetting, response inhibition, set shifting, and a priori planning in autism: abilities that can be lumped together under the term cognitive flexibility. Cognitive flexibility is an aspect of executive functioning, which in turn is mediated by the prefrontal cortical lobes. A group of adults with high-functioning autism (HFA; n = 23) were compared with a normal control group (n = 32), by using a computerized variant of the Sternberg response bias paradigm. Contrary to the results of earlier studies, no deficit was found in presetting, response inhibition, set shifting, and a priori planning in participants with autism, even when the medication factor was taken into account. Methodological issues that could be explanatory for this difference are discussed. An additional finding was, that individuals with HFA (especially those on medication) were slow in reacting. Possible origins and consequences of this slowness, also for cognitive flexibility, are discussed.

Autism spectrum disorders: developmental disconnection syndromes

Autism is a common and heterogeneous childhood neurodevelopmental disorder. Analogous to broad syndromes such as mental retardation, autism has many etiologies and should be considered not as a single disorder but, rather, as 'the autisms'. However, recent genetic findings, coupled with emerging anatomical and functional imaging studies, suggest a potential unifying model in which higher-order association areas of the brain that normally connect to the frontal lobe are partially disconnected during development. This concept of developmental disconnection can accommodate the specific neurobehavioral features that are observed in autism, their emergence during development, and the heterogeneity of autism etiology, behaviors and cognition.

Molecular mechanisms of autism: a possible role for Ca2+ signaling

Autism spectrum disorders (ASDs) are a group of developmental disorders characterized by social and emotional deficits, language impairments and stereotyped behaviors that manifest in early postnatal life. The molecular mechanisms that underlie ASDs are not known, but several recent developments suggest that some forms of autism are caused by failures in activity-dependent regulation of neural development. Mutations of several voltage-gated and ligand-gated ion channels that regulate neuronal excitability and Ca2+ signaling have been associated with ASDs. In addition, Ca2+-regulated signaling proteins involved in synapse formation and dendritic growth have been implicated in ASDs. These recent advances suggest a set of signaling pathways that might have a role in generating these increasingly prevalent disorders.

Post-error adaptation in adults with high functioning autism

Deficits in executive function (EF), i.e. function of the prefrontal cortex, may be central in the etiology of autism. One of the various aspects of EF is error detection and adjusting behavior after an error. In cognitive tests, adults normally slow down their responding on the next trial after making an error, a compensatory mechanism geared toward improving performance on subsequent trials, and a faculty critically associated with activity in the anterior cingulate cortex (ACC). The current study evaluated post-error slowing in people with high functioning autism (HFA) (n=36), taking symptom severity into account, compared to the performance of a normal control group (n=32). Symptom severity in the HFA group was defined in terms of level of adaptation: living independently (outpatients; n=12) and living residentially (inpatients; n=24). Half the group of inpatients was on medication; the results of their performance were analyzed separately. A computerized version of a memory search task was used with two response probability conditions. The subjects in the control group adjusted their reaction time (RT) substantially after an error, while the group of participants with HFA appeared to be overall slow, with no significant adjustment of RT after an error. This finding remained significant if the medication factor was taken into account, and was independent of the degree of severity of the autistic disorder, as defined by the dichotomy 'inpatient versus outpatient'. Possible causes and implications of the finding are discussed.

A review of gene linkage, association and expression studies in autism and an assessment of convergent evidence

Autism is a neurodevelopmental disorder with high heritability and a likely complex genetic architecture. Much genetic evidence has accumulated in the last 20 years but no gene has been unequivocally identified as containing risk variants for autism. In this article we review the past and present literature on neuro-pathological, genetic linkage, genetic association, and gene expression studies in this disorder. We sought convergent evidence to support particular genes or chromosomal regions that might be likely to contain risk DNA variants. The convergent evidence from these studies supports the current hypotheses that there are multiple genetic loci predisposing to autism, and that genes involved in neurodevelopment are especially important for future genetic studies. Convergent evidence suggests the chromosome regions 7q21.2-q36.2, 16p12.1-p13.3, 6q14.3-q23.2, 2q24.1-q33.1, 17q11.1-q21.2, 1q21-q44 and 3q21.3-q29, are likely to contain risk genes for autism. Taken together with results from neuro-pathological studies, genes involved in brain development located at the above regions should be prioritized for future genetic research.

Retinoic acid delineates the topography of neuronal plasticity in postnatal cerebral cortex

Retinoic acid is well recognized to promote neuronal differentiation in the embryonic nervous system, but how it influences the postnatal cerebral cortex remains largely unknown. The domain of highest retinoic acid actions in the cortex of the mouse constricts postnatally to a narrow band that includes the dorsal visual stream and the attentional and executive networks. This band of cortex, which is distinguished by the retinoic acid-synthesizing enzyme RALDH3, exhibits signs of delayed maturation and enhanced plasticity compared to the surrounding cortex, as indicated by suppression of parvalbumin, neurofilament, cytochrome oxidase and perineuronal net maturation, and persistence of the embryonic, polysialated form of the neural cell-adhesion molecule PSA-NCAM. During the first postnatal week, the RALDH3-expressing territory translocates in the caudal cortex from the medial limbic lobe to the adjacent neocortex. This topographical shift requires the neurotrophin NT-3 because in mice lacking neuronal NT-3 the RALDH3 enzyme maintains its early postnatal pattern up to adulthood. In the NT-3-null mutants, expression of the markers, whose topography colocalizes with RALDH3 in the normal cortex, matches the abnormal RALDH3 pattern. This indicates that the uneven retinoic acid distribution serves a role in patterning the maturation and to some extent function of the normal postnatal cerebral cortex.