Ordered-subset analysis of savant skills in autism for 15q11-q13

Giftedness and atypical sexual differentiation: enhanced perceptual functioning through estrogen deficiency instead of androgen excess

Syndromic autism spectrum conditions (ASC), such as Klinefelter syndrome, also manifest hypogonadism. Compared to the popular Extreme Male Brain theory, the Enhanced Perceptual Functioning model explains the connection between ASC, savant traits, and giftedness more seamlessly, and their co-emergence with atypical sexual differentiation. Overexcitability of primary sensory inputs generates a relative enhancement of local to global processing of stimuli, hindering the abstraction of communication signals, in contrast to the extraordinary local information processing skills in some individuals. Weaker inhibitory function through gamma-aminobutyric acid type A (GABAA) receptors and the atypicality of synapse formation lead to this difference, and the formation of unique neural circuits that process external information. Additionally, deficiency in monitoring inner sensory information leads to alexithymia (inability to distinguish one's own emotions), which can be caused by hypoactivity of estrogen and oxytocin in the interoceptive neural circuits, comprising the anterior insular and cingulate gyri. These areas are also part of the Salience Network, which switches between the Central Executive Network for external tasks and the Default Mode Network for self-referential mind wandering. Exploring the possibility that estrogen deficiency since early development interrupts GABA shift, causing sensory processing atypicality, it helps to evaluate the co-occurrence of ASC with attention deficit hyperactivity disorder, dyslexia, and schizophrenia based on phenotypic and physiological bases. It also provides clues for understanding the common underpinnings of these neurodevelopmental disorders and gifted populations.

ADHD-related symptoms and attention profiles in the unaffected siblings of probands with autism spectrum disorder: focus on the subtypes of autism and Asperger's disorder

BACKGROUND

The presence of attention-deficit/hyperactive disorder (ADHD) symptoms and impaired attention performance are commonly noted in individuals with autism spectrum disorder (ASD). However, little is known about attention performance in their unaffected siblings. This study aimed to investigate the ADHD-related traits and attention performance in unaffected siblings of probands with autism and Asperger syndrome (AS), as well as the clinical correlates of ADHD-related traits.

METHODS

We assessed the intention, hyperactivity-impulsivity, and oppositional symptoms, and attention profiles of 199 probands with a diagnosis of ASD (122 autism, 77 AS), their unaffected siblings, and 196 typically developing controls (TD) by their parents' reports on the ADHD-related symptoms and the Connors' Continuous Performance Test (CCPT), respectively.

RESULTS

Compared to TD, unaffected siblings of ASD probands were more hyperactive/impulsive and oppositional, particularly unaffected siblings of AS probands. In CCPT, unaffected siblings of AS have intermediate levels of performance between probands with AS and TD on focused attention and sustained attention but were not statistically different from AS probands or TD in these attention profiles. In contrast, unaffected siblings of autism probands have significantly better CCPT performance when compared to autism probands but not to TD. In addition, stereotyped behaviors predicted ADHD-related traits in both sibling groups, but distinctive patterns of other correlates for ADHD-related traits were found between the two sibling groups.

CONCLUSIONS

This work suggested that unaffected siblings of AS, but not autism, have more hyperactive/impulsive traits and a trend of pervasive attention deficits assessed by CCPT which might serve as potential endophenotypes for genetic studies in AS.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT01582256.

GABAA receptor subunit gene polymorphisms predict symptom-based and developmental deficits in Chinese Han children and adolescents with autistic spectrum disorders

GABA_A receptor subunit genes GABRB3, GABRA5, and GABRG3 located on chromosome 15q11-q13 have been implicated in the etiology of autistic spectrum disorders (ASD). This study intended to investigate the possible role of single-nucleotide polymorphisms (SNPs) present in GABRB3 (rs2081648 and rs1426217), GABRA5 (rs35586628), and GABRG3 (rs208129) genes in ASD susceptibility and symptom-based and developmental phenotypes of ASD in Chinese Han children and adolescents. 99 ASD patients and 231 age- and gender- frequency-matched typical developing (TD) controls were tested by TaqMan® genotyping assay. Symptom-based phenotypes were evaluated by Childhood Autism Rating Scale (CARS) and Autism Behavior Checklist (ABC), and developmental phenotypes were assessed by Early Childhood Development Questionnaire (ECDQ) in ASD patients. Three haplotypes and global χ ² test of all SNPs demonstrated significant associations between ASD and TD groups. Besides, GABRB3 rs2081648, GABRA5 rs35586628, and GABRG3 rs208129 polymorphisms were associated with symptom-based deficits in social interaction, sensorimotor and somatosensory coordination, visual response, imitation, activity level, language expression and adaptability. Developmental abnormalities in late emergences of social interaction and fine motor were detected in GABRB3 rs2081648 polymorphism. Overall results indicated that gene synergy may participate in ASD pathogenesis, and GABA_A receptor gene polymorphisms can predict symptom-based and developmental deficits in ASD individuals.

Identification of genetic loci underlying the phenotypic constructs of autism spectrum disorders

OBJECTIVE

To investigate the underlying phenotypic constructs in autism spectrum disorders (ASD) and to identify genetic loci that are linked to these empirically derived factors.

METHOD

Exploratory factor analysis was applied to two datasets with 28 selected Autism Diagnostic Interview-Revised (ADI-R) algorithm items. The first dataset was from the Autism Genome Project (AGP) phase I (1,236 ASD subjects from 618 families); the second was from the AGP phase II (804 unrelated ASD subjects). Variables derived from the factor analysis were then used as quantitative traits in genome-wide variance components linkage analyses.

RESULTS

Six factors, namely, joint attention, social interaction and communication, nonverbal communication, repetitive sensory-motor behavior, peer interaction, and compulsion/restricted interests, were retained for both datasets. There was good agreement between the factor loading patterns from the two datasets. All factors showed familial aggregation. Suggestive evidence for linkage was obtained for the joint attention factor on 11q23. Genome-wide significant evidence for linkage was obtained for the repetitive sensory-motor behavior factor on 19q13.3.

CONCLUSIONS

This study demonstrates that the underlying phenotypic constructs based on the ADI-R algorithm items are replicable in independent datasets, and that the empirically derived factors are suitable and informative in genetic studies of ASD.

Role of UBE3A and ATP10A genes in autism susceptibility region 15q11-q13 in an Italian population: a positive replication for UBE3A

The aetiology of autism is still largely unknown despite analyses from family and twin studies demonstrating substantial genetic role in the aetiology of the disorder. Data from linkage studies and analyses of chromosomal abnormalities identified 15q11-q13 as a region of particular aetiopathogenesis interest. We screened a set of markers spanning two known imprinted, maternally expressed genes, UBE3A and ATP10A, harboured in this candidate region. We replicated evidence of linkage disequilibrium (LD) at marker D15S122, located at the 5' end of UBE3A and originally reported by Nurmi et al. (2001). The potential role of UBE3A in our family-based association study is further supported by the association of two haplotypes that include one of the alleles of D15S122 and by the transmission disequilibrium test (TDT) evidence of the same allele in a parent of origin effect analysis. In a secondary analysis, we provided the first evidence of a significant association between first word delay and psychomotor regression with the 15q11-q13 region. Our data support a potential role of UBE3A in the complex pathogenic mechanisms of autism.

Genome-wide linkage analyses of two repetitive behavior phenotypes in Utah pedigrees with autism spectrum disorders

BACKGROUND

It has been suggested that efforts to identify genetic risk markers of autism spectrum disorder (ASD) would benefit from the analysis of more narrowly defined ASD phenotypes. Previous research indicates that 'insistence on sameness' (IS) and 'repetitive sensory-motor actions' (RSMA) are two factors within the ASD 'repetitive and stereotyped behavior' domain. The primary aim of this study was to identify genetic risk markers of both factors to allow comparison of those markers with one another and with markers found in the same set of pedigrees using ASD diagnosis as the phenotype. Thus, we empirically addresses the possibilities that more narrowly defined phenotypes improve linkage analysis signals and that different narrowly defined phenotypes are associated with different loci. Secondary aims were to examine the correlates of IS and RSMA and to assess the heritability of both scales.

METHODS

A genome-wide linkage analysis was conducted with a sample of 70 multiplex ASD pedigrees using IS and RSMA as phenotypes. Genotyping services were provided by the Center for Inherited Disease Research using the 6 K single nucleotide polymorphism linkage panel. Analysis was done using the multipoint linkage software program MCLINK, a Markov chain Monte Carlo (MCMC) method that allows for multilocus linkage analysis on large extended pedigrees.

RESULTS

Genome-wide significance was observed for IS at 2q37.1-q37.3 (dominant model heterogeneity lod score (hlod) 3.42) and for RSMA at 15q13.1-q14 (recessive model hlod 3.93). We found some linkage signals that overlapped and others that were not observed in our previous linkage analysis of the ASD phenotype in the same pedigrees, and regions varied in the range of phenotypes with which they were linked. A new finding with respect to IS was that it is positively associated with IQ if the IS-RSMA correlation is statistically controlled.

CONCLUSIONS

The finding that IS and RSMA are linked to different regions that only partially overlap regions previously identified with ASD as the phenotype supports the value of including multiple, narrowly defined phenotypes in ASD genetic research. Further, we replicated previous reports indicating that RSMA is more strongly associated than IS with measures of ASD severity.

A review of Savant Syndrome and its possible relationship to epilepsy

The goal of this article is to review Savant Syndrome, characterized by outstanding islands of mental ability in otherwise handicapped individuals. Two forms exist: the congenital form and the acquired form. Among the many examples of the congenital form are the calendar calculators, who can quickly provide the day of the week for any date in the past; the musical savants, who have perfect pitch; and the hyperlexics, who (in one case) can read a page in 8s and recall the text later at a 99% level. Other types of talents and artistic skills involving three-dimensional drawing, map memory, poetry, painting, and sculpturing are also observed. One savant could recite without error the value of Pi to 22,514 places. Persons with the acquired form develop outstanding skills after brain injury or disease, usually involving the left frontotemporal area. This type of injury seems to inhibit the "tyranny of the left hemisphere," allowing the right hemisphere to develop the savant skills. Another way to inhibit the left frontotemporal area is to use transcranial magnetic stimulation in normal subjects; nearly one-half of these subjects can then perform new skills during the stimulation that they could not perform before. This type of finding indicates the potential in all of us for the development of savant skills in special circumstances. Explanations of congenital Savant Syndrome include enhanced local connectivity as a compensation for underconnectivity of long-range fibers, but also weak central coherence, replaced by great attention to detail, enhanced perceptual functioning, and obsessive preoccupation with specific interests.

Novel clustering of items from the Autism Diagnostic Interview-Revised to define phenotypes within autism spectrum disorders

Heterogeneity in phenotypic presentation of Autism spectrum disorders has been cited as one explanation for the difficulty in pinpointing specific genes involved in autism. Recent studies have attempted to reduce the "noise" in genetic and other biological data by reducing the phenotypic heterogeneity of the sample population. The current study employs multiple clustering algorithms on 123 item scores from the Autism Diagnostic Interview-Revised (ADI-R) diagnostic instrument of nearly 2,000 autistic individuals to identify subgroups of autistic probands with clinically relevant behavioral phenotypes in order to isolate more homogeneous groups of subjects for gene expression analyses. Our combined cluster analyses suggest optimal division of the autistic probands into four phenotypic clusters based on similarity of symptom severity across the 123 selected item scores. One cluster is characterized by severe language deficits, while another exhibits milder symptoms across the domains. A third group possesses a higher frequency of savant skills while the fourth group exhibited intermediate severity across all domains. Grouping autistic individuals by multivariate cluster analysis of ADI-R scores reveals meaningful phenotypes of subgroups within the autistic spectrum, which we show, in a related (accompanying) study, to be associated with distinct gene expression profiles.

Why did the savant syndrome not spread in the population? A psychiatric example of a developmental constraint

A developmental constraint is a mechanism that limits the possibility of a phenotype to evolve. There is growing evidence for the existence of developmental constraints in the biological literature. We hypothesize that a developmental constraint prevents the savant syndrome, despite its positive aspects, from spreading in the population. Here, the developmental constraint is the result of the high interactivity among body parts in an early stage in embryological development, namely early organogenesis or the phylotypic stage. The interactivity during this stage involves all components of the embryo, and as a result mutations that affect one part of the embryo also affect other parts. We hypothesize that a mutation, which gives rise to the development of the positive aspects of the savant syndrome (e.g., an impressive memory capacity), will virtually always have a deleterious effect on the development of other phenotypic traits (e.g., resulting in autism and/or impaired motor coordination). Thus, our hypothesis states that the savant syndrome cannot spread in the population because of this developmental constraint. The finding that children with savant syndrome often have autism and physical anomalies, which are known to be established during early organogenesis, supports our hypothesis.

A neuropsychological assessment of frontal cognitive functions in Prader-Willi syndrome

BACKGROUND

Prader-Willi syndrome (PWS) is associated with a characteristic behavioural phenotype whose main features are, alongside compulsive hyperphagia, deficits in social behaviour: social withdrawal, temper tantrums, perseverative speech and behaviour, mental rigidity, stereotyped behaviour, impulsiveness, etc. Similar symptoms may also be found in autistic spectrum disorders and lesional pathologies of the frontal lobe. In both cases, such symptoms have been related to dysfunctions in frontal cognitive processes such as attention, working memory and executive functions. This study uses standardized neuropsychological instruments to analyse the degree to which these processes are affected in PWS.

METHODS

The sample comprised 16 individuals with a genetically confirmed PWS diagnosis. Subjects' IQ (Wechsler Adult Intelligence Scale), academic level, laterality and body mass index (BMI) were calculated. Attention, memory and executive functions were analysed using standard, widely employed neuropsychological tests. We compared the results of the sample group with the general population. Correlation analyses were carried out with IQ, academic level and BMI.

RESULTS

In all the neuropsychological measures focusing on attention, executive functions and visuoperceptual organization, the study sample scored significantly lower than the normative reference population. The scores of the tests used for measuring immediate memory were also significantly lower when trials required sequential processing, although not when they required simultaneous processing. In the memorization of a list of words, subjects showed an initial deficit which disappeared with repetition, enabling them to obtain scores similar to the reference population. No significant correlations were found with BMI, and a higher IQ or academic level did not improve scores in the majority of tests.

CONCLUSIONS

The study shows a deficit in elementary frontal cognitive processes in PWS patients. This deficit may be involved in the social behaviour disorders that characterize such patients, as described in other development or frontal syndrome pathologies. However, we cannot affirm that the deficits found are specific to PWS; they could also occur in other causes of intellectual disability. Although in the study sample IQ did not correlate with frontal deficits, further research is needed to establish whether the neuropsychological alterations described form part of a cognitive phenotype for PWS. We believe that our understanding of the social behaviours typical of PWS may be improved by taking into consideration the cognitive functioning models of the prefrontal lobe, particularly those applied to pervasive developmental disorders.

Using the autism diagnostic interview--revised to increase phenotypic homogeneity in genetic studies of autism

BACKGROUND

Many chromosomal regions for susceptibility to autism spectrum disorders (ASDs) have been identified, but few have reached genomewide significance. In response, researchers have attempted to increase the power of their analyses by stratifying samples to increase phenotypic homogeneity. Although homogeneity has typically been defined by a single variable, resultant groups often differ in other dimensions that may be directly pertinent. Group differences in age, gender, IQ, and measures of autism severity are examined as related to Autism Diagnostic Interview-Revised (ADI-R) domains previously used for subsetting or Quantitative Trait Analysis (QTL).

METHODS

Participants were research participants and clinic referrals for assessment of possible autism. Assessments included the ADI-R, Autism Diagnostic Observation Schedule, Vineland Adaptive Behavior Scales, and a developmental or cognitive test. Data were collected for 983 individuals, ages 4 to 52 years, with diagnoses of autism and ASDs.

RESULTS

Findings suggest that, of several potential grouping variables, only restricted and repetitive behaviors associated with Insistence on Sameness were independent of age, IQ, and autism severity.

CONCLUSIONS

Results emphasize the potential unintended effects of stratification and the importance of understanding such interrelationships between phenotypic characteristics when defining subgroups or performing QTL.

The genetics of autistic disorders and its clinical relevance: a review of the literature

Twin and family studies in autistic disorders (AD) have elucidated a high heritability of the narrow and broad phenotype of AD. In this review on the genetics of AD, we will initially delineate the phenotype of AD and discuss aspects of differential diagnosis, which are particularly relevant with regard to the genetics of autism. Cytogenetic and molecular genetic studies will be presented in detail, and the possibly involved aetiopathological pathways will be described. Implications of the different genetic findings for genetic counselling will be mentioned.

Enhanced perceptual functioning in autism: an update, and eight principles of autistic perception

We propose an "Enhanced Perceptual Functioning" model encompassing the main differences between autistic and non-autistic social and non-social perceptual processing: locally oriented visual and auditory perception, enhanced low-level discrimination, use of a more posterior network in "complex" visual tasks, enhanced perception of first order static stimuli, diminished perception of complex movement, autonomy of low-level information processing toward higher-order operations, and differential relation between perception and general intelligence. Increased perceptual expertise may be implicated in the choice of special ability in savant autistics, and in the variability of apparent presentations within PDD (autism with and without typical speech, Asperger syndrome) in non-savant autistics. The overfunctioning of brain regions typically involved in primary perceptual functions may explain the autistic perceptual endophenotype.

Genetics of autism spectrum disorder

Autism is a highly heritable complex neurodevelopmental disorder characterized by distinct impairments of cognitive function in the field of social interaction and speech development. Different approaches have been undertaken worldwide to identify susceptibility loci or genes for autism spectrum disorders. No clear conclusions can be made today about genetic loci involved in these disorders. The review will focus on relevant results from the last decade of research with emphasis on whole genome screens and association studies.