Possible tics diagnosed as stereotypies in patients with severe autism spectrum disorder: a video-based evaluation.

BACKGROUND: The association of stereotypies and tics is not rare in children with severe autism spectrum disorder (ASD). The differential diagnosis between stereotypies and tics in this patient population can be difficult; however, it could be clinically relevant because of treatment implications. METHODS: A total of 108 video recordings of repetitive behaviors in young patients with stereotypies in the context of ASD were reviewed by a movement disorders expert and a trainee, in order to assess the prevalence of possible co-morbid tics. The Modified Rush Videotape Rating Scale (MRVS) was used to rate tic frequency and severity. RESULTS: Out of 27 patients with stereotypies (24 males; mean age 14 years), 18 (67%) reported possible tics. The most frequently observed tics were eye blinking, shoulder shrugging, neck bending, staring, and throat clearing. The mean MRVS score was 5, indicating mild tic severity. The only significant difference between patients with tics and patients without tics was the total number of stereotypies, which was higher in the subgroup of patients without tics (p = 0.01). CONCLUSIONS: Expert review of video-recordings of repetitive behaviors in young patients with ASD and stereotypies suggests the possibility of a relatively high rate of co-morbid tics. These findings need to be integrated with a comprehensive clinical assessment focusing on the diagnostic re-evaluation of heterogeneous motor manifestations.

Leg stereotypy syndrome: phenomenology and prevalence.

OBJECTIVES: To describe the phenomenology and prevalence of leg stereotypy syndrome (LSS), characterised chiefly by repetitive, rhythmical, stereotypic leg movement, especially when sitting. METHODS: We sought to characterise LSS in two groups of subjects: (1) general population (GP) group, defined as individuals accompanying patients during their visits to Baylor College of Medicine Parkinson's Disease Center and Movement Disorders Clinic who are not genetically related to the patients; and (2) movement disorders (MD) group, composed of consecutive patients with diagnoses of restless legs syndrome, Parkinson's disease, Tourette syndrome and tardive dyskinesia. RESULTS: There were 92 participants enrolled in this study; 7% of 57 individuals in the GP group and 17% of those in the MD group met the diagnostic criteria for LSS. The mean age of individuals with LSS was 44.5 (±11.9) years and mean age at onset of LSS was 17.5 (±5.7) years. In half of the individuals, the 'shaking' involved predominantly one leg. All had a positive family history of similar disorder and none had diurnal variation. The seven-item Leg Stereotypy Syndrome Questionnaire was developed as a screening tool to aid in differentiating LSS from other movement disorders. CONCLUSIONS: LSS is a common condition, occurring in up to 7% of otherwise healthy individuals, and it is even more common in patients with hyperkinetic movement disorders. Although it phenomenologically may overlap with other stereotypic disorders, we argue that it is a distinct, familial, neurological syndrome.

Overactivity, impulsivity and repetitive behaviour in males with fragile X syndrome: contrasting developmental trajectories in those with and without elevated autism symptoms.

BACKGROUND: Hyperactivity and repetitive behaviour are characteristic features of fragile X syndrome (FXS). However, little is known about the influence of autism symptomatology on how these characteristics develop over time. We investigate the profiles and developmental trajectories of overactivity, impulsivity and repetitive behaviour, in males with FXS over three time points spanning 8 years. METHOD: Participants formed two subgroups, those who displayed elevated symptoms of autism at Time 1 (n = 37; Mage  = 16.32; age range = 6.61-43.51) and those who did not (n = 32; Mage  = 8.43; age range = 8.94-47.49). RESULTS: Participants without elevated symptoms of autism showed a reduction in impulsivity and repetitive questioning over time, whereas those with elevated symptoms of autism did not. Differences between the two subgroups in several topographies of repetitive behaviour emerged at Time 3 only. CONCLUSIONS: These results further understanding of the relationship between autistic phenomenology and behavioural characteristics in FXS.

Attenuated behaviour in Cornelia de Lange and fragile X syndromes.

BACKGROUND: Catatonia-like presentations in people with autism have been increasingly recognised within research and diagnostic guidelines. The recently developed Attenuated Behaviour Questionnaire has identified that attenuated behaviour [autistic catatonia] is very prevalent in people with autism spectrum disorders (ASDs) and associated with repetitive behaviour. In the current study, we investigated attenuated behaviour within two genetic syndromes associated with ASD and examined ASD and repetitive behaviour as longitudinal predictors of attenuated behaviour. METHOD: The Attenuated Behaviour Questionnaire was completed by parents/carers of 33 individuals with Cornelia de Lange syndrome (CdLS) and 69 with fragile X syndrome (FXS). Information collected from the same informants 4 years previously was utilised to examine ASD and repetitive behaviour as predictors of later attenuated behaviour, controlling for age, gender and ability. RESULTS: Catatonia-like attenuated behaviour was reported for individuals with CdLS (30.3%) and FXS (11.6%). Slowed movement was more prevalent in people with CdLS. No other phenotypic differences were observed. Across the two groups, repetitive behaviour predicted the presence of attenuated behaviour 4 years later, after controlling for age, gender and ability. CONCLUSIONS: Attenuated behaviour can be identified in individuals with CdLS and FXS and may have an effect on both adaptive behaviour and quality of life. Repetitive behaviours predicted subsequent risk within both groups and should be assessed by services as part of a pro-active strategy of support.

A Direct Comparison of Self-Injurious and Stereotyped Motor Behavior Between Preschool-Aged Children With and Without Developmental Delays.

OBJECTIVE: To compare the prevalence of self-injurious behavior (SIB) and stereotyped motor behavior (STY) of preschool-aged children with developmental delays (DD group) and their peers without developmental delays (TD group) using a standardized caregiver report scale. METHODS: The Repetitive Behavior Scale-Revised was completed by caregivers of children with developmental delays and their peers without developmental delays. Frequency of occurrence and severity ratings for SIB and STY were compared between groups. RESULTS: SIB and STY were reported more often and at a greater level of severity in the DD group. Older chronological age was associated with more severe STY in the DD group but not the TD group. Gender was not related to STY or SIB for either group. CONCLUSIONS: Differences in STY and SIB were evident between preschoolers with and without DD. Findings are discussed from developmental and behavioral psychology perspectives regarding the expression of repetitive behavior in developmentally at-risk pediatric populations.

Adult-onset stereotypical motor behaviors.

Stereotypies have been defined as non-goal-directed movement patterns repeated continuously for a period of time in the same form and on multiple occasions, and which are typically distractible. Stereotypical motor behaviors are a common clinical feature of a variety of neurological conditions that affect cortical and subcortical functions, including autism, tardive dyskinesia, excessive dopaminergic treatment of Parkinson's disease and frontotemporal dementia. The main differential diagnosis of stereotypies includes tic disorders, motor mannerisms, compulsion and habit. The pathophysiology of stereotypies may involve the corticostriatal pathways, especially the orbitofrontal and anterior cingulated cortices. Because antipsychotics have long been used to manage stereotypical behaviours in mental retardation, stereotypies that present in isolation tend not to warrant pharmacological intervention, as the benefit-to-risk ratio is not great enough.

Motor stereotypies in autism spectrum disorder: Clinical randomized study and classification proposal.

LAY ABSTRACT: Motor stereotypies are one of the most frequent features in children with a diagnosis of autism spectrum disorder. They may disrupt children's functioning and development and be a potential source of stress for families. Several factors, including sex, age, cognitive ability, and severity of autism spectrum disorder, may influence the presence and intensity of stereotypies. The present study aimed to identify the prevalence of motor stereotypies in a group of children with autism spectrum disorder. In addition, it sought to investigate whether sex, age, cognitive ability, verbal language, neurological comorbidities, and severity of autism spectrum disorder were associated with an increased probability and higher number, duration, and variability of stereotypies. A total of 134 participants aged 2.3-17.6 years underwent a clinical protocol with standardized video-recorded sessions. Stereotypies were identified and classified by two independent evaluators. The prevalence of stereotypies was 56.7%, and a total of 1198 motor stereotypies were captured. Children who were younger, nonverbal, and had higher severity of autism spectrum disorder had an increased probability of presenting stereotypies. Being nonverbal or having higher severity of autism spectrum disorder was also associated with presenting a higher number of stereotypies. Children with developmental delay, intellectual disability, or epilepsy displayed longer stereotypies, and children with developmental delay or intellectual disability additionally presented more diverse stereotypies. As part of the study, the authors present a clinical classification model, a glossary, and video samples of motor stereotypies. The findings of this study suggest that children who are younger, nonverbal, have lower cognitive ability, and have higher severity of autism spectrum disorder may have a higher burden of stereotypies. Earlier intervention and monitoring of these children have the potential to improve their long-term outcomes.

The Behavior Problems Inventory-Short Form for individuals with intellectual disabilities: part II: reliability and validity.

BACKGROUND: The Behavior Problems Inventory-01 (BPI-01) is an informant-based behaviour rating instrument for intellectual disabilities (ID) with 49 items and three sub-scales: Self-injurious Behavior, Stereotyped Behavior and Aggressive/Destructive Behavior. The Behavior Problems Inventory-Short Form (BPI-S) is a BPI-01 spin-off with 30 items. METHODS: The psychometric properties of these two versions of the scale were computed using aggregated archival data from nine different sites in the USA, Wales, England, the Netherlands and Romania with a total of 1122 cases with a BPI-01 total score >0. RESULTS: The internal consistency of the BPI-01 and the BPI-S ranged from fair to excellent with the BPI-01 showing slightly stronger reliability. Construct validity (confirmatory and discriminant) was computed by comparing BPI sub-scale scores with the scores of four other behaviour rating scales (the Aberrant Behavior Checklist, the Diagnostic Assessment for the Severely Handicapped-II, the Nisonger Child Behavior Rating Form and the Inventory for Client and Agency Planning). Strong evidence for confirmatory and discriminant validity was found for both the BPI-01 and the BPI-S. Confirmatory fit indices for the BPI and the BPI-S were comparable and suggesting that the factor structures fit the data well. CONCLUSION: In summary, both BPI versions were found to be equally sound psychometrically and can be endorsed for future use. However, independent future studies are needed to replicate the psychometrics of the BPI-S with new data.

The Behavior Problems Inventory-Short Form for individuals with intellectual disabilities: part I: development and provisional clinical reference data.

BACKGROUND: The Behavior Problems Inventory-01 (BPI-01) is an informant-based behaviour rating instrument that was designed to assess maladaptive behaviours in individuals with intellectual disabilities (ID). Its items fall into one of three sub-scales: Self-injurious Behavior (14 items), Stereotyped Behavior (24 items), and Aggressive/Destructive Behavior (11 items). Each item is rated on a frequency scale (0 = never to 4 = hourly), and a severity scale (0 = no problem to 3 = severe problem). The BPI-01 has been successfully used in several studies and has shown acceptable to very good psychometric properties. One concern raised by some investigators was the large number of items on the BPI-01, which has reduced its user friendliness for certain applications. Furthermore, researchers and clinicians were often uncertain how to interpret their BPI-01 data without norms or a frame of reference. METHODS: The Behavior Problems Inventory-Short Form (BPI-S) was empirically developed, based on an aggregated archival data set of BPI-01 data from individuals with ID from nine locations in the USA, Wales, England, the Netherlands, and Romania (n = 1122). The BPI-S uses the same rating system and the same three sub-scales as the BPI-01, but has fewer items: Self-injurious Behavior (8 items), Stereotyped Behavior (12 items), and Aggressive/Destructive Behavior (10 items). Rating anchors for the severity scales of the Self-injurious Behavior and the Aggressive/Destructive Behavior sub-scales were added in an effort to enhance the objectivity of the ratings. RESULTS: The sensitivity of the BPI-S compared with the BPI-01 was high (0.92 to 0.99), and so were the correlations between the analogous BPI-01 and the BPI-S sub-scales (0.96 to 0.99). Means and standard deviations were generated for both BPI versions in a Sex-by-age matrix, and in a Sex-by-ID Level matrix. Combined sex ranges are also provided by age and level of ID. CONCLUSION: In summary, the BPI-S is a very useful alternative to the BPI-01, especially for research and evaluation purposes involving groups of individuals.

The prevalence and clinical characteristics of punding in Parkinson's disease.

BACKGROUND: Punding (the display of stereotyped, repetitive behaviors) is a relatively recently discovered feature of Parkinson's disease (PD). Little is known about the prevalence and clinical characteristics of punding in PD. METHODS: In this review, four large scientific databases were comprehensively searched for literature in relation to punding prevalence and clinical correlates in the context of PD. RESULTS: Prevalence was found to vary greatly (between 0.34 to 14%), although there were large disparities in study populations, assessment methods, and criteria. We observed an association between punding, dopaminergic medications, and impulse control disorder. Other characteristics, which may be more common among punders, include a higher severity of dyskinesia, younger age of disease onset, longer disease duration, and male gender. DISCUSSION: More research in large clinical datasets is required in many areas before conclusions are drawn. The pathophysiology behind the punding phenomenon is also poorly understood at present, rendering it difficult to develop targeted therapy. The current mainstay of treatment is the reduction in the dose of dopaminergic medications, the evidence for other suggested therapies being purely empirical.

Autism spectrum disorder in Down syndrome: cluster analysis of Aberrant Behaviour Checklist data supports diagnosis.

BACKGROUND: The diagnostic validity of autism spectrum disorder (ASD) based on Diagnostic and Statistical Manual of Mental Disorders (DSM) has been challenged in Down syndrome (DS), because of the high prevalence of cognitive impairments in this population. Therefore, we attempted to validate DSM-based diagnoses via an unbiased categorisation of participants with a DSM-independent behavioural instrument. METHODS: Based on scores on the Aberrant Behaviour Checklist - Community, we performed sequential factor (four DS-relevant factors: Autism-Like Behaviour, Disruptive Behaviour, Hyperactivity, Self-Injury) and cluster analyses on a 293-participant paediatric DS clinic cohort. The four resulting clusters were compared with DSM-delineated groups: DS + ASD, DS + None (no DSM diagnosis), DS + DBD (disruptive behaviour disorder) and DS + SMD (stereotypic movement disorder), the latter two as comparison groups. RESULTS: Two clusters were identified with DS + ASD: Cluster 1 (35.1%) with higher disruptive behaviour and Cluster 4 (48.2%) with more severe autistic behaviour and higher percentage of late onset ASD. The majority of participants in DS + None (71.9%) and DS + DBD (87.5%) were classified into Cluster 2 and 3, respectively, while participants in DS + SMD were relatively evenly distributed throughout the four clusters. CONCLUSIONS: Our unbiased, DSM-independent analyses, using a rating scale specifically designed for individuals with severe intellectual disability, demonstrated that DSM-based criteria of ASD are applicable to DS individuals despite their cognitive impairments. Two DS + ASD clusters were identified and supported the existence of at least two subtypes of ASD in DS, which deserve further characterisation. Despite the prominence of stereotypic behaviour in DS, the SMD diagnosis was not identified by cluster analysis, suggesting that high-level stereotypy is distributed throughout DS. Further supporting DSM diagnoses, typically behaving DS participants were easily distinguished as a group from those with maladaptive behaviours.

Developmental and benign movement disorders in childhood.

Developmental and benign movement disorders are a group of movement disorders with onset in the neonatal period, infancy, or childhood. They are characterized by the absence of associated neurological manifestations and by their favorable outcome, although developmental abnormalities can be occasionally observed. Knowledge of the clinical, neurophysiological, and pathogenetic aspects of these disorders is poor. Based on a comprehensive review of the literature and our practical experience, this article summarizes current knowledge in this area. We pay special attention to the recognition and management of these movement disorders in children.

Clinical and anatomical heterogeneity in autistic spectrum disorder: a structural MRI study.

BACKGROUND: Autistic spectrum disorder (ASD) is characterized by stereotyped/obsessional behaviours and social and communicative deficits. However, there is significant variability in the clinical phenotype; for example, people with autism exhibit language delay whereas those with Asperger syndrome do not. It remains unclear whether localized differences in brain anatomy are associated with variation in the clinical phenotype. METHOD: We used voxel-based morphometry (VBM) to investigate brain anatomy in adults with ASD. We included 65 adults diagnosed with ASD (39 with Asperger syndrome and 26 with autism) and 33 controls who did not differ significantly in age or gender. RESULTS: VBM revealed that subjects with ASD had a significant reduction in grey-matter volume of medial temporal, fusiform and cerebellar regions, and in white matter of the brainstem and cerebellar regions. Furthermore, within the subjects with ASD, brain anatomy varied with clinical phenotype. Those with autism demonstrated an increase in grey matter in frontal and temporal lobe regions that was not present in those with Asperger syndrome. CONCLUSIONS: Adults with ASD have significant differences from controls in the anatomy of brain regions implicated in behaviours characterizing the disorder, and this differs according to clinical subtype.

Stereotypic movement disorder: easily missed.

AIM: To expand the understanding of stereotypic movement disorder (SMD) and its differentiation from tics and autistic stereotypies. METHOD: Forty-two children (31 males, mean age 6y 3mo, SD 2y 8mo; 11 females, mean age 6y 7mo, SD 1y 9mo) consecutively diagnosed with SMD, without-self-injurious behavior, intellectual disability, sensory impairment, or an autistic spectrum disorder (ASD), were assessed in a neuropsychiatry clinic. A list of probe questions on the nature of the stereotypy was administered to parents (and to children if developmentally ready). Questionnaires administered included the Stereotypy Severity Scale, Short Sensory Profile, Strengths and Difficulties Questionnaire, Repetitive Behavior Scale--Revised, and the Developmental Coordination Disorder Questionnaire. The stereotyped movement patterns were directly observed and in some cases further documented by video recordings made by parents. The probe questions were used again on follow-up at a mean age of 10 years 7 months (SD 4y 4mo). RESULTS: Mean age at onset was 17 months. Males exceeded females by 3:1. Family history of a pattern of SMD was reported in 13 and neuropsychiatric comorbidity in 30 (attention-deficit-hyperactivity disorder in 16, tics in 18, and developmental coordination disorder in 16). Obsessive-compulsive disorder occurred in only two. The Short Sensory Profile correlated with comorbidity (p<0.001), the Stereotypy Severity Scale (p=0.009), and the Repetitive Behavior Scale (p<0.001); the last correlated with the Stereotypy Severity Scale (p=0.001). Children (but not their parents) liked their movements, which were usually associated with excitement or imaginative play. Mean length of follow-up was 4 years 8 months (SD 2y 10mo). Of the 39 children followed for longer than 6 months, the behavior stopped or was gradually shaped so as to occur primarily privately in 25. Misdiagnosis was common: 26 were initially referred as tics, 10 as ASD, five as compulsions, and one as epilepsy. Co-occurring facial grimacing in 15 children and vocalization in 22 contributed to diagnostic confusion. INTERPRETATION: SMD occurs in children without ASD or intellectual disability. The generally favorable clinical course is largely due to a gradual increase in private expression of the movements. Severity of the stereotypy is associated with sensory differences and psychopathology. Differentiation of SMD from tics and ASD is important to avoid misdiagnosis and unnecessary treatment.

Prevalence and determinants of motor stereotypies in autism spectrum disorder: A systematic review and meta-analysis.

Stereotypies are frequently reported in people with autism spectrum disorder (ASD) but remain one of the less explained phenomena. We aimed to describe, through a systematic review and a meta-analysis, the prevalence of motor stereotypies in ASD and study the factors that influence this prevalence. Our literature search included MEDLINE, Scopus, and PsycINFO databases. Quality and risk of bias were assessed. Thirty-seven studies were included and the median prevalence of motor stereotypies in ASD was 51.8%, ranging from 21.9% to 97.5%. The most frequent determinants associated with a higher number of stereotypies in ASD were a younger age, lower intelligence quotient, and a greater severity of ASD. Moreover, gender did not seem to influence the prevalence of stereotypies. Meta-analytic analysis showed that lower IQ and autism diagnosis (independent of IQ) are associated with a higher prevalence of motor stereotypies (odds ratio = 2.5 and 4.7, respectively). Limitations of the reviewed literature include the use of convenience samples, with small sizes and heterogeneous inclusion criteria, and the predominance of high-functioning autism individuals.

Restricted and Repetitive Behaviors in Males and Females with Fragile X Syndrome: Developmental Trajectories in Toddlers Through Young Adults.

There is limited research on the trajectory of restricted and repetitive behaviors (RRBs) in fragile X syndrome (FXS), with previous studies only examining males and/or examining RRBs as a unitary construct rather than delineating subtypes of RRBs. Thus, we described the trajectory of five subtypes of RRBs in 153 males and females with FXS (aged 1-18 years) with repeated measurement over time (445 total assessments). Multilevel modeling was used to test age-related differences in RRB subtypes between males and females with FXS, controlling for nonverbal IQ. Results showed that lower-order Sensory-Motor behaviors decreased over time for both males and females, while there was no significant change in the higher-order RRBs. The trajectory between males and females differed for Self-Injury.

Sleep Problems and Trajectories of Restricted and Repetitive Behaviors in Children with Neurodevelopmental Disabilities.

Sleep problems are prevalent in children with neurodevelopmental disabilities and are associated with the expression of restricted and repetitive behaviors (RRBs). Children (n = 57) with autism spectrum disorder (ASD, n = 38) or developmental delay (DD, n = 19) participated in multiple assessments of intellectual ability, ASD symptoms, and RRBs (3 timepoints for ASD, 2 for DD). Sleep problems assessed at age 4 via parent report were associated with trajectories of higher-order RRBs (sameness/ritualistic/compulsive behaviors) from age 2-6 in the ASD group, and from age 2-4 in the DD group, even after controlling for intellectual ability, social-affective symptoms, and anxiety. Trajectories of stereotyped/restricted behaviors were unrelated to sleep problems. Sleep problems were associated with trajectories of higher-order (but not lower-order) RRBs in a transdiagnostic sample.

Nonepileptic, Stereotypical, and Intermittent Symptoms (NESIS) in Patients With Subdural Hematoma: Proposal for a New Clinical Entity With Therapeutic and Prognostic Implications.

BACKGROUND: Transient neurological symptoms (TNS) are frequent in patients with subdural hematomas (SDH) and many will receive a diagnosis of epilepsy despite a negative workup. OBJECTIVE: To explore if patients with TNS and a negative epilepsy workup (cases) evolved differently than those with a positive EEG (controls), which would suggest the existence of alternative etiologies for TNS. METHODS: We performed a single-center, retrospective, case-control study of patients with TNS post-SDH. The demographics and clinical and semiological features of cases and controls were compared. The outcome and response to antiepileptic drugs were also assessed and a scoring system developed to predict negative EEG. RESULTS: Fifty-nine patients with SDH-associated TNS were included (39 cases and 20 controls). Demographic characteristics were comparable in both groups. Dysphasia and prolonged episodes were associated with a negative EEG. Clonic movements, impaired awareness, positive symptomatology, complete response to antiepileptic drugs, and mortality were associated with a positive EEG. Using semiological variables, we created a scoring system with a 96.6% sensitivity and 100% specificity in predicting case group patients. The differences observed between both groups support the existence of an alternative etiology to seizures in our case group. We propose the term NESIS (NonEpileptic, Stereotypical, and Intermittent Symptoms) to refer to this subgroup and hypothesize that TNS in these patients might result from cortical spreading depolarization. CONCLUSION: We describe NESIS as a syndrome experienced by SDH patients with specific prognostic and therapeutic implications. Independent validation of this new entity is now required.

Prevalence and Risk-Markers of Self-Harm in Autistic Children and Adults.

Self-harm is purportedly common in autistic individuals, but under-researched, particularly in younger samples and those without intellectual disability. This study aimed to describe prevalence, profile and correlates of self-harm in autistic individuals without impairments in adaptive functioning. Parents of autistic participants (n = 83) completed questionnaires regarding the presence/topography of self-harm, demographic characteristics, autism severity, age of diagnosis, affect, activity levels and repetitive behaviour. 24.10% of participants engaged in self-harm. Self-harm was associated with significantly higher levels of impulsivity, over-activity, negative affect, compulsive behaviour and insistence on sameness. Low mood and overactivity/impulsivity predicted the presence of self-harm, with the model correctly classifying 82.9% of cases. Findings highlight a role for impaired behavioural inhibition and low mood in the aetiological mechanisms underpinning self-harm in autism.

Similar developmental trajectories in autism and Asperger syndrome: from early childhood to adolescence.

OBJECTIVE: The objective of this study was to chart the developmental trajectories of high-functioning children with autism spectrum disorders (ASD) from early childhood to adolescence using the presence and absence of structural language impairment (StrLI) as a way of differentiating autism from Asperger syndrome (AS). METHOD: Sixty-four high-functioning children with ASD were ascertained at 4-6 years of age from several different regional diagnostic and treatment centers. At 6-8 years of age, the ADI-R and the Test of Oral Language Development were used to define an autism group (those with StrLI at 6-8 years of age) and an AS group (those without StrLI). Growth curve analysis was then used to chart the developmental trajectories of these children on measures of autistic symptoms, and adaptive skills in communication, daily living and socialization. RESULTS: Differentiating the ASD group in terms of the presence/absence of StrLI provided a better explanation of the variation in growth curves than not differentiating high-functioning ASD children. The two groups had similar developmental trajectories but the group without StrLI (the AS group) was functioning better and had fewer autistic symptoms than the group with StrLI (the autism group) on all measures across time. The differences in outcome could not be explained by non-verbal IQ or change in early language skills. CONCLUSION: Distinguishing between autism and Asperger syndrome based on the presence or absence of StrLI appears to be a clinically useful way of classifying ASD sub-types.