Developmental and functional outcomes in children with global developmental delay or developmental language impairment

Transcription

1 Developmental and functional outcomes in children with global developmental delay or developmental language impairment Michael Shevell* MD CM FRCP(C), Department of Neurology/Neurosurgery; Annette Majnemer PhD, School of Physical and Occupational Therapy; Robert W Platt PhD, Department of Pediatrics; Richard Webster MBBS, MSc, FRCP(A), Department of Neurology/Neurosurgery; Rena Birnbaum MSc, School of Physical and Occupational Therapy, McGill University, Montreal Children s Hospital- McGill University Health Centre, Montreal, Quebec, Canada. *Correspondence to first author at Room A-514, Montreal Children s Hospital, 2300 Tupper Street, Montreal, Quebec H3H 1P3, Canada. michael.shevell@muhc.mcgill.ca Preschool children diagnosed with either global developmental delay (GDD) or developmental language impairment (DLI) were reassessed during their early school years with standardized developmental (Battelle Developmental Inventory [BDI]) and functional (Vineland Adaptive Behavior Scale [VABS]) outcome measures. Of an original cohort of 99 children with GDD and 70 children with DLI assessed and diagnosed at a mean age of 3 years 5 months (SD 1.1) and 3 years 7 months (SD 0.7) respectively, 48 children (34 [71%] males) with GDD and 43 children (36 [84%] males) with DLI were reassessed at a mean age of 7 years 4 months (SD 0.9) and 7 years 5 months (SD 0.7) respectively. The overall total mean BDI score for children with GDD was 66.4 (SD 4.3) versus 71.9 (SD 8.2) for children with DLI (p=0.002). On each subdomain of the BDI, except communication, mean scores for the GDD group were significantly lower than for the DLI group (p<0.05). Similarly, the VABS total score for the GDD group was significantly lower than for the DLI group (p<0.001). For each subdomain of the VABS, the GDD group scored significantly lower than the DLI group (p<0.001). The proportion of children falling below meaningful cut-offs on the outcome measures selected was significantly higher for those initially diagnosed with GDD. Preschool diagnosis of either GDD or DLI has later prognostic validity with regard to persisting developmental and functional deficits. See end of paper for list of abbreviations. Global developmental delay (GDD) and developmental language impairment (DLI) are the two most common subtypes of early childhood neurodevelopmental disability encountered in clinical practice (Peterson et al. 1998). GDD can be operationally defined as a significant delay, usually two or more standard deviations below the mean, in two or more domains (gross/fine motor skills, cognition, speech/language, personal/social skills, or activities in daily living; Shevell et al. 2003). Typically, all domains are affected. DLI refers to an isolated delay in the age-appropriate use of communicative expressive and/or receptive language skills in the absence of cognitive impairment, hearing loss or abnormal social interactions (Nass and Koch 1992). Children with an acquired language disorder are usually not considered to have a DLI. Longitudinal studies in the outcomes of children diagnosed with either GDD or DLI are surprisingly few and have focused largely on language skills, cognition, or academic achievement (such as reading and handwriting; Silva 1980; Aram et al. 1984; Silva et al. 1983, 1987; Bishop and Edmundson 1987a,b; Montgomery 1988; Shapiro et al. 1990; Stothard et al. 1998; Paul 2000; Nathan et al. 2004). Although originally conceptualized in terms of developmental and functional capabilities, outcomes with regard to development and function for these children are largely unknown. It is at present unclear from this perspective whether distinguishing nosologically in early childhood between these two most common subtypes of neurodevelopmental disability has later prognostic or diagnostic value. Furthermore it has been noted that children with GDD or DLI, unlike children with definite biological risks (namely preterm birth, Down syndrome, or cerebral palsy [CP]), typically do not have in place a longitudinal systematic programoriented approach to ongoing management (Msall et al. 1998). Such an approach would involve intermittent screening at key intervals targeting specific areas of developmental concern. In this way, needs that challenge the child and family could be identified promptly as they arise, leading to the implementation of appropriate new rehabilitation interventions, educational resources or support systems. Such a programmatic approach has been shown to improve functional outcomes and lessen eventual disability in other at risk pediatric populations (Majnemer 1998). Appropriate design of such a programmatic approach is by necessity predicated on prior ascertainment of developmental and functional outcomes for these groups to ensure that services are planned to address their specific needs. The primary objective of the study reported here is to compare directly the developmental and functional outcomes at school entry (ages 7 to 8y) of preschool children initially diagnosed with either GDD or DLI. Methods PARTICIPANTS A prospective study was undertaken with a previously defined and assembled cohort. Children were included in the original cohort if they met the following inclusion criteria: (1) less than 5 years of age; (2) initial specialty medical evaluation of a suspected developmental delay; and (3) referral to ambulatory general pediatric neurology clinic/offices or developmental clinics at the Montreal Children s Hospital, Quebec, Canada. Children were excluded from the original cohort if they had already been evaluated by other specialty services 678 Developmental Medicine & Child Neurology 2005, 47:

2 for developmental delay, if they did not complete requested investigations, or if they did not have a developmental delay confirmed on formal assessment. The cohort was assembled over an 18-month interval at the Montreal Children s Hospital McGill University Health Center as part of an initial study systematically evaluating etiological yield in varying subtypes of developmental disability (Shevell et al. 2000a,b, 2001a). By applying specific decision rules (Shevell et al. 2000a, b, 2001a), the specific types and severity of developmental delay (GDD, DLI, isolated motor delay/cp or autistic-spectrum disorder) were determined by a single investigator (MS). The assigned category and severity were validated independently on a randomly selected subset by a co-investigator (AM) using the same decision rules, with excellent interrater reliability for category (96%, kappa=0.91) and very good interrater reliability for severity (75%, kappa=0.60). A survey of local referring physicians and of rehabilitation intake practices suggests that the original study s cohort can be conceptualized as a comprehensive community-derived sample of children with developmental delay (Shevell et al. 2001b). This is supported by the strong local tendency of community physicians to refer children with suspected developmental delay for specialty diagnostic evaluation at a tertiary center and that most children were considered to have mild to moderate severity at intake. At the time of initial intake, demographic and relevant clinical information was collected systematically. PROCEDURES Of the 224 children in the original cohort, 99 children had GDD and 70 DLI as their original diagnosis. The parents of these children were contacted first in writing and then by telephone. Initial contact for follow-up was made when the children were between 6 and 7 years of age. The protocol was approved by the Research Ethics Board of the Montreal Children s Hospital-McGill University Health Center, and written informed parental consent was a necessary precondition for study participation. Once consent had been obtained, the child, aged around 7 years, underwent a detailed developmental and functional assessment at the hospital. Two occupational therapists, blinded to developmental delay subtypes and past medical or developmental history, performed the standardized developmental and functional assessments using the Battelle Developmental Inventory (BDI; Glascoe and Byrne 1993) and the Vineland Adaptive Behavior Scale (VABS; Sparrow et al. 1984) respectively. These measures follow standardized procedures, have excellent psychometric properties (namely reliability and validity), are widely used in the clinical setting and in pediatric outcome research, and are age appropriate. The age of 7 years for follow-up testing was selected because it coincides with the usual age of formal academic school entry locally (grade 1), which is a key childhood developmental and social milestone to which successful adaptation is essential for future success. The BDI is a discriminative norm-referenced measure of developmental abilities in motor, adaptive, communication, cognitive, and personal social domains for children between 0 and 8 years of age. It is a well-established developmental screening tool used in early intervention and educational settings to identify children with developmental delay. It identifies developmental strengths and weaknesses based on the observation of skills, supplemented by parental report. It is a comprehensive measure of ability (i.e. what a child can do). This structured Table I: Battelle Developmental Inventory scores for children with global developmental delay Personal social 71.1 (10.8) /45; 78 Adaptive 69.1 (9.8) /45; 82 Gross motor 70.3 (10.5) /45; 82 Fine motor 68.7 (8.9) /45; 89 Motor (total) 69.4 (8.4) /45; 84 Communication 66.5 (3.5) /28 a ; 100 Cognitive 69.1 (8.1) /45; 80 Total score 66.4 (4.3) /28; 93 a Testing was limited to those children whose first language was English. Battelle Developmental Inventory (Glascoe and Byrne 1993) mean 100, SD 15. CI, confidence interval. Table II: Vineland Adaptive Behavior Scale scores for children with global developmental delay Communication 66.7 (22.0) /46; 76 Socialization 72.5 (18.0) /46; 61 Daily living 62.1 (21.8) /46; 70 Total score 63.6 (20.8) /46; 72 Vineland Adaptive Behavior Scale (Sparrow et al. 1984) mean 100, SD 15. CI, confidence interval. Outcomes of Global Developmental Delay and Developmental Language Impairment Michael Shevell et al. 679

3 test incorporates a 3-point scoring system that takes into account emerging skills, thus increasing sensitivity. Standard scores on the BDI subdomains were used to classify whether children in our cohort continued to manifest delays in particular developmental domains. As defined by the developers of this instrument, a score of more than 1.5 SD below the normative mean for each subdomain was used as our cutoff for delay (i.e. definitive weakness). For this study the complete version of the BDI was used. Test retest reliability for the BDI is reported to be excellent, with coefficients for 7-year-old children of 0.90 for the total score, ranging from 0.85 to 0.95 for each subdomain. This assessment tool also features very good face validity, internal consistency, and concurrent validity (Glascoe and Byrne 1993). The VABS is a discriminative, norm-referenced measure of functional status in communication, daily living skills, socialization, and motor skills in children (less than 18 years of age) with or without disabilities. This measure was chosen to characterize the functional outcomes (i.e. activity limitations) of our cohort. It is a measure of typical performance (i.e. what a child does do) that assesses an individual s personal and social self-sufficiency. It highlights norm-referenced deficits in adaptive behavior. Unique attributes of the VABS include the assessment of the effects of any developmental impairment on overall adaptive functioning. In a semi-structured interview format, typical performance in all settings (such as home, community, and school) is evaluated, assessing ability with reference to functioning and adaptation in relation to everyday demands and expectations (Sparrow et al. 1984). STATISTICAL ANALYSIS Descriptive statistics were used to characterize developmental and functional outcomes at school entry in our cohort. The outcome measures used (BDI and VABS) are continuous; however, cutoffs of 1.5 SD, as suggested by the manuals for both test instruments, were used to categorize our sample as within the normal range or demonstrating difficulties that are clinically significant (i.e. delayed for age). Developmental and functional outcomes were described by using mean values of continuous measures and proportions for categorical values, with variability of the point estimates (SD, range, and 95% confidence intervals of the mean). Students t-tests were used to compare the means between the GDD and DLI groups, both overall and on the subdomains of the VABS, with p 0.05 selected a priori for statistical significance. Levene s test for equality of variance was applied to ascertain whether or not equal variances could be assumed. Given the floor effect for scoring of the BDI, both overall and on its subdomains, a non-parametric Mann Whitney U test was used to compare the distributions between GDD and DLI groups on this outcome measure. Once again, p 0.05 was chosen for the level of statistical significance. To compare the proportion of children falling below the clinically significant cutoffs on the BDI and VABS overall score and various subdomains, a χ 2 analysis was undertaken with statistical significance set at p Results Of the 99 children (71 males) in the original cohort with GDD and 70 children (51 males) with DLI, 48 (34 males) with GDD, and 43 (36 males) with DLI, were recruited for participation in the present study. For the 51 children with GDD not recruited, 21 had been lost to follow-up, 21 refused follow-up, six were out of the follow-up study s designated age range, one had Table III: Battelle Developmental Inventory scores for children with developmental language impairment Personal 75.4 (11.8) /42; 57 Adaptive 77.3 (13.1) /42; 52 Gross motor 85.0 (13.3) /42; 36 Fine motor 78.3 (11.4) /42; 40 Motor (total) 82.7 (11.9) /42; 29 Communication 69.5 (8.9) /24 a ; 83 Cognitive 80.0 (14.2) /42; 38 Total score 71.9 (8.2) /24; 67 a Testing was limited to those children whose first language was English. Battelle Developmental Inventory (Glascoe and Byrne 1993) mean 100, SD 15. CI, confidence interval. Table IV: Vineland Adaptive Behavior Scale scores for children with developmental language impairment Communication 80.6 (17.0) /42; 48 Socialization 87.1 (13.0) /42; 19 Daily living 83.1 (19.0) /42; 45 Total score 81.1 (16.9) /42; 48 Vineland Adaptive Behavior Scale (Sparrow et al. 1984) mean 100, SD 15. CI, confidence interval. 680 Developmental Medicine & Child Neurology 2005, 47:

4 died in the interval between studies, and for two potential participants it was unclear why follow-up could not be completed. For the 27 children with DLI not recruited, 14 were lost to follow-up and 13 refused participation. On variables such as age at initial parental concern, age of initial specialty assessment, sex, severity of delay, etiological determination, maternal/paternal education and employment status, no differences with regard to those recruited or not recruited within each diagnosis (GDD or DLI) was detected, with the exception of a higher level of paternal post-high-school education among those children with GDD who were subsequently recruited. Children with GDD had been diagnosed and assessed originally at a mean age of 3 years 5 months (SD 1.1), whereas children with DLI had been assessed and diagnosed originally at 3 years 7 months (SD 0.7). Forty-eight children with GDD (mean age 7y 4mo; SD 0.9) were recruited, 45 completed standardized developmental testing with the BDI, and 46 completed functional assessment with the VABS. For the 43 children with DLI who were reassessed (mean age 7y 5 mo; SD 0.7) all except one completed assessment with the BDI and VABS. It should be noted that the BDI communication subdomain is not standardized on children whose first language is French, and 17 children with GDD and 19 children with DLI could not be reliably tested on this particular domain. Group performance on the BDI and VABS is summarized in Tables I and II for children with GDD and in Tables III and IV Table V: Comparison of mean scores on Battelle Developmental Inventory (BDI) and Vineland Adaptive Behavior Scale (VABS) for children with original diagnosis of either global developmental delay (GDD) or developmental language impairment (DLI) Scale and domain GDD DLI p Mean SD Mean SD BDI Total a Personal social a Adaptive <0.001 a Gross motor <0.001 a Fine motor <0.001 a Motor (total) <0.001 a Communication a,b Cognitive <0.001 a VABS Total <0.001 c Communication d Socialization <0.001 c Daily living <0.001 d a Non-significant. b Non-parametric Mann Whitney U test. c Equal variances not assumed (Student s t-test). d Equal variances assumed (Student s t-test). BDI mean 100, SD 15; VABS mean 100, SD 15. Table VI: Comparison of percentage of children falling below clinically significant cutoffs on Battelle Developmental Inventory (BDI) and Vineland Adaptive Behavior Scale (VABS) Scale and domain GDD < 1.5 SD (%) DLI < 1.5 SD (%) χ 2 p BDI Total 26/28 (93) 16/24 (67) Personal social 35/45 (78) 24/42 (57) Adaptive 37/45 (82) 22/42 (52) Gross motor 37/45 (82) 15/42 (36) Fine motor 40/45 (89) 17/42 (40) Motor (total) 38/45 (84) 12/42 (29) Communication 28/28 (100) 20/24 (83) Cognitive 36/45 (80) 16/42 (38) VABS Total 33/46 (72) 20/42 (48) Communication 35/46 (76) 20/42 (48) Socialization 28/46 (61) 8/42 (19) Daily living 32/46 (70) 19/42 (45) BDI mean 100, SD 15; VABS mean 100, SD 15. GDD, global developmental delay; DLI, developmental language impairment. Outcomes of Global Developmental Delay and Developmental Language Impairment Michael Shevell et al. 681

5 for children with DLI. Table V provides a direct comparison of the group means on the BDI and VABS, both overall and on subdomains, between the GDD and DLI cohorts, with corresponding p values. Table VI provides a comparison of the percentage of children in each group falling below the clinically significant cutoff, with corresponding χ 2 and p values. It is noteworthy that the overall total mean BDI score of 66.4 (SD 4.3) for children with GDD originally was significantly lower (p=0.002) than for children with DLI originally (71.9, SD 8.2). Similarly, the total overall mean score for the VABS was significantly lower (p<0.001) for children with GDD (63.6, SD 20.8) than for children with DLI (81.1, SD 16.9). For each subdomain, either the BDI or the VABS mean score was lower at follow-up for the GDD cohort than for the DLI cohort. In each instance, with the exception of the BDI communication subdomain (p=0.18), the difference in means obtained reached the level of statistical significance. Furthermore, in both the BDI and VABS, for the total score and for each subdomain, a higher percentage of children with GDD than children with DLI fell below the clinically significant cutoff. This too reached the level of statistical significance in every instance. Table VII provides a comparison of the educational setting (integrated/regular school, integrated/educational support, special class/special school) distribution for either an original diagnosis of GDD or DLI. Educational support refers to supplemental help provided to the individual child by a special educator, speech language pathologist, or occupational therapist. Discussion The process of diagnosis can be defined as the identification of the nature of an illness or other problem by examination of the symptoms. The word s origin is from the Greek diagignoskein, which means to distinguish or discern (Oxford English Dictionary, 2004 edition). Distinguishing or discerning between entities is particularly challenging and open to debate when objective markers are lacking to support a particular diagnosis. This is the case with early childhood neurodevelopmental disabilities. These diagnostic constructs are essentially clinical symptom complexes lacking an objective marker for validation (Shevell 1998). Although diagnosis ideally rests on multidisciplinary standardized assessments, in clinical practice diagnosis is frequently made after a single visit based on the gestalt of a child s overall developmental and functional profile. Additionally, diagnosis occurs within a context of evolving developmental skills and the ongoing challenge of accurately assessing certain domains in the young child (namely cognition and language). Although such an approach occurs by necessity, this together with a lack of data on natural history calls into question the value and validity of these diagnostic constructs. Review of the literature reveals a lack of prospective outcome data for young children diagnosed with either GDD or DLI, the two most commonly encountered neurodevelopmental disabilities of early childhood. Though conceptualized at original diagnosis in developmental and functional terms, highlighted outcomes have been largely academic in character, such as deficits in mathematics, handwriting, or reading skills (Stothard et al. 1998, Shapiro et al. 1990). Behavioral, social, and cognitive outcomes have also been reported (Trower and Nicol 1996). The lack of developmental and functional outcome data challenges our ability to prognosticate, counsel effectively, target intervention, and provide realistic expectations. By directly comparing outcomes between children with GDD and DLI we can assess whether there is any value in our initial early diagnostic efforts. Our study does suggest that there is value in diagnostic discernment. Although children in both cohorts had developmental and functional outcomes well below normative means on every measure used, children with an initial diagnosis of GDD fared significantly worse overall at outcome than children with DLI. This was evident both in a numerical approach (mean scores) and in a clinical approach (percentage scoring below clinically significant cut-offs). Although the breadth of developmental and functional difficulties for children with an initial diagnosis of DLI widened at outcome to include multiple domains of development and function, the severity was always less than that for children with GDD, who retained their original broad profile of developmental and functional impairment at outcome. Differences at outcome in these developmental diagnostic constructs reinforce the value of developmental screening (American Academy of Pediatrics Committee on Children with Disabilities 2001) and challenge those who have questioned its predictive value. Efforts to implement discriminative developmental screening as a standard of pediatric practice seem to have merit, on the basis of our documentation of outcome differences. It is interesting to note that, for both groups, functional outcome was better than developmental outcome when considering the percentage of children with clinically significant concerns. For the GDD cohort, overall developmental concerns were evident in 93% and impairment was noted in between 78 and 100% of children, depending on the subdomain tested, whereas functional concerns were evident in 72% (range 61 to 76%) on the functional subdomains. Similarly for the DLI cohort, developmental concerns globally were apparent in 67% (range 29 to 83%) of children on the developmental subdomains, and global functional concerns were apparent in 48% (range 19 to 48%) of children on the functional subdomains. This suggests that for both groups, children and their families were able to adapt, to some extent, to their impairments. This was presumably achieved by modifying everyday tasks and/or by altering the child s environment to enable greater independence in some activities. By comparison between the two groups, overall adaptation was better for children originally diagnosed with DLI. Distinguishing between preschool children diagnosed with GDD and DLI has nosologic and prognostic value with regard to eventual performance at early school age in developmental and functional skills. With reference to these aspects, these clinical symptom complexes are distinct and, thus, worthy of Table VII: School placement in global developmental delay (GDD) and developmental language impairment (DLI) Educational setting GDD DLI Integrated (regular school) 8 (17) 27 (64.3) Integrated with educational support 14 (29.8) 6 (14.3) Special class or special school 25 (53.2) 9 (21.4) χ 2 analysis: p< Developmental Medicine & Child Neurology 2005, 47:

6 discernment. The precise trajectory of each child varies, placing limits on generalization of our observations and requiring an individualization of therapeutic approach. Although there is a measurable difference in outcomes, a commonality of approach is suggested. Persisting significant difficulties across developmental and functional domains for both groups suggest the likely benefit of a systematic programmatic approach similar to that already widely implemented for children with definite risk factors for later neurodevelopmental sequelae (namely Down syndrome or neonatal intensive care unit survivors; Msall et al. 1998). Although children with GDD and DLI typically receive therapeutic intervention at the time of initial diagnosis, such interventions are frequently not sustained over time. It has been noted that the demonstrated benefits of early intervention diminish once such interventions are terminated (McCarton et al. 1997). A programmatic approach would involve the identification of ongoing or new difficulties at defined key points in the lifespan. This identification would greatly assist in targeting appropriate additional resources (frequently limited by budgetary concerns) and therapeutic interventions to minimize later impairments and burdens. The broad range of difficulties, both developmental and functional, highlighted in our study in both cohorts (GDD and DLI), suggests that periodic comprehensive assessments of previously identified children with these diagnoses at the time of school entry would be pragmatic and beneficial. Longer-term studies tracking progress, or lack thereof, through the educational system would be of interest. DOI: /S Accepted for publication 23rd November Acknowledgements Alba Rinaldi provided the necessary secretarial assistance. MS is a Chercheur Boursier Clinicien (Clinical Research Scholar) of the Fonds de recherche en Sante du Quebec, and is also grateful for the support of the MCH Foundation during the writing of the manuscript. RWP is a New Investigator of the Canadian Institutes of Health Research. RW is a recipient of a MCH-Research Institute Post Doctoral Fellowship. References American Academy of Pediatrics Committee on Children with Disabilities. (2001) Developmental surveillance and screening of infants and young children. Pediatrics 108: Aram DM, Ekelman BL, Nation JE. (1984) Preschoolers with language disorders: 10 years later. J Speech Lang Hear Res 27: Bishop DVM, Edmundson A. (1987a) Language impaired 4-year olds: distinguishing transient from persistent impairment. J Speech Hear Disord 52: Bishop DVM, Edmundson A. (1987b) Specific language impairment as a maturational lag: evidence from longitudinal data on language and motor development. Dev Med Child Neurol 29: Glascoe FP, Byrne KE. (1993) The usefulness of the Battelle Developmental Inventory Screening Test. Clin Pediatr 32: Majnemer A. (1998) Benefits of early intervention for children with developmental disabilities. Sem Pediatr Neurol 5: McCarton CM, Brooks-Gunn J, Wallace IF, Baver CR, Bennett FC, Bernbaum JC, Broyles RS, Casey PH, McCormick MC, Scott DT, Tyson J, Tonascia J, Meinert CL. (1997) Results at age 8 years of early intervention for low birth weight premature infants. The Infant Health and Developmental Program. JAMA 277: Montgomery TR. (1988) Clinical aspects of mental retardation the chief complaint. Clin Pediatr 27: Msall ME, Bier JA, LaGasse L, Tremont M, Lester B. (1998) The vulnerable preschool child: the impact of biomedical and social risks on new developmental function. Semin Pediatr Neurol 5: Nass RD, Koch D. (1992) Disorders of higher cortical function in preschoolers. In: David RB, editor. Norwalk, Connecticut: Appleton & Lange. p Nathan I, Stackhouse J, Goulandris N, Snowling MJ. (2004). The development of early literacy skills among children with speech difficulties: a test of the critical age hypothesis. J Speech Lang Hear Res 47: Paul R. (2000) Predicting outcome of early expressive language delay: ethical implications. In: Bishop DVM, Leonard LB, editors. Speech and Language Impairments in Children: Causes, Characteristics, Intervention and Outcome. Philadelphia: Psychology Press. p Petersen MC, Kube DA, Palmer FB. (1998) Classification of developmental delay. Semin Pediatr Neurol 5: Shapiro BK, Palmer FB, Antell S, Bilker S, Ross A, Capute AJ. (1990) Precursors of reading delay: neurodevelopmental milestones. Pediatr 85: Shevell MI. (1998) The evaluation of the child with a global developmental delay. Semin Pediatr Neurol 5: Shevell MI, Ashwal S, Donley D, Flint J, Gingold M, Hirtz D, Majnemer A, Noetzel M, Sheth RD. (2003) Practice parameter: evaluation of the child with global developmental delay. Neurology 60: Shevell MI, Majnemer A, Rosenbaum P, Abrahamowicz M. (2000a) Etiologic yield of subspecialists evaluation of young children with global developmental delay. J Pediatr 136: Shevell MI, Majnemer A, Rosenbaum P, Abrahamowicz M. (2000b) Etiologic yield in single domain developmental delay: a prospective study. J Pediatr 137: Shevell MI, Majnemer A, Rosenbaum P, Abrahamowicz M. (2001a) Etiologic yield of autistic spectrum disorders: a prospective study. J Child Neurol 16: Shevell MI, Majnemer A, Rosenbaum P, Abrahamowicz M. (2001b) A profile of referrals for early childhood developmental delay to ambulatory sub-specialty clinics. J Child Neurol 16: Silva PA. (1980) A study of the prevalence, stability, and significance of developmental language delays in preschool children. Dev Med Child Neurol 22: Silva PA, McGee R, Williams SM. (1983) Developmental language delay from three to seven years and its significance for low intelligence and reading difficulties at age seven. Dev Med Child Neurol 25: Silva PA, McGee R, Williams SM. (1987) A longitudinal study of children with developmental language delay at age three: later intelligence, reading, and behavior problems. Dev Med Child Neurol 29: Sparrow SS, Balla DA, Cicchette DV. (1984) Vineland Adaptive Behavior Scales. American Guidance Service: Minnesota. Stothard SE, Snowling MJ, Bishop DV, Chipchase BB, Kaplan CA. (1998) Language-impaired preschoolers: a follow-up into adolescence. J Speech Lang Hear Res 41: Trower T, Nicol AR. (1996) Life-span intellectual development of people with mental retardation. Dev Med Child Neurol 38: List of abbreviations BDI Battelle Developmental Inventory BDI Battelle Developmental Inventory DLI Developmental language impairment GDD Global developmental delay VABS Vineland Adaptive Behavior Scale Outcomes of Global Developmental Delay and Developmental Language Impairment Michael Shevell et al. 683