Defining language phenotypes in autism
Introduction
One of the hallmark features of autism spectrum disorders (ASD) is wide variability in language skills [1]. Although deficits in pragmatic aspects of communication, specifically the ability to use both literal and non literal language appropriately in a range of social contexts, are universal symptoms even among adults with Asperger syndrome [2], [3], formal language deficits are not core features of ASD [4]. [5] did not refer to language problems in his original discussion of the defining features of infantile autism; however, later he described some of the idiosyncratic clinical features of language use among the children he had diagnosed, including echolalia, pronoun reversals and stereotyped language [6].
There is growing interest among researchers and clinicians in delineating different subtypes in autism. For researchers, this would create more homogenous groupings that could facilitate finding the underlying causes of autism; for clinicians, subtyping would enhance the ability to tailor treatments to the specific needs of individuals based on their particular pattern of impairments. Rapin and her colleagues [7], [8], [9] were the first to describe the different types of language disorders found among children with autism, highlighting some of the similarities between autism and other developmental language disorders. More recently, [10] identified two language subtypes among verbal children with autism: children with normal linguistic abilities (phonological skills, vocabulary, syntax and morphology) and children with impaired language [10] argued that the language phenotype of the autistic children in the latter subtype was similar to the language phenotype that has been described for children with specific language impairment (SLI), a disorder characterized by delays and difficulties in language acquisition in absence of other sensory, cognitive or affective disorders [11]. Like autism, SLI represents a heterogeneous population [12]. There is no agreement among clinicians or researchers on uniform diagnostic criteria, including specific instruments, measures, or cut-off points that define this population. Nevertheless, in recent years, some consensus has been reached about language deficits that may be viewed as central to this disorder. Two clinical markers have been highlighted: deficits in phonological processing and grammatical morphology [12]. These clinical markers are now viewed as core features that define the phenotype of SLI, analogous to the social, communicative and restricted behavior patterns that are at the core of an autism diagnosis.
In an initial comprehensive study, [13] investigated language profiles in a large group of verbal children with autism using a battery of standardized language tests tapping articulation, phonological processing, vocabulary, and higher order grammatical and semantic skills. Two subgroups of children with autism were identified, based on their performance on these tests. About one quarter of the children had language test scores that fell within in the normal range (ALN subtype). The remaining children scored significantly below the mean on all the language tests except for the articulation measure. These children had a distinctive profile of performance across the language measures (moderate impairments in vocabulary and phonological processing and more severe impairments in higher order syntax and semantics), suggesting that they formed a subtype of children with autism and language impairment (ALI subtype). Although there was a moderate relationship between language scores and IQ, there were children with high and low IQ scores, and normal or delayed onset of language milestones, in both the ALN and ALI language subgroups. The profile of scores of the ALI children resembled closely the profiles reported for children with SLI [12]. The poor performance of these children on the test of phonological processing, a standardized nonsense word repetition test, was especially significant since, as noted earlier, this kind of measure is considered highly sensitive to the diagnosis of SLI [13], [15], [16], [17]. However, it was not clear from this initial study whether the ALI children made the same types of errors when repeating nonsense words as do children with SLI, or whether deficits in nonword repetition are related to vocabulary knowledge, as has been found in SLI [17].
In addition to impairments in phonological processing SLI is characterized by grammatical deficits, especially in marking verbs for tense [18], [19]. Long after their age-matched peers have stopped making errors, children with SLI continue to omit grammatical morphemes in their speech; for example, marking the past tense (e.g., She play-ed in the garden). Studies by Rice and her colleagues showed that for English-speaking children with SLI children’s grammatical marking of tense distinguished preschool children with SLI from unimpaired children in both conversational speech as well as on experimental probes [19], [20], [21]. Drawing on part of the same sample that had participated in [14] study, [22] investigated grammatical tense marking in children with autism. About half the children had the ALN phenotype and half the ALI phenotype. The children were given experimental probes to elicit past tense and third person present tense (e.g., A firefighter put-s out fires), using the same tasks designed by [20]. The ALI children performed poorly on these probes (30% correct on past tense and 37% correct on third person present tense) compared to the ALN children (76% and 64%, respectively). The most common error pattern among the ALI children was to omit any morphological marking on the verb stem, the error that is most frequently reported for children with SLI.
The studies reviewed here provide support for the view that there are parallels in language profiles between a subgroup of children with autism, ALI, and children with SLI; however, it is not clear whether these parallels are misleading in that the language deficits stem from different underlying mechanisms or whether they reflect more substantive overlap in the phenotypes of these syndromes. The following studies were conducted to follow up on the findings from our earlier research on phonological processing and grammatical morphology among children with autism.
Section snippets
Study 1: Phonological processing
The goal of this study was to follow up on the findings of [14], who found that children with ALI had low scores on a standardized test of nonsense word repetition (NWR), in order to examine the kinds of errors made by children with ALI and to investigate the whether NWR performance is correlated with vocabulary and other phonological processing tasks in children with autism, as has been found for children with SLI [18].
Study 2: Grammatical morphology
The goal of this study was to follow up on the experiment study by [22] who found that children with ALI tended to omit tense morphology on experimental tasks that were designed to elicit sentences that included verbs marked for either third person present singular or past tense. Most studies investigating grammatical morphology deficits in SLI have relied on conversational speech samples to explore grammatical deficits in everyday settings. These studies have found that younger children with
General discussion
The main findings from both these studies confirmed earlier research indicating that in autism, there are different language phenotypes – here referred to as ALN and ALI – reflecting subgroups in which structural, rather than pragmatic, aspects of language are quite different. Thus, we found group differences in the first study in the distribution of errors on a nonword repetition task, and in the second study in the marking of third person present tense morphology. Moreover, these studies
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