This study was developed to examine the predictive value of subclinical autistic traits at age 14–15 months for (1) ASD-symptoms, (2) non-ASD behavioural problems, and (3) cognitive functioning 2–4 years later. We sampled children with high, moderate, and low scores on autistic traits from the general population and excluded children who already had been diagnosed with ASD at an early age because our study focused on children with subclinical autistic traits only.
The children with abnormal scores who are included in the high-scoring group seem to be representative of all children with high ESAT-scores. Therefore, there is no reason to suspect that the results of our high-scoring group cannot be generalized. The children failed on various ESAT-items. More than 50% of the children had a deviating score on the items “asking attention” and “stereotypic movements”. Some deficits in early skills seem to be related to later problems. Difficulties in expressing emotions at age 14–15 months may be predictive of behavioural problems (CBCL 1½–5) at age 3 years. Inadequate eye-contact at age 14–15 months may be a precursor of delays in language comprehension (RTB) and production (STP) at age 4–5 years.
We were unable to find support for our first hypothesis that predicted subclinical autistic traits at age 14–15 months to be homotypic precursors for ASD at age 4–5 years. None of the children satisfied the criteria for a clinical ASD-diagnosis based on the ADI-R or ADOS-G. However, children from the high-scoring ESAT-group scored somewhat higher on the SCQ as a whole and on the domain “social interaction”, and scored significantly higher on the items “abnormal eye contact” and “unusual sensory interests” than children from the moderate- and low-scoring ESAT-groups. Nevertheless, our results indicate that there is hardly any continuity of parent-reported early subclinical autistic traits measured with the ESAT at age 14–15 months and similar autistic traits measured with the SCQ at age 4–5 years. Whereas few children from the high-scoring ESAT-group did present with clinical scores (SCQ 11 and above) at age 4–5 years, the majority had SCQ-scores below the cut-off of 11. Further, some children from the moderate- and low-scoring ESAT-groups reached SCQ-scores equal to or higher than 11. These findings are in contrast with the numerous data pointing to rather strong continuity over time of ASD-conditions reaching the level of clinical severity [20
]. Obviously, clinical severity is closely linked with persistence over time. This may be explained by the fact that greater clinical severity of ASD has been found to be related to a more abnormal early development and functioning of the brain, which in turn may be the driving force affecting the further development of cognitive, language, communicative, social, and emotional functions [2
We found more support for our second hypothesis that predicted subclinical autistic traits to show heterotypic continuity with later externalizing and internalizing behavioural problems. Our results showed that children from the high-scoring ESAT-group had significantly more externalizing and internalizing behavioural problems than children from the other groups at age 3 years. On the individual level, seven children, of whom six belonged to the high-scoring group, had a total-CBCL-score in the clinical range. Early subclinical autistic traits thus seem to be precursors of serious behavioural problems 2 years later. They seem to reflect a more global risk that does not differentiate between externalizing and internalizing types of problems. Mastery of early social and communicative skills may be closely linked with the development of self-regulation and be pivotal for the proper development of other functions. Contrariwise, poor ability to control and regulate activity, impulses, and emotions may pave the way to later externalizing and internalizing behavioural problems [17
With the third hypothesis we investigated the relation between subclinical autistic traits at age 14–15 months and cognitive and language abilities at age 4–5 years. In contrast to our expectations, we did not find differences between the ESAT-groups in levels of non-verbal intelligence (SON-R 2½–7), except for the subtest “situations”. This means that children from the high-scoring ESAT-group, who have an average total IQ-score, perform well overall, but that they are less able to interpret the logical coherence of (social) situations than children from the moderate-scoring ESAT-group. We were also unable to find an unusual degree of unevenness in cognitive abilities often seen in children with ASD [23
], although early subclinical autistic traits were associated with significantly lower levels of language comprehension (RTB) and production (STP) at age 4–5 years. However, significantly more children from the high-scoring ESAT-group than from the other groups had a non-verbal IQ and/or language comprehension and production scores below 85. Our results thus indicate that early subclinical autistic traits are precursors or early manifestations of later cognitive and language problems. This fits with recent findings in a general population sample study in Norway in which parents of infants with high ESAT-scores also report more communication and language problems at the age of 18 months [7
]. Since the ESAT does not comprise items regarding language, this reflects the close link between early social and communication skills measured with the ESAT and the development of language and cognition. Similar results were found in two other longitudinal studies focusing on predictors of language acquisition and communication development in young children with ASD [39
Together, these findings demonstrate that early autistic traits are precursors of or risk factors for especially externalizing and internalizing behavioural problems and/or cognitive and language problems at age 3–5 years. More than 50% of the children in the high-scoring ESAT-group suffer from problems in one or two outcome domains. Though these problems are not well marked clinically, these children can be considered to be at high risk for failing to establish adequate levels of psychosocial functioning and for developing psychiatric disorders. Children with Asperger’s disorder or PDD-NOS are unlikely to show enough symptoms early on to be picked up. A follow-up of this sample may reveal valuable information about the course of development and behaviour in middle childhood. Therefore, we intend to contact the parents in the near future, and to inquire about the child’s present level of functioning in various domains, as well as possible current problems, diagnosis, and treatment.
Our study has some limitations, such as the modest sample size, as well as the use of various measures of autistic symptoms, behavioural problems, cognition, and language at different ages. However, it is not feasible to use exactly the same measures in children as young as 14–15 months to relatively ‘old’ 4- to 5-year-olds. Therefore, we chose to use measures which were most suitable for these domains at a particular age. Another limitation is the shortage of validated parental questionnaires for assessing autistic traits around age 4–5 years. The SCQ might be less suitable for detecting subtle problems in higher functioning and/or younger children in general populations than for determining severe problems in lower functioning and/or older children in high-risk populations [3
]. The strength of this project is the use of a longitudinal design in a sample drawn from the general population.