The Relation of Language Disorder and Developmental Delay to Timing of ASD Diagnosis

Background: The prevalence rate of ASD has increased over the past decade causes of which are unknown.  Studies show that timely identification of ASD leads to earlier intervention and better prognosis.  Analysis of children diagnosed with Developmental Delay (DD) and Language Disorder (LD) may help indicate early ASD signs, thus provide early intervention services.

Objectives: This study investigated the number, proportion and distribution of ASD children with and without diagnosed Language Disorder (LD) and Developmental Delay (DD) as they relate to the average age of ASD diagnosis.

Methods: Data were collected as part of the New Jersey Autism Study (NJAS), an ASD surveillance investigation carried out in a four county New Jersey region.  Using an active case-finding method, ASD surveillance data were developed for children who were born in 1998 and resided in the surveillance region in 2006.  NJAS data were based on review, analysis and independent ASD case-determination derived from information contained in health and education records.  Demographic information and case-specific data, including the pattern of diagnosis were analyzed services.  The socioeconomic status (SES) of children with ASD was represented by the District Factor Group (DFG) ranking, a community-level index.  Statistical analysis was performed using T tests.

Results: In a population of over 30,000 8-year old children, 533 were identified as having ASD.  366 ASD children (67%) had an ASD diagnosis in their records.  97 ASD children (18.2%) had a history of both LD and DD, and an ASD diagnosis (Group A), while 121 ASD children (22.7%) had an ASD diagnosis and neither LD and DD in their history (Group B).  However, there was a significant difference in the age of ASD diagnosis between Groups A and B (T = 4.32, p < 0.0001).  The average age of ASD diagnosis in Group A was 47 months, while the average age of ASD diagnosis in Group B was 59.6 months.

Conclusions: The study findings show that ASD children with a history of Language Disorder and Developmental Delay are diagnosed with ASD almost a year earlier; hence, they are likely to receive intervention earlier than ASD children without previously diagnosed LD and DD.  The findings emphasize the fact that language impairment and developmental delay are key elements of ASD and suggest that more meticulous and sensitive ASD identification methods should be employed to identify children with ASD at an earlier age.