Item-Level Analysis Demonstrates Significant Differences in Word Production and Understanding at 12 Months of Age in Children at Risk for Autism

Background: Autism Spectrum Disorder (ASD) is characterized by persistent deficits in social communication and social interaction as well as restricted, repetitive patterns of behavior, interests or activities.  Several studies, including prospective infant sibling studies, have identified delayed babbling, verbal expression and regression in children with ASD.  Preschoolers with ASD show greater impairment in receptive compared with expressive language abilities.  The recently released DSM-5 eliminated language delay as a diagnostic criterion because it is not specific to ASD.  It instead emphasizes qualitative language deficits in conversation, integrated verbal communication, stereotyped or repetitive speech (echolalia, idiosyncratic phrases), and ritualized patterns of verbal behavior (greeting rituals).  No published research identifies qualitative word use differences in infants who develop ASD.  

Objectives: The purpose of this study was to investigate qualitative differences between ASD and typically developing children in terms of word production and understanding as measured on the McArthur-Bates Communicative Development Inventories (MBCDI).

Methods: Item Response Theory (IRT) was applied to determine the relative probability of understanding and producing each of the 396 words on the MBCDI.  Differential Item Functioning (DIF) was calculated to determine which words understood or produced favored ASD or typically developing (TD) children given equivalence in their levels of ability.  Participants for this cross-sectional analysis were part of a larger ongoing study of infant siblings at risk for ASD.  We analyzed 15 later-born siblings with ASD, and 33 TD controls, followed from 6 months of age through 36 months or until they dropped out.  Diagnosis was based on ADOS classification and independent clinical confirmation.  

Results: At 12 months of age, 14 words were associated with Differential Item Functioning (DIF). These words were significantly more or less likely to be produced or understood as a function of grouping (TD versus ASD children).  Two words were significant in terms of production.  "Hi" was significantly more likely to be produced by TD children and "block" was significantly more likely to be produced by children in our ASD sample.  Twelve words were significantly more likely to be understood by children with ASD - “lion, mouse, car, train, outside, rock, swing, brother, close, open, show and out.”  No words were significantly more likely understood by TD children.  

Conclusions: The results of this study indicate there are qualitative language differences measurable at 12 months of age on the MBCDI between typically developing and ASD children.  Children with ASD’s significantly lower likelihood to produce “Hi” may be early linguistic evidence of reduced social communication.  ASD children’s significantly higher likelihood of producing the word "block" as well as understanding words related to animals, toys and objects may be an early linguistic manifestation of restricted, repetitive interests or activities.  These results may also be influenced by linguistic input heard from other family members, including their affected sibling.  Next Steps:  We will complete an item-level analysis on high-risk siblings without autism.  We will seek more participants to stabilize our 12-month estimates.  We will also analyze 18-month MBCDI data for word production differences.