Infants later diagnosed with autism have lower canonical babbling ratios in the first year of life

Abstract

Background: Canonical babbling-producing syllables with a mature consonant, full vowel, and smooth transition-is an important developmental milestone that typically occurs in the first year of life. Some studies indicate delayed or reduced canonical babbling in infants at high familial likelihood for autism spectrum disorder (ASD) or who later receive an ASD diagnosis, but evidence is mixed. More refined characterization of babbling in the first year of life in infants with high likelihood for ASD is needed.

Methods: Vocalizations produced at 6 and 12 months by infants (n = 267) taking part in a longitudinal study were coded for canonical and non-canonical syllables. Infants were categorized as low familial likelihood (LL), high familial likelihood diagnosed with ASD at 24 months (HL-ASD) or not diagnosed (HL-Neg). Language delay was assessed based on 24-month expressive and receptive language scores. Canonical babble ratio (CBR) was calculated by dividing the number of canonical syllables by the number of total syllables. Generalized linear (mixed) models were used to assess the relationship between group membership and CBR, controlling for site, sex, and maternal education. Logistic regression was used to assess whether canonical babbling ratios at 6 and 12 months predict 24-month diagnostic outcome.

Results: No diagnostic group differences in CBR were detected at 6 months, but HL-ASD infants produced significantly lower CBR than both the HL-Neg and LL groups at 12 months. HL-Neg infants with language delay also showed reduced CBR at 12 months. Neither 6- nor 12-month CBR was significant predictors of 24-month diagnostic outcome (ASD versus no ASD) in logistic regression.

Limitations: Small numbers of vocalizations produced by infants at 6 months may limit the reliability of CBR estimates. It is not known if results generalize to infants who are not at high familial likelihood, or infants from more diverse racial and socioeconomic backgrounds.

Conclusions: Lower canonical babbling ratios are apparent by the end of the first year of life in ASD regardless of later language delay, but are also observed for infants with later language delay without ASD. Canonical babbling may lack specificity as an early marker when used on its own.

Fig. 1

Canonical babbling ratios (CBRs) at 6 and 12 months. The dashed line indicates the commonly used threshold of 0.15, above which infants are considered to have reached the canonical babbling milestone. Dark lines show the median for each group

Fig. 2

Longitudinal change in canonical babbling ratio. Dashed lines represent individual trajectories, and the long-dashed line indicates the commonly used canonical babbling milestone cut-point of 0.15 for reference. HR-ASD infants show significantly reduced growth in CBR between 6 and 12 months relative to HR-Neg and LR groups

Fig. 3

CBR was significantly associated with standardized language measures, controlling for sex, site, and maternal education. a CBR at 6 months was predictive of MSEL Expressive Language at 6 months. CBR at 12 months was predictive of: b MSEL Expressive Language at 12 months, c M-CDI words produced number at 12 months, d MSEL Expressive Language measured at 24 months, and e M-CDI words produced number at 24 months

Fig. 4

Canonical babbling ratios (CBRs) at 12 months by likelihood, diagnostic, and language delay grouping. High-likelihood infants with language delay but not autism (HR-Neg-LD) were not distinguished from high-likelihood infants with autism but not language delay (HR-ASD-No). High-likelihood infants with neither autism nor language delay (HR-Neg-No) and low-likelihood (LR) infants had higher CBR than HR-ASD-No infants. Asterisks indicate significance in Tukey-corrected pairwise comparisons from a GLM controlling for site, sex, and maternal education, *p < 0.05, **p < 0.01, ***p < 0.001