Reconceptualizing developmental language disorder as a spectrum disorder: issues and evidence

Abstract

Background: There is considerable variability in the presentation of developmental language disorder (DLD). Disagreement amongst professionals about how to characterize and interpret the variability complicates both the research on understanding the nature of DLD and the best clinical framework for diagnosing and treating children with DLD. We describe and statistically examine three primary possible models for characterizing the variability in presentation in DLD: predictable subtypes; individual differences; and continuum/spectrum. Aims: To test these three models of DLD in a population-based sample using two distinct types of cluster analyses. Methods & Procedures: This study included children with DLD (n = 505) from the US Epidemiological Study of Language Impairment database. All available language and cognitive measures were included. Two cluster methods were used: Ward’s method and K-means. Optimal cluster sizes were selected using Bayesian information criteria (BIC). Bootstrapping and permutation methods were used to evaluate randomness of clustering. Outcomes & Results: Both clustering analyses yielded more than 10 clusters, and the clusters did not have spatial distinction: many of these clusters were not clinically interpretable. However, tests of random clustering revealed that the cluster solutions obtained did not arise from random aggregation. Conclusions & Implications: Non-random clustering coupled with a large number of non-interpretable subtypes provides empirical support for the continuum/spectrum and individual differences models. Although there was substantial support for the continuum/spectrum model and weaker support for the individual differences model, additional research testing these models should be completed. Based on these results, clinicians working with children with DLD should focus on creating treatment plans that address the severity of functioning rather than seeking to identify and treat distinct subtypes. Additional consideration should be given to reconceptualizing DLD as a spectrum condition.

Reading outcomes in children with developmental language disorder: A person-centered approach

“…Strong EF-average language and PP affected by DLD, which is in line with previous studies (Bishop, 2017;Blom & Boerma, 2020;Lancaster & Camarata, 2018). The inclusion of the three broader constructs oral language proficiency, phonological memory, and executive functioning allowed simultaneous consideration of relevant abilities for learning to read (Bishop & Snowling, 2004).…”

“…In DLD research on subtypes, nonverbal intelligence plays a prominent role (Rice, 2016). It is debated whether it makes sense to use cut-off scores for nonverbal intelligence and distinguish between children with DLD who have average nonverbal intelligence and low-average nonverbal intelligence, or between DLD and a more general intellectual disability (Bishop, 2017;Lancaster & Camarata, 2018). As poor nonverbal intelligence can affect learning in general (Neisser et al, 1996), taking nonverbal intelligence into account is valuable when investigating possible predictors of poor oral and written language learning (Bishop, 2014).…”

“…A third limitation concerns the applicability of a person-centered approach for clinical purposes. A person-centered approach could identify subgroups that might not exist within the population, as heterogeneity of the population might be better explained by other factors (e.g., a continuum approach) rather than by clinically separable subgroups (Lancaster & Camarata, 2018;Williams & Kibowski, 2016). It is, therefore, worth noting that we did not adopt the latent profile approach to detect clinically distinct subgroups, but rather to account for the high levels of variability within the DLD population.…”

“…It occurs frequently and affects about 7% of the population with a higher prevalence among boys than girls (Law et al, 2000;Tomblin et al, 1997). Severity of the impairment and affected domains show high variability (Bishop, 2017;Lancaster & Camarata, 2018). On top of their oral language problems, many children with DLD have difficulties with written language, and develop reading problems (Bishop et al, 2009;De Bree et al, 2012).…”

Language, literacy and cognitive skills of young adults with developmental language disorder (DLD)

“…There is also a body of evidence suggesting overlaps between dyslexia and oral language difficulties (see Adlof and Hogan for an overview). However, for all these difficulties, a wide range of abilities is noted in DLD as a group, perhaps suggesting it is best conceptualized as a spectrum of difficulties (Lancaster and Camarata ).…”