This scenario could presumably be identified as a case of DLD-and not PD-by examining word-final production of, ,, in non-morphemic word-final contexts. For instance, a child might present with DLD, whose omission of word-final grammatical morphemes, such as 3rdSg -s or past tense -ed, mimics a pattern of final consonant deletion or cluster reduction (e.g., goes /ɡoʊz/ as stopped /stɑpt/ as ), which is a relatively common phonological process in children with PD ( Ingram, 1989). Notably, not all children with overlapping morphophonological error patterns fit the profile of a child with co-occurring PD-LD. The issue at hand is a group of children with deficits distributed across the non-mutually exclusive domains of phonology and morphosyntax. Furthermore, children with co-occurring PD-LD also demonstrate poorer language and literacy outcomes in adolescence than those with non-comorbid PD or DLD ( Lewis et al., 2015). The literature also suggests that children with PD-LD are more severely impaired and are more likely to experience lasting cross-domain deficits than those with PD or DLD alone ( Bishop & Edmundson, 1987 Haskill & Tyler, 2007 Ingram, 1976 Lewis, Freebairn, & Taylor, 2000a Macrae & Tyler, 2014). Some have suggested that, in children with co-occurring PD and DLD (henceforth PD-LD), low intelligibility characteristic of PD is often identified before characteristics of DLD (e.g., Panagos, 1974), whose presentation is known to change across the life span (e.g., Conti-Ramsden, St Clair, Pickles, & Durkin, 2012). Heritability has been demonstrated for PD and DLD ( Pennington & Bishop, 2009), and is especially linked to instances of co-occurring PD and DLD ( Lewis, Freebairn, & Taylor, 2000b). PD and DLD are associated with multiple cognitive-linguistic deficits, including some that regularly occur in children with either disorder, such as impaired phonological working memory ( Archibald & Joanisse, 2009 Raitano, Pennington, Tunick, Boada, & Shriberg, 2004). Although these estimates vary, the substantial co-occurrence of phonological and morphosyntactic impairments is well documented, which muddies the distinction between traditional speech and language disorders and demands that this co-occurrence be addressed in the clinical literature.Ĭonverging evidence also suggests that PD and DLD may, at least in some cases, have similar or overlapping etiologies (e.g., Pennington & Bishop, 2009). In two epidemiological studies reviewed by Pennington and Bishop (2009), children with DLD were 3.3 ( Shriberg, Tomblin, & McSweeny, 1999) or 6.1 ( Beitchman, Nair, Clegg, Ferguson, & Patel, 1986) times more likely to also have PD. For instance, Shriberg and Kwiatkowski (1994) found between 10% and 77% of 3-to-6-year-old children with speech production deficits demonstrate expressive language concerns (e.g., low utterance length, grammatical morpheme errors, limited vocabulary). Prevalence estimates for co-occurring PD and DLD (hereafter, PD-LD) vary greatly. Investigators in the areas of PD ( Paul & Shriberg, 1982 Rvachew, Gaines, Cloutier, & Blanchet, 2005) and DLD ( Bishop & Edmundson, 1987 Botting & Conti-Ramsden, 2003 Haskill & Tyler, 2007 van Daal & van Balkom, 2004) have repeatedly documented co-occurring deficits, such that difficulty with language (i.e., morphosyntax) is frequently reported in children with PD, and children with DLD often have co-occurring speech-sound production deficits. However, there is a body of evidence that links PD and DLD and demonstrates the considerable co-morbidity of these disorders. Despite affecting different language components, PD and DLD both prevent development of a child’s linguistic skills in a timely manner, which can impact their communication and literacy skills and later academic, socio-emotional, and occupational outcomes (e.g., Beitchman, Wilson, Brownlie, Walters, Inglis, et al., 1996 Beitchman, Wilson, Brownlie, Walters, & Lancee, 1996).īecause PD has typically been associated with the domain of speech and DLD with the domain of language, the assessment and treatment of each has most frequently been investigated independently. In PD, phonological units (e.g., speech sounds and sequences) are impacted, whereas in DLD, the impact is seen in larger units (e.g., morphemes, words, and phrases). The primary distinction between PD and DLD lies in the types of units affected. Both PD and DLD are of unknown etiology, occurring independently of a primary motivating condition, and both functionally impair the development, manipulation, and production of the linguistic units of language. Two of the most prevalent communication disorders in preschool and early school age children are phonological disorder (PD), a type of speech-sound disorder ( Law, Boyle, Harris, Harkness, & Nye, 2000), and developmental language disorder (DLD), a type of language impairment also referred to as specific language impairment ( Bishop et al., 2017).
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