When nonverbal IQ and vocabulary remain the same over time but morphosyntactic abilities improve: Evidence from DiGeorge Syndrome

Abstract

This study presents an investigation of receptive and expressive language skills in a male child (PI) with DiGeorge syndrome (DGS), an autosomal dominant genetic disorder caused by the deletion of a small piece of chromosome 22 (aka 22q11.2 deletion syndrome). The syndrome is associated with an extensive and variable phenotype. Using case-based methodology we compare PI’s performance on global and structured language tasks in Greek to typically language developing children of the same chronological age, and at two different time points; when PI was 6 and 10 years of age. We also compare his performance to school-aged children with specific language impairment (SLI) on the same tests. Receptive and expressive language scores were derived from the Diagnostic Verbal IQ Test and the Peabody Picture Vocabulary Test prior to the testing on structured language tasks. Non-verbal intelligence was measured with the Raven’s Coloured Progressive Matrices. Structural language testing involved (i) comprehension of subject and object relative clauses, (ii) production of 3rd person accusative clitics within islands, and (iii) a narrative retell task where MLU, number of subordinate clauses produced, and number of t-units produced were calculated. Our results showed that there was no improvement in nonverbal IQ or vocabulary over time. In contrast, morphosyntactic abilities improved. The findings will be discussed in relation to two hypotheses, namely (a) that the profile of language impairment in children with DGS may be distinctive to this syndrome or (b) that there is a possibility of co-morbidity of SLI in DGS.