A systematic review of the potential impacts of 16p11.2 deletion syndrome on motor speech disorders

Introduction and Aims: Speech disorders are a common feature in individuals with deletion carriers, including 16p11.2 deletion syndrome. However, despite this association, the relationship of this genetic disorder with speech has not been sufficiently clarified. This gap in the literature causes a challenge in both diagnosis and treatment planning as there is a lack of clinical information. This systematic review investigated the potential association between 16p11.2 deletion syndrome and motor speech disorders.
Methods: Searches were performed in Web of Science, SCOPUS, PubMed, ProQuest, and MEDLINE databases after identifying keywords and inclusion-exclusion criteria under the aim of the study. Keywords consisted of speech or motor speech disorders and 16p11.2 deletion syndrome and their variances. Inclusion criteria were: the sample should consist of 16p11.2 deletion carriers, the study language must be English, published after January 1, 2010, participants with speech disorders. Exclusion criteria included studies examining the physiological characteristics of 16p11.2 deletion syndrome rather than speech dimension, participants with other syndromes besides 16p11.2 deletion syndrome, conference papers, systematic review and meta-analysis papers. The study was conducted based on the PRISMA 2020 statement. As a result of database searches, 790 studies were found. After applying the inclusion and exclusion criteria, six studies remained. The remaining six studies were evaluated for bias risk and quality assessment. After the quality assessment, it was decided that all six studies were sufficiently strong to be included in the review. A total of 227 16p11.2 deletion carriers and a control group of 235 individuals were included in the studies.
Results: The results revealed the presence of a speech disorder accompanied by disturbances in the auditory feedback mechanism and language domains. With respect to the latter, 16p11.2 deletion carriers had deficits in intellectual function, language sub-domains of the Madison Speech Assessment Protocol (MSAP) and scored below their age level on the Peabody Picture Vocabulary Test-4 (PPVT-4). They also showed lower scores for syllable repetition and non-word repetition tests, percentage of consonants correct and the speech and motor sub-domains of the MSAP. In relation to the auditory feedback mechanism, reduced sensorimotor adaptation to sustained vowel identity changes was reported, and pitch compensation responses were excessive to unpredictable mid vocalization pitch perturbations. Speech problems presented as abnormalities in neuromuscular tone and oral motor movements such as tongue elevation and lateralization, reduced soft palate contraction and decreased range of motion in speech and non-speech tasks were reported. The majority of the 16p11.2 deletion carriers met the childhood apraxia of speech (CAS) criteria. However, the phenotype was different from CAS because of the presence of symptoms such as slow speech rate, equal stress and hypernasality associated with dysarthria for some participants.
Discussion and Conclusions: Based on investigations to date, 16p11.2 deletion syndrome appears to frequently affect both speech and language domains. Speech disorders are primarily caused by motor coordination disorder and auditory feedback disturbances. Characterization of CAS and identifying subtypes of speech disorders in 16p11.2 deletion syndrome will play a crucial role in diagnosis and treatment planning.