Abstract
BACKGROUND: Developmental language disorder (DLD) refers to children who present with language difficulties that are not due to a known biomedical condition or associated with autism spectrum disorder (ASD) or intellectual disability (ID). The clinical heterogeneity of language disorders, the frequent presence of comorbidities, and the inconsistent terminology used over the years have impeded both research and clinical practice. Identifying sub-groups of children (i.e. DLD cases without childhood apraxia of speech (CAS)) with language difficulties is essential for elucidating the underlying genetic causes of this condition. DLD presents along a spectrum of severity, ranging from mild speech delays to profound disturbances in oral language structure in otherwise typically intelligent children. The prevalence of DLD is ~ 7-8% or 2% if severe forms are considered. This study aims to investigate a homogeneous cohort of DLD patients, excluding cases of ASD, ID or CAS, using multiple genomic approaches to better define the molecular basis of the disorder. METHODS: Fifteen families, including 27 children with severe DLD, were enrolled. The majority of cases (n = 24) were included in multiplex families while three cases were sporadic. This resulted in a cohort of 59 individuals for whom chromosomal microarray analysis and exome or genome sequencing were performed. RESULTS: We identified copy number variants (CNVs) predisposing to neurodevelopmental disorders with incomplete penetrance and variable expressivity in two families. These CNVs (i.e., 15q13.3 deletion and proximal 16p11.2 duplication) are interpreted as pathogenic. In one sporadic case, a de novo pathogenic variant in the ZNF292 gene, known to be associated with ID, was detected, broadening the spectrum of this syndrome. LIMITATIONS: The strict diagnostic criteria applied by our multidisciplinary team, including speech-language physicians, neuropsychologists, and paediatric neurologists, resulted in a relatively small sample size, which limit the strength of our findings. CONCLUSION: These findings highlight a common genetic architecture between DLD, ASD and ID, and underline the need for further investigation into overlapping neurodevelopmental pathways. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT06660108.