Prospective and detailed behavioral phenotyping in DDX3X syndrome

Abstract

Background DDX3X syndrome is a recently identified genetic disorder that accounts for 1-3% of cases of unexplained developmental delay (DD) and/or intellectual disability (ID) in females and is associated with motor and language delays, and autism spectrum disorder (ASD). To date, the published phenotypic characterization of this syndrome has primarily relied on medical record review; in addition, the behavioral dimensions of the syndrome have not been fully explored. Methods We carried out multi-day, prospective, detailed phenotyping of DDX3X syndrome in 14 females and 1 male, focusing on behavioral, psychological, and neurological measures; three participants in this cohort have been previously reported. We compared results against population norms and contrasted phenotypes between individuals harboring either (i) protein-truncating variants or (ii) missense variants and in-frame deletions. Results Eighty percent of individuals met criteria for ID, 60% for ASD and 53% for attention- deficit/hyperactivity disorder (ADHD). Motor and language delays were common as were sensory processing abnormalities. The cohort included 5 missense, 3 intronic/splice-site, 2 nonsense, 2 frameshift, 2 in-frame deletions, and one initiation codon variant. Genotype-phenotype correlations indicated that missense variants/in-frame deletions were associated with more severe language, motor, and adaptive deficits in comparison to protein-truncating variants. Limitations Sample size is modest, however, DDX3X is a rare and underdiagnosed disorder. Conclusion This study, representing a first, prospective, detailed characterization of DDX3X syndrome, extends our understanding of the neurobehavioral phenotype. Gold-standard diagnostic approaches demonstrated high rates of ID, ASD, and ADHD. In addition, sensory deficits were observed to be a key part of the syndrome. Even with a modest sample, we observe evidence for genotype-phenotype correlations with missense variants/in-frame deletions yielding a more severe phenotype. Key Words: autism, developmental delay, genotype-phenotype correlation, intellectual disability, DDX3X syndrome