A novel de novo missense variant in ASH1L associated with mild autism spectrum disorder and an uneven cognitive profile: a case report.

BACKGROUND: ASH1L-related intellectual developmental disorder represents an emerging neurodevelopmental syndrome with significant phenotypic heterogeneity (Cordova et al. in Genes (Basel). 15(4):423, 2024). Comprehensive genomic analysis demonstrates superior diagnostic yield compared with targeted approaches in complex neurodevelopmental presentations (Srivastava et al. in Genet Med. 21(11):2413-2421, 2019). CASE PRESENTATION: This report describes a 6-year-old Central Asian (Uzbek) male patient with a history of global developmental delay who was diagnosed with mild autism spectrum disorder, attention-deficit/hyperactivity disorder, and a developmental expressive language disorder. Neuropsychological assessment revealed an uneven cognitive profile with average verbal abilities but below-average nonverbal reasoning. After uninformative targeted genetic panels, trio whole-genome sequencing identified a novel de novo heterozygous missense variant in ASH1L c.4043A > G (p.Lys1348Arg). This variant, absent in population databases, was classified as a variant of uncertain significance. However, in silico analysis predicted this variant to be probably damaging, and therefore, it emerged as the strongest candidate to explain the patient's phenotype. CONCLUSION: This case expands the known phenotypic spectrum of ASH1L-related disorders, demonstrating that a de novo missense variant can be associated with a milder neurodevelopmental phenotype, including borderline-to-average intellectual ability. These findings challenge suggestions that missense variants uniformly lead to more severe outcomes and underscores the importance of comprehensive genomic and deep clinical characterization to refine our understanding of gene-disease relationships.