Uncovering the complexity of structural variants in four individuals with autism spectrum disorder.

Autism spectrum disorder (ASD) is an increasingly recognized childhood developmental disorder. Despite extensive study, causal variants and molecular diagnosis remain elusive. There is both heterogeneity of the phenotype, as well as the genetic landscape associated with phenotype, which includes both inherited and de novo mutations. Currently, diagnosis is complex and behaviourally based, oftentimes occurring years after the ideal 1-2 years of age. Structural variants (SVs) are large and sometimes complex genomic variants that are likely underrepresented contributors to ASD due to the limitations of short-read DNA sequencing, such as alignment in repetitive regions and regions with GC bias. Here, we performed long-read sequencing (LRS) on four individuals with autism spectrum disorder to delineate SV complexity and determine precise breakpoints for SVs, which was not possible with short-read whole-genome sequencing (SRS). We use LRS to interrogate the methylation pattern associated with the SVs and phase the SV haplotypes to further clarify their contribution to disorder. LRS allows insight into the genome and methylome that allow us to uncover variant complexity and contribution that was previously unseen with SRS. Ultimately, this furthers precision diagnosis and contributes to individualized treatment for affected individuals and their families within the clinic.