Clinical Case Report: Mosaic ANK3 Pathogenic Variant in a Patient with Autism Spectrum Disorder and Neurodevelopmental Delay

Ankyrins are a family of proteins that link integral membrane proteins to the underlying spectrin-actin cytoskeleton and play a key role in activities such as cell motility, activation, proliferation, cell-cell contact, and the maintenance of specialized membrane domains. Ankyrin 3 (ANK3) is one of the three major subtypes of the ankyrin protein family. Ankryin genes are ubiquitously expressed, but their expression is highest in the brain. In the central nervous system, ankyrins have critical roles at the axonal initial segment, the nodes of Ranvier, and at synapses. To date, pathogenic variants in ANK3 have been reported in individuals with neuropsychiatric, cognitive, and neurodevelopmental disorders. The clinical severity is variable in these individuals with both autosomal recessive and autosomal dominant patterns of inheritance observed. These findings have suggested genotype-phenotype correlations and even isoform-specific implications for individuals with ANK3 pathogenic variants. Here, we report a patient with speech delay, autism spectrum disorder, and a language disorder in which a de novo nonsense ANK3 alteration was discovered by exome sequencing. Interestingly, the next-generation sequencing data suggested the change was mosaic in the affected child, and it was confirmed by digital polymerase chain reaction (dPCR) at 22% allelic fraction. To our knowledge, this is the first case of an individual with a pathogenic mosaic ANK3 variant. This finding expands upon the existing genotype-phenotype information available for the ANK3 gene while also highlighting potential gene expression correlations with phenotype.