Loss of ANK3 Function Causes a Recessive Neurodevelopmental Disorder with Cerebellar Ataxia

Background ANK3 encodes ankyrin‐G, a key scaffolding protein essential for neuronal function. While both monoallelic and biallelic ANK3 variants have been linked to neurodevelopmental disorders (NDDs), existing evidence for their pathogenicity and clinical correlation remains limited and heterogeneous. Objective To delineate the clinical features associated with biallelic ANK3 predicted loss‐of‐function (pLOF) variants. Methods We employed exome sequencing, Sanger validation, detailed clinical phenotyping, and extensive international data sharing to identify patients with biallelic ANK3 variants. Results We describe five individuals from three unrelated consanguineous families with segregating homozygous ANK3 pLOF variants. These patients presented with a relatively consistent phenotype comprising developmental delay, intellectual disability, hypotonia, variable epilepsy, and cerebellar signs including ataxia, tremor, and dysarthria. Among the three patients for whom brain magnetic resonance imaging was available, cerebellar atrophy was observed, predominantly affecting the superior vermis and cerebellar hemispheres. These clinical findings align with murine models lacking the cerebellar ankyrin‐G isoform, which similarly exhibit ataxic features and high cerebellar ANK3 expression. Conclusion Our findings support a recognizable NDD with non‐progressive cerebellar ataxia linked to biallelic ANK3 pLOF variants.