AbstractIn this study, epilepsy with focal seizures progressing to generalized seizures was diagnosed in a 6‐month‐old Holstein heifer. The seizures were characterized by a brief pre‐ictal phase with depression and vocalization. During the ictal phase eyelid spasms, tongue contractions, nodding and abundant salivation were observed, rapidly followed by a convulsive phase with bilateral tonic, clonic or tonic–clonic activity and loss of consciousness. Finally, during the postictal phase the heifer was obtunded and disorientated, unable to perceive obstacles and hypermetric, and pressed its head against objects. In the inter‐seizure phase, the heifer was clinically normal. Neuropathology revealed axonal degeneration in the brainstem and diffuse astrocytic hypertrophic gliosis. Whole genome sequencing of the affected heifer identified a private heterozygous splice‐site variant in DYRK1B (NM_001081515.1: c.‐101‐1G>A), most likely resulting in haploinsufficiency owing to loss‐of‐function. This represents a report of a DYRK1B‐associated disease in cattle and adds DYRK1B to the candidate genes for epilepsy.