A Case of <scp>HNRNPU</scp> ‐Related Neurodevelopmental Disorder Presenting With Acute Encephalopathy and Basal Ganglia Lesions

We report a case in which a girl diagnosed with HNRNPU-associated neurodevelopmental disorder presented with acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) and generalized hypotonia accompanied by chorea-like involuntary movements. On the first day of hospitalization, she presented with fever and generalized clonic seizures. Twenty four hours later, she continued to experience impaired consciousness and generalized hypotonia. Her consciousness improved gradually, but chorea-like involuntary movements of the limbs were observed. From the seventh day of hospitalization, the patient repeatedly experienced difficulty in making eye contact for 20-30 s for 2-3 days. Brain MRI with diffusion-weighted imaging revealed hyperintensity from the bilateral frontal cortex to subcortical white matter and the bilateral caudate nuclei. This patient presented with chorea-like involuntary movements and generalized hypotonia, and was unable to perform antigravity movements. HNRNPU-related neurodevelopmental disorders often present with congenital hypotonia. When affected children develop acute encephalopathy associated with basal ganglia lesions, the synergistic effect of these conditions may exacerbate the hypotonia.