Familial encephalopathy with neuroserpin inclusion bodies (FENIB) is a rare genetic disorder characterized by progressive cognitive decline and myoclonic epilepsy, caused by pathogenic variants of SERPINI1. We reported a case of genetically confirmed FENIB with de novo H338R mutation in the SERPINI1, in which frontal deficits including inattention and disinhibition, and relevant atrophy in the vmPFC on brain MRI were observed in the early stage of the disease. This evidence concerns the gene SERPINI1 and Mental deterioration.