This report presents an illustrative case of a presenilin-1 mutation presenting with isolated spastic paraplegia. Denovo L381V mutations in the PSEN1 gene have been reported in individuals presenting with spastic paraplegia and followed by EOAD as early as the third decade of life. Given the high penetrance of PSEN1-associated EOAD, the patient will likely develop dementia. This case study illustrates both the yield and challenges of using broad genetic testing such as WES in clinical practice. The results of this patient’s WES demonstrated that they were at risk of a more severe neurodegenerative disease, and demanded intensive genetic counseling and support to the patient and family.