Severe Epilepsy in an Individual With a TSC2 R905Q Variant Prompting Late Diagnosis in Affected Family Members

BACKGROUND: Tuberous sclerosis complex (TSC) is a multisystemic disorder caused by inactivating variants in the mTOR pathway inhibitor genes TSC1 and TSC2. Individuals with TSC are predisposed to benign tumors in multiple organs as well as TSC-associated neuropsychiatric disorders (TAND) and epilepsy. Pathogenic variants in TSC2 are typically associated with a more severe phenotype compared with TSC1; the TSC2 R905Q variant has been shown to be an exception, where patients have been reported to present with unusually mild TSC features that may be undetected. METHODS: We studied the TSC phenotype of a 13-year-old individual and three family members with a TSC2 c.2714G>A (R905Q) pathogenic variant. RESULTS: Patient 1 presented with severe medically refractory epilepsy without tubers or subependymal nodules and only mild dermatologic features of TSC missed on virtual examinations. Her mother and maternal aunt (Patients 2 and 3-diagnosed after age 50 years) presented with a mild phenotype, with dermatologic features and TAND. Her maternal uncle (Patient 4-diagnosed at age 47 years) displayed the most severe phenotype, presenting with intellectual disability, medically refractory epilepsy, obsessive-compulsive disorder, post-traumatic stress disorder, and psychosis. CONCLUSIONS: This study expands the possible phenotypic spectrum of TSC2 R905Q variant, demonstrating an association with severe epilepsy without associated neuroradiological stigmata. This presentation highlights the possibility of occult focal cortical dysplasia in TSC and emphasizes the importance of genetic testing in individuals with severe epilepsy. Moreover, a late adult diagnosis was subsequently made in other family members allowing for appropriate TSC surveillance to occur.