Hannah Fry

Tuberous sclerosis complex (TSC) is an autosomal dominant neurocutaneous disorder caused by heterozygous mutations in either the TSC1 or TSC2 gene. Mutation of the TSC genes leads to constitutive activation of the mechanistic target of the rapamycin (mTOR) signaling pathway. Phenotype variation can be seen even within a single-family called “intrafamilial phenotypic variability (IPV),” where all affected individuals have the same TSC gene mutation. IPV indicates that TSC1 or TSC2 mutation alone does not account for the observed phenotype. We hypothesized that IPV is caused by alterations in protein expression of genes within the mTOR pathway. We established patient-derived fibroblast cell lines from the parent with mild phenotype and children with severe who carried the same TSC2 mutations and analyzed the mTOR pathway activity through western blot. Western blot quantitative analysis revealed increased expression and activation of p70S6K, one of the downstream effectors in mTOR signaling in cells from the child with severe disease compared to both control and parent fibroblasts. Our results indicate a significant difference in the mTOR pathway activity between mild and severely affected patients within a family. We have also found that children with severe phenotypes carry germline variants in mTOR pathway genes. Future functional studies will validate the direct link between genetic variants in the mTOR pathway (genetic modifiers) and mTOR activity that contributes to the phenotypic variability in TSC.