Katarzyna Klonowska, PhD
Katarzyna Klonowska, Joannes M. Grevelink, Krinio Giannikou, Eleonora Aronica, Barbara A. Ogorek, Zachary T. Herbert, Aaron R. Thorner, Thomas N. Darling, Joel Moss, and David J. Kwiatkowski
David J. Kwiatkowski
Research Category: Cancer
Background: Tuberous sclerosis complex (TSC) is due to TSC1/TSC2 mutations and is characterized by multiple tumors, including facial angiofibroma (FAF) and cortical tubers. Here we explored mutation second-hit events in TSC tumors.
Methods: We developed a Multiplex High-sensitivity PCR Assay (MHPA), enabling mutation detection at extremely low (150,000 incipient facial tumors (subclinical ‘micro-FAFs’) in average TSC subject (Klonowska,JCI,2022). TSC1-MHPA of 6 TSC-FAF with TSC1 mosaicism showed that UV-mutations are much less common in TSC1 (average:0.8 mutations) than in TSC2 (average:4.8 mutations,p=0.006). TSC2-MHPA of TSC brain tubers identified 9 nonsynonymous SNV/indel second-hits in 6 of 13 (46%) tubers (median VAF:0.06%).
Conclusions: Our TSC2-MHPA analysis of TSC FAF revealed that TSC facial skin can be viewed as harboring a patchwork of clonal fibroblast proliferations (micro-FAFs) with indolent growth, a small proportion of which develop into clinically observable FAF. Such lesions are much less common in TSC1 than in TSC2 patients. TSC2-MHPA analysis of TSC tubers identified low VAF second-hit TSC2 mutations in some lesions; their relationship to tuber development requires further study.
Tuberous sclerosis complex (TSC) is a human disorder due to genetic changes in one of the two genes, called TSC1 and TSC2. TSC is characterized by tumors in multiple body sites, including facial angiofibromas which are small reddish bumps on the nose and cheeks, and brain tumors called tubers. We have developed a very sensitive method to identify genetic changes in TSC1 and TSC2 that occur at very low frequency, in less than 1% of analyzed cells. We call our new method MHPA for short. Our MHPA analysis revealed that there are thousands of small tumors developing in the facial skin of TSC patients as a result of sunlight UV radiation and mutations in TSC2. Most of these tumors are not visible clinically. We further discovered that such facial tumors are much less common in TSC1 than in TSC2 patients. TSC2-MHPA analysis of TSC brain tubers identified low frequency TSC2 mutations in some samples, that will be studied further and validated. These are novel findings providing new insights for understanding of TSC tumor development.