Comprehensive Genetic Analysis Results of TSC1/TSC2 Genes in Patients with Clinical Suspicion of Tuberous Sclerosis Complex and Definition of 3 Novel Variants

BACKGROUND: Tuberous Sclerosis Complex is an autosomal dominant multi-system disorder with an incidence of about 1 in 6000 live births. Defects in either TSC1 (* 605284) or TSC2 (* 191092) genes encoding the components of the Tuberous Sclerosis Complex are responsible for the disease. Therefore, consideration of TSC1/TSC2 pathogenic variations is recommended in the updated diagnostic criteria of Tuberous Sclerosis Complex. AIMS: To present the TSC1/TSC2 screening results of a mixed patient population as well as possible new variants in 23 cases from 20 different families who were referred to our Genetic Diseases Diagnosis Center with the signs and symptoms of Tuberous Sclerosis Complex. STUDY DESIGN: Retrospective, cross-sectional study. METHODS: Germline TSC1/TSC2 variants were screened in DNA samples extracted from peripheral blood samples of 23 patients from 20 unrelated families using targeted high-throughput sequencing and multiplex ligation-dependent probe amplification methods. The variants identified were classified according to ACMG 2015 guidelines. RESULTS: In total, 5 different pathogenic/likely pathogenic changes have been defined. All these pathogenic/likely pathogenic variants were located in the TSC2 gene. Three of the pathogenic/likely pathogenic variants were novel. Two patients who are twin sisters were found to have TSC2/PKD1 contiguous deletion syndrome. One of the 3 novel variants was a mosaic in-frame deletion. We did not identify any pathogenic variants of the TSC1 gene. CONCLUSION: The novelty of most of the variants found, including a mosaic likely pathogenic variant, and the presence of a large genomic rearrangement, supports the importance of a comprehensive approach in analyzing TSC1/TSC2 genes. Genetic diagnosis should be performed with caution, considering the possibility of mosaic variants with low allelic fractions.