LZTR1 encodes a substrate-specific adapter protein of the BCR (BTB-CUL3-RBX1) E3 ubiquitin-protein ligase complex that functions as a negative regulator of RAS-MAPK signaling 12. LZTR1 mediates ubiquitination of all three RAS isoforms (K-Ras, N-Ras, and H-Ras) at lysine-170, which attenuates their association with cell membranes and suppresses downstream signaling 12. Loss or inactivation of LZTR1 leads to decreased RAS ubiquitination, enhanced MAPK pathway activation, and increased membrane localization of RAS proteins 2. Disease-associated LZTR1 mutations impair either complex formation with CUL3 or RAS protein interaction, disrupting normal RAS regulation 1. Germline LZTR1 mutations predispose to multiple inherited conditions: autosomal dominant schwannomatosis (identified in ~80% of 22q-related cases lacking SMARCB1 mutations) 34, Noonan syndrome in both dominant and autosomal recessive patterns 15, and possibly other conditions including glioma 6. LZTR1 loss in Schwann cells specifically drives cellular dedifferentiation and proliferation 1. Notably, LZTR1 mutations identified in hepatocellular carcinoma genomic analyses suggest broader roles in cancer biology 7. Identifying LZTR1 variants is clinically important for differentiating schwannomatosis from other tumor predisposition syndromes.