Leucine zipper-like transcription regulator 1 (LZTR1) acts as a negative factor that suppresses RAS function and MAPK signaling; mutations in this protein may dysregulate RAS ubiquitination and lead to impaired degradation of RAS superfamily proteins. Germline variants are reported in Noonan syndrome, either autosomal dominant or autosomal recessive, and in susceptibility to schwannomatosis. This article explores the genetic and phenotypic diversity of the autosomal dominant -related disorders, compiling a cohort of previously published patients (51 with the Noonan phenotype and 123 with schwannomatosis) and presenting two additional adult-onset cases: a male with schwannomatosis and Parkinson's disease and a female with Noonan syndrome, generalized joint hypermobility, and breast cancer. This review confirms that autosomal dominant -related disorders exhibit an extreme phenotypic variability, ranging from relatively mild manifestations to severe and multi-systemic involvement, and offers updated frequences of each clinical feature. The aim is to precisely define the clinical spectrum of -related diseases, using also two new emblematic clinical cases. Gaining insight into the mechanisms underneath this variability is crucial to achieve precision diagnostics and the development of therapeutic interventions.