Noonan syndrome-associated biallelic LZTR1 mutations cause cardiac hypertrophy and vascular malformations in zebrafish.

BACKGROUND:Variants in the LZTR1 (leucine-zipper-like transcription regulator 1) gene (OMIM #600574) have been reported in recessive Noonan syndrome patients. In vivo evidence from animal models to support its causative role is lacking. METHODS:By CRISPR-Cas9 genome editing, we generated lztr1-mutated zebrafish (Danio rerio). Analyses of histopathology and downstream signaling were performed to investigate the pathogenesis of cardiac and extracardiac abnormalities in Noonan syndrome. RESULTS:A frameshift deletion allele was created in the zebrafish lztr1. Crosses of heterozygotes obtained homozygous lztr1 null mutants that modeled LZTR1 loss-of-function. Histological analyses of the model revealed ventricular hypertrophy, the deleterious signature of Noonan syndrome-associated cardiomyopathy. Further, assessment for extracardiac abnormalities documented multiple vascular malformations, resembling human vascular pathology caused by RAS/MAPK activation. Due to spatiotemporal regulation of LZTR1, its downstream function was not fully elucidated from western blots of adult tissue. CONCLUSION:Our novel zebrafish model phenocopied human recessive Noonan syndrome and supported the loss-of-function mechanism of disease-causing LZTR1 variants. The discovery of vascular malformations in mutants calls for the clinical follow-up of patients to monitor for its emergence. The model will serve as a novel platform for investigating the pathophysiology linking RAS/MAPK signaling to cardiac and vascular pathology.

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