Kabuki syndrome and rare tumors in a young girl carrying a frameshift KMT2D mutation

Kabuki syndrome (KS) is a genetic disorder characterized by typical facial dimorphisms, various degrees of cognitive disability, and congenital anomalies involving the heart, kidneys, gastrointestinal system, and bones. It is accompanied by hypotonia, failure to thrive, obesity, and immunodeficiency. Association with neoplastic lesions has been recently described. We report a 13-year-old girl with KS, an insulinoma, and a benign phyllodes breast tumor with two hepatic lesions: a neuroendocrine tumor metastasis and a ciliated foregut cyst associated with hepatic fibrosis. She had a pilomatrixoma and a junctional melanocytic nevus with cytological atypia. Genetic analysis revealed a heterozygous frameshift variant in the KMT2D gene. Somatic KMT2D variants are in various types of tumors. The role of KMT2D variants in malignancies in KS appears to be related to defective transcription regulation and altered gene expression; however, the mechanism remains unclear. This aims to clarify the relationship between KMT2D gene variants, KS, and susceptibility to neoplastic lesions. For this purpose, a more extensive case series will be needed to accurately describe the patients' neoplastic phenotypes and precise genetic characterization.