Under the mask of Kabuki syndrome: Elucidation of genetic-and phenotypic heterogeneity in patients with Kabuki-like phenotype.

Kabuki syndrome is mainly caused by dominant de-novo pathogenic variants in the KMT2D and KDM6A genes. The clinical features of this syndrome are highly variable, making the diagnosis of Kabuki-like phenotypes difficult, even for experienced clinical geneticists. Herein we present molecular genetic findings of causal genetic variation using array comparative genome hybridization and a Mendeliome analysis, utilizing targeted exome analysis focusing on regions harboring rare disease-causing variants in Kabuki-like patients which remained KMT2D/KDM6A-negative. The aCGH analysis revealed a pathogenic CNV in the 14q11.2 region, while targeted exome sequencing revealed pathogenic variants in genes associated with intellectual disability (HUWE1, GRIN1), including a gene coding for mandibulofacial dysostosis with microcephaly (EFTUD2). Lower values of the MLL2-Kabuki phenotypic score are indicative of Kabuki-like phenotype (rather than true Kabuki syndrome), where aCGH and Mendeliome analyses have high diagnostic yield. Based on our findings we conclude that for new patients with Kabuki-like phenotypes it is possible to choose a specific molecular testing approach that has the highest detection rate for a given MLL2-Kabuki score, thus fostering more precise patient diagnosis and improved management in these genetically- and phenotypically heterogeneous clinical entities.