Au-Kline syndrome (AKS) is a neurodevelopmental disorder associated with multiple malformations and a characteristic facial gestalt. The first individuals ascertained carried de novo loss-of-function (LoF) variants in HNRNPK. Here, we report 32 individuals with AKS (26 previously unpublished), including 13 with de novo missense variants. We propose new clinical diagnostic criteria for AKS that differentiate it from the clinically overlapping Kabuki syndrome and describe a significant phenotypic expansion to include individuals with missense variants who present with subtle facial features and few or no malformations. Many gene-specific DNA methylation (DNAm) signatures have been identified for neurodevelopmental syndromes. Because HNRNPK has roles in chromatin and epigenetic regulation, we hypothesized that pathogenic variants in HNRNPK may be associated with a specific DNAm signature. Here, we report a unique DNAm signature for AKS due to LoF HNRNPK variants, distinct from controls and Kabuki syndrome. This DNAm signature is also identified in some individuals with de novo HNRNPK missense variants, confirming their pathogenicity and the phenotypic expansion of AKS to include more subtle phenotypes. Furthermore, we report that some individuals with missense variants have an "intermediate" DNAm signature that parallels their milder clinical presentation, suggesting the presence of an epi-genotype phenotype correlation. In summary, the AKS DNAm signature may help elucidate the underlying pathophysiology of AKS. This DNAm signature also effectively supported clinical syndrome delineation and is a valuable aid for variant interpretation in individuals where a clinical diagnosis of AKS is unclear, particularly for mild presentations.

Okamoto syndrome is characterized by severe intellectual disability, generalized hypotonia, stenosis of the ureteropelvic junction with hydronephrosis, cardiac anomalies, and characteristic facial gestalt. Several patients have been reported. The basic mechanism of Okamoto syndrome has not been clarified. Au-Kline syndrome is a new syndrome due to loss-of-function variants in the HNRNPK (heterogeneous nuclear ribonucleoprotein K) gene. A new patient with Okamoto syndrome visited our hospital. We noticed that the patient had features overlapping with Au-Kline syndrome. We studied the HNRNPK gene by Sanger sequencing, and identified a novel splicing variant. We suggest that Okamoto syndrome is identical to Au-Kline syndrome.