RFC2 may contribute to the pathogenicity of Williams syndrome revealed in a zebrafish model.

Williams syndrome (WS) is a rare multisystemic disorder caused by recurrent microdeletions on 7q11.23, characterized by intellectual disability, distinctive craniofacial and dental features, and cardiovascular problems. Previous studies have explored the roles of individual genes within these microdeletions in contributing to WS phenotypes. Here, we report five patients with WS with 1.4 Mb-1.5 Mb microdeletions that include RFC2, as well as one patient with a 167 kb microdeletion involving RFC2 and six patients with intragenic variants within RFC2. To investigate the potential involvement of RFC2 in WS pathogenicity, we generate a rfc2 knockout (KO) zebrafish using CRISPR-Cas9 technology. Additionally, we generate a KO zebrafish of its paralog gene, rfc5, to better understand the functions of these RFC genes in development and disease. Both rfc2 and rfc5 KO zebrafish exhibit similar phenotypes reminiscent of WS, including small head and brain, jaw and dental defects, and vascular problems. RNA-seq analysis reveals that genes associated with neural cell survival and differentiation are specifically affected in rfc2 KO zebrafish. In addition, heterozygous rfc2 KO adult zebrafish demonstrate an anxiety-like behavior with increased social cohesion. These results suggest that RFC2 may contribute to the pathogenicity of Williams syndrome, as evidenced by the zebrafish model.

Variants in ZFX are associated with an X-linked neurodevelopmental disorder with recurrent facial gestalt.

Pathogenic variants in multiple genes on the X chromosome have been implicated in syndromic and non-syndromic intellectual disability disorders. ZFX on Xp22.11 encodes a transcription factor that has been linked to diverse processes including oncogenesis and development, but germline variants have not been characterized in association with disease. Here, we present clinical and molecular characterization of 18 individuals with germline ZFX variants. Exome or genome sequencing revealed 11 variants in 18 subjects (14 males and 4 females) from 16 unrelated families. Four missense variants were identified in 11 subjects, with seven truncation variants in the remaining individuals. Clinical findings included developmental delay/intellectual disability, behavioral abnormalities, hypotonia, and congenital anomalies. Overlapping and recurrent facial features were identified in all subjects, including thickening and medial broadening of eyebrows, variations in the shape of the face, external eye abnormalities, smooth and/or long philtrum, and ear abnormalities. Hyperparathyroidism was found in four families with missense variants, and enrichment of different tumor types was observed. In molecular studies, DNA-binding domain variants elicited differential expression of a small set of target genes relative to wild-type ZFX in cultured cells, suggesting a gain or loss of transcriptional activity. Additionally, a zebrafish model of ZFX loss displayed an altered behavioral phenotype, providing additional evidence for the functional significance of ZFX. Our clinical and experimental data support that variants in ZFX are associated with an X-linked intellectual disability syndrome characterized by a recurrent facial gestalt, neurocognitive and behavioral abnormalities, and an increased risk for congenital anomalies and hyperparathyroidism.