Recessive variants in WSB2 encoding a substrate receptor of E3 ubiquitin ligase underlie a neurodevelopmental syndrome

Abstract

WD40 and SOCS box protein-2 (WSB2), a member of the large family of suppressor of cytokine signaling (SOCS)-box proteins, has recently been identified as a substrate receptor of cullin 5 E3 ligase that plays an important role in proteomic regulation through substrate ubiquitination and proteasomal degradation. Here we report five patients from four unrelated families presenting with neurodevelopmental delay, dysmorphic features, brain structural abnormalities with or without growth restriction, hypotonia, and microcephaly, all of whom are homozygous for extremely rare and predicted loss-of-function (pLoF) or missense variants in WSB2, inherited from consanguineous parents. The Wsb2-mutant mice exhibited several neurological findings that included hyperactivity, altered exploration, and hyper alertness. They also weighed less, had a lower heart rate, and presented an abnormal retinal blood vessel morphology and vasculature pattern along with decreased total thickness of the retina. Our findings suggest that homozygous LoF WSB2 variants cause a novel neurodevelopmental disorder in humans with similar neurologic and developmental findings seen in Wsb2-mutant mouse models.

Fig. 1. Identification of WSB2 variants in five patients featuring syndromic NDDs.

A Representative schematic of WSB2 gene (NM_018639.5) containing seven WD-repeats and a suppressor of cytokine signaling (SOCS) box in the C-terminus. The WSB2 variants are positioned in WD1, WD2, and SOCS box domain, respectively. B Molecular modeling of WSB2 missense variant (NM_018639.5: c.1121G>A, p.Arg374Gln). As shown in the top panel, the wildtype residue’s (Arg374, red) positively charged side chain interacts with the aromatic rings of Phe398 and Phe404 (shown in blue), helping stabilize this region. In contrast, the side chain of Gln374 (red, bottom panel) forms weaker hydrophobic contacts with these phenylalanine, thereby potentially increasing local flexibility of the SOCS box domain. C Representative magnetic resonance imaging (MRI) of patient 2 with homozygous c.399del p.(Q134Rfs*14) at 12 months of age. (i) Sagittal T1-weighted MRI showing microcephaly, callosal hypogenesis (white arrow), tectal dysplasia (yellow arrow), and severe cerebellar hypoplasia/atrophy (dotted oval). (ii and iii) Axial T1- and T2-weighted MRI show undersulcation and white matter hypomyelination for age. (iv-vi) Coronal T2-weighted with fat suppression show small olfactory bulbs (black arrows), optic nerves (white arrows), and hippocampi (yellow arrows).

Fig. 2. Wsb2-mutant mice exhibited with lower body weight and retinal abnormalities in both males and females.

A Shows the body weight at different ages (4–15 week) between control and Wsb2-mut mice. n = 7–8 mice per group and per genotype, median and interquartile range shown. B–E Show the retinal abnormalities in Wsb2-mut mice, including irregular retinal blood vessel morphology (B, D) and reduced total retinal thickness (C, E) as shown in the left eye. For control group: n = 15, 8 females and 7 males; and for Wsb2-mut mice: n = 11, 6 females and 5 males. The right eye showed a similar phenotype. Red boxes in (C) represent an arbitrary evaluation of total retinal thickness, using equally sized rectangles over the retinal layers in control and Wsb2-mut mice to illustrate the reduction in thickness across all retinal layers.

Fig. 3. Behavioral testing revealed decreased exploratory behavior in response to a novel environment and blunted acoustic reactivity in Wsb2-mutant mice.

In the novel open field test, the mutant mice showed decreased rearing activity (A) and decreased resting time (B) when compared to control mice. C Prepulse Inhibition (PPI)/Acoustic Startle Response (ASR) testing showed decreased acoustic reactivity in the mutant mice at lower non-startling sound pressure levels. Con control, mut mutant, NS no stimulus.