Weiss–Kruszka syndrome (WSKA, MIM: 618,619) is a multiple congenital anomaly syndrome. WSKA is characterized by ptosis, growth restriction, craniofacial deformities, and corpus callosum hypoplasia (Weiss et al., 2017). Recent evidence revealed that WSKA is caused by the loss-of-function (LOF) variations in the ZNF462 gene or deletions on chromosome 9 p 31.2 containing the ZNF462 gene. Additionally, this genetic disease is inherited in an autosomal dominant manner, which often results from new variants. So far, only 27 cases of ZNF462 gene variation have been reported globally (Weiss et al., 2017; Cosemans et al., 2018; Kruszka et al., 2019; González-Tarancón et al., 2020; Iivonen et al., 2021; Park et al., 2021), and the underlying mechanism of the syndrome has not been extensively studied. This study reported a family in which both the child and his father had WSKA with ptosis and hearing loss. The diagnosis was established based on clinical symptoms and gene tests. Through trio-whole-exome sequencing (trio-WES), a novel nonsense variant in the ZNF462 gene was identified in the child and his father. With the first pedigree analysis of WSKA in China, the study enriched the variant spectrum of the ZNF462 gene and enhanced the knowledge of clinical features, genetic characteristics, and diagnostic protocols for WSKA.

The ZNF462 gene, consisting of 13 exons, is located on chromosome 9q31.2. It encodes a protein (2,506 amino acids) with 27 C2H2 zinc finger structures, which participates in transcriptional regulation and the remodeling of the chromosome by bonding with DNA molecules (Nagase et al., 2001; Massé et al., 2010; Eberl et al., 2013). The zinc finger protein is highly conserved in most mammals. It is localized in the nucleus and widely expressed in various human tissues (Fagerberg et al., 2014). While the specific function of the protein has not been established, some studies on animal models demonstrated that ZNF462 could play a vital role in embryonic development. For instance, the downregulation of Zfp462 (ZNF462) gene expression in Xenopus laevis could interfere with early embryonic development by altering the cell division at the cleavage stage; however, this phenotype could be compensated through the introduction of additional human ZNF462 mRNA (Laurent et al., 2009). In another study, the Zfp462 knockout mice showed prenatal lethality and the heterozygous (Zfp462 ^+/−) mice developed diverse symptoms including low body weight, delayed brain weight development, anxiety-like behavior, and hair loss (Wang et al., 2017).

Given the evidence obtained from previous articles, the haploinsufficiency of the ZNF462 gene is the genetic cause of WSKA. In clinical studies, WSKA is characterized by the mild and overall developmental delay with variable craniofacial abnormalities (typically ptosis, abnormal skull shape, lower oblique eyelid fissure, epicanthus, arched eyebrows, and short nose, etc.), while hypotonia and feeding difficulty are usually observed. Furthermore, a few cases reported dysplasia of the corpus callosum on brain imaging (Kruszka et al., 2019). By summarizing the existing cases (27 patients in the published reports and two patients from this study, in Table 1), it was found that ptosis, developmental delay, and autism are common manifestations in WSKA patients. Also, four out of the 27 patients had hearing impairments. Most patients were studied individually. Out of the reported cases, two cases resulted from the paternal inheritance, with a case resulting from the maternal inheritance, while another case was found to be due to maternal low-proportion mosaic (the mosaic ratio was 17%). This study discovered a new case with paternal inheritance in the Chinese population: the child had a paternal inheritance, but his father was de novo. They carried a novel nonsense variant c.6431C > A (p.S2144∗) in the ZNF462 gene (NM_021224.6) found by using whole-exome sequencing, whereas the variant was not present in other tested family members. Both of them showed typical unilateral ptosis and unilateral hearing impairment. These findings indicated that the variant c.6431C > A (p.S2144∗) in the ZNF462 gene could be associated with WSKA. The child showed a mild asymmetrical crying face during the neonatal period, and further had mild hypotonia and developmental delay. Pathogenic CNV was undetectable. Therefore, it is speculated that the observed clinical feature of WSKA could be individually specific.

By January 2021, the HGMD® database has recorded 24 ZNF462 gene variants, including five nonsense variants, 12 frameshift variants, three missense variants, one splicing variant, two large fragment deletion variants, and one chromosome balanced translocation. These reported variants are mostly found in exon 3 of the ZNF462 gene (Figures 1C,a), which may be related to exon 3 is the largest exon of the gene. The variant c.6431C > A (p.S2144∗) found in this study was located in exon 8 of the ZNF462 gene, and there were several pathogenic nonsense variants reported in the downstream of c.6431C > A (p.S2144∗). This point further confirms the pathogenicity of the variant. In addition, the variant may undergo nonsense-mediated decay (NMD), which may lead to heterozygous loss of ZNF462 transcript and consequently result in the disease phenotype. Moreover, the variant c.6431C > A (p.S2144∗) was located in the region between the 21st and 22nd C2H2 zinc finger structures, and it causes amino acid deletion from amino acids 2,144 (Figure 1C,b), leading to the absence of the last six zinc finger structures. Hence, this variant was assumed to be responsible for DNA binding impairment and the subsequent protein dysfunction, which needs to be investigated in subsequent studies.

This is the first pedigree of WSKA in China. A novel nonsense variant c.6431C > A (p.S2144∗) in the ZNF462 gene was identified in the proband and his father; this finding enriched the variant spectrum of the ZNF462 gene. The proband and his father showed unilateral ptosis and unilateral hearing impairment which were typical symptoms of WSKA (Table 1), so they were diagnosed combined with the sequencing result. The mild asymmetrical crying face during the neonatal period only showed in the proband could be individually specific, and the role of the pathogenic variant in this case required further investigation. The inheritance type of the proband was paternal, and de novo mutations were still the main way of inheritance in all the reported WSKA cases (Table 1). This study provided more clinical and genetic evidence to support the haploinsufficiency of the ZNF462 gene proposed by earlier studies. The novel variant and phenotypes seen in this family contributed to understanding the clinical features, genetic characteristics, and diagnostic protocols for WSKA.

While WES has facilitated the identification of pathogenic gene variants for many rare diseases (Yang et al., 2014), the increasing knowledge will improve the diagnosis accuracy of rare diseases and contribute to the prediction or the prevention of birth defects. Combined with trio-WES analysis, the patients in this study were finally diagnosed. Besides the traditional diagnostic approach, the introduction of trio-WES can lead to the effective identification and differentiation of the variants, and thus offer feasible support for clinical diagnosis and treatment.