Chinese Family With Knobloch Syndrome Associated With a Novel PAK2 Variant Leading to Reduced Phosphorylation Levels.

Background: Biallelic variants of COL18A1 cause Knobloch syndrome (KNO), a rare genetic disorder, characterized by oculopathy and structural defects. Recently, several studies have suggested that novel de novo missense variants in PAK2 may be associated with KNO; however, there are few case reports. This study aimed to investigate a patient with KNO who initially presented with seizures and expand the PAK2 genotype and phenotype spectrum.

Methods: This study included a Chinese family with a proband who primarily presented with epilepsy and developmental delay. Whole-exome sequencing and Sanger sequencing were performed to analyze potential variants. Structural modeling was performed to assess the impact of the variant on the protein structure. In vitro, a mutant plasmid was constructed and transfected into 293T cells to conduct phosphorylation assays, and phosphorylation levels at Ser141 of PAK2 were assessed. The PAK kinase inhibitor FRAX597 was used to confirm the specificity of the western blot results.

Results: A de novo variant of PAK2 gene, NM_002577.4: c.1049G>A (p.Arg350Lys) was found in the patient but not in his parents or sister. This variant was found to be located in the kinase domain and may alter the hydrogen-bond network, potentially affecting kinase activity. In vitro functional experiments demonstrated that the variant may lead to reduced protein levels. Moreover, Western blot analysis showed a significant decrease in the phosphorylation level at Ser141 compared to the wild-type plasmid, indicating that the variant may lead to decreased PAK2 phosphorylation levels.

Conclusion: The clinical manifestations in this patient may be associated with a novel PAK2 variant, and the atypical presentation of KNO suggests that PAK2-related KNO may have a broader phenotypic spectrum.