New variation and clinical phenotype analysis of CRYBA4 gene in a family with congenital cataract

Objective  To explore the clinical characteristics and genetic etiology of a congenital cataract family.

Methods  A pedigree investigation was performed. A Chinese Han family with congenital cataract diagnosed in the Department of Ophthalmology of the Fourth Hospital of Shijiazhuang in May 2022 was enrolled. Ophthalmological clinical diagnoses were performed on the proband and certain members of the family. Whole exome sequencing (WES) was performed on the proband to screen for congenital cataract-related variants, and Sanger sequencing was performed on other family members. MutationTaster, PolyPhen-2, PROVEN, and REVEL software were used to analyze the pathogenicity of newly discovered variant sites; UGENE software was used to assess the conservation of variant sites in multiple species; SWISS-MODEL software was used to compare the differences in three-dimensional structure between variant proteins and wild-type proteins. The data of the new variation site were analyzed according to the American College of Medical Genetics and Genomics (ACMG) classification and guidelines for genetic variation. This study adhered to the Declaration of Helsinki. The research protocol was approved by the Ethics Committee of The Fourth Hospital of Shijiazhuang (No. 20230074). Both the subjects and their guardians were informed of the study purpose and voluntarily signed the informed consent form.

Results  This family consisted of 50 individuals in 4 generations, including 11 patients, with the male to female ratio of 1∶1, and every generation had patients. This family conformed to autosomal dominant inheritance. The clinical manifestation was total opacification of the crystalline lens in both eyes, all of which had free onset. WES results indicated that there was a new heterozygous variation c. 220T>C in exon 4 of the CRYBA4 gene in the proband, which resulted in the variation of amino acid 74 from tyrosine to histidine (p.Y74H). Sanger sequencing results confirmed that the variation was consistent with family co-segregation. The prediction results of MutationTaster, PolyPhen-2, PROVEN and REVEL software all showed that the variation was pathogenic or harmful; the analysis results of UGENE software showed that this locus was highly conserved among many species including human, horse, dog, cattle and chimpanzee; protein structure prediction showed that after the variation of this locus, the two hydrogen bonds between TYR-74 and GLU-70 were lost, and the structure around the mutation site in Greek Key Domain II was partially destroyed, which might affect the stability and function of the protein structure. According to the ACMG guideline score (PM2+ PP3+ PP1+ PP4+ PP5), the variation site might cause disease.

Conclusions  The missense variation of the CRYBA4 gene, c. 220T>C (p.Y74H), might be the genetic cause of congenital cataract in this family. This is the first report of this variant.