Variants in PAX6, PITX3 and HSF4 causing autosomal dominant congenital cataracts

Abstract

Background: Lens development is orchestrated by transcription factors. Disease-causing variants in transcription factors and their developmental target genes are associated with congenital cataracts and other eye anomalies.

Methods: Using whole exome sequencing, we identified disease-causing variants in two large British families and one isolated case with autosomal dominant congenital cataract. Bioinformatics analysis confirmed these disease-causing mutations as rare or novel variants, with a moderate to damaging pathogenicity score, with testing for segregation within the families using direct Sanger sequencing.

Results: Family A had a missense variant (c.184 G>A; p.V62M) in PAX6 and affected individuals presented with nuclear cataract. Family B had a frameshift variant (c.470-477dup; p.A160R*) in PITX3 that was also associated with nuclear cataract. A recurrent missense variant in HSF4 (c.341 T>C; p.L114P) was associated with congenital cataract in a single isolated case.

Conclusions: We have therefore identified novel variants in PAX6 and PITX3 that cause autosomal dominant congenital cataract.

Fig. 1. Pedigrees and sequence analysis.

a Family A: Abridged pedigree with nuclear cataract; Family B: Abridged pedigree with nuclear cataract. The diagonal line indicates a deceased family member. Squares and circles symbolise males and females, respectively. Open and filled symbols indicate unaffected and affected individuals, respectively. Diamond symbolises-number of unaffected siblings grouped together. The arrow indicates the family members who participated in the WES analysis. All the available members in the family were sequenced to show the segregation. b Sequence analysis of (a): PAX6–missense variant c.184 G>A in affected member of family A with nuclear cataract; (c) PITX3-a frameshift variant at c.470–477dup in an affected member of family B with nuclear cataract; (d) HSF4- missense variant c.341 T>C in an affected individual with congenital cataract.

Fig. 2. Structural view of PAX6 and HSF4 proteins.

A Crystal structure of the human PAX-6 paired domain-dna complex reveals a general model for PAX protein-dna interactions- X-ray diffraction, 2.50 A monomer (4-133 aminoacids). Wt -V62 PAX6: https://swissmodel.expasy.org/repository/uniprot/P26367 Mut - M62-PAX6: https://swissmodel.expasy.org/interactive/1hpd5p/models/. B Structure of the DNA-binding domain of HSF2 with sequence homology to HSF4 at aminoacids position (pro18-Val121). Wt: L114 https://swissmodel.expasy.org/interactive/0QmfH7/models/ Heat shock factor protein 2-Human HSF2 DNA Binding Domain in complex with 3-site HSE DNA at 2.1 Angstroms Resolution; Mut: P114 https://swissmodel.expasy.org/interactive/Fx4QGZ/models/.

Fig. 3. Frequency and phenotypic presentation of PITX3.

a Spectrum of PITX3 variants showing cataract phenotypes and anterior segment dysgenesis; (b) Frequency pie chart of PITX3 variants to date.