Novel SIX6 mutations cause recessively inherited congenital cataract, microcornea, and corneal opacification with or without coloboma and microphthalmia

• Published in: Molecular vision Vol. 28; pp. 57 - 69
• Main Authors: Panagiotou, Evangelia S, Fernandez-Fuentes, Narcis, Farraj, Layal Abi, McKibbin, Martin, Elçioglu, Nursel H, Jafri, Hussain, Cerman, Eren, Parry, David A, Logan, Clare V, Johnson, Colin A, Inglehearn, Chris F, Toomes, Carmel, Ali, Manir
• Format: Journal Article
• Language: English
• Published: United States Molecular Vision 2022
• Subjects: Amino acids; Aspartic acid; Cataract - congenital; Cataract - genetics; Cataracts; Coloboma - genetics; Congenital diseases; Conserved sequence; Copy number; Cornea; Corneal Diseases - genetics; Deoxyribonucleic acid; DNA; DNA - genetics; DNA Copy Number Variations; DNA microarrays; DNA Mutational Analysis; Evolutionary conservation; Eye Abnormalities - genetics; Eye diseases; Gene deletion; Gene mapping; Histidine; Homeobox; Homeodomain Proteins - genetics; Humans; Microphthalmia; Microphthalmos - genetics; Mutation; Nucleotide sequence; Pedigree; Phenotype; Phenotypes; Proteins; Single-nucleotide polymorphism; SIX gene family; Trans-Activators - genetics
• ISSN: 1090-0535; 1090-0535

To investigate the molecular basis of recessively inherited congenital cataract, microcornea, and corneal opacification with or without coloboma and microphthalmia in two consanguineous families. Conventional autozygosity mapping was performed using single nucleotide polymorphism (SNP) microarrays. Whole-exome sequencing was completed on genomic DNA from one affected member of each family. Exome sequence data were also used for homozygosity mapping and copy number variation analysis. PCR and Sanger sequencing were used to confirm the identification of mutations and to screen further patients. Evolutionary conservation of protein sequences was assessed using CLUSTALW, and protein structures were modeled using PyMol. In family MEP68, a novel homozygous nucleotide substitution in was found, c.547G>C, that converts the evolutionarily conserved aspartic acid residue at the 183 amino acid in the protein to a histidine, p.(Asp183His). This residue mapped to the third helix of the DNA-binding homeobox domain in SIX6, which interacts with the major groove of double-stranded DNA. This interaction is likely to be disrupted by the mutation. In family F1332, a novel homozygous 1034 bp deletion that encompasses the first exon of was identified, chr14:g.60975890_60976923del. Both mutations segregated with the disease phenotype as expected for a recessive condition and were absent from publicly available variant databases. Our findings expand the mutation spectrum in this form of inherited eye disease and confirm that homozygous human mutations cause a developmental spectrum of ocular phenotypes that includes not only the previously described features of microphthalmia, coloboma, and congenital cataract but also corneal abnormalities.