DNA SEQUENCING OF CYP1B1 GENE IN FAMILIES WITH INHERITED GLAUCOMA

Abstract

Primary congenital glaucoma (PCG) is a rare autosomal recessive disorder which presents during early infancy. The signs and symptoms of PCG include reduced visual acuity, enlargement of globe, blepharospasm, edema, corneal opacification and photophobia. Two genes, CYP1B1 and LTBP2 along with two chromosomal loci have been mapped for PCG so far. CYP1B1 (cytochrome P4501B1) located at GLC3A locus is considered as most commonly mutated gene in PCG. Frequency of CYP1B1 mutations which cause PCG differs among different populations ranging from less than 10% to 100%. There is great diversity of mutation spectrum of CYP1B1 gene studied in the pathogenesis of PCG worldwide. In this study affected and healthy individuals of 7 Pakistani families, affected with congenital or early onset glaucoma, were collected for CYP1B1 mutation analysis. Sanger sequencing of coding exons and splice sites of CYP1B1 gene identify potentially pathogenic variants in three families. The identified variants include a novel homozygous c.353C>T (p.Pro118Leu) mutation and a known mutation c.1169G>A(p.Arg390His) in family B and F respectively. Both the mutations were predicted as pathogenic and disease causing by majority of the bioinformatics tools. A known mutation (p.Glu229Lys) was also identified in family C but further testing in Pakistani control individuals indicated high frequency of variant allele. This finding in family C casts doubt on the pathogenic nature of p.Glu229Lys variant and probably indicates a Pakistani population specific polymorphism. Additionally we also found other novel variants including c.673C>A (p.Leu225Ile), c.355G>T (p.Ala119Ser), c.1347T>C, c.515G>A (p.Ser172Asn), c.142C>G (p.Arg48Gly), c.1358A>G (p.Asn453Ser) and c.1059G>AinCYP1B1. But further analyses failed to indicate the pathogenic nature of these variants and majority of these were also present in public databases. The identification of CYP1B1 mutations in 28% families (2 out of 7) in this study indicates that mutations in this gene are the major cause of PCG in Pakistan as well. Additional work is required to identify the underlying mutations in the remaining five families.