Whole-exome screening for primary congenital glaucoma in Lebanon

Purpose: Mutations were previously identified in the CYP1B1 gene in six out of 18 Lebanese families (33%) with primary congenital glaucoma (PCG). The purpose of this study is to determine the frequency and type of pathogenic mutations in other genes and compare to other populations using whole-exome sequencing and perform genotype-phenotype correlations.

Methods: Twelve PCG patients previously negative for CYP1B1/MYOC mutations were subjected to whole-exome sequencing. Targeted screening for glaucoma-associated genes was performed. Candidate variants were verified by Sanger sequencing and evaluated in family members for segregation analysis and in 100 normal controls. Clinical correlations were established as to severity of disease presentation, course, and visual outcomes.

Results: Six mutations in known PCG-causing genes were identified in five patients: homozygous mutations in CYP1B1 (p.R368G), LTBP2 (p.E1013G), and TEK (p.T693I), and heterozygous mutations in FOXC1 (p.Q92*), TEK (c.3201-1 G>A), ANGPT1 (p.K186N), and CYP1B1 (p.R368G). Two patients, negative for CYP1B1 in the previous study, were revealed positive in the current study, due to different sets of primers and PCR conditions. Potentially damaging variants were noted in several candidate genes. Except for FOXC1 mutations, all genetic variants described here are novel. Intra-ocular pressure and final optic nerve cup-to-disc ratio were highest in the patient with three mutations in LTBP2/TEK/ANGPT1 genes.

Conclusion: This study provides new data on the spectrum of mutations of PCG in Lebanon. This highlights the genetic heterogeneity of the Lebanese population, noted for high rates of consanguinity in 50% in this cohort. This study emphasizes the importance of whole-exome sequencing in elucidating new candidate genes for PCG in the Lebanese.