Abstract
Purpose :
Primary congenital glaucoma (PCG) is a rare, leading cause of childhood blindness. Increased intraocular pressure (IOP) leads to globe and corneal enlargement, and retinal ganglion cell/optic nerve damage. To date, genetic studies have identified ~25% of PCG molecular etiology. We sought novel variants in glaucoma-implicated genes in a cohort of PCG families lacking mutations in known PCG genes (CYP1B1, LTBP2, TEK, and ANGPT1).
Methods :
PCG patients referred to our study were consented, and medical histories and blood samples for DNA extraction were acquired. Probands were exome sequenced using the Sure Select Human All Exon v6 or Roche/Nimblegen SeqCap EZ v2 capture kits on an Illumina HiSeq 2000 platform. Variants that were synonymous, not in coding/splice site regions, or with an allele frequency >0.002 in the gnomAD database were removed using Golden Helix SVS software. Sanger sequencing confirmed the variants in probands and enabled co-segregation analyses in additional family members where available.
Results :
Six families with PIEZO1 and/or PIEZO2 variants were identified by exome sequencing. For PIEZO1, two families were identified with compound heterozygous variants (p.Arg351Trp, p.Gln1519Pro; p.Met711Lys, p.Arg1404Trp) and another had a single heterozygous variant (p.Val499Ile). For PIEZO2, two families had a single heterozygous variant (p.Arg2731Gln, p.Val971Ile). Digenic inheritance of PIEZO1 (p.Pro913Ala) and PIEZO2(p.Glu1863Gly) variants were identified in a further family. All variants showed low frequencies in global and all ethnic populations (gnomAD), had CADD scores >20, and involved highly evolutionarily conserved residues, strongly suggesting pathogenicity.
Conclusions :
Maintenance of IOP involves regulation of aqueous humor outflow via Schlemm's canal (SC), a unique hybrid vessel in the ocular anterior chamber angle with lymphatic and vascular properties. In mice, PIEZO1 and PIEZO2 proteins form mechanically activated ion channels expressed in lymphatic and vascular endothelial cells. PIEZO1 localizes to SC and is important for lymphatic valve formation in mice. Additionally, PIEZO2 is associated with regulation of aqueous outflow in mice. PIEZO1 expression in human trabecular meshwork cells has also been reported. These findings strongly suggest that PIEZO1 and PIEZO2 are involved in IOP regulation and that rare pathogenic variants are causal for PCG.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.