Abstract
Purpose :
Childhood glaucoma (CG) is a leading cause of early-onset blindness, primarily attributed to increased intraocular pressure (IOP) as a result of abnormal development of the aqueous humor outflow (AHO) pathway. To date, the molecular etiology remains elusive in over 40% of cases. In families lacking mutations in 110 Mendelian known childhood glaucoma-associated genes, we sought novel pathogenic variants using exome sequencing.
Methods :
Study consent was obtained for 91 families with CG. Exome sequencing was performed using a Twist exome 34MB capture kit and NovaSeq6000 platform. Noncoding, synonymous, and variants with a global population allele frequency greater than 0.002 (gnomAD v2.1.1 data) were excluded using SNP and Variation Suite software (Golden Helix). Candidate pathogenic variants were validated by direct Sanger sequencing. Reference and variant proteins with a FLAG-tag were over-expressed in transfected human TM-1 cells. The cell lysates and culture medium were analyzed by Western blotting.
Results :
Heterozygous variants in the Angiopoietin-like-7 (ANGPTL7) gene were identified in two patients. First, a p.Val56Ala (c.167T>C) missense substitution most commonly observed at low frequency in North-Western Europeans (0.00032). The valine-56 residue was moderately conserved in 100 vertebrate species, with a GERP score of 5.07 and a CADD (Phred) score of 23.6. Second, a p.Arg334Trp (c.1000C>T) missense change with highest observed population frequency in East Asians (0.00045). The arginine-334 residue is well conserved across 100 vertebrate species, has a GERP score of 5.58, and a CADD (Phred) score of 27.7. Both missense changes were predicted to be damaging by MutationTaster and FATHMM. Western blotting showed the variant protein levels were reduced in cell lysates and were minimally secreted.
Conclusions :
Herein, we present rare ANGPTL7 variants identified in patients with CG and supportive data that suggests loss of protein function. ANGPTL7 is located within one of the three genomic loci for primary congenital glaucoma (GLC3B, chr 1p36), a severe subtype of CG with disease onset before 3 years of age. ANGPTL7 is a component of the extracellular matrix that is highly expressed within the trabecular meshwork, a sieve-like structural component of the AHO pathway, in which dysfunction can increase resistance to fluid outflow, raise IOP resulting in glaucoma.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.