PFKFB1 is a novel candidate gene identified in a family with a complex retinal disorder

Abstract

Purpose : Pigmented paravenous retinochoroidal atrophy (PPRCA) is a rare disorder characterized by pigment accumulation in a venous distribution. A few cases have been reported with genetic variants, but most cases remain unexplained. Here we describe a family including three brothers with PPRCA-like retinal findings, partial posterior vitreous detachment, and varying degrees of vision loss; asymptomatic mother with mild overlapping retinal abnormalities; and unaffected father. We hypothesize that a genetic variant is causing the phenotype.

Methods : Exome sequencing was performed on all five family members. Familial analysis was performed, and variants were annotated and evaluated for pathogenicity. Candidate genes were evaluated in zebrafish for expression and function during embryonic development using RNAScope in situ and CRISPR-Cas9- mediated gene editing. Zebrafish embryos and adults were evaluated by gross examination under a microscope and histological studies.

Results : We identified a predicted loss of function variant in PFKFB1 (NM_002625.4:c.318-2A>G) that is hemizygous in the brothers, heterozygous in the mother, and not present in the father. The variant is ultra-rare (1/1073580 in gnomADv4 with 0 hemizygotes) and predicted to be deleterious by in silico programs with a CADD score of 33 and splicing disruption leading to frameshift predicted by Splice AI and Pangolin. PFKFB1 encodes a bifunctional enzyme known to regulate glycolysis, notably important in retinal tissues. Analysis of the zebrafish genome identified a single ortholog, pfkfb1, with 80% identity at the protein level. Expression studies revealed a dynamic expression pattern including strong presence in various ocular structures. We generated a zebrafish line, c.173_177del, with a predicted frameshift, similar to the expected effect of the human variant. No gross ocular phenotype was observed in the pfkfb1 homozygous or heterozygous zebrafish larvae at 1-7 dpf (n=100) or at adult stages (6mpf, n=9). Further characterization through histology of the retina is underway.

Conclusions : Exome sequencing identified a strong candidate variant in PFKFB1 in a family with a complex retinal disorder. This is further supported by the dynamic expression of pfkfb1 in the developing eye of zebrafish, necessitating further studies into the effects of pfkfb1 deficiency on retinal development and function in vertebrates.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.