Involvement of the novel gene IFT43 in causing early onset non-syndromic retinal degeneration.

Abstract

Purpose : To identify the underlying cause of retinal degeneration (RD) in a consanguineous Pakistani pedigree and establishing the functional impact of the mutation identified.

Methods : A complete ophthalmic evaluation was carried out in four affected and two unaffected family members from a four-generation family with four consanguineous marriages. Blood samples were collected from eight affected and nine unaffected family members for DNA isolation. Exomes of four affected and two unaffected individuals were sequenced using Nimblegen V3 exome capture kit and sequenced on Illumina HiSeq. Sequence reads were mapped using BWA and variants were annotated using Genome analysis tool kit (GATK). Variants were filtered using exomeSuite to identify rare or novel, homozygous or compound heterozygous and potentially pathogenic changes in genes expressed in the retina. Segregation analysis and ethnicity-matched control sample screening was performed using Sanger sequencing. Expression profile of Intraflagellar transport protein 43 (IFT43) in the retina was determined by RT-PCR and immunohistochemistry. Effect of the causative variant in IFT43 was evaluated by expressing the mutant and wild type IFT43 in miMCD3 cells.

Results : Clinical examination revealed the presence of bone spicules throughout the retina at younger ages while the older affected members showed severe central choroidal atrophy. Night blindness was reported as the primary symptom in all affected patients. Exome sequencing, variant filtering and segregation analysis identified a novel missense change p.Glu34Lys in IFT43 that segregated with RD. This variant was not observed in ethnicity-matched controls. IFT43 expression is localized to the photoreceptor layer of the retina and the cilium in cells. Expression of mutant IFT43 was observed to alter the structure of cilia in transfected miMCD3 while the cells expressing the wild-type protein had normal cilia.

Conclusions : This study revealed the involvement of a novel ciliary protein IFT43 as the underlying cause of recessive non-syndromic RD in a Pakistani family. This protein is a component of IFT complex-A involved in ciliary transport. Abnormal ciliary structures in cells transfected with the mutant IFT43 suggest its potential involvement in ciliary structure maintenance and possible disruption of ciliary transport in photoreceptors of patients with the homozygous p.Glu34Lys mutation leading to RD.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.