IFT81, encoding an IFT-B core protein, as a very rare cause of a ciliopathy phenotype.

Perrault I, Halbritter J, Porath JD, Gérard X, Braun DA, Gee HY, Fathy HM, Saunier S, Cormier-Daire V, Thomas S, Attié-Bitach T, Boddaert N, Taschner M, Schueler M, Lorentzen E, Lifton RP, Lawson JA, Garfa-Traore M, Otto EA, Bastin P, Caillaud C, Kaplan J, Rozet JM, Hildebrandt F.

Source : J Med Genet

2015 Oct 1

Pmid : 26275418

Abstract

BACKGROUND: Bidirectional intraflagellar transport (IFT) consists of two major protein complexes, IFT-A and IFT-B. In contrast to the IFT-B complex, all components of IFT-A have recently been linked to human ciliopathies when defective. We therefore hypothesised that mutations in additional IFT-B encoding genes can be found in patients with multisystemic ciliopathies.

METHODS: We screened 1628 individuals with reno-ocular ciliopathies by targeted next-generation sequencing of ciliary candidate genes, including all IFT-B encoding genes.

RESULTS: Consequently, we identified a homozygous mutation in IFT81 affecting an obligatory donor splice site in an individual with nephronophthisis and polydactyly. Further, we detected a loss-of-stop mutation with extension of the deduced protein by 10 amino acids in an individual with neuronal ceroid lipofuscinosis-1. This proband presented with retinal dystrophy and brain lesions including cerebellar atrophy, a phenotype to which the IFT81 variant might contribute. Cultured fibroblasts of this latter affected individual showed a significant decrease in ciliated cell abundance compared with controls and increased expression of the transcription factor GLI2 suggesting deranged sonic hedgehog signalling.

CONCLUSIONS: This work describes identification of mutations of IFT81 in individuals with symptoms consistent with the clinical spectrum of ciliopathies. It might represent the rare case of a core IFT-B complex protein found associated with human disease. Our data further suggest that defects in the IFT-B core are an exceedingly rare finding, probably due to its indispensable role for ciliary assembly in development.

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