Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2019 Mar 12;10(1):1180.
doi: 10.1038/s41467-019-08547-w.

Homozygous frameshift mutations in FAT1 cause a syndrome characterized by colobomatous-microphthalmia, ptosis, nephropathy and syndactyly

Najim Lahrouchi  1 , Aman George  2 , Ilham Ratbi  3 , Ronen Schneider  4 , Siham C Elalaoui  3 , Shahida Moosa  5   6 , Sanita Bharti  2   7 , Ruchi Sharma  7 , Mones Abu-Asab  8 , Felix Onojafe  2 , Najlae Adadi  3 , Elisabeth M Lodder  1 , Fatima-Zahra Laarabi  9 , Yassine Lamsyah  10 , Hamza Elorch  10 , Imane Chebbar  10 , Alex V Postma  11 , Vassilios Lougaris  12 , Alessandro Plebani  12 , Janine Altmueller  13   14   15 , Henriette Kyrieleis  16 , Vardiella Meiner  17 , Helen McNeill  18 , Kapil Bharti  7 , Stanislas Lyonnet  19 , Bernd Wollnik  5 , Alexandra Henrion-Caude  20 , Amina Berraho  10 , Friedhelm Hildebrandt  4 , Connie R Bezzina  21 , Brian P Brooks  22 , Abdelaziz Sefiani  23   24
Affiliations

Homozygous frameshift mutations in FAT1 cause a syndrome characterized by colobomatous-microphthalmia, ptosis, nephropathy and syndactyly

Najim Lahrouchi et al. Nat Commun. .

Abstract

A failure in optic fissure fusion during development can lead to blinding malformations of the eye. Here, we report a syndrome characterized by facial dysmorphism, colobomatous microphthalmia, ptosis and syndactyly with or without nephropathy, associated with homozygous frameshift mutations in FAT1. We show that Fat1 knockout mice and zebrafish embryos homozygous for truncating fat1a mutations exhibit completely penetrant coloboma, recapitulating the most consistent developmental defect observed in affected individuals. In human retinal pigment epithelium (RPE) cells, the primary site for the fusion of optic fissure margins, FAT1 is localized at earliest cell-cell junctions, consistent with a role in facilitating optic fissure fusion during vertebrate eye development. Our findings establish FAT1 as a gene with pleiotropic effects in human, in that frameshift mutations cause a severe multi-system disorder whereas recessive missense mutations had been previously associated with isolated glomerulotubular nephropathy.

PubMed Disclaimer

Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Recessive frameshift mutations in FAT1 cause a new clinical syndrome. Pedigree of family 1–5 (a). A schematic of human FAT1 start/stop codon, exons, location of mutations previous published and identified in this study (top panel). The FAT1 protein is 4588 amino acids long and contains 34 cadherin repeats (CA), followed by five epidermal growth factor (EGF)-like repeat domains (E), a laminin G domain (LamG), a transmembrane domain (green), and an intracellular domain (bottom panel). Family 1 and 2 were found to carry the same homozygous frameshift variant c.2207dupT (p.I737NfsX7) in FAT1 (NM_005245). In Families 3–5 we identified, respectively, the following homozygous frameshift FAT1 variants: c.2600_2601delCA (p.T867IfsX4), c.9729del p.(V3245LfsX25), and c.3093_3096del (p.P1032CgsX11). H homozygous, h heterozygous (b). Ophthalmic features observed in patients included ptosis; bilateral in patients F1-IV-1, F1-IV-3, F1-IV-5, F2-III-3, F2-IV-3, F3-IV-1 and unilateral in F2-IV-1, F4-II-3 (c), microphthalmia (d), iris coloboma (e), large chorioretinal coloboma containing the papilla/optic nerve with two other smaller circumscribed chorioretinal colobomas localized above the papilla (f), and retinal coloboma (g). Skeletal abnormalities included syndactyly in the majority of patients and bone fusion of phalanges 3–4 on the right foot and hypotrophy of phalanx 2 of the left foot in patient F3-II-2 (h). X-ray of the feet demonstrating cutaneous syndactyly in patient F2-IV-1 (i)
Fig. 2
Fig. 2
FAT1-/- mouse exhibit microphthalmia and completely penetrant coloboma. FAT1 mRNA expression pattern in sagittal (a–c) and coronal (d–f) mouse optic cup sections at E10.5 (a, d), E11.5 (b, e), and E12.5 (c, f). Compared to wild-type (WT) embryos (g–i, E14.5) FAT1−/− mouse exhibited microphthalmia (j, m). Fused optic fissure margins of WT mouse embryos (E14.5, h, i; sagittal section) and unfused margins were seen in Fat1−/− mice (n, o) and/or persistence of POM—including early hyaloid vessel precursors (k, l, arrow) interposing between the closing edges of the fissure (E14.5). D dorsal, V ventral, T temporal, N nasal
Fig. 3
Fig. 3
FAT1 knockdown disrupts F-ACTIN and ZO-1 localization in RPE. ShRNA-mediated knockdown of FAT1 in RPE cells was confirmed using Western blotting (a, N = 3). Disorganization of F-ACTIN fibers (b) and loss of ZO-1 staining pattern (c) was observed in RPE cells upon knockdown of FAT1. Trans-epithelial electrical resistance was measured at week one and two post-FAT1 knockdown to determine junctional integrity (d, N = 6). Scale bar is 20 µm. Error bars represent standard error of mean, and statistical significance is at P < 0.05 (two tailed t-test) denoted by “*”. Raw data is provided in supplementary section
Fig. 4
Fig. 4
FAT1 knockdown results in a failure to organize RPE cells into a monolayer. Transmission electron miscroscopy (TEM) of RPE cells cultured on trans-wells for 2 weeks following treatment with scrambled (a, c) and FAT1 shRNA (b, d). A transverse section depicting RPE cells (*, scale bar is 2 µm) sitting on top of trans-well membrane (a, arrow). A higher magnification showing epithelial tight junction (c, d, arrow, scale bar is 500 nm) between two neighboring cells
Fig. 5
Fig. 5
Zebrafish embryos with homozygous alleles of truncated fat1a display coloboma. CRISPR/Cas9-mediated introduction of frame-shift mutations in FAT1 C-terminal resulted in optic fissure closure defects (a and e, scale bar is 0.1 mm). A higher magnification of eye depicting fused margins in WT and unfused margins in homozygous mutant (*, b and f, scale bar is 0.05 mm). Sagittal sections of zebrafish embryos (24–30 hpf) followed by toludene blue staining showing organization of the optic cup (c and g, scale bar is 50 µm). Higher magnification of the optic cup shows morphology of optic fissure margins in WT and homozygous mutant (d, h, scale bar is 20 µm)
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Chang L, Blain D, Bertuzzi S, Brooks BP. Uveal coloboma: clinical and basic science update. Curr. Opin. Ophthalmol. 2006;17:447–470. doi: 10.1097/01.icu.0000243020.82380.f6. - DOI - PubMed
    1. Patel, A. & Sowden, J. C. Genes and pathways in optic fissure closure. Semin. Cell. Dev. Biol. 10.1016/j.semcdb.2017.10.010 (2017). - PubMed
    1. Tanoue T, Takeichi M. Mammalian Fat1 cadherin regulates actin dynamics and cell–cell contact. J. Cell. Biol. 2004;165:517–528. doi: 10.1083/jcb.200403006. - DOI - PMC - PubMed
    1. Saburi S, Hester I, Goodrich L, McNeill H. Functional interactions between Fat family cadherins in tissue morphogenesis and planar polarity. Development. 2012;139:1806–1820. doi: 10.1242/dev.077461. - DOI - PMC - PubMed
    1. Hou R, Sibinga NES. Atrophin proteins interact with the Fat1 cadherin and regulate migration and orientation in vascular smooth muscle cells. J. Biol. Chem. 2009;284:6955–6965. doi: 10.1074/jbc.M809333200. - DOI - PMC - PubMed

Publication types

MeSH terms