Homozygous nonsense mutation in the FOXE3 gene as a cause of congenital primary aphakia in humans

Abstract

Congenital primary aphakia (CPA) is a rare developmental disorder characterized by the absence of lens, the development of which is normally induced during the 4th-5th wk of human embryogenesis. This original failure leads, in turn, to complete aplasia of the anterior segment of the eye, which is the diagnostic histological criterion for CPA. So far, the genetic basis for this human condition has remained unclear. Here, we present the analysis of a consanguineous family with three siblings who had bilateral aphakia, microphthalmia, and complete agenesis of the ocular anterior segment. We show that a null mutation in the FOXE3 gene segregates and, in the homozygous state, produces the mutant phenotype in this family. Therefore, this study identifies--to our knowledge, for the first time--a causative gene for CPA in humans. Furthermore, it indicates a possible critical role for FOXE3 very early in the lens developmental program, perhaps earlier than any role recognized elsewhere for this gene.

Figure 1.

Identification of the FOXE3 nonsense mutation in the family with CPA. A, Pedigree of the family with CPA, showing double consanguinity and recessive inheritance pattern of the ocular phenotype. The affected individuals are identified by a blackened symbol. Phenotypically normal carriers of the mutation are indicated by a dot within the unblackened symbol. B, Sequence electrophoregrams of the novel C240X mutation. Left, Partial sequence data from affected individual IV.3, indicating homozygosity (one peak: the mutated nucleotide A) for the C240X mutation. Right, Sequence data from his clinically asymptomatic mother (III.2), showing heterozygosity (two peaks: the normal nucleotide C and the mutated nucleotide A). Arrowheads indicate the position of the mutated nucleotide. C, Comparison of human (Hs) and mouse (Mm) FOXE3 C-terminal amino acid sequences. Red background, Identical amino acids. Yellow background, Conservative substitutions. The arrow points to the residue substituted in our patient.

Figure 2.

Clinical phenotypes of patient IV.3. A, MRI (T2-weighted image) sagittal section at 28.5 wk of gestation. The fetal eyeball appears as a white sphere (arrow), and the lens, normally visible inside as a black and well-circumscribed sphere, is absent. B, Aspect of eyes of proband IV.3 at the age of 1 mo, revealing bilateral microphthalmia with aphakia in the right eye and extreme microphthalmia of the left eye, preventing correct examination. C and D, Axial and sagittal sections of cerebral MRI (T1-weighted images) at the age of 4 years, showing absence of lens, asymmetric eyeballs, and normal appearance of brain structures.

Figure 3.

Clinical phenotypes of patient IV.4, the affected daughter. A, Ocular appearance showing bilateral and symmetric microphthalmia. B, Higher magnification of her left orbit, illustrating the sclerocornea. C and D, Axial and sagittal sections of cerebral MRI (T1-weighted images) at the age of 3 years, showing absence of lens, symmetric eyeballs, and normal appearance of brain structures.

Figure 4.

Histologic aspect of eyes from proband IV.1. A, Photograph representing section through the entire eye (hematoxylin-eosin staining [HES]). Note the absence of lens, with a empty cavity most probably corresponding to the vitreous (*), the aplasia of the anterior chamber (arrow), the dysplastic retina, and the presence of the optic nerve (magnification 4×). c = Cornea; on = optic nerve; r = retina. B, Histological photograph of the anterior segment of the eye, stained with anti–α-smooth muscular actin antibody. The anterior chamber space, including iris and ciliary body, is not formed, and the posterior face of the corneal stroma is lined by a layer of muscular smooth cells, a fibroconnective tissue, and a continuous layer of pigmented cells (*). pe = Pigmented epithelium. C, Abnormal folds of the retina with rosette-like structures in which the retinal lamination is disturbed (HES; magnification 20×).

Figure 5.

Histologic and immunohistochemical analyses of eyes from proband IV.1. A, HES (left panel) and immunohistochemical staining with anti–α-smooth muscular actin (right panel) of the posterior corneal stroma, showing absence of corneal endothelium and Descemet’s membrane, vascularized corneal stroma (arrowhead), and the different abnormal tissues that adhered to the posterior face of the cornea (magnification 10× and 20×, respectively). The arrow points to the site where corneal endothelium and Descemet's membrane normally take place in the cornea. cs = Corneal stroma; fvt = fibrovascular tissue; pe = pigmented epithelium; smc = smooth muscular cells. B, HES showing the pigmented epithelium that occasionally forms some folds resembling ciliary processes, with higher magnification (20×) shown in the box. C, HES (panel a) and immunohistochemical staining with antivimentin (panel b), anti–α-smooth actin (panel c), and anti-CK7 (panel d) antibodies of the pigmented ciliary epithelium. Only vimentin immunohistochemical staining is positive (magnification 40×). D, Immunohistochemical staining with antidesmin antibody (magnification 40×). Only smooth muscular cells lining the posterior face of the corneal stroma are positive. E and F, Immunohistochemical positive staining with anti-HMB45 antibody in the choroid and in some cells (arrow) within the ectopic fibromuscular tissue adherent to the cornea.