Genetics and clinical investigations: The transmission form of this family was consistent with an autosomal dominant inheritance (Figure 1).
Clinical examinations demonstrated bilaterally multiple superficial, epithelial and stromal anterior granular opacities; in different stages of severity among three patients of this family. The three patients on the same mutation who shared a mixed phenotype with a superficial form of granular corneal dystrophy type 1 and Thiel-Behnke corneal dystrophy patterns: Clinical features of patients are given below.
The patient 1 (IV-7) was a 34-year-old woman who complained of recurrent episodes of corneal pain since the age of 18, associated with a decrease in visual acuity. Her vision was 4/10 OD and 6/10 OS. Slit-lamp examinations revealed, in the two eyes, anterior epithelial and stromal corneal dystrophy, in the form of spaced microvacuoles by a heterogeneous thickening of the epithelium due to thickening of an abnormal subepithelial fibrous layer and poorly individualized anterior opacities, with fuzzy edges (Figure 2). The rest of the examination of the anterior segment is normal, including a normal iris, a clear lens, and an intraocular pressure at 17mmHg in ODG. The Optical Coherence Tomography (OCT) scan shows an unevenness of the epithelial layers by a homogeneous confluent layer of hyper-reflected deposits with a serrated anterior border taking the sawtooth appearance, replacing the Bowman layer and reaching the anterior stroma (Figure 3 (A , B, C, D)). It is thicker and becomes thinner on the periphery and disappears towards the limb. The pachymetry is 512 μm in OD and 523 μm in OS.
The patient 2 (IV-8) is a woman 44 years old; she presents episodes of recurrent keratitis with a decrease in visual acuity of progressive installation since the age of 20 years. Visual acuity in OD shows that she counts the fingers at 3m / OS at 2/10 (irremovable). Examination with the slit lamp shows in OD and OS anterior epithelial and stromal corneal dystrophy in the form of microvacuoles, especially in the periphery, with a heterogeneous thickening of the epithelium, more pronounced in the center giving a large central opacity with fuzzy edges at both eyes (Figure 4), Clear lens; ocular tone at 15 mmHg in OD 14 mmHg in OS, and normal fundus. The OCT of the cornea shows an unevenness of the anterior epithelial and stromal layers with thicker hyper-reflective deposits and a clear central opacity in both eyes (Figure 5: A, B, C, D), As well as a pachymetry at 538 μm in OD, 543 μm in OS.
The patient 3 (III-2) is a woman 72 years old, she has bilateral osteoarthritis, and she reports episodes of recurrent corneal pain. As for her visual acuity, in far vision OD, she can barely see the movement of the fingers / OS: (she counts the fingers at 3m). The Slit lamp examination showed in the right eye, central and paracentric yellowish and gelatinous central and paracentric deposition associated with a corneal opacity deeper than the previous one and affecting the epithelial layers of the Bowman's membrane and the anterior stroma in the form of an epithelial fibrous layer, taking almost the entire corneal surface (Figure: 6). The rest of the examination is hampered by the very important dystrophy of the right eye, (i.e., ineclairable fundus). In the left eye, the slit lamp examination showed corneal dystrophy involving the epithelial layers of the Bowman's membrane and the anterior stroma in the form of a heterogeneous thickening more important at the center, associated with opacity with fuzzy boundaries and a corticonuclear cataract (Figure 6). In the Fundus, the pupillary glow with flattened retina was noted. The OCT of the cornea shows in the right eye: the form of microvacuoles as thin patches (blue arrows) associated with a significant loss of epithelial cells with disorganization of the epithelial layers, the absence of Bowman's membrane, and an anterior intrastromal bubble (white arrows). The Pachymetry is at 586 μm (Figure 7). In the Left eye, the OCT shows an irregularity of the corneal surface with disorganization of the epithelial layers, a discontinuous Bowman’s membrane, and anterior stromal reshaping especially in the center (Figure 7). The process of corneal transplantation, in this patient, is ongoing.
Whole Exome Sequencing and Variant Validation: WES was performed on three family members (IV-7, IV-8 and III-2). The analysis of the expression of the three patients shows 30887 variants in 19 712 genes. Filtering of variants is illustrated in Figure 9. After filtering, this number was reduced to a single allelic variant in the TGFBI gene. Only a heterozygous (c.1772C>A; p.Ser591Tyr) mutation in the TGFBI gene, identified in these three patients, was proposed as the potential pathogenic mutation within this family.
Bioinformatics analysis using Polyphen-2 and SIFT suggested that this mutation was a disease causing mutation and was predicted to be probably damaging., By Sanger sequencing, the mutation was confirmed in all patients and absent among the unaffected family.
The genomic and clinical data both supported a diagnosis of Thiel-Behnke corneal dystrophy (TBCD) in this family.