Brittle cornea syndrome: an heritable connective tissue disorder distinct from Ehlers-Danlos syndrome type VI and fragilitas oculi, with spontaneous perforations of the eye, blue sclerae, red hair, and normal collagen lysyl hydroxylation

Mechanobiology in the Comorbidities of Ehlers Danlos Syndrome

Ehlers-Danlos Syndromes (EDSs) are a group of connective tissue disorders, characterized by skin stretchability, joint hypermobility and instability. Mechanically, various tissues from EDS patients exhibit lowered elastic modulus and lowered ultimate strength. This change in mechanics has been associated with EDS symptoms. However, recent evidence points toward a possibility that the comorbidities of EDS could be also associated with reduced tissue stiffness. In this review, we focus on mast cell activation syndrome and impaired wound healing, comorbidities associated with the classical type (cEDS) and the hypermobile type (hEDS), respectively, and discuss potential mechanobiological pathways involved in the comorbidities.

The Ehlers-Danlos syndromes

The Ehlers-Danlos syndromes (EDS) are a heterogeneous group of hereditary disorders of connective tissue, with common features including joint hypermobility, soft and hyperextensible skin, abnormal wound healing and easy bruising. Fourteen different types of EDS are recognized, of which the molecular cause is known for 13 types. These types are caused by variants in 20 different genes, the majority of which encode the fibrillar collagen types I, III and V, modifying or processing enzymes for those proteins, and enzymes that can modify glycosaminoglycan chains of proteoglycans. For the hypermobile type of EDS, the molecular underpinnings remain unknown. As connective tissue is ubiquitously distributed throughout the body, manifestations of the different types of EDS are present, to varying degrees, in virtually every organ system. This can make these disorders particularly challenging to diagnose and manage. Management consists of a care team responsible for surveillance of major and organ-specific complications (for example, arterial aneurysm and dissection), integrated physical medicine and rehabilitation. No specific medical or genetic therapies are available for any type of EDS.

Brittle cornea syndrome: current perspectives

Brittle cornea syndrome (BCS) is a rare autosomal recessive connective tissue disorder characterised by severe corneal thinning, with the major ocular risk being spontaneous ocular perforation due to progressive stromal thinning and ectasia. It is a complex condition with limited treatment options. The purpose of this review is to highlight the difficulties associated with the condition and examine the available published evidence with regards to management.

Brittle cornea syndrome: a case report and review of the literature

Background

To report a patient who presented with bluish scleral discoloration, keratoconus, and progressive high myopia.

Case presentation

A 6-year-old Chinese female patient presented with a significant bluish discoloration of the sclera in both eyes and extreme corneal thinning with anterior corneal protrusion. General pediatric physical examination was normal for all systems and no genetic disorders known were observed.

Conclusions

We aim to highlight the importance of diagnosis and treatment of patients suffering from Brittle cornea syndrome. Timely diagnosis and early provision of protective glasses seem to be the most important step in treating BCS. To our knowledge, this is the first case of BCS being reported in the Asia area.

The Ehlers-Danlos syndromes, rare types

The Ehlers-Danlos syndromes comprise a clinically and genetically heterogeneous group of heritable connective tissue disorders, which are characterized by joint hypermobility, skin hyperextensibility, and tissue friability. In the Villefranche Nosology, six subtypes were recognized: The classical, hypermobile, vascular, kyphoscoliotic, arthrochalasis, and dermatosparaxis subtypes of EDS. Except for the hypermobile subtype, defects had been identified in fibrillar collagens or in collagen-modifying enzymes. Since 1997, a whole spectrum of novel, clinically overlapping, rare EDS-variants have been delineated and genetic defects have been identified in an array of other extracellular matrix genes. Advances in molecular testing have made it possible to now identify the causative mutation for many patients presenting these phenotypes. The aim of this literature review is to summarize the current knowledge on the rare EDS subtypes and highlight areas for future research. © 2017 Wiley Periodicals, Inc.

ZNF469 frequently mutated in the brittle cornea syndrome (BCS) is a single exon gene possibly regulating the expression of several extracellular matrix components

Brittle cornea syndrome (BCS; MIM 229200) is an autosomal recessive generalized connective tissue disorder caused by mutations in ZNF469 and PRDM5. It is characterized by extreme thinning and fragility of the cornea that may rupture in the absence of significant trauma leading to blindness. Keratoconus or keratoglobus, high myopia, blue sclerae, hyperelasticity of the skin without excessive fragility, and hypermobility of the small joints are additional features of BCS. Transcriptional regulation of extracellular matrix components, particularly of fibrillar collagens, by PRDM5 and ZNF469 suggests that they might be part of the same pathway, the disruption of which is likely to cause the features of BCS. In the present study, we have performed molecular analysis of a cohort of 23 BCS affected patients on both ZNF469 and PRDM5, including those who were clinically reported previously [1]; the clinical description of three additional patients is reported in detail. We identified either homozygous or compound heterozygous mutations in ZNF469 in 18 patients while, 4 were found to be homozygous for PRDM5 mutations. In one single patient a mutation in neither ZNF469 nor PRDM5 was identified. Furthermore, we report the 12 novel ZNF469 variants identified in our patient cohort, and show evidence that ZNF469 is a single exon rather than a two exon gene.

Ocular features in joint hypermobility syndrome/ehlers-danlos syndrome hypermobility type: a clinical and in vivo confocal microscopy study

PURPOSE

To investigate ocular anomalies in joint hypermobility syndrome/Ehlers-Danlos syndrome, hypermobility type (JHS/EDS-HT).

DESIGN

Prospective, cross-sectional study.

METHODS

Forty-four eyes of 22 consecutive patients with an established diagnosis of JHS/EDS-HT and 44 eyes of 22 age- and gender-matched control subjects. Administration of a standardized questionnaire (Ocular Surface Disease Index) and a complete ophthalmologic examination, including assessment of best-corrected visual acuity, slit-lamp biomicroscopy, intraocular pressure measurement, indirect ophthalmoscopy, tear-film break-up time, Schirmer I testing, axial length and anterior chamber depth measurement, corneal topography, corneal pachymetry, and confocal microscopy. Main outcome measures included comparing ocular anomalies in JHS/EDS-HT and control eyes.

RESULTS

JHS/EDS-HT patients reported dry eye symptoms more commonly than controls (P < .0001). Scores of tear-film break-up time and Schirmer I test were significantly lower in JHS/EDS-HT eyes (P < .0001). Minor lens opacities were significantly more common in the JHS/EDS-HT group (13.6%; P < .05). Pathologic myopia with abnormal vitreous was found in 7 JHS/EDS-HT eyes (15.9%) and 0 controls (P = .01). Corneas were significantly steeper and the best-fit sphere index was significantly higher in JHS/EDS-HT group (P < .01). By confocal microscopy, the JHS/EDS-HT group showed lower density of cells in the superficial epithelium (P < .001) and higher density of stromal keratocytes in anterior and posterior stroma (P < .0001).

CONCLUSIONS

The most consistent association of eye anomalies in the JHS/EDS-HT group included xerophthalmia, steeper corneas, pathologic myopia, and vitreous abnormalities, as well as a higher rate of minor lens opacities. These findings indicate the need for ophthalmologic survey in the assessment and management of patients with JHS/EDS-HT.

Peripartum anesthetic management of a patient with brittle cornea syndrome

Brittle cornea syndrome (BCS) is a rare autosomal recessive disease that affects the connective tissue. The syndrome is caused by genetic changes in the 4.7-Mb interval between the D16S3423 and D16S3425 markers on the 16q24 chromosome and mutations in the Zinc-Finger 469 gene (ZNF469). BCS is characterized by thin and fragile cornea that tends to perforate spontaneously or as a result of minor trauma to the eye. In addition, the patient usually suffers from hearing loss, mental retardation, hyperextensibility of skin and joints, as well as varying degrees of scoliosis. This phenotypical expression presents an interesting challenge to anesthetic care. We briefly present the perioperative management of a patient with BCS who underwent three cesarean sections.

Deleterious mutations in the Zinc-Finger 469 gene cause brittle cornea syndrome

Brittle cornea syndrome (BCS) is an autosomal-recessive disorder characterized by a thin cornea that tends to perforate, causing progressive visual loss and blindness. Additional systemic symptoms such as joint hypermotility, hyperlaxity of the skin, and kyphoscoliosis place BCS among the connective-tissue disorders. Previously, we assigned the disease gene to a 4.7 Mb interval on chromosome 16q24. In order to clone the BCS gene, we first narrowed the disease locus to a 2.8 Mb interval and systematically sequenced genes expressed in connective tissue in this chromosomal segment. We have identified two frameshift mutations in the Zinc-Finger 469 gene (ZNF469). In five unrelated patients of Tunisian Jewish ancestry, we found a 1 bp deletion at position 5943 (5943 delA), and in an inbred Palestinian family we detected a single-nucleotide deletion at position 9527 (9527 delG). The function of ZNF469 is unknown. However, a 30% homology to a number of collagens suggests that it could act as a transcription factor involved in the synthesis and/or organization of collagen fibers.

Generation of hybrid transgenic silkworms that express Bombyx mori prolyl-hydroxylase alpha-subunits and human collagens in posterior silk glands: Production of cocoons that contained collagens with hydroxylated proline residues

Prolyl 4-hydroxylase (P4H) is a heterotetramer enzyme consisting of alpha-subunits (P4Halpha) and beta-subunits (P4Hbeta), and is required for collagen biosynthesis. Previously, we generated transgenic silkworms that produced human type III collagen fragments (mini-collagens) in the posterior silk gland (PSG). However, prolyl 4-hydroxylation did not occur on the mini-collagens, because in spite of an abundant expression of P4Hbeta in PSGs, P4Halpha expression was quite low there, thus resulting in an insufficient activity of P4H. In this study we aimed at generating hybrid transgenic silkworms whose PSGs are capable of producing mini-collagens and enough P4H for their prolyl 4-hydroxylation. Isolated PSGs were bombarded with fibroin L-chain gene promoter-driven vectors containing Bombyx mori P4Halpha (BmP4Halpha) cDNAs and were transplanted into the hemolymphatic cavity. The P4H activity in the PSG cells significantly increased, indicating that the expressed BmP4Halpha formed active tetramers with endogenous BmP4Hbeta. Using germ-line transgenesis technology, silkworms were generated that synthesized BmP4Halpha in PSG cells. The P4H activity in the transgenic silkworms was 130-fold higher than that of wild-type counterparts. Finally, we generated hybrid transgenic silkworms that expressed cDNAs of both BmP4Halpha and mini-collagen in PSG cells. They spun cocoons that contained mini-collagens whose appropriate proline residues had been adequately hydroxylated.

Synthesis of prolyl 4-hydroxylase alpha subunit and type IV collagen in hemocytic granular cells of silkworm, Bombyx mori: Involvement of type IV collagen in self-defense reaction and metamorphosis

The present study shows that hemocytic granular cells synthesize and secrete type IV collagen (ColIV) in the silkworm Bombyx mori (B. mori) and suggests that these cells play roles in the formation of basement membrane, the encapsulation of foreign bodies, and the metamorphic remodeling of the gut. The full- and partial-length cDNA of B. mori prolyl 4-hydroxylase alpha subunit (BmP4Halpha) and B. mori ColIV (BmColIV) were cloned, respectively. In situ hybridization and immunocytochemistry on larval tissues and cells identified hemocytic granular cells as the cells that express mRNAs and proteins of both BmP4Halpha and BmColIV. Immunohistochemistry and immunocytochemistry demonstrated that BmColIV was present in the basement membrane and in the secretory granules of granular cells, respectively. Granular cells in culture secreted BmColIV without accompanying the degranulation and discharged it from the granules when the cells were degranulated. Nylon threads were inserted into the hemocoel of larvae. Granular cells concentrated around the nylon threads and encapsulated them as a self-defense reaction. BmColIV was found to be a component of the capsules. Furthermore, the present study showed that actively BmColIV-expressing granular cells accumulated around the midgut epithelium and formed BmColIV-rich thick basal lamina-like structures there in larval to pupal metamorphosis.

Brittle cornea syndrome and its delineation from the kyphoscoliotic type of Ehlers-Danlos syndrome (EDS VI): Report on 23 patients and review of the literature

The brittle cornea syndrome (BCS) is a generalized connective tissue disorder characterized by corneal rupture following only minor trauma, keratoconus or keratoglobus, blue sclerae, hyperelasticity of the skin without excessive fragility, and hypermobility of the joints. It is inherited as an autosomal recessive trait but the underlying genetic defect remains undetermined. We present 23 patients (11 male) from 13 nuclear families followed at the King Khaled Eye Specialist Hospital, Riyadh, Saudi Arabia, aged 3-28 years at last follow-up. A total of 28 events of corneal rupture were noted in 17 patients (eight male), among whom nine had had bilateral ruptures, and eight had had unilateral ruptures (four of the right cornea), while two had experienced re-rupture 2 and 4 years, respectively, after surgery; six patients (aged 3-21 years) had had no ruptures. We describe the natural history of our cases and discuss them together with those others reported in the literature. Because of similarities between the BCS and the kyphoscoliotic type of the Ehlers-Danlos syndrome (EDS VI), both disorders tend to have been confounded. Here, we show that all of our BCS patients tested in this regard had biochemical findings reflective of normal activity of lysyl hydroxylase, characteristically deficient in EDS VI, such as normal urinary total pyridinoline ratios and/or normal electrophoretic migration of collagen chains produced by dermal fibroblasts. The BCS is, therefore, an entity distinct from the kyphoscoliotic type of EDS, which has a much poorer prognosis.

Ehlers-Danlos syndromes: revised nosology, Villefranche, 1997. Ehlers-Danlos National Foundation (USA) and Ehlers-Danlos Support Group (UK)

Categorization of the Ehlers-Danlos syndromes began in the late 1960s and was formalized in the Berlin nosology. Over time, it became apparent that the diagnostic criteria established and published in 1988 did not discriminate adequately between the different types of Ehlers-Danlos syndromes or between Ehlers-Danlos syndromes and other phenotypically related conditions. In addition, elucidation of the molecular basis of several Ehlers-Danlos syndromes has added a new dimension to the characterization of this group of disorders. We propose a revision of the classification of the Ehlers-Danlos syndromes based primarily on the cause of each type. Major and minor diagnostic criteria have been defined for each type and complemented whenever possible with laboratory findings. This simplified classification will facilitate an accurate diagnosis of the Ehlers-Danlos syndromes and contribute to the delineation of phenotypically related disorders.

Biosynthesis of recombinant human pro-alpha 1(III) chains in a baculovirus expression system: production of disulphide-bonded and non-disulphide-bonded species containing full-length triple helices

We have investigated the expression of human procollagen III by insect cells infected with a recombinant baculovirus carrying cDNA for the pro-alpha1(III) chain of type-III collagen. A high level of expression was obtained, and a small proportion of the heterologously expressed pro-alpha1(III) chains formed normally disulphide-bonded procollagen III, which was secreted into the culture medium. This species displayed a melting temperature (Tm) of approx. 38 degrees C as assessed by its resistance to digestion by a mixture of trypsin and chymotrypsin, slightly lower than that of 39.5 degrees C for procollagen III synthesized by cultured human dermal fibroblasts, and reflected a slight degree of under-hydroxylation of prolyl residues. This is possibly a consequence of the lower incubation temperature of insect cells, or of an insufficiency of prolyl hydroxylase activity within them. A significant proportion of the expressed chains formed trimeric molecules of similar thermal stability containing an apparently full-length triple-helical region, but were not disulphide-bonded and not secreted. In addition to providing a source of recombinant human procollagen III, the system promises to be useful in the study of procollagen chain association and subsequent folding.

Clinical, ultrastructural and biochemical studies in two sibs with Ehlers-Danlos syndrome type VI-B-like features

Two Turkish sibs with clinical features of Ehlers-Danlos syndrome type VI-B are presented. The hydroxylysine contents of dermis and gel electrophoresis of type I and type III collagen produced by fibroblasts were normal. Ultrastructural studies of skin collagen and elastic fibers showed discrete abnormalities. Other syndromes with similar clinical, biochemical and ultrastructural features are discussed.