X-linked megalocornea. Ocular findings and linkage analysis

Novel disease-causing variants and phenotypic features of X-linked megalocornea

PURPOSE

The aim of the study was to describe the phenotype and molecular genetic causes of X-linked megalocornea (MGC1). We recruited four British, one New Zealand, one Vietnamese and four Czech families.

METHODS

All probands and three female carriers underwent ocular examination and Sanger sequencing of the CHRDL1 gene. Two of the probands also had magnetic resonance imaging (MRI) of the brain.

RESULTS

We identified nine pathogenic or likely pathogenic and one variant of uncertain significance in CHRDL1, of which eight are novel. Three probands had ocular findings that have not previously been associated with MGC1, namely pigmentary glaucoma, unilateral posterior corneal vesicles, unilateral keratoconus and unilateral Fuchs heterochromic iridocyclitis. The corneal diameters of the three heterozygous carriers were normal, but two had abnormally thin corneas, and one of these was also diagnosed with unilateral keratoconus. Brain MRI identified arachnoid cysts in both probands, one also had a neuroepithelial cyst, while the second had a midsagittal neurodevelopmental abnormality (cavum septum pellucidum et vergae).

CONCLUSION

The study expands the spectrum of pathogenic variants and the ocular and brain abnormalities that have been identified in individuals with MGC1. Reduced corneal thickness may represent a mild phenotypic feature in some heterozygous female carriers of CHRDL1 pathogenic variants.

Decentration of a toric intraocular lens implant in a patient with simple megalocornea

Purpose

To describe a patient who developed radial displacement of the capsular bag and toric intraocular lens implant within approximately 5 weeks after surgery.

Observations

A patient underwent uncomplicated cataract extraction and implantation of a toric IOL for 2.5 diopters (D) of preoperative corneal astigmatism. Uncorrected visual acuity (UCVA) on postoperative day 1 was 20/20. Blurriness developed 5 weeks after surgery when UCVA was 20/70 but corrected to 20/20 with 2 D of cylinder in a new axis. The IOL was in the proper axis, but it and the capsular bag were radially displaced. Dilated examination revealed posterior capsular opacification superotemporally, outside the visual axis. The patient's biometry revealed axial myopia and megalocornea (white-to-white measurement of 13.44 mm), suggesting a larger than average capsular bag. Surgery was performed at postoperative week 6 to expand the capsular bag using a capsular tension ring and to re-center the IOL keeping the same axis. The patient recovered UCVA of 20/25 after the IOL was recentered.

Conclusions and Importance

It is important to review biometry for large white-to-white measurements. Eyes with megalocornea may require capsular tension rings at time of toric IOL implantation so as to maintain IOL centration and good UCVA.

Descemet Membrane Detachment in a Child With Anterior Megalophthalmos Managed Using Intracameral Perflouropropane (C3F8) Gas Injection

PURPOSE

To report a case of spontaneous Descemet-membrane detachment in a patient with anterior megalophthalmos managed by intracameral perflouropropane (C3F8) gas instillation.

METHODS

Retrospective case review.

RESULTS

A 12-year-old boy presented with spontaneous corneal edema in the left eye. The anterior segment findings were suggestive of anterior megalophthalmos. Slit-lamp examination of the left eye revealed a detached Descemet membrane superiorly. Anterior segment optical coherence tomography delineated the detached Descemet membrane. Descemetopexy with nonexpansile 14% perflouropropane (C3F8) gas resulted in rapid and complete resolution of corneal edema.

CONCLUSIONS

Patients with anterior megalophthalmos can develop spontaneous detachment of Descemet membrane, which can be effectively managed by intracameral gas instillation.

Association of CHRDL1 mutations and variants with X-linked megalocornea, Neuhäuser syndrome and central corneal thickness

We describe novel CHRDL1 mutations in ten families with X-linked megalocornea (MGC1). Our mutation-positive cohort enabled us to establish ultrasonography as a reliable clinical diagnostic tool to distinguish between MGC1 and primary congenital glaucoma (PCG). Megalocornea is also a feature of Neuhäuser or megalocornea-mental retardation (MMR) syndrome, a rare condition of unknown etiology. In a male patient diagnosed with MMR, we performed targeted and whole exome sequencing (WES) and identified a novel missense mutation in CHRDL1 that accounts for his MGC1 phenotype but not his non-ocular features. This finding suggests that MMR syndrome, in some cases, may be di- or multigenic. MGC1 patients have reduced central corneal thickness (CCT); however no X-linked loci have been associated with CCT, possibly because the majority of genome-wide association studies (GWAS) overlook the X-chromosome. We therefore explored whether variants on the X-chromosome are associated with CCT. We found rs149956316, in intron 6 of CHRDL1, to be the most significantly associated single nucleotide polymorphism (SNP) (p = 6.81×10⁻⁶) on the X-chromosome. However, this association was not replicated in a smaller subset of whole genome sequenced samples. This study highlights the importance of including X-chromosome SNP data in GWAS to identify potential loci associated with quantitative traits or disease risk.

X-linked Megalocornea Associated with the Novel CHRDL1 Gene Mutation p.(Pro56Leu*8)

BACKGROUND

The genetic basis of X-linked megalocornea (MGC1) was reported in 2012 to be caused by mutations in the CHRDL1 gene. We sought to confirm that mutations in CHRDL1 are associated with MGC1 in a previously unreported pedigree.

MATERIALS AND METHODS

Slit lamp examination, corneal pachymetry, corneal topography and DNA collection for screening of the CHRDL1 gene were performed for members of an affected family.

RESULTS

Examination of a woman and her four sons, ranging in age between 3 and 15 years, demonstrated horizontal corneal diameters of 14 mm in three of the four sons and a normal corneal diameter of 12 mm in the mother and other son. Central corneal thickness in the individuals with enlarged corneal diameters averaged 474 microns, compared to 604 microns in their unaffected brother. Corneal topographic imaging demonstrated an average K value of 44.4 D in the affected individuals compared with 41.6 D in their unaffected sibling. Screening of the CHRDL1 gene demonstrated the novel hemizygous frameshift mutation c.167delC (p.(Pro56Leu*8)) in exon 3 in the affected individuals and in the heterozygous state in their mother. This mutation was not present in the unaffected brother or in unrelated controls.

CONCLUSION

We provide the initial confirmation that X-linked megalocornea is associated with mutations in the CHRDL1 gene.

X-linked megalocornea caused by mutations in CHRDL1 identifies an essential role for ventroptin in anterior segment development

X-linked megalocornea (MGC1) is an ocular anterior segment disorder characterized by an increased cornea diameter and deep anterior chamber evident at birth and later onset of mosaic corneal degeneration (shagreen), arcus juvenilis, and presenile cataracts. We identified copy-number variation, frameshift, missense, splice-site and nonsense mutations in the Chordin-like 1 gene (CHRDL1) on Xq23 as the cause of the condition in seven MGC1 families. CHRDL1 encodes ventroptin, a bone morphogenic protein antagonist with a proposed role in specification of topographic retinotectal projections. Electrophysiological evaluation revealed mild generalized cone system dysfunction and, in one patient, an interhemispheric asymmetry in visual evoked potentials. We show that CHRDL1 is expressed in the developing human cornea and anterior segment in addition to the retina. We explored the impact of loss of ventroptin function on brain function and morphology in vivo. CHRDL1 is differentially expressed in the human fetal brain, and there is high expression in cerebellum and neocortex. We show that MGC1 patients have a superior cognitive ability despite a striking focal loss of myelination of white matter. Our findings reveal an unexpected requirement for ventroptin during anterior segment development and the consequences of a lack of function in the retina and brain.

In vivo confocal microscopy in primary congenital glaucoma with megalocornea

PURPOSE

To report the microscopic findings of congenital glaucoma-related megalocornea using in vivo confocal microscopy.

PATIENTS AND METHODS

Two consecutive adult patients presenting the typical features of glaucomatous megalocornea underwent a complete ophthalmologic examination. The first patient presented with progressive glaucoma with bilateral megalocornea. The second patient's left eye was affected by megalocornea without actual evidence of glaucoma, whereas the right eye was healthy. Both patients were examined using a new-generation scanning slit corneal confocal microscope.

RESULTS

In both patients, confocal microscopy revealed a mild reduction of keratocyte density in the mid and rear stroma, a particular abnormal "clew-shaped" morphology of stromal nerves, and the presence of discontinuous hyperreflective structures overhanging the endothelial layer at the level of the Descemet membrane. The endothelium showed severe polymegethism, pleomorphism, and a markedly decreased cell density, and focal cellular lesions were noted.

CONCLUSION

Confocal microscopy is a diagnostic tool used to evaluate microscopic aspects of Haab striae and endothelial morphologic changes in glaucomatous megalocornea. Unsuspected alterations, such as nerves abnormalities and focal endothelial tractions by scar tissue, were observed.

Genetics of the corneal dystrophies: what we have learned in the past twenty-five years

PURPOSE

To indicate important changes in our understanding of the corneal dystrophies.

METHODS

A review of the literature of the last quarter of a century.

RESULTS

The earliest clinical classifications of the corneal dystrophies were based on the application of clinical, biological, histochemical, and ultrastructural methods. Since then, the first great impetus to our understanding has come from the application of techniques to map disorders to specific chromosome loci, using polymorphic markers. More recently, using candidate gene and related approaches, it has been possible to identify genes causing several of the corneal dystrophies and the mutations responsible for their phenotypic variation. A notable success has been to show that several important "stromal" dystrophies result from mutations in the gene beta ig-h3, which encodes for the protein keratoepithelin (beta ig-h3).

CONCLUSIONS

For the corneal dystrophies, as with other inherited disorders, there is room for two sorts of classification system, one based mainly on clinical presentation and the other on an up-to-date understanding of the genetic mechanisms. They are not mutually exclusive. Some developmental corneal disorders are also discussed.

Biometry in X linked megalocornea: pathognomonic findings

Biometric study in a series of 11 affected males provides characteristic findings. The patients present with a large cornea with short radius, very deep anterior chamber depth (AC depth) exceeding the normal mean value of plus 2 SD, and a short vitreous length. Calculation of the postlimbal depth, a method applied in this study to obtain information about positioning of the iris and the lens, reveals a posterior positioning of the iris and lens. The posterior positioning of the iris and lens was proved to occur at the expense of the vitreous. The importance of biometric data for diagnosis and for differential diagnosis in primary infantile glaucoma and other diseases with megalocornea is discussed.

Heterogeneity versus variability in megalocornea-mental retardation (MMR) syndromes: report of new cases and delineation of 4 probable types

Megalocornea (corneal diameter > or = 13 mm) is associated with mental and neurological impairment, and minor anomalies in Neuhäuser syndrome (megalocornea-mental retardation syndrome). Here we report 4 new cases of megalocornea and mental retardation. Those unrelated patients have a consistent pattern of anomalies with possible recessive inheritance which clearly differs from that of the original patients of Neuhäuser et al. [1975]. We discuss the heterogeneity of the syndromes with megalocornea and mental retardation. Based on these cases and on a review of the literature, we suggest a provisional clinically oriented classification in 5 subtypes: (1) a recessive form type Neuhäuser (with iris hypoplasia and minor anomalies), (2) a recessive form type Frank-Temtamy (with camptodactyly, scoliosis and growth retardation), (3) a recessive type 3, including our 4 personal cases (with normal irides, severe hypotonia, relative or absolute macrocephaly and minor anomalies), (4) a possible Frydman type (with normal irides, megalencephaly and obesity), and (5) provisionally unclassifiable cases.