SOX2, OTX2 and PAX6 analysis in subjects with anophthalmia and microphthalmia

Non-syndromic OTX2-associated pattern dystrophy: a 10-year multimodal imaging study

PURPOSE

To report novel multimodal imaging features and long-term follow-up of Orthodenticle Homeobox 2 (OTX2)-associated pattern Gdystrophy.

METHODS

A 14-year-old boy referred with glaucoma suspect and macular pigmentation underwent fundus autofluorescence imaging, optical coherence tomography, fluorescein and indocyanine green angiography, visual field test, microperimetry and electrophysiology over a ten-year period. Next-generation sequencing panel identified a de novo heterozygous likely pathogenic OTX2 variant, c.259G>A, [p.(Glu87Lys)].

RESULTS

Visual acuity was 20/40 OD and 20/30 OS. Examination showed bilateral enlarged optic nerve heads and increased disc cupping, multiple cilioretinal arteries, a pigmentary maculopathy with stellate-shaped region of hypoautofluorescence, shallow serous macular detachment, subretinal deposits and temporal avascular retina. Angiography showed no source of leakage and absence of retinal neovascularisation despite extensive peripheral non perfusion. Electrophysiological assessments demonstrated mild progressive rod and cone pathway abnormalities, reduced light-adapted b:a ratio, and reduced Arden ratio on electro-oculogram. Ten-year follow-up confirmed a stable disease course despite persistent submacular fluid. There was no associated pituitary structural abnormality or dysfunction.

CONCLUSIONS

This case study contributes to further understanding of OTX2-associated pattern dystrophy, highlighting its stability over 10 years. Further investigation into inter-individual and intrafamilial variability is warranted.

Demographics and histopathological characteristics of enucleated microphthalmic globes

Microphthalmia is a rare ocular anomaly with a poorly understood etiology that is most likely related to heritable and/or environmental factors. Many papers have been published pertaining to the clinical manifestations and management of this condition; however, few reports have reported detailed histopathological findings, which are the focus of this study, in addition to highlighting the basic demographics in these cases. This was a retrospective, observational study of all consecutive enucleated microphthalmic globes (with or without cysts) at 2 tertiary eye hospitals in Riyadh, Saudi Arabia. Globes were classified into 2 groups: severe microphthalmos (axial length or mean diameter less than 10 mm in infancy or 12 mm after age 1 year) and mild microphthalmos based on larger measurements. Clinical and demographic data collected included sex, age at enucleation, eye involvement, nationality/region, consanguinity, family history of eye anomaly, pregnancy, systemic disease, or syndromes. For histopathological data, a descriptive analysis was mostly performed. For correlations of some of our qualitative data, Fisher's exact test was used. Eleven cases (6 mild and 5 severe microphthalmos) were initially identified with a female to male ratio of 4:7. Ten patients were Saudis, 7 of whom were from the central region. Consanguinity was found in 36% (4/11), and 3 of them had other ocular or systemic abnormalities (duodenal atresia, microcephaly, kidney agenesis, cryptophthalmos, and dysmorphic facial features). Histopathological data were available for 10 cases, half of which showed a coloboma and/or anterior segment anomaly. There was no significant correlation among gender, severity of microphthalmos or the presence of coloboma, although severe microphthalmic globes had a higher median of abnormal intraocular structures (9-interquartile range = 2 compared to 6-interquartile range = 1 in the mild group). Aphakia was found in half of the globes with associated anterior segment dysgenesis. We have concluded that microphthalmos is a visually disabling congenital anomaly that can be isolated or associated with other periocular or systemic anomalies, possibly in relation to consanguinity in our cases. Congenital aphakia was found in half of these cases and was mostly associated with absent Descemet's membrane and agenesis of anterior chamber angle structures, supporting previously suggested embryological concepts. These findings necessitate further wider genetic testing and proper premarital counseling in Saudi Arabia.

Long-read genome sequencing resolves a complex 13q structural variant associated with syndromic anophthalmia

Microphthalmia, anophthalmia, and coloboma (MAC) are a heterogeneous spectrum of anomalous eye development and degeneration with genetic and environmental etiologies. Structural and copy number variants of chromosome 13 have been implicated in MAC; however, the specific loci involved in disease pathogenesis have not been well-defined. Herein we report a newborn with syndromic degenerative anophthalmia and a complex de novo rearrangement of chromosome 13q. Long-read genome sequencing improved the resolution and clinical interpretation of a duplication-triplication/inversion-duplication (DUP-TRP/INV-DUP) and terminal deletion. Sequence features at the breakpoint junctions suggested microhomology-mediated break-induced replication (MMBIR) of the maternal chromosome as the origin. Comparing this rearrangement to previously reported copy number alterations in 13q, we refine a putative dosage-sensitive critical region for MAC that might provide new insights into its molecular etiology.

Identification of a novel de novo variant in OTX2 in a patient with congenital microphthalmia using targeted next-generation sequencing followed by prenatal diagnosis

BACKGROUND

Next-generation sequencing has been proven to be a reliable method for the detection of genetic causes in heterogeneous ocular disorders. In this report an NGS-based diagnostic approach was taken to uncover the genetic etiology in a patient with coloboma and microphthalmia, a highly heterogeneous disease with intrafamilial phenotypic variability.

MATERIALS AND METHODS

Next generation sequencing using a targeted panel of 316 genes, was carried out in the proband. Prioritized variants were then identified and confirmed using Sanger sequencing. Prenatal diagnosis of the detected variant was then performed in the family.

RESULTS

A novel de novo frameshift variant c.157_164delTTCACTCG (p.Phe53fs) in OTX2, leading to a truncated protein, was identified. Prenatal diagnosis identified the same variant in the fetus.

CONCLUSIONS

This report demonstrates the importance of genetic counseling and underscores the efficiency and effectiveness of targeted NGS as a means of detecting variants in inherited eye disorders.

A Finite Element Analysis Model is Suitable for Biomechanical Analysis of Orbital Development

ABSTRACT

The authors investigated orbital bone development in congenital microphthalmia (CM) using a three-dimensional finite element analysis model, after the orbital dimension deficiency was improved with a self-inflating hydrogel expander implant.Data of a 2-year-old male CM patient were examined. The orbital structure, eyeball, eye muscles, and self-inflating hydrogel expander were constructed according to computed tomography examination data. The effects of self-expanding spherical hydrogel at various locations in the muscle cone on orbital bone development were examined using 3-mL self-expanding expanders placed at shallow (model 1: 2 mm depth) and deep (model 2: 8 mm depth) muscle cone positions. This model simulated the hydrogel expansion process; the orbital bone biomechanics and radial displacement nephograms were obtained when the hydrogel volume increased 3, 5, 7, and 9 times and analyzed.The orbital bone biomechanics were concentrated at the medial orbital wall center, gradually spreading to the whole orbital wall. Biomechanics and radial displacement of the inferior temporal and lateral distal orbital wall region were the most significant, and were more significant in model 1 than in model 2.Finite element analysis is suitable for the biomechanical analysis of orbital development in CM. The shallow position inside CM patients' muscle cone is the optimal site for hydrogel implantation.

Classification for treatment urgency for the microphthalmia/anophthalmia spectrum using clinical and biometrical characteristics

PURPOSE

Current clinical classifications do not distinguish between the severity of the MICrophthalmia/Anophthalmia (MICA) spectrum with regard to treatment urgency. We aim to provide parameters for distinguishing mild, moderate and severe MICA using clinical and biometrical characteristics.

METHODS

We performed a single-centre, cross-sectional analysis of prospective cohort of 58 MICA children from September 2013 to February 2018 seen at the Amsterdam University Medical Center, The Netherlands. All patients with a visible underdeveloped globe were included. We performed full ophthalmic evaluation including horizontal palpebral fissure length, axial length by ultrasound and/or MRI measurements, paediatric and genetic evaluation. Cases were subdivided based on clinical characteristics. Biometrical data were used to calculate the relative axial length (rAL) and the relative horizontal palpebral fissure length (rHPF) compared with the healthy contralateral eye for unilateral cases.

RESULTS

In previously untreated patients, a strong correlation exists between rAL and rHPF, distinguishing between severe, moderate and mild subjects using rAL of 0-45%, 45-75% and 75%-100%, respectively. Clinical subgroups were randomly dispersed throughout the scatterplot.

CONCLUSION

Current classifications lack clinical implications for MICA patients. We suggest measuring eyelid length and axial length to classify the severity and determine treatment strategy. The 'severe' group has obvious asymmetry and abnormal socket configuration for which therapy should quickly be initiated; the 'moderately' affected group has normal socket anatomy with a microphthalmic eye with disturbing asymmetry for which treatment should be initiated within months of development; the 'mild' group has a slightly smaller axial length or less obvious eyelid asymmetry for which reconstructive correction is possible, but expansive conformer treatment is unnecessary.

Extension of the mutational and clinical spectrum of SOX2 related disorders: Description of six new cases and a novel association with suprasellar teratoma

SOX2 is a transcription factor that is essential for maintenance of pluripotency and has several conserved roles in early embryonic development. Heterozygous loss-of-function variants in SOX2 are identified in approximately 40% of all cases of bilateral anophthalmia/micropthalmia (A/M). Increasingly SOX2 mutation-positive patients without major eye findings, but with a range of other developmental disorders including autism, mild to moderate intellectual disability with or without structural brain changes, esophageal atresia, urogenital anomalies, and endocrinopathy are being reported, suggesting that the clinical phenotype associated with SOX2 loss is much broader than previously appreciated. In this report we describe six new cases, four of which carry novel pathogenic SOX2 variants. Four cases presented with bilateral anophthalmia in addition to extraocular involvement. Another individual presented with only unilateral anophthalmia. One individual did not have any eye findings but presented with a suprasellar teratoma in infancy and was found to have the recurrent c.70del20 mutation in SOX2 (c.70_89del, p.Asn24Argfs*65). This is this first time this tumor type has been reported in the context of a de novo SOX2 mutation. Notably, individuals with hypothalamic hamartomas and slow-growing hypothalamo-pituitary tumors have been reported previously, but it is still unclear how SOX2 loss contributes to their formation.

Epistasis between Pax6Sey and genetic background reinforces the value of defined hybrid mouse models for therapeutic trials

The small eye (Sey) mouse is a model of PAX6-aniridia syndrome (aniridia). Aniridia, a congenital ocular disorder caused by heterozygous loss-of-function mutations in PAX6, needs new vision saving therapies. However, high phenotypic variability in Sey mice makes development of such therapies challenging. We hypothesize that genetic background is a major source of undesirable variability in Sey mice. Here we performed a systematic quantitative examination of anatomical, histological, and molecular phenotypes on the inbred C57BL/6J, hybrid B6129F1, and inbred 129S1/SvImJ backgrounds. The Sey allele significantly reduced eye weight, corneal thickness, PAX6 mRNA and protein levels, and elevated blood glucose levels. Surprisingly, Pax6^Sey/Sey brains had significantly elevated Pax6 transcripts compared to Pax6^+/+ embryos. Genetic background significantly influenced 12/24 measurements, with inbred strains introducing severe ocular and blood sugar phenotypes not observed in hybrid mice. Additionally, significant interactions (epistasis) between Pax6 genotype and genetic background were detected in measurements of eye weight, cornea epithelial thickness and cell count, retinal mRNA levels, and blood glucose levels. The number of epistatic interactions was reduced in hybrid mice. In conclusion, severe phenotypes in the unnatural inbred strains reinforce the value of more naturalistic F1 hybrid mice for the development of therapies for aniridia and other disorders.

Long-term outcomes after cosmetic customized prostheses and dermis fat graft in congenital anophthalmia: a retrospective multicentre study

PURPOSE

To evaluate long-term outcomes of progressively enlarging cosmetic customized prostheses (CCP) early after birth followed by dermis fat graft (DFG), as a strategy of socket rehabilitation in children with clinical congenital anophthalmia (CCA).

METHODS

Twenty patients with unilateral and two patients with bilateral CCA were enrolled. All patients were treated by inserting a CCP at the time of their first assessment which was then enlarged. Subsequently they underwent DFG. Differences in vertical palpebral aperture (VPA) and horizontal palpebral length (HPL), between affected and unaffected sides, were recorded at the first CCP fitting as well as before and after DFG. Satisfaction with cosmetic results, prosthetic retention, and complications rate were assessed. Magnetic resonance imaging of the orbit was performed in all patients before and after surgery.

RESULTS

A significant decrease in the difference between the normal and the anophthalmic side of both PA and HPL was found over follow-up. Both VPA and HPL differences decreased by 47.6% (10.5 mm, range 1-28 mm) and by 7.1% (5.8 mm, range 0-18 mm), respectively. Satisfaction in terms of cosmetic outcomes proved to be very positive, being "very satisfied" for families and "satisfied" for physicians. Excellent retention of prostheses was observed in all cases.

CONCLUSIONS

A rehabilitating strategy combining early CCP and further DFG proved to be a valuable approach in children with CCA, offering significant benefits in terms of socket expansion, prosthetic retention, psychological impact, and cosmetic outcomes.

Case series: Pyramidal cataracts, intact irides and nystagmus from three novel PAX6 mutations

Purpose

To investigate the association between novel PAX6 mutations to bilateral anterior pyramidal congenital cataracts (APyC), complete and intact irides, and nystagmus.

Observations

This is a retrospective observational case series in a multi-center setting with genetic testing. Three female patients were diagnosed with bilateral APyC, intact irides and nystagmus. Genetic testing identified the three patients had novel missense mutations in PAX6 – c.128C > T; p.Ser43Phe (S43F), c. 197T > A; p.Ile66Asn (I66N) and c.781C > G; p.Arg261Gly (R261G).

Conclusions and importance

This study demonstrates a novel phenotype of bilateral APyC, intact irides, and nystagmus in whom genetic testing for PAX6 identified novel missense mutations (S43F, I66N, R261G) in highly conserved DNA-binding domains. Implications of understanding why the iris is present in these cases is discussed.

A novel OTX2 gene frameshift mutation in a child with microphthalmia, ectopic pituitary and growth hormone deficiency

OTX2 mutations are reported in patients with eye maldevelopment and in some cases with brain or pituitary abnormalities. We describe a child carrying a novel OTX2 heterozygous mutation. She presented microphthalmia, absence of retinal vascularization, vitreal spots and optic nerve hypoplasia in the right eye and mild macular dystrophy in the left eye. Midline brain structures and cerebral parenchyma were normal, except for the ectopic posterior pituitary gland. OTX2 sequencing showed a heterozygous c.402del mutation. Most of OTX2 mutations are nonsense or frameshift introducing a premature termination codon and resulting in a truncated protein. More rarely missense mutations occur. Our novel OTX2 mutation (c.402del) is a frameshift mutation (p.S135Lfs*43), never reported before, causing a premature codon stop 43 amino-acids downstream, which is predicted to generate a premature truncation. The mutation was associated with microphthalmia and ectopic posterior pituitary.