Posterior microphthalmia and nanophthalmia in Tunisia caused by a founder c.1059_1066insC mutation of the PRSS56 gene

Heterozygous variants c.781G>A and c.1066dup of serine protease 56 cause familial nanophthalmos by impairing serine-type endopeptidase activity

BACKGROUND/AIMS

Nanophthalmos is a rare developmental, bilateral, sporadic or hereditary form of microphthalmos. In this study, the heterozygous variants c.781G>A and c.1066dup of the PRSS56 gene were identified in two patients with nanophthalmos. This study reports the clinical manifestation and the underlying pathogenic mechanism.

METHODS

Whole-exome sequencing was performed to identify the pathogenic genes in a Chinese family with nanophthalmos. The molecular simulation was used to predict the structures of wild-type or mutant PRSS56. The PRSS56 wild-type or mutation overexpression cellular models have been constructed accordingly. The subcellular localisation was then observed using immunofluorescence and Western-blot techniques. The Folin-Ciocalteu assay was carried out to evaluate serine-type endopeptidase activity, and a wound-healing assay was used to examine the cellular migratory ability.

RESULTS

The whole-exome sequencing revealed that heterozygous variants c.781G>A and c.1066dup of the PRSS56 gene might contribute to nanophthalmos. Both variants were not identified in the dbSNP, 1000 Genome project or ESP6500 databases. Furthermore, the variants were highly conserved and were involved in biological functions. The mutations result in destructive protein structure and impede serine-type endopeptidase activity, thereby impairing subcellular localisation and cellular migration.

CONCLUSION

The c.781G>A and c.1066dup variants of the PRSS56 gene might negatively affect protein structures, subcellular localisation, serine-type endopeptidase activity and cellular migratory ability. Together, these changes could lead to the development of nanophthalmos. This study identifies the PRSS56 gene as a potential target for nanophthalmos diagnosis and treatment.

Pathogenic variants of MFRP and PRSS56 genes are major causes of nanophthalmos in Japanese patients

BACKGROUND

Nanophthalmos (NNO) is a rare condition with significantly shorter axial length than normal. Several genes are known to cause NNO, among them the MFRP and PRSS56 genes have been reported to cause majority of NNOs. The purpose of this study was to determine the genetic basis of Japanese patients with NNO.

MATERIALS AND METHODS

We studied seven patients with NNO. Whole exome sequencing (WES) and Sanger sequencing were performed to determine the variants causing the NNO. We also reviewed the medical charts of the patients to determine the phenotype of these seven patients.

RESULTS

WES revealed that four patients from three families carried homozygous frameshift variants of the PRSS56 gene (c.1066dupC). Two novel variants of the MFRP gene were detected in the other two patients: one proband had a homozygous missense variant (c.1486 G>A) and the other had a compound heterozygous variant (c.1486 G>A and c.662_663insT). The axial length of the eight eyes with the PRSS56 variant was 15.69 ± 0.48 mm (mean ± SD) and that for the 4 eyes with the MFRP variant was 15.63 ± 0.69 mm. Three of the six cases with the PRSS56 or MFRP variant had the uveal effusion syndrome.

CONCLUSIONS

NNOs in Japanese patients are caused by variants of the PRSS56 and MFRP genes as in other ethnic populations. In addition, two new variants of the MFRP gene were found in our cohort. The phenotypes and anomalies in Japanese patients with NNO were similar to those reported for other ethnic populations.

Spectrum of Genetic Diseases in Tunisia: Current Situation and Main Milestones Achieved

Genetic diseases in Tunisia are a real public health problem given their chronicity and the lack of knowledge concerning their prevalence and etiology, and the high rates of consanguinity. Hence, we performed systematic reviews of the literature in order to provide a more recent spectrum of these disorders and to expose the challenges that still exist to tackle these kinds of diseases. A manual textual data mining was conducted using MeSH and PubMed databases. Collected data were classified according to the CIM-10 classification and the transmission mode. The spectrum of these diseases is estimated to be 589 entities. This suggests remarkable progress through the development of biomedical health research activities and building capacities. Sixty percent of the reported disorders are autosomal recessive, which could be explained by the high prevalence of endogamous mating. Congenital malformations (29.54%) are the major disease group, followed by metabolic diseases (22%). Sixty percent of the genetic diseases have a known molecular etiology. We also reported additional cases of comorbidity that seem to be a common phenomenon in our population. We also noticed that epidemiological data are scarce. Newborn and carrier screening was only limited to pilot projects for a few genetic diseases. Collected data are being integrated into a database under construction that will be a valuable decision-making tool. This study provides the current situation of genetic diseases in Tunisia and highlights their particularities. Early detection of the disease is important to initiate critical intervention and to reduce morbidity and mortality.

Genotype-phenotype spectrum in isolated and syndromic nanophthalmos

PURPOSE

To (i) describe a series of patients with isolated or syndromic nanophthalmos with the underlying genetic causes, including novel pathogenic variants and their functional characterization and (ii) to study the association of retinal dystrophy in patients with MFRP variants, based on a detailed literature review of genotype-phenotype correlations.

METHODS

Patients with nanophthalmos and available family members received a comprehensive ophthalmological examination. Genetic analysis was based on whole-exome sequencing and variant calling in core genes including MFRP, BEST1, TMEM98, PRSS56, CRB1, GJA1, C1QTNF5, MYRF and FAM111A. A minigene assay was performed for functional characterization of a splice site variant.

RESULTS

Seven patients, aged between three and 65 years, from five unrelated families were included. Novel pathogenic variants in MFRP (c.497C>T, c.899-3C>A, c.1180G>A), and PRSS56 (c.1202C>A), and a recurrent de novo variant in FAM111A (c.1706G>A) in a patient with Kenny-Caffey syndrome type 2, were identified. In addition, we report co-inheritance of MFRP-related nanophthalmos and ADAR-related Aicardi-Goutières syndrome.

CONCLUSION

Nanophthalmos is a genetically heterogeneous condition, and the severity of ocular manifestations appears not to correlate with variants in a specific gene. However, retinal dystrophy is only observed in patients harbouring pathogenic MFRP variants. Furthermore, heterozygous carriers of MFRP and PRSS56 should be screened for the presence of high hyperopia. Identifying nanophthalmos as an isolated condition or as part of a syndrome has implications for counselling and can accelerate the interdisciplinary care of patients.

Long-term follow-up of a case of posterior microphthalmos (PRSS56) with hyperautofluorescent retinal pigment epithelial deposits

PURPOSE

To report a case of posterior microphthalomos (PM) related to PRSS56 gene mutation with long term follow up with multimodal imaging findings.

METHODS

Single retrospective case report.

RESULTS

A 43-year old male patient presented in 2009 with bilateral reduced vision. Clinical examination and multimodal imaging showed features consistent with posterior microphthalmos with prominent bilateral horizontal papillomacular retinal folds. Posterior pole hyperautofluorescent RPE deposits were present. Gradual worsening of visual acuity and rod and cone photoreceptor function more so on the left was demonstrated during the 8 years of follow up.

CONCLUSION

Hyperautofluorescent RPE deposits may occur in patients with posterior microphthalmos and such patient's may experience only gradual disease progression over long term follow up.

Pseudodominant Nanophthalmos in a Roma Family Caused by a Novel PRSS56 Variant

Background

The aim of the study was to identify the molecular genetic cause of two different Mendelian traits with ocular involvement present in the members of a single consanguineous Czech Roma family.

Methods

We have performed ocular examination and review of medical records in two individuals diagnosed with nanophthalmos (proband and her father) and one individual followed for bilateral congenital cataract and microcornea (uncle of the proband). DNA of subjects with nanophthalmos was analysed by exome sequencing. Sanger sequencing was applied for targeted screening of potentially pathogenic variants and to follow segregation of identified variants within the family.

Results

A homozygous variant c.1509G>C; p.(Met503Ile), in PRSS56 was found in the two individuals affected with nanophthalmos. The change was absent from the gnomAD dataset, but two out of 118 control Roma individuals were also shown to be heterozygous carriers. Analysis of single nucleotide polymorphisms in linkage disequilibrium with the c.1509G>C in PRSS56 suggested a shared chromosomal segment. The nanophthalmos phenotype, characterized in detail in the younger individual, encompassed bilateral corneal steepening, retinal folds, buried optic head drusen, and restricted visual fields, but no signs of retinal dystrophy. A known pathogenic founder CTDP1 variant c.863+389C>T in a homozygous state was identified in the other family member confirming the suspected diagnosis of congenital cataracts, facial dysmorphism, and demyelinating neuropathy syndrome.

Conclusions

Herein, we report the first occurrence of nanophthalmos in the Roma population. We have identified pseudodominant inheritance for this phenotype caused by a novel variant in PRSS56, representing a possible founder effect. Despite advances in genetic technologies such as exome sequencing, careful phenotype evaluation in patients from an isolated population, along with an awareness of population-specific founder effects, is necessary to ensure that accurate molecular diagnoses are made.

The genetic and clinical landscape of nanophthalmos and posterior microphthalmos in an Australian cohort

Nanophthalmos and posterior microphthalmos are ocular abnormalities in which both eyes are abnormally small, and typically associated with extreme hyperopia. We recruited 40 individuals from 13 kindreds with nanophthalmos or posterior microphthalmos, with 12 probands subjected to exome sequencing. Nine probands (69.2%) were assigned a genetic diagnosis, with variants in MYRF, TMEM98, MFRP, and PRSS56. Two of four PRSS56 families harbored the previously described c.1066dupC variant implicated in over half of all reported PRSS56 kindreds, with different surrounding haplotypes in each family suggesting a mutational hotspot. Individuals with a genetic diagnosis had shorter mean axial lengths and higher hyperopia than those without, with recessive forms associated with the most extreme phenotypes. These findings detail the genetic architecture of nanophthalmos and posterior microphthalmos in a cohort of predominantly European ancestry, their relative clinical phenotypes, and highlight the shared genetic architecture of rare and common disorders of refractive error.

Novel mutations in MFRP and PRSS56 are associated with posterior microphthalmos

Background: Biallelic pathogenic variants in MFRP and PRSS56 genes can be responsible for nanophthalmos (NO) or posterior microphthalmos (PM). This study describes detailed clinical and molecular findings in a series of five patients affected by PM from four unrelated families.Materials and Methods: All patients underwent a complete ophthalmological and genetic evaluation. For proper and deep phenotyping a multimodal instrumental approach was used for all cases: B-scan ultrasound, spectral domain optical coherence tomography (SD-OCT), fundus retinal imaging and anterior segment data were obtained. Molecular analysis of PRSS56 and MFRP genes was performed with Next-Generation Sequencing (NGS) methodology and segregation analysis on parents and one affected sibling was performed with Sanger sequencing.Results: A very high hyperopia of +14.00D or more was the main refractive error and macular abnormalities were identified in all patients. Axial length ranged from 15.3 mm to 17.86 mm (mean 16.58 mm) and age at first presentation ranged from 6 to 36 months (mean 18 months). Anterior chamber depth was within normal values, according to age, while total axial length was severely reduced in all patients. All our patients met the diagnostic criteria for PM. Three patients, including a pair of siblings, carried compound heterozygous mutations in the PRSS56 gene; in the other two patients, one homozygous or two compound heterozygous mutations in the MFRP gene were detected.Conclusion: Our study describes four novel mutations in the PRSS56 gene and one in the MFRP gene in patients with non-syndromic posterior microphthalmos. Proper genotype-phenotype correlation and early diagnosis could lead to good functional results.

OPTICAL COHERENCE TOMOGRAPHY AND OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY FINDINGS AND VISUAL PROGNOSIS IN TWO PATIENTS WITH POSTERIOR MICROPHTHALMOS

BACKGROUND/PURPOSE

Posterior microphthalmos is a rare ocular condition characterized by a disproportionately small posterior segment and multiple retinal abnormalities. The diagnosis can be challenging, and novel findings on optical coherence tomography (OCT) angiography may help to identify this unusual disorder. The purpose of this study is to report OCT and OCT angiography findings in two siblings with posterior microphthalmos.

METHODS

Case series at an academic eye institute including two affected siblings with posterior microphthalmos.

RESULTS

The results of OCT testing in two siblings with posterior microphthalmos illustrated bilateral papillomacular retinal fold and loss of the foveal depression. Optical coherence tomography angiography findings included loss of the foveal avascular zone and complete vascularization across the fovea.

CONCLUSION

Unique OCT angiography findings in posterior microphthalmos are described herein. These findings may support the diagnosis of posterior microphthalmos and aid in the understanding of the pathogenesis of this disease.

Detection of Clinically Relevant Genetic Variants in Chinese Patients With Nanophthalmos by Trio-Based Whole-Genome Sequencing Study

Purpose

Nanophthalmos is a rare genetic disorder commonly characterized by a short axial length (AL) and severe hyperopia. Mutations that have been identified through Mendelian genetic analysis can only explain a fraction of nanophthalmic cases. We investigate the clinically relevant genetic variants in nanophthalmos by whole-genome sequencing (WGS), including de novo mutations (DNMs) and inherited mutations.

Methods

Clinically relevant genetic variants of 11 trios (11 nanophthalmic probands and their unaffected parents) from the Zhongshan Ophthalmic Center, China, were analyzed by WGS. We further screened three trios and 10 sporadic cases to identify the MYRF mutations.

Results

In two of 11 trios, without evidence of the presence of deleterious inherited autosomal variants, two DNMs of MYRF (c.789delC, p.S264fs and c.789dupC, p.S264fs) were identified in the probands. These loss-of-function DNMs were predicted to result in premature stop codons and protein structure damage in both probands. In addition, deleterious inherited genetic variants in PRSS56 and MFRP were found in eight probands of the other nine trios. Expanded screening found an additional MYRF DNM (c.1433G>C, p.R478P) in one trio and a stop-gain MYRF mutation (c.2956C>T, p.R986X) in one sporadic case, suggesting the recurrence of MYRF mutations in nanophthalmic patients.

Conclusions

This is the first trio-based WGS study for nanophthalmos, revealing the potential role of DNMs in MYRF and rare inherited genetic variants in PRSS56 and MFRP. The underlying mechanism of MYRF in the development of nanophthalmos needs to be further investigated.

Novel truncation mutations in MYRF cause autosomal dominant high hyperopia mapped to 11p12-q13.3

High hyperopia is a common and severe form of refractive error. Genetic factors play important roles in the development of high hyperopia but the exact gene responsible for this condition is mostly unknown. We identified a large Chinese family with autosomal dominant high hyperopia. A genome-wide linkage scan mapped the high hyperopia to chromosome 11p12-q13.3, with maximum log of the odds scores of 4.68 at theta = 0 for D11S987. Parallel whole-exome sequencing detected a novel c.3377delG (p.Gly1126Valfs*31) heterozygous mutation in the MYRF gene within the linkage interval. Whole-exome sequencing in other 121 probands with high hyperopia identified additional novel mutations in MYRF within two other families: a de novo c.3274_3275delAG (p.Leu1093Profs*22) heterozygous mutation and a c.3194+2T>C heterozygous mutation. All three mutations are located in the C-terminal region of MYRF and are predicted to result in truncation of that portion. Two patients from two of the three families developed angle-closure glaucoma. These three mutations were present in neither the ExAC database nor our in-house whole-exome sequencing data from 3280 individuals. No other truncation mutations in MYRF were detected in the 3280 individuals. Knockdown of myrf resulted in small eye size in zebrafish. These evidence all support that truncation mutations in the C-terminal region of MYRF are responsible for autosomal dominant high hyperopia in these families. Our results may provide useful clues for further understanding the functional role of the C-terminal region of this critical myelin regulatory factor, as well as the molecular pathogenesis of high hyperopia and its associated angle-closure glaucoma.

Genetics of anophthalmia and microphthalmia. Part 1: Non-syndromic anophthalmia/microphthalmia

Eye formation is the result of coordinated induction and differentiation processes during embryogenesis. Disruption of any one of these events has the potential to cause ocular growth and structural defects, such as anophthalmia and microphthalmia (A/M). A/M can be isolated or occur with systemic anomalies, when they may form part of a recognizable syndrome. Their etiology includes genetic and environmental factors; several hundred genes involved in ocular development have been identified in humans or animal models. In humans, around 30 genes have been repeatedly implicated in A/M families, although many other genes have been described in single cases or families, and some genetic syndromes include eye anomalies occasionally as part of a wider phenotype. As a result of this broad genetic heterogeneity, with one or two notable exceptions, each gene explains only a small percentage of cases. Given the overlapping phenotypes, these genes can be most efficiently tested on panels or by whole exome/genome sequencing for the purposes of molecular diagnosis. However, despite whole exome/genome testing more than half of patients currently remain without a molecular diagnosis. The proportion of undiagnosed cases is even higher in those individuals with unilateral or milder phenotypes. Furthermore, even when a strong gene candidate is available for a patient, issues of incomplete penetrance and germinal mosaicism make diagnosis and genetic counseling challenging. In this review, we present the main genes implicated in non-syndromic human A/M phenotypes and, for practical purposes, classify them according to the most frequent or predominant phenotype each is associated with. Our intention is that this will allow clinicians to rank and prioritize their molecular analyses and interpretations according to the phenotypes of their patients.

Identification of novel pathogenic variants and novel gene-phenotype correlations in Mexican subjects with microphthalmia and/or anophthalmia by next-generation sequencing

Severe congenital eye malformations, particularly microphthalmia and anophthalmia, are one of the main causes of visual handicap worldwide. They can arise from multifactorial, chromosomal, or monogenic factors and can be associated with extensive clinical variability. Genetic analysis of individuals with these defects has allowed the recognition of dozens of genes whose mutations lead to disruption of normal ocular embryonic development. Recent application of next generation sequencing (NGS) techniques for genetic screening of patients with congenital eye defects has greatly improved the recognition of monogenic cases. In this study, we applied clinical exome NGS to a group of 14 Mexican patients (including 7 familial and 7 sporadic cases) with microphthalmia and/or anophthalmia. Causal or likely causal pathogenic variants were demonstrated in ~60% (8 out of 14 patients) individuals. Seven out of 8 different identified mutations occurred in well-known microphthalmia/anophthalmia genes (OTX2, VSX2, MFRP, VSX1) or in genes associated with syndromes that include ocular defects (CHD7, COL4A1) (including two instances of CHD7 pathogenic variants). A single pathogenic variant was identified in PIEZO2, a gene that was not previously associated with isolated ocular defects. NGS efficiently identified the genetic etiology of microphthalmia/anophthalmia in ~60% of cases included in this cohort, the first from Mexican origin analyzed to date. The molecular defects identified through clinical exome sequencing in this study expands the phenotypic spectra of CHD7-associated disorders and implicate PIEZO2 as a candidate gene for major eye developmental defects.

Prenatal diagnosis and implications of microphthalmia and anophthalmia with a review of current ultrasound guidelines: two case reports

BACKGROUND

Microphthalmia and anophthalmia are rare congenital fetal abnormalities. The combined incidence is estimated at 1 in 10,000 births. These two conditions arise from complex and incompletely understood genetic and/or environmental causes. Prenatal diagnosis is neither frequent nor easy and relies on precise, high-quality ultrasonography. Current antenatal ultrasound protocols for imaging of the fetal eye are inconsistent and inadequate to screen for the spectrum of ocular malformations, and there are no clear guidelines on detection of these rare abnormalities. Our study of two cases highlights the importance of early detection, and we review current practice and suggest a definitive fetal imaging protocol.

CASE PRESENTATION

We present two antenatal cases, one each of microphthalmia and anophthalmia, both diagnosed at the morphology scan at our tertiary fetal medicine unit. In both cases, the parents (a 36-year-old woman of Mauritanian ethnicity and a non-consanguineous partner of Nepalese descent, and a 31-year-old Caucasian woman and non-consanguineous Caucasian partner) elected to terminate their pregnancies and made unremarkable recoveries. Subsequent fetal autopsy confirmed the ultrasound scan findings.

CONCLUSIONS

We recommend that antenatal ultrasound guidelines are updated to specify use of a curvilinear transducer (2-9 MHz) to image both orbits in the axial and coronal planes, aided by use of a transvaginal probe when the transabdominal approach is inadequate to generate these images. When applicable, three-dimensional reverse-face imaging should be obtained to aid the diagnosis. The presence, absence, or non-visualization of lenses and hyaloid arteries should be documented in reports and these cases referred for a tertiary-level ultrasound scan and fetal medicine review. Imaging of the orbits should occur from 12 weeks' gestation. Magnetic resonance imaging and amniocentesis with chromosome microarray testing may provide additional genetic and structural information that may affect the overall morbidity associated with a diagnosis of microphthalmia or anophthalmia.

Nanophthalmos: A Review of the Clinical Spectrum and Genetics

Nanophthalmos is a clinical spectrum of disorders with a phenotypically small but structurally normal eye. These disorders present significant clinical challenges to ophthalmologists due to a high rate of secondary angle-closure glaucoma, spontaneous choroidal effusions, and perioperative complications with cataract and retinal surgeries. Nanophthalmos may present as a sporadic or familial disorder, with autosomal-dominant or recessive inheritance. To date, five genes (i.e., MFRP, TMEM98, PRSS56, BEST1, and CRB1) and two loci have been implicated in familial forms of nanophthalmos. Here, we review the definition of nanophthalmos, the clinical and pathogenic features of the condition, and the genetics of this disorder.

Gene profiling of postnatal Mfrprd6 mutant eyes reveals differential accumulation of Prss56, visual cycle and phototransduction mRNAs

Mutations in the membrane frizzled-related protein (MFRP/Mfrp) gene, specifically expressed in the retinal pigment epithelium (RPE) and ciliary body, cause nanophthalmia or posterior microphthalmia with retinitis pigmentosa in humans, and photoreceptor degeneration in mice. To better understand MFRP function, microarray analysis was performed on eyes of homozygous Mfrp^rd6 and C57BL/6J mice at postnatal days (P) 0 and P14, prior to photoreceptor loss. Data analysis revealed no changes at P0 but significant differences in RPE and retina-specific transcripts at P14, suggesting a postnatal influence of the Mfrp^rd6 allele. A subset of these transcripts was validated by quantitative real-time PCR (qRT-PCR). In Mfrp^rd6 eyes, a significant 1.5- to 2.0-fold decrease was observed among transcripts of genes linked to retinal degeneration, including those involved in visual cycle (Rpe65, Lrat, Rgr), phototransduction (Pde6a, Guca1b, Rgs9), and photoreceptor disc morphogenesis (Rpgrip1 and Fscn2). Levels of RPE65 were significantly decreased by 2.0-fold. Transcripts of Prss56, a gene associated with angle-closure glaucoma, posterior microphthalmia and myopia, were increased in Mfrp^rd6 eyes by 17-fold. Validation by qRT-PCR indicated a 3.5-, 14- and 70-fold accumulation of Prss56 transcripts relative to controls at P7, P14 and P21, respectively. This trend was not observed in other RPE or photoreceptor mutant mouse models with similar disease progression, suggesting that Prss56 upregulation is a specific attribute of the disruption of Mfrp. Prss56 and Glul in situ hybridization directly identified Müller glia in the inner nuclear layer as the cell type expressing Prss56. In summary, the Mfrp^rd6 allele causes significant postnatal changes in transcript and protein levels in the retina and RPE. The link between Mfrp deficiency and Prss56 up-regulation, together with the genetic association of human MFRP or PRSS56 variants and ocular size, raises the possibility that these genes are part of a regulatory network influencing postnatal posterior eye development.