Diagnosing the cause of bilateral paediatric cataracts: comparison of standard testing with a next-generation sequencing approach

Identification of pathogenic genetic variants in patients with acquired early-onset bilateral cataracts using next-generation sequencing

BACKGROUND

Acquired early-onset bilateral cataracts can result from systemic etiologies or genetic disorders.

METHODS

In this observational study, we analyzed individuals 18 months to 35 years of age with acquired bilateral cataracts via a next-generation sequencing panel of 66 genes to identify disease-causing genetic variants.

RESULTS

Of 347 patients enrolled, 313 (90.2%) were <19 years (median, 8 years). We identified 74 pathogenic or likely pathogenic variants in 69 patients. Of the variants, we observed 64 single nucleotide variants (SNV) in 24 genes and 10 copy number variants (CNV) of varying size and genomic location. SNVs in crystallin genes were most common, accounting for 27.0% of all variants (20 of 74). Of those, recurrent variants included known cataract-causing variants CRYBA1 c.215+1G>A, observed in 3 patients, and CRYBA1 c.272_274delGAG, CRYBB2 c.463C>T and c.562C>T, and CRYAA c.62G>A, each observed in 2 patients. In 5 patients, we identified CNV deletions ranging from 1.32-2.41 Mb in size associated with 1q21.1 microdeletion syndrome. Biallelic variants in CYP27A1 were identified in two siblings, one as part of targeted follow-up family testing, who were subsequently diagnosed with cerebrotendinous xanthomatosis, a rare but treatable autosomal recessive disease that often presents with acquired early-onset bilateral cataracts.

CONCLUSIONS

This study demonstrates the utility of genetic testing in individuals with acquired early-onset bilateral cataracts to help clarify etiology. Identification of causative genetic variants can inform patient management and facilitate genetic counseling by identifying genetic conditions with risk of recurrence in families.

Early Diagnosis of Syndromic Congenital Cataracts in a Large Cohort of Congenital Cataracts

PURPOSE

To explore the factors related to the diagnosis yield of syndromic congenital cataracts and describe the phenotype-genotype correlation in congenital cataract patients.

DESIGN

Prospective cohort study.

METHODS

Setting: the participants from underwent clinical examinations between 2021 and 2022. Facial and anterior eye segment photographs, pre- and postoperative ocular parameters, and medical and family histories were recorded. Bioinformatics analysis was performed using whole-exome sequencing data. Statistical and correlation analyses were performed using the basic characteristics, deep phenotype, and genotype data.

PARTICIPANTS

115 patients with unrelated congenital cataract.

INTERVENTIONS

performing clinical examinations, whole-exome sequencing, and bioinformatics analysis for all participants.

MAIN OUTCOMES AND MEASURES

factors related to the genetic diagnosis yield of syndromic congenital cataracts.

RESULTS

Bilaterally asymmetrical cataracts were identified to be associated with syndromic congenital cataracts. The overall genetic diagnostic yield in the cohort was 72.2%. In total, 34.8% of the probands were early diagnosed with various syndromes with the help of genetic information. A phenotype-genotype correlation was detected for some genes and deep phenotypes.

CONCLUSIONS

We highlight the importance of screening syndromic diseases in the patients with asymmetrical congenital cataracts. Application of whole-exome sequencing helps provide early diagnosis and treatment for the patients with syndromic congenital cataracts. This study also achieved a high genetic diagnostic yield, expanded the genotypic spectrum, and found phenotype-genotype correlations. A comprehensive analysis of cataract symmetricity, family history, and deep phenotypes makes the genotype prediction of some congenital cataract patients possible.

Diagnostic yield of workups ordered by pediatric ophthalmologists for bilateral pediatric cataracts at a tertiary pediatric hospital in the United States

BACKGROUND

Children with unexplained bilateral cataracts routinely undergo testing for genetic, infectious, and metabolic etiologies. We evaluated the diagnostic yield of various tests ordered by pediatric ophthalmologists to evaluate bilateral cataracts in children at a single institution.

METHODS

We retrospectively identified all children with bilateral unexplained cataracts who underwent cataract surgery by a pediatric ophthalmologist at Children's Hospital Colorado from 2006 to 2022. We reviewed the results of genetic, infectious, and metabolic testing ordered by pediatric ophthalmologists to evaluate the cataracts in these children.

RESULTS

A total of 43 children met inclusion criteria. Of these, 34 (79%) had genetic testing, 34 (79%) had infectious disease testing, 33 (77%) had galactosemia testing, and 17 (40%) had urine-reducing substances testing performed during their cataract evaluation. Of the genetic tests ordered, 17 (50%) revealed a pathogenic mutation associated with cataracts. Twenty-three (68%) patients were IgG-positive for a TORCH infection, but no child was found to be positive on confirmatory testing. Of the galactosemia and URS tests ordered, 3 tests (9%) and 1 (6%) test were initially found to be abnormal, respectively, but confirmatory testing and clinical judgment ruled out metabolic disease in each case.

CONCLUSIONS

Genetic testing should be strongly considered in all cases of unexplained bilateral pediatric cataracts. Metabolic and infectious testing is best considered only after consultation with the child's pediatrician, guided by the patient's clinical context and the availability of genetic testing.

Burden and clinical profile of genetic eye diseases in children in Nigeria: a descriptive cross-sectional study

Introduction

ophthalmic genetics is rapidly evolving globally but is still nascent in much of sub-Saharan Africa, with gaps in knowledge about the burden in the region. This study evaluated the burden and manifestations of genetic eye diseases in children in Ibadan, Nigeria.

Methods

this was a hospital-based cross-sectional study in which new and follow-up paediatric eye clinic patients were recruited consecutively at the University College Hospital, Ibadan. Children with genetic eye diseases had comprehensive ocular and systemic examinations, and their pedigrees were charted to determine the probable modes of inheritance. The main outcome variables were the proportion of study participants with genetic eye diseases, the probable modes of inheritance, and the clinical diagnoses. Summary statistics were performed using means and standard deviations for numerical variables and proportions for categorical variables.

Results

fifty-two (12%) of 444 children had genetic eye diseases, and their mean (SD) age was 88.8 ± 50.4 months. Thirteen different phenotypic diagnoses were made following the evaluation of the 52 children, including primary congenital glaucoma (13, 25%) and familial non-syndromic cataracts (8, 15%). The probable modes of inheritance were derived from the pedigree charts, and 30 (58%) conditions were presumed to be sporadic.

Conclusion

this study demonstrated a significant burden and a wide range of paediatric genetic eye diseases in this tertiary referral centre in Nigeria. This information provides invaluable evidence for planning ophthalmic genetic services.

Evolution and trends of childhood cataract research in the past 10 years: A scientometric analysis

Purpose

To present a panoramic review of childhood cataract knowledge networks, hotspots and trends.

Methods

The Web of Science Core Collection was used to retrieve the global literature on childhood cataract published between 2012 and 2021. Scientometric data were analyzed and visualized using VOSviewer and CiteSpace for metrics including publication count, citation count, country, journal, author, cited reference, subject category and their temporal trends.

Results

A total of 3395 analyzed publications showed an inconsistent annual increasing trend. The USA (n = 939) was the leading contributor among countries. The Journal of American Association for Pediatric Ophthalmology and Strabismus (n = 113) had the highest number of publications among journals. Eight clusters of author collaboration network including 183 authors were identified. Gene mutation, cataract surgery management, intraocular lens implantation complications, prevalence, and glaucoma were identified as the research hotspots. Pediatric cataract surgery, new mutations, artificial intelligence, and cerebrotendinous xanthomatosis were identified as frontier research topics. "Biochemistry and molecular biology", "neurosciences", and "radiology, nuclear medicine and medical imaging" had the highest betweenness centrality values (0.38, 0.32, and 0.22). Multidisciplinary (burst years: 2020 to 2021; strength = 4.32) had the greatest strength as of 2021.

Conclusions

Childhood cataract research intensely focuses on revealing the genetic background and pheno-spectrum of the diseases, innovating and/or optimizing surgical techniques, and preventing and treating postoperative complications. Artificial intelligence has shed light on the diagnosis and treatment of childhood cataracts. The advance in the research on molecular mechanisms of childhood cataracts depends on multidisciplinary cooperation.

Fish to learn: insights into the effects of environmental chemicals on eye development and visual function in zebrafish

Vision is the most essential sense system for the human being. Congenital visual impairment affects millions of people globally. It is increasingly realized that visual system development is an impressionable target of environmental chemicals. However, due to inaccessibility and ethical issues, the use of humans and other placental mammals is constrained, which limits our better understanding of environmental factors on ocular development and visual function in the embryonic stage. Therefore, as complementing laboratory rodents, zebrafish has been the most frequently employed to understand the effects of environmental chemicals on eye development and visual function. One of the major reasons for the increasing use of zebrafish is their polychromatic vision. Zebrafish retinas are morphologically and functionally analogous to those of mammalian, as well as evolutionary conservation among vertebrate eye. This review provides an update on harmful effects from exposure to environmental chemicals, involving metallic elements (ions), metal-derived nanoparticles, microplastics, nanoplastics, persistent organic pollutants, pesticides, and pharmaceutical pollutants on the eye development and visual function in zebrafish embryos. The collected data provide a comprehensive understanding of environmental factors on ocular development and visual function. This report highlights that zebrafish is promising as a model to identify hazardous toxicants toward eye development and is hopeful for developing preventative or postnatal therapies for human congenital visual impairment.

Prospective cholestanol screening of cerebrotendinous xanthomatosis among patients with juvenile-onset unexplained bilateral cataracts

BACKGROUND

Cerebrotendinous xanthomatosis (CTX) is a rare genetic disorder related to CYP27A1 biallelic mutations, leading to decreased synthesis of bile acids and increased cholestanol. Juvenile bilateral cataracts are one of the most common findings in the disease, frequently occurring before the onset of neurological manifestations. While early treatment with chenodeoxycholic acid can prevent the onset of neurological impairment, poor awareness of CTX accounts for a markedly delayed diagnosis. The objective of this study was to evaluate the utility of plasma cholestanol analysis at the moment of cataract diagnosis and before the onset of neurological impairment in CTX.

METHODS

Multicenter prospective cohort study of patients with juvenile-onset unexplained bilateral cataracts recruited from seven French ophthalmology departments. Plasma cholestanol analysis was performed at diagnosis from January 2018 to January 2020. CYP27A1 genetic testing was performed at the ophthalmologist's discretion. Cholestanol levels were compared with those of a similar population of patients without cataracts (control cohort).

RESULTS

30 patients were finally recruited, with a mean age at cataract diagnosis of 7.1 years (± 4.8 SD, range 1-19 years). One patient had a very high cholestanol level (68 μmol/L, reference < 10) and carried two pathogenic heterozygous mutations in CYP27A1 confirming CTX. This patient was a 19-year-old female, reporting chronic diarrhea only in childhood, and diagnosed with bilateral posterior cataracts with cortical fleck-like opacities. Therefore, the incidence of CTX in our cohort of patients was 3.3%. Five further patients (5/29; 17.2%) had moderate elevations of cholestanol level (between 10.3 and 16.5 μmol/L), compared to 12/286 (4.2%) in the control cohort (p = 0.014) after adjustment for age.

CONCLUSION

Our study argue for the relevance of plasma cholestanol CTX screening in all patients with juvenile-onset unexplained cataracts, even without other CTX identified manifestations. Whether moderate elevations of plasma cholestanol unrelated to CTX may be a risk factor for bilateral cataracts occurrence needs further examination.

Descriptive and risk factor analysis of infantile cataracts: National Birth Defects Prevention Study, 2000-2011

Using National Birth Defects Prevention Study (NBDPS) data, we sought to estimate birth prevalence, describe clinical characteristics, and examine risk factors for infantile cataracts. We calculated birth prevalence using the numbers of NBDPS-eligible cataract cases and live births in the study area. We described case infants by the presence of associated ipsilateral eye defects (IEDs) and non-eye-related major birth defects. Using maternal exposure information collected via telephone interview, we conducted logistic regression analyses among the interviewed cases and controls. Birth prevalence of infantile cataracts was 1.07/10,000 live births. Unilateral cataracts were more often associated with IEDs, while infants with bilateral cataracts were more often preterm, full-term with low birth weight, or had non-eye-related major birth defects. Unilateral cataracts were positively associated with maternal nulliparity (adjusted odds ratio [aOR] = 1.61, 95% confidence interval [CI] = 1.18, 2.20; reference: multiparity), whereas bilateral cataracts were positively associated with maternal education <12 years (aOR = 2.08, 95% CI = 1.13, 3.82; reference: education >12 years), and foreign-born nativity (aOR = 1.92, 95% CI = 1.04, 3.52; reference: U.S.-born nativity). The current analysis can inform future epidemiological studies aimed at identifying mechanisms underlying the associations between infantile cataracts and complex maternal exposures, such as lower levels of education and foreign-born nativity.

Prominent and Regressive Brain Developmental Disorders Associated with Nance-Horan Syndrome

Nance-Horan syndrome (NHS) is a rare X-linked developmental disorder caused mainly by loss of function variants in the NHS gene. NHS is characterized by congenital cataracts, dental anomalies, and distinctive facial features, and a proportion of the affected individuals also present intellectual disability and congenital cardiopathies. Despite identification of at least 40 distinct hemizygous variants leading to NHS, genotype-phenotype correlations remain largely elusive. In this study, we describe a Sicilian family affected with congenital cataracts and dental anomalies and diagnosed with NHS by whole-exome sequencing (WES). The affected boy from this family presented a late regression of cognitive, motor, language, and adaptive skills, as well as broad behavioral anomalies. Furthermore, brain imaging showed corpus callosum anomalies and periventricular leukoencephalopathy. We expand the phenotypic and mutational NHS spectrum and review potential disease mechanisms underlying the central neurological anomalies and the potential neurodevelopmental features associated with NHS.

Spinal cerebrotendinous xanthomatosis: A case report and literature review

Background

Classic cerebrotendinous xanthomatosis (CTX; OMIM #213700) manifests with chronic diarrhea, juvenile cataracts, tendon xanthomas and neurological symptoms. It is due to biallelic inactivation of CYP27A1 wich leads to cholestanol accumulation in the central nervous system, eyes and tendons. Less commonly, the disease can present in young adults as spastic paraparesis in the absence of xanthomas.

Case presentation

We report a 38-year old woman who presented with chronic diarrhea and progressive spastic paraparesis in her twenties. Brain magnetic resonance imaging (MRI) showed cerebral atrophy with diffuse periventricular white matter hyperintensities. Spinal MRI was normal. CYP27A1 gene sequencing confirmed the diagnosis of CTX. Chenodeoxycholic acid (CDCA) treatment was introduced with remission of diarrhea. Unfortunately, the treatment had to be discontinued several times and the patient developed psychosis and an severe ataxospastic gait. Spinal MRI revealed new linear hyperintensities of the corticospinal and gracile tracts. Thirty-three spinal CTX patients were identified by searching in Pubmed, EMBASE™ and Web of Science databases. All patients presented pyramidal signs and 48% had dorsal column signs. Juvenile cataracts were described in 78% of patients, chronic diarrhea in 65%, and tendon xanthomas in 31%. Disease improvement or stabilization with chenodeoxycholic acid was observed in 69% of patients. A higher prevalence of the Arg395Cys allele was observed in patients with spinal CTX as compared to CTX in general (ᵡ²; p < 0.00001).

Conclusions

The diagnosis of spinal CTX can be easily missed or delayed in absence of xanthomas. There is a higher prevalence of the Arg395Cys allele in spinal CTX as compared to classic childhood-onset CTX. CDCA treatment seems to stabilize or improve clinical symptoms in most patients. However, as seen in our patient and in two previously reported cases, sudden interruption of CDCA may lead to irreversible neurological complications.

Elongated axial length and myopia-related fundus changes associated with the Arg130Cys mutation in the LIM2 gene in four Chinese families with congenital cataracts

Background

Congenital cataract (CC) is a congenital abnormality characterized by lens opacity present at birth and is associated with highly heterogeneous clinical manifestations. Lens-specific integral membrane protein (LIM2) gene expression is localized to tight junctional domains of different lens fiber membranes. To date, only four mutations in LIM2 have been reported to be associated with congenital or presenile cataracts. Due to the rarity of variants detected in the gene, there is limited progress in understanding the correlation between the genotype and phenotype of patients with mutations in LIM2.

Methods

A total of four Chinese families with CCs were recruited for this study, including three families inheriting in an autosomal dominant (AD) pattern and one sporadic case. Genomic DNA was extracted from the leukocytes of peripheral blood collected from all available patients. Whole-exome sequencing (WES) was performed on all probands and at least one of their parents. Bioinformatics analysis was performed to evaluate the pathogenicity of the candidate variants. Exon 4 of LIM2 was amplified by polymerase chain reaction and directly sequenced. All patients underwent full ocular examinations. This was an observational study to explore the genotype-phenotype relationships in the four families with a common candidate variant.

Results

Various ocular phenotypes were detected in these families, mainly including CCs, elongated axial length, and myopia-related fundus changes. The LIM2 gene mutation, p.Arg130Cys, was detected in all patients. This was further confirmed by Sanger sequencing. The proportion of probands with this mutation in our CCs database was 3.1% (4/130), which indicated that this mutation appears to be a frequent cause of cataracts in the Han Chinese population. This variation has been reported by other investigators before and was correlated with isolated cataracts.

Conclusions

This is the first study that reports various ocular phenotypes associated with the p.Arg130Cys mutation in the LIM2 gene, which indicated the phenotypic heterogeneity of this gene. LIM2 might not only function as an integral membrane protein in lens fiber cells but also be associated with the axial development of the eyeball. Functional studies of the LIM2 gene are important and should receive more attention.

Clinical Spectrum and Genetic Diagnosis of 54 Consecutive Patients Aged 0-25 with Bilateral Cataracts

Childhood cataract affects 2.5-3.5 per 10,000 children in the UK, with a genetic mutation identified in 50-90% of bilateral cases. However, cataracts can also manifest in adolescence and early adulthood in isolation, as part of a complex ocular phenotype or with systemic features making accurate diagnosis more challenging. We investigate our real-world experience through a retrospective review of consecutive bilateral cataract patients (0-25 years) presenting to the ocular genetics service at Moorfields Eye Hospital between 2017 and 2020. Fifty-four patients from 44 unrelated families were identified, with a median age of 13.5 years (range 1 to 68 years) and a median age at diagnosis of 43.9 months IQR (1.7-140.3 months); 40.7% were female and 46.3% were Caucasian. Overall, 37 patients from 27 families (61.4%) were genetically solved (50%) or likely solved (additional 11.4%), with 26 disease-causing variants (8 were novel) in 21 genes; the most common were crystallin genes, in 8 (29.6%) families, with half occurring in the CRYBB2 gene. There was no significant difference in the molecular diagnostic rates between sporadic and familial inheritance (P = 0.287). Associated clinical diagnoses were retinal dystrophies in five (18.5%) and aniridia in three (11.1%) families. Bilateral cataracts were the presenting feature in 27.3% (6/22) of either complex or syndromic cases, and isolated cataract patients were 11.5 years younger (rank-sum Z = 3.668, P = 0.0002). Prompt genetic investigation with comprehensive panel testing can aid with diagnosis and optimise management of cataract patients.

Molecular diagnostic challenges for non-retinal developmental eye disorders in the United Kingdom

Overall, approximately one‐quarter of patients with genetic eye diseases will receive a molecular diagnosis. Patients with developmental eye disorders face a number of diagnostic challenges including phenotypic heterogeneity with significant asymmetry, coexisting ocular and systemic disease, limited understanding of human eye development and the associated genetic repertoire, and lack of access to next generation sequencing as regarded not to impact on patient outcomes/management with cost implications. Herein, we report our real world experience from a pediatric ocular genetics service over a 12 month period with 72 consecutive patients from 62 families, and that from a cohort of 322 patients undergoing whole genome sequencing (WGS) through the Genomics England 100,000 Genomes Project; encompassing microphthalmia, anophthalmia, ocular coloboma (MAC), anterior segment dysgenesis anomalies (ASDA), primary congenital glaucoma, congenital cataract, infantile nystagmus, and albinism. Overall molecular diagnostic rates reached 24.9% for those recruited to the 100,000 Genomes Project (73/293 families were solved), but up to 33.9% in the clinic setting (20/59 families). WGS was able to improve genetic diagnosis for MAC patients (15.7%), but not for ASDA (15.0%) and congenital cataracts (44.7%). Increased sample sizes and accurate human phenotype ontology (HPO) terms are required to improve diagnostic accuracy. The significant mixed complex ocular phenotypes distort these rates and lead to missed variants if the correct gene panel is not applied. Increased molecular diagnoses will help to explain the genotype–phenotype relationships of these developmental eye disorders. In turn, this will lead to improved integrated care pathways, understanding of disease, and future therapeutic development.

Cataract management in children: a review of the literature and current practice across five large UK centres

Congenital and childhood cataracts are uncommon but regularly seen in the clinics of most paediatric ophthalmology teams in the UK. They are often associated with profound visual loss and a large proportion have a genetic aetiology, some with significant extra-ocular comorbidities. Optimal diagnosis and treatment typically require close collaboration within multidisciplinary teams. Surgery remains the mainstay of treatment. A variety of surgical techniques, timings of intervention and options for optical correction have been advocated making management seem complex for those seeing affected children infrequently. This paper summarises the proceedings of two recent RCOphth paediatric cataract study days, provides a literature review and describes the current UK 'state of play' in the management of paediatric cataracts.

Congenital cataract: a guide to genetic and clinical management

Worldwide 20,000-40,000 children with congenital or childhood cataract are born every year with varying degrees and patterns of lens opacification with a broad aetiology. In most cases of bilateral cataract, a causative genetic mutation can be identified, with autosomal dominant inheritance being most common in 44% of cases. Variants in genes involve lens-specific proteins or those that regulate eye development, thus giving rise to other associated ocular abnormalities. Approximately 15% of cases have systemic features, hence paediatric input is essential to minimise comorbidities and support overall development of children at high risk of visual impairment. In some metabolic conditions, congenital cataract may be the presenting sign, and therefore prompt diagnosis is important where there is an available treatment. Multidisciplinary management of children is essential, including ophthalmic surgeons, orthoptists, paediatricians, geneticists and genetic counsellors, and should extend beyond the medical team to include school and local paediatric visual support services. Early surgery and close follow up in ophthalmology is important to optimise visual potential and prevent amblyopia. Routine genetic testing is essential for the complete clinical management of patients, with next-generation sequencing of 115 genes shown to expedite molecular diagnosis, streamline care pathways and inform genetic counselling and reproductive options for the future.

Lay abstract

Childhood cataract: how to manage patients Cataract is a clouding of the lens in the eye. Cataract occurring in children has many different causes, which may include infections passed from mother to child during pregnancy, trauma, medications and exposure to radiation. In most cases of cataract occurring in both eyes, a genetic cause can be found which may be inherited from parents or occur sporadically in the developing baby itself while in the womb. Cataracts may occur on their own, with other eye conditions or be present with other disorders in the body as part of a syndrome. Genetic testing is important for all children with cataract as it can provide valuable information about cause, inheritance and risk to further children and signpost any other features of the disease in the rest of the body, permitting the assembly of the correct multidisciplinary care team. Genetic testing currently involves screening for mutations in 115 genes already known to cause cataract and has been shown to expedite diagnosis and help better manage children. Genetic counselling services can support families in understanding their diagnosis and inform future family planning. In order to optimise vision, early surgery for cataract in children is important. This is because the brain is still developing and an unobstructed pathway for light to reach the back of the eye is required for normal visual development. Any obstruction (such as cataract) if left untreated may lead to permanent sight impairment or blindness, even if it is removed later. A multidisciplinary team involved in the care of a child with cataract should include ophthalmic surgeons, orthoptists, paediatricians, geneticists and genetic counsellors, and should extend beyond the medical team to include school and local child visual support services. They will help to diagnose and manage systemic conditions, optimise vision potential and help patients and their families access best supportive care.

Clinical utility of genetic testing in 201 preschool children with inherited eye disorders

Purpose

A key property to consider in all genetic tests is clinical utility, the ability of the test to influence patient management and health outcomes. Here we assess the current clinical utility of genetic testing in diverse pediatric inherited eye disorders (IEDs).

Methods

Two hundred one unrelated children (0–5 years old) with IEDs were ascertained through the database of the North West Genomic Laboratory Hub, Manchester, UK. The cohort was collected over a 7-year period (2011–2018) and included 74 children with bilateral cataracts, 8 with bilateral ectopia lentis, 28 with bilateral anterior segment dysgenesis, 32 with albinism, and 59 with inherited retinal disorders. All participants underwent panel-based genetic testing.

Results

The diagnostic yield of genetic testing for the cohort was 64% (ranging from 39% to 91% depending on the condition). The test result led to altered management (including preventing additional investigations or resulting in the introduction of personalized surveillance measures) in 33% of probands (75% for ectopia lentis, 50% for cataracts, 33% for inherited retinal disorders, 7% for anterior segment dysgenesis, 3% for albinism).

Conclusion

Genetic testing helped identify an etiological diagnosis in the majority of preschool children with IEDs. This prevented additional unnecessary testing and provided the opportunity for anticipatory guidance in significant subsets of patients.

Molecular genetics of congenital cataracts

Congenital cataracts, the most common cause of visual impairment and blindness in children worldwide, have diverse etiologies. According to statistics analysis, about one quarter of congenital cataracts caused by genetic defects. Various mutations of more than one hundred genes have been identified in hereditary cataracts so far. In this review, we briefly summarize recent developments about the genetics, molecular mechanisms, and treatments of congenital cataracts. The studies of these pathogenic mutations and molecular genetics is making it possible for us to comprehend the underlying mechanisms of cataractogenesis and providing new insights into the preventive, diagnostic and therapeutic approaches of cataracts.

Prevalence of Cerebrotendinous Xanthomatosis Among Patients Diagnosed With Acquired Juvenile-Onset Idiopathic Bilateral Cataracts

Importance

Cerebrotendinous xanthomatosis (CTX) is a rare autosomal recessive bile acid synthesis disorder caused by mutations in CYP27A1, the gene encoding sterol 27-hydroxylase, which results in elevated levels of plasma cholestanol and urinary bile alcohols. Clinical symptoms and signs may include early-onset chronic diarrhea, juvenile-onset bilateral cataracts, cholestatic jaundice, tendon xanthomas, and progressive neurological deterioration. Although initiation of treatment at a young age can prevent disease complications, diagnosis often occurs after the onset of permanent neurologic damage. Strategies are needed to facilitate early diagnosis.

Objective

To evaluate the prevalence of CTX in a patient population diagnosed with early-onset idiopathic bilateral cataracts.

Design, Setting, and Participants

This interim analysis of the Cerebrotendinous Xanthomatosis Prevalence Study was conducted in 26 active US sites from November 2015 to June 2017. The study included patients diagnosed as having idiopathic bilateral cataracts from ages 2 to 21 years. Potentially eligible study participants were identified through retrospective medical record review or on receiving care for cataracts at an active site. Data were analyzed from July 2017 to October 2018.

Main Outcomes and Measures

Measurement of plasma cholestanol levels and optional urine bile alcohol screening were performed. A plasma cholestanol concentration of 0.4 mg/dL or greater or a positive urine bile alcohol result prompted CYP27A1 genetic testing to confirm the diagnosis of CTX.

Results

Of 170 tested patients, 88 (51.8%) were male, and the median (range) age was 10 (2-49) years. A total of 3 patients (1.8%) had biochemical and genetic confirmation of newly diagnosed CTX (plasma cholestanol level greater than 1.0 mg/dL, positive urine bile alcohol result, and disease-causative mutations in CYP27A1). The mean (range) age at cataract diagnosis for patients with CTX was 12 (8-16) years. Reported symptoms included abnormal gait or balance (n = 3), learning disability (n = 2), cognitive decline (n = 2), seizures (n = 2), frequent bone fractures (n = 2), and chronic diarrhea (n = 1).

Conclusions and Relevance

To date, 1.8% of patients in this study were diagnosed as having CTX, which is approximately 500-fold the currently estimated prevalence of CTX in the general population (3 to 5 per 100 000). These data suggest that juvenile-onset idiopathic bilateral cataracts may be useful as a screening marker for CTX and that ophthalmologists can play an important role in facilitating early identification of this condition.

The Oculome Panel Test: Next-Generation Sequencing to Diagnose a Diverse Range of Genetic Developmental Eye Disorders

PURPOSE

To develop a comprehensive next-generation sequencing panel assay that screens genes known to cause developmental eye disorders and inherited eye disease and to evaluate its diagnostic yield in a pediatric cohort with malformations of the globe, anterior segment anomalies, childhood glaucoma, or a combination thereof.

DESIGN

Evaluation of diagnostic test.

PARTICIPANTS

Two hundred seventy-seven children, 0 to 16 years of age, diagnosed with nonsyndromic or syndromic developmental eye defects without a genetic diagnosis.

METHODS

We developed a new oculome panel using a custom-designed Agilent SureSelect QXT target capture method (Agilent Technologies, Santa Clara, CA) to capture and perform parallel high-throughput sequencing analysis of 429 genes associated with eye disorders. Bidirectional Sanger sequencing confirmed suspected pathogenic variants.

MAIN OUTCOME MEASURES

Collated clinical details and oculome molecular genetic results.

RESULTS

The oculome design covers 429 known eye disease genes; these are subdivided into 5 overlapping virtual subpanels for anterior segment developmental anomalies including glaucoma (ASDA; 59 genes), microphthalmia-anophthalmia-coloboma (MAC; 86 genes), congenital cataracts and lens-associated conditions (70 genes), retinal dystrophies (RET; 235 genes), and albinism (15 genes), as well as additional genes implicated in optic atrophy and complex strabismus (10 genes). Panel development and testing included analyzing 277 clinical samples and 3 positive control samples using Illumina sequencing platforms; more than 30× read depth was achieved for 99.5% of the targeted 1.77-Mb region. Bioinformatics analysis performed using a pipeline based on Freebayes and ExomeDepth to identify coding sequence and copy number variants, respectively, resulted in a definitive diagnosis in 68 of 277 samples, with variability in diagnostic yield between phenotypic subgroups: MAC, 8.2% (8 of 98 cases solved); ASDA, 24.8% (28 of 113 cases solved); other or syndromic, 37.5% (3 of 8 cases solved); RET, 42.8% (21 of 49 cases solved); and congenital cataracts and lens-associated conditions, 88.9% (8 of 9 cases solved).

CONCLUSIONS

The oculome test diagnoses a comprehensive range of genetic conditions affecting the development of the eye, potentially replacing protracted and costly multidisciplinary assessments and allowing for faster targeted management. The oculome enabled molecular diagnosis of a significant number of cases in our sample cohort of varied ocular birth defects.

Bilateral cataracts as the presenting feature of type 1 diabetes in an 11-year-old girl

Paediatric cataracts can present a diagnostic dilemma to ophthalmologists. Next-generation DNA sequencing (NGS) has been promoted as a tool to expedite the diagnosis of an underlying cause in such cases.1 The authors present an unusual case of bilateral cataracts in an 11-year-old girl as the first presenting feature of new type 1 diabetes mellitus. Prompt diagnosis and subsequent management of this potentially life-threatening condition were achieved through careful history taking and targeted biochemical testing. The authors feel this case highlights the significance of simple measures such as thorough history taking in the assessment of paediatric cataracts. It is important that these skills are not lost through the availability of clinical tools such as NGS.

Genetic Testing in Pediatric Ophthalmology

The authors review the utility of genetic testing in ophthalmic disorders - precise diagnosis, accurate prognosis, genetic counseling, prenatal diagnosis, and entry into gene-specific therapeutic trials. The prerequisites for a successful outcome of a genetic test are an accurate clinical diagnosis, a careful family history that guides which genes to study, and genetic counseling (both pre-test and post-test). The common eye disorders for which genetic testing is commonly requested are briefly discussed - anophthalmia, microphthalmia, coloboma, anterior segment dysgenesis, corneal dystrophies, cataracts, optic atrophy, congenital glaucoma, congenital amaurosis, retinitis pigmentosa, color blindness, juvenile retinoshisis, retinoblastoma etc. A protocol for genetic testing is presented. If specific mutations in a gene are common, they should form the first tier test, as the mutations in Leber hereditary optic neuropathy. If mutations in one gene are likely, sequencing of that gene should be carried out, e.g. GALT gene in galactosemia, RS1 gene in retinoshisis. Disorders with genetic heterogeneity require multi-gene panel tests, and if these show no abnormality, then deletion / duplication or microarray studies are recommended, followed in sequence by clinical exome (5000 to 6000 genes), full exome (about 20,000 genes or whole genome studies (includes all introns). It is fortunate that most genetic tests in ophthalmology are available in India, including gene panel and whole exome/genome sequencing tests.

Germ-line and somatic EPHA2 coding variants in lens aging and cataract

Rare germ-line mutations in the coding regions of the human EPHA2 gene (EPHA2) have been associated with inherited forms of pediatric cataract, whereas, frequent, non-coding, single nucleotide variants (SNVs) have been associated with age-related cataract. Here we sought to determine if germ-line EPHA2 coding SNVs were associated with age-related cataract in a case-control DNA panel (> 50 years) and if somatic EPHA2 coding SNVs were associated with lens aging and/or cataract in a post-mortem lens DNA panel (> 48 years). Micro-fluidic PCR amplification followed by targeted amplicon (exon) next-generation (deep) sequencing of EPHA2 (17-exons) afforded high read-depth coverage (1000x) for > 82% of reads in the cataract case-control panel (161 cases, 64 controls) and > 70% of reads in the post-mortem lens panel (35 clear lens pairs, 22 cataract lens pairs). Novel and reference (known) missense SNVs in EPHA2 that were predicted in silico to be functionally damaging were found in both cases and controls from the age-related cataract panel at variant allele frequencies (VAFs) consistent with germ-line transmission (VAF > 20%). Similarly, both novel and reference missense SNVs in EPHA2 were found in the post-mortem lens panel at VAFs consistent with a somatic origin (VAF > 3%). The majority of SNVs found in the cataract case-control panel and post-mortem lens panel were transitions and many occurred at di-pyrimidine sites that are susceptible to ultraviolet (UV) radiation induced mutation. These data suggest that novel germ-line (blood) and somatic (lens) coding SNVs in EPHA2 that are predicted to be functionally deleterious occur in adults over 50 years of age. However, both types of EPHA2 coding variants were present at comparable levels in individuals with or without age-related cataract making simple genotype-phenotype correlations inconclusive.

Novel phenotypes and loci identified through clinical genomics approaches to pediatric cataract

Pediatric cataract is highly heterogeneous clinically and etiologically. While mostly isolated, cataract can be part of many multisystem disorders, further complicating the diagnostic process. In this study, we applied genomic tools in the form of a multi-gene panel as well as whole-exome sequencing on unselected cohort of pediatric cataract (166 patients from 74 families). Mutations in previously reported cataract genes were identified in 58% for a total of 43 mutations, including 15 that are novel. GEMIN4 was independently mutated in families with a syndrome of cataract, global developmental delay with or without renal involvement. We also highlight a recognizable syndrome that resembles galactosemia (a fulminant infantile liver disease with cataract) caused by biallelic mutations in CYP51A1. A founder mutation in RIC1 (KIAA1432) was identified in patients with cataract, brain atrophy, microcephaly with or without cleft lip and palate. For non-syndromic pediatric cataract, we map a novel locus in a multiplex consanguineous family on 4p15.32 where exome sequencing revealed a homozygous truncating mutation in TAPT1. We report two further candidates that are biallelically inactivated each in a single cataract family: TAF1A (cataract with global developmental delay) and WDR87 (non-syndromic cataract). In addition to positional mapping data, we use iSyTE developmental lens expression and gene-network analysis to corroborate the proposed link between the novel candidate genes and cataract. Our study expands the phenotypic, allelic and locus heterogeneity of pediatric cataract. The high diagnostic yield of clinical genomics supports the adoption of this approach in this patient group.