Human TUBB3 mutations perturb microtubule dynamics, kinesin interactions, and axon guidance.

We report that eight heterozygous missense mutations in TUBB3, encoding the neuron-specific beta-tubulin isotype III, result in a spectrum of human nervous system disorders that we now call the TUBB3 syndromes. Each mutation causes the ocular motility disorder CFEOM3, whereas some also result in intellectual and behavioral impairments, facial paralysis, and/or later-onset axonal sensorimotor polyneuropathy. Neuroimaging reveals a spectrum of abnormalities including hypoplasia of oculomotor nerves and dysgenesis of the corpus callosum, anterior commissure, and corticospinal tracts. A knock-in disease mouse model reveals axon guidance defects without evidence of cortical cell migration abnormalities. We show that the disease-associated mutations can impair tubulin heterodimer formation in vitro, although folded mutant heterodimers can still polymerize into microtubules. Modeling each mutation in yeast tubulin demonstrates that all alter dynamic instability whereas a subset disrupts the interaction of microtubules with kinesin motors. These findings demonstrate that normal TUBB3 is required for axon guidance and maintenance in mammals.

Towards a national pre-school vision screening programme.

The aim of the study is to examine common approaches to pre-school vision screening, including the current New South Wales model which is known as Statewide Eyesight Preschooler Screening (StEPS) to determine whether the criteria set by the World Health Organization are fulfilled by StEPS, and therefore, whether there is sufficient justification to deploy a similar model nationally. A literature review was conducted to answer four key questions related to vision screening. The authors sought to review (i) the justification for vision screening of a pre-school population; (ii) the principles and best approaches to vision screening such as how, where and who should conduct vision screening; (iii) the conditions that are targeted in vision screening; and (iv) the acceptable pass/fail vision screening criteria. The StEPS vision screening model is an accurate, reliable and economical way of screening for reduced vision at a time when neural plasticity allows improvement in vision following intervention. It fulfils World Health Organization criteria for a successful screening programme. StEPS has very high participation rates compared to other screening methods in Australia due to its unique model whereby screeners utilise early childhood settings to recruit and screen 4-year-old children. Due consideration should be given to deploying the StEPS vision screening model nationally.

Genome sequencing in congenital cataracts improves diagnostic yield.

Congenital cataracts are one of the major causes of childhood-onset blindness around the world. Genetic diagnosis provides benefits through avoidance of unnecessary tests, surveillance of extraocular features, and genetic family information. In this study, we demonstrate the value of genome sequencing in improving diagnostic yield in congenital cataract patients and families. We applied genome sequencing to investigate 20 probands with congenital cataracts. We examined the added value of genome sequencing across a total cohort of 52 probands, including 14 unable to be diagnosed using previous microarray and exome or panel-based approaches. Although exome or genome sequencing would have detected the variants in 35/52 (67%) of the cases, specific advantages of genome sequencing led to additional diagnoses in 10% (5/52) of the overall cohort, and we achieved an overall diagnostic rate of 77% (40/52). Specific benefits of genome sequencing were due to detection of small copy number variants (2), indels in repetitive regions (2) or single-nucleotide variants (SNVs) in GC-rich regions (1), not detectable on the previous microarray, exome sequencing, or panel-based approaches. In other cases, SNVs were identified in cataract disease genes, including those newly identified since our previous study. This study highlights the additional yield of genome sequencing in congenital cataracts.

Revealing hidden genetic diagnoses in the ocular anterior segment disorders.

PURPOSE: Ocular anterior segment disorders (ASDs) are clinically and genetically heterogeneous, and genetic diagnosis often remains elusive. In this study, we demonstrate the value of a combined analysis protocol using phenotypic, genomic, and pedigree structure data to achieve a genetic conclusion. METHODS: We utilized a combination of chromosome microarray, exome sequencing, and genome sequencing with structural variant and trio analysis to investigate a cohort of 41 predominantly sporadic cases. RESULTS: We identified likely causative variants in 54% (22/41) of cases, including 51% (19/37) of sporadic cases and 75% (3/4) of cases initially referred as familial ASD. Two-thirds of sporadic cases were found to have heterozygous variants, which in most cases were de novo. Approximately one-third (7/22) of genetic diagnoses were found in rarely reported or recently identified ASD genes including PXDN, GJA8, COL4A1, ITPR1, CPAMD8, as well as the new phenotypic association of Axenfeld-Rieger anomaly with a homozygous ADAMTS17 variant. The remainder of the variants were in key ASD genes including FOXC1, PITX2, CYP1B1, FOXE3, and PAX6. CONCLUSIONS: We demonstrate the benefit of detailed phenotypic, genomic, variant, and segregation analysis to uncover some of the previously "hidden" heritable answers in several rarely reported and newly identified ocular ASD-related disease genes.

Sporadic and Familial Congenital Cataracts: Mutational Spectrum and New Diagnoses Using Next-Generation Sequencing.

Congenital cataracts are a significant cause of lifelong visual loss. They may be isolated or associated with microcornea, microphthalmia, anterior segment dysgenesis (ASD) and glaucoma, and there can be syndromic associations. Genetic diagnosis is challenging due to marked genetic heterogeneity. In this study, next-generation sequencing (NGS) of 32 cataract-associated genes was undertaken in 46 apparently nonsyndromic congenital cataract probands, around half sporadic and half familial cases. We identified pathogenic variants in 70% of cases, and over 68% of these were novel. In almost two-thirds (20/33) of these cases, this resulted in new information about the diagnosis and/or inheritance pattern. This included identification of: new syndromic diagnoses due to NHS or BCOR mutations; complex ocular phenotypes due to PAX6 mutations; de novo autosomal-dominant or X-linked mutations in sporadic cases; and mutations in two separate cataract genes in one family. Variants were found in the crystallin and gap junction genes, including the first report of severe microphthalmia and sclerocornea associated with a novel GJA8 mutation. Mutations were also found in rarely reported genes including MAF, VIM, MIP, and BFSP1. Targeted NGS in presumed nonsyndromic congenital cataract patients provided significant diagnostic information in both familial and sporadic cases.

An inherited TUBB2B mutation alters a kinesin-binding site and causes polymicrogyria, CFEOM and axon dysinnervation.

Microtubules are essential components of axon guidance machinery. Among ß-tubulin mutations, only those in TUBB3 have been shown to cause primary errors in axon guidance. All identified mutations in TUBB2B result in polymicrogyria, but it remains unclear whether TUBB2B mutations can cause axon dysinnervation as a primary phenotype. We have identified a novel inherited heterozygous missense mutation in TUBB2B that results in an E421K amino acid substitution in a family who segregates congenital fibrosis of the extraocular muscles (CFEOM) with polymicrogyria. Diffusion tensor imaging of brains of affected family members reveals aberrations in the trajectories of commissural projection neurons, implying a paucity of homotopic connections. These observations led us to ask whether axon dysinnervation is a primary phenotype, and why the E421K, but not other, TUBB2B substitutions cause CFEOM. Expression of exogenous Tubb2b-E421K in developing callosal projection neurons is sufficient to perturb homotopic connectivity, without affecting neuronal production or migration. Using in vitro biochemical assays and yeast genetics, we find that TUBB2B-E421K αß-heterodimers are incorporated into the microtubule network where they alter microtubule dynamics and can reduce kinesin localization. These data provide evidence that TUBB2B mutations can cause primary axon dysinnervation. Interestingly, by incorporating into microtubules and altering their dynamic properties, the E421K substitution behaves differently than previously identified TUBB2B substitutions, providing mechanistic insight into the divergence between resulting phenotypes. Together with previous studies, these findings highlight that ß-tubulin isotypes function in both conserved and divergent ways to support proper human nervous system development.

Timing of surgery in essential infantile esotropia - What more do we know since the turn of the century?

This review summarizes the results and interpretations of studies pertaining to the long-standing debate regarding the timing of surgery in infantile esotropia, more recently referred to as essential infantile esotropia. A systematic search of studies from the year 2000 onward pertaining to the timing of surgery in infantile esotropia as listed in PubMed, Google Scholar, and the Cochrane database was performed. Appropriate cross-references from the articles were also included. Data collected included demographics, presentation, time of surgery, complications, and outcomes. Very early surgery, that is, within 6 months of the onset of infantile esotropia, offers significant advantages in terms of the quality of stereopsis and binocular vision as well as promoting the development of cortical visual processing, thereby benefiting cortical development in human infants. However, the postoperative alignment was not found to be significantly different in the very early, early, or late surgery groups. The reduction in the incidence of manifest dissociated vertical deviation postoperatively in the very early surgery group also showed measurable benefits. The results of this recent literature review demonstrated that very early surgery, within 6 months of misalignment, showed demonstrable benefits in essential infantile esotropia.

Reporting on Australian childhood visual impairment: the first 10 years.

BACKGROUND: Visual impairment is rare but has significant impact on the neurobehavioural development and quality of life of children. This paper presents the key findings from the Australian Childhood Vision Impairment Register, which commenced in 2008 to report on children diagnosed with permanent visual impairment. SUBJECTS/METHODS: Families consent to completing a data form related to their child and for contact with the child's ophthalmologist. Ophthalmologists complete and return a comprehensive data form on the child's primary and secondary ocular diagnoses, associated disabilities and health conditions, visual acuity and visual fields. Data is stored on a secure database and anonymised data is available to researchers and for planning purposes. RESULTS: Nine-hundred four children and their families provided informed consent for participation, with 57% males and 43% females. Most children spoke English in their home. Eighty-three percent of children were born full term, with a birth weight of >2500 g (81%). Children were commonly suspected to have visual impairment by a parent, with 68% of families receiving a diagnosis of visual impairment by their child's first birthday. The most common primary diagnoses were retinal dystrophy (17%), CVI (15%) and Albinism (11%). A secondary diagnosis of infantile nystagmus occurred in 33% of children. Additional disabilities and/or developmental delay were reported for 44% of children. Corrected binocular visual acuity was reported for 75% of children, with moderate visual impairment being most common. CONCLUSIONS: These findings contribute to knowledge of rare diseases affecting the eye and visual pathway and represent Australian childhood visual impairment.

Paediatric Horner Syndrome: How much further to investigate?

We report an infant with an early-onset Horner syndrome and normal urinary catecholamine levels. Further investigations with Nuclear medicine imaging with123I-MIBG (meta-iodo benzyl-guanidine) confirmed a right thoracic inlet mass consistent with a neuroblastoma, a tumor of neural crest origin. The authors emphasize the need for investigating idiopathic acquired pediatric Horner syndrome and the value of an MIBG scan as a diagnostic test for suspected neuroblastoma.

Neurofibromatosis Type 1: Review and Update on Emerging Therapies.

Neurofibromatosis type 1 is an autosomal dominant neurocutaneous disorder affecting 1 in 3000 births. This familial tumor predisposition syndrome is diagnosed clinically and affects the skin, bones, and nervous system. Malignant tumors can arise in childhood or adulthood and are the most common cause of mortality in this population. Early diagnosis and management led by a multidisciplinary team remains the standard of care, particularly in the management of optic pathway glioma. Emerging concepts in the genetic patterns of this condition have led to the introduction of new treatment modalities that target the mitogen-activated protein kinase and the mammalian target of rapamycin pathways. In this review, the role of the ophthalmologist and approach to screening for optic pathway glioma are outlined based on previous recommendations. Updates on choroidal involvement, as a diagnostic criterion, will also be discussed, further highlighting the pivotal role of the ophthalmologist in the diagnosis and management of this complex condition.

Chromosomal rearrangements and novel genes in disorders of eye development, cataract and glaucoma.

Disorders of eye development such as microphthalmia and anophthalmia (small and absent eyes respectively), anterior segment dysgenesis where there may be pupillary and iris anomalies, and associated cataract and glaucoma, often lead to visual impairment or blindness. Currently treatment options are limited, as much is unknown about the molecular pathways that control normal eye development and induce the aberrant processes that lead to ocular defects. Mutation detection rates in most of the known genes are generally low, emphasizing the genetic heterogeneity of developmental ocular defects. Identification of the disease genes in these conditions improves the clinical information available for affected individuals and families, and provides new insights into the underlying biological processes for facilitation of better treatment options. Investigation of chromosomal rearrangements associated with an ocular phenotype has been especially powerful for disease gene identification. Molecular characterization of such rearrangements, which pinpoints the region by physically disrupting the causative gene or its regulatory sequences, allows for rapid elucidation of underlying genetic factors that contribute to the phenotype. Genes including PAX6, PITX2, FOXC1, MAF, TMEM114, SOX2, OTX2 and BMP4 have been identified in this way to be associated with developmental eye disorders. More recently, new methods in chromosomal analysis such as comparative genomic hybridization (CGH) microarray, have also enhanced our ability in disease gene identification.

Corneal arcus as the presenting sign of familial hypercholesterolemia in a young child.

A 2.6-year-old boy presented with prominent corneal arcus. This clinical sign is rarely seen at such a young age and led to the diagnosis of familial hypercholesterolemia (FH). Genetic analysis detected biallelic pathogenic sequence variants c.1069G>A and c.2034C>A in the LDLR gene. There is significant cardiovascular morbidity and mortality associated with FH, hence early diagnosis and treatment is imperative.

Free-floating unilateral pigmented vitreous cyst in a child.

Free-floating vitreous cysts have been ocular curiosities, especially in children. Various etiologies have been proposed. Most of these cysts are asymptomatic except for subtle symptoms of visual floaters. When the visual axis is obscured, treatment options include surgery and laser treatment. We report a case of a unilateral pigmented vitreous cyst in a child.

Ocular and electrophysiological findings in a patient with Sly syndrome.

BACKGROUND: Sly syndrome (Mucopolysaccharidosis Type VII) is an autosomal recessive metabolic storage disorder due to mutations in the GUSB gene encoding the enzyme beta-glucuronidase. Deficiency of this lysosomal enzyme impairs the body's ability to break down the glycosaminoglycans - dermatan, heparan and chondroitin sulphate. Coarse facial features and macrocephaly are typically seen along with bony and skeletal abnormalities, including joint contractures and short stature. Widespread involvement occurs in many other tissues including cardiopulmonary, gastrointestinal, and neurological systems. In view of the rarity of Sly syndrome the ophthalmic features have not been well described. MATERIALS AND METHODS: Case report of a 16-year-old boy with Sly syndrome with serial OCT, ocular ultrasound, and electroretinogram (ERG). RESULTS: Corneal clouding was present but there was no evidence of glaucoma or optic neuropathy. Despite no clinical evidence of retinopathy, electrophysiology showed reduced photopic and scotopic responses, particularly involving the b-wave which appears progressive. OCT showed normal foveal architecture and normal retinal nerve fiber thickness. CONCLUSION: Corneal clouding was noted in this patient and there is no evidence of glaucoma or optic neuropathy. Although retinopathy has not been previously described in Sly syndrome, the ERG changes in this patient suggest that retinopathy may be a feature of MPS VII.

Assessment and diagnosis of suspected glaucoma in patients with mucopolysaccharidosis.

PURPOSE: The mucopolysaccharidoses (MPS) are a group of rare lysosomal storage disorders, characterized by the accumulation of glycosaminoglycans within multiple organ systems including the eye. This study aimed to determine the prevalence of glaucoma in patients with MPS, as well as the characteristics, diagnosis and management of patients with MPS and glaucoma. METHODS: A multicentre retrospective case-note review was carried out by ophthalmologists from four tertiary referral centres to identify patients with MPS who had been treated for glaucoma. Clinical ophthalmological data were collected using standardized data collection forms. RESULTS: Fourteen patients were identified (27 eyes) of 294 patients with MPS. The prevalence of glaucoma ranged from 2.1% to 12.5%. The median age at diagnosis of glaucoma was 8 years. Diagnostic evaluation of glaucoma was incomplete in many patients: intraocular pressure was documented in all eyes, but optic disc appearance was only assessed in 67%, central corneal thickness in 26%, visual fields in 19% and iridocorneal angle in 15%. CONCLUSIONS: Patients with MPS need regular assessment for possible glaucoma including during childhood. Multiple factors contribute to the challenges of assessment, diagnosis and monitoring of glaucoma in these patients.

Advantage of Whole Exome Sequencing over Allele-Specific and Targeted Segment Sequencing in Detection of Novel TULP1 Mutation in Leber Congenital Amaurosis.

BACKGROUND: Leber congenital amaurosis (LCA) is a severe form of retinal dystrophy with marked underlying genetic heterogeneity. Until recently, allele-specific assays and Sanger sequencing of targeted segments were the only available approaches for attempted genetic diagnosis in this condition. A broader next-generation sequencing (NGS) strategy, such as whole exome sequencing, provides an improved molecular genetic diagnostic capacity for patients with these conditions. MATERIALS AND METHODS: In a child with LCA, an allele-specific assay analyzing 135 known LCA-causing variations, followed by targeted segment sequencing of 61 regions in 14 causative genes was performed. Subsequently, exome sequencing was undertaken in the proband, unaffected consanguineous parents and two unaffected siblings. Bioinformatic analysis used two independent pipelines, BWA-GATK and SOAP, followed by Annovar and SnpEff to annotate the variants. RESULTS: No disease-causing variants were found using the allele-specific or targeted segment Sanger sequencing assays. Analysis of variants in the exome sequence data revealed a novel homozygous nonsense mutation (c.1081C > T, p.Arg361*) in TULP1, a gene with roles in photoreceptor function where mutations were previously shown to cause LCA and retinitis pigmentosa. The identified homozygous variant was the top candidate using both bioinformatic pipelines. CONCLUSIONS: This study highlights the value of the broad sequencing strategy of exome sequencing for disease gene identification in LCA, over other existing methods. NGS is particularly beneficial in LCA where there are a large number of causative disease genes, few distinguishing clinical features for precise candidate disease gene selection, and few mutation hotspots in any of the known disease genes.

Exome sequencing in developmental eye disease leads to identification of causal variants in GJA8, CRYGC, PAX6 and CYP1B1.

Developmental eye diseases, including cataract/microcornea, Peters anomaly and coloboma/microphthalmia/anophthalmia, are caused by mutations encoding many different signalling and structural proteins in the developing eye. All modes of Mendelian inheritance occur and many are sporadic cases, so provision of accurate recurrence risk information for families and affected individuals is highly challenging. Extreme genetic heterogeneity renders testing for all known disease genes clinically unavailable with traditional methods. We used whole-exome sequencing in 11 unrelated developmental eye disease patients, as it provides a strategy for assessment of multiple disease genes simultaneously. We identified five causative variants in four patients in four different disease genes, GJA8, CRYGC, PAX6 and CYP1B1. This detection rate (36%) is high for a group of patients where clinical testing is frequently not undertaken due to lack of availability and cost. The results affected clinical management in all cases. These variants were detected in the cataract/microcornea and Peters anomaly patients. In two patients with coloboma/microphthalmia, variants in ABCB6 and GDF3 were identified with incomplete penetrance, highlighting the complex inheritance pattern associated with this phenotype. In the coloboma/microphthalmia patients, four other variants were identified in CYP1B1, and CYP1B1 emerged as a candidate gene to be considered as a modifier in coloboma/microphthalmia.

Microphthalmia, anophthalmia, and coloboma and associated ocular and systemic features: understanding the spectrum.

IMPORTANCE: Microphthalmia, anophthalmia, and coloboma form an interrelated spectrum of congenital eye abnormalities. OBJECTIVE: To document the ocular and systemic findings and inheritance patterns in patients with microphthalmia, anophthalmia, and coloboma disease to gain insight into the underlying developmental etiologies. DESIGN, SETTING, AND PARTICIPANTS: This retrospective consecutive case series was conducted at a tertiary referral center. Included in the study were 141 patients with microphthalmia, anophthalmia, and coloboma disease without a recognized syndromic etiology who attended the Westmead Children's Hospital, Sydney, from 1981-2012. EXPOSURE: Cases were grouped on the basis of the presence or absence of an optic fissure closure defect (OFCD); those with OFCD were further subdivided into microphthalmic and nonmicrophthalmic cases. Anophthalmic cases were considered as a separate group. MAIN OUTCOMES AND MEASURES: Associated ocular and systemic abnormalities and inheritance patterns were assessed. RESULTS: Of 141 cases, 61 (43%) were microphthalmic non-OFCD (NOFCD), 34 (24%) microphthalmic OFCD, 32 (23%) nonmicrophthalmic coloboma (OFCD), 9 (6%) anophthalmic, and 5 (4%) were unclassified. Sixty-three (45%) had bilateral disease. Eighty-four patients (60%) had an associated ocular abnormality; of these, cataract (P < .001) and posterior segment anomalies (P < .001) were most common in the NOFCD group. Forty-eight (34%) had an associated systemic abnormality, most commonly neurological, musculoskeletal and facial, urological and genital, or cardiac. Neurological abnormalities were most common in the anophthalmic group (P = .003), while urological abnormalities were particularly seen in the OFCD groups (P = .009). Familial cases were identified in both the OFCD and NOFCD groups, with a likely autosomal dominant inheritance pattern in 9 of 10 families. CONCLUSIONS AND RELEVANCE: This series indicated that the OFCD/NOFCD distinction may be useful in guiding evaluation for ocular and systemic associations, as well as the direction and analysis of genetic investigation.