[Show abstract][Hide abstract] ABSTRACT: 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 non-syndromic 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 non-syndromic congenital cataract patients provided significant diagnostic information in both familial and sporadic cases. This article is protected by copyright. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: Background
Several retinal dystrophies are associated with syndromic features including such conditions as Bardet-Biedl and Joubert syndromes. Cohen syndrome (CS) is an autosomal recessive disorder associated with multiple clinical manifestations including developmental delay, acquired microcephaly, myopia, pigmentary retinopathy, joint hypermobility, truncal obesity, friendly disposition and intermittent neutropenia. In young patients, diagnosis is difficult, since several of the characteristic features may not be present until school age or later years and the intermittent neutropenia is not always detectable.DesignThis was a prospective study using whole exome sequencing (WES) in syndromic retinal dystrophy. It was undertaken in a hospital and research institute setting.ParticipantsParticipants in this study were members of a consanguineous Australian family of Lebanese ethnicity with two siblings with retinal dystrophy, microcephaly and developmental delay.Methods
Detailed clinical evaluation was undertaken. Whole exome capture and sequencing of patient genomic DNA samples was followed by sequence alignment, variant detection, comparison and prioritisation.Main Outcome MeasuresPathogenic variant identification in the disease-causing gene in affected individuals.ResultsWe identified a novel homozygous deletion leading to a frameshift mutation in VPS13B, c.11327del, p.(Asn3776Thrfs*102), the disease gene associated with Cohen syndrome.Conclusions
This report emphasises the value of a broad-based WES approach in disease gene identification in the syndromic retinal dystrophies, where all disease characteristics may not be present in young patients to allow a clinical diagnosis. This facilitates improved prognostic and genetic information for patients and families.
[Show abstract][Hide abstract] ABSTRACT: Delineating candidate genes at the chromosomal breakpoint regions in the apparently balanced chromosome rearrangements (ABCR) has been shown to be more effective with the emergence of next-generation sequencing (NGS) technologies. We employed a large-insert (7-11 kb) paired-end tag sequencing technology (DNA-PET) to systematically analyze genome of four patients harbouring cytogenetically defined ABCR with neurodevelopmental symptoms, including developmental delay (DD) and speech disorders. We characterized structural variants (SVs) specific to each individual, including those matching the chromosomal breakpoints. Refinement of these regions by Sanger sequencing resulted in the identification of five disrupted genes in three individuals: guanine nucleotide binding protein, q polypeptide (GNAQ), RNA-binding protein, fox-1 homolog (RBFOX3), unc-5 homolog D (C.elegans) (UNC5D), transmembrane protein 47 (TMEM47), and X-linked inhibitor of apoptosis (XIAP). Among them, XIAP is the causative gene for the immunodeficiency phenotype seen in the patient. The remaining genes displayed specific expression in the fetal brain and have known biologically relevant functions in brain development, suggesting putative candidate genes for neurodevelopmental phenotypes. This study demonstrates the application of NGS technologies in mapping individual gene disruptions in ABCR as a resource for deciphering candidate genes in human neurodevelopmental disorders (NDDs).
[Show abstract][Hide abstract] ABSTRACT: 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.
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.
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.
No preview · Article · Feb 2014 · Ophthalmic Genetics
[Show abstract][Hide abstract] ABSTRACT: 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.European Journal of Human Genetics advance online publication, 27 November 2013; doi:10.1038/ejhg.2013.268.
No preview · Article · Nov 2013 · European journal of human genetics: EJHG
[Show abstract][Hide abstract] ABSTRACT: Visual electrophysiology is an important ancillary investigation in children with poor vision and nystagmus. Cone dystrophy with supranormal rod electroretinogram (KCNV2 retinopathy) has pathognomonic electrophysiology findings that, if identified, direct molecular genetic testing. We report the case of a 6-year-old boy with typical electrophysiology findings of KCNV2 retinopathy but with abnormal cone dysfunction compared to other patients with mutations in KCNV2. Molecular genetic testing revealed complete homozygous deletion of KCNV2. To our knowledge, this is the first such report. The greater cone dysfunction seen in this case suggests a phenotypic link to the genetic changes.
No preview · Article · Nov 2013 · Journal of AAPOS: the official publication of the American Association for Pediatric Ophthalmology and Strabismus / American Association for Pediatric Ophthalmology and Strabismus
[Show abstract][Hide abstract] ABSTRACT: 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.
No preview · Article · Oct 2013 · Jama Ophthalmology
[Show abstract][Hide abstract] ABSTRACT: Microtubules are essential components of axon guidance machinery. Among b-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 ab-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 b-tubulin isotypes function in both conserved and divergent ways
to support proper human nervous system development.
Full-text · Article · Sep 2012 · Human Molecular Genetics
[Show abstract][Hide abstract] ABSTRACT: This study aimed to describe the phenotype of Australian patients with a clinical diagnosis of dominant optic atrophy (DOA) and provide long-term follow-up data on its natural history.
All patients with the clinical diagnosis of DOA observed during a 30-year period at a single tertiary referral center (Save Sight Institute, Sydney Eye Hospital, Sydney, Australia) with at least 12 months of follow-up were included in the study. Clinical characteristics were assessed with particular attention to change in visual acuity (VA).
There were 36 patients with DOA from 26 different Australian families. The most common clinical presentation of DOA was insidious onset of visual difficulties beginning in childhood. Mean (SD) age at diagnosis of DOA was 16 (14) years. During a mean follow-up period of 10.6 years (median, 10 years), 44% of study eyes had no change in VA, 35% had reduction of VA by 1 Snellen line, 13% had a reduction of VA by 2 Snellen lines, and 8% of the study eyes had a VA reduction of more than 2 Snellen lines. Six of 36 patients were legally blind at last follow-up.
There is considerable heterogeneity in the presenting VA and natural history of DOA between individual patients and within families with DOA, with VA ranging from 6/6 to hand motion perception. This study provides valuable information to aid the clinician counseling the long-term visual outcome in patients with DOA and their families.
[Show abstract][Hide abstract] ABSTRACT: The microphthalmia-associated transcription factor (MITF) is a basic helix-loop-helix leucine zipper transcription factor, which regulates melanocyte development and the biosynthetic melanin pathway. A notable relationship has been described between non-truncating mutations of its basic domain and Tietz syndrome, which is characterized by albinoid-like hypopigmentation of the skin and hair, rather than the patchy depigmentation seen in Waardenburg syndrome, and severe hearing loss. Twelve patients with new or recurrent non-truncating mutations of the MITF basic domain from six families were enrolled in this study. We observed a wide range of phenotypes and some unexpected features. All the patients had blue irides and pigmentation abnormalities that ranged from diffuse hypopigmentation to Waardenburg-like patches. In addition, they showed congenital complete hearing loss, diffuse hypopigmentation of the skin, freckling and ocular abnormalities, more frequently than patients with MITF mutations outside the basic domain. In conclusion, the non-truncating mutations of the basic domain do not always lead to Tietz syndrome but rather to a large range of phenotypes. Sun-exposed freckles are interestingly observed more frequently in Asian populations. This variability argues for the possible interaction with modifier loci.
Full-text · Article · Jan 2012 · European journal of human genetics: EJHG
[Show abstract][Hide abstract] ABSTRACT: Isolated hypogonadotropic hypogonadism (IHH) is a genetically heterogeneous condition in which patients frequently require assisted reproduction to achieve fertility. In patients with IHH who are otherwise well, no particular increased risk of congenital anomalies in the resultant offspring has been highlighted. Heterozygous mutations in SOX2 are the commonest single-gene cause of anophthalmia/microphthalmia (A/M) and sometimes result in pituitary abnormalities. We report a family with a novel frameshift mutation in the SOX2 transactivation domain, p.Gly280AlafsX91, resulting in bilateral anophthalmia and subtle endocrinological abnormalities in a male sibling, and unilateral microphthalmia in a female sibling. The mutation is present in their mother who has IHH, but has no eye disorders or other anomalies. She underwent assisted reproduction to achieve fertility. This report has important implications for the evaluation of patients with IHH, particularly in the setting of planned infertility treatment.
Full-text · Article · Feb 2011 · European journal of human genetics: EJHG
[Show abstract][Hide abstract] ABSTRACT: Twist2 is a member of a family of bHLH transcription factors critical for normal mesenchymal proliferation and differentiation. In this study, the authors analyzed the role of Twist2 in the eye and cornea through examination of a Twist2 loss-of-function mouse mutant.
Twist2 expression during eye development in the mouse was investigated using RT-PCR and mRNA slide in situ hybridization. Lineage tracing was performed using Cre reporter mice. Morphometric analyses were performed, and cell proliferation and cell death were investigated by immunohistochemistry using Ki67 and cleaved caspase 3 antibodies, respectively.
In the mouse, Twist2 is expressed first in the periocular mesenchyme and subsequently in the corneal stroma and endothelium of the developing eye. Loss of Twist2 function leads to corneal thinning and a reduced population of stromal keratocytes. The reduction in the stromal cell population can be traced back to embryonic stages during which the proliferation of stromal progenitor cells is impaired and to the reduced number of proliferating cells in the corneal limbus postnatally. Adult Twist2-null mice display enophthalmia and blepharophimosis. Corneal thinning in mutant mice is not accompanied by glaucoma, an association reported in human patients.
Twist2 is required for normal corneal keratocyte proliferation and eyelid morphogenesis in the mouse. Loss of Twist2 function leads to corneal thinning because of the reduction in stromal keratocyte proliferation.
No preview · Article · Nov 2010 · Investigative ophthalmology & visual science