In daily life, myopia is a frequent cause of reduced visual acuity (VA) due to missing or incomplete optical correction. While the genetic cause of high myopia itself is not well understood, a ...significant number of cases are secondary to hereditary malfunctions or degenerations of the retina. The mechanism by which this occurs remains yet unclear. Two female siblings, 4 y and 2 y, respectively, from a consanguineous Pakistani family were referred to our department for reduced VA and strabismus. Both girls were highly myopic and hence were further examined using standard clinical tests and electroretinography (ERG). The latter confirmed confounded electrical coupling of photoreceptors and bipolar cells. Further inquiry and testing confirmed a similar condition for the father including impaired night vision, reduced VA, photophobia, and an equally characteristic ERG. Findings in the mother were unremarkable. Subsequent genetic analysis of autosomal recessive and X-linked genes for congenital stationary night blindness (CSNB) revealed a novel homozygous splice site mutation in CACNA1F in the two girls transmitted from both the father and the mother. While in males the above clinical constellation is a frequent finding, this report, to the authors’ knowledge, is the first demonstrating biallelic mutations at the CACNA1F locus in females.
From the ophthalmological view, albinism is a disorder of reduced pigmentation of the retinal and irdial pigment epithelium and the iris and choroid stroma. The reduced pigmentation is accompanied by ...morphological changes in the retina and the optic nerve. The functional relationship of these morphological changes is not yet well understood. This review summarises the genetic causes of reduced pigment synthesis and impaired pigment distribution, and discusses the variability of expression of albinism symptoms, in the light of other disorders affecting retinal development.
The knowledge of the genetic basis of many eye diseases is constantly increasing. Besides retinal degeneration, developmental defects of the anterior segment, cataracts, and the development of the ...basic structure are often associated with genetic defects. Moreover, a lot of genetic syndromes involve eye abnormalities. The impact of genetics has become more and more evident in ophthalmological practice. Although genetic counselling is usually carried out by human geneticists, the increasing availability of therapeutic options requires ophthalmologists to have some basic knowledge of the genetic causes and how to identify them. The first step in this regard is to recognise potential genetic eye disorders and to initiate an adequate genetic analysis to confirm the diagnosis. This review discusses possible and necessary investigations within the patient's family facing ophthalmologists after the genetic cause of an eye disease has been identified.
Leber congenital amaurosis (LCA) is an early-onset inherited disorder of childhood blindness characterized by visual impairment noted soon after birth. Variants in at least six genes (AIPL1, CRB1, ...CRX, GUCY2D, RPE65, and RPGRIP1) have been associated with a diagnosis consistent with LCA or early-onset retinitis pigmentosa (RP). Genetically heterogeneous inheritance complicates the analyses of LCA cases, especially in patients without a family history of the disorder, and conventional methods are of limited value.
To overcome these limitations, arrayed primer extension (APEX) technology was used to design a genotyping microarray for early-onset, severe retinal degenerations that includes all of the >300 disease-associated variants currently described in eight genes (in addition to the six just listed, the early-onset RP genes LRAT and MERTK were added). The resultant LCA array allows simultaneous detection of all known disease-associated alleles in any patient with early-onset RP. The array was validated by screening 93 confirmed patients with LCA who had known mutations. Subsequently, 205 novel LCA cases were screened on the array, followed by segregation analyses in families, if applicable.
The microarray was >99% effective in determining the existing genetic variation and yielded at least one disease-associated allele in approximately one third of the novel patients. More than two (expected) variants were discovered in a substantial fraction (22/300) of the patients, suggesting a modifier effect from more than one gene. In support of the latter hypothesis, the third allele segregated with a more severe disease phenotype in at least five families.
The LCA genotyping microarray is a robust and cost-effective screening tool, representing the prototype of a disease chip for genotyping patients with a genetically heterogeneous condition. Simultaneous screening for all known LCA-associated variants in large LCA cohorts allows systematic detection and analysis of genetic variation, facilitating prospective diagnosis and ultimately predicting disease progression.
To describe the genotype-phenotype correlation in a German family with a novel CRX mutation and to perform a comparative analysis of published cases.
Retrospective observational case series, ...systematic review, and comparative analysis of the literature.
Four related patients with progressive retinal degeneration.
Mutation screening by single-strand polymorphism analysis and direct sequencing. Clinical examination included kinetic visual fields (VFs), 2-color threshold perimetry (2CTP), full-field electroretinography, fundus photography, optical coherence tomography, and fundus autofluorescence (FA) recording.
Visual fields, subjective and objective cone- and rod-specific function, fundus aspect, retinal stratification, and FA.
A novel heterozygous complex mutation (c.816delCACinsAA) in CRX predicting the substitution of 27 C-terminal amino acids by 44 novel amino acids, thus abolishing the OTX tail, was identified in a 2-generation family finally diagnosed with cone-rod dystrophy (CRD), which was confirmed by 2CTP. Patients presented with variability in progression, nystagmus, and nyctalopia. Most of the patients were hyperopic. Electroretinography recordings showed residual rod and mixed cone-rod responses in 2 of the subjects. Age-dependent VF losses followed funduscopic changes of progressive atrophy of the retinal pigment epithelium and neuroretina in the macula and midperiphery marked by disturbed FA. Optical coherence tomography showed decreased central retinal thickness. Comparative analysis of the 131 published data sets revealed 2 groups: patients with early and late onset.
We described a 2-generation family with a novel mutation in CRX. The resulting phenotype is that of CRD with variable age at onset and progression. The phenotype description of previously published cases is conclusive only for CRD.
Retinitis pigmentosa (RP) and Leber congenital amaurosis (LCA) are major causes of blindness. They result from mutations in many genes which has long hampered comprehensive genetic analysis. ...Recently, targeted next-generation sequencing (NGS) has proven useful to overcome this limitation. To uncover "hidden mutations" such as copy number variations (CNVs) and mutations in non-coding regions, we extended the use of NGS data by quantitative readout for the exons of 55 RP and LCA genes in 126 patients, and by including non-coding 5' exons. We detected several causative CNVs which were key to the diagnosis in hitherto unsolved constellations, e.g. hemizygous point mutations in consanguineous families, and CNVs complemented apparently monoallelic recessive alleles. Mutations of non-coding exon 1 of EYS revealed its contribution to disease. In view of the high carrier frequency for retinal disease gene mutations in the general population, we considered the overall variant load in each patient to assess if a mutation was causative or reflected accidental carriership in patients with mutations in several genes or with single recessive alleles. For example, truncating mutations in RP1, a gene implicated in both recessive and dominant RP, were causative in biallelic constellations, unrelated to disease when heterozygous on a biallelic mutation background of another gene, or even non-pathogenic if close to the C-terminus. Patients with mutations in several loci were common, but without evidence for di- or oligogenic inheritance. Although the number of targeted genes was low compared to previous studies, the mutation detection rate was highest (70%) which likely results from completeness and depth of coverage, and quantitative data analysis. CNV analysis should routinely be applied in targeted NGS, and mutations in non-coding exons give reason to systematically include 5'-UTRs in disease gene or exome panels. Consideration of all variants is indispensable because even truncating mutations may be misleading.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A broad spectrum of pigmentation of the skin and hair is found among patients diagnosed with ocular albinism (OA) and oculocutaneous albinism (OCA). Even though complexion is variable, three ocular ...features, i.e., hypopigmentation of the fundus, hypoplasia of the macula, and nystagmus, are classical pathological findings in these patients. We screened 172 index patients with a clinical diagnosis of OA or OCA based on the classical findings, to evaluate the frequency of sequence variants in tyrosinase (TYR), P-gene, P-protein (OCA2), and the G-protein-coupled receptor 143 gene, OA1 (GPR143). In addition, we investigated the association of sequence variants in the melanocortin receptor 1 gene (MC1R) and OCA2.
Pigmentation of the hair, skin, iris, and fundus were included in the evaluation of OCA and OA. Male OA patients showing X-linked inheritance were screened for GPR143. Females showing OA without family history were regarded as representing autosomal recessive OA (OA3). Direct sequencing was applied to PCR products showing aberrant single-strand conformation polymorphism-banding patterns.
Fifty-seven male index patients were screened for OA. We identified 16 potentially pathogenic sequence variations in GPR143 (10 novel) in 22 males. In TYR, we identified 23 (7 novel), and in OCA2 28 (11 novel) possibly pathogenic variants. Variants on both alleles were identified in TYR or OCA2 in 29/79 OCA patients and 14/71 OA patients. Sequence changes in TYR were identified almost exclusively in OCA patients, while sequence changes in OCA2 occurred in OCA and OA patients. MC1R sequencing was performed in 47 patients carrying mutations in OCA2 and revealed MC1R mutations in 42 of them.
TYR gene mutations have a more severe effect on pigmentation than mutations in OCA2 and the GPR143 gene. Nevertheless, mutations in these genes affect the development of visual function either directly or by interaction with other genes like MC1R, which can be deduced from a frequent association of MC1R variants with p.R305W or p.R419Q in OCA2.
To describe the genotype and phenotype in a 9-year-old boy with bilateral retinopathy.
The patient, his healthy (by history) nonconsanguineous parents and his sister were examined by best-corrected ...visual acuity, matrix frequency doubling technology, monocular static field analysis, fundus autofluorescence imaging, optical coherence tomography, Ganzfeld electroretinography (ERG), pattern ERG, multifocal ERG, electro-oculography and genotyping of the BEST1 gene.
The patient presented with an Arden ratio of 1.25, an unremarkable ERG and fluorescent yellow deposits distributed throughout the fundus suggestive of autosomal recessive bestrophinopathy (ARB). Genotyping revealed a homozygous nonsense mutation in BEST1 (p.R200X). The parents and the sister, who were heterozygous mutation carriers, presented with normal ophthalmological function.
ARB is a rare retinal disorder. We contribute a novel patient report indicative of ARB, assessed by clinical examination and confirmed by genotyping of BEST1, to the short list of ARB cases in the literature.
Mutations in the
gene were identified in patients with early-onset severe retinal dystrophy (EOSRD), childhood-onset and juvenile-onset rod-cone dystrophy. This study describes the phenotypic ...spectrum of disease-causing
-mutations in the first two decades of life.
Eight patients, aged three months to 20 years, underwent a full comprehensive ophthalmological examination including best corrected visual acuity testing (BCVA), color vision testing, funduscopy, spectral-domain optical coherence tomography (SD-OCT), and fundus autofluorescence (FAF) recording. Automated and manual retinal layer segmentation of SD-OCT recordings was performed using DIOCTA software. A full-field electroretinography (ffERG, ISCEV Standard) and visual fields were performed in cooperative patients.
Five patients carried mutations causing a loss of the corresponding gene product (splice-mutation, nonsense-mutation, frame-shifting mutation). These patients presented with generally reduced vision in the first months of life that never exceeded 0.04 during the observational period. The sixth patient carried a homozygous missense mutation and reached maximal BCVA 0.05 at the age of 6 years. Two further patients, carrying at least one hypomorphic missense-mutation, presented with better preserved visual function with up to 0.5 at the age of 20 years. The recorded ffERG was below threshold in the majority of patients. Visual fields were severely restricted. The photoreceptor layers were significantly reduced in SD-OCT whenever stratification of retinal layers was possible. The inner nuclear layer thickness increased with progressing retinal degeneration. A-Scan analysis revealed better preservation of the retinal stratification in patients with missense mutations.
Patients with
-mutations presented with a severe phenotype with severely reduced visual acuity from birth. Missense mutations with predicted residual function of the gene product were associated with moderate expression of the disease. Severe and progressive restriction of visual fields occurred in the first decade of life. The reduced retinal stratification indicates a general loss of structural integrity of the retinal layers.
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