[Genetic diagnostics of retinal dystrophies : Breakthrough with new methods of DNA sequencing]. / Genetische Diagnostik von Netzhautdystrophien : Revolutionierung durch neue Methoden der DNA-Sequenzierung.

Until the mid-2000s, knowledge about the genetic causes of retinal dystrophies was not adequately translated into molecular diagnostics and genetic counselling offered to the patients. Although many genes whose mutations underlie retinal degeneration, e.g., retinitis pigmentosa, Leber congenital amaurosis and cone-rod dystrophies were known, they could not be analyzed on a routine diagnostic basis because DNA sequencing was too expensive and time-consuming. New methods summarized under the term next-generation sequencing (NGS) procedures for high-throughput sequencing have changed this completely. In its initial application in research NGS greatly accelerated the pace of novel disease gene identification: the mutations of most patients with retinal dystrophies can today be found in genes which are known to be associated with the condition. Since approximately 2010, NGS has expanded into routine diagnostics. In most patients, this now enables a genetic diagnosis and therefore specific genetic counselling and medical treatment. Constantly improving bioinformatics and comprehensive databases facilitate the evaluation of the complex NGS data. Nevertheless, profound scientific knowledge regarding the genetics of retinal dystrophies is indispensable to avoid erroneous data interpretation. This is also true for the close interaction between ophthalmologists and medical geneticists.

Genome-wide linkage and sequence analysis challenge CCDC66 as a human retinal dystrophy candidate gene and support a distinct NMNAT1-related fundus phenotype.

To uncover the genotype underlying early-onset cone-rod dystrophy and central nummular macular atrophic lesion in 2 siblings from an endogamous Arab family, we performed targeted next-generation sequencing (NGS) of 44 retinal dystrophy genes, whole-exome sequencing (WES) and genome-wide linkage analysis. Targeted NGS and WES in the index patient highlighted 2 homozygous variants, a CCDC66 frameshift deletion and a novel missense NMNAT1 variant, c.500G>A (p.Asn167Ser). Linkage and segregation analysis excluded the CCDC66 variant and confirmed the NMNAT1 mutation. Biallelic NMNAT1 mutations cause Leber congenital amaurosis with a central nummular macular atrophic lesion (LCA9). The NMNAT1 mutation reported here underlied cone-rod dystrophy rather than LCA but the fundus lesion was compatible with that of LCA9 patients, highlighting that such a fundus appearance should raise suspicion for biallelic mutations in NMNAT1 when in the context of any retinal dystrophy. Although Ccdc66 mutations have been proposed to cause retinal disease in dogs, our results and public databases challenge CCDC66 as a candidate gene for human retinal dystrophy.

[Segregation Analysis in Inherited Eye Disorders: An Academic Add-on or An Essential Effort?] / Die Segregationsanalyse bei erblichen Augenerkrankungen ­ akademisches Extra oder notwendiger Aufwand?

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.

[Next-Generation Sequencing: A Quantum Leap in Ophthalmology Research and Diagnostics]. / Next-Generation Sequencing: Quantensprung für Forschung und Diagnostik in der Ophthalmologie.

Many eye diseases have a genetic basis, and most can be caused by mutations in many different genes (extensive genetic heterogeneity). The retinal dystrophies are a good example: More than 200 genes have been identified for the isolated forms (Leber's congenital amaurosis, retinitis pigmentosa, cone-rod dystrophy, congenital stationary night blindness), and for syndromes that comprise additional dysfunctions or malformations of extraocular tissues and organs. Selecting genes for diagnostic testing has been difficult, and their analysis with the hitherto predominant DNA sequencing method (Sanger sequencing) has been extremely laborious: The phenotype rarely indicates the affected gene, and the contributions of the particular genes to the disease (e.g., to LCA) were largely unknown. Consequently, comprehensive genetic analyses were impossible in most cases. In the recent years, high-throughput sequencing technologies, summarized as next-generation sequencing (NGS), have revolutionized genetic research and, subsequently, genetic diagnostics. The latter has far-reaching implications for the individual management of patients with genetic eye diseases and their families.

[Genotype-Phenotype Correlations in Patients with CRB1 Mutations]. / Genotyp-Phänotyp-Korrelation bei Patienten mit CRB1-Mutationen.

Background Mutations in the CRB1 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 CRB1-mutations in the first two decades of life. Materials and Methods 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. Results 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. Conclusions Patients with CRB1-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.

Extension of the clinical and molecular phenotype of DIAPH1-associated autosomal dominant hearing loss (DFNA1).

In about 20% of non-syndromic hearing loss (NSHL) cases, inheritance is autosomal dominant (ADNSHL). DIAPH1 mutations define the ADNSHL locus DFNA1. We identified two new families with heterozygous truncating DIAPH1 mutations (p.Ala1210Serfs*31 and p.Arg1213*). In contrast to the extensively studied original DFNA1 family, hearing loss was not confined to low frequencies, but congenital manifestation and rapid progression were confirmed. In line with a recent unrelated study, we identified an association with thrombocytopenia, reclassifying DFNA1 as a syndrome. Consequently, we suggest to include the blood count into the initial clinical workup of patients with autosomal dominant hearing loss to guide the genetic diagnosis. We provide the first data on DIAPH1 expression in the organ of Corti, where it localizes to the inner pillar cells, at the base of the outer hair cells. Homozygous truncating DIAPH1 mutations located N-terminally to the DFNA1 mutations have recently been identified in autosomal recessive microcephaly. It is therefore noteworthy that we found DIAPH1 expression also in spiral ganglion neurons and in the barrier between the myelinating glia of the peripheral nervous system and oligodendrocytes that form the myelinating glia of the central nervous system (CNS).

[Genetics of congenital aniridia]. / Genetik der kongenitalen Aniridie.

BACKGROUND: Mutations in the PAX6 gene mostly cause non-syndromic aniridia with autosomal dominant inheritance and familial occurrence. The underlying point mutations and deletions in the PAX6 locus cause loss-of-function of one gene copy (haploinsufficiency). Mutations with residual PAX6 function often result in milder disease expression but may also cause distinct and more severe ocular phenotypes. Combined deletion of PAX6 and the adjacent WT1 tumor suppressor gene causes Wilms tumor, aniridia, genitourinary anomalies and mental retardation (WAGR) syndrome with a high risk for Wilms tumors in infancy. PURPOSE: Genetic diagnostics are important for confirming the clinical diagnosis, for the assessment of the risk of recurrence and early recognition of children with associated tumor risk. RESULTS AND DISCUSSION: Sequencing of the PAX6 gene and quantitative analysis of the PAX6 locus allow for efficient molecular genetic evaluation of the clinical diagnosis of both isolated and syndromic aniridia. In cases of clinical overlap with other entities, high-throughput sequencing of multiple additional genes can simultaneously cover genes for differential diagnoses (e.g. microphthalmia syndromes). Optimal care of aniridia patients requires close cooperation of ophthalmologists and medical geneticists.

[Genetics of Usher syndrome]. / Genetik des Usher-Syndroms.

Since the first gene (MYO7A) for Usher syndrome was identified 14 years ago, there has been substantial progress in the elucidation of the genetic basis of this disorder, revealing extensive genetic heterogeneity (with nine genes known to date). Most Usher genes have similar functions, localize to similar regions in inner ear hair cells and retinal photoreceptors, and interact with each other. Approximately 80% of the patients carry mutations in one of the known Usher genes. One major challenge for the scientific community is to identify the remaining causative genes. Moreover, it is still largely unclear which genetic factors are responsible for the clinical variability that can be observed even between affected siblings. The establishment of high-throughput techniques shall soon provide comprehensive genetic testing covering all genes, which would be desirable: Early confirmation (or exclusion) of the diagnosis would be important for the individual patient, as it could help predict whether retinal degeneration can be expected in addition to the congenital hearing impairment.

Characterisation of severe rod-cone dystrophy in a consanguineous family with a splice site mutation in the MERTK gene.

AIM: To characterise the ocular phenotype of a family segregating the splice site mutation c.2189+1G>T in the tyrosine kinase receptor gene MERTK. METHODS: Five affected children of a consanguineous Moroccan family were investigated by ophthalmic examinations, including fundus photography, autofluorescence (FAF) imaging, optical coherence tomography (OCT), psychophysical and electrophysiological methods. RESULTS: Affected children were between 5 and 19 years of age, allowing an estimation of disease progression. Electroretinography demonstrated loss of scotopic and photopic function in the first decade of life. Younger siblings showed drusen-like deposits with focal relatively increased FAF in the macular area. With increasing age, a yellowish lesion with relatively increased FAF and subsequent macular atrophy developed. Visual acuity deteriorated with age and ranged between 20/50 in the best eye of the youngest affected and 20/400 in the worst eye of the oldest affected sibling. Spectral-domain OCT revealed debris-like material in the subneurosensory space. CONCLUSION: The splice site mutation c.2189+1G>T in MERTK causes rod-cone dystrophy with a distinct macular phenotype. The debris in the subneurosensory space resembles that in the Royal College of Surgeons (RCS) rat being the mertk animal model. Patients might therefore benefit from advances in gene therapy that were previously achieved in the RCS rat.

GPR98 mutations cause Usher syndrome type 2 in males.

Mutations in the large GPR98 gene underlie Usher syndrome type 2C (USH2C), and all patients described to date have been female. It was speculated that GPR98 mutations cause a more severe, and eventually lethal, phenotype in males. We describe for the first time two male patients with USH2 with novel GPR98 mutations. Clinical characterization of a male patient and his affected sister revealed a typical USH2 phenotype in both. GPR98 may have been excluded from systematic investigation in previous studies, and the proportion of patients with USH2C probably underestimated. GPR98 should be considered in patients with USH2 of both sexes.