ABCA4 and ROM1: implications for modification of the PRPH2-associated macular dystrophy phenotype

PURPOSE: To identify the causative mutation leading to autosomal dominant macular dystrophy, cone dystrophy, and cone-rod dystrophy in a five-generation family and to explain the high intrafamilial phenotypic variation by identifying possible modifier genes. METHODS: Fifteen family members were investigated by detailed ophthalmic and electrophysiologic phenotyping. Mutation screening was initially performed with microarrays that detect known mutations in genes associated with retinal degeneration. Furthermore, the patients' genomic DNA was analyzed by sequencing analysis of PRPH2, ABCA4, and ROM1. RESULTS: Heterozygous mutations were identified in three genes and showed five different combinations within the studied family. All clearly affected family members carried the heterozygous PRPH2 mutation p.R172W. Patients with heterozygous sequence alterations only in ROM1 (p.R229H) or ABCA4 (p.V2050L) showed a mild ocular phenotype and were otherwise asymptomatic. The phenotypic severity of patients carrying the PRPH2 mutation increased with an additional mutation in ROM1. Patients carrying all three mutations were the most severely affected. CONCLUSIONS: Features of a PRPH2-associated phenotype might be modulated by additional mutations in other genes (in this family ABCA4 and/or ROM1) accounting for intrafamilial variability and resulting in a cumulative effect worsening the phenotype. Families showing a variable macular dystrophy phenotype caused by mutations in PRPH2 should be tested for additional mutations in ABCA4 and ROM1, as they may alter the progression of the PRPH2 phenotype. This testing will influence genetic counseling, as patients with additional mutations may be confronted with a faster progression of visual loss

Syndromic choroideremia: sublocalization of phenotypes associated with Martin-Probst deafness mental retardation syndrome

PURPOSE: To identify the mutation leading to syndromic choroideremia (CHM) in two families and to define fundus autofluorescence (FAF) in CHM carriers. METHODS: The ophthalmic and clinical phenotype was investigated including FAF, neuropediatric, otorhinolaryngologic, cardiologic, and nephrologic examinations of three male patients (age, 11-46 years) and three female carriers (age, 11-46 years) from two families. Genomic DNA amplification (PCR) of the REP1 gene as well as adjacent loci was used to determine the molecular basis of the phenotype. RESULTS: Analysis of genomic DNA revealed large deletions that asymmetrically flank REP1 in both families, ranging from a minimum size of 6.3 and 8.5 mega base pairs (Mbp) to a maximum size of 9.7 and 14.1 Mbp, respectively. In addition to CHM, patients from these families exhibited mild syndromic features, including mental and motor retardation and low-frequency hearing loss. FAF showed a distinctive pattern characterized by small areas of reduced and increased autofluorescence in all female carriers. CONCLUSIONS: Both CHM families are the first to be described with large deletions that manifest with a mild syndromic phenotype. The location of the deletions indicates that they may allow sublocalization of the syndromic features to the most proximal region of X-linked distal spinal muscular atrophy (DSMAX) and Martin-Probst deafness mental retardation syndrome (MPDMRS). The FAF pattern is specific to CHM carriers and thus will help to identify and differentiate between carriers of other X-linked recessive carrier states such as in X-linked retinitis pigmentosa

Probleme der Bildung und Verwendung des Fonds Wissenschaft und Technik zur Sicherung der wissenschaftlich-technischen Aufgaben der zentralgeleiteten Industriekombinate in der DDR

DB Leipzig(101) - Di 1983 B VD 121, T. 1, 2 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Genotyping Microarray for CSNB-Associated Genes

PURPOSE. Congenital stationary night blindness (CSNB) is a clinically and genetically heterogeneous retinal disease. Although electroretinographic (ERG) measurements can discriminate clinical subgroups, the identification of the underlying genetic defects has been complicated for CSNB because ofgenetic heterogeneity, the uncertainty about the mode of inheritance, and time-consuming and costly mutation scanning and direct sequencing approaches. METHODS. To overcome these challenges and to generate a time- and cost-efficient mutation screening tool, the authors developed a CSNB genotyping microarray with arrayed primer extension (APEX) technology. To cover as many mutations as possible, a comprehensive literature search was performed, and DNA samples from a cohort of patients with CSNB were first sequenced directly in known CSNB genes. Subsequently, oligonucleotides were designed representing 126 sequence variations in RHO, CABP4, CACNA1F, CACNA2D4, GNAT1,GRM6, NYX, PDE6B, and SAG and spotted on the chip. RESULTS. Direct sequencing of genes known to be associated with CSNB in the study cohort revealed 21 mutations (12 novel and 9 previously reported). The resultant microarray containing oligonucleotides, which allow to detect 126 known and novel mutations, was 100% effective in determining the expected sequence changes in all known samples assessed. In addition, investigation of 34 patients with CSNB who were previously not genotyped revealed sequence variants in 18%, of which 15% are thought to be disease-causing mutations. CONCLUSIONS. This relatively inexpensive first-pass genetic testing device for patients with a diagnosis of CSNB will improve molecular diagnostics and genetic counseling of patients and their families and gives the opportunity to analyze whether, for example, more progressive disorders such as cone or cone–rod dystrophies underlie the same gene defects

Panel-based next generation sequencing as a reliable and efficient technique to detect mutations in unselected patients with retinal dystrophies

Hereditary retinal dystrophies (RD) constitute a group of blinding diseases that are characterized by clinical variability and pronounced genetic heterogeneity. The different forms of RD can be caused by mutations in >100 genes, including >1600 exons. Consequently, next generation sequencing (NGS) technologies are among the most promising approaches to identify mutations in RD. So far, NGS is not routinely used in gene diagnostics. We developed a diagnostic NGS pipeline to identify mutations in 170 genetically and clinically unselected RD patients. NGS was applied to 105 RD-associated genes. Underrepresented regions were examined by Sanger sequencing. The NGS approach was successfully established using cases with known sequence alterations. Depending on the initial clinical diagnosis, we identified likely causative mutations in 55% of retinitis pigmentosa and 80% of Bardet–Biedl or Usher syndrome cases. Seventy-one novel mutations in 40 genes were newly associated with RD. The genes USH2A, EYS, ABCA4, and RHO were more frequently affected than others. Occasionally, cases carried mutations in more than one RD-associated gene. In addition, we found possible dominant de-novo mutations in cases with sporadic RD, which implies consequences for counseling of patients and families. NGS-based mutation analyses are reliable and cost-efficient approaches in gene diagnostics of genetically heterogeneous diseases like RD

The mutation p.E113K in the Schiff base counterion of rhodopsin is associated with two distinct retinal phenotypes within the same family

The diagnoses of retinitis pigmentosa (RP) and stationary night blindness (CSNB) are two distinct clinical entities belonging to a group of clinically and genetically heterogeneous retinal diseases. The current study focused on the identification of causative mutations in the RP-affected index patient and in several members of the same family that reported a phenotype resembling CSNB. Ophthalmological examinations of the index patient confirmed a typical form of RP. In contrast, clinical characterizations and ERGs of another affected family member showed the Riggs-type CSNB lacking signs of RP. Applying whole exome sequencing we detected the non-synonymous substitution c.337G > A, p.E113 K in the rhodopsin (RHO) gene. The mutation co-segregated with the diseases. The identification of the pathogenic variant p.E113 K is the first description of a naturally-occurring mutation in the Schiff base counterion of RHO in human patients. The heterozygous mutation c.337G > A in exon 1 was confirmed in the index patient as well as in five CSNB-affected relatives. This pathogenic sequence change was excluded in a healthy family member and in 199 ethnically matched controls. Our findings suggest that a mutation in the biochemically well-characterized counterion p.E113 in RHO can be associated with RP or Riggs-type CSNB, even within the same family