Britta Fiebig

Acetylcholine Receptor Pathway Mutations Explain Various Fetal Akinesia Deformation Sequence Disorders

Impaired fetal movement causes malformations, summarized as fetal akinesia deformation sequence (FADS), and is triggered by environmental and genetic factors. Acetylcholine receptor (AChR) components are suspects because mutations in the fetally expressed gamma subunit (CHRNG) of AChR were found in two FADS disorders, lethal multiple pterygium syndrome (LMPS) and Escobar syndrome. Other AChR subunits alpha1, beta1, and delta (CHRNA1, CHRNB1, CHRND) as well as receptor-associated protein of the synapse (RAPSN) previously revealed missense or compound nonsense-missense mutations in viable congenital myasthenic syndrome; lethality of homozygous null mutations was predicted but never shown. We provide the first report to our knowledge of homozygous nonsense mutations in CHRNA1 and CHRND and show that they were lethal, whereas novel recessive missense mutations in RAPSN caused a severe but not necessarily lethal phenotype. To elucidate disease-associated malformations such as frequent abortions, fetal edema, cystic hygroma, or cardiac defects, we studied Chrna1, Chrnb1, Chrnd, Chrng, and Rapsn in mouse embryos and found expression in skeletal muscles but also in early somite development. This indicates that early developmental defects might be due to somite expression in addition to solely muscle-specific effects. We conclude that complete or severe functional disruption of fetal AChR causes lethal multiple pterygium syndrome whereas milder alterations result in fetal hypokinesia with inborn contractures or a myasthenic syndrome later in life.

PTHR1 Loss-of-Function Mutations in Familial, Nonsyndromic Primary Failure of Tooth Eruption

Tooth eruption is a complex developmental process requiring coordinated navigation through alveolar bone and oral epithelium. Primary failure of tooth eruption (PFE) is associated with several syndromes primarily affecting skeletal development, but it is also known as a nonsyndromic autosomal-dominant condition. Teeth in the posterior quadrants of the upper and lower jaw are preferentially affected and usually result in an open bite extending from anterior to posterior. In this study, we show that familial, nonsyndromic PFE is caused by heterozygous mutations in the gene encoding the G protein-coupled receptor for parathyroid hormone and parathyroid hormone-like hormone (PTHR1). Three distinct mutations, namely c.1050-3C > G, c.543+1G > A, and c.463G > T, were identified in 15 affected individuals from four multiplex pedigrees. All mutations truncate the mature protein and therefore should lead to a functionless receptor, strongly suggesting that haplo-insufficiency of PTHR1 is the underlying cause of nonsyndromic PFE. Although complete inactivation of PTHR1 is known to underlie the autosomal-recessive Blomstrand osteochondrodysplasia (BOCD), a lethal form of short-limbed dwarfism, our data now imply that dominantly acting PTHR1 mutations that lead to haplo-insufficiency of the receptor result in a nonsyndromic phenotype affecting tooth development with high penetrance and variable expressivity.

Lipofuscin- and melanin-related fundus autofluorescence visualize different retinal pigment epithelial alterations in patients with retinitis pigmentosa

AimsTo compare melanin-related near-infrared fundus autofluorescence (FAF; NIA, excitation 787 nm, emission >800 nm) with lipofuscin-related FAF (excitation 488 nm, emission >500 nm) in retinitis pigmentosa (RP).MethodsThirty-three consecutive RP patients with different modes of inheritance were diagnosed clinically, with full-field ERG, and if possible with molecular genetic methods. FAF and NIA imaging were performed with a confocal scanning laser ophthalmoscope (Heidelberg Retina Angiograph 2).ResultsRings of increased FAF were present within an area of preserved retinal pigment epithelium (RPE) at the posterior pole (31/33). Rings of increased NIA were located in the same region as rings of increased FAF. In contrast to FAF, NIA showed a precipitous decline of NIA peripheral to the ring. In larger areas of preserved NIA (11/31), pericentral and foveal NIA were of similar intensity with an area of lower NIA in between. In smaller areas of preserved NIA (20/31), NIA was homogeneous from the perifovea to the fovea. In one patient without a ring of increased FAF, NIA distribution was normal. In the remaining patient with severely advanced RP, no residual RPE as well as no FAF and NIA were detectable.ConclusionCharacteristic features for FAF and NIA alterations in a heterogeneous group of RP patients indicate a common pathway of RPE degeneration. Patterns of NIA and FAF indicate different pathophysiologic processes involving melanin and lipofuscin. Combined NIA and FAF imaging will provide further insight into the pathogenesis of RP and non-invasive monitoring of future therapeutic interventions.

A Subgroup of Age-Related Macular Degeneration is Associated With Mono-Allelic Sequence Variants in the ABCA4 Gene

Purpose. Age-related macular degeneration (AMD) is a heterogeneous condition of high prevalence and complex etiology involving genetic as well as environmental factors. By fundus autofluorescence (FAF) imaging, AMD can be classified into several distinct phenotypes, with one subgroup characterized by fine granular pattern with peripheral punctate spots (GPS[+]). Some features of GPS[+] overlap with Stargardt disease (STGD1), a recessive macular dystrophy caused by biallelic sequence variants in the ATP-binding cassette transporter 4 (ABCA4) gene. The aim of this study was to investigate the role of ABCA4 in GPS[+]. Methods. The ABCA4 gene was sequenced in 25 patients with the GPS[+] phenotype and 29 with geographic atrophy (GA)-AMD but no signs of GPS (GPS[-]). In addition, frequencies of risk-increasing alleles at three known AMD susceptibility loci, including complement factor H (CFH), age-related maculopathy susceptibility 2 (ARMS2), and complement component 3 (C3), were evaluated. Results. We demonstrate that GPS[+] is associated significantly with monoallelic ABCA4 sequence variants. Moreover, frequencies of AMD risk-increasing alleles at CFH, ARMS2, and C3 are similar in GPS[+] and STGD1 patients, with risk allele frequencies in both subcategories comparable to population-based control individuals estimated from 3,510 individuals from the NHLBI Exome Sequencing Project. Conclusions. Our data suggest that the GPS[+] phenotype is accounted for by monoallelic variants in ABCA4 and unlikely by the well-established AMD risk-increasing alleles at CFH, ARMS2, and C3. These findings provide support for a complex role of ABCA4 in the etiology of a minor proportion of patients with AMD.

Lipofuscin- and Melanin-related Fundus Autofluorescence in Patients with ABCA4-associated Retinal Dystrophies

PURPOSE To compare melanin-related near-infrared fundus autofluorescence (NIA; excitation 787 nm, emission > 800 nm) to lipofuscin-related fundus autofluorescence (FAF; excitation 488 nm, emission > 500 nm) in patients with retinal dystrophies associated with ABCA4 gene mutations (ABCA4-RD). DESIGN Observational case series. METHODS Sixteen consecutive patients with ABCA4-RD diagnosed in one institution were included. FAF and NIA imaging were performed with a confocal scanning laser ophthalmoscope (Heidelberg Retina Angiograph 2; Heidelberg Engineering, Heidelberg, Germany). The pattern and size of retinal pigment epithelial (RPE) alterations detected with FAF and NIA were evaluated. RESULTS FAF and NIA alterations were detected in all patients. In 7 of 16 patients, the alterations progressed beyond the vascular arcades, and in 9 of 16, they were confined to the macula. Spots of increased NIA (4/16) were less frequent compared with spots of increased FAF (15/16). Confluent patches of reduced NIA were frequent (12/16), and severely reduced NIA was observed in 3 cases. Areas with reduced NIA corresponded to either increased or reduced FAF. Preservation of subfoveal FAF or NIA corresponded to visual acuity > or = 0.4. Abnormalities detected with NIA were more extensive or more severe compared to FAF in 15 of 16 patients. CONCLUSION Patterns of FAF and NIA indicate different involvement of lipofuscin and melanin and their derivates in the pathophysiologic process of ABCA4-RD. NIA imaging provides a noninvasive in vivo visualization of RPE abnormalities that may precede FAF alterations during the degenerative process. Combined FAF and NIA imaging will provide further insight in the development of ABCA4-RD and could help to monitor future therapeutic interventions.

Phenotypic variability and long-term follow-up of patients with known and novel PRPH2/RDS gene mutations.

PURPOSE To describe the phenotypic variability in 22 patients with PRPH2 gene mutations and to report six novel mutations. DESIGN Retrospective study. METHODS Clinical examinations included color vision testing, perimetry, fundus autofluorescence (FAF), fluorescein angiography, optical coherence tomography (OCT), and full-field and multifocal electroretinography (International Society for Clinical Electrophysiology of Vision standards). Blood samples were taken for deoxyribonucleic acid (DNA) extraction and mutation screening was performed by direct sequencing of polymerase chain reaction amplicons. RESULTS Eleven unrelated patients and four unrelated families each with two affected members as well as one family with three affected members were examined. Diagnoses included central areolar choroidal dystrophy (CACD; n = 9), autosomal dominant retinitis pigmentosa (adRP; n = 7), adult vitelliform macular dystrophy (n = 3), and cone-rod dystrophy (CRD; n = 3). FAF was abnormal in all patients and showed various retinal pigment epithelial alterations, in CACD with a speckled FAF pattern. OCT revealed reduced retinal thickness, mostly in CACD, subretinal lesions, macula edema, or was normal. Follow-up (n = 12; range, 1.3 to 26 years) showed a slow progression of the retinal dystrophies. DNA testing revealed previously reported PRPH2 mutations in two families and eight individuals of whom two carried the same mutation but had different phenotypes. Novel PRPH2 mutations were detected in two families with adRP, in identical twins with CACD, and in each of an individual with CACD, CRD, and adRP. CONCLUSIONS This series describes the broad spectrum of phenotypes associated with PRPH2 mutations. FAF and OCT are helpful tools for diagnosis and evaluation of disease progression. We report novel PRPH2 mutations in patients with CACD, CRD, and adRP.

Progression of Retinal Pigment Epithelial Alterations During Long-term Follow-up in Female Carriers of Choroideremia and Report of a Novel CHM Mutation

OBJECTIVES To report clinical and functional findings in 2 female carriers of choroideremia who were followed up for 11 and 17 years and who showed progression of fundus alterations; and to report a novel CHM mutation. METHODS We performed follow-ups in 2 female carriers of choroideremia, including repeated clinical and electrophysiologic examinations and fundus autofluorescence. Molecular analysis of the CHM gene was done by direct sequencing of the coding exons. RESULTS Follow-up of female carrier 327 took place during 17 years. A second female carrier (subject 869) with a novel gene mutation in CHM was followed up for 11 years. The 2 carriers showed marked pigmentary alterations in the periphery of the retina. At the initial visit, carrier 869 had multiple small, yellowish flecks in the macula. Both carriers developed subnormal 30-Hz flicker responses on full-field electroretinography during follow-up, whereas electrooculography responses were normal. In both carriers, progression of fundus alterations was noted. Fundus autofluorescence images showed multiple small flecks with reduced autofluorescence. CONCLUSIONS Over time, fundus alterations in female carriers of choroideremia are visible, and mild cone dysfunction might develop. Multiple yellowish flecks can exist in the macula. The typical mottled irregularity in fundus autofluorescence is a valuable diagnostic criterion that facilitates specific genetic testing. Clinical Relevance Fundus alterations in female carriers of choroideremia can progress over time and a mild generalized cone dysfunction can develop. Characteristic irregularities are seen in fundus autofluorescence imaging, which is helpful in identifying female carriers of choroideremia.

Identification of an oncostatin M receptor mutation associated with familial primary cutaneous amyloidosis

Amyloid and amyloidosis describe a heterogeneous group of diseases which are characterized by the pathological extracellular deposition of autologous proteins in an antiparallel b-sheet conformation forming nonbranching linear fibrils of indefinite length and an approximate diameter of 10–12 nm. These depositions share a common tinctorial property, i.e. the presence of a characteristic green birefringence in polarized light after staining with Congo red or with thioflavin T. More than 26 different proteins and peptides have been identified that are able to form amyloid and, depending on the histoanatomical distribution and amount, amyloid may cause progressive and life-threatening organ dysfunction. Dependent on the deposition pattern amyloidosis may present as a localized or as a systemic disease and can be acquired or hereditary in nature. Hereditary amyloidoses are caused by germline mutations, which increase the propensity of the respective protein to form cross-b aggregates and deposit as amyloid. The further classification discriminates between primary amyloidosis (in the absence of an obvious predisposing disease) and secondary amyloidosis (if caused by a certain underlying disease). The subclassification of amyloidoses is based on the main protein constituent and therefore on the chemical composition of the amyloid fibrils. While primary cutaneous amyloidosis (PCA) is a relatively common skin disease in South America and Southwest Asia, it is rare in caucasians. The cutaneous amyloid is believed to originate mainly from degenerated keratin of apoptotic epidermal cells (amyloid K-component). The secondary originators of cutaneous amyloid are immunoglobulins and the normal plasma glycoprotein serum amyloid P-component. The histological correlate is a focal deposition of amyloid in the papillary dermis with a fibrillar degeneration of basal keratinocytes. While PCA is not associated with other systemic forms of amyloidosis, an accidental coexistence with multiple endocrine neoplasia type 2a has been reported. Even though the exact aetiology of PCA is still unknown to date, it is believed to be multifactorial in origin, including environmental and frictional epidermal damage, and immunological and other factors. While most cases of PCA are sporadic, familial aggregation has been reported from South America, Taiwan and Southeast Asia. With only three pedigrees published to date, hereditary cases appear extremely rare in caucasians. Familial aggregation and differences in susceptibility among ethnic groups have drawn the attention of amyloidosis researchers to investigate the genetic factors. In 2006 Lee et al. performed a genome-wide scan for familial PCA (FPCA) in Taiwanese families and found evidence for significant linkage to chromosome 5p13.1–q11.2 in a subset of FPCA pedigrees. Subsequently, a candidate gene analysis in the genetically linked region on chromosome 5 revealed two distinct missense mutations in affected individuals of Brazilian pedigrees and pedigrees from the U.K. and South Africa in the OSMR gene, which encodes the oncostatin M (OSM) receptor (OSMR)-b. In this work we analysed a caucasian family with FPCA for mutations in the OSMR gene.

Fundus Autofluorescence and SD-OCT Document Rapid Progression in Autosomal Dominant Vitreoretinochoroidopathy (ADVIRC) Associated with a c.256G > A Mutation in BEST1

ABSTRACT Purpose: To report the variability of clinical findings, rapid concentric progression, and successful treatment of macular edema in autosomal dominant vitreoretinochoroidopathy (ADVIRC) associated with a heterozygous c.256G > A missense mutation in the bestrophin-1 (BEST1) gene. Methods: Three affected members of a four-generation ADVIRC family were examined with fundus autofluorescence (FAF), near-infrared autofluorescence (NIA) and spectral domain optical coherence tomography (SD-OCT). Direct sequence analysis of coding and flanking intronic regions of the BEST1 gene was performed. Results: Disease manifestations presented with high variability with visual problems manifesting between 10 and 40 years of age. Two probands showed marked signs of peripheral degeneration, while this retinal area was not noticeably affected in the third. Cystoid macular edema was present in one proband, which responded to long-term treatment with topic dorzolamide with improved visual acuity. FAF and NIA revealed mid-peripheral retinal degeneration in areas that appeared normal on ophthalmoscopy. The full-field ERG was markedly reduced in two probands. Within a 5-year period a marked increase in concentric progression of degeneration including the posterior pole was documented with FAF, NIA and SD-OCT in one proband after the age of 63 years. Direct sequence analysis of the BEST1 gene revealed a heterozygous c.256G > A missense mutation in the three affected probands. Conclusion: The findings in this family emphasize the previously noted variability of clinical manifestations in BEST1-associated ADVIRC and the relevance of FAF and NIA imaging. Cystoid macular edema and vascular leakage can be successfully treated using dorzolamide.

Evidence-Based Diagnostic Approach to Inherited Retinal Dystrophies 2009

BACKGROUND Hereditary retinal dystrophies comprise a heterogeneous group of inherited retinal disorders with variable clinical presentation and multiple associated genes. Clinical diagnosis and differential diagnosis are difficult. The purpose of the current paper is to provide guidelines for an effective diagnostic approach. METHODS A literature search was carried out and our own data on clinical (n = 3200) and molecular genetic (n = 4050) diagnosis of patients with retinal dystrophies were evaluated. RESULTS For an early diagnosis it is of importance to include inherited retinal dystrophies in the differential diagnosis of unexplained visual disturbances. The most important clinical test is the full-field electroretinogram (ERG), which allows detection or exclusion of generalised retinal dystrophies. If the full-field ERG is normal, a multifocal ERG will distinguish macular dystrophies. Fundus autofluorescence, near-infrared autofluorescence and high resolution optical coherence tomography improve the early diagnosis because morphological alterations can be detected prior to their ophthalmoscopic visibility. In addition, these non-invasive imaging techniques reveal new phenomena which are important for the differential diagnosis and follow-up of retinal dystrophies as well as for an improved understanding of their pathogenesis. Routine molecular genetic diagnosis is available for an increasing number of retinal dystrophies. A succinct clinical diagnosis is a prerequisite to allow selection of the gene(s) to be analysed. If genetic testing is indicated, a human geneticist should be involved for counselling of the patient and possibly further family members and initiation of the necessary steps for DNA testing. CONCLUSION The combination of electrophysiological testing, retinal imaging and molecular genetic analysis allows a differentiated diagnosis of inherited retinal dystrophies and an individual counselling of patients. If inherited retinal dystrophies are suspected, a detailed examination in a retinal centre specialised on inherited retinal dystrophies is recommended.