Karmen M Trzupek

Frequency of Usher syndrome in two pediatric populations: implications for genetic screening of deaf and hard of hearing children.

Purpose: Usher syndrome is a major cause of genetic deafness and blindness. The hearing loss is usually congenital and the retinitis pigmentosa is progressive and first noticed in early childhood to the middle teenage years. Its frequency may be underestimated. Newly developed molecular technologies can detect the underlying gene mutation of this disorder early in life providing estimation of its prevalence in at risk pediatric populations and laying a foundation for its incorporation as an adjunct to newborn hearing screening programs.Methods: A total of 133 children from two deaf and hard of hearing pediatric populations were genotyped first for GJB2/6 and, if negative, then for Usher syndrome. Children were scored as positive if the test revealed ≥1 pathogenic mutations in any Usher gene.Results: Fifteen children carried pathogenic mutations in one of the Usher genes; the number of deaf and hard of hearing children carrying Usher syndrome mutations was 15/133 (11.3%). The population prevalence was estimated to be 1/6000.Conclusion: Usher syndrome is more prevalent than has been reported before the genome project era. Early diagnosis of Usher syndrome has important positive implications for childhood safety, educational planning, genetic counseling, and treatment. The results demonstrate that DNA testing for Usher syndrome is feasible and may be a useful addition to newborn hearing screening programs.

Mutations in RPGR and RP2 Account for 15% of Males with Simplex Retinal Degenerative Disease

PURPOSE To determine the proportion of male patients presenting simplex retinal degenerative disease (RD: retinitis pigmentosa [RP] or cone/cone-rod dystrophy [COD/CORD]) with mutations in the X-linked retinal degeneration genes RPGR and RP2. METHODS Simplex males were defined as patients with no known affected family members. Patients were excluded if they had a family history of parental consanguinity. Blood samples from a total of 214 simplex males with a diagnosis of retinal degeneration were collected for genetic analysis. The patients were screened for mutations in RPGR and RP2 by direct sequencing of PCR-amplified genomic DNA. RESULTS We identified pathogenic mutations in 32 of the 214 patients screened (15%). Of the 29 patients with a diagnosis of COD/CORD, four mutations were identified in the ORF15 mutational hotspot of the RPGR gene. Of the 185 RP patients, three patients had mutations in RP2 and 25 had RPGR mutations (including 12 in the ORF15 region). CONCLUSIONS This study represents mutation screening of RPGR and RP2 in the largest cohort, to date, of simplex males affected with RP or COD/CORD. Our results demonstrate a substantial contribution of RPGR mutations to retinal degenerations, and in particular, to simplex RP. Based on our findings, we suggest that RPGR should be considered as a first tier gene for screening isolated males with retinal degeneration.

The Phenotype of Severe Early Childhood Onset Retinal Dystrophy (SECORD) from Mutation of RPE65 and Differentiation from Leber Congenital Amaurosis

PURPOSE To describe in detail the characteristic clinical phenotype and electrophysiological features of Severe Early Childhood Onset Retinal Dystrophy (SECORD) caused by mutation of RPE65. METHODS Ophthalmological examination, color fundus photography, visual field testing, detailed electrophysiological assessment, and screening of RPE65 were undertaken in five subjects. Selected patients also had spectral domain optical coherence tomography. RESULTS All five patients had life-long, extremely poor night vision. Variable degrees of nystagmus were present; three cases lacked nystagmus at the time of assessment. Bilateral disc drusen were evident in three subjects. While case 1 had an undetectable electroretinogram and features supporting a diagnosis of Leber congential amaurosis (LCA) as an infant, her level of acuity and function into the second decade of life was more consistent with SECORD. In two cases, both vision and electrophysiological responses were seen to improve into the second decade of life. The objective demonstration of improved retinal function over time, with electrophysiological testing, has not been previously reported. Cases 4 and 5 had evidence of fine white retinal dots. The authors propose that these represent abnormal accumulations of retinyl esters, as has been demonstrated in animal models, and has also been observed as lipid droplets within the retinal pigment epithelium (RPE). These white dots were seen to fade with time in the patients and were replaced by RPE changes. CONCLUSIONS The identification of patients with mutations in RPE65 has attained greater significance now that gene replacement trials have begun. The features presented in this article assist in the recognition of this form of LCA/SECORD.

Choroideremia: Analysis of the retina from a Female Symptomatic Carrier

Purpose: To define the retinal pathology in a 91 year-old affected matriarch of a three-generation choroideremia family with multiple manifesting carriers. Methods: Tissue from three different retinal areas was processed for immunohistochemistry. The macular area was processed for transmission electron microscopy. Cryosections were studied by indirect immunofluorescence, using well-characterized antibodies to cone cytoplasm, rhodopsin and cone opsins. The affected donor eyes were compared to a postmortem matched normal eye. Results: The retina displayed areas of severe degeneration, with no photoreceptor outer segments, photoreceptor nuclear atrophy, and atrophy of the inner retina. Other retinal areas were near to normal. The RPE was severely degenerated, with thinning, pigment clumping and sub-epithelial debris deposition in all the areas examined. The choroid displayed depigmentation. Labeling with cone opsin antibodies revealed that cones were drastically affected: blue opsin was almost completely absent, while red/green opsins were distributed along the entire plasma membrane of the cell. Rhodopsin was also distributed along the entire rod plasma membrane. Ultrastructural analysis of the affected macula revealed the absence of RPE apical microvilli and basal infoldings. Instead, RPEs basal surface and choroid displayed the presence of banded fibers composed of clumps of wide-spacing collagen. Bruchs membrane was filled with vesicular structures, some smooth and others with bristle-like projections. Conclusions: The histological data suggests that the clinical manifestation in this donor is related to degenerative changes in the retina, RPE, and choroid.

Treatment of retinal and choroidal degenerations and dystrophies: current status and prospects for gene-based therapy

Inherited retinal and choroidal degenerations account for a significant portion of blindness in children and young adults. This article reviews the current status and future prospects for the treatment of these disorders. Current treatment strategies include nutritional intervention for gyrate atrophy of the choroid and retina with hyperornithinemia, abetalipoproteinemia, and Refsums disease, as well as vitamin A supplementation for retinitis pigmentosa. Future therapeutic prospects include gene therapy for both recessive and dominant disease, secondary gene-based therapies, such as pharmaceutic gene product replacement and treatment with survival factors, anti-apoptotic agents, and calcium blockers, and, finally, stem cell therapy.

Novel Mutations in the KCNV2 Gene in Patients with Cone Dystrophy and a Supernormal Rod Electroretinogram

Purpose: To identify mutations in KCNV2 in patients with a form of cone dystrophy characterized by a supernormal rod electroretinogram (ERG). Methods: The 2 exons and flanking intron DNA of KCNV2 from 8 unrelated patients were PCR amplified and sequenced. Results: We found 1 frameshift, 2 nonsense, 1 non-stop, and 6 missense mutations. Every patient had one or two mutations identified. Of the missense mutations, 4 affected residues were in the amino terminal region of the protein, and two in the pore region. Conclusions: KCNV2 mutations account for most if not all cases of cone dystrophy with a supernormal rod ERG.

Microcephaly with chorioretinopathy in a brother–sister pair: Evidence for germ line mosaicism and further delineation of the ocular phenotype†

Microcephaly with chorioretinopathy (OMIM 156590) is an autosomal dominant syndrome, characterized primarily by chorioretinal lesions and microcephaly. The phenotype is variable, and has been described in association with retinal dysplasia that can be stable or show progressive degeneration, retinal folds, lymphedema, and mental retardation. We describe two siblings with microcephaly, mental retardation, and variable retinal and choroidal abnormalities. Patient 1 has multiple atrophic and dysplastic‐appearing lesions of the retina and choroid in each eye. An ERG at 5 months of age disclosed markedly subnormal scotopic and photopic responses with delayed flicker timing. Patient 2 has bilateral macular folds with vitreoretinopathy, serous retinal detachments, glaucoma, and cataracts OU. Both have mental retardation with hypotonia and severe microcephaly. Chorioretinopathy and retinal folds have been described independently in microcephaly with chorioretinopathy. The present sibs are the first in whom these features are observed while the parents are normal. Our findings support an expansion of the ocular phenotype and suggest the existence of germ line mosaicism.

Combined Retinal Hamartomas Leading to the Diagnosis of Neurofibromatosis Type 2

Purpose: To report two cases of neurofibromatosis type 2 (NF2) initially presenting with isolated bilateral combined hamartomas of the retina and retinal pigment epithelium (RPE). Methods: Retrospective observational case reports. Results: Two unrelated children presented to ophthalmology with isolated combined hamartomas of the retina and RPE. Patient one presented to ophthalmology at the age of 2 years; by 4 years, he developed what was thought to be a plexiform neurofibroma and, with more than 6 café au lait spots, was diagnosed with neurofibromatosis type 1 (NF1). By the age of 5, he had developed bilateral vestibular schwannomas, and was diagnosed with NF2. Subsequent molecular testing revealed a truncating mutation in exon 13 (c.1396C > T; p.R466X) of the NF2 gene. Patient two presented to ophthalmology at the age of 7 months; by age 6 she had developed two subcutaneous masses on her forehead, a mass in her left lower abdomen, and in her gumline. Despite lack of pathological evidence of neurofibroma upon biopsy, molecular testing was initiated at age 6 and revealed a truncating mutation in exon 8 (c.734delA) of the NF2 gene in the blood. Conclusions: Bilateral combined hamartomas of the retina and retinal pigment epithelium (RPE) in a young child should alert the clinician to the possibility of neurofibromatosis type 2. The recognition of this rare finding as a presenting feature of NF2 can lead to earlier diagnosis, which is vital to appropriate surveillance and possible surgical intervention.

Novel mutations in the KCNV2 gene in patients with cone dystrophy and a supernormal rod electroretinogram (Opthalmic Genetics (2007) 28, (135-142))

Thiagalingam S, McGee TL, Weleber RG, Sandberg MA, Trzupek KM, Berson EL, Dryja TP. Novel Mutations in the KCNV2 Gene in Patients with Cone Dystrophy and a Supernormal Rod Electroretinogram. Ophthalmic Genet. 2007;28:135– 142. The authors of this article would like to notify the Ophthalmic Genetics readers of an error in Table 3, the last line of the middle column should read: c.778T/c.866delC (not c.778T/c.867delC). This was also referred to in text, on page 137 left column, second paragraph.