New Recognized Ophthalmic Morphologic Anomalies in CHARGE Syndrome Caused by the R2319C Mutation in theCHD7Gene

Cellular and Molecular Mechanisms of Pathogenesis Underlying Inherited Retinal Dystrophies

Inherited retinal dystrophies (IRDs) are congenital retinal degenerative diseases that have various inheritance patterns, including dominant, recessive, X-linked, and mitochondrial. These diseases are most often the result of defects in rod and/or cone photoreceptor and retinal pigment epithelium function, development, or both. The genes associated with these diseases, when mutated, produce altered protein products that have downstream effects in pathways critical to vision, including phototransduction, the visual cycle, photoreceptor development, cellular respiration, and retinal homeostasis. The aim of this manuscript is to provide a comprehensive review of the underlying molecular mechanisms of pathogenesis of IRDs by delving into many of the genes associated with IRD development, their protein products, and the pathways interrupted by genetic mutation.

A Case of Polypoidal Choroidal Vasculopathy Associated With Optic Disc Drusen

We report a case of optic disc drusen (ODD) associated with peripapillary polypoidal choroidal vasculopathy (PCV). A 62-year-old Malay lady presented with both eye ODD and the left eye associated with peripapillary subretinal hemorrhage. Ultrasound B-scan and red-free photography confirmed the optic nerve head drusen findings bilaterally. Optical coherence tomography (OCT) of the left eye showed sharply elevated peripapillary pigment epithelial detachment with subretinal fluid. The presence of peripapillary polyps with branching vascular network in indocyanine green angiography of the left eye further confirmed the diagnosis of PCV and excluded choroidal neovascularization (CNV) secondary to ODD. Subsequently, the patient was treated with a combination of verteporfin photodynamic therapy with three monthly intravitreal ranibizumab injections. Three months after the combined treatment, OCT showed completely resolved subretinal fluid. ODD can cause compression of the subretinal vessels at the optic disc that results in retinal ischemia and release of vascular endothelial growth factor, which may trigger the development of CNV or PCV. The rarity of this combination makes it interesting to study more cases of ODD with PCV. Importantly, a thorough evaluation in distinguishing the PCV from the CNV that mimics it is crucial for early detection and prompt intervention. In this case, indocyanine green angiography (ICGA) is the diagnostic method to differentiate the PCV from CNV secondary to ODD.

Polypoidal Choroidal Vasculopathy Associated with Optic Disc Coloboma

Purpose

To report a case of polypoidal choroidal vasculopathy associated with optic disc coloboma.

Methods

Case report.

Results

A 50-year-old woman presented with optic disc coloboma and retinochoroidal coloboma associated with subretinal hemorrhage and serous retinal detachment (SRD) in her left eye. Optical coherence tomography (OCT) confirmed SRD at the macula and showed a sharply elevated retinal epithelial detachment at the choroidal excavation. OCT also revealed choroidal cavitation along the temporal side of the optic coloboma. Fluorescein angiography showed hyperfluorescent dye leakage and indocyanine green angiography revealed polypoidal lesions. We diagnosed polypoidal choroidal vasculopathy (PCV). PCV was located at the end of the choroidal cavitation. Her left eye was treated with an intraocular injection of the anti-vascular endothelial growth factor aflibercept (2 mg). Photodynamic therapy was performed using the standard protocol 1 week after the intravitreal application of aflibercept. One month after the combined treatment, OCT showed completely resolved SRD and her symptoms disappeared. Her best-corrected visual acuity remained stable and no recurrence was found during a 12-month follow-up period.

Conclusion

PCV associated with optic disc coloboma has not been previously reported. The morphological abnormality of choroidal cavitation and choroidal excavation connecting with optic disc coloboma may contribute to the development of PCV in this case.

A novel classification system to predict the pathogenic effects of CHD7 missense variants in CHARGE syndrome

CHARGE syndrome is characterized by the variable occurrence of multisensory impairment, congenital anomalies, and developmental delay, and is caused by heterozygous mutations in the CHD7 gene. Correct interpretation of CHD7 variants is essential for genetic counseling. This is particularly difficult for missense variants because most variants in the CHD7 gene are private and a functional assay is not yet available. We have therefore developed a novel classification system to predict the pathogenic effects of CHD7 missense variants that can be used in a diagnostic setting. Our classification system combines the results from two computational algorithms (PolyPhen-2 and Align-GVGD) and the prediction of a newly developed structural model of the chromo- and helicase domains of CHD7 with segregation and phenotypic data. The combination of different variables will lead to a more confident prediction of pathogenicity than was previously possible. We have used our system to classify 145 CHD7 missense variants. Our data show that pathogenic missense mutations are mainly present in the middle of the CHD7 gene, whereas benign variants are mainly clustered in the 5' and 3' regions. Finally, we show that CHD7 missense mutations are, in general, associated with a milder phenotype than truncating mutations.

Ophthalmic features of CHARGE syndrome with CHD7 mutations

Coloboma and various ocular abnormalities have been described in CHARGE syndrome, although the severity of visual impairment varies from case to case. We conducted a multicenter study to clarify the ophthalmic features of patients with molecularly confirmed CHARGE syndrome. Thirty-eight eyes in 19 patients with CHARGE syndrome and confirmed CHD7 mutations treated at four centers were retrospectively studied. Colobomata affected the posterior segment of 35 eyes in 18 patients. Both retinochoroidal and optic disk colobomata were bilaterally observed in 15 patients and unilaterally observed in 3 patients. The coloboma involved the macula totally or partially in 21 eyes of 13 patients. We confirmed that bilateral large retinochoroidal colobomata represents a typical ophthalmic feature of CHARGE syndrome in patients with confirmed CHD7 mutations; however, even eyes with large colobomata can form maculas. The anatomical severity of the eye defect was graded according to the presence of colobomata, macula defect, and microphthalmos. A comparison of the severity in one eye with that in the other eye revealed a low-to-moderate degree of agreement between the two eyes, reflecting the general facial asymmetry of patients with CHARGE syndrome. The location of protein truncation and the anatomical severity of the eyes were significantly correlated. We suggested that the early diagnosis of retinal morphology and function may be beneficial to patients, since such attention may determine whether treatment for amblyopia, such as optical correction and patching, will be effective in facilitating the visual potential or whether care for poor vision will be needed.

Mutations in the CHD7 gene: the experience of a commercial laboratory

CHARGE syndrome is an autosomal dominant multisystem disorder caused by mutation in the CHD7 gene, encoding chromodomain helicase DNA-binding protein 7. Molecular diagnostic testing for CHD7 mutation has been available in a clinical setting since 2005. We report here the results from the first 642 unrelated proband samples submitted for testing. Thirty-two percent (n = 203) of patient samples had a heterozygous pathogenic variant identified. The lower mutation rate than that published for well-characterized clinical samples is likely due to referral bias, as samples submitted for clinical testing may be for "rule-out" diagnoses, rather than solely to confirm clinical suspicion. We identified 159 unique pathogenic mutations, and of these, 134 mutations were each seen in a single individual and 25 mutations were found in two to five individuals (n =69). Of the 203 mutations, only 9 were missense, with 107 nonsense, 69 frameshift, and 15 splice-site mutations likely leading to haploinsufficiency at the cellular level. An additional 72 variations identified in the 642 tested samples (11%) were considered to have unknown clinical significance. Copy number changes (deletion/duplication of the entire gene or one/several exons) were found to account for a very small number of cases (n = 3). This cohort represents the largest CHARGE syndrome sample size to date and is intended to serve as a resource for clinicians, genetic counselors, researchers, and other diagnostic laboratories.