Emad B. Abboud

Autozygome-guided exome sequencing in retinal dystrophy patients reveals pathogenetic mutations and novel candidate disease genes

Retinal dystrophy (RD) is a heterogeneous group of hereditary diseases caused by loss of photoreceptor function and contributes significantly to the etiology of blindness globally but especially in the industrialized world. The extreme locus and allelic heterogeneity of these disorders poses a major diagnostic challenge and often impedes the ability to provide a molecular diagnosis that can inform counseling and gene-specific treatment strategies. In a large cohort of nearly 150 RD families, we used genomic approaches in the form of autozygome-guided mutation analysis and exome sequencing to identify the likely causative genetic lesion in the majority of cases. Additionally, our study revealed six novel candidate disease genes (C21orf2, EMC1, KIAA1549, GPR125, ACBD5, and DTHD1), two of which (ACBD5 and DTHD1) were observed in the context of syndromic forms of RD that are described for the first time.

Mutations in SPATA7 cause Leber congenital amaurosis and juvenile retinitis pigmentosa.

Leber congenital amaurosis (LCA) and juvenile retinitis pigmentosa (RP) are the most common hereditary causes of visual impairment in infants and children. Using homozygosity mapping, we narrowed down the critical region of the LCA3 locus to 3.8 Mb between markers D14S1022 and D14S1005. By direct Sanger sequencing of all genes within this region, we found a homozygous nonsense mutation in the SPATA7 gene in Saudi Arabian family KKESH-060. Three other loss-of-function mutations were subsequently discovered in patients with LCA or juvenile RP from distinct populations. Furthermore, we determined that Spata7 is expressed in the mature mouse retina. Our findings reveal another human visual-disease gene that causes LCA and juvenile RP.

A novel locus for Leber congenital amaurosis on chromosome 14q24

Abstract Leber congenital amaurosis (LCA) is a clinically and genetically heterogeneous autosomal recessive retinal dystrophy and the most common genetic cause of congenital visual impairment. We used a DNA pooling strategy comparing the genotypes of affected to unaffected control pools in a genome-wide search for identity-by-descent on a consanguineous Saudi Arabian LCA family. A shift to homozygosity was observed in the affected DNA pool compared with the control pool at linked markers D14S606 and D14S610. Genotyping of individual DNA samples from the entire pedigree for marker D14S74, closely linked to these loci, and several flanking markers confirmed linkage with a ZMAX=13.29 at θ=0.0. These data assign a third locus (LCA3) for LCA to chromosome 14q24. This locus and the previously identified loci are excluded for other Saudi Arabian pedigrees, both confirming that this clinical disorder is genetically heterogeneous and that additional LCA genes remain to be identified.

Whole-exome sequencing identifies ALMS1, IQCB1, CNGA3, and MYO7A mutations in patients with leber congenital amaurosis†

It has been well documented that mutations in the same retinal disease gene can result in different clinical phenotypes due to difference in the mutant allele and/or genetic background. To evaluate this, a set of consanguineous patient families with Leber congenital amaurosis (LCA) that do not carry mutations in known LCA disease genes was characterized through homozygosity mapping followed by targeted exon/whole‐exome sequencing to identify genetic variations. Among these families, a total of five putative disease‐causing mutations, including four novel alleles, were found for six families. These five mutations are located in four genes, ALMS1, IQCB1, CNGA3, and MYO7A. Therefore, in our LCA collection from Saudi Arabia, three of the 37 unassigned families carry mutations in retinal disease genes ALMS1, CNGA3, and MYO7A, which have not been previously associated with LCA, and 3 of the 37 carry novel mutations in IQCB1, which has been recently associated with LCA. Together with other reports, our results emphasize that the molecular heterogeneity underlying LCA, and likely other retinal diseases, may be highly complex. Thus, to obtain accurate diagnosis and gain a complete picture of the disease, it is essential to sequence a larger set of retinal disease genes and combine the clinical phenotype with molecular diagnosis. 32:1450–1459, 2011. ©2011 Wiley Periodicals, Inc.

High-Power Handheld Blue Laser-Induced Maculopathy: The Results of the King Khaled Eye Specialist Hospital Collaborative Retina Study Group

PURPOSE To report various types of maculopathy caused by momentary exposure to a high-power handheld blue laser. DESIGN Consecutive case series. PARTICIPANTS Fourteen eyes of 14 patients. METHODS Patients with a history of eye exposure to a blue laser device (450 nm and a power range of 150-1200 mW) to a single institution were included. Evaluation included a full ophthalmic examination, fundus photography, macular spectral-domain optical coherence tomography, and fundus fluorescein angiography. MAIN OUTCOME MEASURES Analysis of the types of maculopathy and vitreoretinal pathologic features. RESULTS All patients were young males. The most common setting for injury was accidental at play. The types of maculopathies encountered were: a full-thickness macular hole (FTMH) in 4 eyes, a premacular subhyaloid hemorrhage in 5 eyes, premacular sub-internal limiting membrane hemorrhage in 2 eyes, an outer retinal disruption at the fovea in 1 eye, an epimacular membrane in 1 eye, and a schisis-like cavity in 1 eye. Best-corrected Snellen visual acuity at presentation ranged from 20/40 to 4/200 (mean, 20/290). Only 4 eyes (29%) improved spontaneously with increase in vision, whereas 10 eyes (71%) required intervention. The latter consisted of neodymium:yttrium-aluminum-garnet hyaloidotomy in the 5 eyes with subhyaloid hemorrhage and pars plana vitrectomy (PPV) for the eyes with FTMH and epimacular membrane. All 4 FTMH were closed successfully after PPV. Final mean best-corrected visual acuity in all cases was 20/35 (range, 20/15-20/300). CONCLUSIONS Exposure to high-power handheld laser devices can cause a variety of maculopathies that can reduce central vision permanently. Although vision may improve spontaneously, most cases require intervention. Unrestricted access to commercially available high-power handheld laser devices is dangerous and public awareness should be encouraged.

Expanding the clinical, allelic, and locus heterogeneity of retinal dystrophies

Purpose:Retinal dystrophies (RD) are heterogeneous hereditary disorders of the retina that are usually progressive in nature. The aim of this study was to clinically and molecularly characterize a large cohort of RD patients.Methods:We have developed a next-generation sequencing assay that allows known RD genes to be sequenced simultaneously. We also performed mapping studies and exome sequencing on familial and on syndromic RD patients who tested negative on the panel.Results:Our panel identified the likely causal mutation in >60% of the 292 RD families tested. Mapping studies on all 162 familial RD patients who tested negative on the panel identified two novel disease loci on Chr2:25,550,180-28,794,007 and Chr16:59,225,000-72,511,000. Whole-exome sequencing revealed the likely candidate as AGBL5 and CDH16, respectively. We also performed exome sequencing on negative syndromic RD cases and identified a novel homozygous truncating mutation in GNS in a family with the novel combination of mucopolysaccharidosis and RD. Moreover, we identified a homozygous truncating mutation in DNAJC17 in a family with an apparently novel syndrome of retinitis pigmentosa and hypogammaglobulinemia.Conclusion:Our study expands the clinical and allelic spectrum of known RD genes, and reveals AGBL5, CDH16, and DNAJC17 as novel disease candidates.Genet Med 18 6, 554–562.

Mutation of IGFBP7 Causes Upregulation of BRAF/MEK/ERK Pathway and Familial Retinal Arterial Macroaneurysms

Insulin-like growth factor binding proteins (IGFBPs) play important physiological functions through the modulation of IGF signaling as well as IGF-independent mechanisms. Despite the established role of IGFs in development, a similar role for the seven known IGFBPs has not been established in humans. Here, we show that an autosomal-recessive syndrome that consists of progressive retinal arterial macroaneurysms and supravalvular pulmonic stenosis is caused by mutation of IGFBP7. Consistent with the recently established inhibitory role of IGFBP7 on BRAF signaling, the BRAF/MEK/ERK pathway is upregulated in these patients, which may explain why the cardiac phenotype overlaps with other disorders characterized by germline mutations in this pathway. The retinal phenotype appears to be mediated by a role in vascular endothelium, where IGFBP7 is highly expressed.

Role of Intravitreal Antivascular Endothelial Growth Factor Injections for Choroidal Neovascularization due to Choroidal Osteoma

We treated 26 eyes of 25 young patients having a mean age of 30 years with intravitreal vascular endothelial growth factor (VEGF) inhibitor for choroidal new vessel (CNV) formation overlying choroidal osteoma over a mean follow-up of 26 months. Mean number of injections was 2.4 at 6 months, 3.2 at 12 months, and 5.5 at 24 months. CNV was subfoveal in 14 eyes, juxtafoveal in 5, extrafoveal in 5, and peripapillary in 2. By paired comparison, mean decrease from baseline was 119.7 microns at 6 months (n = 15; P = 0.001), 105.3 microns at 1 year (n = 10; P = 0.03), and 157.6 microns at 2 years (n = 7; P = 0.08). BCVA improved by 3.3 lines at 6 months after therapy (n = 26; P < 0.001), 2.8 lines (n = 20; P = 0.01) at 1 year, and 3.1 lines (n = 13; P = 0.049) at 2 years. We conclude that intravitreal anti-VEGF injections improve vision in majority of eyes with CNV from choroidal osteoma.

Vitreous levels of placental growth factor correlate with activity of proliferative diabetic retinopathy and are not influenced by bevacizumab treatment.

PurposePlacental growth factor (PlGF) is a member of the VEGF family that plays an important role in experimental models of diabetic retinopathy and retinal neovascularization. We aimed to investigate whether vitreous levels of PlGF correlated with proliferative diabetic retinopathy (PDR) status, VEGF levels, and bevacizumab treatment. We also analysed PDR membranes to confirm the presence of the PlGF receptor, FLT1, in endothelial cells.MethodsThis was a case-control study: undiluted vitreous fluid samples were obtained from 28 active PDR patients without preoperative bevacizumab treatment, 21 active PDR patients with preoperative bevacizumab treatment, 18 inactive PDR patients, and 21 control patients. PlGF and VEGF levels in samples were determined by enzyme-linked immunosorbent assay. Immunohistochemistry for FLT1 was performed on human PDR membranes.ResultsCompared to control, vitreous PlGF levels were higher in both active PDR without bevacizumab (P<0.0001) and with bevacizumab (P<0.0001). There was no significant difference in PlGF between active PDR patients without and with bevacizumab (P=0.56). Compared to active PDR, PlGF levels were significantly reduced in inactive PDR (P=0.004). PlGF levels were highly correlated with VEGF levels in active PDR. VEGFR1 was expressed in endothelial cells in human PDR membranes.ConclusionThe strong correlation of PlGF levels with PDR disease status and expression of FLT1 in human PDR membranes suggest that PlGF has a pathogenic role in proliferative diabetic retinopathy. Therapeutic targeting of PlGF with agents like aflibercept may be beneficial.

OUTCOMES OF PARS PLANA VITRECTOMY IN THE MANAGEMENT OF REFRACTORY AQUEOUS MISDIRECTION SYNDROME.

Purpose: To determine the efficacy and complications of pars plana vitrectomy (PPV) and adjunct surgeries for aqueous misdirection refractory to medical therapy. Methods: A retrospective review of consecutive eyes with refractory aqueous misdirection at the King Khaled Eye Specialist Hospital between 2002 and 2010. Patients underwent two-port and three-port pars plana vitrectomy (PPV) with adjunct procedures including pars plana lensectomy combined with posterior capsulectomy, hyaloido-zonulo-iridectomy, and synechiolysis. Main outcome measures included anatomical success, functional success, and factors associated with the outcomes. Results: Sixty-nine eyes were evaluated over a mean follow-up period of 17.6 ± 3.8 months (3–156 months). Anatomical success was achieved in 62 eyes (90%) and functional success in 54 eyes (78%) that underwent PPV as a primary surgery. The factors associated with the altering misdirected aqueous flow and reducing intraocular pressure significantly associated with a two-line improvement of best-corrected visual acuity included surgical treatment within 4 weeks of presentation (P = 0.004) and preoperative intraocular pressure (P = 0.001). The success of two-port PPV and standard three-port PPV was similar (P = 0.7). The intraoperative and postoperative complications included retinal detachment in two eyes and endophthalmitis in one eye. Conclusion: The PPV was effective for managing aqueous misdirection refractory to medical therapy. Two-port or three-port PPV did not change the success rate but early surgery improved both anatomical and functional outcomes.