Ocular genetic disease in the Middle East

Usher syndrome in the United Arab Emirates

PURPOSE

Usher syndrome, a common form of syndromic inherited retinal dystrophy in the Arabian Gulf, has not been molecularly defined in the United Arab Emirates. The current study addresses this gap in knowledge.

METHODS

A retrospective case series of Emirati patients referred to the Ocular Genetics Clinic of Cleveland Clinic Abu Dhabi who (1) were clinically diagnosed with Usher syndrome and underwent genetic testing (whole exome sequencing, 2019 to 2023, inclusive) and (2) were identified to have biallelic pathogenic variants in Usher syndrome genes during the same time period.

RESULTS

Ten probands (thirteen patients) were identified-seven probands (nine patients) with clinically diagnosed Usher syndrome and three additional probands (four patients) with biallelic homozygous USH2A variants. Among the seven probands initially diagnosed with Usher syndrome, six had different homozygous variants (three in MYO7A, one in ADGRV1, and one in CLRN1), one had dual diagnoses rather than Usher syndrome (i.e. separate cause for retinal dystrophy and deafness), and one had no identifiable genetic cause. Regarding the three additional probands identified with homozygous USH2A variants, all three had retinitis pigmentosa only rather than Usher syndrome and all three had different variants.

DISCUSSION

Clinically diagnosed Usher syndrome was genetically heterogenous without evidence for founder effect in this Emirati cohort. MYO7A was the most common associated gene. Dual diagnosis rather than single cause can mimic Usher syndrome. Homozygous USH2A variants were not identified as a cause for Usher syndrome in this cohort but were a recurrent cause for retinitis pigmentosa without hearing impairment and without founder effect.

Comparison of Glaucoma Therapy Escalation After Penetrating Keratoplasty to Descemet Stripping Automated Endothelial Keratoplasty for the Treatment of Pseudophakic Bullous Keratopathy: A Cohort Study

PURPOSE

The purpose of this study was to compare glaucoma therapy escalation (GTE), graft survival, vision, and glaucoma following penetrating keratoplasty (PK group) and Descemet stripping automated endothelial keratoplasty (DSAEK group) to treat pseudophakic bullous keratopathy (PBK).

METHODS

This cohort included cases of PBK managed with PK from 2009 to 2014. We compared the incidences and determinants of GTE, graft survival, and visual disability. P < 0.05 was statistically significant.

RESULTS

There were 58 eyes in the PK group and 117 eyes in the DSAEK group. The incidence of GTE in the PK and DSAEK groups at the last follow-up was 34.2% (95% confidence interval [CI]: 19.5-48.9) and 46.6% (95% CI: 27.7-65.4), respectively. The risk of GTE was similar between the groups (relative risk [RR] = 1.36 [95% CI: 0.94-1.98], P = 0.12). GTE was significantly associated with graft survival in the PK group (RR = 3.25 [95% CI: 1.5-7.0], P < 0.001) and the DSAEK group (RR = 3.77 [95% CI: 2.6-5.6], P < 0.001). Glaucoma (P = 0.001) and previous keratoplasty (P < 0.001) were significant predictors for GTE. At the final follow-up visit, severe visual disability was not significantly different between the groups (RR = 0.9 [95% CI: 0.3-2.9], P = 0.88). There was a statistically significant improvement in vision after DSAEK (P < 0.001) but not after PK (P = 0.67).

CONCLUSION

GTE was similar in eyes with PBK managed by PK or DSAEK. Glaucoma and previous keratoplasty were predictors of GTE post-keratoplasty. DSAEK gave better visual outcomes than PK for managing PBK.

PHENOTYPE-GUIDED GENETIC TESTING OF PEDIATRIC INHERITED RETINAL DISEASE IN THE UNITED ARAB EMIRATES

PURPOSE

Inherited retinal disease is relatively common in the Arabian Gulf, but details regarding pediatric inherited retinal disease in the region are lacking. The purpose of this study is to report the experience of a regional Ocular Genetics Service with childhood-onset inherited retinal disease in the United Arab Emirates.

METHODS

Retrospective series of consecutive Emirati patients referred to the Ocular Genetics Service of Cleveland Clinic Abu Dhabi over a 3-year period (2016-2018) who were diagnosed with childhood-onset inherited retinal disease (onset before 16 years old) and underwent diagnostic genetic testing guided by clinical phenotype (single gene, next-generation panel, or exome sequencing).

RESULTS

Seventy-one probands were identified (38 male and 33 females), the majority of whom were symptomatic with visual problems within the first 5 years of life. All patients had disease causing mutations in 1 of 26 retinal disease genes. Recessive disease was frequently due to homozygous mutations. The most frequently mutated genes (and number of probands) were ABCA4 (14), KCNV2 (8), CRB1 (6), and CNGA3 (5). Recurrent specific gene mutations included ABCA4 p.Gly1961Glu/p.Leu857Pro, KCNV2 p.Glu143*, MERTK p.Cys738Trpfs*32, and RS1 c.52+3A>G. Some probands had mutations in syndromic genes and were confirmed to have extraocular findings.

CONCLUSION

Phenotype-guided genetic testing had a remarkable yield for this patient population. Recessive disease is often from homozygous mutations. Cone-dominated phenotypes are common. There are apparent founder mutations for several genes that could be used in a targeted genetic testing strategy. Molecular diagnosis is particularly important in affected children when inherited retinal dystrophy could be a sign of syndromic disease as proper earlier diagnosis minimizes potential extraocular morbidity.

Genetic testing results of children suspected to have Stickler syndrome type collagenopathy after ocular examination

Purpose

Stickler syndrome is a collagenopathy that is typically COL2A1‐related (autosomal dominant) and less commonly related to other collagen gene mutations. Diagnosis is straightforward when a child has myopia or retinal detachment in the setting of classic diagnostic criteria such as hearing impairment, midfacial hypoplasia, and arthropathy. However, some children have primarily ocular disease with mild or no extraocular features. Such children can remain undiagnosed unless suspicion is raised by the ophthalmologist.

Methods

Retrospective consecutive case series (2014–2016) of children (<12 years old) suspected to have Stickler syndrome type collagenopathy by a single ophthalmologist and able to complete genetic testing for this possibility. Suspicion was based on vitreous abnormalities and myopia or lens opacities in the setting of prior retinal detachment, hearing impairment, or facial flatness.

Results

Average age of the 12 identified children was 8 years old (range 3–11; five boys). Average spherical equivalent for phakic eyes was −13 (range −3.5 to −30). Nine children had lens opacities or aphakia; two with aphakia also had lens subluxation or iridodonesis. Other recurrent clinical features included flat facies (12/12), hearing impairment (5/12), and prior retinal detachment (4/12). Pathogenic variants for collagenopathy were uncovered in 10/12 children: COL11A1 (heterozygous) in six, COL2A1 (heterozygous) in two, and COL9A1 (homozygous) in two. One child was homozygous for pathogenic variation in LRPAP1. One child had no detectable gene mutations.

Conclusions

Taken together, these clinical features (particularly vitreous abnormality, myopia, and lens opacity) had a high molecular yield for collagen gene mutation. Ophthalmologists who see such children should suspect Stickler syndrome, even in the absence of overt systemic disease. COL11A1‐related rather than COL2A1‐related autosomal dominant disease may be more common when undiagnosed children are identified based on ocular examination. Biallelic mutations in LRPAP1 can result in a phenotype that may resemble Stickler syndrome.

Clinical and histological features and outcomes of upper eyelid colobomas in the Saudi population

PURPOSE

To study the clinical features, histopathology, and management of congenital upper eyelid coloboma (CEC) in the Saudi population.

METHODS

A retrospective review of health records evaluated the demographics, histopathology, and surgical outcomes of patients with CEC.

RESULTS

Thirty-nine eyelids of 27 patients were included in this study. CEC was bilateral in 12 (44.4%) patients, isolated in 17 (62.9%), and as part of a syndrome in 10 (37.1%) patients. CEC was commonly located in the medial upper lid (22 lids, 56.4%) and mostly involved the full thickness of the lid (27 lids, 69.2%). Corneal adhesion (18 eyes, 46.1%) and poorly formed eyebrows (21 eyebrows, 53.8%) were the most common ocular/adnexa associations. Histopathology was similar in all cases and the main features were scarred dermis, atrophic orbicularis oculi, and atrophic or absent tarsus. Visual acuity at the final follow-up was 20/50 or better in 13 (33.3%) eyes. Complete lid closure without lagophthalmos after one or more surgical procedures was achieved in 11 (40.7%) cases.

CONCLUSIONS

CEC features in Saudi patients are similar to those described in the literature. Dermal scarring and defective orbicularis muscles are common. Achieving cosmetic and functional success after management remains challenging.

Electronegative Electroretinograms in the United Arab Emirates

PURPOSE

An electronegative electroretinogram (ERG), defined as having a b:a wave ratio ≤1 in the scotopic flash ERG response, indicates relative inner retinal dysfunction. Causes vary depending upon the study population. In the Arabian Gulf, where inherited retinal disease is relatively prevalent, common diagnoses associated with electronegative ERGs have not been described. In this study, we report the frequency and causes of electronegative ERGs in a cohort of Emirati patients with inherited retinal disease.

METHODS

A retrospective review was performed of all full-field ERGs done for Emirati patients in the Ocular Genetics Service of Cleveland Clinic Abu Dhabi from January 2017 to December 2019. Those who had an electronegative ERG in at least one eye were included in the study.

RESULTS

Out of 137 patients, 9 probands (6.6%) had an electronegative ERG. The mean age at presentation was 24 years (range 5-48 years), and five patients (55.6%) were male. The final clinical diagnoses were congenital stationary night blindness (CSNB) (two TRPM1-related and one Oguchi disease), X-linked retinoschisis (XLRS) (one genetically confirmed and two not genetically tested), cone-rod dystrophy (one CRX-related and one not genetically tested), and enhanced S-cone syndrome (ESCS) (one NRL-related). The one patient who did not have bilateral electronegative ERGs was a male with XLRS whose fellow eye had an unrecordable ERG.

CONCLUSIONS

In this series of Emirati patients, an electronegative ERG was most commonly associated with the inherited retinal diseases recessive CSNB and XLRS. An electronegative ERG was noted in a case of NRL-related ESCS.

Indications for Pediatric Ocular Prosthesis Fitting at a Referral Center in the Middle East

Trauma is the major reason for globe loss in adults; however, there are less data regarding the causes for globe loss in children. We reviewed the underlying diagnoses of children who underwent ocular prosthesis fitting over a 1-year period at a referral eye hospital in the Middle East and found retinoblastoma, trauma, and congenital microphthalmia or anophthalmia to be the most common diagnoses, respectively. Enucleation and evisceration were the most common procedures and were exclusively performed for retinoblastoma and trauma, respectively. Ocular morbidity from the most common diagnoses related to pediatric globe loss in the region could be decreased by improved family education, safety precautions, and genetic counseling.

Clinical features of LONP1-related infantile cataract

Biallelic mutations in the nuclear gene LONP1 (LON peptidase 1, mitochondrial) cause CODAS syndrome (cerebral, ocular, dental, auricular, and skeletal anomalies), a systemic disease that can include infantile cataract. However, we have found that biallelic mutations in the gene can also underlie infantile cataract in the setting of minimal or no apparent extraocular findings. This report highlights our clinical experience with children referred for the management of infantile cataract who were found to harbor biallelic LONP1 gene mutations. Ptosis, external ear abnormalities, and joint abnormalities were accompanying findings and thus should raise suspicion for mutations in the gene when one or more are present in children with infantile cataract.

Genome-wide linkage and sequence analysis challenge CCDC66 as a human retinal dystrophy candidate gene and support a distinct NMNAT1-related fundus phenotype

To uncover the genotype underlying early-onset cone-rod dystrophy and central nummular macular atrophic lesion in 2 siblings from an endogamous Arab family, we performed targeted next-generation sequencing (NGS) of 44 retinal dystrophy genes, whole-exome sequencing (WES) and genome-wide linkage analysis. Targeted NGS and WES in the index patient highlighted 2 homozygous variants, a CCDC66 frameshift deletion and a novel missense NMNAT1 variant, c.500G>A (p.Asn167Ser). Linkage and segregation analysis excluded the CCDC66 variant and confirmed the NMNAT1 mutation. Biallelic NMNAT1 mutations cause Leber congenital amaurosis with a central nummular macular atrophic lesion (LCA9). The NMNAT1 mutation reported here underlied cone-rod dystrophy rather than LCA but the fundus lesion was compatible with that of LCA9 patients, highlighting that such a fundus appearance should raise suspicion for biallelic mutations in NMNAT1 when in the context of any retinal dystrophy. Although Ccdc66 mutations have been proposed to cause retinal disease in dogs, our results and public databases challenge CCDC66 as a candidate gene for human retinal dystrophy.

Reconciling genotype with phenotype: Lessons learned on the Arabian Peninsula

On the Arabian Peninsula, where consanguineous/endogamous marriages are customary, hereditary eye disease is often autosomal recessive and genotype-phenotype correlation is typically straightforward. However, this is not always the case. Lessons I have learned in the course of reconciling genotype with phenotype in the region include the following: (1) although autosomal recessive disease is common, autosomal dominant disease still occurs; (2) an individual or family can be affected by more than one genetic eye disease; and (3) phenotype trumps genotype.

Novel phenotypes and loci identified through clinical genomics approaches to pediatric cataract

Pediatric cataract is highly heterogeneous clinically and etiologically. While mostly isolated, cataract can be part of many multisystem disorders, further complicating the diagnostic process. In this study, we applied genomic tools in the form of a multi-gene panel as well as whole-exome sequencing on unselected cohort of pediatric cataract (166 patients from 74 families). Mutations in previously reported cataract genes were identified in 58% for a total of 43 mutations, including 15 that are novel. GEMIN4 was independently mutated in families with a syndrome of cataract, global developmental delay with or without renal involvement. We also highlight a recognizable syndrome that resembles galactosemia (a fulminant infantile liver disease with cataract) caused by biallelic mutations in CYP51A1. A founder mutation in RIC1 (KIAA1432) was identified in patients with cataract, brain atrophy, microcephaly with or without cleft lip and palate. For non-syndromic pediatric cataract, we map a novel locus in a multiplex consanguineous family on 4p15.32 where exome sequencing revealed a homozygous truncating mutation in TAPT1. We report two further candidates that are biallelically inactivated each in a single cataract family: TAF1A (cataract with global developmental delay) and WDR87 (non-syndromic cataract). In addition to positional mapping data, we use iSyTE developmental lens expression and gene-network analysis to corroborate the proposed link between the novel candidate genes and cataract. Our study expands the phenotypic, allelic and locus heterogeneity of pediatric cataract. The high diagnostic yield of clinical genomics supports the adoption of this approach in this patient group.

Genetic analysis of strictly defined Leber congenital amaurosis with (and without) neurodevelopmental delay

BACKGROUND

Leber congenital amaurosis (LCA) is a severe infantile retinal dystrophy that is non-syndromic other than neurodevelopmental delay, reported in up to 20% of cases according to one older study. The phenotype is typically autosomal recessive and is genetically heterogeneous. Although LCA is defined by a non-recordable electroretinogram (ERG) during infancy, many LCA studies include infants with low ERG readings and/or older children not phenotyped during infancy. More recent series of genetically confirmed LCA do not document the recurrent neurodevelopmental delay of older studies. We investigate the possibility that neurodevelopmental delay is not actually a recurrent feature of strictly defined otherwise non-syndromic LCA.

METHODS

Retrospective consecutive case series (2012-2014) of children with strictly defined LCA, all of whom underwent targeted next-generation sequencing with a panel of 14 LCA genes.

RESULTS

All families were endogamous and/or consanguineous. 18/19 (22/23 children) had detectable causative recessive mutations, and these were in one of three genes only: 11 in RPGRIP1, 5 in GUCY2D and 2 in RPE65. 9/11 children with RPGRIP1 mutations harboured homozygous c.1007delA (p.Glu370Asnfs*5) mutation. 5/23 children (22%) had concomitant neurodevelopmental delay, and these five children harboured recessive mutations in RPGRIP1 (2) or GUCY2D (3). Haplotype analysis for cases with the RPGRIP1 deletion suggested a single ancestral mutation.

CONCLUSIONS

Neurodevelopmental delay is a potential feature of strictly defined LCA, documented in our series for some children with homozygous RPGRIP1 and GUCY2D mutations. Strictly defining LCA can limit genetic heterogeneity. On the Arabian Peninsula, the phenotype is frequently from recessive RPGRIP1 mutations, most of which are a founder RPGRIP1 deletion.

Results of fibrillin-1 gene analysis in children from inbred families with lens subluxation

BACKGROUND

Autosomal dominant mutation of the FBN1 gene (fibrillin-1) results in a spectrum of disease (type 1 fibrillopathies) ranging from Marfan syndrome with lens subluxation and cardiovascular complications to milder connective tissues phenotypes. The likelihood of FBN1 mutation in children referred to ophthalmologists because of lens subluxation is unclear. We report the results of routine FBN1 sequencing for children from inbred families referred with nontraumatic lens subluxation without cataract or vitreoretinal degeneration.

METHODS

Medical records of such patients from 2009 to 2012 were retrospectively reviewed.

RESULTS

Eight identified probands (3-11 years old; 4 boys) from consanguineous and/or endogamous Saudi Arabian families all harbored FBN1 mutation--7 autosomal dominant and 1 autosomal recessive (homozygous). Four mutations were novel. One child had a family history for lens subluxation. Seven had facial and/or skeletal features suggestive of type 1 fibrillinopathy. The parents of the autosomal recessive case were confirmed to be heterozygous carriers without lens subluxation or other clinical signs of type 1 fibrillinopathy.

CONCLUSIONS

Autosomal dominant type 1 fibrillinopathy was the major cause for lens subluxation in this cohort despite the fact that families were inbred and thus at higher risk for recessive disease. This highlights the frequency of new mutations in the gene and has important implications for genetic counseling and systemic assessment. The autosomal recessive case represents the fourth such case reported to date. Her heterozygous parents were unaffected carriers, suggesting that some FBN1 mutations can act as hypomorphic alleles rather than exhibiting the dominant negative effect typically attributed to FBN1 mutations.