A G1103R Mutation in CRB1 is Co-Inherited with High Hyperopia and Leber Congenital Amaurosis

Purpose: To identify the genetic basis of recessive inheritance of high hyperopia and Leber congenital amaurosis (LCA) in a family of Middle Eastern origin. Materials and methods: The patients were examined using standard ophthalmic techniques. DNA samples were obtained and genetic linkage was carried out using polymorphic markers flanking the known genes and loci for LCA. Exons were amplified and sequenced. Results: All four members of this family affected by LCA showed high to extreme hyperopia, with average spherical refractive errors ranging from +5.00 to +10.00. Linkage was obtained to 1q31.3 with a maximal LOD score of 5.20 and a mutation found in exon 9 of the CRB1 gene, causing a G1103R substitution at a highly conserved site in the protein. CRB1 is a vertebrate homolog of the Drosophila crumbs gene, which is required for photoreceptor morphogenesis, and has been associated with either retinitis pigmentosa (RP) or LCA. This sequence variant has previously been reported as a compound heterozygote in one sporadic LCA patient. Conclusion: Although hyperopia has been associated with LCA, it is typically moderate and variable between patients with the same mutation. In addition, some CRB1 mutations can be associated with either RP or LCA. We have shown that hyperopia and LCA are linked to the mutant CRB1 gene itself and are not dependent on unlinked modifiers.     

A novel mutation disrupting the cytoplasmic domain of CRB1 in a large consanguineous family of Palestinian origin affected with Leber congenital amaurosis

Leber congenital amaurosis (LCA) is a genetically heterogeneous autosomal recessive condition responsible for congenital blindness or greatly impaired vision since birth. Eight LCA loci have been mapped, but only six out of eight genes have been hitherto identified. A genome-wide screen for homozygosity was conducted in a large consanguineous family originating from Palestine, for which no mutation was found in any of the six known LCA genes and that excluded the LCA3 and LCA5 loci. Evidence for homozygosity, however, was found in all affected patients of the family on chromosome 1q31, a region in which the human homologue of the Drosophila melanogaster crumbs gene (CRB1) has been mapped. Consequently, we proposed a hypothesis that the disease-causing mutation in this family might lie in an unexplored region of this LCA gene. As a matter of fact, while no mutation was found in any of the 11 CRB1 exons originally reported, we identified a 10-bp (del 4121-4130) deletion segregating with the disease in a later reported 12th exon lying in the 3' end of the gene. Interestingly, this deletion disrupts an amino acid sequence that was shown to be crucial for the function of the protein in the Drosophila counterpart (CRB).     

A CRX null mutation is associated with both Leber congenital amaurosis and a normal ocular phenotype

PURPOSE: To identify and characterize new cone rod homeobox (CRX) mutations associated with the Leber congenital amaurosis phenotype. METHODS: The human CRX gene was sequenced in 74 consecutive patients carrying the diagnosis of Leber congenital amaurosis. RESULTS: Two mutations were identified in CRX that cause frameshifts and predict severe truncations of the encoded protein. One of these, a 1-bp insertion, spares only nine N-terminal amino acids, removing the homeodomain, WSP motif, and conserved OTX domain at the C terminus. Of the CRX mutations described in the literature, this is the first that convincingly represents a null allele of the gene. Although the patient heterozygous for this null allele is affected with Leber congenital amaurosis, it was surprising that her father, who had normal vision, was heterozygous for the same mutation. CONCLUSIONS: These results strongly suggest that haploinsufficiency of CRX is not sufficient to cause a retinal disorder. Loss of function alleles of CRX appear to cause Leber congenital amaurosis through a recessive or multigenic mechanism.     

RPGRIP1 is mutated in Leber congenital amaurosis: a mini-review

RPGRIP1 encodes the retinitis pigmentosa GTPase interacting protein 1 and interacts with RPGR, the latter represents the major X-linked RP (XRRP) gene, as it accounts for 70-80% of the XRRP patients and up to 13% of all RP patients. RPGRIP1 contains a C-terminal RPGR interacting domain (RID) and a coiled-coil (CC) domain, which is homologous to proteins involved in vesicular trafficking. The interactions between the two proteins is between the RCC1-homologous domain of RPGR (RHD) and the RPGR-interacting domain of RPGRIP1 (RID). Both proteins co-localize to the photoreceptor connecting cilium and RPGRIP1 appears to be a structural component of the ciliary axoneme of the connecting cilium (which connects the inner to the outer segment of the photoreceptors) of both rods and cones and functions to anchor RPGR within the cilium.RPGRIP1 loci encode several different isoforms, which have distinct cellular, sub cellular and biochemical properties. RPGRIP1 is uniquely expressed in amacrine cells of the inner retina. Knockout mice studies have shown that RPGRIP1 is required for disc morphogenesis of the outer segments in the mouse, perhaps by regulating cytoskeleton dynamics. Thus far RPGRIP1 appears to be only mutated in LCA and is associated with 6% of LCA in two series. The purpose of this review is to highlight recent advances in our understanding of RPGRIP1 function in normal and diseased retinas.     

Microarray-based mutation detection and phenotypic characterization of patients with Leber congenital amaurosis

PURPOSE: To test the efficiency of a microarray chip as a diagnostic tool in a cohort of northwestern European patients with Leber congenital amaurosis (LCA) and to perform a genotype-phenotype analysis in patients in whom pathologic mutations were identified. METHODS: DNAs from 58 patients with LCA were analyzed using a microarray chip containing previously identified disease-associated sequence variants in six LCA genes. Mutations identified by chip analysis were confirmed by sequence analysis. On identification of one mutation, all protein coding exons of the relevant genes were sequenced. In addition, sequence analysis of the RDH12 gene was performed in 22 patients. Patients with mutations were phenotyped. RESULTS: Pathogenic mutations were identified in 19 of the 58 patients with LCA (32.8%). Four novel sequence variants were identified. Mutations were most frequently found in CRB1 (15.5%), followed by GUCY2D (10.3%). The p.R768W mutation was found in 8 of 10 GUCY2D alleles, suggesting that it is a founder mutation in the northwest of Europe. In early childhood, patients with AIPL1 or GUCY2D mutations show normal fundi. Those with AIPL1-associated LCA progress to an RP-like fundus before the age of 8, whereas patients with GUCY2D-associated LCA still have relatively normal fundi in their mid-20s. Patients with CRB1 mutations present with distinct fundus abnormalities at birth and consistently show characteristics of RP12. Pathogenic GUCY2D mutations result in the most severe form of LCA. CONCLUSIONS: Microarray-based mutation detection allowed the identification of 32% of LCA sequence variants and represents an efficient first-pass screening tool. Mutations in CRB1, and to a lesser extent, in GUCY2D, underlie most LCA cases in this cohort. The present study establishes a genotype-phenotype correlation for AIPL1, CRB1, and GUCY2D.     

A novel exon 17 deletion mutation of RPGRIP1 gene in two siblings with Leber congenital amaurosis

Purpose

To investigate mutations of causal genes in two affected male siblings of a Japanese family with suspected Leber congenital amaurosis (LCA) and to characterize the related clinical features.

Methods

After obtaining informed consent, genomic DNA was extracted from peripheral blood of the proband and his family members. Mutation screening was initially performed with microarrays. The PCR and direct sequencing were successively done for confirmation of mutation detected by microarray, and the two patients who are the subjects of this study were also clinically examined.

Results

Results of the microarray suggested deletion of exon 17 of RPGRIP1. Confirmation by PCR and direct sequencing following microarray analysis revealed that both siblings had homozygous deletion of exon 17 of the RPGRIP1 gene, while their unaffected parents were heterozygous carriers. Length of the deletion was 1339 bp including exon 17 at the position of c.2710+372_2895+76del1339. Clinical features of the two siblings showed nystagmus, poor visual acuity, hyperopia, and photophobia since early childhood; but there was no oculo-digital sign, vessel attenuation or RPE mottling from the mid-retina to the periphery. Full-field single flash ERG was recordable but 30 Hz flicker ERG was not detectable.

Conclusions

Although the present patients did not show sufficient clinical findings as LCA, PCR findings and direct sequencing following microarray analysis confirmed that they were LCA. Genetic analyses are helpful for confirmation of clinical diagnosis.     

Recurrent keratoconus in a patient with Leber congenital amaurosis

PURPOSE: Clinical history of a 17-year-old patient with Leber congenital amaurosis (LCA) with histologically proven recurrent keratoconus (KC) two years after corneal transplantation in one eye and a recurrence-like appearance with a more global contour on the other eye four years after corneal grafting is reported. The possible mechanisms for this recurrence are discussed in light of the fact that this is, to the best of our knowledge, the first penetrating keratoplasty reported in LCA. METHODS: Computerized videokeratography (CVKG) and specular microscopy were performed preoperatively. The patient underwent regrafting, and the excised corneal button was examined by light microscopy and transmission electron microscopy. RESULTS: Analysis of CVKG showed a keratoconus-like pattern on the right eye, with the left eye demonstrating the aspects usually seen in keratoglobus. Histologic examination revealed the features usually observed in progressed keratoconus. CONCLUSION: Recurrence of keratoconus in a graft has not yet been described after such a short time until now. A "true" recurrence of the disease is postulated; it could be caused by an "aggressive" genetic factor that also leads to the frequent KC in patients with LCA. This mechanism also could explain the high incidence and rapid progress of KC in this disease.     

RPGRIP1基因新突变致Leber先天性黑矇一家系

目的确定1个汉族Leber先天性黑矇(LCA)家系的致病基因突变。方法回顾性研究。2018年10月在河南省立眼科医院就诊的LCA一家系1例患者和3名家系成员纳入研究。详细询问患者病史并行物体注视性质、追随试验、裂隙灯显微镜、散瞳验光、眼底照相及全视野ERG检查;家系成员行BCVA、裂隙灯显微镜联合前置镜、验光、眼底照相及全视野ERG检查。采集先证者及其兄长、父母的外周静脉血5 ml,提取全基因组DNA。应用包含441个致病基因的遗传眼病捕获芯片进行靶向捕获富集高通量测序以获得致病基因及突变。对可疑致病突变位点通过Sanger进行验证,并行生物信息学分析确定基因突变位点的致病性。结果患者表现为自幼不追物但有明显畏光和眼球震颤;双眼眼前节及眼底无异常;全视野ERG检查可见双眼视锥、视杆系统功能严重下降。基因检测结果显示,患者RPGRIP1基因存在c.1635dupA和c.3565C>T两个突变。其中,RPGRIP1 c.1635dupA为新发突变。RPGRIP1基因c.1635dupA和c.3565C>T构成复合杂合突变。生物信息学分析结果显示,c.3565C>T为致病突变,c.1635dupA为可能致病突变。结论RPGRIP1基因新发突变c.1635dupA与c.3565C>T构成复合杂合突变可能是本家系的致病原因。     

Leber congenital amaurosis in an infant with Down syndrome.

A male infant had defects of atrial and ventricular septa and trisomy 21. At 2 months of age, the patient had markedly sluggish pupillary reactions to light OU. Searching nystagmus, multiple chorioretinal atrophic spots in mottled retinas, and unrecordable electroretinograms also were found in the patient when he was 6 months of age. We believe that this infant represents a rare case of Leber congenital amaurosis in association with Down syndrome.     

Leber先天性黑矇患者血清脂质浓度的变化

目的：分析Leber先天性黑矇(Leber congenital amaurosis,LCA)患者血清脂质浓度的变化。

方法：采用回顾性序列病例研究方法,选取临床诊断为LCA的患者50例作为LCA组,选取52例正常人作为正常对照组,按盲法由专业技术人员测量两组受检者血清中低密度脂蛋白胆固醇(low density lipoprotein cholesterol,LDL-C)、高密度脂蛋白胆固醇(high density lipoprotein cholesterol,HDL-C)、甘油三酯(triglycerides,TG)、总胆固醇(total cholesterol,TC)含量,并对两组受检者的测量结果进行比较。

结果：LCA患者50例中,血脂水平异常者占46%,其中低HDL-C血症者占26%,高TG血症者占48%,高TC血症者占17%,混合型高脂血症者占9%。LCA患者血清HDL-C浓度为1.221±0.317mmol/L,较正常对照组明显下降,差异有统计学意义(P<0.05); 血清TG浓度(1.377±1.171mmol/L)和TC浓度(4.506±0.694mmol/L)与正常对照组相比均明显升高,差异有统计学意义(均P<0.01); LDL-C浓度与正常对照组相比,差异无统计学意义(P>0.05)。

结论：LCA患者血清HDL-C、TG和TC浓度异常变化可能与LCA的发病相关。     

Mutational analysis and clinical correlation in Leber congenital amaurosis

Leber congenital amaurosis (LCA, MIM 204001) is a clinically and genetically heterogeneous retinal disorder characterized by severe visual loss from birth, nystagmus, poor pupillary reflexes, retinal pigmentary or atrophic changes, and a markedly diminished electroretinogram (ERG). Purpose: To examine 100 consecutive patients with LCA in order to assess the relative burden of the three known genes involved in LCA, namely retinal guanylyl cyclase ( GUCY2D ), retinal pigment epithelium protein ( RPE65 ), and the cone-rod homeobox ( CRX ), and to define their clinical correlates. Methods: Mutational analysis and detailed clinical examinations were performed in patients diagnosed with LCA at the Johns Hopkins Center for Hereditary Eye Diseases and the Montreal Children’s Hospital. Results: Mutations were identified in 11% of our patients: GUCY2D mutations accounted for 6%, while RPE65 and CRX gene mutations accounted for 3% and 2%, respectively. The clinical presentation was variable; however, the visual evolution in patients with mutations in GUCY2D and CRX remained stable, while individuals with mutations in the RPE65 gene showed progressive visual loss. Conclusions: This study suggests that molecular diagnosis of Leber congenital amaurosis could provide important information concerning prognosis and course of treatment.     

利用目标区域捕获测序筛查Leber先天性黑矇的致病基因及其临床表型

目的探讨我国一个散发的Leber先天性黑矇（LCA）家系的致病基因变异位点及其临床表型。方法实验研究。收集嘉兴市妇幼保健院一个散发LCA家系共7名家庭成员的临床资料,其中1名LCA患者,6名正常家属。完善该家系内所有成员的眼科检查,采集该家系成员的外周静脉血,提取基因组DNA,运用目标区域捕获测序技术来筛查患者的283个视网膜疾病相关的基因,测序结果运用生物信息学分析得到候选基因,最后用Sanger测序验证。结果临床检查结果表明患者呈现典型的LCA临床症状。遗传学筛查结果证实患者在NMNAT1基因上存在2个复合杂合变异和1个纯合变异：具体为杂合的错义变异（c.634G>A,p.V212M）,杂合的内含子变异（c.-57+7T>G）和纯合的错义变异（c.764G>A,p.S255N）。结论本例患者的NMNAT1基因上存在3个不同的变异,很可能是导致其患有Leber 先天性黑矇的原因。     

Leber congenital amaurosis associated with optic disk neovascularization and vitreous hemorrhage

PURPOSE: To report an unusual case of optic disk neovascularization and vitreous hemorrhage associated with Leber congenital amaurosis (LCA). DESIGN: Interventional case report. METHODS: A 16-year-old Caucasian girl with a history of LCA presented with decreased vision in her left eye, diffuse retinal pigmentary abnormalities characteristic of LCA, and hemorrhage over the left optic disk and macula. Six months of follow-up revealed optic disk neovascularization. A small amount of neovascularization was noted in the right eye at 6 months. RESULTS: An extensive systemic evaluation indicated no other cause for the neovascularization. Panretinal photocoagulation was performed in both eyes, and subsequently the neovascularization regressed. CONCLUSIONS: Leber congenital amaurosis like retinitis pigmentosa, can rarely be associated with neovascularization of the disk, which is amenable to treatment with peripheral photocoagulation if it does not spontaneously regress.