Evidence of a founder effect for the RETGC1 (GUCY2D) 2943DelG mutation in Leber congenital amaurosis pedigrees of Finnish origin

GUCY2D mutations in retinal guanylyl cyclase 1 provide biochemical reasons for dominant cone-rod dystrophy but not for stationary night blindness

Mutations in the GUCY2D gene coding for the dimeric human retinal membrane guanylyl cyclase (RetGC) isozyme RetGC1 cause various forms of blindness, ranging from rod dysfunction to rod and cone degeneration. We tested how the mutations causing recessive congenital stationary night blindness (CSNB), recessive Leber's congenital amaurosis (LCA1), and dominant cone-rod dystrophy-6 (CORD6) affected RetGC1 activity and regulation by RetGC-activating proteins (GCAPs) and retinal degeneration-3 protein (RD3). CSNB mutations R666W, R761W, and L911F, as well as LCA1 mutations R768W and G982VfsX39, disabled RetGC1 activation by human GCAP1, -2, and -3. The R666W and R761W substitutions compromised binding of GCAP1 with RetGC1 in HEK293 cells. In contrast, G982VfsX39 and L911F RetGC1 retained the ability to bind GCAP1 in cyto but failed to effectively bind RD3. R768W RetGC1 did not bind either GCAP1 or RD3. The co-expression of GUCY2D allelic combinations linked to CSNB did not restore RetGC1 activity in vitro The CORD6 mutation R838S in the RetGC1 dimerization domain strongly dominated the Ca2+ sensitivity of cyclase regulation by GCAP1 in RetGC1 heterodimer produced by co-expression of WT and the R838S subunits. It required higher Ca2+ concentrations to decelerate GCAP-activated RetGC1 heterodimer-6-fold higher than WT and 2-fold higher than the Ser838-harboring homodimer. The heterodimer was also more resistant than homodimers to inhibition by RD3. The observed biochemical changes can explain the dominant CORD6 blindness and recessive LCA1 blindness, both of which affect rods and cones, but they cannot explain the selective loss of rod function in recessive CSNB.

Genetic spectrum of retinal dystrophies in Tunisia

We report the molecular basis of the largest Tunisian cohort with inherited retinal dystrophies (IRD) reported to date, identify disease-causing pathogenic variants and describe genotype-phenotype correlations. A subset of 26 families from a cohort of 73 families with clinical diagnosis of autosomal recessive IRD (AR-IRD) excluding Usher syndrome was analyzed by whole exome sequencing and autozygosity mapping. Causative pathogenic variants were identified in 50 families (68.4%), 42% of which were novel. The most prevalent pathogenic variants were observed in ABCA4 (14%) and RPE65, CRB1 and CERKL (8% each). 26 variants (8 novel and 18 known) in 19 genes were identified in 26 families (14 missense substitutions, 5 deletions, 4 nonsense pathogenic variants and 3 splice site variants), with further allelic heterogeneity arising from different pathogenic variants in the same gene. The most common phenotype in our cohort is retinitis pigmentosa (23%) and cone rod dystrophy (23%) followed by Leber congenital amaurosis (19.2%). We report the association of new disease phenotypes. This research was carried out in Tunisian patients with IRD in order to delineate the genetic population architecture.

The genetic aetiology of retinal degeneration in children in Finland - new founder mutations identified

PURPOSE

To study the genetic aetiology and phenotypes of retinal degeneration (RD) in Finnish children born during 1993-2009.

METHODS

Children with retinal degeneration (N = 68) were investigated during 2012-2014 with a targeted gene analysis or a next-generation sequencing (NGS) based gene panel. Also, a full clinical ophthalmological examination was performed.

RESULTS

The cohort covered 44% (68/153) of the Finnish children with inherited RD born 1993-2009. X-linked retinoschisis, retinitis pigmentosa, Leber congenital amaurosis and cone-rod dystrophy were the most common clinical diagnoses in the study group. Pathogenic mutations were found in 17 retinal genes. The molecular genetic aetiology was identified in 77% of the patients (in 77% of the families) analysed by NGS method. Several founder mutations were detected including three novel founder mutations c.148delG in TULP1, c.2314C>R (p.Gln772Ter) in RPGRIP1 and c.533G>A (Trp178Ter) in TYR. We also confirmed the previous tentative finding of c.2944 + 1delG in GYCU2D being the most frequent cause of Leber congenital amaurosis (LCA) in Finland.

CONCLUSIONS

Globally, RD is genetically heterogeneous with over 260 disease genes reported so far. This was shown not to be the case in Finland, where the genetic aetiology of RD is caused by a small group of genes, due to several founder mutations that are enriched in the population. We found that X-chromosomal retinoschisis constitutes the major group in Finnish paediatric RD population and is almost exclusively caused by two founder mutations. Several other founder mutations were detected including three novel founder mutations. All in all, the genetic aetiology of 77% of families was identified which is higher than previously reported from other populations, likely due to the specific genomic constitution of the Finns.

Possible dual contribution of a novel GUCY2D mutation in the development of retinal degeneration in a consanguineous population

Molecular characterization of novel mutations in Leber Congenital Amaurosis (LCA) disease improves the disease diagnosis and contributes to the development of preventive and therapeutic approaches. We studied an isolated inbred population in Iran with a high prevalence of retinal degeneration with clinical variability. The clinical examinations were performed on eight patients belonging to three consanguineous families. The identical-by-descent (IBD) mapping technique was employed to identify the shared loci in patients. Subsequently, Sanger sequencing of the GUCY2D gene, in silico analysis, as well as segregation study were conducted. The whole-exome sequencing method was applied for negative cases of GUCY2D mutation, followed by segregation study in suspected variants among families. A novel deletion mutation in the GUCY2D gene can explain the emergence of LCA-1 in most patients but not all. Besides, a heterozygous variant of uncertain significance (VUS) was observed in the BEST1 gene in some healthy and participant patients. These results further support inter/intra-familial clinical heterogeneity in retinal dystrophy and suggest that screening the GUCY2D gene would be needed for the diagnosis of LCA in Iranian people living in the central regions. The variant in the BEST1 gene might be considered a benign heterozygous variant; however, we hypothesized a possible double heterozygosity in both GUCY2D and BEST1 genes that may cause the pathogenesis of cone-rod dystrophy-6 (CRD-6) disease. This would propose a new scenario for the pathogenesis of a monogenic disorder such as CRD-6 disease in which other genetic elements may be involved in the development of the disease.

Expanded Retinal Disease Spectrum Associated With Autosomal Recessive Mutations in GUCY2D

PURPOSE

GUCY2D has been associated with autosomal recessive Leber congenital amaurosis and autosomal dominant cone-rod dystrophy. This report expands the phenotype of autosomal recessive mutations to congenital night blindness, which may slowly progress to mild retinitis pigmentosa.

DESIGN

Retrospective case series.

METHODS

Multicenter study of 5 patients (3 male, 2 female).

RESULTS

All patients presented with night blindness since childhood. Age at referral was 9-45 years. Length of follow-up was 1-7 years. Best-corrected visual acuity at presentation ranged from 20/15 to 20/30 and at most recent visit averaged 20/25. No patient had nystagmus or high refractive error. ISCEV standard electroretinography revealed nondetectable dark-adapted dim flash responses and reduced amplitude but not electronegative dark-adapted bright flash responses with similar waveforms to the reduced-amplitude light-adapted single flash responses. The 30 Hz flicker responses were relatively preserved. Macular optical coherence tomography revealed normal lamination in 3 patients, with abnormalities in 2. Goldmann visual fields were normal at presentation in children but constricted in 1 adult. One child showed loss of midperipheral fields over time. Fundus appearance was normal in childhood; the adult had sparse bone spicule-like pigmentation. Full-field stimulus testing (FST) revealed markedly decreased retinal sensitivity to light. Dark adaptation demonstrated lack of rod-cone break. Two patients had tritanopia. All 5 had compound heterozygous mutations in GUCY2D. Three of the 5 patients harbor the Arg768Trp mutation reported in GUCY2D-associated Leber congenital amaurosis.

CONCLUSIONS

Autosomal recessive GUCY2D mutations may cause congenital night blindness with normal acuity and refraction, and unique electroretinography. Progression to mild retinitis pigmentosa may occur.

A founder mutation in CERKL is a major cause of retinal dystrophy in Finland

PURPOSE

To study the genetic aetiology of retinal dystrophies (RD) in Finnish patients.

METHODS

A targeted next-generation sequencing (NGS) panel of 105 retinal dystrophy genes was used in a cohort of 55 RD patients.

RESULTS

The overall diagnostic yield was 60% demonstrating the power of this approach. Interestingly, a missense mutation c.375C>G p.(Cys125Trp) in the CERKL gene was found in 18% of the patients in either a homozygous or compound heterozygous state. Data from Exome Aggregation Consortium (ExAC) Browser show that the CERKL c.375C>G p.(Cys125Trp) allele is enriched in the Finnish population and thus is a founder mutation. Furthermore, we report the clinical picture of 18 patients with mutations in the CERKL gene. CERKL mutations cause a macular-onset disease, in which symptoms first become apparent at the second decade. We also detected other novel founder mutations in the CERKL, EYS, RP1, ABCA4 and GUCY2D genes.

CONCLUSION

Our report indicates that the first diagnostic test for Finnish patients with sporadic or autosomal recessive RD should be a targeted test for founder mutations in the CERKL, EYS, RP1, ABCA4 and GUCY2D genes. These results confirm the utility of NGS-based gene panels as a powerful method for mutation identification in RD, thus enabling improved genetic counselling for these families.

Novel GUCY2D mutation causes phenotypic variability of Leber congenital amaurosis in a large kindred

Background

Leber congenital amaurosis (LCA) is a severe retinal degenerative disease that manifests as blindness or poor vision in infancy. The purpose of this study was to clinically characterize and identify the cause of disease in a large inbred Bedouin Israeli tribe with LCA.

Methods

Thirty individuals of a single kindred, including eight affected with LCA, were recruited for this study. Patients’ clinical data and electroretinography (ERG) findings were collected. Molecular analysis included homozygosity mapping with polymorphic markers and Sanger sequencing of candidate genes.

Results

Of the eight affected individuals of the kindred, nystagmus was documented in five subjects and keratoconus in three. Cataract was found in 5 of 16 eyes. Photopic and scotopic ERG performed in 5 patients were extinguished. All affected subjects were nearly blind, their visual acuity ranged between finger counting and uncertain light perception. Assuming autosomal recessive heredity of a founder mutation, studies using polymorphic markers excluded homozygosity of affected individuals at the genomic loci of all previously known genes associated with LCA, except GUCY2D. Sequencing of GUCY2D identified a novel missense mutation (c.2129C>T; p.Ala710Val) resulting in substitution of alanine by valine at position 710 within the protein kinase domain of the retina-specific enzyme guanylate cyclase 1 (GC1) encoded by GUCY2D. Molecular modeling implied that the mutation changes the conformation of the regulatory segment within the kinase styk-domain of GC1 and causes loss of its helical structure, likely inhibiting phosphorylation of threonine residue within this segment, which is needed to activate the catalytic domain of the protein.

Conclusions

This is the first documentation of the p.Ala710Val mutation in GC1 and the second ever described mutation in its protein kinase domain. Our findings enlarge the scope of genetic variability of LCA, highlight the phenotypic heterogeneity found amongst individuals harboring an identical LCA mutation, and possibly provide hope for gene therapy in patients with this congenital blinding disease. As the Bedouin kindred studied originates from Saudi Arabia, the mutation found might be an ancient founder mutation in that large community.

Comprehensive genotyping reveals RPE65 as the most frequently mutated gene in Leber congenital amaurosis in Denmark

Leber congenital amaurosis (LCA) represents the most severe form of inherited retinal dystrophies with an onset during the first year of life. Currently, 21 genes are known to be associated with LCA and recurrent mutations have been observed in AIPL1, CEP290, CRB1 and GUCY2D. In addition, sequence analysis of LRAT and RPE65 may be important in view of treatments that are emerging for patients carrying variants in these genes. Screening of the aforementioned variants and genes was performed in 64 Danish LCA probands. Upon the identification of heterozygous variants, Sanger sequencing was performed of the relevant genes to identify the second allele. In combination with prior arrayed primer extension analysis, this led to the identification of two variants in 42 of 86 cases (49%). Remarkably, biallelic RPE65 variants were identified in 16% of the cases, and one novel variant, p.(D110G), was found in seven RPE65 alleles. We also collected all previously published RPE65 variants, identified in 914 alleles of 539 patients with LCA or early-onset retinitis pigmentosa, and deposited them in the RPE65 Leiden Open Variation Database (LOVD). The in silico pathogenicity assessment of the missense and noncanonical splice site variants, as well as an analysis of their frequency in ~60 000 control individuals, rendered 864 of the alleles to affect function or probably affect function. This comprehensive database can now be used to select patients eligible for gene augmentation or retinoid supplementation therapies.

Union makes strength: a worldwide collaborative genetic and clinical study to provide a comprehensive survey of RD3 mutations and delineate the associated phenotype

Leber congenital amaurosis (LCA) is the earliest and most severe retinal degeneration (RD), and the most common cause of incurable blindness diagnosed in children. It is occasionally the presenting symptom of multisystemic ciliopathies which diagnosis will require a specific care of patients. Nineteen LCA genes are currently identified and three of them account for both non-syndromic and syndromic forms of the disease. RD3 (LCA12) was implicated as a LCA gene based on the identification of homozygous truncating mutations in two LCA families despite the screening of large cohorts of patients. Here we provide a comprehensive survey of RD3 mutations and of their clinical expression through the screening of a cohort of 852 patients originating worldwide affected with LCA or early-onset and severe RD. We identified three RD3 mutations in seven unrelated consanguineous LCA families - i.e., a 2 bp deletion and two nonsense mutations – predicted to cause complete loss of function. Five families originating from the Southern Shores of the Mediterranean segregated a similar mutation (c.112C>T, p.R38*) suggesting that this change may have resulted from an ancient founder effect. Considering the low frequency of RD3 carriers, the recurrence risk for LCA in non-consanguineous unions is negligible for both heterozygote and homozygote RD3 individuals. The LCA12 phenotype in our patients is highly similar to those of patients with mutant photoreceptor-specific guanylate cyclase (GUCY2D/LCA1). This observation is consistent with the report of the role of RD3 in trafficking of GUCYs and gives further support to a common mechanism of photoreceptor degeneration in LCA12 and LCA1, i.e., inability to increase cytoplasmic cGMP concentration in outer segments and thus to recover the dark-state. Similar to LCA1, LCA12 patients have no extraocular symptoms despite complete inactivation of both RD3 alleles, supporting the view that extraocular investigations in LCA infants with RD3 mutations should be avoided.

Genetic isolates in ophthalmic diseases

In recent years, noteworthy gains have been made in unravelling the genetic contribution to some complex ocular diseases, principally age-related macular degeneration. Yet, a relatively poor understanding of the genetic aetiology for many other heritable blinding diseases, such as glaucoma, keratoconus and myopia, remains. Genetic isolates, populations with varying degrees of geographical or cultural seclusion, provide an effective means for investigating the molecular mechanisms involved in human diseases. This is particularly true for rare diseases in which founded alleles can be rapidly driven to a high frequency due to restriction of gene flow in the population. Recent success in complex gene mapping has resulted from the widened linkage disequilibrium (LD) in the genome of genetically isolated populations. An improved understanding of the predisposing genetic risk factors allows for enhanced screening modalities and paves the foundations for the translation of genomic technology into the clinic. This review focuses on the role population isolates have had in the investigation of genes underlying complex eye diseases and discusses their likely usefulness given the expansion of large-scale case-control association studies.

Leber congenital amaurosis: genes, proteins and disease mechanisms

Leber congenital amaurosis (LCA) is the most severe retinal dystrophy causing blindness or severe visual impairment before the age of 1 year. Linkage analysis, homozygosity mapping and candidate gene analysis facilitated the identification of 14 genes mutated in patients with LCA and juvenile retinal degeneration, which together explain approximately 70% of the cases. Several of these genes have also been implicated in other non-syndromic or syndromic retinal diseases, such as retinitis pigmentosa and Joubert syndrome, respectively. CEP290 (15%), GUCY2D (12%), and CRB1 (10%) are the most frequently mutated LCA genes; one intronic CEP290 mutation (p.Cys998X) is found in approximately 20% of all LCA patients from north-western Europe, although this frequency is lower in other populations. Despite the large degree of genetic and allelic heterogeneity, it is possible to identify the causative mutations in approximately 55% of LCA patients by employing a microarray-based, allele-specific primer extension analysis of all known DNA variants. The LCA genes encode proteins with a wide variety of retinal functions, such as photoreceptor morphogenesis (CRB1, CRX), phototransduction (AIPL1, GUCY2D), vitamin A cycling (LRAT, RDH12, RPE65), guanine synthesis (IMPDH1), and outer segment phagocytosis (MERTK). Recently, several defects were identified that are likely to affect intra-photoreceptor ciliary transport processes (CEP290, LCA5, RPGRIP1, TULP1). As the eye represents an accessible and immune-privileged organ, it appears to be uniquely suitable for human gene replacement therapy. Rodent (Crb1, Lrat, Mertk, Rpe65, Rpgrip1), avian (Gucy2D) and canine (Rpe65) models for LCA and profound visual impairment have been successfully corrected employing adeno-associated virus or lentivirus-based gene therapy. Moreover, phase 1 clinical trials have been carried out in humans with RPE65 deficiencies. Apart from ethical considerations inherently linked to treating children, major obstacles for the treatment of LCA could be the putative developmental deficiencies in the visual cortex in persons blind from birth (amblyopia), the absence of sufficient numbers of viable photoreceptor or RPE cells in LCA patients, and the unknown and possibly toxic effects of overexpression of transduced genes. Future LCA research will focus on the identification of the remaining causal genes, the elucidation of the molecular mechanisms of disease in the retina, and the development of gene therapy approaches for different genetic subtypes of LCA.

Leber congenital amaurosis - a model for efficient genetic testing of heterogeneous disorders: LXIV Edward Jackson Memorial Lecture

PURPOSE

To critically evaluate our experience in molecular testing of Leber congenital amaurosis (LCA) and to use this information to devise a general approach to heterogeneous recessive disorders. Careful clinical and molecular characterization of large cohorts of patients affected with inherited eye diseases will be an essential step in the development of effective therapy for these diseases, especially when the therapy involves gene replacement.

DESIGN

A molecular genetic case-control study.

METHODS

Six hundred forty-two unrelated individuals with the clinical diagnosis of LCA and 200 unrelated control individuals were screened for disease-causing sequence variations in eight genes using various combinations of single-strand conformational polymorphism analysis (SSCP), automated DNA sequencing, multiplex allele-specific ligation analysis (SNPlex), and high-density solid-phase single nucleotide polymorphism genotyping.

RESULTS

Four hundred forty instances of 189 different disease-causing sequence variations were observed in this study, 98 of which have not been previously reported. One hundred forty-six of the 189 variations (77%) were observed in only a single individual. The observed variations were not evenly distributed among the LCA patients or among the eight genes. Empirical analysis of this uneven distribution was used to devise a multi-platform mutation detection strategy that is four times more efficient than a more conventional strategy of completely sequencing all of the coding regions of all LCA genes in all subjects. Hardy-Weinberg analysis of the observed mutations suggests that these eight genes are collectively responsible for about 70% of the cases of LCA in North America. The carrier frequency of the most common LCA allele (an intron 26 variation in CEP290) was found to be 2/3,248, which suggests that the overall prevalence of LCA in this population is about 1/81,000. An allele-specific ligation assay (SNPlex) was designed to detect 68 of the most common LCA-causing alleles, and semi-quantitative analysis of the data from this assay also revealed examples of gene deletion and isodisomy in the cohort.

CONCLUSIONS

The data demonstrates that a tiered screening strategy combining allele-specific detection with automated DNA sequencing can increase the efficiency of autosomal recessive mutation detection four-fold when compared with DNA sequencing alone. However, the very high rate of unique mutations observed in this study (77%) suggests that DNA sequencing will remain an important part of the overall strategy if high sensitivity is to be achieved.

[Genetic and clinical heterogeneity in LCA patients. The end of uniformity]

BACKGROUND

Leber congenital amaurosis (LCA) usually describes patients with severely reduced vision due to a retinal dystrophy in early childhood.

METHODS

In 135 families in a case series with severely reduced vision due to a retinal dystrophy in early childhood a complete ophthalmologic examination was extended by two-color threshold perimetry, fundus autofluorescence (FAF), und optical coherence tomography (OCT). Mutation screening included AIPL1, CRB1, CRX, GUCY2D, LRAT, RPE65, RPGRIP, and TULP1.

RESULTS

GUCY2D mutations caused the most severe phenotype with severely reduced vision from birth but unremarkable fundus appearance. RPE65 mutations were correlated with an obvious lack of FAF. CRB1 mutations showed a significantly thickened retina on OCT. CRX mutations were associated with a progressive form of cone-rod dystrophy.

CONCLUSION

A genotype-phenotype correlation for selected genes allows an optimized strategy for the molecular genetic work-up.

[Leber congenital amaurosis: comprehensive survey of genetic heterogeneity. A clinical definition update]

Leber congenital amaurosis (LCA) is the earliest and most severe form of all inherited retinal dystrophies, responsible for congenital blindness. Disease-associated mutations have been hitherto reported in seven genes. These genes are all expressed preferentially in the photoreceptor cells or the retinal pigment epithelium, but they are involved in strikingly different physiologic pathways, resulting in an unforeseeable pathophysiologic variety. This broad genetic and physiologic heterogeneity, which could greatly increase in the coming years, hinders molecular diagnosis in LCA patients. Genotyping is, however, required to establish genetically defined subgroups of patients ready for therapy. Here we report a comprehensive mutational analysis of all the known genes in 179 unrelated LCA patients, including 52 familial and 127 sporadic (27/127 consanguineous) cases. Mutations were identified in 47.5% of patients. GUCY2D accounted for by far the largest part of the LCA cases in our series (21.2%), followed by CRB1 (10%), RPE65 (6.1%), RPGRIP1 (4.5%), AIPL1 (3.4%), TULP1 (1.7%) and CRX (0.6%). The clinical history of all patients with mutations was carefully revisited in the search for phenotype variations. Genotype-phenotype correlations were found that made it possible to divide patients into two main groups. The first one includes patients whose symptoms fit the traditional definition of LCA, i.e., congenital or very early cone-rod dystrophy, while the second group gathers patients affected with severe yet progressive rod-cone dystrophy. In addition, objective ophthalmologic data subdivided each group into two subtypes. Based on these findings, we have drawn decisional flowcharts directing the molecular analysis of LCA genes in a given case. These flowcharts will hopefully lighten the onerous task of genotyping new patients, but only if the most precise clinical history since birth is available.

Leber congenital amaurosis: comprehensive survey of the genetic heterogeneity, refinement of the clinical definition, and genotype-phenotype correlations as a strategy for molecular diagnosis

Leber congenital amaurosis (LCA) is the earliest and most severe form of all inherited retinal dystrophies, responsible for congenital blindness. Disease-associated mutations have been hitherto reported in seven genes. These genes are all expressed preferentially in the photoreceptor cells or the retinal pigment epithelium but they are involved in strikingly different physiologic pathways resulting in an unforeseeable physiopathologic variety. This wide genetic and physiologic heterogeneity that could largely increase in the coming years, hinders the molecular diagnosis in LCA patients. The genotyping is, however, required to establish genetically defined subgroups of patients ready for therapy. Here, we report a comprehensive mutational analysis of the all known genes in 179 unrelated LCA patients, including 52 familial and 127 sporadic (27/127 consanguineous) cases. Mutations were identified in 47.5% patients. GUCY2D appeared to account for most LCA cases of our series (21.2%), followed by CRB1 (10%), RPE65 (6.1%), RPGRIP1 (4.5%), AIPL1 (3.4%), TULP1 (1.7%), and CRX (0.6%). The clinical history of all patients with mutations was carefully revisited to search for phenotype variations. Sound genotype-phenotype correlations were found that allowed us to divide patients into two main groups. The first one includes patients whose symptoms fit the traditional definition of LCA, i.e., congenital or very early cone-rod dystrophy, while the second group gathers patients affected with severe yet progressive rod-cone dystrophy. Besides, objective ophthalmologic data allowed us to subdivide each group into two subtypes. Based on these findings, we have drawn decisional flowcharts directing the molecular analysis of LCA genes in a given case. These flowcharts will hopefully lighten the heavy task of genotyping new patients but only if one has access to the most precise clinical history since birth.

Analysis of three genes in Leber congenital amaurosis in Indonesian patients

PURPOSE

To assess the frequency, the pattern of disease causing mutations, and phenotypic variations in patients with Leber congenital amaurosis (LCA) from Indonesia.

PATIENTS AND METHODS

Twenty-one unrelated index cases with a clinical diagnosis of LCA were screened for mutations in the coding sequence of RetGC1, RPE65 and AIPL1 gene with single strand conformation polymorphism analysis followed by direct sequencing and restriction enzyme digestion.

RESULTS

Four novel disease causing mutations were identified: Three in the RPE65 gene (106del9bp, G32V and Y435C) in two of 21 index cases and one in the AIPL1 (K14E). Two of them were homozygous and one was compound-heterozygous. No disease causing mutation was identified in RetGC1.

CONCLUSIONS

The four novel disease causing mutations identified in this study confirmed the diagnosis of LCA which has not been recognized before in Indonesia. The frequency of RPE65 mutations was 9.5%; and of AIPL1 mutations 4.8%. This was in general accordance with previous studies reported from other countries. Unlike in those studies, no disease causing RetGC1 mutations could be identified in our patients. Phenotypically, the RPE65 and AIPL1 mutations identified in this study caused nearly total blindness by the second decade of life, but had a different onset of symptoms. The patients with the RPE65 mutations retained some useful visual function until the end of the first decade, which progressed to total blindness during the second decade of life, whereas the (homozygous) AIPL1 mutation was associated with nearly total blindness from infancy on. Therefore, RPE65 mutations have to be considered to cause early onset severe retinal degeneration (EOSRD), and AIPL1 mutations a form of LCA.

Recent advances in early-onset severe retinal degeneration: more than just basic research?

Successful treatment of early-onset sever retinal degeneration (EOSRD) in an animal model of the disease has provided the first proof-o-principle for retinal gene therapy of higher mammals. Currently, large sets of DNA samples are screened to identify patients with Leber's congenital amaurosis (LCA) carrying mutations in RPE65 as possible candidates for gene therapy trials. Research into EOSRD and LCA aims to identify the function of proteins involved or phenotypic changes upon mutation. These data will be used to describe the disease phenotype and identify parameters that can predict the outcome of gene therapy trials.