Knockdown of Dehydrodolichyl Diphosphate Synthase in the Drosophila Retina Leads to a Unique Pattern of Retinal Degeneration.

Dehydrodolichyl diphosphate synthase (DHDDS) is a ubiquitously expressed enzyme that catalyzes cis-prenyl chain elongation to produce the poly-prenyl backbone of dolichol. It appears in all tissues including the nervous system and it is a highly conserved enzyme that can be found in all animal species. Individuals who have biallelic missense mutations in the DHDDS gene are presented with non-syndromic retinitis pigmentosa with unknown underlying mechanism. We have used the Drosophila model to compromise DHDDS ortholog gene (CG10778) in order to look for cellular and molecular mechanisms that, when defective, might be responsible for this retinal disease. The Gal4/UAS system was used to suppress the expression of CG10778 via RNAi-mediated-knockdown in various tissues. The resulting phenotypes were assessed using q-RT-PCR, transmission-electron-microscopy (TEM), electroretinogram, antibody staining and Western blot analysis. Targeted knockdown of CG10778-mRNA in the early embryo using the actin promoter or in the developing wings using the nub promoter resulted in lethality, or wings loss, respectively. Targeted expression of CG10778-RNAi using the glass multiple reporter (GMR)-Gal4 driver (GMR-DHDDS-RNAi) in the larva eye disc and pupal retina resulted in a complex phenotype: (a) TEM retinal sections revealed a unique pattern of retinal-degeneration, where photoreceptors R2 and R5 exhibited a nearly normal structure of their signaling-compartment (rhabdomere), but only at the region of the nucleus, while all other photoreceptors showed retinal degeneration at all regions. (b) Western blot analysis revealed a drastic reduction in rhodopsin levels in GMR-DHDDS-RNAi-flies and TEM sections showed an abnormal accumulation of endoplasmic reticulum (ER). To conclude, compromising DHDDS in the developing retina, while allowing formation of the retina, resulted in a unique pattern of retinal degeneration, characterized by a dramatic reduction in rhodopsin protein level and an abnormal accumulation of ER membranes in the photoreceptors cells, thus indicating that DHDDS is essential for normal retinal formation.

Identification of genomic deletions causing inherited retinal degenerations by coverage analysis of whole exome sequencing data.

BACKGROUND: Inherited retinal degenerations (IRDs) are a common cause of visual disturbance with a high clinical and genetic heterogeneity. Recent sequencing techniques such as whole exome sequencing (WES) contribute to the discovery of novel genes. The aim of the current study was to use WES data to identify large deletions that include at least one exon in known IRD genes. METHODS: Patients diagnosed with IRDs underwent a comprehensive ophthalmic evaluation. WES was performed using the NimbleGen V2 paired-end kit and HiSeq 2000. An analysis of exon coverage data was performed on 60 WES samples. Exonic deletions were verified by 'PCR walking' analysis. RESULTS: We analysed data obtained from 60 WES samples of index patients with IRDs. By calculating the average coverage for all exons in the human genome, we were able to identify homozygous and hemizygous deletions of at least one exon in six families (10%), including a single-exon deletion in EYS, deletions of three consecutive exons in MYO7A and NPHP4, deletions of four and eight consecutive exons in RPGR and a multigene deletion on the X-chromosome, including CHM. By using PCR-walking analysis, we were able to identify the borders of five of the deletions and to screen our set of patients for these deletions. CONCLUSIONS: We performed here a comprehensive analysis of WES data as a tool for identifying large genomic deletions in patients with IRDs. Our analysis indicates that large deletions are relatively frequent (about 10% of our WES cohort) and should be screened when analysing WES data.

Whole Exome Sequencing Reveals Mutations in Known Retinal Disease Genes in 33 out of 68 Israeli Families with Inherited Retinopathies.

Whole exome sequencing (WES) is a powerful technique for identifying sequence changes in the human genome. The goal of this study was to delineate the genetic defects in patients with inherited retinal diseases (IRDs) using WES. WES was performed on 90 patient DNA samples from 68 families and 226 known genes for IRDs were analyzed. Sanger sequencing was used to validate potential pathogenic variants that were also subjected to segregation analysis in families. Thirty-three causative mutations (19 novel and 14 known) in 25 genes were identified in 33 of the 68 families. The vast majority of mutations (30 out of 33) have not been reported in the Israeli and the Palestinian populations. Nine out of the 33 mutations were detected in additional families from the same ethnic population, suggesting a founder effect. In two families, identified phenotypes were different from the previously reported clinical findings associated with the causative gene. This is the largest genetic analysis of IRDs in the Israeli and Palestinian populations to date. We also demonstrate that WES is a powerful tool for rapid analysis of known disease genes in large patient cohorts.

Association between missense mutations in the BBS2 gene and nonsyndromic retinitis pigmentosa.

IMPORTANCE: A large number of genes can cause inherited retinal degenerations when mutated. It is important to identify the cause of disease for a better disease prognosis and a possible gene-specific therapeutic intervention. OBJECTIVE: To identify the cause of disease in families with nonsyndromic retinitis pigmentosa. DESIGN, SETTING, AND PARTICIPANTS: Patients and family members were recruited for the study and underwent clinical evaluation and genetic analyses. MAIN OUTCOMES AND MEASURES: Identification of sequence variants in genes using next-generation sequencing. RESULTS: We performed exome sequencing for 4 families, which was followed by Sanger sequencing of the identified mutations in 120 ethnicity-matched patients. In total, we identified 4 BBS2 missense mutations that cause nonsyndromic retinitis pigmentosa. Three siblings of Moroccan Jewish ancestry were compound heterozygotes for p.A33D and p.P134R, and 6 patients belonging to 4 families of Ashkenazi Jewish ancestry were homozygous for either p.D104A or p.R632P, or compound heterozygous for these 2 mutations. The mutations cosegregated with retinitis pigmentosa in the studied families, and the affected amino acid residues are evolutionarily conserved. CONCLUSIONS AND RELEVANCE: Our study shows that BBS2 mutations can cause nonsyndromic retinitis pigmentosa and highlights yet another candidate for this genetically heterogeneous condition.

Whole exome sequencing reveals GUCY2D as a major gene associated with cone and cone-rod dystrophy in Israel.

PURPOSE: The Israeli population has a unique genetic make-up, with a high prevalence of consanguineous marriages and autosomal recessive diseases. In rod-dominated phenotypes, disease-causing genes and mutations that differ from those identified in other populations often are incurred. We used whole exome sequencing (WES) to identify genetic defects in Israeli families with cone-dominated retinal phenotypes. METHODS: Clinical analysis included family history, detailed ocular examination, visual function testing, and retinal imaging. Whole exome sequencing, followed by segregation analysis, was performed in 6 cone-dominated retinopathy families in which prior mutation analysis did not reveal the causative gene. Based on the WES findings, we screened 106 additional families with cone-dominated phenotypes. RESULTS: The WES analysis revealed mutations in known retinopathy genes in five of the six families: two pathogenic mutations in the GUCY2D gene in three families, and one each in CDHR1 and C8orf37. Targeted screening of additional cone-dominated families led to identification of GUCY2D mutations in four other families, which included two highly probable novel disease-causing variants. CONCLUSIONS: Our study suggested that GUCY2D is a major cause of autosomal dominant cone and cone-rod dystrophies in Israel; this is similar to other Caucasian populations and is in contrast with retinitis pigmentosa (primary rod disease), where the genetic make-up of the Israeli population is distinct from other ethnic groups. We also conclude that WES permits more comprehensive and rapid analyses that can be followed by targeted screens of larger samples to delineate the genetic structure of retinal disease in unique population cohorts.

A homozygous nonsense CEP250 mutation combined with a heterozygous nonsense C2orf71 mutation is associated with atypical Usher syndrome.

BACKGROUND: Usher syndrome (USH) is a heterogeneous group of inherited retinitis pigmentosa (RP) and sensorineural hearing loss (SNHL) caused by mutations in at least 12 genes. Our aim is to identify additional USH-related genes. METHODS: Clinical examination included visual acuity test, funduscopy and electroretinography. Genetic analysis included homozygosity mapping and whole exome sequencing (WES). RESULTS: A combination of homozygosity mapping and WES in a large consanguineous family of Iranian Jewish origin revealed nonsense mutations in two ciliary genes: c.3289C>T (p.Q1097*) in C2orf71 and c.3463C>T (p.R1155*) in centrosome-associated protein CEP250 (C-Nap1). The latter has not been associated with any inherited disease and the c.3463C>T mutation was absent in control chromosomes. Patients who were double homozygotes had SNHL accompanied by early-onset and severe RP, while patients who were homozygous for the CEP250 mutation and carried a single mutant C2orf71 allele had SNHL with mild retinal degeneration. No ciliary structural abnormalities in the respiratory system were evident by electron microscopy analysis. CEP250 expression analysis of the mutant allele revealed the generation of a truncated protein lacking the NEK2-phosphorylation region. CONCLUSIONS: A homozygous nonsense CEP250 mutation, in combination with a heterozygous C2orf71 nonsense mutation, causes an atypical form of USH, characterised by early-onset SNHL and a relatively mild RP. The severe retinal involvement in the double homozygotes indicates an additive effect caused by nonsense mutations in genes encoding ciliary proteins.

Ocular phenotype analysis of a family with biallelic mutations in the BEST1 gene.

PURPOSE: To investigate the genetic cause and perform a comprehensive clinical analysis of a Danish family with autosomal recessive bestrophinopathy; to investigate whether Bestrophin may be expressed in normal human retina. DESIGN: Retrospective clinical and molecular genetic analysis and immunohistochemical observational study. METHODS: setting: National referral center. participants: A family with 5 individuals and biallelic BEST1 mutations, and enucleated eyes from 2 individuals with nonaffected retinas. observation procedures: Molecular genetic analysis included sequencing of BEST1 and co-segregation analysis. Clinical investigations included electro-oculography, full-field electroretinography, multifocal electroretinography, spectral-domain optical coherence tomography, and fundus autofluorescence imaging. Immunohistochemical analysis was performed. main outcome measures: BEST1 mutations, imaging findings, electroretinography amplitudes, and implicit times. RESULTS: The index case was compound heterozygous for p.A195V and a novel 15 base pair deletion leading to p.Q238L. The index case at age 10 demonstrated multifocal vitelliform changes that were hyperautofluorescent, cystoid macular edema in the inner nuclear layer, no light rise in the electro-oculography, and a reduced central but preserved peripheral retinal function by multifocal electroretinography. Full-field electroretinography demonstrated a reduced rod response and inner retina dysfunction. Retinal structure was normal in all 3 family members who carried a sequence change in BEST1. Electro-oculography light peak was reduced in both the mother and sister (heterozygous for p.Q238L). Immunohistochemistry could not confirm the presence of Bestrophin in normal human retina. CONCLUSIONS: Because of a relatively well preserved retinal function, autosomal recessive bestrophinopathy may be a suitable first candidate, among the BEST1-related ocular conditions, for gene replacement therapy.

The effect of cone opsin mutations on retinal structure and the integrity of the photoreceptor mosaic.

PURPOSE: To evaluate retinal structure and photoreceptor mosaic integrity in subjects with OPN1LW and OPN1MW mutations. METHODS: Eleven subjects were recruited, eight of whom have been previously described. Cone and rod density was measured using images of the photoreceptor mosaic obtained from an adaptive optics scanning light ophthalmoscope (AOSLO). Total retinal thickness, inner retinal thickness, and outer nuclear layer plus Henle fiber layer (ONL+HFL) thickness were measured using cross-sectional spectral-domain optical coherence tomography (SD-OCT) images. Molecular genetic analyses were performed to characterize the OPN1LW/OPN1MW gene array. RESULTS: While disruptions in retinal lamination and cone mosaic structure were observed in all subjects, genotype-specific differences were also observed. For example, subjects with "L/M interchange" mutations resulting from intermixing of ancestral OPN1LW and OPN1MW genes had significant residual cone structure in the parafovea (∼25% of normal), despite widespread retinal disruption that included a large foveal lesion and thinning of the parafoveal inner retina. These subjects also reported a later-onset, progressive loss of visual function. In contrast, subjects with the C203R missense mutation presented with congenital blue cone monochromacy, with retinal lamination defects being restricted to the ONL+HFL and the degree of residual cone structure (8% of normal) being consistent with that expected for the S-cone submosaic. CONCLUSIONS: The photoreceptor phenotype associated with OPN1LW and OPN1MW mutations is highly variable. These findings have implications for the potential restoration of visual function in subjects with opsin mutations. Our study highlights the importance of high-resolution phenotyping to characterize cellular structure in inherited retinal disease; such information will be critical for selecting patients most likely to respond to therapeutic intervention and for establishing a baseline for evaluating treatment efficacy.

BBS1 mutations in a wide spectrum of phenotypes ranging from nonsyndromic retinitis pigmentosa to Bardet-Biedl syndrome.

OBJECTIVE: To investigate the involvement of the Bardet-Biedl syndrome (BBS) gene BBS1 p.M390R variant in nonsyndromic autosomal recessive retinitis pigmentosa (RP). METHODS: Homozygosity mapping of a patient with isolated RP was followed by BBS1 sequence analysis. We performed restriction fragment length polymorphism analysis of the p.M390R allele in 2007 patients with isolated RP or autosomal recessive RP and in 1824 ethnically matched controls. Patients with 2 BBS1 variants underwent extensive clinical and ophthalmologic assessment. RESULTS: In an RP proband who did not fulfill the clinical criteria for BBS, we identified a large homozygous region encompassing the BBS1 gene, which carried the p.M390R variant. In addition, this variant was detected homozygously in 10 RP patients and 1 control, compound heterozygously in 3 patients, and heterozygously in 5 patients and 6 controls. The 14 patients with 2 BBS1 variants showed the entire clinical spectrum, from nonsyndromic RP to full-blown BBS. In 8 of 14 patients, visual acuity was significantly reduced. In patients with electroretinographic responses, a rod-cone pattern of photoreceptor degeneration was observed. CONCLUSIONS: Variants in BBS1 are significantly associated with nonsyndromic autosomal recessive RP and relatively mild forms of BBS. As exemplified in this study by the identification of a homozygous p.M390R variant in a control individual and in unaffected parents of BBS patients in other studies, cis - or trans -acting modifiers may influence the disease phenotype. CLINICAL RELEVANCE: It is important to monitor patients with an early diagnosis of mild BBS phenotypes for possible life-threatening conditions.

Frequency, genotype, and clinical spectrum of best vitelliform macular dystrophy: data from a national center in Denmark.

PURPOSE: To estimate the prevalence, genotype, and clinical spectrum of Best vitelliform macular dystrophy (Best disease). DESIGN: Retrospective epidemiologic and clinical and molecular genetic observational study. METHODS: setting: National referral center. participants: Forty-five individuals diagnosed with Best disease. observation procedures: Retrospective review of patients diagnosed according to clinical findings and sequencing of BEST1. Patients with recently established molecular genetic diagnosis were followed up including multifocal electroretinography (mfERG), spectral-domain optical coherence tomography (SD-OCT), and fundus autofluorescence (FAF) imaging. main outcome measures:BEST1 mutations, SD-OCT and FAF findings, mfERG amplitudes, prevalence estimate of Best disease. RESULTS: BEST1 mutations described previously in Danish patients with Best disease are reviewed. In addition, we identified a further 8 families and 1 sporadic case, in whom 6 BEST1 missense mutations were found, 4 of which are novel. The mutation c.904G>T (p.Asp302Asn) was identified in members of 4 unrelated families. Structural alterations ranged from precipitate-like alterations at the level of the photoreceptor outer segments (OS) to choroidal neovascularization. The extent of the former correlated with the reduction of retinal function. A prevalence estimate of Best disease in Denmark based on the number of diagnosed cases was 1.5 per 100 000 individuals. CONCLUSIONS: Our data expand the mutation spectrum of BEST1 in patients with Best disease. Alterations of the OS overlying lesions with subretinal fluid are similar to those seen in central serous retinopathy and may indicate impaired turnover of OS. Our frequency estimate confirms that Best disease is one of the most common causes of early macular degeneration.

A tapetal-like fundus reflex in a healthy male: evidence against a role in the pathophysiology of retinal degeneration?

PURPOSE: To report on the retinal function and structure in a 37-year-old male who presented with a tapetal-like reflex (TLR) indistinguishable from that seen in female carriers of X-linked retinitis pigmentosa (XLRP). METHODS: Clinical examination included dark adaptometry, full-field electroretinography (ERG), multifocal ERG, optical coherence tomography, and fundus autofluorescence photography. Molecular genetic testing included screening for known mutations in autosomal dominant, autosomal recessive, and X linked retinitis pigmentosa (RP) genes with a commercially available chip, and sequencing analysis of retinitis pigmentosa GTPase regulator (RPGR)-open reading frame 15 (ORF15). RESULTS: Fundus examination revealed a bilateral TLR, which is typical of female carriers of XLRP. Imaging studies and electrophysiological testing was unremarkable, except for a significant increase in full-field ERG amplitudes after prolonged dark adaptation as compared to after standard dark adaptation. Mutation screening was negative. CONCLUSIONS: TLR was found for the first time, to the best of our knowledge, in a male subject. There were no definitive signs of retinal degeneration, suggesting that this reflex in itself is not necessarily a precursor of the retinal degeneration that can be seen in female carriers of XLRP.

Enhanced S-cone function with preserved rod function: a new clinical phenotype.

PURPOSE: To describe the clinical findings and genetic analysis in two brothers having a novel retinal disease characterized by an enhanced S-cone phenotype with normal rod function. METHODS: Both patients underwent complete ophthalmologic examinations, including fundus photography, electroretinography (ERG), fluorescein angiography and optical coherence tomography (OCT). Mutation analysis of the following candidate genes was performed: nuclear receptor subfamily 2 group E member 3 (NR2E3), neural retina leucine zipper (NRL), nuclear receptor subfamily 1 group D member 1 (NR1D1), and thyroid hormone receptor beta (THRB). RESULTS: Spectral photopic ERG responses demonstrated enhanced S-cone function in both patients. Their scotopic b-wave ERG amplitude responses, however, were within normal limits. Their scotopic a-wave amplitude responses were within the lower limit of normal. The a- and b-wave latencies were normal for one sibling and on the upper limit of normal for the other. Peripheral retinal findings were normal. OCT showed flattening of the macular curvature and thinning of the photoreceptor layer. Mutation analysis of NR2E3, NRL, NR1D1, and THRB genes was negative. CONCLUSIONS: We describe what appears to be a previously unidentified familial retinal phenotype with enhanced S-cone function and well preserved rod system function in contrast to the severely reduced rod function seen in the enhanced S-cone syndrome (ESCS). Genetic analysis of candidate genes did not reveal the cause of disease. We postulate that the disease might be caused by mutation of another, as yet unidentified gene, which encodes a protein that functions as a negative inhibitor of rod and S-cone development.

A homozygous frameshift mutation in BEST1 causes the classical form of Best disease in an autosomal recessive mode.

PURPOSE: Best disease is a monogenic macular degeneration caused mainly by heterozygous mutations in the BEST1 gene. The objective was to characterize the molecular and clinical features of patients with the classical form of Best disease that is inherited in an autosomal recessive mode. METHODS: Clinical evaluation included detailed family history, a full ophthalmologic examination, electro-oculography (EOG), electroretinography, color vision testing, and ocular imaging. Mutation analysis was performed by direct sequencing of PCR products. RESULTS: Two young siblings affected by Best disease, as confirmed by funduscopy, retinal imaging, and electrophysiologic assessment, were recruited for the study. Molecular analysis revealed a novel homozygous deletion (c.1415delT) in the BEST1 gene leading to a frameshift followed by a premature stop codon, which cosegregated with the disease in a recessive mode. The heterozygous parents had normal visual acuity, retinal appearance, and function. The two heterozygous grandmothers, ages 61 and 62, also had normal Arden ratios on EOG, but one of them manifested moderate-to-severe dry non-neovascular age-related macular degeneration. CONCLUSIONS: We show here that the typical vitelliform phenotype of Best disease, usually transmitted in an autosomal dominant fashion, can be inherited as an autosomal recessive disease due to homozygosity for a frameshift mutation.

A missense mutation in DHDDS, encoding dehydrodolichyl diphosphate synthase, is associated with autosomal-recessive retinitis pigmentosa in Ashkenazi Jews.

Retinitis pigmentosa (RP) is a heterogeneous group of inherited retinal degenerations caused by mutations in at least 50 genes. Using homozygosity mapping in Ashkenazi Jewish (AJ) patients with autosomal-recessive RP (arRP), we identified a shared 1.7 Mb homozygous region on chromosome 1p36.11. Sequence analysis revealed a founder homozygous missense mutation, c.124A>G (p.Lys42Glu), in the dehydrodolichyl diphosphate synthase gene (DHDDS) in 20 AJ patients with RP of 15 unrelated families. The mutation was not identified in an additional set of 109 AJ patients with RP, in 20 AJ patients with other inherited retinal diseases, or in 70 patients with retinal degeneration of other ethnic origins. The mutation was found heterozygously in 1 out of 322 ethnically matched normal control individuals. RT-PCR analysis in 21 human tissues revealed ubiquitous expression of DHDDS. Immunohistochemical analysis of the human retina with anti-DHDDS antibodies revealed intense labeling of the cone and rod photoreceptor inner segments. Clinical manifestations of patients who are homozygous for the c.124A>G mutation were within the spectrum associated with arRP. Most patients had symptoms of night and peripheral vision loss, nondetectable electroretinographic responses, constriction of visual fields, and funduscopic hallmarks of retinal degeneration. DHDDS is a key enzyme in the pathway of dolichol, which plays an important role in N-glycosylation of many glycoproteins, including rhodopsin. Our results support a pivotal role of DHDDS in retinal function and may allow for new therapeutic interventions for RP.

Homozygosity mapping reveals null mutations in FAM161A as a cause of autosomal-recessive retinitis pigmentosa.

Retinitis pigmentosa (RP) is a heterogeneous group of inherited retinal degenerations caused by mutations in at least 45 genes. Using homozygosity mapping, we identified a ∼4 Mb homozygous region on chromosome 2p15 in patients with autosomal-recessive RP (arRP). This region partially overlaps with RP28, a previously identified arRP locus. Sequence analysis of 12 candidate genes revealed three null mutations in FAM161A in 20 families. RT-PCR analysis in 21 human tissues revealed high levels of FAM161A expression in the retina and lower levels in the brain and testis. In the human retina, we identified two alternatively spliced transcripts with an intact open reading frame, the major one lacking a highly conserved exon. During mouse embryonic development, low levels of Fam161a transcripts were detected throughout the optic cup. After birth, Fam161a expression was elevated and confined to the photoreceptor layer. FAM161A encodes a protein of unknown function that is moderately conserved in mammals. Clinical manifestations of patients with FAM161A mutations varied but were largely within the spectrum associated with arRP. On funduscopy, pallor of the optic discs and attenuation of blood vessels were common, but bone-spicule-like pigmentation was often mild or lacking. Most patients had nonrecordable electroretinographic responses and constriction of visual fields upon diagnosis. Our data suggest a pivotal role for FAM161A in photoreceptors and reveal that FAM161A loss-of-function mutations are a major cause of arRP, accounting for ∼12% of arRP families in our cohort of patients from Israel and the Palestinian territories.

Variable retinal phenotypes caused by mutations in the X-linked photopigment gene array.

PURPOSE: To examine the involvement of the long (L) and middle (M) wavelength-sensitive cone opsin genes in cone-dominated phenotypes. METHODS: Clinical and molecular analyses included family history, color vision testing, full-field electroretinography (ERG), linkage analysis, and mutation detection. RESULTS: Eighteen families were recruited that had X-linked retinal disease characterized by cone impairment in which affected males usually had nystagmus, reduced visual acuity, normal to subnormal rod ERG, and reduced or extinguished cone ERG responses. A search for mutations in the L-M pigment gene array revealed disease-causing mutations in six families. In two of them, novel mutations were identified: a large deletion affecting both opsin genes and a single L opsin gene harboring a likely pathogenic mutation, p.Val120Met. A third family carried a single hybrid gene with the p.Cys203Arg mutation. Patients from the three remaining families carried a single opsin gene harboring two similar rare haplotypes. Although the phenotype of members in one of the families was compatible with blue cone monochromacy (BCM), patients from the two other families, who shared an identical haplotype, had only reduced or even normal full-field cone ERGs, but maculopathy was evident. CONCLUSIONS: Novel and known mutations affecting the L-M opsin gene array were identified in families with X-linked cone-dominated phenotypes. The results show that different mutations in this gene array can cause a variety of phenotypes, including BCM, cone dystrophy, and maculopathy. Males with X-linked cone-dominated diseases should be routinely analyzed for mutations in the L-M opsin gene array.

Prenatal molecular diagnosis of oculocutaneous albinism (OCA) in a large cohort of Israeli families.

OBJECTIVES: To present our accumulated data on prenatal molecular diagnosis of oculocutaneous albinism (OCA) in a large cohort of Israeli albino families. METHODS: Albinism consists of variable phenotypes, but only families with predicted severely handicapped albino offspring, who declared their wish to terminate a pregnancy of such a fetus, are eligible for prenatal testing. Prenatal testing is not offered otherwise. Following detailed genetic investigation and counseling, molecular prenatal testing was performed using the combination of mutation screening, direct sequencing, and haplotype analysis. RESULTS: A total of 55 prenatal tests were performed in 37 families; in 26 families the propositus was the child, and in 11, a parent or a close relative. In 32 families tyrosinase (TYR) mutations were diagnosed. In 5 families a P gene mutation was detected. Twelve albino fetuses were diagnosed. Following further genetic counseling, all couples elected to terminate the pregnancy. Three additional pregnancies were terminated for other reasons. CONCLUSIONS: Families with increased risk for an albino child with severe visual handicap, seek premarital and prenatal genetic counseling and testing, for the prevention of affected offspring. Our combined methods of molecular genetic testing enable a nationwide approach for prevention of albinism. The same paradigm can be applied to other populations affected with albinism.

Homozygosity for a novel ABCA4 founder splicing mutation is associated with progressive and severe Stargardt-like disease.

PURPOSE: To clinically characterize and genetically analyze members of six families who reside in the same village and manifest a rare form of retinal degeneration. METHODS: Ophthalmic evaluation included a full clinical examination, perimetry, color vision testing, and electroretinography. Genomic DNA was screened for ABCA4 mutations with the use of microarray analysis and direct sequencing. RNA analysis was performed with RT-PCR and sequencing. RESULTS: The authors recruited 15 patients with a unique retinal disease who are members of six highly consanguineous Arab-Muslim families from a single village. During early stages of disease, funduscopic and angiographic findings as well as retinal function resemble those of Stargardt disease. However, later in life, severe, widespread cone-rod degeneration ensues. Marked progressive involvement of the retinal periphery distinguishes this phenotype from classic Stargardt disease. Genetic analysis of ABCA4 revealed two novel deletions, p.Cys1150del and c.4254-15del23. One patient, who was a compound heterozygote, manifested typical Stargardt disease. The remaining 14 patients were homozygote for the c.4254- 15del23 intronic deletion and had the progressive form of disease. We identified an identical ABCA4 haplotype in all alleles carrying this mutation, indicating a founder mutation. Detailed RT-PCR analysis in normal retina and lymphoblastoid cells revealed expression of the full-length ABCA4 transcript and three novel transcripts produced by alternative splicing. The full-length ABCA4 transcript, however, could not be detected in lymphoblastoid cells of affected homozygote patients. CONCLUSIONS: These results expand the genotype-phenotype correlation of ABCA4, showing that homozygosity for the novel c.4254-15del23 splicing mutation is associated with a severe progressive form of disease.

A non-ancestral RPGR missense mutation in families with either recessive or semi-dominant X-linked retinitis pigmentosa.

Most X-linked diseases show a recessive pattern of inheritance in which female carriers are unaffected. In X-linked retinitis pigmentosa (XLRP), however, both recessive and semi-dominant inheritance patterns have been reported. We identified an Israeli family with semi-dominant XLRP due to a missense mutation (p.G275S) in the RPGR gene. The mutation was previously reported in two Danish families with recessive XLRP. Obligate carriers from the two Danish families had no visual complaints and normal to slightly reduced retinal function, while those from the Israeli family suffered from high myopia, low visual acuity, constricted visual fields, and severely reduced electroretinogram (ERG) amplitudes. The disease-related RPGR haplotype of the Israeli family was found to be different from the one found in the two Danish families, indicating that the mutation arose twice independently on different X-chromosome backgrounds. A series of genetic analyses excluded skewed X-inactivation pattern, chromosomal abnormalities, distorted RPGR expression level, and mutations in candidate genes as the cause for the differences in disease severity of female carriers. To the best of our knowledge, this is the first detailed analysis of an identical mutation causing either a recessive or a semi-dominant X-linked pattern of disease in different families. Our results indicate that an additional gene (or genes), linked to RPGR, modulate disease expression in severely affected carriers. These may be related to the high myopia concomitantly found in affected carriers from the Israeli family.