Phenotyping and genotyping inherited retinal diseases: Molecular genetics, clinical and imaging features, and therapeutics of macular dystrophies, cone and cone-rod dystrophies, rod-cone dystrophies, Leber congenital amaurosis, and cone dysfunction syndromes

Inherited retinal diseases (IRD) are a leading cause of blindness in the working age population and in children. The scope of this review is to familiarise clinicians and scientists with the current landscape of molecular genetics, clinical phenotype, retinal imaging and therapeutic prospects/completed trials in IRD. Herein we present in a comprehensive and concise manner: (i) macular dystrophies (Stargardt disease (ABCA4), X-linked retinoschisis (RS1), Best disease (BEST1), PRPH2-associated pattern dystrophy, Sorsby fundus dystrophy (TIMP3), and autosomal dominant drusen (EFEMP1)), (ii) cone and cone-rod dystrophies (GUCA1A, PRPH2, ABCA4, KCNV2 and RPGR), (iii) predominant rod or rod-cone dystrophies (retinitis pigmentosa, enhanced S-Cone syndrome (NR2E3), Bietti crystalline corneoretinal dystrophy (CYP4V2)), (iv) Leber congenital amaurosis/early-onset severe retinal dystrophy (GUCY2D, CEP290, CRB1, RDH12, RPE65, TULP1, AIPL1 and NMNAT1), (v) cone dysfunction syndromes (achromatopsia (CNGA3, CNGB3, PDE6C, PDE6H, GNAT2, ATF6), X-linked cone dysfunction with myopia and dichromacy (Bornholm Eye disease; OPN1LW/OPN1MW array), oligocone trichromacy, and blue-cone monochromatism (OPN1LW/OPN1MW array)). Whilst we use the aforementioned classical phenotypic groupings, a key feature of IRD is that it is characterised by tremendous heterogeneity and variable expressivity, with several of the above genes associated with a range of phenotypes.

Placental cytochrome P450 methylomes in infants exposed to prenatal opioids: exploring the effects of neonatal opioid withdrawal syndrome on health horizons

Background: Neonatal opioid withdrawal syndrome (NOWS), arises due to increased opioid use during pregnancy. Cytochrome P450 (CYP) enzymes play a pivotal role in metabolizing a wide range of substances in the human body, including opioids, other drugs, toxins, and endogenous compounds. The association between CYP gene methylation and opioid effects is unexplored and it could offer promising insights. Objective: To investigate the impact of prenatal opioid exposure on disrupted CYPs in infants and their anticipated long-term clinical implications. Study Design: DNA methylation levels of CYP genes were analyzed in a cohort of 96 placental tissues using Illumina Infinium MethylationEPIC (850 k) BeadChips. This involved three groups of placental tissues: 32 from mothers with infants exposed to opioids prenatally requiring pharmacologic treatment for NOWS, 32 from mothers with prenatally opioid-exposed infants not needing NOWS treatment, and 32 from unexposed control mothers. Results: The study identified 20 significantly differentially methylated CpG sites associated with 17 distinct CYP genes, with 14 CpGs showing reduced methylation across 14 genes (CYP19A1, CYP1A2, CYP4V2, CYP1B1, CYP24A1, CYP26B1, CYP26C1, CYP2C18, CYP2C9, CYP2U1, CYP39A1, CYP2R1, CYP4Z1, CYP2D7P1 and), while 8 exhibited hypermethylation (CYP51A1, CYP26B1, CYP2R1, CYP2U1, CYP4X1, CYP1A2, CYP2W1, and CYP4V2). Genes such as CYP1A2, CYP26B1, CYP2R1, CYP2U1, and CYP4V2 exhibited both increased and decreased methylation. These genes are crucial for metabolizing eicosanoids, fatty acids, drugs, and diverse substances. Conclusion: The study identified profound methylation changes in multiple CYP genes in the placental tissues relevant to NOWS. This suggests that disruption of DNA methylation patterns in CYP transcripts might play a role in NOWS and may serve as valuable biomarkers, suggesting a future pathway for personalized treatment. Further research is needed to confirm these findings and explore their potential for diagnosis and treatment.

Clinical and genetic characterization of a large cohort of Chinese patients with Bietti crystalline retinopathy

PURPOSE

To investigate the clinical and genetic characteristics for a large cohort of Chinese patients with Bietti crystalline retinopathy (BCR).

METHODS

A total of 208 Chinese BCR patients from 175 families were recruited. Comprehensive clinical evaluations and genetic analysis were performed. Genotype-phenotype correlations were evaluated through statistical analysis.

RESULTS

The patients' median age was 37 years (range, 20-76 years). The median best corrected visual acuity (BCVA) was 0.8 LogMAR unit (range, 2.8 to -0.12). A significant decline of BCVA was revealed in patients over 40 years old (P<0.001). Two clinical types were observed: peripheral type (type P) and central type (type C). Significantly more type C patients had a worse central visual acuity, but a more preserved retinal function (P<0.05). Molecular screening detected biallelic CYP4V2 pathogenic variants in 98.3% (172/175) of the families, including 19 novel ones. The most frequent pathogenic variant was c.802-8_810del17insGC, with the allele frequency of 55.7% (195/350), followed by c.992A>C (28/350, 8%) and c.1091-2A>G (23/350, 6.6%). BCR patients with one c.802-8_810del17insGC and one truncating variant (IVS6-8/Tru) had BCVA>1.3 LogMAR unit (Snellen equivalent<20/400) at a younger age than those with homozygous c.802-8_810del17insGC variants (homo IVS6-8) (P=0.031).

CONCLUSIONS

BCR patients preserved relatively good vision before 40 years old. Two distinct clinical types of BCR were observed. BCR patients with IVS6-8/Tru had an earlier decline in visual acuity than those with homo IVS6-8. Our findings enhance the knowledge of BCR and will be helpful in patient selection for gene therapy.

CYP4V2 rs56413992 C > T was associated with the risk of coronary heart disease in the Chinese Han population: a case-control study

PURPOSE

The research aimed to detect the association between single nucleotide polymorphisms (SNPs) in CYP4V2 gene and coronary heart disease (CHD) risk.

METHODS

This case-control study included 487 CHD subjects and 487 healthy individuals. Logistic regression was performed to analyze the connection between five SNPs in CYP4V2 (rs1398007, rs13146272, rs3736455, rs1053094, and rs56413992) and CHD risk, and odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to evaluate the connection.

RESULTS

As a result, we found that rs56413992 T allele (OR = 1.36, 95% CI = 1.09-1.70, p = 0.007) and CT genotype (OR = 1.40, 95% CI = 1.06-1.83, p = 0.017) were significantly associated with an increased risk of CHD in the overall analysis. Precisely, rs56413992 was linked to an elevated risk of CHD in people aged > 60, males, smokers and drinkers. The study also indicated that rs1398007 was linked to an increased CHD risk in drinkers. In addition, rs1053094 was correlated with a decreased risk of CHD complicated with diabetes mellitus (DM), and rs1398007 was correlated with a decreased risk of CHD complicated with hypertension (HTN).

CONCLUSION

This study was the first to experimentally demonstrate that CYP4V2 rs56413992 was associated with the risk of CHD, which will provide a certain reference for revealing the pathogenesis of CHD.

CYP4V2 fatty acid omega hydroxylase, a druggable target for the treatment of metabolic associated fatty liver disease (MAFLD)

Fatty acids are essential in maintaining cellular homeostasis by providing lipids for energy production, cell membrane integrity, protein modification, and the structural demands of proliferating cells. Fatty acids and their derivatives are critical bioactive signaling molecules that influence many cellular processes, including metabolism, cell survival, proliferation, migration, angiogenesis, and cell barrier function. The CYP4 Omega hydroxylase gene family hydroxylate various short, medium, long, and very-long-chain saturated, unsaturated and polyunsaturated fatty acids. Selective members of the CYP4 family metabolize vitamins and biochemicals with long alkyl side chains and bioactive prostaglandins, leukotrienes, and arachidonic acids. It is uncertain of the physiological role of different members of the CYP4 omega hydroxylase gene family in the metabolic control of physiological and pathological processes in the liver. CYP4V2 is a unique member of the CYP4 family. CYP4V2 inactivation in retinal pigment epithelial cells leads to cholesterol accumulation and Bietti's Crystalline Dystrophy (BCD) pathogenesis. This commentary provides information on the role CYP4V2 has in metabolic syndrome and nonalcoholic fatty liver disease progression. This is accomplished by identifying its role in BCD, its control of cholesterol synthesis and lipid droplet formation in C. elegans, and the putative function in cardiovascular disease and gastrointestinal/hepatic pathologies.

Crystals deposits in the anterior and posterior lens cortex in Bietti corneo-retinal dystrophy

BACKGROUND

Whereas crystals deposit in the retina, the cornea and limbus in Bietty corneo-retinal dystrophy (BCD) is now well established and documented, only two published cases report their findings in the lens and no cases deep in the lens cortex.

MATERIAL AND METHODS

Four consecutive adult patients from three different unrelated families presenting lens crystals associated with advanced genetically confirmed BCD were enrolled with advanced disease and long follow up (>12 years). Demographics, visual acuity, slit lamp biomicroscopy, lens and posterior pole photography, optical coherence tomography (OCT), autofluorescence, and screening for CYP4V2 type of mutation were performed. The setting was Jules Gonin Eye Hospital, Switzerland, between 1.1 2013 and 1.11. 2019.

RESULTS

All patients were European women. The ages ranged from 40 to 81 years. Best Snellen visual acuity ranged from light perception to 1.0. All patients presented with limbus and retinal crystals deposit that disappeared over time and the development of severe chorioretinal atrophy. With long-term follow up, multiple crystal-like deposits appeared in the anterior, posterior lens capsule and cortex. All patients, but one, had homozygous or compound heterozygous mutations in CYP4V2 gene.

CONCLUSIONS

To the best of our knowledge, there are no published cases of crystal deposits in the cortex of the lens of patients diagnosed with BCD associated with CYP4V2 gene mutation. This could be a feature of advanced BCD, and their presence in the lens cortex questions the hypothesis of floating deposits from posterior pole although their exact etiology remains to be determined.

New compound heterozygous CYP4V2 mutations in bietti crystalline corneoretinal dystrophy

Bietti crystalline corneoretinal dystrophy (BCD) is an autosomal recessive retinal dystrophy which is caused by the mutations of CYP4V2, usually progressing to legal blindness by the 5th or 6th decade of life. Here we identified CYP4V2 compound heterozygous mutations in two female siblings with BCD without subjective symptoms. After 381 pathogenic genes related to retinal diseases were screened by targeted sequence capture array techniques and confirmed by Sanger sequencing, two compound heterozygous mutations in CYP4V2 were found. One was missense mutation c.1198C>T (p.R400C) and the other was frameshift mutation c.802-8_810delinsGC (p.V268_E329del). Optical coherence tomography (OCT) showed that the ellipsoid zone was absent in the macular regions and electroretinogram (ERG) revealed poor cone and rod responses. Compound heterozygous mutations in CYP4V2 are related to the BCD. Our study expands our knowledge of heterogenic phenotypes and genotypes through genetic diagnosis of the BCD patients.

Genotype and Long-term Clinical Course of Bietti Crystalline Dystrophy in Korean and Japanese Patients

PURPOSE

To investigate the genotype and long-term clinical phenotype of patients with Bietti crystalline dystrophy (BCD) in Korea and Japan.

DESIGN

Retrospective case series.

PARTICIPANTS

We analyzed 62 patients with clinical features of BCD who harbor pathogenic biallelic CYP4V2 variants in their homozygote or compound heterozygote.

METHODS

Data were collected from patient charts, including age, best-corrected visual acuity (BCVA), Goldmann perimetry results, fundus photography, OCT findings, fundus autofluorescence results, and electroretinography findings. We compared the clinical course of the patients with homozygous c.802-8_810de117insGC [exon7del], the most common mutation in the East Asian population, with those of the patients with other genotypes.

MAIN OUTCOME MEASURES

Best-corrected visual acuity, visual field (VF), and their changes during follow-up.

RESULTS

The mean age at the first visit was 55.2 years, with a mean follow-up of 7.1 years. The mean BCVAs at the first and last visits were 0.28 logarithm of the minimum angle of resolution (logMAR) and 0.89 logMAR, respectively. In genetic testing, c.802-8_810de117insGC was detected in 86 of 124 alleles of the patients, and 36 patients were homozygous for this mutation. The age, BCVA, VF area, central foveal thickness, and abnormal hypoautofluorescent area at either the first or last visit were not different between the exon7del homozygotes and the others. The mean BCVA changes per year were 0.089 logMAR in the exon7del homozygotes and 0.089 logMAR in the others. An age- and gender-adjusted linear regression analysis showed no association between the exon7del homozygote status and the rate of vision loss. Characteristic crystalline deposits in the posterior pole were generally observed in younger patients and disappeared over time along with progressive retinochoroidal atrophy.

CONCLUSIONS

Patients with BCD and a homozygote for c.802-8_810de117insGC accounted for more than 50% of this cohort of Korean and Japanese patients, and the clinical effect of this deleterious variant was not severe in the spectrum of CYP4V2 retinopathy.

Identification and functional characterization of CYP4V2 genetic variants exhibiting decreased activity of lauric acid metabolism

The objectives of the present study were to identify CYP4V2 genetic variants and characterize their functional consequences. A total of 26CYP4V2 genetic variants were identified, including seven novel variants in 60 randomly selected healthy subjects. Six protein-coding variants were studied, including three novel variants (L22V, R287T, and G410C) and three previously reported variants (R36S, Q259K, and H331P). The cDNA sequences encoding each amino acid variant and the wild-type CYP4V2 protein were cloned into the pcDNA/PDEST40 expression vector and transfected into eukaryotic 293T cells for overexpression of the CYP4V2 coding variants. CYP4V2 H331P and CYP4V2 G410C exhibited significant decreases in activity for lauric acid oxidation (20-30% of wild-type activity), when compared to the wildtype, which was correlated with low expression of CYP4V2 H331P and G410C substituted proteins. The other four CYP4V2 amino variants were comparable to wild-type CYP4V2 for lauric acid metabolism. The CYP4V2 H331P and G410C substitutions were predicted to cause a structural change through in silico analysis. In conclusion, the present study provides functional information about CYP4V2 genetic variants. These findings will be valuable for interpreting individual variations in phenotypes associated with CYP4V2 function in the clinical setting.

Presence of corneal crystals confirms an unusual presentation of Bietti's retinal dystrophy

Background: Bietti crystalline corneoretinal dystrophy (BCD) (OMIM 210370) is a rare autosomal recessive retinal dystrophy typically characterized by multiple intraretinal crystals over the posterior pole of the retina. Degeneration of the retina and sclerosis of the choroidal vessels results in progressive night blindness and central visual field loss.Methods: Detailed ophthalmic and genetic testing of the patient and his father were performed.Results: We report on a 41-year-old male patient with advanced chorioretinal dystrophy at the posterior pole extending into the peripheral retina. His sister and his father were similarly affected with nyctalopia and decreased visual acuity, although his father had a milder phenotype of a typical macular dystrophy. On close slit-lamp examination, however, both patient and his father had multiple yellow-white crystals in the peripheral cornea. Corneal findings and consanguinity of the patient's parents lead to suspicion of BCD. Molecular genetic results of the patient and his father showed homozygous for CYP4V2, c. 197T>G p.(Met66Arg) confirming the diagnosis of BCD.Conclusions: The patient's pedigree shows pseudodominant inheritance due to consanguineous parents. However, careful examination of the corneal findings strengthened the clinical suspicion of BCD, facilitating the molecular genetic confirmation of this autosomal recessive disease.

CYP4V2 mutation screening in an Iranian Bietti crystalline dystrophy pedigree and evidence for clustering of CYP4V2 mutations

Purpose

To report the genetic analysis of an Iranian Bietti crystalline dystrophy (BCD)-affected family, and to review previously reported mutations in the gene and assess the distribution of affected amino acids in the encoded protein.

Methods

The eleven exons of CYP4V2 were sequenced in the DNA of the proband of the Iranian BCD family. The putative disease-causing variation was screened in all affected and non-affected members. BCD causing CYP4V2 mutations previously reported in the literature were compiled, and positions of amino acids affected by nonsense and missense mutations were mapped onto the primary structure of the CYP4V2 protein.

Results

C.1219G > T in CYP4V2 that causes p.Glu407* was identified as cause of BCD in the Iranian family. The mutation segregated with disease status. Clinical presentations were similar among affected members, except that one patient presented with retinal macular hole. Twelve nonsense and 47 missense mutations in CYP4V2 were compiled. Inspection of distribution of amino acids affected by the mutations suggested non-random distribution and clustering of affected amino acids in nine regions of the protein, including regions that contain the heme binding site, the metal binding site, and a region between these binding sites. The most C-terminus proximal nonsense mutation affected position 482.

Conclusions

This study presents results of the genetic analysis of an Iranian BCD family. Protein regions affected by mutations within the nine mutation clusters include regions well conserved among orthologous proteins and human CYP4 proteins, some of which are associated with known functions. The findings may serve to identify reasonable candidate gene region targets for gene editing therapy approaches.

Identification of novel CYP4V2 genotypes associated with Bietti crystalline dystrophy and atypical anterior segment phenotypes in Spanish patients

PURPOSE

To identify the spectrum of disease-causing CYP4V2 variants in Spanish patients with clinically diagnosed Bietti crystalline dystrophy (BCD) over an 8-year period and to analyse the phenotype-genotype correlation of the identified variants.

METHODS

Four unrelated Spanish probands with a clinical diagnosis of BCD were recruited. Ophthalmological examination included visual acuity (VA), slit lamp examination, in vivo corneal confocal microscopy, funduscopy and fluoresceinic angiography. Genomic DNA was obtained from blood samples, and the exons and flanking intron sequences of the CYP4V2 gene were screened by Sanger sequencing. Family members of the patients with mutations in CYP4V2 gene were subsequently studied.

RESULTS

Clinical examination revealed retinal and corneal patterns compatible with BCD in all the participants. We identified a total of six CYP4V2 variants among the four carriers. As far as we know, the variant p.(Trp244Cysfs*33) has not previously been reported. This variant along with p.(Ala204Thr) and p.(Arg443Trp) were combined in three novel pathogenic phenotypes that share the presence of bilateral limbic glistening deposits, severe retinal damage and visual impairment and a fast rate of progression of the disease.

CONCLUSION

To the best of our knowledge, this study represents the largest effort to determine the genetic alterations underlying BCD in Spain to date. Our results show that analysis of CYP4V2 variants is required for a reliable diagnosis of BCD. We report a high prevalence of anterior segment changes in this Spanish BCD cohort, which we consider representative of the Spanish patients.

Association of the CYP4V2 polymorphism rs13146272 with venous thromboembolism in a Chinese population

Genome-wide association studies have identified the CYP4V2 polymorphism (rs13146272) as a risk factor associated with venous thromboembolism (VTE). However, due to the small sample size and variance in genetic analysis models, the relationship between VTE and rs13146272 remains unclear. Here, we performed a case-control study to analyse the associations between rs13146272 and VTE in a Chinese population and to compare the differences among various ethnicities. In this study, 226 VTE patients and 205 healthy controls were recruited, and the allele frequency of variant rs13146272 was analysed by a MassARRAY SNP genotyping assay. In addition, 9 case-control cohorts from 5 studies involving 6667 VTE-affected individuals and 8716 control subjects were included in this meta-analysis. Pooled ORs and 95% CIs were calculated to assess the association between rs13146272 and VTE by using different genetic models. Our case-control study results showed that there was no significant association between VTE and rs13146272 under the additive model (OR = 0.92, 95% CIs: 0.70-1.21, p = 0.55) in this Chinese population. However, the results of the meta-analysis performed by merging all cohorts showed that rs13146272 was significantly associated with VTE under the additive model, recessive model and dominant model. In the additive and recessive models, the association reached the threshold for genome-wide significance (p < 5.0e^-08). In conclusion, our pooled systematic study results indicated that individuals with the A allele had a higher risk of developing VTE than those with the C allele of the rs13146272 variant, but the risk was inconsistent among different ethnicities. Further validation of this association with larger sample sizes and multiple ethnicities is warranted.

Expression of CYP4V2 in human THP1 macrophages and its transcriptional regulation by peroxisome proliferator-activated receptor gamma

Because macrophages respond to a variety of pathological and pharmacological reagents, understanding the role of P450s in macrophages is important for therapeutic intervention. There has been a lack of research on CYP4 in macrophages, but fatty acid accumulation and lipid trafficking in macrophages have been suggested to be a main cause of atherosclerosis. All human CYP4 genes (n=12) were screened in THP1 macrophages by gene-specific reverse transcriptase-polymerase chain reaction (RT-PCR). Only CYP4V2 exhibited strong expression of both mRNA and protein. Expression levels of both CYP4V2 mRNA and protein were significantly reduced after treatment with peroxisome proliferator-activated receptor gamma (PPARγ) antagonist GW9662. However, the expression levels of CYP4V2 were not changed by PPARα antagonist (GW6471) and liver X receptor alpha antagonist (22-S hydroxycholesterol). A metabolite of the CYP4V2 enzyme, 12-hydroxydodecanoic acid, was detected in THP1 macrophages, and this metabolite was significantly decreased after treatment with the PPARγ inhibitor GW9662 (>80% decreased, p<0.05). In summary, fatty acid metabolizing protein CYP4V2 was identified in human THP1 macrophages, and its expression was regulated by PPARγ. Further study is required to understand the role of CYP4V2 with regard to fat accumulation in the activated macrophage and atherosclerotic plaque development.

Longitudinal characterisation of function and structure of Bietti crystalline dystrophy: report on a novel homozygous mutation in CYP4V2

BACKGROUND

Bietti crystalline dystrophy (BCD) is a rare inherited disorder characterised by fine crystalline deposits in the corneal limbus and retinal posterior pole. In 2004, mutations in the CYP4V2 gene were identified as the cause of BCD. Here, we describe the report of a homozygous point mutation in a patient with BCD and provide detailed characterisation of functional and structural changes over 20 years.

METHODS

At regular intervals, the patient underwent repeat ophthalmic evaluations. DNA was extracted from buccal swabs, amplified by standard PCR and analysed for homology to the CYP4V2 sequence. Homology modelling was conducted using Iterative Threading ASSEmbly Refinement and molecular dynamics simulations using GROningen MAchine for Chemical Simulations.

RESULTS

The proband, a 47-year-old woman of German ancestry was diagnosed with crystalline retinopathy at age 25. Over the next 20 years, visual acuity and function gradually declined with progression of retinal pigment epithelium and choroidal atrophy. When first tested at 39 years of age, the multifocal electroretinogram (ERG) was markedly abnormal, more so for the right eye, whereas the full-field ERG was more symmetrical and lagged other measures of visual function. Gene sequencing showed a single C>T point mutation in exon 9 encoding a R400C amino acid change. Computational modelling suggests the mutation impairs function due to loss of a hydrogen bonding interaction with the propionate side chains of the haeme prosthetic group.

CONCLUSION

This is the first report of a homozygous R400C mutation in CYP4V2 with protein modelling showing high likelihood of enzyme dysfunction. The comprehensive long-term clinical follow-up provides insight into disease progression and highlights possible anti-inflammatory modulation of disease severity.

Detailed functional and structural phenotype of Bietti crystalline dystrophy associated with mutations in CYP4V2 complicated by choroidal neovascularization

PURPOSE

To describe in detail the phenotype of a patient with Bietti crystalline dystrophy (BCD) complicated by choroidal neovascularization (CNV) and the response to intravitreal Bevacizumab (Avastin^®; Genentech/Roche).

METHODS

A 34-year-old woman with BCD and mutations in CYP4V2 (c.802-8_806del13/p.H331P:c992A>C) underwent a complete ophthalmic examination, full-field flash electroretinography (ERG), kinetic and two-color dark-adapted perimetry, and dark-adaptometry. Imaging was performed with spectral domain optical coherence tomography (SD-OCT), near infrared (NIR) and short wavelength (SW) fundus autofluorescence (FAF), and fluorescein angiography (FA).

RESULTS

Best-corrected visual acuity (BCVA) was 20/20 and 20/60 for the right and left eye, respectively. There were corneal paralimbal crystal-like deposits. Kinetic fields were normal in the peripheral extent. Retinal crystals were most obvious on NIR-reflectance and corresponded with hyperreflectivities within the RPE on SD-OCT. There was parafoveal/perifoveal hypofluorescence on SW-FAF and NIR-FAF. Rod > cone sensitivity loss surrounded fixation and extended to ~10° of eccentricity corresponding to regions of photoreceptor outer segment-retinal pigmented epithelium (RPE) interdigitation abnormalities. The outer nuclear layer was normal in thickness. Recovery of sensitivity following a ~76% rhodopsin bleach was normal. ERGs were normal. A subretinal hemorrhage in the left eye co-localized with elevation of the RPE on SD-OCT and leakage on FA, suggestive of CNV. Three monthly intravitreal injections of Bevacizumab led to restoration of BCVA to baseline (20/25).

CONCLUSION

crystals in BCD were predominantly located within the RPE. Photoreceptor outer segment and apical RPE abnormalities underlie the relatively extensive retinal dysfunction observed in relatively early-stage BCD. Intravitreal Bevacizumab was effective in treating CNV in this setting.

Identification of CYP4V2 mutation in 36 Chinese families with Bietti crystalline corneoretinal dystrophy

Bietti crystalline corneoretinal dystrophy (BCD) is an inherited eye disease that is most common in the Chinese. It is caused by a mutation in the CYP4V2 gene. In this study, 43 Chinese BCD families were recruited; most patients manifested the characteristic phenotype of BCD, with 2 families initially misdiagnosed with retinitis pigmentosa. Five patients in our cohort presented with BCD and choroidal neovascularization (CNV), and 1 patient presented with typical BCD and abnormality in the terminals of both fingers and toes. A total of 17 pathogenic mutations involving 68 alleles were identified from 36 families using targeted exon sequencing and Sanger sequencing; we achieved a diagnostic rate of approximately 84%. Fifteen families were found to carry homozygous mutations, 17 families carried compound heterozygous mutations, and 4 families carried a single heterozygous mutation. Of the mutations identified, four variants c.802-8_810del17bpinsGC, c.802-8_810del17bpinsGT, c.992A > C (p.H331P), and c.1091-2A > G accounted for 71% of the mutations identified in CYP4V2. These mutations were hotspots in Chinese populations for BCD. Five among them were novel and predicted to be disease-causing, including c.65T > A (p.L22H), c.681_4delTGAG (p.S227Rfs*1), c.802-8_810del17bpinsGT, c.965_7delAAG (p.321delE), and c.994G > A (p.D332N). No apparent correlation between genotype and phenotype was identified. Our findings broaden the spectrum of CYP4V2 mutations that cause BCD and the phenotypic spectrum of the disease in Chinese families. These results will be useful for the genetic diagnosis of BCD, genetic consultation, and gene therapy in the future.

Novel insights into the molecular pathogenesis of CYP4V2-associated Bietti's retinal dystrophy

Bietti's crystalline dystrophy (BCD) is a rare, autosomal recessive retinal degenerative disease associated with mutations in CYP4V2. In this study, we describe the genetic and clinical findings in 19 unrelated BCD patients recruited from five international retinal dystrophy clinics. Patients underwent ophthalmic examinations and were screened for CYP4V2 mutations by Sanger sequencing and quantitative polymerase chain reaction (qPCR) copy number variation screening. Eight CYP4V2 mutations were found in 10/19 patients, including three patients in whom only monoallelic mutations were detected. Four novel mutations were identified: c.604G>A; p.(Glu202Lys), c.242C>G; p.(Thr81Arg), c.604+4A>G; p.(?), and c.1249dup; p.(Thr417Asnfs*2). In addition, we identified a heterozygous paternally inherited genomic deletion of at least 3.8 Mb, encompassing the complete CYP4V2 gene and several other genes, which is novel. Clinically, patients demonstrated phenotypic variability, predominantly showing choroidal sclerosis, attenuated vessels, and crystalline deposits of varying degrees of severity. To our knowledge, our study reports the first heterozygous CYP4V2 deletion and hence a novel mutational mechanism underlying BCD. Our results emphasize the importance of copy number screening in BCD. Finally, the identification of CYP4V2-negative patients with indistinguishable phenotypes from CYP4V2-positive patients might suggest the presence of mutations outside the coding regions of CYP4V2, or locus heterogeneity, which is unreported so far.

Generation and characterization of a murine model of Bietti crystalline dystrophy

PURPOSE

Bietti crystalline dystrophy (BCD) is a rare, autosomal recessive, progressive, degenerative eye disease caused by mutations in the CYP4V2 gene, for which no treatments are currently available. Cyp4v3 is the murine ortholog to CYP4V2, and to better understand the molecular pathogenesis of this disease we have established a Cyp4v3-null mouse line.

METHODS

Cyp4v3(-/-) mice were generated by homologous recombination in embryonic stem cells. Ocular morphologic characteristics were evaluated via fundus imaging, plasma lipid profiling, and histologic analysis via Oil Red O reactivity, hematoxylin and eosin staining, and transmission electron microscopy.

RESULTS

The Cyp4v3(-/-) mouse recapitulates the characteristic features of corneoretinal crystal accumulation and systemic dyslipidemia seen in BCD. The Cyp4v3(-/-) mice behave normally and are viable and fertile when maintained under specific pathogen-free (SPF) housing conditions.

CONCLUSIONS

Cyp4v3(-/-) mice represent a promising preclinical model that may be used to better understand the disease etiology and to evaluate pharmacotherapies for this devastating condition.

Ocular cytochrome P450s and transporters: roles in disease and endobiotic and xenobiotic disposition

Drug metabolism and transport processes in the liver, intestine and kidney that affect the pharmacokinetics and pharmacodynamics of therapeutic agents have been studied extensively. In contrast, comparatively little research has been conducted on these topics as they pertain to the eye. Recently, however, catalytic functions of ocular cytochrome P450 enzymes have gained increasing attention, in large part due to the roles of CYP1B1 and CYP4V2 variants in primary congenital glaucoma and Bietti's corneoretinal crystalline dystrophy, respectively. In this review, we discuss challenges to ophthalmic drug delivery, including Phase I drug metabolism and transport in the eye, and the role of three specific P450s, CYP4B1, CYP1B1 and CYP4V2 in ocular inflammation and genetically determined ocular disease.

Comparative modeling and molecular docking of orphan human CYP4V2 protein with fatty acid substrates: Insights into substrate specificity

Cytochromes P450 (CYPs) are a super family of heme-containing enzymes well-known for their monooxgenase reaction. There are 57 CYP isoenzymes found in human which exhibit specific physiological functions. Thirteen members of this super family are classified as “orphan” CYP because of their unknown enzymatic functions. CYP4V2 is found to be a potential drug target for Bietti crystalline corneoretinal dystrophy (BCD). However, three-dimensional structure, the active site topology and substrate binding modes of CYP4V2 remain unclear. In this study, the three-dimensional model of CYP4V2 was constructed using the homology modeling method. Four possible fatty acid substrates namely, caprylic, lauric, myrisitc and palmitic acids were optimized and evaluated for drug likeness using Lipinski's rule of five. Further, these substrates were docked into active sites of CYP4V2 and several key residues responsible for substrate binding were identified. These findings will be helpful for the structure-based drug design and detailed characterization of the biological roles of CYP4V2.