Identification and population history of CYP4V2 mutations in patients with Bietti crystalline corneoretinal dystrophy.

To identify known and novel CYP4V2 mutations in patients with Bietti crystalline cornea (BCD), expand the spectrum of CYP4V2 mutations, and characterize the population history of the c.802-8_810del17insGC mutation common in Asian populations, genomic DNA was isolated from peripheral blood samples from 58 unrelated patients with clinical diagnoses of BCD. Exons and flanking intronic regions of the CYP4V2 gene were dideoxy DNA sequenced. Nonpathogenic polymorphisms were excluded and known mutations were identified by sequencing 192 unaffected individuals from similar ethnic backgrounds and examination of online databases. The age of the c.802-8_810del17insGC mutation was estimated using three independent approaches. A total of 28 CYP4V2 mutations, 9 of which were novel, were detected in the 58 patients with BCD. These included 19 missense, 4 nonsense, 2 deletion, 2 splice site, and 1 insertion-deletion mutations. Two missense variants of uncertain significance were also detected. The age of the c.802-8_810del17insGC mutation was estimated to be 1040-8200 generations in the Chinese and 300-1100 generations in the Japanese populations. These results expand the mutation spectrum of CYP4V2, and provide insight into the origin of the c.802-8_810del17insGC mutation in the Chinese population and its transmission to the Japanese population.

Clinical and genetic features in Italian Bietti crystalline dystrophy patients.

AIM: The aim of the study was to describe the clinical and genetic features of 15 Italian patients with Bietti crystalline dystrophy (BCD). METHODS: All study participants underwent a complete ophthalmological examination, including standard electroretinogram (ERG), optical coherence tomography, microperimetry, autofluorescence and multifocal electroretinogram. The 11 exons of the CYP4V2 gene were sequenced. The effect of mutations on protein function was estimated by a combination of web based programs. RESULTS: 15 patients (eight women, 7 men, aged 29-60 years) with BCD were recruited into this study. Sequencing of CYP4V2 revealed nine sequence variants in four unrelated families and six isolated individuals with BCD. Seven of these variants were novel. Among the patients, even with the same genotype, considerable variability in phenotypic expression with different degrees of accumulation of the typical intraretinal crystalline deposits was detected. Moreover, we found that more than 50% of patients had recordable standard ERG responses and in two patients the responses were within normal limits after 20 years of symptom onset. CONCLUSIONS: In conclusion, we have reported seven new mutations and illustrated the large range of genotypic and phenotypic variability in BCD, highlighting the lack of a clear genotype-phenotype correlation and underlining the existence of less severe clinical manifestations, probably linked to relatively mild mutations.

Association of markers at chromosome 15q14 in Chinese patients with moderate to high myopia.

PURPOSE: To investigate the association of two reported regions on chromosome 15 with moderate to high myopia in two Chinese cohorts from southern China. METHODS: Two candidate regions on 15q14 and 15q25 were selected based on reported association with refractive error in the literature. Five single nucleotide polymorphisms (SNPs) were genotyped in 300 university students with high myopia at Guangzhou and 308 without refractive error, and 96 university students of Chaoshan Chinese origin with moderate to high myopia and 96 without refractive error. Genotypes were evaluated using direct sequencing and analyzed with chi-square, Armitage trend, and Mantel-Haenszel tests, and regression analysis. RESULTS: Of the five SNPs screened, alleles of rs634990 and rs524952 in the 15q14 region showed evidence of allelic association with moderate to high myopia (p<8.81×10(-7) and p<1.57×10(-6), respectively) in the Guangzhou group, but not in the Chaoshan group. The SNPs at 15q25 did not show significant association in any group. Association of rs634990 and rs524952 were still significant when both groups were combined into a single analysis (p<1.66×10(-6) and p<2.72×10(-6), respectively), and for genotypic, additive, and dominant models. CONCLUSIONS: This study confirms the significant association of rs634990 and rs524952 on chromosome 15q14 previously reported in European and Japanese populations with high myopia in the Guangzhou but not the Chaoshan Chinese populations, suggesting that genetic contributors to high myopia in the Chaoshan population might be different from other Chinese populations.

An atypical form of Bietti crystalline dystrophy.

PURPOSE: To describe clinical and functional features of a patient with Bietti crystalline dystrophy and atypical electroretinogram responses. METHODS: The patient underwent a thorough medical anamnesis, genetic counseling, peripheral blood draw for CYP4V2 gene analysis and electron microscopy, and a complete ophthalmological assessment including optical coherence tomography, indocyanine green angiography, microperimetry, full-field electroretinogram and multifocal electroretinogram. RESULTS: The most striking features of the retina were deposits of yellowish-white glistening crystals and focal lobular areas of choriocapillary atrophy at the posterior pole and midperiphery. The full-field electroretinogram was normal and the multifocal electroretinogram showed extinguished central recordings. Mutation analysis revealed a homozygous c. 332T>C p.I111T mutation in exon 3 of the CYP4V2 gene. Typical cytoplasmic inclusions containing crystalline-like structure and large degenerative lysosomes were seen on electron microscopy of peripheral leukocytes. CONCLUSION: Here we describe a patient with Bietti crystalline dystrophy with a CYP4V2 gene mutation and typical leukocyte inclusions who showed the classical retinal lesions but had a normal electroretinogram. This suggests the existence of less severe forms of BCD related to relatively mild CYP4V2 mutations.

The EPHA2 gene is associated with cataracts linked to chromosome 1p.

PURPOSE: Cataracts are a clinically and genetically heterogeneous disorder affecting the ocular lens, and the leading cause of treatable vision loss and blindness worldwide. Here we identify a novel gene linked with a rare autosomal dominant form of childhood cataracts segregating in a four generation pedigree, and further show that this gene is likely associated with much more common forms of age-related cataracts in a case-control cohort. METHODS: Genomic DNA was prepared from blood leukocytes, and genotyping was performed by means of single nucleotide polymorphism (SNP) markers, and short tandem repeat (STR) markers. Linkage analyses were performed with the GeneHunter and MLINK programs, and association analyses were performed with the Haploview and Exemplar programs. Mutation detection was achieved by PCR amplification of exons and di-deoxy cycle-sequencing. RESULTS: Genome-wide linkage analysis with SNP markers, identified a likely disease-haplotype interval on chromosome 1p (rs707455-[approximately 10 Mb]-rs477558). Linkage to chromosome 1p was confirmed using STR markers D1S2672 (LOD score [Z]=3.56, recombination distance [theta]=0), and D1S2697 (Z=2.92, theta=0). Mutation profiling of positional-candidate genes detected a heterozygous transversion (c.2842G>T) in exon 17 of the gene coding for Eph-receptor type-A2 (EPHA2) that cosegregated with the disease. This missense change was predicted to result in the non-conservative substitution of a tryptophan residue for a phylogenetically conserved glycine residue at codon 948 (p.G948W), within a conserved cytoplasmic domain of the receptor. Candidate gene association analysis further identified SNPs in the EPHA2 region of chromosome 1p that were suggestively associated with age-related cataracts (p=0.007 for cortical cataracts, and p=0.01 for cortical and/or nuclear cataracts). CONCLUSIONS: These data provide the first evidence that EPHA2, which functions in the Eph-ephrin bidirectional signaling pathway of mammalian cells, plays a vital role in maintaining lens transparency.

Mutations in KCNJ13 cause autosomal-dominant snowflake vitreoretinal degeneration.

Snowflake vitreoretinal degeneration (SVD, MIM 193230) is a developmental and progressive hereditary eye disorder that affects multiple tissues within the eye. Diagnostic features of SVD include fibrillar degeneration of the vitreous humor, early-onset cataract, minute crystalline deposits in the neurosensory retina, and retinal detachment. A genome-wide scan previously localized the genetic locus for SVD to a 20 Mb region flanked by D2S2158 and D2S2202. This region contains 59 genes, of which 20 were sequenced, disclosing a heterozygous mutation (484C > T, R162W) in KCNJ13, member 13 of subfamily J of the potassium inwardly rectifying channel family in all affected individuals. The mutation in KCNJ13, the gene encoding Kir7.1, was not present in unaffected family members and 210 control individuals. Kir7.1 localized to human retina and retinal pigment epithelium and was especially prevalent in the internal limiting membrane adjacent to the vitreous body. Molecular modeling of this mutation predicted disruption of the structure of the potassium channel in the closed state located immediately adjacent to the cell-membrane inner boundary. Functionally, unlike wild-type Kir7.1 whose overexpression in CHO-K1 cells line produces highly selective potassium current, overexpression of R162W mutant Kir7.1 produces a nonselective cation current that depolarizes transfected cells and increases their fragility. These results indicate that the KCNJ13 R162W mutation can cause SVD and further show that vitreoretinal degeneration can arise through mutations in genes whose products are not structural components of the vitreous.

Bietti crystalline corneoretinal dystrophy is caused by mutations in the novel gene CYP4V2.

Bietti crystalline corneoretinal dystrophy (BCD) is an autosomal recessive retinal dystrophy characterized by multiple glistening intraretinal crystals scattered over the fundus, a characteristic degeneration of the retina, and sclerosis of the choroidal vessels, ultimately resulting in progressive night blindness and constriction of the visual field. The BCD region of chromosome 4q35.1 was refined to an interval flanked centromerically by D4S2924 by linkage and haplotype analysis; mutations were found in the novel CYP450 family member CYP4V2 in 23 of 25 unrelated patients with BCD tested. The CYP4V2 gene, transcribed from 11 exons spanning 19 kb, is expressed widely. Homology to other CYP450 proteins suggests that CYP4V2 may have a role in fatty acid and steroid metabolism, consistent with biochemical studies of patients with BCD.