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.

CHMP4B, a novel gene for autosomal dominant cataracts linked to chromosome 20q.

Cataracts are a clinically diverse and genetically heterogeneous disorder of the crystalline lens and a leading cause of visual impairment. Here we report linkage of autosomal dominant "progressive childhood posterior subcapsular" cataracts segregating in a white family to short tandem repeat (STR) markers D20S847 (LOD score [Z] 5.50 at recombination fraction [theta] 0.0) and D20S195 (Z=3.65 at theta =0.0) on 20q, and identify a refined disease interval (rs2057262-(3.8 Mb)-rs1291139) by use of single-nucleotide polymorphism (SNP) markers. Mutation profiling of positional-candidate genes detected a heterozygous transversion (c.386A-->T) in exon 3 of the gene for chromatin modifying protein-4B (CHMP4B) that was predicted to result in the nonconservative substitution of a valine residue for a phylogenetically conserved aspartic acid residue at codon 129 (p.D129V). In addition, we have detected a heterozygous transition (c.481G-->A) in exon 3 of CHMP4B cosegregating with autosomal dominant posterior polar cataracts in a Japanese family that was predicted to result in the missense substitution of lysine for a conserved glutamic acid residue at codon 161 (p.E161K). Transfection studies of cultured cells revealed that a truncated form of recombinant D129V-CHMP4B had a different subcellular distribution than wild type and an increased capacity to inhibit release of virus-like particles from the cell surface, consistent with deleterious gain-of-function effects. These data provide the first evidence that CHMP4B, which encodes a key component of the endosome sorting complex required for the transport-III (ESCRT-III) system of mammalian cells, plays a vital role in the maintenance of lens transparency.

A novel missense mutation in the gene for gap-junction protein alpha3 (GJA3) associated with autosomal dominant "nuclear punctate" cataracts linked to chromosome 13q.

PURPOSE: Autosomal dominant cataracts are a clinically and genetically heterogeneous eye-lens disorder that usually present in childhood with symptoms of impaired vision. The purpose of this study was to map and identify the mutation underlying autosomal dominant nuclear punctate cataracts segregating in a six generation Caucasian pedigree. METHODS: Genomic DNA was prepared from blood leucocytes, genotyping was performed using microsatellite markers, and LOD scores were calculated using the LINKAGE programs. Mutation detection was performed using direct sequencing and restriction fragment length analysis. RESULTS: Significant evidence of linkage was obtained at marker D13S175 (LOD score [Z]=4.11, recombination fraction [theta]=0.0) and haplotyping indicated that the disease gene lay in the about 2 Mb physical interval between D13S1316 and D13S1236, which contained the gene for gap-junction protein a3 (GJA3) or connexin46. Sequencing of GJA3 detected a C->T transition in exon 2 that resulted in the gain of an Alu 1 restriction site and was predicted to cause a conservative substitution of proline to leucine at codon 59 (P59L). Restriction analysis confirmed that the novel Alu 1 site co-segregated with cataracts in the family but was not detected in a control panel of 170 normal unrelated individuals. CONCLUSIONS: The present study has identified a fifth mutation in GJA3, rendering this connexin gene one of the most common non-crystallin genes associated with autosomal dominant cataracts in humans.

A nonsense mutation in CRYBB1 associated with autosomal dominant cataract linked to human chromosome 22q.

Autosomal dominant cataract is a clinically and genetically heterogeneous lens disorder that usually presents as a sight-threatening trait in childhood. Here we have mapped dominant pulverulent cataract to the beta-crystallin gene cluster on chromosome 22q11.2. Suggestive evidence of linkage was detected at markers D22S1167 (LOD score [Z] 2.09 at recombination fraction [theta] 0) and D22S1154 (Z=1.39 at theta=0), which closely flank the genes for betaB1-crystallin (CRYBB1) and betaA4-crystallin (CRYBA4). Sequencing failed to detect any nucleotide changes in CRYBA4; however, a G-->T transversion in exon 6 of CRYBB1 was found to cosegregate with cataract in the family. This single-nucleotide change was predicted to introduce a translation stop codon at glycine 220 (G220X). Expression of recombinant human betaB1-crystallin in bacteria showed that the truncated G220X mutant was significantly less soluble than wild type. This study has identified the first CRYBB1 mutation associated with autosomal dominant cataract in humans.