Further genetic heterogeneity for autosomal dominant human sutural cataracts

A unique sutural cataract was observed in a 4-generation German family to be transmitted as an isolated autosomal, dominant trait. Since mutations in the gamma-crystallin encoding CRYG genes have previously been demonstrated to be the most frequent reason for isolated congenital cataracts, all 4 active CRYG genes have been sequenced. A single base-pair change in the CRYGA gene has been shown, leading to a premature stop codon. This was not observed in 170 control individuals. However, it did not segregate with the disease phenotype. This is the first truncating mutation in an active CRYG gene without a dominant phenotype. As the CRYGA mutation did not explain the cataract, several other candidate loci (CCV, GJA8, CRYBB2, BFSP2, MIP, GJA8, central pouch-like, CRYBA1) were investigated by micro-satellite markers and linkage analysis, but they were excluded based on the combination of haplotype analysis and two-point linkage analysis. The phenotype in this family is due to a mutation in another sutural cataract gene yet to be identified

A novel GJA8 mutation causing a recessive triangular cataract

The aim of the study was to characterize the underlying mutation in a consanguineous family having cataracts. METHODS: Family D having congenital cataracts was treated at the University Eye Clinics at Giessen (Germany). Lens material from surgeries was collected, immediately frozen at -80 degrees C, and used for cDNA production. Blood was taken from the proband and available family members. Polymerase chain reaction (PCR)-amplified DNA fragments were characterized by sequencing and restriction digestion. RESULTS: The proband, AD, has a dense, triangular nuclear cataract. The parents are consanguineous, and the mother and grandmother suffer from a discrete, symmetric opacity of the fetal lens nucleus. The proband's lens cDNA showed a homozygous insertion of one G after position 776 of the GJA8 gene, leading to a frame shift and 123 novel amino acids. The homozygous mutation was confirmed in the genomic DNA and is also present in the cataract-operated brother of the proband; all other family members investigated were heterozygous. The mutation could not be detected in 96 healthy controls from Germany. CONCLUSIONS: The ins776G mutation most likely causes a recessive triangular cataract with variable expressivity of a weak phenotype in heterozygotes

Mutation analysis in a German family identified a new cataract-causing allele in the CRYBB2 gene

The study demonstrates the functional candidate gene analysis in a cataract family of German descent. METHODS: We screened a German family, clinically documented to have congenital cataracts, for mutation in the candidate genes CRYG (A to D) and CRYBB2 through polymerase chain reaction analyses and sequencing. RESULTS: Congenital cataract was first observed in a daughter of healthy parents. Her two children (a boy and a girl) also suffer from congenital cataracts and have been operated within the first weeks of birth. Morphologically, the cataract is characterized as nuclear with an additional ring-shaped cortical opacity. Molecular analysis revealed no causative mutation in any of the CRYG genes. However, sequencing of the exons of the CRYBB2 gene identified a sequence variation in exon 5 (383 A>T) with a substitution of Asp to Val at position 128. All three affected family members revealed this change but it was not observed in any of the unaffected persons of the family. The putative mutation creates a restriction site for the enzyme TaiI. This mutation was checked for in controls of randomly selected DNA samples from ophthalmologically normal individuals from the population-based KORA S4 study (n=96) and no mutation was observed. Moreover, the Asp at position 128 is within a stretch of 12 amino acids, which are highly conserved throughout the animal kingdom. For the mutant protein, the isoelectric point is raised from pH 6.50 to 6.75. Additionally, the random coil structure of the protein between the amino acids 126-139 is interrupted by a short extended strand structure. In addition, this region becomes hydrophobic (from neutral to +1) and the electrostatic potential in the region surrounding the exchanged amino acid alters from a mainly negative potential to an enlarged positive potential. CONCLUSIONS: The D128V mutation segregates only in affected family members and is not seen in representative controls. It represents the first mutation outside exon 6 of the human CRYBB2 gene

Analysis of mitochondrial DNA variations in Indian patients with congenital cataract

PURPOSE: Identification of mitochondrial DNA (mtDNA) variations in the inherited cataract patients from south India. METHODS: Three families with inherited cataract of maternal origin were evaluated. Clinical and ophthalmologic examinations were performed on available affected as well as unaffected family members. Samples of mtDNA were amplified using 24 pairs of overlapping primers to analyze the entire mitochondrial genome to screen for variations and analyzed for both coding and non-coding regions. Bioinformatic analysis was performed to evaluate the effect of nucleotide variations. RESULTS: DNA sequence analysis of inherited cataract families showed 72 nucleotide variations, of which 15 were observed in the major non-coding D-loop region, 3 in the tRNA genes, 5 in the rRNA genes, and 49 in the protein coding region. Among these variations 56 were reported previously and 16 were novel of which, 12 synonymous substitutions, 2 non-synonymous substitutions along with a frameshift mutation, and one was in the non-coding region. Nicotinamide adenine dinucleotide dehydrogenase (NADH) subunit (ND) gene of mtDNA was highly altered, in general, and found to contain 4 variations specific for cataract patients of the first family, six for the second, and one for the third family. CONCLUSIONS: Seventy-two variations were observed in three inherited cataract families. Four variations were specific for cataract patients of the first family, six for the second, and one for the third family. This is perhaps the first report on the presence of mitochondrial mutations in inherited cataracts

Relative roles of the different Pax6 domains for pancreatic alpha cell development

<p>Abstract</p> <p>Background</p> <p>The transcription factor Pax6 functions in the specification and maintenance of the differentiated cell lineages in the endocrine pancreas. It has two DNA binding domains, the paired domain and the homeodomain, in addition to a C-terminal transactivation domain. The phenotype of Pax6^-/-knockout mice suggests non-redundant functions of the transcription factor in the development of glucagon-expressing α-cells as this cell type is absent in the mutants. We ask the question of how the differentiation of pancreatic endocrine cells, in particular that of α-cells, is affected by selective inactivation of either one of the three major domains of Pax6.</p> <p>Results</p> <p>The Pax6^Aey18mutant mouse line, in which the paired domain is inactivated, showed a phenotype similar to that of Pax6^-/-knockout mice with a near complete absence of glucagon-positive α-cells (0-4 cells/section; ≤1% of wt), reduced β-cell area (74% of wt) and disorganized islets. The proportion of ghrelin-positive ε-cells was expanded. In Pax6^Sey-Neumutants, which lack the transactivation domain, α-and β-cells where reduced to 25 and 40% of wt, respectively. We also studied two mouse lines with mutations in the homeodomain, Pax6^4Neuand Pax6^132-14Neu. Neighboring amino acids are affected in the two lines and both point mutations abolish DNA binding of the classical P3 homeodomain target sequence. The pancreatic phenotype of the two mutants however was divergent. While Pax6^4Neuhomozygotes showed a reduction of α- and β-cells to 59 and 61%, respectively, pancreatic endocrine development was unaltered in the Pax6^132-14Neumutant strain.</p> <p>Conclusions</p> <p>We show that inactivation of the Pax6 paired domain leads to a more severe phenotype with regards to the differentiation of pancreatic α-cells than the loss of the transactivation domain. The analysis of two different homeodomain mutants suggests that the binding of Pax6 to P3 homeodomain consensus sequences is not required for α-cell development. It rather seems that the homeodomain has a modulating role in Pax6 function, possibly by facilitating a PH0-like binding confirmation on paired domain target genes like proglucagon. This function is differentially affected by the two homeodomain mutations analyzed in this study.</p

Mice with an induced mutation in collagen 8A2 develop larger eyes and are resistant to retinal ganglion cell damage in an experimental glaucoma model

PURPOSE: To study susceptibility to glaucoma injury as it may be affected by mutations in ocular connective tissue components. METHODS: Mice homozygous for an N-ethyl-N-nitrosourea induced G257D exchange (Gly to Asp) missense mutation (Aca23) in their collagen 8A2 gene were studied to measure intraocular pressure (IOP), axial length and width, number of retinal ganglion cells (RGC), and inflation responses. Three month old homozygous Aca23 mutant and wild type (WT) mice had 6 weeks exposure to elevated IOP induced by polystyrene microbead injection. Additional Aca23 and matched controls were studied at ages of 10 and 18 months. RESULTS: Aca23 mice had no significant difference from WT in IOP level, and in both strains IOP rose with age. In multivariable models, axial length and width were significantly larger in Aca23 than WT, became larger with age, and were larger after exposure to glaucoma (n=227 mice). From inflation test data, the estimates of scleral stress resultants in Aca23 mice were similar to age-matched and younger WT C57BL/6 (B6) mice, while the strain estimates for Aca23 were significantly less than those for either WT group in the mid-sclera and in some of the more anterior scleral measures (p&lt;0.001; n=29, 22, 20 eyes in Aca23, older WT, younger WT, respectively). With chronic IOP elevation, Aca23 eyes increased 9% in length and 7% in width, compared to untreated fellow eyes (p&lt;0.05, &lt;0.01). With similar elevated IOP exposure, WT eyes enlarged proportionately twice as much as Aca23, increasing in length by 18% and in nasal-temporal width by 13% (both p&lt;0.001, Mann-Whitney test). In 4 month old control optic nerves, mean RGC axon number was not different in Aca23 and WT (46,905&plusmn;7,592, 43,628&plusmn;11,162, respectively; p=0.43, Mann-Whitney test, n=37 and 29). With chronic glaucoma, Aca23 mice had a mean axon loss of only 0.57&plusmn;17%, while WT mice lost 21&plusmn;31% (median loss: 1% versus 10%, n=37, 29, respectively; p=0.001; multivariable model adjusting for positive integral IOP exposure). CONCLUSIONS: The Aca23 mutation in collagen 8&alpha;2 is the first gene defect found to alter susceptibility to experimental glaucoma, reducing RGC loss possibly due to differences in mechanical behavior of the sclera. Detailed study of the specific changes in scleral connective tissue composition and responses to chronic IOP elevation in this strain could produce new therapeutic targets for RGC neuroprotection