Mutational analysis of PAX6: 16 novel mutations including 5 missense mutations with a mild aniridia phenotype.
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Mutations in the developmental control gene PAX6 have been shown to be the genetic cause of aniridia, which is a severe panocular eye disease characterised by iris hypoplasia. The inheritance is autosomal dominant with high penetrance but variable expressivity. Here we describe a mutational analysis of 27 Danish patients using a dideoxy fingerprinting method, which identified PAX6 mutations in 18 individuals with aniridia. A thorough phenotype description was made for the 18 patients. A total of 19 mutations, of which 16 were novel, are described. Among these were five missense mutations which tended to be associated with a milder aniridia phenotype, and in fact one of them seemed to be non-penetrant. Four of the five missense mutations were located in the paired domain. We also describe a third alternative spliced PAX6 isoform in which two of the four missense mutations would be spliced out. Our observations support the concept of dosage effects of PAX6 mutations as well as presenting evidence for variable expressivity and gonadal mosaicism. (+info)
Goniosurgery for prevention of aniridic glaucoma.
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PURPOSE: We conducted a retrospective study to report the long-term success and complications of modified goniosurgery to prevent aniridic glaucoma, an entity that typically is difficult to control medically or surgically. METHODS: Fifty-five eyes in 33 patients who had aniridia without glaucoma and who had goniosurgery were identified. Ninety-one procedures were performed on 55 eyes by 1 surgeon (D.S.W.). Each eye had an average of 1.65 procedures and an average of 200 degrees of goniosurgery. Average patient age at time of initial goniosurgery was 37 months. There were no operative complications. RESULTS: No eye had a decrease in visual acuity at last follow-up. All eyes had a preoperative intraocular pressure (IOP) of less than 21 mm Hg. At last follow-up (average, 9 years 6 months; range, 8 months to 24 years), 49 eyes (89%) had IOP of less than 22 mm Hg without medications. The remaining 6 eyes (11%) had IOP of less than or equal to 22 mm Hg with up to 2 eye drops. Of 224 aniridic eyes of 112 patients that were seen for eye care by 1 of the authors (D.S.W.), 119 eyes (53%) demonstrated glaucoma, as defined by IOP of greater than 21 mm Hg. CONCLUSIONS: Without prophylactic goniotomy, aniridic glaucoma may be expected in half of patients, and when it occurs, it is extremely difficult to control. Prophylactic goniosurgery in selected eyes of young patients with aniridia is effective in preventing aniridic glaucoma. (+info)
The horse homolog of congenital aniridia conforms to codominant inheritance.
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Anterior segment dysgenesis syndrome occurs frequently in Rocky Mountain horses and has two distinct ocular phenotypes: (1) large cysts originating from the temporal ciliary body or peripheral retina and (2) multiple anterior segment anomalies including ciliary cysts, iris hypoplasia, iridocorneal adhesions and opacification, nuclear cataract, and megalocornea. To determine if anterior segment dysgenesis syndrome is heritable in horses we performed ophthalmic examinations and collected pedigree information on horses (n = 516) in an extended Rocky Mountain horse pedigree. Logistic regressive segregation analysis of a subset of animals (n = 337) in which the ocular phenotypes of progeny and both parents were known indicated that the codominant inheritance model best fit the data. This model predicted cyst phenotype expression in heterozygous animals and multiple anterior segment anomalies in homozygous animals. Several cases of nonpenetrance of the cyst phenotype were detected in one lineage. The close resemblance between the inheritance and lesions observed in Small eye mice and rats, humans with congenital aniridia or anterior segment malformation, and horses with anterior segment dysgenesis syndrome supported the conclusion that anterior segment dysgenesis syndrome in the horse may be homologous to similar ophthalmic anomalies in other species. (+info)
3' deletions cause aniridia by preventing PAX6 gene expression.
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Aniridia is a panocular human eye malformation caused by heterozygous null mutations within PAX6, a paired-box transcription factor, or cytogenetic deletions of chromosome 11p13 that encompass PAX6. Chromosomal rearrangements also have been described that disrupt 11p13 but spare the PAX6 transcription unit in two families with aniridia. These presumably cause a loss of gene expression, by removing positive cis regulatory elements or juxtaposing negative DNA sequences. We report two submicroscopic de novo deletions of 11p13 that cause aniridia but are located >11 kb from the 3' end of PAX6. The clinical manifestations are indistinguishable from cases with chain-terminating mutations in the coding region. Using human x mouse retinoblastoma somatic cell hybrids, we show that PAX6 is transcribed only from the normal allele but not from the deleted chromosome 11 homolog. Our findings suggest that remote 3' regulatory elements are required for initiation of PAX6 expression. (+info)
Missense mutation at the C-terminus of PAX6 negatively modulates homeodomain function.
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PAX6 is essential for ocular morphogenesis. Mutations in the PAX6 gene produce various phenotypes, including aniridia, Peters' anomaly, foveal hypoplasia, autosomal dominant keratitis and congenital cataracts. PAX6 functions as a transcription factor and has two DNA binding domains (a paired domain and a homeodomain) which are joined by a linker, and a transactivation domain enriched in proline, serine and threonine (PST) at the C-terminus. The mechanism of PAX6 function is not clearly understood, and few target genes in vertebrates have been identified. We examined disease-causing missense mutations in the PST domain to understand how they affect the function of PAX6. Upon examining the DNA samples of aniridia patients, we identified three missense mutations in the PST domain: P375Q (a novel mutation) and the previously reported Q422R and X423L mutations. On the basis of functional analysis, the P375Q mutant appears to have a normal transactivation activity but lower DNA binding through the paired domain than the wild-type. The Q422R mutation resulted in the loss of DNA binding ability of the PAX6 homeodomain. Substitution analyses of the C-terminal amino acid (codon 422) indicated that an amino acid at codon 422 is required for DNA binding of the homeodomain of intact PAX6 and that the polarity and charge of the side-chain of the terminal amino acid influence this binding. (+info)
Alveolar capillary dysplasia with misalignment of pulmonary veins and anterior segment dysgenesis of the eye: a report of a new association and review of the literature.
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The association of alveolar capillary dysplasia with misalignment of pulmonary veins (ACD-MPV) and ocular abnormalities has not been previously reported. We present a case of ACD-MPV and anterior segment dysgenesis of the eye in a full-term infant as well as a review of the relevant literature. (+info)
Aniridia-associated translocations, DNase hypersensitivity, sequence comparison and transgenic analysis redefine the functional domain of PAX6.
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The transcription factor PAX6 plays a critical, evolutionarily conserved role in eye, brain and olfactory development. Homozygous loss of PAX6 function affects all expressing tissues and is neonatally lethal; heterozygous null mutations cause aniridia in humans and the Small eye (Sey) phenotype in mice. Several upstream and intragenic PAX6 control elements have been defined, generally through transgenesis. However, aniridia cases with chromosomal rearrangements far downstream of an intact PAX6 gene suggested a requirement for additional cis-acting control for correct gene expression. The likely location of such elements is pinpointed through YAC transgenic studies. A 420 kb yeast artificial chromosome (YAC) clone, extending well beyond the most distant patient breakpoint, was previously shown to rescue homozygous Small eye lethality and correct the heterozygous eye phenotype. We now show that a 310 kb YAC clone, terminating just 5' of the breakpoint, fails to influence the Sey phenotypes. Using evolutionary sequence comparison, DNaseI hypersensitivity analysis and transgenic reporter studies, we have identified a region, >150 kb distal to the major PAX6 promoter P1, containing regulatory elements. Components of this downstream regulatory region drive reporter expression in distinct partial PAX6 patterns, indicating that the functional PAX6 gene domain extends far beyond the transcription unit. (+info)
PAX6 mutation as a genetic factor common to aniridia and glucose intolerance.
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A paired homeodomain transcription factor, PAX6, is a well-known regulator of eye development, and its heterozygous mutations in humans cause congenital eye anomalies such as aniridia. Because it was recently shown that PAX6 also plays an indispensable role in islet cell development, a PAX6 gene mutation in humans may lead to a defect of the endocrine pancreas. Whereas heterozygous mutations in islet-cell transcription factors such as IPF1/IDX-1/STF-1/PDX-1 and NEUROD1/BETA2 serve as a genetic cause of diabetes or glucose intolerance, we investigated the possibility of PAX6 gene mutations being a genetic factor common to aniridia and diabetes. In five aniridia and one Peters' anomaly patients, all of the coding exons and their flanking exon-intron junctions of the PAX6 gene were surveyed for mutations. The results of direct DNA sequencing revealed three different mutations in four aniridia patients: one previously reported type of mutation and two unreported types. In agreement with polypeptide truncation and a lack of the carboxyl-terminal transactivation domain in all of the mutated PAX6 proteins, no transcriptional activity was found in the reporter gene analyses. Oral glucose tolerance tests revealed that all of the patients with a PAX6 gene mutation had glucose intolerance characterized by impaired insulin secretion. Although we did not detect a mutation within the characterized portion of the PAX6 gene in one of the five aniridia patients, diabetes was cosegregated with aniridia in her family, and a single nucleotide polymorphism in intron 9 of the PAX6 gene was correlated with the disorders, suggesting that a mutation, possibly located in an uncharacterized portion of the PAX6 gene, can explain both diabetes and aniridia in this family. In contrast, the patient with Peters' anomaly, for which a PAX6 gene mutation is a relatively rare cause, showed normal glucose tolerance (NGT) and did not show a Pax6 gene mutation. Taken together, our present observations suggest that heterozygous mutations in the PAX6 gene can induce eye anomaly and glucose intolerance in individuals harboring these mutations. (+info)