Posterior polar cataract is the predominant consequence of a recurrent mutation in the PITX3 gene

Retrospective analysis of the role of anterior segment optical coherence tomography and outcomes of cataract surgery in posterior polar cataract

Purpose

To evaluate the visual and surgical outcomes of cataract surgery in patients with posterior polar cataract (PPC) and to evaluate the benefits of preoperative anterior segment optical coherence tomography (AS-OCT).

Methods

This was a retrospective, single-center study. Case records of patients diagnosed with PPC who underwent cataract surgery either by phacoemulsification or manual small-incision cataract surgery (MSICS) from January to December 2019 were analyzed. Data collected include demographic details, preoperative best corrected visual acuity (BCVA), AS-OCT, type of cataract surgery, intraoperative and postoperative complications, and visual outcome at 1-month follow-up.

Results

One hundred patients were included in the study. Preoperative posterior capsular defect was noted on AS-OCT in 14 patients (14%). Seventy-eight underwent phacoemulsification and 22 underwent MSICS. Intraoperatively, posterior capsular rupture (PCR) was seen in 13 patients (13%) and cortex drop was noted in one among them (1%). Out of 13 PCRs, 12 were found to have posterior capsular dehiscence preoperatively in AS-OCT. The sensitivity of AS-OCT for detecting posterior capsule dehiscence was 92.3% and specificity was 97.7%. The positive predictive value and negative predictive value were 85.7% and 98.8%, respectively. There was no significant difference in the incidence of PCR between phacoemulsification and MSICS (P = 0.475). The mean BCVA at 1 month was found to be better with phacoemulsification than MSICS (P = 0.004).

Conclusion

Preoperative AS-OCT has excellent specificity and negative predictive value in identifying posterior capsular dehiscence. It thus helps to plan the surgery and counsel patients appropriately. Both phacoemulsification and MSICS provide good visual outcome with similar complication rates.

Role of preoperative anterior segment optical coherence tomography in identifying intraoperative posterior capsular dehiscence in posterior polar cataract

INTRODUCTION

The presence of preoperative posterior capsular dehiscence in posterior polar cataracts (PPCs) increases the chances of intraoperative posterior capsular rent. Our study aims to demonstrate the efficacy of preoperative anterior segment optical coherence tomography (ASOCT) to predict intraoperative posterior capsular rupture (PCR) in PPC.

MATERIALS AND METHODS

This was an observational study including patients within 25-75 years of age, having PPC, undergoing phacoemulsification. ASOCT was done for evaluating preoperative posterior capsular status and was graded as "intact" or "dehiscent, and eventually ,intraoperative-posterior capsular status was noted.

STATISTICAL ANALYSIS

SPSS (version 27.0) was used, and P value of ≤ 0.05 was considered statistically significant.

RESULTS

ASOCT of 44 eyes had 9 (20.5%) dehiscent posterior capsules and 35 (79.5%) intact. Out of these 9 eyes, 7 (77.8%) had intraoperative PCR and 2 (22.2%) did not. Out of these 35, 34 (97.1%) were actually intact intraoperatively and 1 (2.9%) had intraoperative PCR. The sensitivity and specificity of ASOCT for detecting dehiscence were 94.4% and 87.5%, respectively. The positive and negative predictive values were 97.1 and 77.8, respectively. The diagnostic accuracy of the test was 95.45% with a Chi-square value of 27.01 (P < 0.0001). The diagnostic validity of ASOCT grading for detecting preoperative dehiscence was confirmed. The association between intraoperative PCR and preoperative dehiscence was statistically significant (Chi-square test - P < 0.0001). Our objective was established.

DISCUSSION AND CONCLUSION

The demographics and clinical parameters were comparable with other studies. Two eyes with preoperative dehiscence on ASOCT had intact posterior capsule during surgery. The cause can be a dense opacity with increased optical density causing an obscured a clear capsule view on ASOCT, an artifact defect, giving a false impression of dehiscence. One eye who had nondehiscent PC on ASOCT was found to have PCR on the table, which can be due to an extremely thin PC or tightly adherent polar opacity to the capsule. According to our study, the diagnostic accuracy of ASOCT for detecting preoperative dehiscence was 94.4% (sensitivity)and of nondehiscence was 87.5%(specificity). 97.1% of eyes with dehiscence on ASOCT, had actual posterior capsular rent (positive predictive value). To conclude, ASOCT can be used as a reliable diagnostic modality.

Investigating the Clinical Characteristics and PITX3Mutations of a Large Chinese Family with Anterior Segment Mesenchymal Dysgenesis and Congenital Posterior Polar Cataract

Objective

To investigate the clinical characteristics and pathogenic genetic mutations of a Chinese family with anterior segment mesenchymal dysgenesis and congenital posterior polar cataract.

Methods

Through family investigation, the family members were examined via slit lamp anterior segment imaging and screened for eye and other diseases by eye B-ultrasound. Genetic test was performed on the blood samples of the fourth family generation (23 people) via whole exome sequencing (trio-WES) and Sanger sequencing.

Results

Among the 36 members in four family generations, there were 11 living cases with different degrees of ocular abnormalities, such as cataracts, leukoplakia, and small cornea. All patients who received the genetic test had the heterozygous frameshift mutation c.640_656dup (p.G220Pfs∗95) on exon 4 of the PITX3 gene. This mutation was cosegregated with the clinical phenotypes in the family and thus might be one of the genetic factors that cause the corresponding ocular abnormalities in this family.

Conclusion

The congenital posterior polar cataract with or without anterior interstitial dysplasia (ASMD) of this family was inherited in an autosomal dominant manner, and the frameshift mutation (c.640_656dup) in the PITX3 gene was the cause of ocular abnormalities observed in this family. This study is of great significance for guiding prenatal diagnosis and disease treatment.

Unilateral buphthalmos, corneal staphyloma and corneal fistula caused by pathogenic variant in the PITX3 gene: a case report

Introduction

PITX3 has been reported to be associated with congenital cataracts, anterior segment mesenchymal dysgenesis, Peters’ anomaly, and microphthalmia. In this case, an infant with unilateral buphthalmos, corneal staphyloma and corneal fistula carrying a variant in PITX3 was reported.

Case description

We describe a 4-month-old female infant who was referred to our Eye Clinic because of gradual enlargement of the eyeball in the right eye and whitish opacity in both eyes. Buphthalmos with long axial length (22.04 mm), macrocornea with diffuse corneal oedema and opacity (14.50 mm*14.50 mm) and high intraocular pressure (23.78 mmHg) were detected in the right eye. Microphthalmia with short axial length (16.23 mm), microcornea with diffuse corneal oedema and opacity (7.50 mm*6.50 mm) were detected in the left eye. A 360° trabeculotomy was performed for the right eye. However, corneal staphyloma and corneal fistula in the right eye were detected 6 months after the surgery. A variant in exon 4 of PITX3 (c.640_656dup (p. Gly220Profs*95)) was identified in the proband but was not detected in her healthy parents.

Conclusion

A novel phenotype characterized by unilateral buphthalmos, corneal staphyloma and corneal fistula in an infant were reported to be associated with PITX3 in our study. Our study expands the scope of the clinical heterogeneity of PITX3 variants. It also improves our understanding and increases the attention given to patients with PITX3 variants.

Phacoemulsification without hydroprocedure: A novel technique to deal with posterior polar cataracts

PURPOSE

The purpose of the study was to describe a new phacoemulsification technique without hydroprocedures in patients of posterior polar cataract (PPC) and determine the posterior capsular rupture (PCR) and postoperative outcomes.

METHODS

We conducted a retrospective study with 115 eyes of 77 patients. After capsulorhexis, we insert the phaco tip inside the eye and do shaving of the cortex and epinucleus within the capsulorhexis area. The tip of the phacoemulsification probe is buried deep into the center of the nucleus and a anterior-poserior crack is fashioned. Then, the tip is placed at 7 o'clock position to chop away a triangular piece of the nucleus. A similar maneuver is done at 4 o'clock position to take out another piece. The phacoemulsification tip and the chopper are now positioned at the cracked site of the lower fragments. Using the two instruments, the fragments are now pushed away and easily emulsified.

RESULTS

The mean age of the study population was 51.87 ± 14.19 years (range: 22-87 years). Of 77 patients, 39 (50.64%) patients had unilateral PPC and 38 (49.35%) had bilateral PPC. PCR occurred in 9 eyes (7.82%), among them two patients had fragment drop and only 1 (0.87%) patient was left aphakic. Best-corrected visual acuity (BCVA) at postoperative day 30 was 20/20 or better in 102 (88.69%) eyes, 20/32-20/80 was in 11 (9.56%) eyes, and BCVA 20/80-20/200 was in 2 (1.73%) eyes.

CONCLUSION

Phacoemulsification without hydroprocedure is a novel technique that can be successfully implemented in cases of PPC and can expect an excellent visual outcome.

Phacoemulsification in posterior polar cataract: Experience from a tertiary eye care Centre in North India

Purpose:

To determine the rate of posterior capsular rupture (PCR) and assess the postoperative outcomes in patients of posterior polar cataract (PPC) undergoing phacoemulsification using a combination of “V” or “λ” nucleofractis and viscodissection.

Methods:

It was a retrospective study of 80 eyes of 64 patients undergoing surgery for PPC. All surgeries were performed by a single surgeon. After completion of the continuous curvilinear capsulorrhexis (CCC), controlled hydrodelineation was used to separate the endonucleus from the epinuclear shell with limited viscodissection. Phacoemulsification was then carried out by making a “V” or lambda-shaped nucleofractis with the phaco tip followed by multiple chopping of the nucleus, ensuring the integrity of the epinuclear part of the lens. The epinuclear plate was removed after viscodissection.

Results:

The overall rate of PCR was 7.5% (6 out of 80 eyes). Of the 6 eyes, 4 eyes had been documented to have a pre-existing posterior capsular defect on slit-lamp examination. The rate of “on table” PCR, that is, PCR occurring intraoperatively was only 2.6% (2 of 76 eyes). Nucleus drop was not encountered in any case. Overall 87.5% eyes achieved a final visual acuity of 20/40 or better with 68.75% being 20/20 or better. Of the eyes developing PCR, two-third achieved a visual acuity of 20/30 or better.

Conclusion:

Using a combination of surgical techniques of V groove or lambda technique for nucleofractis and removal of epinucleus by viscodissection can result in a low rate of PCR and extremely good postoperative outcomes in cases of PPC.

Molecular and Genetic Mechanism of Non-Syndromic Congenital Cataracts. Mutation Screening in Spanish Families

Our purpose was to identify mutations responsible for non-syndromic congenital cataracts through the implementation of next-generation sequencing (NGS) in our center. A sample of peripheral blood was obtained from probands and willing family members and genomic DNA was extracted from leukocytes. DNA was analyzed implementing a panel (OFTv2.1) including 39 known congenital cataracts disease genes. 62 probands from 51 families were recruited. Pathogenic or likely pathogenic variants were identified in 32 patients and 25 families; in 16 families (64%) these were de novo mutations. The mutation detection rate was 49%. Almost all reported mutations were autosomal dominant. Mutations in crystallin genes were found in 30% of the probands. Mutations in membrane proteins were detected in seven families (two in GJA3 and five in GJA8). Mutations in LIM2 and MIP were each found in three families. Other mutations detected affected EPHA2, PAX6, HSF4 and PITX3. Variants classified as of unknown significance were found in 5 families (9.8%), affecting CRYBB3, LIM2, EPHA2, ABCB6 and TDRD7. Mutations lead to different cataract phenotypes within the same family.

Posterior polar cataract: Minimizing risks

BACKGROUND

Comparing surgical outcomes of management of posterior polar cataract, a congenital cataract, which is difficult to manage surgically and has been associated with poor surgical outcomes.

METHODS

46 eyes of 38 patients with posterior polar cataract underwent phacoemulsification and PCIOL implantation.

RESULTS

In a prospective analytical study, 46 eyes of 38 patients with posterior polar cataracts underwent surgery at a zonal hospital of the armed forces. The posterior polar cataract incidence was 1.23 per 1000 with confidence interval (CI) of 0.0012. Of the 46 eyes operated, 6 had a posterior capsular rupture (PCR) (13.04%). The PCR incidence in normal cataracts is reported at approx. 1.1%, whereas, various studies have reported incidence of 6-36% in posterior polar cataracts. 41 eyes achieved a visual acuity of 6/12 or better (89.13%) and 39 eyes of 6/9 or better (84.78%). 4 patients had amblyopia (8.6%), Two patients developed macular edema (4.34%). Mean follow-up was 7 months (range 3-11 months). There was no case of nucleus drop or retinal detachment.

CONCLUSION

Posterior polar cataracts are a surgical challenge. With controlled surgery, well defined techniques, a good surgical outcome can be achieved with reduced incidence of PCR.

Mutations of RagA GTPase in mTORC1 Pathway Are Associated with Autosomal Dominant Cataracts

Cataracts are a significant public health problem with no proven methods for prevention. Discovery of novel disease mechanisms to delineate new therapeutic targets is of importance in cataract prevention and therapy. Herein, we report that mutations in the RagA GTPase (RRAGA), a key regulator of the mechanistic rapamycin complex 1 (mTORC1), are associated with autosomal dominant cataracts. We performed whole exome sequencing in a family with autosomal dominant juvenile-onset cataracts, and identified a novel p.Leu60Arg mutation in RRAGA that co-segregated with the disease, after filtering against the dbSNP database, and at least 123,000 control chromosomes from public and in-house exome databases. In a follow-up direct screening of RRAGA in another 22 families and 142 unrelated patients with congenital or juvenile-onset cataracts, RRAGA was found to be mutated in two unrelated patients (p.Leu60Arg and c.-16G>A respectively). Functional studies in human lens epithelial cells revealed that the RRAGA mutations exerted deleterious effects on mTORC1 signaling, including increased relocation of RRAGA to the lysosomes, up-regulated mTORC1 phosphorylation, down-regulated autophagy, altered cell growth or compromised promoter activity. These data indicate that the RRAGA mutations, associated with autosomal dominant cataracts, play a role in the disease by acting through disruption of mTORC1 signaling.

A group of guanine nucleotide-binding molecules called Rag GTPases are known to play a crucial role in regulation of mTORC1 signaling cascade. In the current study, whole exome sequencing has led to the identification of the RagA GTPase (RRAGA) gene for cataracts and we proceeded to study properties of the RRAGA protein. We captured and sequenced the whole exome for four affected patients from a family with autosomal dominant juvenile-onset posterior cataracts, and found a novel rare mutation in RagA GTPase (RRAGA). To validate this finding, we then sequenced more families and patients, and observed RRAGA mutations in unrelated patients with related phenotypes, suggesting that RRAGA could be mutated in congenital and juvenile-onset cataracts. We further demonstrated supporting evidence that in human lens epithelial cells the RRAGA mutations exerted deleterious effects on relocation of RRAGA to the lysosomes, mTORC1 phosphorylation, autophagy and cell growth. This study gives important new insight into the roles of RRAGA and mTROC1 signaling in the etiology of cataracts.

From eyeless to neurological diseases

Age-related cataracts are frequently associated with degenerative changes in the ocular lens including the aggregation of proteins - mainly crystallins, but also other proteins including amyloids (Aβ) leading to the hypothesis that cataracts could be used as "biomarkers" for Alzheimer disease. Even if this hypothesis was rejected by David Beebe's last paper (Bei et al., Exp. Eye Res., 2015), it is a fascinating aspect to look for commonalities between eye diseases and neurological disorders. In this review, I discuss such commonalities between eye and brain mainly from a developmental point of view. The finding of the functional homology of the Drosophila eyeless gene with the mammalian Pax6 gene marks a first highlight in the developmental genetics of the eye - this result destroyed the "dogma" of the different evolutionary routes of eye development in flies and mammals. The second highlight was the finding that Pax6 is also involved in the development of the forebrain supporting the pleiotropic role of many genes. These findings opened a new avenue for research showing that a broad variety of transcription factors, but also structural proteins are involved both, in eye and brain development as well as into the maintenance of the functional integrity of the corresponding tissue(s). In this review recent findings are summarized demonstrating that genes whose mutations have been identified first to be causative for congenital or juvenile eye disorders are also involved in regenerative processes and neurogenesis (Pax6), but also in neurodegenerative diseases like Parkinson (e.g. Pitx3) or in neurological disorders like Schizophrenia (e.g. Crybb1, Crybb2).

Novel and recurrent PITX3 mutations in Belgian families with autosomal dominant congenital cataract and anterior segment dysgenesis have similar phenotypic and functional characteristics

Background

Congenital cataracts are clinically and genetically heterogeneous with more than 45 known loci and 38 identified genes. They can occur as isolated defects or in association with anterior segment developmental anomalies. One of the disease genes for congenital cataract with or without anterior segment dysgenesis (ASD) is PITX3, encoding a transcription factor with a crucial role in lens and anterior segment development. Only five unique PITX3 mutations have been described, of which the 17-bp duplication c.640_656dup, p.(Gly220Profs*95), is the most common one and the only one known to cause cataract with ASD. The aim of this study was to perform a genetic study of the PITX3 gene in five probands with autosomal dominant congenital cataract (ADCC) and ASD, to compare their clinical presentations to previously reported PITX3-associated phenotypes and to functionally evaluate the PITX3 mutations found.

Methods

Sanger sequencing of the coding region and targeted exons of PITX3 was performed in probands and family members respectively. Transactivation, DNA-binding and subcellular localization assays were performed for the PITX3 mutations found. Ophthalmological examinations included visual acuity measurement, slit-lamp biomicroscopy, tonometry and fundoscopy.

Results

In four Belgian families with ADCC and ASD the recurrent 17-bp duplication c.640_656dup, p.(Gly220Profs*95), was found in a heterozygous state. A novel PITX3 mutation c.573del, p.(Ser192Alafs*117), was identified in heterozygous state in a Belgo-Romanian family with a similar phenotype. Functional assays showed that this novel mutation retains its nuclear localization but results in decreased DNA-binding and transactivation activity, similar to the recurrent duplication.

Conclusions

Our study identified a second PITX3 mutation leading to congenital cataract with ASD. The similarity in phenotypic expression was substantiated by our in vitro functional studies which demonstrated comparable molecular consequences for the novel p.(Ser192Alafs*117) and the recurrent p.(Gly220Profs*95) mutations.

A novel p.R890C mutation in EPHA2 gene associated with progressive childhood posterior cataract in a Chinese family

AIM

To identify the genetic defect in a Chinese family with bilateral progressive childhood posterior cataract.

METHODS

A two-generation family was recruited in this study. Family history and clinical data were recorded. All reported candidate genes associated with congenital posterior cataract were screened by direct DNA sequencing.

RESULTS

All affected individuals presented posterior opacities in the lens. Direct sequencing of the candidate genes showed a heterozygous c. 2668C>T variation in EPHA2 gene, which resulted in the replacement of arginine by cysteine at codon 890 (p. R890C). This mutation was found in two affected individuals, but was not observed in 200 normal controls.

CONCLUSION

We report a novel mutation (p. R890C) in the EPHA2 receptor tyrosine kinase gene. The finding expands the mutation spectrum of EPHA2 in association with posterior cataract.

Posterior polar cataract: A review

Posterior polar cataract is a rare form of congenital cataract. It is usually inherited as an autosomal dominant disease, yet it can be sporadic. Five genes have been attributed to the formation of this disease. It is highly associated with complications during surgery, such as posterior capsule rupture and nucleus drop. The reason for this high complication rate is the strong adherence of the opacity to the weak posterior capsule. Different surgical strategies were described for the handling of this challenging entity, most of which emphasized the need for gentle maneuvering in dealing with these cases. It has a unique clinical appearance that should not be missed in order to anticipate, avoid, and minimize the impact of the complications associated with it.

Molecular characteristics of inherited congenital cataracts

Congenital cataracts are a major cause of induced blindness in children, and inherited cataracts are the major cause of congenital cataracts. Inherited congenital cataracts have been associated with mutations in specific genes, including those of crystallins, gap junction proteins, membrane transport and channel proteins, the cytoskeleton, and growth and transcription factors. Locating and identifying the genes and mutations involved in cataractogenesis are essential to gaining an understanding of the molecular defects and pathophysiologic characteristics of inherited congenital cataracts. In this review, we summarize the current research in this field.

A splice site mutation in CRYBA1/A3 causing autosomal dominant posterior polar cataract in a Chinese pedigree

PURPOSE

To identify the mutant gene for autosomal dominant posterior polar congenital cataract in a four-generation Chinese pedigree.

METHODS

The clinical data of patients from the family were recorded by slit-lamp photography. Genomic DNA samples from peripheral blood of the pedigree members were then isolated to map the relevant gene, using microsatellite markers for two-point linkage analysis. Genotype and haplotypes of the pedigree were constructed using Cyrillic software to locate the relevant region. Direct sequencing was performed to screen out the disease-causing mutation.

RESULTS

The congenital cataract phenotype of the pedigree was labeled as the posterior polar type by using slit-lamp photography. Linkage analysis results indicated a maximum logarithm of odds LOD score of (Z(max)) 2.02 at D17S1800 (theta(max)=0.00). Haplotyping identified a 26-cM region flanked by D17S921 and D17S800 on 17p12-21.2, namely at the betaA1/A3-crystallin (CRYBA1/A3) gene locus. Sequencing revealed a splice site mutation, G-->A, at the first base of intron 3 of CRYBA1/A3, which co-segregated with the affected individuals in the pedigree but which was not found in the unaffected members of the family or in the 50 unrelated controls.

CONCLUSIONS

Our results demonstrated that a splice site mutation of CRYBA1/A3 was responsible for the autosomal dominant posterior polar congenital cataract in a four-generation Chinese pedigree. The same mutation in this gene had previously been reported to be associated with other phenotype cataracts. This study is the first report relating a mutation of CRYBA1/A3 to posterior polar cataract.

Anterior segment mesenchymal dysgenesis in a large Australian family is associated with the recurrent 17 bp duplication in PITX3

PURPOSE

A recurrent 17 bp duplication (c.657ins17bp) of a segment of the paired-like homeodomain transcription factor 3 (PITX3) gene on human chromosome 10 has been reported in seven families with autosomal dominant posterior polar cataracts with or without anterior segment mesenchymal dysgenesis (ASMD). ASMD can include Peters anomaly with corneal clouding, iridolenticular corneal adhesions, displaced Schwalbe's line, and cataract as described previously in a large Australian family. This study reports the examination of PITX3 in this Australian family.

METHODS

Clinical examinations of the proband and her relatives were performed as part of routine follow up. A polymerase chain reaction (PCR) based test for the duplication in PITX3 was developed, and DNA from 21 members of the proband's family was tested.

RESULTS

All clinically affected members of the family had the same 17 bp duplication of PITX3. There was no difference in the size of the duplication between the severely affected individuals and the more mildly affected individuals. Prenatal diagnosis was performed for two offspring of one affected person. In the first pregnancy, the fetus was shown to carry the duplication while in the second pregnancy, the fetus was shown to be homozygous for the normal allele.

CONCLUSIONS

The results show that in some individuals within one family, duplication of this segment of PITX3 can result in severe symptoms leading to functional blindness while in other individuals in the same family or in other families, the same duplication leads to treatable cataract with minimal visual impairment.

Functional analysis of human mutations in homeodomain transcription factor PITX3

BACKGROUND

The homeodomain-containing transcription factor PITX3 was shown to be essential for normal eye development in vertebrates. Human patients with point mutations in PITX3 demonstrate congenital cataracts along with anterior segment defects in some cases when one allele is affected and microphthalmia with brain malformations when both copies are mutated. The functional consequences of these human mutations remain unknown.

RESULTS

We studied the PITX3 mutant proteins S13N and G219fs to determine the type and severity of functional defects. Our results demonstrate alterations in DNA-binding profiles and/or transactivation activities and suggest a partial loss-of-function in both mutants with the G219fs form being more severely affected. No anomalies in cellular distribution and no dominant-negative effects were discovered for these mutants. Interestingly, the impairment of the G219fs activity varied between different ocular cell lines.

CONCLUSION

The G219fs mutation was found in multiple families affected with congenital cataracts along with anterior segment malformations in many members. Our data suggest that the presence/severity of anterior segment defects in families affected with G219fs may be determined by secondary factors that are expressed in the developing anterior segment structures and may modify the effect(s) of this mutation. The S13N mutant showed only minor alteration of transactivation ability and DNA binding pattern and may represent a rare polymorphism in the PITX3 gene. A possible contribution of this mutation to human disease needs to be further investigated.

A heterozygous c-Maf transactivation domain mutation causes congenital cataract and enhances target gene activation

MAF, one of a family of large Maf bZIP transcription factors, is mutated in human developmental ocular disorders that include congenital cataract, microcornea, coloboma and anterior segment dysgenesis. Expressed early in the developing lens vesicle, it is central to regulation of lens crystallin gene expression. We report a semi-dominant mouse c-Maf mutation recovered after ENU mutatgenesis which results in the substitution, D90V, at a highly conserved residue within the N-terminal 35 amino-acid minimal transactivation domain (MTD). Unlike null and loss-of-function c-Maf mutations, which cause severe runting and renal abnormalities, the phenotype caused by the D90V mutation is isolated cataract. In reporter assays, D90V results in increased promoter activation, a situation similar to MTD mutations of NRL that also cause human disease. In contrast to wild-type protein, the c-Maf D90V mutant protein is not inhibited by protein kinase A-dependent pathways. The MTD of large Maf proteins has been shown to interact with the transcriptional co-activator p300 and we demonstrate that c-Maf D90V enhances p300 recruitment in a cell-type dependent manner. We observed the same for the pathogenic human NRL MTD mutation S50T, which suggests a common mechanism of action.

Posterior polar cataract: genetic analysis of a large family

Congenital cataracts are clinically and genetically heterogeneous. Loci for autosomal dominant posterior polar cataracts have been mapped to chromosomes 1p36, 11q22-q22.3, 16q22, and 20p12-q12. We investigated a large four-generation family with 20 individuals affected with congenital posterior polar cataracts. After exclusion of known loci for posterior polar cataracts, a genome-wide screen was conducted. In this family, we mapped dominant congenital posterior polar cataracts to chromosome 10q24. On haplotype analysis, we identified an 11-cM interval between loci D10S1680 and D10S467, which included the PITX3 gene. On sequencing the coding region of PITX3, we found a 17-base-pair duplication in exon 4. Although the same genotype was described in a family with ASMD and cataracts, the common phenotype of this mutation is probably posterior polar cataract; a modifier gene is presumed to cause anterior segment abnormalities in the previously described patients. The same mutation was recently identified in four families with congenital cataracts. This study provides further evidence of genetic heterogeneity of autosomal dominant posterior polar cataract.

Novel phenotype of craniosynostosis and ocular anterior chamber dysgenesis with a fibroblast growth factor receptor 2 mutation

Fibroblast growth factor receptor 2 (FGFR2) mutations are associated with syndromic and non-syndromic craniosynostoses. More recently it has been recognized that FGFR2 may have a role in the development of the anterior chamber of the eye following the finding of a specific FGFR2 mutation (p.Ser351Cys, c.1231 C --> G) with anterior chamber dysgenesis. Affected patients had a severe craniofacial phenotype and clinical course. A child with a different FGFR2 mutation (p.Ala344Ala, c1032 G --> A heterozygote), premature fusion of the sagittal suture, and an Axenfeld-Rieger anomaly but otherwise normal clinical course is reported. The case provides further evidence that FGFR2 has a role in anterior chamber embryogenesis.