Psychiatric disorder and cognitive function in a family with an inherited novel mutation of the developmental control gene PAX6

Epidemiology of PAX6 Gene Pathogenic Variants and Expected Prevalence of PAX6-Associated Congenital Aniridia across the Russian Federation: A Nationwide Study

This study investigates the distribution of PAX6-associated congenital aniridia (AN) and WAGR syndrome across Russian Federation (RF) districts while characterizing PAX6 gene variants. We contribute novel PAX6 pathogenic variants and 11p13 chromosome region rearrangements to international databases based on a cohort of 379 AN patients (295 families, 295 probands) in Russia. We detail 100 newly characterized families (129 patients) recruited from clinical practice and specialized screening studies. Our methodology involves multiplex ligase-dependent probe amplification (MLPA) analysis of the 11p13 chromosome, PAX6 gene Sanger sequencing, and karyotype analysis. We report novel findings on PAX6 gene variations, including 67 intragenic PAX6 variants and 33 chromosome deletions in the 100 newly characterized families. Our expanded sample of 295 AN families with 379 patients reveals a consistent global PAX6 variant spectrum, including CNVs (copy number variants) of the 11p13 chromosome (31%), complex rearrangements (1.4%), nonsense (25%), frameshift (18%), and splicing variants (15%). No genetic cause of AN is defined in 10 patients. The distribution of patients across the Russian Federation varies, likely due to sample completeness. This study offers the first AN epidemiological data for the RF, providing a comprehensive PAX6 variants spectrum. Based on earlier assessment of AN prevalence in the RF (1:98,943) we have revealed unexamined patients ranging from 55% to 87%, that emphases the need for increased awareness and comprehensive diagnostics in AN patient care in Russia.

Self-reported symptoms of everyday executive dysfunction, daytime sleepiness, and fatigue and health status among adults with congenital aniridia: a descriptive study

Background

Congenital aniridia is a rare genetic disorder of the eye characterized by visual impairment and progressive vision loss. While prior research has focused on ocular manifestations in individuals with aniridia, there is a dearth of research on impacts on cognition and mental health. The aims of this study were to describe subjective symptoms of everyday executive functioning, fatigue and sleepiness in adults with aniridia and to compare self-reported health status with that of a normative reference group.

Methods

Twenty-nine adults (aged 18-79 years) with congenital aniridia were included in this online survey, of whom 52% were females. Participants completed self-report measures of executive functioning (The Behavior Rating Inventory of Executive Function-Adult Version), sleepiness, fatigue, and health status (EQ-5D-5L).

Results

Participants reported relatively few problems in everyday executive functioning, with only 14% experiencing impaired executive functioning. Scores on the five EQ-5D-5L domains (mobility, self-care, usual activities, pain, and anxiety/depression) did not differ from those of the normative reference group. The frequencies of excessive daytime sleepiness and severe fatigue were 17% and 38%, respectively. Ocular pain was experienced by 62% of participants.

Conclusions

The findings show that cognitive problems are related to and reflect self-reported health status and extent of fatigue. Moreover, those who suffered from ocular pain reported more difficulties with executive functioning, sleepiness and fatigue. These findings are important for understanding this disorder and supporting patients.

Congenital aniridia beyond black eyes: From phenotype and novel genetic mechanisms to innovative therapeutic approaches

Congenital PAX6-aniridia, initially characterized by the absence of the iris, has progressively been shown to be associated with other developmental ocular abnormalities and systemic features making congenital aniridia a complex syndromic disorder rather than a simple isolated disease of the iris. Moreover, foveal hypoplasia is now recognized as a more frequent feature than complete iris hypoplasia and a major visual prognosis determinant, reversing the classical clinical picture of this disease. Conversely, iris malformation is also a feature of various anterior segment dysgenesis disorders caused by PAX6-related developmental genes, adding a level of genetic complexity for accurate molecular diagnosis of aniridia. Therefore, the clinical recognition and differential genetic diagnosis of PAX6-related aniridia has been revealed to be much more challenging than initially thought, and still remains under-investigated. Here, we update specific clinical features of aniridia, with emphasis on their genotype correlations, as well as provide new knowledge regarding the PAX6 gene and its mutational spectrum, and highlight the beneficial utility of clinically implementing targeted Next-Generation Sequencing combined with Whole-Genome Sequencing to increase the genetic diagnostic yield of aniridia. We also present new molecular mechanisms underlying aniridia and aniridia-like phenotypes. Finally, we discuss the appropriate medical and surgical management of aniridic eyes, as well as innovative therapeutic options. Altogether, these combined clinical-genetic approaches will help to accelerate time to diagnosis, provide better determination of the disease prognosis and management, and confirm eligibility for future clinical trials or genetic-specific therapies.

Analysis of color vision and cognitive function in first-episode schizophrenia before and after antipsychotic treatment

BACKGROUND

A large body of recent research has demonstrated that patients with schizophrenia exhibit significant changes in visual function and ocular tissue structure in the early stages of onset. It is therefore possible to explore a novel scientific breakthrough in the etiology of schizophrenia by transforming the traditional study of brain structure and function with a view to examining the potential field of eye tissue and function. However, few studies have investigated the correlation between iris characteristics and schizophrenia, and evidence is lacking in this regard. Thus, further exploration is needed.

PURPOSE

This study was designed to analyze the characteristics of iris structure, color vision function and cognitive function, as well as the changes therein in patients with the first-episode drug-free schizophrenia before and after antipsychotic treatment. It aimed to preliminarily identify easily-measurable biomarkers for early clinical screening and diagnosis of schizophrenia.

METHODS

This study recruited 61 patients (22 males) with first-episode schizophrenia. Prior to the commencement of treatment with antipsychotic drugs, the Montreal Cognitive Assessment (MoCA) and Farnsworth-Munsell Dichotomous (D-15 Hue Test) were used as assessment tools to evaluate cognitive function and color vision function, respectively. Over a 6-week period, patients received a second-generation antipsychotic treatment (all converted to olanzapine equivalent dose) as prescribed by the doctor, and the Positive and Negative Syndrome Scale (PANSS) was applied to evaluate the clinical treatment effects before treatment (baseline), as well as at the 2nd, 4th, and 6th weeks after drug treatment. On the basis of iris characteristics, the patients were divided into groups. The observed differences in drug treatment effects between the groups were then compared and analyzed to further clarify the relationship between treatment efficacy and iris characteristics. Finally, changes in the cognitive function and color vision function of patients at baseline and at the 6th week after drug treatment were compared, and the effects of antipsychotic drug treatment on the above-mentioned functions were analyzed.

RESULTS

On the basis of structural iris characteristics, 61 patients were classified as follows: 28 patients without iris crypts and 33 with iris crypts; 35 without iris pigment dots and 26 with iris pigment dots; 42 without iris wrinkles and 19 with iris wrinkles. No significant difference was observed in the PANSS scores of all of the patients at baseline; however, significant differences were found in patients with iris crypts and iris pigment dots at each follow-up timepoint (i.e., at the 2nd, 4th, and 6th week). Moreover, it is noteworthy that, compared with other patients, the PANSS scores of patients without specific iris structure characteristics (iris crypts and pigment dots) decreased significantly (P<0.05), which indicated that the drug therapy was highly effective. Excluding the interference of drug factors, a significant correlation was found between the results of the D-15 (color vision function) and MoCA (cognitive function) in first-episode untreated patients (r = -0.401, P < 0.05). In addition, the MoCA scores (mean difference = 2.36, t = 10.05, P ˂ 0.01) were significantly higher after 6 weeks of antipsychotic drug treatment compared to conditions at baseline.

CONCLUSIONS

The findings of this study demonstrated that color vision function of patients with schizophrenia improved with the improvement of cognitive function. The structural characteristics of the iris with crypts and pigment dots could have a significant impact on the drug treatment effect of schizophrenia and could be considered as a potential biomarker for detecting and recognizing schizophrenia.

Study on the Correlation Between Iris Characteristics and Schizophrenia

BACKGROUND

Recently, researchers have conducted many studies on the potential contribution of the retina and other eye structures on schizophrenia. This study aimed to evaluate differences in iris characteristics between patients with schizophrenia and healthy individuals so as to find more easily accessible and easily measurable biomarkers with a view to improving clinical assessments and furthering our understanding of the disease.

METHODS

Overall, 80 patients with schizophrenia and 52 healthy individuals were included in the case group and the control group, respectively. Iris images were collected from all subjects to compare differences in the structure and color of the iris. The Positive and Negative Symptom Scale (PANSS) and the Modified Overt Aggression Scale (MOAS) were used to evaluate the clinical symptoms and characteristics of 45 first-episode untreated schizophrenics, and analyzed correlations between iris characteristics and schizophrenia symptoms.

RESULTS

There were significant differences in iris crypts (P<0.05) and pigment spots (P<0.01) between the case and control group, but no significant difference was found in iris wrinkles (P<0.05). The logistic regression analysis demonstrated that the total iris crypts [odds ratio (OR) 1.166, 95% confidence interval (CI) 1.022-1.330] and total iris pigment spots (OR 1.815, 95% CI 1.186-2.775) increased the risk of suffering from schizophrenia. Furthermore, it was demonstrated that the number of iris crypts was positively associated with the MOAS score (r=0.474, P<0.01). Moreover, the number of the iris pigment spots (r=0.395, P<0.01) and wrinkles (r=0.309, P<0.05) were positively correlated with the subjects' negative symptom scores, respectively.

CONCLUSION

Iris crypts and pigment spots were identified as potential biomarkers for detecting schizophrenia. In patients with first-episode untreated schizophrenia, iris characteristics may help psychiatrists to identify the illness and its severity, and to detect characteristic clinical symptoms.

Longitudinal genotype-phenotype analysis in 86 patients with PAX6-related aniridia

Aniridia is most commonly caused by haploinsufficiency of the PAX6 gene, characterized by variable iris and foveal hypoplasia, nystagmus, cataracts, glaucoma, and aniridia-related keratopathy (ARK). Genotype-phenotype correlations have previously been described; however, detailed longitudinal studies of aniridia are less commonly reported. We identified 86 patients from 62 unrelated families with molecularly confirmed heterozygous PAX6 variants from a UK-based single-center ocular genetics service. They were categorized into mutation groups, and a retrospective review of clinical characteristics (ocular and systemic) from baseline to most recent was recorded. One hundred and seventy-two eyes were evaluated, with a mean follow-up period of 16.3 ± 12.7 years. Nystagmus was recorded in 87.2% of the eyes, and foveal hypoplasia was found in 75%. Cataracts were diagnosed in 70.3%, glaucoma in 20.6%, and ARK in 68.6% of eyes. Prevalence, age of diagnosis and surgical intervention, and need for surgical intervention varied among mutation groups. Overall, the missense mutation subgroup had the mildest phenotype, and surgically naive eyes maintained better visual acuity. Systemic evaluation identified type 2 diabetes in 12.8% of the study group, which is twice the UK prevalence. This is the largest longitudinal study of aniridia in the UK, and as such, it can provide insights into prognostic indicators for patients and guiding clinical management of both ocular and systemic features.

Congenital aniridia - A comprehensive review of clinical features and therapeutic approaches

Congenital aniridia is a rare genetic eye disorder with total or partial absence of the iris from birth. In most cases the genetic origin of aniridia is a mutation in the PAX6 gene, leading to involvement of most eye structures. Hypoplasia of the fovea is usually present and is associated with reduced visual acuity and nystagmus. Aniridia-associated keratopathy, glaucoma, and cataract are serious and progressive complications that can further reduce visual function. Treatment of the ocular complications of aniridia is challenging and has a high risk of side effects. New approaches such as stem cell therapy may, however, offer better prognoses. We describe the various ocular manifestations of aniridia, with a special focus on conditions that commonly require treatment. We also review the growing literature reporting systemic manifestations of the disease.

Iris structure and minor physical anomalies in schizophrenia

This study compared five human iris characteristics and minor physical anomalies (MPAs) between patients with schizophrenia (n = 32) and controls (n = 31). Correlations between iris characteristics and MPAs were expected, due to their same ectodermic origin. Iris macro photos were taken and quantified in five categories mentioned before. MPAs were also examined in both groups. Our results show significant differences in the frequency of pigment dots of the iris and total number of MPAs between groups. Other significant differences were found in the extension of concentric furrows, as they were more common in healthy subjects, while Wolfflin nodules occurred significantly more often in patients with schizophrenia. Expected difference in Fuch's crypts could not be observed between groups. Light eye color was positively correlated to pigment dots and Wolfflin nodules, and negatively correlated with concentric furrows. Dark eye color showed positive correlation with concentric furrows, and negative correlation with pigment dots and concentric furrows. A gender effect could also been observed: male individuals showed moderate positive correlations between pigment dots and total MPAs frequency, while this couldn't be observed in the female group. Our findings suggest possible connections between iris characteristics and MPAs, where males are more prone to deviations.

Regional Volume Decreases in the Brain of Pax6 Heterozygous Mutant Rats: MRI Deformation-Based Morphometry

Pax6 is a transcription factor that pleiotropically regulates various developmental processes in the central nervous system. In a previous study, we revealed that Pax6 heterozygous mutant (rSey²/+) adult rats exhibit abnormalities in social interaction. However, the brain malformations underlying the behavioral abnormality are unknown. To elucidate the brain malformations in rSey²/+ rats, we morphometrically analyzed brains of rSey²/+ and wild type rats using small-animal magnetic resonance imaging (MRI). Sixty 10-week-old rats underwent brain MRI (29 rSey²/+ rats and 31 wild type rats). SPM8 software was used for image preprocessing and statistical image analysis. Normalized maps of the Jacobian determinant, a parameter for the expansion and/or contraction of brain regions, were obtained for each rat. rSey²/+ rats showed significant volume decreases in various brain regions including the neocortex, corpus callosum, olfactory structures, hippocampal formation, diencephalon, and midbrain compared to wild type rats. Among brain regions, the anterior commissure showed significant interaction between genotype and sex, indicating the effect of genotype difference on the anterior commissure volume was more robust in females than in males. The rSey²/+ rats exhibited decreased volume in various gray and white matter regions of the brain, which may contribute to manifestation of abnormal social behaviors.

Pax6 influences expression patterns of genes involved in neuro- degeneration

Background

Pax6, a highly conserved multifunctional transcription factor, has been critical for neurogenesis and neuronal plasticity. It is presumed that if level of Pax6 approaches either low or null, critical genes responsible for maintaining functional status of neurons or glia would be modulated.

Purpose

Therefore, it has been intended to explore possibility of either direct or indirect influence of Pax6 in neurodegeneration.

Methods

The cell lines having origin of murine embryonic fibroblast (Pax6-non expressing, NIH3T3-cell line), murine neuroblastoma (Pax6-expressing brain-derived, Neuro-2a-cell line), and human glioblastoma-astrocytoma (U87MG) were cultured and maintained in a CO₂ incubator at 37°C and 5% CO₂ in DMEM containing 10% fetal bovine serum. The knockdown of endogenous Pax6 in Neuro-2a cells was achieved through siRNA based gene knock-down approach. The efficiency and validation of knock-down was done by real time PCR. The knock-down of Pax6 was successfully achieved.

Results

The levels of expression of transcripts of some of the proposed putative markers of neurodegeneration like Pax6, S100β, GFAP, BDNF, NGN2, p73α, p73δ, LDH, SOD, and Catalase were analyzed in Pax6 knockdown condition for analysis of role of Pax6 in neurodegeneration. Since the Pax6 has been proposed to bind to promoter sequences of catalase, and catalase suppresses TGFβ, relative lower levels of catalase in Neuro-2a and U-87MG as compared to NIH-3T3 indicates a possible progressive dominant negative impact of Pax6. However, presence of SOD and LDH indicates alternative protective mechanism.

Conclusion

Presence of BDNF and TGFβ indicates association between them in glioblastoma-astrocytoma. Therefore, Pax6 seems to be involved directly with p53 and TGFβ mediated pathways and indirectly with redox-sensitive pathway regulation. The neurodegenerative markers S100β, GFAP, BDNF, NGN2, p73α, p73δ, observed downregulated in Pax6 knockdown condition suggest Pax6-mediated regulation of these markers. Observations enlighten Pax6-mediated influences on cascades of genes involved in growth, differentiation and maturation of neurons and glia.

Increased functional connectivity in intrinsic neural networks in individuals with aniridia

Mutations affecting the PAX6 gene result in aniridia, a condition characterized by the lack of an iris and other panocular defects. Among humans with aniridia, structural abnormalities also have been reported within the brain. The current study examined the functional implications of these deficits through "resting state" or task-free functional magnetic resonance imaging (fMRI) in 12 individuals with aniridia and 12 healthy age- and gender-matched controls. Using independent components analysis (ICA) and dual regression, individual patterns of functional connectivity associated with three intrinsic connectivity networks (ICNs; executive control, primary visual, and default mode) were compared across groups. In all three analyses, the aniridia group exhibited regions of greater connectivity correlated with the network, while the controls did not show any such regions. These differences suggest that individuals with aniridia recruit additional neural regions to supplement function in critical intrinsic networks, possibly due to inherent structural or sensory abnormalities related to the disorder.

Aniridia

Aniridia is a rare congenital disorder in which there is a variable degree of hypoplasia or the absence of iris tissue associated with multiple other ocular changes, some present from birth and some arising progressively over time. Most cases are associated with dominantly inherited mutations or deletions of the PAX6 gene. This article will review the clinical manifestations, the molecular basis including genotype-phenotype correlations, diagnostic approaches and management of aniridia.

Discovery and assessment of conserved Pax6 target genes and enhancers

The characterization of transcriptional networks (TNs) is essential for understanding complex biological phenomena such as development, disease, and evolution. In this study, we have designed and implemented a procedure that combines in silico target screens with zebrafish and mouse validation, in order to identify cis-elements and genes directly regulated by Pax6. We chose Pax6 as the paradigm because of its crucial roles in organogenesis and human disease. We identified over 600 putative Pax6 binding sites and more than 200 predicted direct target genes, conserved in evolution from zebrafish to human and to mouse. This was accomplished using hidden Markov models (HMMs) generated from experimentally validated Pax6 binding sites. A small sample of genes, expressed in the neural lineage, was chosen from the predictions for RNA in situ validation using zebrafish and mouse models. Validation of DNA binding to some predicted cis-elements was also carried out using chromatin immunoprecipitation (ChIP) and zebrafish reporter transgenic studies. The results show that this combined procedure is a highly efficient tool to investigate the architecture of TNs and constitutes a useful complementary resource to ChIP and expression data sets because of its inherent spatiotemporal independence. We have identified several novel direct targets, including some putative disease genes, among them Foxp2; these will allow further dissection of Pax6 function in development and disease.

Selective cortical layering abnormalities and behavioral deficits in cortex-specific Pax6 knock-out mice

The transcription factor Pax6 has been implicated in neocortical neurogenesis in vertebrates, including humans. Analyses of the role of Pax6 in layer formation and cognitive abilities have been hampered by perinatal lethality of Pax6 mutants. Here, we generated viable mutants exhibiting timed, restricted inactivation of Pax6 during early and late cortical neurogenesis using Emx1-Cre and hGFAP-Cre lines, respectively. The disruption of Pax6 at the onset of neurogenesis using Emx1-Cre line resulted in premature cell cycle exit of early progenitors, increase of early born neuronal subsets located in the marginal zone and lower layers, and a nearly complete absence of upper layer neurons, especially in the rostral cortex. Furthermore, progenitors, which accumulated in the enlarged germinal neuroepithelium at the pallial/subpallial border in the Pax6 mutants, produced an excess of oligodendrocytes. The inactivation of Pax6 after generation of the lower neuronal layers using hGFAP-Cre line did not affect specification or numbers of late-born neurons, indicating that the severe reduction of upper layer neurons in Pax6 deficiency is mostly attributable to a depletion of the progenitor pool, available for late neurogenesis. We further show that Pax6(fl/fl);Emx1-Cre mutants exhibited deficiencies in sensorimotor information integration, and both hippocampus-dependent short-term and neocortex-dependent long-term memory recall. Because a majority of the morphological and behavior disabilities of the Pax6 mutant mice parallel abnormalities reported for aniridia patients, a condition caused by PAX6 haploinsufficiency, the Pax6 conditional mutant mice generated here represent a valuable genetic tool to understand how the developmental cortical disruption can lead to a human behavior abnormality.

A novel missense mutation (Leu46Val) of PAX6 found in an autistic patient

The paired box 6 (PAX6) is a transcription factor expressed early in development, predominantly in the eye, brain and pancreas. Mutations in PAX6 are responsible for eye abnormalities including aniridia, and it is also known that some PAX6 mutations result in autism with incomplete penetrance. We resequenced all the exons and flanking introns of PAX6 in 285 autistic patients in the Japanese, with the possibility that novel mutations may underlie autism. Fifteen different polymorphisms were identified: 13 are novel, and 2 were previously reported (rs667773 and rs3026393). Among the novel ones, there is one missense mutation that was found in a patient: 136C>G (Leu46Val) (single nucleotide polymorphism ID "ss130452457" is temporarily assigned). Leu46 is extremely conserved from fly to human, and we did not detect Val46 in 2120 nonautistic subjects. The autistic patient carrying this heterozygous mutation showed reduced vision, photophobia and eyelid ptosis, but no other ocular abnormality such as aniridia. Our findings suggest the necessity of further studies on the causal relationship between PAX6 and autism.

In vivo MRI of altered brain anatomy and fiber connectivity in adult pax6 deficient mice

The impact of developmental ablation of Pax6 function on morphology and functional connectivity of the adult cerebrum was studied in cortex-specific Pax6 knockout mice (Pax6cKO) using structural magnetic resonance imaging (MRI), manganese-enhanced MRI, and diffusion tensor MRI in conjunction with fiber tractography. Mutants presented with decreased volumes of total brain and olfactory bulb, reduced cortical thickness, and altered layering of the piriform cortex. Tracking of major neuronal fiber bundles revealed a disorganization of callosal fibers with an almost complete lack of interhemispheric connectivity. In Pax6cKO mice intrahemispheric callosal fibers as well as intracortical fibers were predominantly directed along a rostrocaudal orientation instead of a left-right and dorsoventral orientation found in controls. Fiber disorganization also involved the septohippocampal connection targeting mostly the lateral septal nucleus. The hippocampus was rostrally extended and its volume was increased relative to that of the forebrain and midbrain. Manganese-induced MRI signal enhancement in the CA3 region suggested a normal function of hippocampal pyramidal cells. Noteworthy, several morphologic disturbances in gray and white matter of Pax6cKO mice were similar to observations in human aniridia patients. The present findings indicate an important role of Pax6 in the development of both the cortex and cerebral fiber connectivity.

Pax6 3' deletion results in aniridia, autism and mental retardation

The PAX6 gene is a transcription factor expressed early in development, predominantly in the eye, brain and gut. It is well known that mutations in PAX6 may result in aniridia, Peter's anomaly and kertatisis. Here, we present mutation analysis of a patient with aniridia, autism and mental retardation. We identified and characterized a 1.3 Mb deletion that disrupts PAX6 transcriptional activity and deletes additional genes expressed in the brain. Our findings provide continued evidence for the role of PAX6 in neural phenotypes associated with aniridia.

Associations between iris characteristics and personality in adulthood

Variable and person-oriented analyses were used to explore the associations between personality and three previously untested general iris characteristics: crypts, pigment dots and contraction furrows. Personality data, as measured by the NEO PI-R and ratings of iris characteristics from 428 undergraduate students were collected. Crypts were significantly associated with five approach-related behaviors, i.e., feelings, tendermindedness, warmth, trust and positive emotions, whereas furrows were associated with impulsiveness. These findings suggest that because Pax6 induces tissue deficiencies in both the iris and the left anterior cingulate cortex, Pax6 may influence the extent people engage in approach-related behaviors. The results from using a person-oriented analysis suggested that people with different iris configurations tend to develop along different personality trajectories. Future longitudinal studies, twin-studies and genetic association studies, may benefit from collecting iris data and testing candidate genes for crypts and furrows.

Association of Aniridia and Dry Eyes

PURPOSE

To study the association between congenital aniridia and dry eyes, and the status of limbal stem cells.

DESIGN

Single-center, retrospective, noninterventional, comparative case series.

PARTICIPANTS

Twenty patients (36 eyes) diagnosed with congenital aniridia.

METHODS

Retrospective review of medical records at the King Khaled Eye Specialist Hospital in Riyadh, Saudi Arabia to identify all cases of congenital aniridia. Selected patients were requested to undergo further testing, especially for evaluation of dry eyes. Full ocular examinations were performed, including examination of the meibomian gland orifices and dry eye evaluation (by predetermined criteria of tear breakup time, tear meniscus level, presence of mucoid secretions, Schirmer's test with and without anesthesia, and fluorescein and rose Bengal staining patterns of the cornea and conjunctiva). Cytological evaluation was performed in 23 aniridic eyes by impression cytology to determine limbal stem cell status relative to control normal eyes.

MAIN OUTCOME MEASURES

Abnormal tear film production and stability, meibomian gland dysfunction, severity of corneal involvement, and limbal stem cell deficiency.

RESULTS

Twenty patients (36 eyes) diagnosed with congenital aniridia were classified into 3 groups according to the severity of corneal involvement: mild (2 eyes), moderate (21 eyes), and advanced (13 eyes) corneal changes. Tear breakup time was reduced by an average of 5 seconds in 90.7% of cases, tear meniscus levels were reduced to <0.5 mm in 88.6% of cases, and stenosed meibomian orifices were found in 77.8% of patients. Dry eyes (94%) correlated with the severity of corneal involvement (P = 0.001). Impression cytology revealed metaplasia in all tested cases. Furthermore, 8 of 23 eyes (35%) and 15 of 23 eyes (65%) had early and advanced limbal stem cell deficiency, respectively.

CONCLUSIONS

Abnormal tear film stability and meibomian gland dysfunction are newly identified factors in patients with aniridia. Both correlate to the severity of ocular surface disease. Impression cytology is informative in diagnosing various degrees of limbal stem cell deficiency, which is present in all tested aniridia eyes.

A screen for proteins that interact with PAX6: C-terminal mutations disrupt interaction with HOMER3, DNCL1 and TRIM11

Background

The PAX6 protein is a transcriptional regulator with a key role in ocular and neurological development. Individuals with heterozygous loss-of-function mutations in the PAX6 gene have malformations of the eye and brain. Little is known about the interactions of PAX6 with other proteins, so we carried out a systematic screen for proteins that interact with PAX6.

Results

We used bioinformatics techniques to characterise a highly conserved peptide at the C-terminus of the PAX6 protein. Yeast two-hybrid library screens were then carried out to identify brain-expressed proteins that interact with the C-terminal peptide and with the entire PAX6 proline-serine-threonine-rich domain. Three novel PAX6-interacting proteins were identified: the post-synaptic density (PSD) protein HOMER3, the dynein subunit DNCL1, and the tripartite motif protein TRIM11. Three C-terminal PAX6 mutations, previously identified in patients with eye malformations, all reduced or abolished the interactions.

Conclusion

Our preliminary data suggest that PAX6 interacts with HOMER3, DNCL1 and TRIM11. We propose that the interaction of PAX6 with HOMER3 and DNCL1 is a mechanism by which synaptic activation could lead to changes in neuronal transcriptional activity, and that some of the neural anomalies in patients with PAX6 mutations could be explained by impaired protein-protein interactions.

Pathological aggression in "fierce" mice corrected by human nuclear receptor 2E1

"Fierce" mice, homozygous for the deletion of nuclear receptor 2E1 (NR2E1), show abnormal brain-eye development and pathological aggression. To evaluate functional equivalency between mouse and human NR2E1, we generated mice transgenic for a genomic clone spanning the human NR2E1 locus and bred these animals to fierce mice deleted for the corresponding mouse gene. In fierce mutants carrying human NR2E1, structural brain defects were eliminated and eye abnormalities ameliorated. Excitingly, behavior in these "rescue" mice was indistinguishable from controls. Because no artificial promoter was used to drive transgene expression, promoter and regulatory elements within the human NR2E1 clone are functional in mouse. Normal behavior in rescue animals suggests that mechanisms underlying the behavioral abnormalities in fierce mice may also be conserved in humans. Our data support the hypothesis that variation at NR2E1 may contribute to human behavioral disorders. Use of this rescue paradigm with other genes will permit the direct evaluation of human genes hypothesized to play a causal role in psychiatric disease but for which evidence is lacking or equivocal.

PAX6 mutations: genotype-phenotype correlations

BACKGROUND

The PAX6 protein is a highly conserved transcriptional regulator that is important for normal ocular and neural development. In humans, heterozygous mutations of the PAX6 gene cause aniridia (absence of the iris) and related developmental eye diseases. PAX6 mutations are archived in the Human PAX6 Allelic Variant Database, which currently contains 309 records, 286 of which are mutations in patients with eye malformations.

RESULTS

We examined the records in the Human PAX6 Allelic Variant Database and documented the frequency of different mutation types, the phenotypes associated with different mutation types, the contribution of CpG transitions to the PAX6 mutation spectrum, and the distribution of chain-terminating mutations in the open reading frame. Mutations that introduce a premature termination codon into the open reading frame are predominantly associated with aniridia; in contrast, non-aniridia phenotypes are typically associated with missense mutations. Four CpG dinucleotides in exons 8, 9, 10 and 11 are major mutation hotspots, and transitions at these CpG's account for over half of all nonsense mutations in the database. Truncating mutations are distributed throughout the PAX6 coding region, except for the last half of exon 12 and the coding part of exon 13, where they are completely absent. The absence of truncating mutations in the 3' part of the coding region is statistically significant and is consistent with the idea that nonsense-mediated decay acts on PAX6 mutant alleles.

CONCLUSION

The PAX6 Allelic Variant Database is a valuable resource for studying genotype-phenotype correlations. The consistent association of truncating mutations with the aniridia phenotype, and the distribution of truncating mutations in the PAX6 open reading frame, suggests that nonsense-mediated decay acts on PAX6 mutant alleles.

Three patients with hallucal polydactyly and WAGR syndrome, including discordant expression of Wilms tumor in MZ twins

The WAGR contiguous gene deletion syndrome is a combination of Wilms tumor, Aniridia, Genito-urinary abnormalities, and growth and mental retardation which is invariably associated with an 11p13 deletion. We report two monozygotic twins and a third, unrelated patient with WAGR syndrome and additional clinical features not usually associated with WAGR. Both twins had developmental delay, growth deficiency, severe ocular involvement (nystagmus, aniridia, cataracts), atrial septal defect and two uncommon findings: agenesis of the corpus callosum and duplication of the halluces. One twin developed Wilms tumors aged 19 months while her sister remained tumor free by the age of 6.5 years. The singleton patient showed typical WAGR syndrome and preaxial hallucal polydactyly. Molecular cytogenetic studies refined the identification of the extent of the deleted segments, which were not identical in the two families. The two deletions included the PAX6 and WT1 genes as previously reported in typical WAGR patients. The unusual anomalies described in this report, may represent the expression of low penetrant traits associated with haploinsufficency of one or more of the genes present in the deletion (PAX6 is expressed in CNS) or may indicate epistatic influences of modifier genes on the expression of gene(s) present in the WAGR region.

Inherited eye disease: cause and late effect

Molecular genetics has provided relatively few insights into late-onset eye disorders, but epidemiological data indicate that genetic factors are important in some late-onset eye disorders that cause major health burdens. Much clinical genetic research is based on the belief that developmental and late-onset disorders are not necessarily the result of defects in different genes, but are often caused by different mutations in the same collection of genes. Thus, mutations that either abolish or radically change gene function might cause early-onset disorders, whereas more-subtle changes in gene expression might underlie late-onset diseases. We present arguments and examples that indicate that this principle might be a fruitful guide to investigating the causes of late-onset eye disorders.

Ocular and nonocular findings in patients with aniridia

BACKGROUND

Aniridia typically appears as a familial condition with autosomal dominant inheritance but can present as an isolated disease or sporadically in association with several syndromes. In this report we describe the various ocular manifestations of aniridia as well as the association of familial aniridia with two different ocular and systemic abnormalities present across three generations in two different families.

METHODS

Descriptive case series of 33 patients (66 eyes) with aniridia. A full eye examination was performed at the beginning of the study, including past medical history, family history and type of inheritance, assessment for fixation pattern and presence of nystagmus, visual acuity testing, refraction, slit-lamp examination, gonioscopy, fundus examination with pupil dilation and anterior segment photography; additional glaucoma testing was done if the patient had high intraocular pressure. Patients were followed for at least 2 years. The interval between follow-up visits, which included gonioscopy and fundus examination with pupil dilation, depended on the findings in each case. A urology consultation was requested in all sporadic aniridia cases; consultations in psychiatry and gynecology were requested on the basis of the medical history or clinical suspicion during the ophthalmologic examination.

RESULTS

Ten patients (30%) had sporadic aniridia, with no previous family history; Wilms' tumour did not develop in any of them during the follow-up period. In the autosomal dominant group, ocular and systemic findings present in combination with aniridia were observed in 20 patients in the two families. Family I had aniridia and developmental delay or behavioural disorders in three generations as well as high myopia (greater than 6.00 dioptres) in all affected adults. Family 2 presented a wide phenotypic variability of aniridia with myopia in three generations. Open-angle glaucoma developed in three young adults in this family, and two members were found to have gynecologic abnormalities (hypoplastic uterus and imperforate vagina). Myopia was the most prevalent refractive error (64%) in the 33 patients. Refractive correction significantly improved the visual acuity in half of these cases. Glaucoma was present in 10 patients (30%) and was the main cause of vision loss, provoking blindness in two cases (6%). Affected patients manifested progressive angle closure or presented with open-angle glaucoma.

INTERPRETATION

Ophthalmologists should consider aniridia in patients with unusual iris malformations. Examination of family members may be key in making the diagnosis. Any refractive error should be corrected, as this may improve vision. All aniridic patients should be screened regularly for glaucoma, as this condition may occur at any age and can lead to permanent vision loss. Systemic and ocular associations should be considered as they may present in combination with anirida. In our series, developmental delay or behavioural disorders and myopia were associated conditions.

Heterozygous PAX6 mutation, adult brain structure and fronto-striato-thalamic function in a human family

Recent progress in developmental neurobiology and neuroimaging can be drawn together to provide new insight into the links between genetically specified processes of embryonic brain development and adult human brain structure and function. We used magnetic resonance imaging (MRI) to show that individuals with aniridia and deficits in executive and social cognition, due to heterozygous mutation of the neurodevelopmental control gene PAX6, have structural abnormalities of grey matter in anterior cingulate cortex, cerebellum and medial temporal lobe, as well as white matter deficits in corpus callosum. Functional MRI demonstrated reduced activation of fronto-striato-thalamic systems during performance of overt verbal fluency and nonsense sentence completion; the most consistent abnormality of verbal executive activation was located in the thalamus. These results provide the first evidence for brain functional differences in humans with PAX6 mutation that are compatible both with anatomical abnormalities in the same subjects and, more circumstantially, with the known roles of murine Pax6 in regional differentiation, axonal guidance and other aspects of early forebrain development. Highly conserved homeobox genes may be critical for normal ontogenesis of large-scale neurocognitive networks supporting phylogenetically advanced mental functions.

Cognitive functioning in humans with mutations of thePAX6gene

Fourteen patients with PAX6 gene mutations and previously identified MRI abnormalities were administered tests of cognitive functioning. No deficits were found. A subgroup with agenesis of the anterior commissure performed significantly more poorly on measures of working memory than those without this abnormality, suggesting the anterior commissure may play a role in cognitive processing in addition to an earlier identified role in sensory development and processing.

PAX6 and congenital eye malformations

The PAX6 gene is a paradigm for our understanding of the molecular genetics of mammalian eye development. Twelve years after its identification it is one of the most intensively studied genes, both in terms of its diverse and complex functions during oculogenesis and its role in an ever-increasing variety of human congenital eye malformations. The PAX6 field has benefited greatly from the continued input of clinicians, human geneticists and developmental biologists. This review summarizes the latest data on the PAX6 mutation spectrum and recent insights into Pax6 function from the mouse.

A comparative cDNA microarray analysis reveals a spectrum of genes regulated by Pax6 in mouse lens

BACKGROUND

Pax6 is a transcription factor that is required for induction, growth, and maintenance of the lens; however, few direct target genes of Pax6 are known.

RESULTS

In this report, we describe the results of a cDNA microarray analysis of lens transcripts from transgenic mice over-expressing Pax6 in lens fibre cells in order to narrow the field of potential direct Pax6 target genes. This study revealed that the transcript levels were significantly altered for 508 of the 9700 genes analysed, including five genes encoding the cell adhesion molecules beta1-integrin, JAM1, L1 CAM, NCAM-140 and neogenin. Notably, comparisons between the genes differentially expressed in Pax6 heterozygous and Pax6 over-expressing lenses identified 13 common genes, including paralemmin, GDIbeta, ATF1, Hrp12 and Brg1. Immunohistochemistry and Western blotting demonstrated that Brg1 is expressed in the embryonic and neonatal (2-week-old) but not in 14-week adult lenses, and confirmed altered expression in transgenic lenses over-expressing Pax6. Furthermore, EMSA demonstrated that the BRG1 promoter contains Pax6 binding sites, further supporting the proposition that it is directly regulated by Pax6.

CONCLUSIONS

These results provide a list of genes with possible roles in lens biology and cataracts that are directly or indirectly regulated by Pax6.

Identification of genes downstream of Pax6 in the mouse lens using cDNA microarrays

Pax6 is a transcription factor that regulates the development of the visual, olfactory, and central nervous systems, pituitary, and pancreas. Pax6 is required for induction, growth, and maintenance of the lens; however, few direct Pax6 target genes are known. This study was designed to identify batteries of differentially expressed genes in three related systems: 8-week old Pax6 heterozygous lenses, 8-week old Pax6 heterozygous eyes, and transgenic lenses overexpressing PAX6(5a), using high throughput cDNA microarrays containing about 9700 genes. Initially, we obtained almost 400 differentially expressed genes in lenses from mice heterozygous for a Pax6 deletion, suggesting that Pax6 haploinsufficiency causes global changes in the lens transcriptome. Comparisons between the three sets of analyses revealed that paralemmin, molybdopterin synthase sulfurylase, Tel6 oncogene (ETV6), a cleavage-specific factor (Cpsf1) and tangerin A were abnormally expressed in all three experimental models. Semiquantitative reverse transcription (RT)-PCR analysis confirmed that all five of these genes were differentially expressed in Pax-6 heterozygous and Pax6(5a) transgenic lenses. Western blotting and immunohistochemistry demonstrated that paralemmin is found at high levels in the adult lens and confirmed its down-regulation in the Pax6(5a)-transgenic lenses. Collectively, our data provide insights into the genetic programs regulated by Pax6 in the lens.

Pax6 controls the expression of Lewis x epitope in the embryonic forebrain by regulating alpha 1,3-fucosyltransferase IX expression

Pax6 is a transcription factor involved in brain patterning and neurogenesis. Expression of Pax6 is specifically observed in the developing cerebral cortex, where Lewis x epitope that is thought to play important roles in cell interactions is colocalized. Here we examined whether Pax6 regulates localization of Lewis x using Pax6 mutant rat embryos. The Lewis x epitope disappeared in the Pax6 mutant cortex, and activity of alpha1,3-fucosyltransferase, which catalyzed the last step of Lewis x biosynthesis, drastically decreased in the mutant cortex as compared with the wild type. Furthermore, expression of a fucosyltransferase gene, FucT-IX, specifically decreased in the mutant, while no change was seen for expression of another fucosyltransferase gene, FucT-IV. These results strongly suggest that Pax6 controls Lewis x expression in the embryonic brain by regulating FucT-IX gene expression.

PAX6 mutation in a family with aniridia, congenital ptosis, and mental retardation

Congenital aniridia is due to deletions and point mutations in the PAX6 gene. We describe here a case of a mother and her two sons with a syndrome comprising congenital aniridia, ptosis, and slight mental retardation. The sons also show behavioral changes. The possibility of deletion around the PAX6 locus was excluded by polymorphism studies and fluorescence in situ hybridization analysis. Mutation screening of the PAX6 gene revealed the presence of a transversion C719A, resulting in the substitution of arginine for serine at residue 119. We suggest that this missense mutation is responsible both for aniridia and ptosis, and possibly also for the observed cognitive dysfunction in this family.