Familial Axenfeld-Rieger anomaly, cardiac malformations, and sensorineural hearing loss: a provisionally unique genetic syndrome?

Case report: Congenital mitral and tricuspid valve insufficiency in a patient with Axenfeld-Rieger syndrome

Axenfeld-Rieger syndrome (ARS) is an autosomal dominant disorder that is primarily due to disruption of the development of neural crest cells. The onset of associated symptoms in both eyes accompanied by extraocular developmental defects is referred to as ARS. Cardiac defects associated with ARS have been reported, but the extent of the cardiac defects has yet to be defined. We report a case of a 17-year-old girl with ARS with typical facial malformations and severe mitral and tricuspid valve insufficiency. The patient was diagnosed with secondary glaucoma detected on ophthalmologic examination. Echocardiography showed severe mitral and tricuspid valve insufficiency. This case provides further evidence of the association of ARS with cardiac malformations and extends the reported range of cardiac malformations in patients with ARS.

Axenfeld-Rieger syndrome: orthopedic and orthodontic management in a pediatric patient: a case report

Axenfeld–Rieger Syndrome (ARS) is a rare autosomal dominant genetic disease with considerable expressive variability, characterized by ocular and non-ocular manifestations, cardiovascular, mild craniofacial abnormalities and dental malformations. Current data report an incidence of Xenfeld-Rieger syndrome in the population of 1: 200,000.

The case described is that of a 14-year-old female patient whose ARS is suspected and investigated following a dental specialist visit for orthodontic reasons, acquired the patient’s family and clinical data following a medical approach multidisciplinary, we proceed to the orthodontic involved the use of the Rapid Palatal Expander (RPE) and a fixed orthodontic treatment.

The aim of this study is to report the case of the orthopaedic and orthodontic treatment in a patient affected by ARS and with facial dysmorphism and teeth anomalies associated to ocular anomalies.

De novo PBX1 variant in a patient with glaucoma, kidney anomalies, and developmental delay: An expansion of the CAKUTHED phenotype

An infant was referred for evaluation of congenital glaucoma and corneal clouding. In addition, he had a pelvic kidney, hypotonia, patent ductus arteriosus, abnormal pinnae, and developmental delay. Exome sequencing identified a previously unpublished de novo single nucleotide insertion in PBX1 c.400dupG (NM_002585.3), predicted to cause a frameshift resulting in a truncated protein with loss of function (p.Ala134Glyfs*65). Identification of this loss of function variant supports the diagnosis of congenital anomalies of the kidney and urinary tract syndrome with or without hearing loss, abnormal ears, or developmental delay (CAKUTHED). Here, we propose glaucoma as an extra-renal manifestation associated with PBX1-related disease due to the relationship of PBX1 with MEIS1, MEIS2, and FOXC1 transcription factors associated with eye development.

The Axenfeld-Rieger Syndrome Gene FOXC1 Contributes to Left-Right Patterning

Precise spatiotemporal expression of the Nodal-Lefty-Pitx2 cascade in the lateral plate mesoderm establishes the left–right axis, which provides vital cues for correct organ formation and function. Mutations of one cascade constituent PITX2 and, separately, the Forkhead transcription factor FOXC1 independently cause a multi-system disorder known as Axenfeld–Rieger syndrome (ARS). Since cardiac involvement is an established ARS phenotype and because disrupted left–right patterning can cause congenital heart defects, we investigated in zebrafish whether foxc1 contributes to organ laterality or situs. We demonstrate that CRISPR/Cas9-generated foxc1a and foxc1b mutants exhibit abnormal cardiac looping and that the prevalence of cardiac situs defects is increased in foxc1a^−/−; foxc1b^−/− homozygotes. Similarly, double homozygotes exhibit isomerism of the liver and pancreas, which are key features of abnormal gut situs. Placement of the asymmetric visceral organs relative to the midline was also perturbed by mRNA overexpression of foxc1a and foxc1b. In addition, an analysis of the left–right patterning components, identified in the lateral plate mesoderm of foxc1 mutants, reduced or abolished the expression of the NODAL antagonist lefty2. Together, these data reveal a novel contribution from foxc1 to left–right patterning, demonstrating that this role is sensitive to foxc1 gene dosage, and provide a plausible mechanism for the incidence of congenital heart defects in Axenfeld–Rieger syndrome patients.

Aniridia and Axenfeld-Rieger Syndrome: Clinical presentations, molecular genetics and current/emerging therapies

Aniridia and Axenfeld-Rieger Syndrome are related, human ocular disorders that are typically inherited in an autosomal dominant manner. Both result from incorrect development of the eye and have, as their most serious consequences, elevated risk to develop the blinding condition glaucoma. This review will focus on describing the clinical presentations of Aniridia and Axenfeld-Rieger Syndrome as well as the molecular genetics and current and emerging therapies used to treat patients.

Functionally significant, rare transcription factor variants in tetralogy of Fallot

Objective

Rare variants in certain transcription factors involved in cardiac development cause Mendelian forms of congenital heart disease. The purpose of this study was to systematically assess the frequency of rare transcription factor variants in sporadic patients with the cardiac outflow tract malformation tetralogy of Fallot (TOF).

Methods and Results

We sequenced the coding, 5′UTR, and 3′UTR regions of twelve transcription factor genes implicated in cardiac outflow tract development (NKX2.5, GATA4, ISL1, TBX20, MEF2C, BOP/SMYD1, HAND2, FOXC1, FOXC2, FOXH, FOXA2 and TBX1) in 93 non-syndromic, non-Mendelian TOF cases. We also analysed Illumina Human 660W-Quad SNP Array data for copy number variants in these genes; none were detected. Four of the rare variants detected have previously been shown to affect transactivation in in vitro reporter assays: FOXC1 p.P297S, FOXC2 p.Q444R, FOXH1 p.S113T and TBX1 p.P43_G61del PPPPRYDPCAAAAPGAPGP. Two further rare variants, HAND2 p.A25_A26insAA and FOXC1 p.G378_G380delGGG, A488_491delAAAA, affected transactivation in in vitro reporter assays. Each of these six functionally significant variants was present in a single patient in the heterozygous state; each of the four for which parental samples were available were maternally inherited. Thus in the 93 TOF cases we identified six functionally significant mutations in the secondary heart field transcriptional network.

Significance

This study indicates that rare genetic variants in the secondary heart field transcriptional network with functional effects on protein function occur in 3–13% of patients with TOF. This is the first report of a functionally significant HAND2 mutation in a patient with congenital heart disease.

Lgr4 in ocular development and glaucoma

The leucine-rich repeat-containing G protein-coupled receptor 4 (LGR4, also called GPR48) plays a key role in multiple developmental processes, and mice lacking Lgr4 display anterior segment dysgenesis leading to early-onset glaucomatous retinal ganglion cell loss as well as defective eyelid formation. This paper will review Lgr4 signaling and its regulation of the Axenfeld-Rieger syndrome gene Pitx2, a crucial developmental transcription factor. In addition, Wnt signaling plays an important role in eye development, with Norrin functioning to activate the Wnt receptor Frizzled 4 required for proper retinal vascularization. Recent discoveries identifying Lgr4 as a receptor for Norrin highlight the potential for Lgr4 function in retinal vascularization. Finally, several unanswered questions impeding a full understanding of Lgr4 in glaucoma are considered as avenues for further research.

Magnetic resonance imaging findings in Axenfeld-Rieger syndrome

Axenfeld–Rieger syndrome (ARS) is a genetic disorder representing a disease spectrum resulting from neural crest cell maldevelopment. Glaucoma is a common complication from the incomplete formation of the iridocorneal angle structures. Neural crest cells also form structures of the forebrain and pituitary gland, dental papillae, aortic arch walls, genitalia, and long bones; therefore, patients with ARS manifest a wide range of systemic findings. To our knowledge, detailed magnetic resonance imaging findings have not been previously reported. We report a case of a 19-month-old Indian male diagnosed with ARS with emphasis on magnetic resonance imaging findings of the globes, brain, teeth, and skull base.

Cardiac anomalies in Axenfeld-Rieger syndrome due to a novel FOXC1 mutation

Axenfeld-Rieger syndrome (ARS) is an autosomal dominant condition characterized by ophthalmologic anterior segment abnormalities and extraocular findings including dental anomalies and redundant periumbilical skin. Intragenic mutations in the homeobox gene PITX2 or the transcription factor encoding FOXC1 were identified, and genomic rearrangements encompassing either gene also cause ARS. A molecular etiology is identified in 40-60%. Extraocular anomalies occur more often with intragenic PITX2 than FOXC1 mutations. We report on a patient with infantile glaucoma presenting at age 21 months with congestive heart failure due to a dysplastic arcade mitral valve necessitating valve replacement, and mildly hypoplastic left ventricular outflow tract and aortic arch. Family history included early onset glaucoma in four relatives; congenital hip dysplasia requiring surgery in three; and an atrial septal defect in the affected maternal grandmother. Despite the absence of dental or umbilical abnormalities, anterior chamber abnormalities consistent with ARS were present in affected individuals. Molecular testing revealed a novel FOXC1 mutation (c.508C>T; p.Arg170Trp) in the proband and his affected mother; other family members were unavailable. A literature review revealed four reports of congenital heart disease associated with intragenic FOXC1 mutations, and none with intragenic PITX2 mutations. Previously, mouse studies showed Foxc1 (Mf1) expression in the developing valves and atrial septum, supporting a causal relationship of FOXC1 mutations for valvar anomalies and ASD. Hip dysplasia in three family members suggests a role for FOXC1 in the femoral head dysplasia of de Hauwere syndrome with 6p25 deletions. Further reports of clinical and molecular diagnoses will clarify genotype-phenotype correlation.

Xenopus: An emerging model for studying congenital heart disease

Congenital heart defects affect nearly 1% of all newborns and are a significant cause of infant death. Clinical studies have identified a number of congenital heart syndromes associated with mutations in genes that are involved in the complex process of cardiogenesis. The African clawed frog, Xenopus, has been instrumental in studies of vertebrate heart development and provides a valuable tool to investigate the molecular mechanisms underlying human congenital heart diseases. In this review, we discuss the methodologies that make Xenopus an ideal model system to investigate heart development and disease. We also outline congenital heart conditions linked to cardiac genes that have been well studied in Xenopus and describe some emerging technologies that will further aid in the study of these complex syndromes.

Glaucoma: genes, phenotypes, and new directions for therapy

Glaucoma, a leading cause of blindness worldwide, is characterized by progressive optic nerve damage, usually associated with intraocular pressure. Although the clinical progression of the disease is well defined, the molecular events responsible for glaucoma are currently poorly understood and current therapeutic strategies are not curative. This review summarizes the human genetics and genomic approaches that have shed light on the complex inheritance of glaucoma genes and the potential for gene-based and cellular therapies that this research makes possible.

Axenfeld–Rieger syndrome and pseudotruncus arteriosus

Axenfeld-Rieger syndrome (ARS) is an autosomal dominant disorder. It is described as the association of malformation of the anterior chamber of the eye with extraocular anomalies. Cardiovascular defects are considered an occasional findings with this syndrome. We present a patient having the features of Axenfeld-Rieger syndrome with pseudotruncus arteriosus as a different cardiac association.

Clinical presentation of a variant of Axenfeld–Rieger syndrome associated with subtelomeric 6p deletion

We report a 22-year-old female with a variant of the Axenfeld-Rieger Syndrome (ARS) and discuss its relation with the subtelomeric 6p deletion. An ARS variant has been described in two familial cases of Axenfeld-Rieger Anomaly (ARA) featuring specific extra ocular manifestations-hypertelorism, midface hypoplasia, mild sensorial deafness, hydrocephaly, psychomotor delay and flattened femoral epiphyses. We proposed that this set of characteristics represents a separate syndrome within the ARS. On the other hand, there have been reported four cases with cryptic de novo pure 6pter microdeletions detected by specific subtelomeric probes in patients with ARS characteristics. We describe a 6pter deletion detected by SNP genotyping and confirmed by FISH and MLPA involving the FOXC1 gene in a patient with ocular and systemic findings that fit perfectly with the variant mentioned above. We conclude that the ARS variant belongs to the ARS phenotypic spectrum, which includes flattened femoral epiphyses as a feature.

Concordant familial segregation of atrial septal defect and Axenfeld–Rieger anomaly in father and son

The association of congenital heart defect and ocular malformations is involved in several genetic syndromes, metabolic diseases and environmental entities. We report here on father and son, both presenting with the combination of atrial septal defect and congenital ocular anomalies in Axenfeld-Rieger anomaly. The son had anterior iridotrabecular dysgenesis and posterior embryotoxon bilaterally, corneal leucoma and marked iridial vascularization at right. The father had bilateral anterior iridotrabecular dysgenesis, posterior embryotoxon and nystagmus, and corneal leucoma at left. No additional malformations were noted in these patients. The Axenfeld-Rieger syndrome seems to be a spectrum of developmental disorders. The present report confirms the existence of a specific Axenfeld-Rieger phenotype associated with congenital heart defect. Atrial septal defect is the anatomic type of congenital heart defect linked to this condition.

Analysis of RNA splicing defects in PITX2 mutants supports a gene dosage model of Axenfeld-Rieger syndrome

BACKGROUND

Axenfeld-Rieger syndrome (ARS) is associated with mutations in the PITX2 gene that encodes a homeobox transcription factor. Several intronic PITX2 mutations have been reported in Axenfeld-Rieger patients but their effects on gene expression have not been tested.

METHODS

We present two new families with recurrent PITX2 intronic mutations and use PITX2c minigenes and transfected cells to address the hypothesis that intronic mutations effect RNA splicing. Three PITX2 mutations have been analyzed: a G>T mutation within the AG 3' splice site (ss) junction associated with exon 4 (IVS4-1G>T), a G>C mutation at position +5 of the 5' (ss) of exon 4 (IVS4+5G>C), and a previously reported A>G substitution at position -11 of 3'ss of exon 5 (IVS5-11A>G).

RESULTS

Mutation IVS4+5G>C showed 71% retention of the intron between exons 4 and 5, and poorly expressed protein. Wild-type protein levels were proportionally expressed from correctly spliced mRNA. The G>T mutation within the exon 4 AG 3'ss junction shifted splicing exclusively to a new AG and resulted in a severely truncated, poorly expressed protein. Finally, the A>G substitution at position -11 of the 3'ss of exon 5 shifted splicing exclusively to a newly created upstream AG and resulted in generation of a protein with a truncated homeodomain.

CONCLUSION

This is the first direct evidence to support aberrant RNA splicing as the mechanism underlying the disorder in some patients and suggests that the magnitude of the splicing defect may contribute to the variability of ARS phenotypes, in support of a gene dosage model of Axenfeld-Rieger syndrome.

Dental anomalies in Axenfeld-Rieger syndrome

The authors describe the case of a 10-year-old girl presenting with Axenfeld-Rieger syndrome (ARS), a rare autosomal dominant condition. The patient showed severe hypodontia, microdontia and short roots. Early diagnosis of the syndrome from its dento-facial and systemic features is important so that subsequent ocular complications may be prevented.

Axenfeld-Rieger malformation and distinctive facial features: Clues to a recognizable 6p25 microdeletion syndrome

Deletion of distal 6p is associated with a distinctive clinical phenotype including Axenfeld-Rieger malformation, hearing loss, congenital heart disease, dental anomalies, developmental delay, and a characteristic facial appearance. We report the case of a child where recognition of the specific ocular and facial phenotype, led to identification of a 6p microdeletion arising from a de novo 6:18 translocation. Detailed analysis confirmed deletion of the FOXC1 forkhead gene cluster at 6p25. CNS anomalies included hydrocephalus and hypoplasia of the cerebellum, brainstem, and corpus callosum with mild to moderate developmental delay. Unlike previous reports, hearing was normal.

A model for left juxtaposition of the atrial appendages in the chick

The morphogenesis of most types of human congenital cardiac malformations is still obscure. The reasons for this are, first, the paucity of data from human embryos and fetuses and, second, the paucity of appropriate animal models. During the past few years, we have tested several chemicals for their teratogenic potential, hoping to find, particularly in the chick, substances that could be used for the development of models for specific cardiac malformations. We have now discovered that suramin, an antitrypanosomal drug, can induce a special type of congenital cardiac defect in which the two atrial appendages are positioned to the left of the great arteries. This situation resembles the situation found in humans and classified as left juxtaposition of the atrial appendages. In the present study, we have analysed the pathomorphological features of a series of our chicken hearts to assess precisely how accurately these cardiac malformations in the chick correspond to the situation seen in the human. We found that the cases observed in the chick did, indeed, have many features in common with the human cases described in the literature. This suggests that we have developed an animal model for human left juxtaposition. Our model could be used for two kinds of embryological studies: first, documentation of the morphogenesis of left juxtaposition; and second, studies on the mechanisms driving the normal positional changes between the atriums and outflow tract of the embryonic heart during the late phase of cardiac looping. The fact that left juxtaposition of the atrial appendages can be induced by suramin might help to elucidate the molecular mechanisms underlying this type of congenital cardiac malformation. Furthermore, the fact that suramin is used for the chemotherapy of frequent tropical diseases, such as African trypanosomiasis and onchocerciasis, poses the question as to whether this drug might play a role in the aetiology of left juxtaposition in some human populations.

Teratogenic effects of suramin on the chick embryo

Suramin, a polysulfonated naphthylamine, has been used for the chemotherapy of trypanosomiasis and onchocerciasis since about the 1920s. Currently, it is also being tested as an anticancer agent. It is hoped that suramin might stop the progression of some kinds of cancer since it has been found to inhibit the proliferation and migration of cells and the formation of new blood vessels. These processes are not only essential for the development and progression of cancer, but also for normal embryonic development. Suramin might, therefore, be a potent teratogen. In the literature, however, we have found only scant information on this subject. In the present study, we demonstrate the teratogenic effects of suramin on chick embryos. Suramin was injected into the coelomic cavity of chick embryos on incubation day (ID) 3. Following reincubation until ID 8, suramin-treated embryos ( n=50) were examined for congenital malformations and compared with a control group ( n=30). The survival rate of suramin-treated embryos was markedly reduced compared with controls (50% vs 90%). Among the 25 survivors the following malformations were recorded: caudal dysgenesia (100%), median facial clefts with hypertelorism (92%), malformations of the aortic arch arteries (88%), hypo-/aplasia of the allantoic vesicle (84%), microphthalmia (52%), abnormalities of the great arterial trunks (44%), unilateral or bilateral cleft lips (40%), heart defects with juxtaposition of the right atrial appendage (36%), persistence of the lens vesicle (32%), median clefts of the lower beak (8%), omphalocele (4%), and cloacal exstrophy (4%). These results show that suramin is a potent teratogen. The possible implications of our findings for human beings and the possible teratogenic mechanisms of suramin are discussed. Use of suramin in experimental teratology might help to clarify the morphogenesis of median facial clefts and of some congenital heart defects.