Linkage of autosomal dominant iris hypoplasia to the region of the Rieger syndrome locus (4q25)

A novel PITX2 mutation causing iris hypoplasia

Iris hypoplasia (IH) is rare autosomal dominant disorder characterized by a poorly developed iris stroma and malformations of the eyes and umbilicus. This disorder is caused by mutation of the paired-like homeodomain 2 (PITX2) gene. Here, we describe a novel PITX2 mutation (c.205C>T) in an IH family presenting with very mild eye features but with tooth agenesis as the most obvious clinical feature.

The genetics of pigment dispersion syndrome and pigmentary glaucoma

We review the inheritance patterns and recent genetic advances in the study of pigment dispersion syndrome (PDS) and pigmentary glaucoma (PG). Both conditions may result from combinations of mutations in more than one gene or from common variants in many genes, each contributing small effects. We discuss the currently known genetic loci that may be related with PDS/PG in humans, the role of animal models in expanding our understanding of the genetic basis of PDS, the genetic factors underlying the risk for conversion from PDS to PG and the relationship between genetic and environmental--as well as anatomical--risk factors.

A novel PITX2 mutation and a polymorphism in a 5-generation family with Axenfeld-Rieger anomaly and coexisting Fuchs' endothelial dystrophy

PURPOSE

To investigate the clinical and genetic appearance of Axenfeld-Rieger anomaly or syndrome (ARAS) and Fuchs' endothelial dystrophy (FED) in a 5-generation pedigree coexpressing both pathologic features in a large number of family members.

DESIGN

Observational case-control and DNA linkage and screening study.

PARTICIPANTS

Of 114 family members, 50 underwent clinical investigation and DNA analysis between July 2001 and March 2004.

METHODS

Linkage at the PITX2 locus was demonstrated using a number of microsatellites mapping to the critical region 4q25 to 4q26. The PITX2 gene was subsequently screened for mutations in all investigated family members.

MAIN OUTCOME MEASURE

Linkage of the ARAS and FED phenotype and mutation detection in the PITX2 gene.

RESULTS

Twenty-seven patients were identified as being affected by ARAS. Fuchs' endothelial dystrophy was found in 19 patients. Fifteen patients presented both kinds of anomaly. Deoxyribonucleic acid sequencing revealed 2 heteroallelic DNA variants that segregated together (on the same allele) and were present in all severely affected ARAS individuals. The first variant, g.20913G>T, assumed to be the causative mutation for ARAS, causes amino acid substitution at codon 137 (G137V). A statistically significant 2-point logarithm of the odds score of 4.06 was obtained with marker D4S406. The second variant is likely a polymorphism in the intron between exons 2 and 3 (IVS2+8delCinsGTT) and was detected in heterozygous form in 20% of control individuals.

CONCLUSION

This gene analysis revealed a novel PITX2 mutation and a polymorphism in a family with ARAS. Whether FED, also manifested in the severely affected individuals, is due to a different but cosegregating gene is to be determined.

A Review of Anterior Segment Dysgeneses

The anterior segment dysgeneses are an ill-defined group of ocular developmental abnormalities that share some common features and have a high prevalence of glaucoma. Current classification of what are and what are not anterior segment dysgeneses seems to vary and our knowledge of them is incomplete. As the limits of classical clinical medicine based on evaluation of signs and symptoms are reached, further advancements increasingly will come from molecular medicine and genetics. In this article we review the normal and abnormal development of the anterior segment (concentrating primarily upon neural crest derived dysgeneses), describe the various clinical entities produced and their diagnosis, and discuss the current knowledge of the genetics of these disorders. We also suggest a new approach to the classification of anterior segment dysgeneses, based upon the embryological contribution to the formation of the anterior segment of the eye.

Functional interactions between FOXC1 and PITX2 underlie the sensitivity to FOXC1 gene dose in Axenfeld-Rieger syndrome and anterior segment dysgenesis

Axenfeld-Rieger ocular dysgenesis is associated with mutations of the human PITX2 and FOXC1 genes, which encode transcription factors of the homeodomain and forkhead types, respectively. We have identified a functional link between FOXC1 and PITX2 which we propose underpins the similar Axenfeld-Rieger phenotype caused by mutations of these genes. FOXC1 and PITX2A physically interact, and this interaction requires crucial functional domains on both proteins: the C-terminal activation domain of FOXC1 and the homeodomain of PITX2. Immunofluorescence further shows PITX2A and FOXC1 to be colocalized within a common nuclear subcompartment. Furthermore, PITX2A can function as a negative regulator of FOXC1 transactivity. This work ties both proteins into a common pathway and offers an explanation of why increased FOXC1 gene dosage produces a phenotype resembling that of PITX2 deletions and mutations. Ocular phenotypes arise despite the deregulated expression of FOXC1-target genes through mutations in FOXC1 or PITX2. Ultimately, PITX2 loss of function mutations have a compound effect: the reduced expression of PITX2-target genes coupled with the extensive activation of FOXC1-regulated targets. Our findings indicate that the functional interaction between FOXC1 and PITX2A underlies the sensitivity to FOXC1 gene dosage in Axenfeld-Rieger syndrome and related anterior segment dysgeneses.

The new bone biology: Pathologic, molecular, and clinical correlates

Bone and cartilage and their disorders are addressed under the following headings: functions of bone; normal and abnormal bone remodeling; osteopetrosis and osteoporosis; epithelial-mesenchymal interaction, condensation and differentiation; osteoblasts, markers of bone formation, osteoclasts, components of bone, and pathology of bone; chondroblasts, markers of cartilage formation, secondary cartilage, components of cartilage, and pathology of cartilage; intramembranous and endochondral bone formation; RUNX genes and cleidocranial dysplasia (CCD); osterix; histone deacetylase 4 and Runx2; Ligand to receptor activator of NFkappaB (RANKL), RANK, osteoprotegerin, and osteoimmunology; WNT signaling, LRP5 mutations, and beta-catenin; the role of leptin in bone remodeling; collagens, collagenopathies, and osteogenesis imperfecta; FGFs/FGFRs, FGFR3 skeletal dysplasias, craniosynostosis, and other disorders; short limb chondrodysplasias; molecular control of the growth plate in endochondral bone formation and genetic disorders of IHH and PTHR1; ANKH, craniometaphyseal dysplasia, and chondrocalcinosis; transforming growth factor beta, Camurati-Engelmann disease (CED), and Marfan syndrome, types I and II; an ACVR1 mutation and fibrodysplasia ossificans progressiva; MSX1 and MSX2: biology, mutations, and associated disorders; G protein, activation of adenylyl cyclase, GNAS1 mutations, McCune-Albright syndrome, fibrous dysplasia, and Albright hereditary osteodystrophy; FLNA and associated disorders; and morphological development of teeth and their genetic mutations.

Recent advances in molecular genetics of glaucoma

Glaucoma represents a heterogeneous group of optic neuropathies, with different genetic bases. It can affect all ages generally with a rise in intra-ocular pressure. Three major types of glaucoma have been reported: primary open angle glaucoma (POAG), primary acute closed angle glaucoma (PACG) and primary congenital glaucoma (PCG), as well as a few others associated with developmental abnormalities. In recent years impressive progress has been made in the molecular genetic studies of POAG and PCG. These include the discovery of three genes--Myocilin, Optineurin and CYP1B1--defects in which results in Mendelian transmission of glaucoma. Identification of single nucleotide polymorphisms in multiple other genes that are associated with glaucoma and alteration of drug sensitivity are enriching our knowledge regarding the complex nature of the disease. This review attempts to present the recent progress made in the molecular genetics of glaucoma.

PRDM5 is silenced in human cancers and has growth suppressive activities

Several genes that contain the PR (PRDI-BF1 and RIZ) domain have been linked with human cancers. We describe here a new PR-domain-containing gene designated as PRDM5 (PFM2). A PRDM5 cDNA was isolated based on its homology to the PR domain of RIZ1 (PRDM2). The gene encodes an open reading frame of 630 amino acids and contains a PR domain in the NH-terminal region followed by 16 zinc finger motifs. Radiation hybrid analysis mapped PRDM5 to human chromosome 4q26, a region thought to harbor tumor suppressor genes for breast, ovarian, liver, lung, colon, and other cancers. The gene has a CpG island promoter and is silenced in human breast, ovarian, and liver cancers. A recombinant adenovirus expressing PRDM5 caused G2/M arrest and apoptosis upon infection of tumor cells. These results suggest that inactivation of PRDM5 may play a role in carcinogenesis.

Familial iridogoniodysgenesis and skeletal anomalies: a probable new autosomal recessive disorder

Three sibs with congenital glaucoma, skeletal anomalies, and peculiar facial appearance were studied. At birth, enlarged eyes and corneae were present in the proposita and her two brothers due to congenital glaucoma secondary to iridogoniodysgenesis (IGD). The purpose of this article is to describe the second familial case with IGD and skeletal anomalies as the family previously described by García-Cruz et al. in 1990, corroborating this new distinct dysmorphic syndrome with probable autosomal recessive inheritance.

A family with Axenfeld-Rieger syndrome and Peters Anomaly caused by a point mutation (Phe112Ser) in the FOXC1 gene

PURPOSE

Mutations of the forkhead transcription factor gene FOXC1 result in anterior segment anomalies. No description of the spectrum of defects resulting from a single point mutation of this gene exists in the ophthalmology literature. We have screened all available patients with Axenfeld-Rieger genes (PITX2 and FOXC1). In this report, we clinically characterize the spectrum of ocular and systemic manifestations in one family resulting from a previously reported point mutation (Phe112Ser) in FOXC1.

DESIGN

Observational case series.

METHODS

Ten members of a multigenerational family were examined for signs of glaucoma, anterior segment abnormalities, and systemic features of Axenfeld-Rieger syndrome. The examinations were performed in an ophthalmology examination room or in the patients' homes. Blood was obtained from 10 members and screened for mutations in FOXC1 using direct DNA sequencing.

RESULTS

A single mutation causing a T to C change in codon 112 (Phe112Ser) of FOXC1 was present in six members of the family. Five of these six patients were examined and all demonstrated anterior segment anomalies. One patient had Axenfeld anomaly, one had Rieger syndrome, and one had both Axenfeld anomaly and Peters anomaly. Additionally, some members demonstrated cardiac abnormalities, which may be secondary to their FOXC1 mutation.

CONCLUSIONS

A wide spectrum of clinical phenotypes can result from a single point mutation of FOXC1. This report confirms that Rieger syndrome (with dental and facial abnormalities) can be caused by a mutation in FOXC1. It is also the first report of Peters anomaly being caused by a FOXC1 mutation.

Digenic inheritance of early-onset glaucoma: CYP1B1, a potential modifier gene

"Early-onset glaucoma" refers to genetically heterogeneous conditions for which glaucoma manifests at age 5-40 years and for which only a small subset is molecularly characterized. We studied the role of MYOC, CYP1B1, and PITX2 in a population (n=60) affected with juvenile or early-onset glaucoma from the greater Toronto area. By a combination of single-strand conformation polymorphism and direct cycle sequencing, MYOC mutations were detected in 8 (13.3%) of the 60 individuals, CYP1B1 mutations were detected in 3 (5%) of the 60 individuals, and no PITX2 mutations were detected. The range of phenotypic expression associated with MYOC and CYP1B1 mutations was greater than expected. MYOC mutations included cases of juvenile glaucoma with or without pigmentary glaucoma and mixed-mechanism glaucoma. CYP1B1 mutations involved cases of juvenile open-angle glaucoma, as well as cases of congenital glaucoma. The study of a family with autosomal dominant glaucoma showed the segregation of both MYOC and CYP1B1 mutations with disease; however, in this family, the mean age at onset of carriers of the MYOC mutation alone was 51 years (range 48-64 years), whereas carriers of both the MYOC and CYP1B1 mutations had an average age at onset of 27 years (range 23-38 years) (P=.001). This work emphasizes the genetic heterogeneity of juvenile glaucoma and suggests, for the first time, that (1) congenital glaucoma and juvenile glaucoma are allelic variants and (2) the spectrum of expression of MYOC and CYP1B1 mutations is greater than expected. We also propose that CYP1B1 may act as a modifier of MYOC expression and that these two genes may interact through a common pathway.

Axenfeld-Rieger syndrome in the age of molecular genetics

PURPOSE

To review the molecular genetics of Axenfeld-Rieger syndrome and related phenotypes and to discuss how this information might affect the way that we classify these disorders.

METHODS

A review of historical and recent literature on Axenfeld-Rieger syndrome and related disorders. The review includes clinical and molecular genetic literature relevant to these phenotypes.

RESULTS

Three chromosomal loci have recently been demonstrated to link to Axenfeld-Rieger syndrome and related phenotypes. These loci are on chromosomes 4q25, 6p25, and 13q14. The genes at chromosomes 4q25 and 6p25 have been identified as PITX2 and FKHL7, respectively. Mutations in these genes can cause a wide variety of phenotypes that share features with Axenfeld-Rieger syndrome. Axenfeld anomaly, Rieger anomaly, Rieger syndrome, iridogoniodysgenesis anomaly, iridogoniodysgenesis syndrome, iris hypoplasia, and familial glaucoma iridogoniodysplasia all have sufficient genotypic and phenotypic overlap that they should be considered one condition.

CONCLUSIONS

Axenfeld-Rieger syndrome is a term that can be used to describe a variety of overlapping phenotypes. To date, at least three known genetic loci can cause these disorders. The single most important feature of these phenotypes is that they confer a 50% or greater risk of developing glaucoma. Currently there is a fairly arbitrary grouping of disorders into small categories. Considering all of these phenotypes under the heading of Axenfeld-Rieger syndrome will allow easier communication between clinicians and scientists and eliminate arbitrary and confusing subclassification.

Advances in molecular genetics of glaucoma: a perspective for the clinician

Extraordinary progress has been made over the last 5 years in improving our understanding of the molecular causes of various glaucomas. Identification of the myocilin gene and of 5 additional genetic loci that play a role in development of primary open angle glaucoma provides us with an opportunity to reclassify this complex phenotype based on underlying cause of disease. Clinicians who obtain a detailed family history from their patients and who have referred families with glaucoma to laboratory investigators are at the forefront of this revolution in molecular genetics. As a result, all clinicians will soon be poised to profit from genetic discoveries by being able to order diagnostic tests that will identify specific genetic mutations. These mutations will provide a detailed understanding of the natural history of the patient's glaucoma, as well as information for genetic counseling. Individuals at risk in the family will be able to be identified, permitting closer follow-up and earlier institution of glaucoma therapy. A new understanding of pathophysiology is developing and will provide the basis for more rational pharmacological and gene therapy approaches in the future. The hope of primary prevention for various glaucomas, once a distant dream, may become reality within our lifetimes.

Glaucoma genetics: where are we? Where will we go?

The understanding of the genetic basis of the glaucomas has advanced rapidly. Mutations in the myocilin gene (previously known as TIGR) at the GLC1A locus on chromosome 1q21-q31 occur in a subset of patients with juvenile- and adult-onset primary open-angle glaucoma. Five other genetic localizations for primary open-angle glaucoma have now been reported. In patients with primary congenital glaucoma, mutations have been found in the CYP1B1 gene on chromosome 2p21. At least one other locus for primary congenital glaucoma is mapped. In the developmental glaucomas, mutations in the PITX2 gene on chromosome 4q25 have been associated with Rieger syndrome, iris hypoplasia, and iridogoniodysgenesis. A second locus for Rieger syndrome resides on chromosome 13q14. Mutations in the FKHL7 gene on chromosome 6p25 have been described in patients with Axenfeld-Rieger anomaly. A new ocular finding of glaucoma in pedigrees with the nailpatella syndrome has been described, and mutations in the LMX1B gene on chromosome 9q34 are now known to underlie nail-patella syndrome. Two loci for the pigment dispersion syndrome have been mapped. This paper provides an overview of recent literature, summarizes developments in glaucoma genetics, and addresses their potential relevance to the clinical management of glaucoma.

Ocular malformations and developmental genes

New insights into the pathogenesis of ocular malformations came with the discovery of transcription factors that determine the fate of cells in the developing eye. Several malformations have been matched to individual developmental genes that share conserved DNA sequences such as the homeobox. These disease/gene matches include the oculorenal syndrome and PAX2; aniridia and PAX6; Rieger syndrome and RIEG1/PITX2; cyclopia and Sonic hedgehog; cone-rod dystrophy, Leber's congenital amaurosis and CRX; and recessive septooptic dysplasia and HESX1. Gene mapping and mutation analysis have allowed a more accurate and meaningful classification of genetically heterogeneous diseases such as the anterior segment dysgenesis syndromes. This paper reviews current information on the genetics of ocular malformations.

A novel Asp380Ala mutation in the GLC1A/myocilin gene in a family with juvenile onset primary open angle glaucoma

Glaucoma describes a clinically and genetically heterogeneous group of diseases that result in optic neuropathy and progressive loss of visual fields. A gene for juvenile onset primary open angle glaucoma JOAG) has recently been mapped to 1q21-31. Mutations in the trabecular meshwork induced glucocorticoid response gene (TIGR, also known as myocilin or the GLC1A locus) have been found to cause both juvenile and later onset primary open angle glaucoma. Family TCD-POAG1 is a Spanish kindred, which segregates JOAG in an autosomal dominant fashion. This family was found to be linked to the previously identified GLC1A locus on chromosome 1q. Direct sequencing of the TIGR/myocilin gene showed a heterozygous A to C transition in codon 380, resulting in the substitution of alanine for aspartic acid (Asp380Ala). This substitution created a StyI restriction site, which segregated with the JOAG phenotype and permitted rapid screening of all members of the family. This restriction site was not present in 60 controls.

Anterior segment dysgenesis and congenital glaucoma associated with partial trisomy of chromosome 1 (1q32-qter)

A child born with partial trisomy of chromosome 1 (1q32-qter) survived and was seen for anterior segment dysgenesis and congenital glaucoma. Pure trisomy 1q is rarely seen in live-born infants and has not previously been described in association with congenital glaucoma. The genetic basis for glaucoma is complicated and multifactorial and probably determined by a number of genes on a variety of chromosomes. The current case provides some evidence that part of chromosome 1 may be involved with the etiology of a glaucomatous process.

Mapping of a congenital microcoria locus to 13q31-q32

Congenital microcoria is an autosomal dominant disorder characterized by a pupil with a diameter <2 mm. It is thought to be due to a maldevelopment of the dilator pupillae muscle of the iris, and it is associated with juvenile-onset glaucoma. A total genome search for the location of the congenital microcoria gene was launched in a single large family. We found linkage between the disease and markers located on 13q31-q32 (Zmax = 9.79; theta = 0). Haplotype analysis narrowed the linked region to an interval <8 cM between markers D13S1239 proximally and D13S1280 distally.

Summary of ocular genetic disorders and inherited systemic conditions with eye findings

Of the close to 10,000 known inherited disorders that affect humankind, a disproportionately high number affect the eye. The total number of genes responsible for the normal structure, function, and differentiation of the eye is unknown, but the list of these genes is rapidly and constantly growing. The objective of this paper is to provide a current list of mapped and/or cloned human eye genes that are responsible for inherited diseases of the eye. The ophthalmologist should be aware of recent advances in molecular technology which have resulted in significant progress towards the identification of these genes. The implications of this new knowledge will be discussed herein.

Construction and analysis of a sequence-ready map in 4q25: Rieger syndrome can be caused by haploinsufficiency of RIEG, but also by chromosome breaks approximately 90 kb upstream of this gene

The autosomal dominant disorder Rieger syndrome (RIEG) shows genetic heterogeneity and has a phenotype characterized by malformations of the anterior segment of the eye, failure of the periumbilical skin to involute, and dental hypoplasia. The main locus for RIEG was mapped to the 4q25-q27 chromosomal segment using a series of cytogenetic abnormalities as well as by genetic linkage to DNA markers. Recently, a bicoid-related homeobox transcription factor gene called RIEG has been cloned, characterized, and proven to cause the 4q25 linked RIEG. Its mode of action in the pathogenesis of RIEG was not conclusively proven, since most etiological mutations detected in the RIEG sequence caused amino acid substitutions or splice changes in the homeodomain. Through FISH analysis of a 460-kb sequence-ready map (PAC contig) around RIEG that we report in this paper, we demonstrate that the 4q25 linked RIEG disorder can arise from the haploid, whole-gene deletion of RIEG, but also from a translocation break 90 kb upstream from the gene. The data provide conclusive evidence that physical or functional haploinsufficiency of RIEG is the pathogenic mechanism for Rieger syndrome. The map also defines restriction fragments bearing sequences with a potential key regulatory role in the control of homeobox gene expression.

Autosomal dominant iris hypoplasia is caused by a mutation in the Rieger syndrome (RIEG/PITX2) gene

PURPOSE

To determine whether autosomal dominant iris hypoplasia is caused by mutations in the newly described gene for Rieger syndrome (RIEG/PITX2).

METHOD

Mutation screening and sequence analysis was performed in a single family.

RESULTS

A novel mutation in the RIEG/PITX2 gene was found in all affected but no unaffected individuals. This mutation would be expected to result in an arginine to tryptophan amino acid change in the homeodomain of solurshin, the RIEG/ITX2 gene product.

CONCLUSION

Autosomal dominant iris hypoplasia is caused by a defect in the same gene that is defective in many cases of Rieger syndrome.

Ultrastructural studies of primary congenital glaucoma in rabbits

BACKGROUND

The cause of congenital glaucoma is unknown.

METHODS

To determine whether the site of impaired aqueous outflow is the entrance to the trabecular meshwork (TM), within the TM, the aqueous drainage plexus, or a combination thereof, the process of TM development was examined by scanning and transmission electron microscopy on postnatal day 3 and weeks 1, 2, 3, 4, and 6 in New Zealand rabbits homozygous for the buphthalmic (bu/bu) gene compared with age-matched controls.

RESULTS

Openings to the entrance of the TM in congenital glaucoma were observed, and there was no evidence of an endothelial membrane occluding aqueous flow to the TM. The morphology of the congenital glaucoma TM was abnormal in all bu/bu rabbits by 2 weeks and was characterized by a smaller entrance to the TM at the iris base, smaller intertrabecular openings within and between the trabecular lamellae, and at 6 weeks, iris pillars with extensive lateral extensions in the angle recess. Most intertrabecular spaces were open, however, the inner intertrabecular spaces adjacent to the aqueous plexus were compressed.

CONCLUSION

These results suggest the development of congenital glaucoma, which involves a mutation in an autosomal recessive gene and leads to loss of function of a gene(s) required for the differentiation of the TM.

Familial glaucoma iridogoniodysplasia maps to a 6p25 region implicated in primary congenital glaucoma and iridogoniodysgenesis anomaly

Familial glaucoma iridogoniodysplasia (FGI) is a form of open-angle glaucoma in which developmental anomalies of the iris and irido-corneal angle are associated with a juvenile-onset glaucoma transmitted as an autosomal dominant trait. A single large family with this disorder was examined for genetic linkage to microsatellite markers. A peak LOD score of 11.63 at a recombination fraction of 0 was obtained with marker D6S967 mapping to chromosome 6p25. Haplotype analysis places the disease gene in a 6.4-cM interval between the markers D6S1713 and D6S1600. Two novel clinical appearances extend the phenotypic range and provide evidence of variable expressivity. The chromosome 6p25 region is now implicated in FGI, primary congenital glaucoma, and iridogoniodysgenesis anomaly. This may indicate the presence of a common causative gene or, alternatively, a cluster of genes involved in eye development/function.

Genetic heterogeneity of primary open angle glaucoma and ocular hypertension: linkage to GLC1A associated with an increased risk of severe glaucomatous optic neuropathy

The GLC1A locus for autosomal dominant juvenile and middle age onset primary open angle glaucoma (OAG) has been mapped to chromosome 1q21-q31. OAG, however, is a heterogeneous disease. We tested linkage of OAG and ocular hypertension (OHT), a major risk factor for OAG, to GLC1A in eight French families with multiple cases of juvenile and middle age onset OAG. There was strong evidence of genetic heterogeneity, four families being linked to GLC1A and two or three others being unlinked, depending on whether the complete OAG phenotype was analysed alone or jointly with OHT. Peak intraocular pressure (IOP) did not differ significantly between the two groups of families, while linkage to GLC1A conferred a highly increased risk of developing OAG and of having severe glaucomatous optic neuropathy. Testing linkage of familial OAG to GLC1A may therefore have prognostic value too.

Rieger syndrome locus: a new reciprocal translocation t(4;12)(q25;q15) and a deletion del(4)(q25q27) both break between markers D4S2945 and D4S193

Rieger syndrome (RS) is an autosomal dominant disorder of morphogenesis characterised by malformation of the anterior segment of the eye, dental hypoplasia, and failure of the periumbilical skin to involute. RS has been mapped to the 4q25-q27 chromosomal segment by a series of cytogenetic studies as well as by genetic linkage to DNA markers. It was first localised to chromosome 4q based on an association with a constitutional deletion of 4q23-q27. In this paper we localise the proximal breakpoint of this deletion from the original patient, and we describe a new family with a de novo balanced reciprocal translocation t(4;12)(q25;q15) segregating with full RS in two generations. Using FISH and the P1 artificial chromosomes (PACs) as probes, we have physically localised both the deletion and the translocation breakpoints between genetic markers which are known to be strongly linked to RS. We have mapped both the proximal deletion breakpoint and the translocation breakpoint within a region between two groups of PACs bearing the markers D4S2945 (on the centromeric side) and D4S193 and D4S2940 (on the telomeric side). We believe that these recombinant bacterial clones derived directly from genomic DNA (not subcloned from YACs) will be valuable complementary tools in the efforts to clone the RS gene and to construct a full transcriptional and sequence ready map of this region.

Cloning and characterization of a novel bicoid-related homeobox transcription factor gene, RIEG, involved in Rieger syndrome

Rieger syndrome (RIEG) is an autosomal-dominant human disorder that includes anomalies of the anterior chamber of the eye, dental hypoplasia and a protuberant umbilicus. We report the human cDNA and genomic characterization of a new homeobox gene, RIEG, causing this disorder. Six mutations in RIEG were found in individuals with the disorder. The cDNA sequence of Rieg, the murine homologue of RIEG, has also been isolated and shows strong homology with the human sequence. In mouse embryos Rieg mRNA localized in the periocular mesenchyme, maxillary and mandibular epithelia, and umbilicus, all consistent with RIEG abnormalities. The gene is also expressed in Rathke's pouch, vitelline vessels and the limb mesenchyme. RIEG characterization provides opportunities for understanding ocular, dental and umbilical development and the pleiotropic interactions of pituitary and limb morphogenesis.

Autosomal-dominant iridogoniodysgenesis and Axenfeld-Rieger syndrome are genetically distinct

PURPOSE

To determine whether there is a locus for iridogoniodysgenesis (IGD)/ familial iris hypoplasia in the region of the known Axenfeld-Rieger syndrome (ARS) locus at 4q25 and to determine the ocular phenotype within the autosomal-dominant iris hypoplasia group of disorders.

METHODS

Clinical examinations were performed on 27 members, with 11 affected from one family in which the IGD occurred in association with the nonocular features of ARS, and on 70 members with 30 affected from a second IGD family with ocular features only. Family members were genotyped for markers within the 4q25 region known to contain a locus for ARS. LOD scores were calculated with the MLINK option of the LINKAGE program.

RESULTS

The iris hypoplasia in each IGD family was similar. In the IGD family with only ocular features (IGD anomaly), however, a majority of those affected had a goniodysgenesis with excess tissue in the angle and anomalous angle vascularity. These findings were absent in the IGD family with syndromic features (IGD syndrome). Linkage to the 4q25 region was excluded in the IGD anomaly family, whereas the family with IGD syndrome was found to be completely linked to the 4q25 region (peak LOD score with D4S407 of 7.827 at theta = 0.00).

CONCLUSIONS

The authors' results suggest that mutations at the 4q25 locus can result in variable ocular features that also occur in combination with nonocular (dental and jaw) anomalies. Mutation of a separate locus must underlie IGD with ocular features only. A re-evaluation of the relation between the various forms of autosomal-dominant iris hypoplasia, therefore, may be warranted.

Genetic heterogeneity in Hispanic families with autosomal dominant juvenile glaucoma

A gene for autosomal dominant, juvenile-onset, primary open angle glaucoma (GLCIA) has been previously mapped to 1q21-31 in several Caucasian pedigrees. We studied two Hispanic families with this disease to determine if their disease genes also map to this region. Individuals were considered as being affected if they had 1OP > 30 mmHg (without treatment) and glaucomatous optic nerve damage or visual field defects. Persons older than 40 years with intraocular pressures < or = 21 mmHg and no evidence of optic nerve damage or visual field loss were scored as unaffected. Individuals not falling into these two categories were considered unknown. Genomic DNA was extracted from blood samples and subjected to PCR-based microsatellite marker analysis. Computer-based linkage analysis was used to determine if the disease gene mapped to chromosome 1q2I-31. In the family from the Canary Islands, the disease gene was linked to the chromosome 1q2I-31 region previously identified by other researchers. Markers D1S212 and D1S218 produced maximum lod scores of 3.38 and 2.99, respectively. In the family from the Balearic Islands, the disease gene was excluded from this region by genetic linkage analysis. Haplotype analysis also excluded the disease gene from chromosome 1q21-31. Our Hispanic families showed genetic heterogeneity with respect to autosomal dominant, juvenile-onset, primary open angle glaucoma.

Clinical phenotype of juvenile-onset primary open-angle glaucoma linked to chromosome 1q

PURPOSE

Recent reports have suggested that a gene responsible for juvenile-onset primary open-angle glaucoma exists on the long arm of chromosome 1 (1q). This report describes a previously unpublished family (UM:JG3) in which juvenile-onset glaucoma is segregating in an autosomal dominant manner. The clinical features in this family were compared with those seen in other pedigrees with this condition. Linkage analysis was performed to evaluate whether a glaucoma-causing gene in UM:JG3 is linked to genetic markers on chromosome 1q.

METHODS

Affected family members, their siblings, children, and spouses were examined to identify the presence of glaucoma. Linkage studies were performed using short tandem repeat polymorphisms from chromosome 1q. Results of these studies were compared with those found for other families in which juvenile-onset primary open-angle glaucoma is linked genetically to the same chromosome 1q region.

RESULTS

The UM:JG3 family includes 22 affected individuals over five generations, including 12 still living. The average age at diagnosis for living affected individuals was 26 years. An association between myopia and glaucoma was observed in this family, but the glaucoma was not associated with iris processes or other structural anomalies. The clinical course of disease and response to treatment were similar to other families with this disease. The disease phenotype in this family is linked to markers on chromosome 1q with a maximum lod score of 3.52 at a recombination fraction of 0.00 for marker D1S433. Haplotype analysis suggests the gene responsible for glaucoma in this family is located in an 8-cM region between markers D1S445 and D1S218.

CONCLUSIONS

The glaucoma in UM:JG3 is linked to markers on chromosome 1q, with a candidate interval smaller than that in previous reports. In individuals with juvenile-onset open-angle glaucoma linked to chromosome 1q, the phenotype can range from mild ocular hypertension to blindness, resulting from marked elevations in intraocular pressure, with age at diagnosis ranging from 6 to 62 years. However, most affected individuals display a characteristic phenotype that includes onset in the first three decades of life, unusually high intraocular pressures, and the need for surgical therapy to prevent loss of vision. Whether differences in expression among families is due to allelic heterogeneity remains to be determined.