Screening for mutations of Axenfeld-Rieger syndrome caused by FOXC1 gene in Japanese patients.

PURPOSE: Mutations in the forkhead transcription factor gene (FOXC1) have been recently shown to cause some cases of juvenile glaucoma associated with a variety of anterior-segment anomalies. The purpose of this study was to investigate the clinical features of Axenfeld-Rieger syndrome caused by FOXC1 mutations in Japanese patients. PATIENTS AND METHODS: After informed consent was obtained, genomic DNA was isolated from peripheral blood. The DNA-sequence changes were analyzed using single-strand conformation polymorphism analysis and automated sequencing in six Japanese probands with Axenfeld-Rieger syndrome. RESULTS: The authors identified four mutations: pedigree 1 (26-47ins22), 2 (Ile91Ser), 3 (286ins1), and 4 (Arg127His). Two pedigrees showed new mutations in FOXC1. In pedigrees 1,2, and 4, younger generations had iris hypoplasia with severe early-onset glaucoma, whereas their parents had posterior embryotoxon without glaucoma. Pedigree 3 had a single affected person with iris hypoplasia and posterior embryotoxon with a mild increase of intraocular pressure. CONCLUSION: Four different FOXC1 mutations were found in four of six Japanese pedigrees with Axenfeld-Rieger syndrome. This was a new mutation in two pedigrees that was not found in earlier generations. This study confirms that mutations in this gene cause maldevelopment of the anterior segment of the eye.

Positional cloning of a novel gene on chromosome 16q causing Bardet-Biedl syndrome (BBS2).

Bardet-Biedl syndrome (BBS) is a genetically heterogeneous autosomal recessive disorder with the primary clinical features of obesity, pigmented retinopathy, polydactyly, hypogenitalism, mental retardation and renal anomalies. Associated features of the disorder include diabetes mellitus, hypertension and congenital heart disease. There are six known BBS loci, mapping to chromosomes 2, 3, 11, 15, 16 and 20. The BBS2 locus was initially mapped to an 18 cM interval on chromosome 16q21 with a large inbred Bedouin kindred. Further analysis of the Bedouin population allowed for the fine mapping of this locus to a 2 cM region distal to marker D16S408. Physical mapping and sequence analysis of this region resulted in the identification of a number of known genes and expressed sequence tag clusters. Mutation screening of a novel gene (BBS2) with a wide pattern of tissue expression revealed homozygous mutations in two inbred pedigrees, including the large Bedouin kindred used to initially identify the BBS2 locus. In addition, mutations were found in three of 18 unrelated BBS probands from small nuclear families.

Optimal procedure for extracting RNA from human ocular tissues and expression profiling of the congenital glaucoma gene FOXC1 using quantitative RT-PCR.

PURPOSE: To develop methods for obtaining high quality RNA from human donor eyes and to determine the expression profile of the congenital glaucoma gene FOXC1 in human ocular tissues. METHODS: To obtain high quality RNA from donor eyes, several different preservation methods were tested including storing eyes on ice, freezing eyes, and placing eyes in the commercial fixative RNAlaterTM prior to dissection and RNA extraction. Nine different ocular tissues from human donors were dissected and examined. Pigment-free total RNA was isolated and used for quantitative real-time RT-PCR using FOXC1 and GAPDH (internal standard) primers to assess the quality and expression of FOXC1. RESULTS: An expression profile of FOXC1 in human ocular tissues was determined using quantitative PCR of RNA isolated using a simple and effective procedure for ocular tissue preservation and pigment-free RNA isolation. Higher quality RNA was obtained from human donor eyes preserved in RNAlaterTM compared to RNA extracted from eyes stored on ice or frozen at -80 degrees C. RNA extraction techniques that removed interfering pigment from ocular tissues produced RNA that could be easily amplified by PCR. In the adult human eye, expression of FOXC1 was greatest in the trabecular meshwork (TM) followed by the optic nerve head, choroid/RPE, ciliary body, cornea, and iris. FOXC1 expression levels were much lower in other non-ocular human tissues, such as liver, muscle, lung, heart, and kidney. CONCLUSIONS: Using an optimized donor eye preservation method and tissue RNA isolation procedure, we show that the FOXC1 transcription factor gene, which is known to be associated with developmental glaucoma, also may have an important role in the adult eye.

Generation of a high-density rat EST map.

We have developed a high-density EST map of the rat, consisting of >11,000 ESTs. These ESTs were placed on a radiation hybrid framework map of genetic markers spanning all 20 rat autosomes, plus the X chromosome. The framework maps have a total size of approximately 12,400 cR, giving an average correspondence of 240 kb/cR. The frameworks are all LOD 3 chromosomal maps consisting of 775 radiation-hybrid-mapped genetic markers and ESTs. To date, we have generated radiation-hybrid-mapping data for >14,000 novel ESTs identified by our Rat Gene Discovery and Mapping Project (http://ratEST.uiowa.edu), from which we have placed >11,000 on our framework maps. To minimize mapping errors, ESTs were mapped in duplicate and consensus RH vectors produced for use in the placement procedure. This EST map was then used to construct high-density comparative maps between rat and human and rat and mouse. These maps will be a useful resource for positional cloning of genes for rat models of human diseases and in the creation and verification of a tiling set of map order for the upcoming rat-genome sequencing.

A spectrum of FOXC1 mutations suggests gene dosage as a mechanism for developmental defects of the anterior chamber of the eye.

Mutations in the forkhead transcription-factor gene (FOXC1), have been shown to cause defects of the anterior chamber of the eye that are associated with developmental forms of glaucoma. Discovery of these mutations was greatly facilitated by the cloning and characterization of the 6p25 breakpoint in a patient with both congenital glaucoma and a balanced-translocation event involving chromosomes 6 and 13. Here we describe the identification of novel mutations in the FOXC1 gene in patients with anterior-chamber defects of the eye. We have detected nine new mutations (eight of which are novel) in the FOXC1 gene in patients with anterior-chamber eye defects. Of these mutations, five frameshift mutations predict loss of the forkhead domain, as a result of premature termination of translation. Of particular interest is the fact that two families have a duplication of 6p25, involving the FOXC1 gene. These data suggest that both FOXC1 haploinsufficiency and increased gene dosage can cause anterior-chamber defects of the eye.

Haploinsufficiency of the transcription factors FOXC1 and FOXC2 results in aberrant ocular development.

Anterior segment developmental disorders, including Axenfeld-Rieger anomaly (ARA), variably associate with harmfully elevated intraocular pressure (IOP), which causes glaucoma. Clinically observed dysgenesis does not correlate with IOP, however, and the etiology of glaucoma development is not understood. The forkhead transcription factor genes Foxc1 (formerly Mf1 ) and Foxc2 (formerly Mfh1 ) are expressed in the mesenchyme from which the ocular drainage structures derive. Mutations in the human homolog of Foxc1, FKHL7, cause dominant anterior segment defects and glaucoma in various families. We show that Foxc1 (+/-)mice have anterior segment abnormalities similar to those reported in human patients. These abnormalities include small or absent Schlemm's canal, aberrantly developed trabecular meshwork, iris hypoplasia, severely eccentric pupils and displaced Schwalbe's line. The penetrance of clinically obvious abnormalities varies with genetic background. In some affected eyes, collagen bundles were half normal diameter, or collagen and elastic tissue were very sparse. Thus, abnormalities in extracellular matrix synthesis or organization may contribute to development of the ocular phenotypes. Despite the abnormalities in ocular drainage structures in Foxc1 (+/-)mice, IOP was normal in almost all mice analyzed, on all genetic backgrounds and at all ages. Similar abnormalities were found in Foxc2 (+/-)mice, but no disease-associated mutations were identified in the human homolog FKHL14 in 32 ARA patients. Foxc1 (+/-)and Foxc2 (+/-)mice are useful models for studying anterior segment development and its anomalies, and may allow identification of genes that interact with Foxc1 and Foxc2 (or FKHL7 and FKHL14 ) to produce a phenotype with elevated IOP and glaucoma.

An autosomal genomic screen for autism. Collaborative linkage study of autism.

Autism is a severe neurodevelopmental disorder defined by social and communication deficits and ritualistic-repetitive behaviors that are detectable in early childhood. The etiology of idiopathic autism is strongly genetic, and oligogenic transmission is likely. The first stage of a two-stage genomic screen for autism was carried out by the Collaborative Linkage Study of Autism on individuals affected with autism from 75 families ascertained through an affected sib-pair. The strongest multipoint results were for regions on chromosomes 13 and 7. The highest maximum multipoint heterogeneity LOD (MMLS/het) score is 3.0 at D13S800 (approximately 55 cM from the telomere) under the recessive model, with an estimated 35% of families linked to this locus. The next highest peak is an MMLS/het score of 2.3 at 19 cM, between D13S217 and D13S1229. Our third highest MMLS/het score of 2.2 is on chromosome 7 and is consistent with the International Molecular Genetic Study of Autism Consortium report of a possible susceptibility locus somewhere within 7q31-33. These regions and others will be followed up in the second stage of our study by typing additional markers in both the original and a second set of identically ascertained autism families, which are currently being collected. By comparing results across a number of studies, we expect to be able to narrow our search for autism susceptibility genes to a small number of genomic regions. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 88:609-615, 1999.

Expression of the Mf1 gene in developing mouse hearts: implication in the development of human congenital heart defects.

The transcription factor FKHL7 gene has recently been associated with the anterior segment dysgenesis disorder of the eye known as Axenfeld-Rieger anomaly (ARA). A growing body of evidence indicates that mutations in FKHL7 cause not only defects in the anterior segment of the eye but defects in the heart valves and septa as well. In order to evaluate its contribution to normal heart septation and valve formation, expression of the mouse homologue Mf1 in embryonic hearts was analyzed by in situ hybridization. A weak but significant level of Mf1 expression could be detected in the endocardium of mouse embryos as early as day 8.5 post-conception (p.c.). Mf1 expression was undetectable in the hearts of day 9.5 p.c. embryos, but by day 10.5-11 p.c., Mf1 transcripts could be found again in the endocardium of both the atrium and ventricle and a relatively strong signal was observed in the dorsal portion of the septum primum, in what appeared to be the spinal vestibule. At day 13 p.c. when aortic and pulmonary trunks are separated, relatively more Mf1 transcripts were detected in the leaflets of aortic, pulmonary, and venous valves, the ventral portion of the septum primum, as well as in the single layer of cells on the edges of the atrioventricular cushion tissues. Surprisingly, there was no signal detected in the developing interventricular septum. At day 15 p.c., overall Mf1 signals were greatly decreased. However, significant levels of expression could still be observed in the atrial septum, the tricuspid valve, the mitral valve, and in the venous valve but not in the interventricular septum. The temporal and spatial expression patterns of the Mf1 gene in developing mouse hearts suggest that Mf1 may play a critical role in the formation of valves and septa with the exception of the interventricular septum. This is further supported by our studies showing that mutations in the FKHL7 gene were associated with defects in the anterior segment of the eye as well as atrial septal defects or mitral valve defects. Dev Dyn 1999;216:16-27.

Exclusion of AR-CHED from the chromosome 20 region containing the PPMD and AD-CHED loci.

Congenital hereditary endothelial dystrophy (CHED) is a disorder of the corneal endothelium and has been recognized to segregate in families with both autosomal dominant (AD) and autosomal recessive (AR) modes of transmission. AD-CHED has been previously linked to the pericentric region of chromosome 20. Posterior polymorphous dystrophy (PPMD), a corneal endothelial disorder showing phenotypic overlap with CHED, has also been previously genetically mapped to this region. The genetic interval containing AD-CHED is within the larger genetic interval containing the PPMD locus. This study sought to determine whether AR-CHED segregating in a consanguineous Saudi Arabian pedigree is linked to the previously mapped and overlapping loci for AD-CHED and PPMD on the pericentric region of chromosome 20. Forty members of a consanguineous Saudi Arabian pedigree segregating AR-CHED were ascertained. Short tandem-repeat polymorphic markers from the 20 cM interval on chromosome 20 containing both the PPMD and AD-CHED loci were used to genotype these individuals. LOD score analysis of the genotype data with the MENDEL software package utilizing a model of autosomal recessive inheritance with complete penetrance showed exclusion of CHED from the entire PPMD/AD-CHED interval by utilizing overlapping intervals of LOD scores of at least -2. The results obtained demonstrate that AR-CHED is not allelic to either AD-CHED or PPMD, although it has been proposed that AD-CHED may be allelic to PPMD. Thus, there are at least two genes responsible for CHED and PPMD.

The forkhead transcription factor gene FKHL7 is responsible for glaucoma phenotypes which map to 6p25.

A number of different eye disorders with the presence of early-onset glaucoma as a component of the phenotype have been mapped to human chromosome 6p25. These disorders have been postulated to be either allelic to each other or associated with a cluster of tightly linked genes. We have identified two primary congenital glaucoma (PCG) patients with chromosomal anomalies involving 6p25. In order to identify a gene involved in PCG, the chromosomal breakpoints in a patient with a balanced translocation between 6p25 and 13q22 were cloned. Cloning of the 6p25 breakpoint led to the identification of two candidate genes based on proximity to the breakpoint. One of these, FKHL7, encoding a forkhead transcription factor, is in close proximity to the breakpoint in the balanced translocation patient and is deleted in a second PCG patient with partial 6p monosomy. Furthermore, FKHL7 was found to harbour mutations in patients diagnosed with Rieger anomaly (RA), Axenfeld anomaly (AA) and iris hypoplasia (IH). This study demonstrates that mutations in FKHL7 cause a spectrum of glaucoma phenotypes.

A gene for familial juvenile polyposis maps to chromosome 18q21.1.

Familial juvenile polyposis (FJP) is a hamartomatouspolyposis syndrome in which affected family members develop upper and lower gastrointestinal juvenile polyps and are at increased risk for gastrointestinal cancer. A genetic locus for FJP has not yet been identified by linkage; therefore, the objective of this study was to perform a focused genome screen in a large family segregating FJP. No evidence for linkage was found with markers near MSH2, MLH1, MCC, APC, HMPS, CDKN2A, JP1, PTEN, KRAS2, TP53, or LKB1. Linkage to FJP was established with several markers from chromosome 18q21.1. The maximum LOD score was 5.00, with marker D18S1099 (recombination fraction of .001). Analysis of critical recombinants places the FJP gene in an 11.9-cM interval bounded by D18S1118 and D18S487, a region that also contains the tumor-suppressor genes DCC and DPC4. These data demonstrate localization of a gene for FJP to chromosome 18q21.1 by linkage, and they raise the possibility that either DCC or DPC4 could be responsible for FJP.

Linkage of autosomal dominant radial drusen (malattia leventinese) to chromosome 2p16-21.

OBJECTIVE: To identify the chromosomal location of the gene involved in the pathogenesis of autosomal dominant radial drusen (malattia leventinese). PATIENTS: Eighty-six members of four families affected with radial drusen; one family of American origin and three families of Swiss origin. METHODS: Family members were clinically examined for the presence of radial drusen. Affected patients and potentially informative spouses were genotyped with short tandem repeat polymorphisms distributed across the autosomal genome. The clinical and genotypic data were subjected to linkage analysis. RESULTS: Fifty-six patients were found to be clinically affected. Significant linkage was observed between the disease phenotype and markers known to lie on the short arm of chromosome 2. The maximum two-point lod score (Zmax) observed for all four families combined was 10.5 and was obtained with marker D2S378. Multipoint analysis yielded a Zmax of 12, centered on marker D2S378. The lod-1 confidence interval was 8 cM, while the disease interval defined by observed recombinants was 14 cM. CONCLUSIONS: The gene responsible for autosomal dominant radial drusen has been mapped to the short arm of chromosome 2. This is an important step toward actually isolating the disease-causing gene. In addition, this information can be used to evaluate other familial drusen phenotypes such as Doyne's macular dystrophy for a possible allelic relationship.

Novel approaches to linkage mapping.

The recent progress seen in the development of high-quality genetic markers and high-density human genetic maps is facilitating new strategies for mapping disease-causing and disease-susceptibility genes. These strategies, which include homozygosity mapping, DNA pooling, and the utilization of linkage disequilibrium, have been successfully applied to the mapping and fine mapping of several loci causing diseases segregating in genetically isolated populations.

Linkage localization of TGFB2 and the human homeobox gene HLX1 to chromosome 1q.

We have identified genetic variation within two human genes, transforming growth factor-beta 2 (TGFB2) and the homeobox gene HB24 (HLX1). Reported here are four human RFLPs and SSCPs for TGFB2 in humans and gorillas. In addition, we describe an RFLP and a SSCP for HLX1. We propose that HLX1 is the human homologue of the mouse homeobox gene Hlx based on extensive sequence homology between the genes and the close proximity of both genes to TGFB2 in their respective species. We also report the chromosomal localization of HLX1 to the long arm of human chromosome 1. Finally, utilizing the polymorphisms described for TGFB2 and HLX1, we have been able to localize these genes within a framework map of the distal long arm of chromosome 1 and to study the linkage relationship between these two genes. Pairwise linkage analysis shows that these two genes are linked, with a recombination fraction of 3.1% and a lod score of 14.49.

The CEPH consortium linkage map of human chromosome 1.

This paper describes the Centre d'Etude du Polymorphisme Humain (CEPH) consortium linkage map of human chromosome 1. The map contains 101 loci defined by genotypes generated from CEPH family DNAs with 146 different contributions from 11 laboratories. A total of 58 loci are uniquely placed on the map with likelihood support of at least 1000:1. The map extends from loci in the terminal bands of both chromosome arms (locus D1Z2 in 1p36.3 and D1S68 in 1q44) and is anchored at the centromere by the D1Z5 alpha-satellite polymorphism. With the exception of a single locus, the remaining loci are arrayed on the fixed map in short intervals and their possible locations are indicated. Multipoint linkage analyses provided estimates that the male, female, and sex-averaged maps extend for 308, 478, and 390 cM, respectively. The sex-averaged map contains only four intervals greater than 15 cM, and the mean genetic distance between the 58 uniquely placed loci is 6.7 cM.

Linkage of an autosomal dominant clefting syndrome (Van der Woude) to loci on chromosome Iq.

Van der Woude syndrome (VWS) is an autosomal dominant disorder in which affected individuals have one or more of the following manifestations: cleft lip, cleft palate, hypodontia, or paramedian lower-lip pits. VWS is a well-characterized example of a single-gene abnormality that disturbs normal craniofacial morphogenesis. As a first step in identifying genes involved in human development, we used a candidate-gene-and-region approach to look for a linkage to VWS. Six families with 3 or more generations of affected individuals were studied. Evidence for linkage (theta = 0.02, lod score = 9.09) was found between the renin (REN) gene on 1q and VWS. Other linked loci included CR1, D1S58, and D1S53. The genes for laminin B2 (LAMB2), a basement-membrane protein, and for decay-accelerating factor (DAF) were studied as possible candidate genes on 1q. Recombinants between VWS and both LAMB2 and DAF excluded these genes from a causal role in the etiology of VWS for the families studied in this report. Multipoint linkage analysis indicated that the VWS locus was flanked by REN and D1S65 at a lod score of 10.83. This tight linkage with renin and other nearby loci provides a first step in identifying the molecular abnormality underlying this disturbance of human development.