Mapping the Treacher Collins syndrome locus to 5q31.3→q33.3

How Do We Study the Dynamic Structure of Unstructured Proteins: A Case Study on Nopp140 as an Example of a Large, Intrinsically Disordered Protein

Intrinsically disordered proteins (IDPs) represent approximately 30% of the human genome and play key roles in cell proliferation and cellular signaling by modulating the function of target proteins via protein-protein interactions. In addition, IDPs are involved in various human disorders, such as cancer, neurodegenerative diseases, and amyloidosis. To understand the underlying molecular mechanism of IDPs, it is important to study their structural features during their interactions with target proteins. However, conventional biochemical and biophysical methods for analyzing proteins, such as X-ray crystallography, have difficulty in characterizing the features of IDPs because they lack an ordered three-dimensional structure. Here, we present biochemical and biophysical studies on nucleolar phosphoprotein 140 (Nopp140), which mostly consists of disordered regions, during its interaction with casein kinase 2 (CK2), which plays a central role in cell growth. Surface plasmon resonance and electron paramagnetic resonance studies were performed to characterize the interaction between Nopp140 and CK2. A single-molecule fluorescence resonance energy transfer study revealed conformational change in Nopp140 during its interaction with CK2. These studies on Nopp140 can provide a good model system for understanding the molecular function of IDPs.

Clinical applications of whole-genome association studies: future applications at the bedside

Until now, performing whole-genome association studies has been an unattainable, but highly desirable, goal for geneticists. With the recent advent of high-throughput genotyping platforms, this goal is now a reality for geneticists today and for clinicians in the not-so-distant future. This review will cover a broad range of topics to provide an overview of this emerging branch of genetics, and will provide references to more specific sources. Specifically, this review will cover the technologies available today and in the near future, the specific types of whole-genome association studies, the benefits and limitations of these studies, the applications to complex disease-gene interactions, diagnostic devices, therapeutics, and finally, we will describe the 5-year perspective and key issues.

A range of malar and masseteric hypoplasia exists in Treacher Collins syndrome

BACKGROUND

Treacher Collins syndrome (TCS) is a facial dysostosis, the hallmark being bilateral malar hypoplasia. The purpose of this study is to morphologically classify the TCS malar deformity and to volumetrically characterise both the TCS zygoma and masseter muscle, including for left-right symmetry, compared to controls. We hypothesise that the TCS zygoma will be smaller than controls and zygomatic deficiency will portend masseteric hypoplasia.

METHODS

Demographic and computed tomography (CT) data were recorded. The CT scans were converted into three-dimensional facial renderings, and the zygomatic morphology was grossly evaluated. A classification was reported based on malar structure and presence/absence of normal zygomaticomaxillary complex articulations. The zygoma and masseter muscles were then digitally isolated using 3-D planning software (Materialise, Leuven, Belgium). Volumes and sidedness ratios were calculated and compared using two-sided t-tests.

RESULTS

58 sides were identified (24 TCS: 34 controls), mean age of 60.0 months and normally distributed. The phenotypic dysmorphology was graded as mild, moderate or severe (I, II and III, respectively). TCS malar and masseteric volumes were significantly smaller than controls (p < 0.0001 in both cases). The TCS zygomatic side-side symmetry ratio was 0.66 ± 0.28, compared to 0.97 ± 0.02 for controls (p = 0.002). The TCS masseteric side-side ratio was 0.74 ± 0.20, compared to 0.92 ± 0.09 for controls (p = 0.001).

CONCLUSIONS

A range of zygomatic hypoplasia exists in TCS (mild-severe). The decrease in malar volume occurs in concert with masseteric hypoplasia, and the left and right sides are not equally affected.

Cytogenetic and clinical assessment of a family with treacher collins syndrome

Treacher Collins syndrome (TCS) is a rare autosomal dominant disorder characterized by craniofacial deformities. It is the most common type of mandibulofacial dysostosis (MFD). The objective of this study is to do cytogenetic analysis of a TCS family. Physical examination and all available medical records were reviewed. 50 GTG-banded metaphases were analysed to detect any structural or numerical chromosomal abnormality. Downward slanting of palpebral fissures, hypoplasia of zygomatic arch complex, and hypoplasia of mandible were present in all. Cytogenetic findings show interstitial deletion in chromosomes 5(q32-q33) and 3(q23-q25). We report four members of three generations of a family having TCS in a unique way that the deletion has been found in 3q and 5q which has not been reported. Mosaicism of deletion on 5q was detected in all affected members whereas 3q deletion was found only in one member (II.2). This finding may represent a more severe manifestation of the TCS. Thus the evaluation and counselling of the TCS patients should be undertaken with caution.

TCOF1 mutation database: novel mutation in the alternatively spliced exon 6A and update in mutation nomenclature

Recently, a novel exon was described in TCOF1 that, although alternatively spliced, is included in the major protein isoform. In addition, most published mutations in this gene do not conform to current mutation nomenclature guidelines. Given these observations, we developed an online database of TCOF1 mutations in which all the reported mutations are renamed according to standard recommendations and in reference to the genomic and novel cDNA reference sequences (www.genoma.ib.usp.br/TCOF1_database). We also report in this work: 1) results of the first screening for large deletions in TCOF1 by Southern blot in patients without mutation detected by direct sequencing; 2) the identification of the first pathogenic mutation in the newly described exon 6A; and 3) statistical analysis of pathogenic mutations and polymorphism distribution throughout the gene.

Surgical Treatment of Treacher Collins Syndrome

Morphology, genetic conditioning, terminology, and the principles of treatment of Treacher Collins syndrome have been presented on the basis of our own material, as well as review of literature. Fifty patients (27 males, 23 females) were operated on at the Hospital of Plastic Surgery in Polanica Zdrój from 1976 to 2005. The patients were first seen when they were from 1 to 32 years of age (mean, 7). The disease was hereditary in 17 patients, while the remaining subjects did not reveal any genetic conditioning. The lifesaving surgical treatment was undertaken in 4 children with the most severe form of the disease who presented with dyspnea and paroxysmal apnea. In those cases, the treatment aimed at improving the respiratory function by restoring patency of the nostrils and distraction of the mandible. Twelve patients were operated on for cleft palate between 1 and 2 years of age. Twelve patients had eyelid correction with the use of musculocutaneous flap transposition from the upper eyelid (Z-plasty). The zygomatic bone and lateral wall of the orbit were reconstructed by means of iliac bone grafts in 26 patients. The auricular reconstruction was usually undertaken after 10 years of age. Nine patients underwent bilateral auricular reconstruction by means of a modified Brent method. Fifteen patients aged 12-14 had chin osteotomy according to the Obwegeser method. Nasal osteotomy was performed in 10 patients with characteristic broad, long, and hooked noses, who were operated on after 16 years of age and after completion of orthognathic treatment. In total, 258 surgical procedures were performed in 50 patients, an average of 5.2 operations per every patient. Apart from a multistage surgical treatment, the patients required a combined multidisciplinary approach, mainly due to hearing impairment and occlusal disturbances. The obtained outcome of treatment, although far from being perfect, but still beneficial, confirmed the correctness of applied approach but at the same time pointed to the necessity of introducing new methods of treatment aiming, among others, at compensating for the tissue deficiency by means of tissue engineering.

The Treacher Collins syndrome (TCOF1) gene product is involved in ribosomal DNA gene transcription by interacting with upstream binding factor

Treacher Collins syndrome (TCS) is an autosomal dominant disorder characterized by an abnormality of craniofacial development that arises during early embryogenesis. TCS is caused by mutations in the gene TCOF1, which encodes the nucleolar phosphoprotein treacle. Even though the genetic alterations causing TCS have been uncovered, the mechanism underlying its pathogenesis and the function of treacle remain unknown. Here, we show that treacle is involved in ribosomal DNA gene transcription by interacting with upstream binding factor (UBF). Immunofluorescence labeling shows treacle and UBF colocalize to specific nucleolar organizer regions and cosegregate within nucleolar caps of actinomycin d-treated HeLa cells. Biochemical analysis shows the association of treacle and UBF with chromatin. Immunoprecipitation and the yeast two-hybrid system both suggest physical interaction of the two nucleolar phosphoproteins. Down-regulation of treacle expression using specific short interfering RNA results in inhibition of ribosomal DNA transcription and cell growth. A similar correlation is observed in Tcof(+/-) mouse embryos that exhibit craniofacial defects and growth retardation. Thus, treacle haploinsufficiency in TCS patients might result in abnormal development caused by inadequate ribosomal RNA production in the prefusion neural folds during the early stages of embryogenesis. The elucidation of a physiological function of treacle provides important information of relevance to the molecular dissection of the biochemical pathology of TCS.

CT imaging of craniofacial malformations

Because of its superior depiction of bone detail, CT is a useful tool in the characterization of CF deformities and presurgical planning. Modern CT scanners and workstations provide 2D techniques such as multiplanar reformats and 3D techniques, such as MIP and volume renderings, which may be used effectively in the diagnosis and management of patients with CF malformations.

Craniofacial Growth in Unoperated Craniofacial Malformations

Objective and Purpose

To review current information on craniofacial growth of unoperated patients with craniofacial malformations and stimulate the study of abnormal craniofacial growth through conventional and newer methods. This will lead to improved diagnosis and the understanding of the etiopathogenesis of craniofacial malformations. It is expected that this knowledge will also assist clinicians in planning treatment strategies to better manage these challenging conditions.

Treacher Collins syndrome: current evaluation, treatment, and future directions

OBJECTIVE

Treacher Collins syndrome (TCS) is an inherited disorder in which there are general bilateral symmetric anomalies of the structures within the first and second branchial arches. In general, there is complete penetrance and variable expressivity of the trait. The craniofacial rehabilitation of a child with TCS is tailored to the extent of the deformities involved: the orbitozygomatic region, the maxillomandibular region, the nose, facial soft tissues, and external and middle ear structures.

CONCLUSION

This article reviews the range of clinical features and specific dysmorphology observed in TCS. Functional and aesthetic objectives are discussed, and a comprehensive staged reconstructive approach is outlined, which may be used as a roadmap for treatment planning.

Treacher Collins Syndrome: Current Evaluation, Treatment, and Future Directions

Objective

Treacher Collins syndrome (TCS) is an inherited disorder in which there are bilateral symmetric anomalies of the structures within the first and second branchial arches. In general, there is complete penetrance and variable expressivity of the trait. The craniofacial rehabilitation of a child with TCS is tailored to the extent of the deformities involved: the orbitozygomatic region, the maxillomandibular region, the nose, facial soft tissues, and external and middle ear structures.

Conclusion

This article reviews the range of clinical features and specific dysmorphology observed in TCS. Functional and aesthetic objectives are discussed, and a comprehensive staged reconstructive approach is outlined, which may be used as a roadmap for treatment planning.

Craniofacial growth in unoperated craniofacial malformations

OBJECTIVE

To review current information on craniofacial growth of unoperated patients with craniofacial malformations and stimulate the study of abnormal craniofacial growth through conventional and newer methods. This will lead to improved diagnosis and the understanding of the etiopathogenesis of craniofacial malformations. It is expected that this knowledge will also assist clinicians in planning treatment strategies to better manage these challenging conditions.

Detection of an appropriate kinase activity in branchial arches I and II that coincides with peak expression of the Treacher Collins syndrome gene product, treacle

Treacher Collins syndrome (TCS) is an autosomal dominant craniofacial disorder involving the mid and lower face and, in particular, the tissues affected arise solely from embryonic branchial arches I and II. TCOF1, the gene involved in TCS, has been cloned and although the function of the encoded protein, treacle, has not yet been established, it exhibits peak expression in the branchial arches. Treacle contains a series of repeating units of acidic and basic residues, which are predicted to contain putative casein kinase II (CKII) and protein kinase C (PKC) phosphorylation site motifs. In addition, treacle has weak homology to two phosphorylation-dependent nucleolar proteins, which shuttle between the cytoplasm and nucleolus. Based on these observations, phosphorylation of treacle may be important for its function. In this study, GST-treacle fusion peptides were constructed using particular TCOF1 exons that contained potential CKII and PKC phosphorylation sites. These were used as substrates in in vitro kinase assays and showed that treacle fusion peptides can be phosphorylated by the appropriate kinases. Furthermore, using tissue extracts we have demonstrated that in avian embryonic branchial arches I and II there is a kinase activity that can phosphorylate treacle peptides that is consistent with CKII site recognition. This activity coincides with the reported high expression of treacle in these tissues at early developmental stages and declines later in development.

The whole nucleotide sequence and chromosomal localization of the gene for human metabotropic glutamate receptor subtype 6

Metabotropic glutamate receptor subtype 6 (mGluR6) is restrictedly expressed in the retinal ON bipolar cells and ablation of mouse mGluR6 by gene targeting results in a loss of ON responses to light stimulus and impairs the detection of visual contrasts. We have isolated genomic clones containing the human mGluR6 gene and determined the whole nucleotide sequence of the mGluR6 gene. The transcription initiation site of the human mGluR6 gene has been identified using primer extension analysis in combination with reverse transcriptase-mediated polymerase chain reaction analysis of human retinal RNA, while the termination of the mGluR6 mRNA has been assigned by the analysis of rapid amplification of 3'-cDNA ends. The human mGluR6 gene consists of 16,742 base pairs with 10 exons separated by nine introns. The human mGluR6 is composed of 877 amino acid residues with a signal peptide of 24 amino acid residues and the mature protein shows a 94.6% homology with the rat counterpart. A CpG-rich island is present at exon 1 and its preceding putative promoter region and this unusual sequence, like several tissue-specific genes, may be important for a specific expression of the mGluR6 gene in the retinal bipolar cells. The human mGluR6 gene has been mapped to chromosome 5q35 by the analyses of blot hybridization of a DNA panel of human/mouse/hamster somatic cell hybrids and fluorescence in situ hybridization of human chromosomes. This study should provide the genetic basis for not only better understanding the molecular mechanism underlying a tissue-specific expression of the mGluR6 gene but also exploring a potential defect in human mGluR6 in a certain inherited eye disease.

TCOF1 gene encodes a putative nucleolar phosphoprotein that exhibits mutations in Treacher Collins Syndrome throughout its coding region

Treacher Collins Syndrome (TCS) is the most common of the human mandibulofacial dysostosis disorders. Recently, a partial TCOF1 cDNA was identified and shown to contain mutations in TCS families. Here we present the entire exon/intron genomic structure and the complete coding sequence of TCOF1. TCOF1 encodes a low complexity protein of 1,411 amino acids, whose predicted protein structure reveals repeated motifs that mirror the organization of its exons. These motifs are shared with nucleolar trafficking proteins in other species and are predicted to be highly phosphorylated by casein kinase. Consistent with this, the full-length TCOF1 protein sequence also contains putative nuclear and nucleolar localization signals. Throughout the open reading frame, we detected an additional eight mutations in TCS families and several polymorphisms. We postulate that TCS results from defects in a nucleolar trafficking protein that is critically required during human craniofacial development.

Identification of the complete coding sequence and genomic organization of the Treacher Collins syndrome gene

Treacher Collins syndrome (TCS) is an autosomal dominant disorder of craniofacial development, the features of which include conductive hearing loss and cleft palate. Recently, the demonstration of a series of 10 mutations within a partial-length cDNA clone have indicated that the TCS gene (TCOF1) has been positionally cloned. Although it has been shown that the gene is expressed in a wide variety of fetal and adult tissues, database sequence comparisons have failed to provide significant information on the function of the gene. In the current investigation, a combination of cDNA library screening and rapid amplification of cDNA ends has permitted the isolation of the complete coding sequence of TCOF1, which is encoded by 26 exons and predicts a low complexity, serine/alanine-rich protein of approximately 144 kD. The use of a variety of bioinformatics tools has resulted in the identification of repeated units within the gene, each of which maps onto an individual exon. The predicted protein Treacle contains numerous potential phosphorylaiton sites, a number of which map to similar positions within the repeated units, and shows weak but significant homology to the nucleolar phosphoproteins. Although the precise function of Treacle remains unknown, these observations suggest that phosphorylation may be important for its role in early embryonic development and that it may play a role in nucleolar-cytoplasmic shuttling. The information presented in this study will allow continued mutation analysis in families with a history of TCS and should facilitate continued experimentation to shed further light on the function of the gene/protein during development of the craniofacial complex.

Treacher Collins syndrome

Treacher Collins syndrome is an autosomal dominant disorder of craniofacial development, the features of which include conductive hearing loss and cleft palate. In the absence of a candidate gene, a positional cloning approach has been used to isolate the mutated gene which maps to chromosome 5q31.3-32. Flanking markers were identified and a yeast artificial chromosome and cosmid contig of the region defined by these markers was created as a prelude to the creation of a transcript map of the region. Analysis of genes isolated using this approach resulted in the identification of the mutated gene. While the function of the gene remains unknown, the identification of 20 mutations spread throughout the gene, all of which would result in the insertion of a premature termination codon into the reading frame, suggests that the mechanism underlying the disease is haploinsufficiency.

Prenatal diagnosis in Treacher Collins syndrome using combined linkage analysis and ultrasound imaging

Treacher Collins syndrome is an autosomal dominant disorder of facial development, the features of which include conductive hearing loss and cleft palate. In the current investigation, linkage analysis has been used to make first trimester diagnostic predictions in a pregnancy at high risk of producing an affected child. The results of this analysis predicted that the child would be affected. As predictions of the severity of the disease were not possible, the pregnancy was also assessed by ultrasound imaging. This confirmed the affected diagnosis and predicted that the child would be severely affected.

A contiguous high-resolution radiation hybrid map of 44 loci from the distal portion of the long arm of human chromosome 5

A contiguous high-resolution map of 44 loci from a 35-Mb portion of the distal region of the long arm of human chromosome 5, q21-q35, was produced using radiation hybrid (RH) mapping in conjunction with a natural deletion mapping panel. The map includes 30 genes, four sequence-tagged site (STS) loci, and 10 DNA markers. Newly mapped markers fill two gap regions that were present in previous maps, between markers FER-IL4 and IL3-IL9. Identifying the position of genes on the physical map aids in positional cloning efforts and contributes to our understanding of the overall organization of the human genome.

Positional cloning of a gene involved in the pathogenesis of Treacher Collins syndrome. The Treacher Collins Syndrome Collaborative Group

Treacher Collins syndrome is an autosomal dominant disorder of craniofacial development, which has been localized to chromosome 5q32-33.1. In the present study, the isolation of new polymorphic markers has allowed the identification of overlapping recombination events in two affected individuals. Extension of the transcription map of the critical region proximally has resulted in the isolation of a new gene (which has been named Treacle) of unknown function. The identification of different mutations in five unrelated families, all of which would result in premature termination of the predicted protein, indicates that the Treacher Collins syndrome gene has been positionally cloned.

Transcriptional map of the Treacher Collins candidate gene region

Treacher Collins syndrome (TCOF1) is a dominant disorder of craniofacial development that has been linked previosuly to a region of chromosome 5q31.3-32. Identification of recombination events in affected individuals has reduced the candidate gene region to a 0.5-Mb area between the loci RPS14 (proximal) and ANX6 [distal]. A transcriptional map of this candidate gene region, generated by analysis of exon amplification clones, has identified the genomic location of four genes, heparan sulfate-N-sulfotransferase-N-deacetylase, glutathione peroxidase, as well as two novel, previously uncharacterized genes. Each of these genes, based on their location, must be considered candidates for TCOF1 locus.

Treacher Collins syndrome

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Abnormal craniofacial growth

Treatment of patients with craniofacial (CF) anomalies necessitates knowledge about normal CF growth and how it deviates in the abnormal state. There are different basic types of CF anomalies and various kinds of aberrations that influence CF development. These factors might help to explain why patients display growth variations. The effect of surgery on subsequent development is significant, but the heterogeneity among patients with regards to the morphology, etiology, and pathogenesis of the anomalies could also explain certain growth results. Roentgencephalometric findings related to CF growth in three different groups of anomalies are discussed.

Cloning of the human heparan sulfate-N-deacetylase/N-sulfotransferase gene from the Treacher Collins syndrome candidate region at 5q32-q33.1

Treacher Collins syndrome is an autosomal dominant disorder of craniofacial development, the features of which include conductive hearing loss and cleft palate. Previous studies have shown that the Treacher Collins syndrome locus is flanked by D5S519 and SPARC, and a yeast artificial chromosome contig encompassing this "critical region" has been completed. In the current investigation a cosmid containing D5S519 has been used to screen a human placental cDNA library. This has resulted in the cloning of the human heparan sulfate-N-deacetylase/N-sulfotransferase gene. Two different mRNA species that have identical protein coding sequences but that differ in the size and sequence of the 3' untranslated regions (3' UTR) have been identified. The smaller species has a 3' UTR of 1035 bp, whereas that of the larger is 4878 bp.

Molecular genetic approaches to the study of human craniofacial dysmorphologies

Craniofacial dysmorphologies are common, ranging from simple facial disfigurement to complex malformations involving the whole head. With the advent of gene mapping and cloning techniques, the genetic element of both simple and complex human craniofacial dysmorphologies can be investigated. For many of the dysmorphic syndromes, it is possible to find families that display a particular phenotype in either an autosomal dominant, recessive, or X-linked manner. This article focuses on a subgroup of craniofacial dysmorphologies, covering these three main inheritance patterns, that are being studied using molecular biology techniques: DiGeorge syndrome, Treacher Collins syndrome, Greig cephalopolysyndactyly syndrome, acrocallosal syndrome, amelogenesis imperfecta, and X-linked cleft palate with ankyloglossia. Once the mutated or deleted gene or genes for each syndrome have been cloned, patterns of normal and abnormal craniofacial development should be elucidated. This should enhance both diagnosis and treatment of these common and disfiguring disorders.

Apparent genetic homogeneity of the Treacher Collins-Franceschetti syndrome

The Treacher Collins-Franceschetti syndrome (TCOF) or mandibulofacial dysostosis (MFD) is an autosomal dominant disorder characterized by craniofacial abnormalities and hearing loss. A refined genetic linkage map of the TCOF locus was established in 8 independent families, using 12 microsatellite DNA markers of the distal 5q. Positive lod score values were obtained for all markers with a maximum at the D5S413 locus (Zmax = 3.79 at theta = 0%). Multipoint linkage analysis and haplotype analysis supported the location of the gene between loci D5S434 and D5S412. These results are consistent with previous linkage analyses [Dixon et al.: Am J Hum Genet 49:17-22, 1991, Am J Hum Genet 52:907-914, 1993; Jabs et al.: Genomics 11:193-198, 1991, Genomics 18:7-13, 1993] and provide further evidence of genetic homogeneity in this syndrome.

Cranial base and face in mandibulofacial dysostosis

Using longitudinal roentgencephalometry, we studied craniofacial growth in two children with mandibulofacial dysostosis. In one child, data were supplemented by three-dimensional reconstructions of CT scans and stereolithographic models of the craniofacial skeleton. Progressive basilar kyphosis was found in both children, the hypothesized caused being bending of the cranial base at the level of the sphenofrontal suture. Such bending acting in concert with abnormal growth of the mandible led to impairment of the airway. We advocate careful monitoring of craniofacial growth and respiratory function in mandibulofacial dysostosis from birth through adolescence.

Mild mandibulofacial dysostosis in a child with a deletion of 3p

We report on a patient with mild mandibulofacial dysostosis and a small interstitial deletion of 3p, 46,XY,del(3)(p23p24.12). Linkage of Treacher Collins syndrome, the most common of the mandibulofacial dysostoses, to the 5q31.3-->q33.3 region of chromosome 5 has been established. This is the fourth report of a patient with mandibulofacial dysostosis with a chromosome abnormality outside the 5q31.3 area. Mandibulofacial dysostosis is a heterogeneous entity, and evaluation and counseling of affected individuals should be undertaken with caution.

Radiation hybrid map spanning the Huntington disease gene region of chromosome 4

Radiation hybrid (RH) mapping was used to construct a map of 11 markers in the distal 4 Mb of the short arm of chromosome 4, the region containing the Huntington disease gene. Two different methods for deriving the order of the markers were compared and both arrived at the same order as being the most likely. This order is also consistent with both the physical map constructed using pulsed-field gel electrophoresis (PFGE) and the meiotic linkage map. Comparing the RH map to the map determined by PFGE provided the means to equate RH map units (centirays) with actual physical distance in kilobases of DNA. In addition, a simple procedure for reducing the complexity of human DNA in radiation hybrids is described. One cell line isolated using this procedure contains, as its only human DNA, approximately 2 Mb surrounding the Huntington disease gene.

A radiation hybrid map of 18 growth factor, growth factor receptor, hormone receptor, or neurotransmitter receptor genes on the distal region of the long arm of chromosome 5

The distal portion of the long arm of human chromosome 5 contains an impressive number of genes encoding growth factors, growth factor receptors, and hormone/neurotransmitter receptors. The order of and relative distance between 18 of these genes was determined by radiation hybrid mapping. There is only a single gap in a contiguous radiation map from 5q22-5q35. For this set of radiation hybrids, one map unit (centiray) corresponds to 20-50 kb of DNA. Close physical proximity for several pairs of loci was predicted by the map. Two sets of these were found to be contained in single YAC clones. The physical map produced by radiation hybrid mapping should prove useful in efforts to identify four disease genes that have been assigned to distal 5q by linkage studies.

Mapping of human chromosome 5 microsatellite DNA polymorphisms

Thirteen moderately to highly informative microsatellite DNA polymorphisms based on (dC-dA)n.(dG-dT)n repeats were mapped to segments of human chromosome 5 using both linkage analysis and a panel of somatic cell hybrids which contained rearranged chromosomes. The markers were distributed throughout most of the length of the chromosome from the regions p15.3-p15.1 to q33.3-qter. Maps of the sites of meiotic recombination within the reference families proved particularly useful for the purpose of integrating new polymorphisms into the existing linkage map.