Linkage analyses of chromosome 18 markers do not identify a major susceptibility locus for bipolar affective disorder in the Old Order Amish.

Previously reported linkage of bipolar affective disorder to DNA markers in the pericentromeric region of chromosome 18 was reexamined in a larger homogeneous sample of Old Order Amish families. Four markers (D18S21, D18S53, D18S44, and D18S40) were examined in three kindreds containing 31 bipolar I (BP I) individuals. Although linkage findings were replicated in the one previously studied Amish pedigree containing four BP I individuals, linkage to this region was excluded in the larger sample. If a susceptibility locus for bipolar disorder is located in this region of chromosome 18, it is of minor significance in this population.

Characterization of radiation/fusion hybrids containing parts of human chromosome 10 and their use in mapping chromosome 10-specific probes.

We have characterized a panel of somatic cell hybrid cell lines which contain different portions of human chromosome 10. Genomic DNA from the somatic cell hybrids was tested for hybridization with each of an ordered set of probes used previously to construct a genetic map of chromosome 10, as well as several additional probes, previously localized by in situ hybridization. Hybridization of an unmapped probe to the cell line DNAs can be used to determine its most likely position on the chromosome relative to the mapped set of probes. Genomic DNA from two of the cell lines has been used to construct region-specific cosmid and bacteriophage libraries, and clones derived from these libraries were localized by hybridization to the panel of hybrid cell lines. Several of these probes reveal restriction fragment length polymorphisms which have been genetically mapped. Three of the probes map near the locus for multiple endocrine neoplasia type 2A, and one of these probes, BG-JC353 (D10S167), maps between RBP3 and TB14.34 (D10S34). Another probe, CRI-J282 (D10S104), is close to the FNRB locus. The panel of hybrid cell lines is thus useful for rapidly localizing unmapped probes and as a source of DNA for the construction of recombinant libraries derived from specific regions of the chromosome.

Identification of genetic markers flanking the locus for maturity-onset diabetes of the young on human chromosome 20.

A systematic search for genetic linkage with maturity-onset diabetes of the young (MODY) as expressed in the R.-W. pedigree has been carried out. Evidence for linkage was found with restriction-fragment-length polymorphism loci that map to human chromosome 20. Two-point linkage analysis with CRI-L1214 (D20S16) and MODY gave a log of the odds (lod) score of 4.16 at theta = 0.08. Multipoint linkage analysis with nine restriction-fragment-length polymorphism loci resulted in a lod score of 4.81 with the MODY locus in an approximately 20-cM region bounded by D20S16 and D20S14-D20S18. Examination of the pattern of MODY segregation suggests that additional factors, possibly genetic could be involved in the age of onset of the disease.

Linkage relationships of human arginine vasopressin-neurophysin-II and oxytocin-neurophysin-I to prodynorphin and other loci on chromosome 20.

The structural genes for human prepro-arginine-vasopressin-neurophysin II (prepro-AVP-NPII; ARVP) locus and prepro-oxytocin-neurophysin-I (prepro-OT-NPI; OT) locus are closely linked separated by only 12 kilobasepairs of DNA. These two loci have been assigned to chromosome 20 by previous studies of somatic cell hybrids. We used Southern blots to analyze a restriction fragment length polymorphism detected by a probe for prepro-OT-NPI to determine the linkage relationships for the ARVP/OT loci using samples from the Centre d'Etude du Polymorphisme Humain (Paris, France) collection of families. The ARVP/OT loci demonstrated extremely close linkage with the prodynorphin (PDYN) locus, with no recombinants (theta of 0) and a log10 odds score of 5.2. Previous observations have shown the ARVP and PDYN peptides to be coexcreted in the same neurosecretory granules of some pituitary axons and that increased transcription of both genes occurs with osmotic stimulation. The combined ARVP/PT/PDYN group was also found to demonstrate linkage with other anonymous DNA segments on chromosome 20, including D20S4, D20S5, and D20S6. Using multilocus linkage analysis, the ARVP/OT loci map to the distal short arm of chromosome 20 about 15 centimorgans toward the telomere from the D20S5 locus, which is located near the middle of the short arm at 20p 12.21. These linkage relationships establish that the secretory and transcriptional associations of ARVP and PDYN extend to a close physical relationship in the human genome. Furthermore, the restriction fragment length polymorphism detected by these loci can serve as accurate markers in segregation studies of putative defects involving the OT, ARVP, or PDYN loci as well as provide a tool for studying the location of other genes, such as GH-releasing hormone.

A genetic linkage map of 32 loci on human chromosome 10.

We have constructed a genetic linkage map of human chromosome 10 based on DNA probes that detect 47 restriction fragment length polymorphisms (RFLPs) at 32 different loci. Segregation data were collected on a set of multigenerational families provided by the Centre d'Etude du Polymorphisme Humain and maps were constructed using recently developed multipoint analysis techniques. The length of the sex-averaged map is 178 cM and the sex-specific map lengths are 131 cM in males and 255 cM in females. Recombination is significantly higher in female meioses. The mean distance between loci is 5.6 cM for the sex-averaged map. The genetic map spans the length of the chromosome as judged by physical localization of probes by in situ hybridization techniques and mapping of the probes on human-hamster hybrid cell lines containing all or part of chromosome 10. The informativeness of two loci near the locus responsible for multiple endocrine neoplasia type 2A (MEN-2A) has been increased by isolation of cosmids that reveal additional RFLPs at these loci.

Identification and characterization of 23 RFLP loci by screening random cosmid genomic clones.

As part of our search for polymorphic DNA probes, we have screened cosmids from a human genomic DNA library for their ability to reveal RFLPs. A total of 101 randomly isolated cosmid clones were tested in Southern hybridizations for polymorphic band patterns. Fifty-four of these clones revealed RFLPs with one or more of nine restriction enzymes. Twenty-three of these clones have been further characterized and assigned to 10 different chromosomes by linkage analysis or by hybridization to panels of human-hamster hybrid cell lines. Fifteen of the probes have heterozygosities greater than or equal to .5. The relative efficiency of RsaI and PstI restriction enzymes in detecting polymorphism was different from results obtained with libraries constructed in bacteriophage vectors. Screening randomly selected cosmid probes is an efficient method for detecting RFLPs.

Studies on locus expansion, library representation, and chromosome walking using an efficient method to screen cosmid libraries.

We have developed an efficient screening method to search for clones in cosmid libraries prepared from human genomic DNA. Genomic, cDNA, and cosmid probes have been used to isolate homologous cosmids from human chromosomes 7, 10, 16, 17 and X as part of a search for polymorphic nucleotide sequences. This method has been successfully applied to chromosome walking experiments at the interstitial retinol-binding protein locus on chromosome 10, and may be a useful tool for investigating representation of cloned sequences in cosmid libraries. Our library was prepared in the vector c2RB (Bates and Swift, 1983), but the method is applicable to any cosmid cloning system in which the inserted DNA can be separated from the vector by restriction enzyme digestion. A cosmid library containing five human genome equivalents can be rapidly screened using three to four Southern hybridization filters. This results in substantial labor saving, particularly when screening genomes of high complexity with many different probes. Another advantage of the system is that it allows for the long-term storage of the cosmids so that they can be screened whenever necessary. As a consequence, cosmid screening can be made a routine laboratory procedure.

Prenatal diagnosis of cystic fibrosis by chorionic villus sampling using 12 polymorphic deoxyribonucleic acid markers.

This report describes the application of a genetic prenatal diagnostic test for cystic fibrosis to a family with a cystic fibrosis-affected child. The test uses 12 deoxyribonucleic acid (DNA) markers that bracket the cystic fibrosis gene on chromosome 7, and chorionic villus tissue as a source of DNA from the fetus at risk for cystic fibrosis. The fetus was predicted by DNA analysis to be unaffected (although a carrier of one cystic fibrosis gene); this diagnosis was confirmed postnatally by the standard sweat electrolyte test. The genetic linkage test is informative in more than 99% of families with cystic fibrosis-affected members and is also useful for determination of carrier status. The test is both more informative and more accurate than one based upon the markers Met and D7S8 (J3.11) alone. The analysis can be done directly from chorionic villus tissue, and therefore can provide a diagnosis as early as nine to 12 weeks after conception.

Identification of more than 500 RFLPs by screening random genomic clones.

As part of our genome-mapping effort, we undertook a large-scale screening study to identify RFLPs useful as genetic markers. Some 1,664 single-copy or repeat-containing phage clones from a Charon 4A genomic library were tested for polymorphism against a panel of DNAs, from five unrelated individuals, digested with eight restriction enzymes. Approximately 30% (515) of the clones revealed polymorphism by Southern hybridization; 67 loci detected had PIC values greater than .5. Restriction enzymes MspI, TaqI, and RsaI were most efficient in detecting polymorphism within the 1-20-kb-fragment size range resolved. With only one exception each of the clones detected polymorphism originating from a single locus.

Genetic linkage map of human chromosome 7 with 63 DNA markers.

High-density genetic maps of individual human chromosomes will permit accurate localization of disease-associated genes and provide signposts that will be useful in the construction of physical maps. We have constructed a genetic map of chromosome 7 with 63 polymorphic DNA markers by using segregation data from 23 three-generation families and recently developed multilocus linkage-analysis techniques. The map spans 250 centimorgans in females and 170 centimorgans in males, with much of the difference being concentrated in a few intervals. The density and informativeness of the markers are such that there is a high probability of detecting linkage to any disease gene on this chromosome for which 20 phase-known meioses are available.

Expression of calf prochymosin in Saccharomyces cerevisiae.

A yeast strain which synthesizes activatable calf prochymosin (also known as prorennin) has been constructed by transformation with a vector carrying the methionyl-prochymosin coding sequence attached to efficient yeast transcriptional promoter and terminator sequences. Cloned preprochymosin cDNA was altered by restriction endonuclease cleavage and addition of a synthetic oligonucleotide to yield a DNA sequence encoding methionyl-prochymosin. This methionyl-prochymosin gene was ligated to a yeast chromosomal fragment containing the GAL1 promoter, and the construction was placed in an Escherichia coli-Saccharomyces cerevisiae shuttle vector with or without a transcriptional terminator DNA fragment from the yeast SUC2 gene. In yeast the two constructions result in equal amounts of prochymosin protein and mRNA. The prochymosin from yeast is activatable to chymosin by incubation at low pH and exhibits milk-clotting activity indistinguishable from calf chymosin.