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J Horst

Publications and source records attributed to J Horst.

At least 127 records · Page 7Linked to original sources
PubMed1990

Inactivation of human alpha-globin gene expression by a de novo deletion located upstream of the alpha-globin gene cluster.

Synthesis of normal human hemoglobin A, alpha 2 beta 2, is based upon balanced expression of genes in the alpha-globin gene cluster on chromosome 16 and the beta-globin gene cluster on chromosome 11. Full levels of erythroid-specific activation of the beta-globin cluster depend on sequences located at a considerable distance 5' to the beta-globin gene, referred to as the locus-activating or dominant control region. The existence of an analogous element(s) upstream of the alpha-globin cluster has been suggested from observations on naturally occurring deletions and experimental studies. We have identified an individual with alpha-thalassemia in whom structurally normal alpha-globin genes have been inactivated in cis by a discrete de novo 35-kilobase deletion located approximately 30 kilobases 5' from the alpha-globin gene cluster. We conclude that this deletion inactivates expression of the alpha-globin genes by removing one or more of the previously identified upstream regulatory sequences that are critical to expression of the alpha-globin genes.

Adult↗
PubMed1990

Ratio of fetal to maternal DNA is less than 1 in 5000 at different gestational ages in maternal blood.

Using Southern hybridization with the DNA probe pY3.4, we were not able to detect fetal DNA in blood of 36 pregnant women carrying male fetuses. Gestational ages ranged from 8-40 weeks of pregnancy. Using the same DNA probe, we were able to detect the male-specific signal in experimental dilution series down to 1/5000 on autoradiograms. We conclude that the ratio of fetal DNA in maternal circulation, in contrast to previous estimations, must be lower than 1/5000.

Autoradiography↗
PubMed1990

Phenylalanine hydroxylase gene: silent mutation uncovers evolutionary origin of different alleles.

Analyzing a panel of 94 phenylketonuria (PKU) alleles for mutations within the phenylalanine hydroxylase (PAH) gene, we identified a G to A transition in exon 7 corresponding to nucleotide 957 in the cDNA sequence. This nucleotide substitution generates a new Alu I site (...GTGGCT...----...GTAGCT...), but does not change the encoded amino acid (GTG245----GTA245 = VAL). In our panel of patients the Alu I polymorphism is exclusively associated with haplotypes 4 (mutant or normal alleles) and 3, 16, 17, 28 (normal alleles).

Alleles↗
PubMed1990

Classical phenylketonuria in Bulgaria: RFLP haplotypes and frequency of the major mutations.

RFLP haplotypes and common mutations in the phenylalanine hydroxylase gene have been studied in a group of 29 Bulgarian PKU families. Haplotype distribution differs from that in other European populations, with a predominance of haplotypes 2 and 6 and a total absence of haplotype 3. The amino acid substitution in codon 408 is the most frequent molecular defect. The splicing defect in intron 12 is not found in Bulgarian PKU patients. Testing for three mutations, reported to be common among haplotype 1 and 4 alleles, has shown that they occur less frequently in Bulgarian PKU patients. Screening with five pairs of allele specific oligonucleotides failed to show the mutation in 59% of the patients. These findings add to the evidence that PKU is heterogeneous and that significant interpopulation differences exist. At present, DNA data cannot be used as an aid in early clinical classification and prognosis of hyperphenylalaninaemia in Bulgaria.

Bulgaria↗
PubMed1990

Transabdominal placental biopsy in the second and third trimesters of pregnancy: what is the risk of maternal contamination in DNA diagnosis?

We investigated the risk of maternal contamination in antenatal DNA diagnosis after second- and third-trimester transabdominal placental biopsy. For this purpose, we compared the restriction fragment length polymorphism (RFLP) patterns of 11 chorionic villus DNA samples after late chorionic villus sampling (CVS) with those of the corresponding maternal DNA. Ten of 11 aspirated tissue samples were not separated from maternal contamination before DNA extraction. All 11 mother-embryo pairs were informative for analysis of maternal contamination, ie, the mother showed one RFLP allele not present in the embryo. In none of the 11 cases did the fetal DNA show maternal contamination after molecular hybridization, although ten samples were contaminated with maternal tissue macroscopically and microscopically. Despite some maternal tissue admixture, the risk of contamination seems to be lower in the second- and third-trimester CVS than in first-trimester CVS, based on previous reports and our own experiences. This is most likely due to the anatomically closer contact of villi and decidua in the first trimester of pregnancy.

Alleles↗
PubMed1989

Molecular defects in hemophilia A: identification and characterization of mutations in the factor VIII gene and family analysis.

Hemophilia A is an X-linked bleeding disorder caused by a deficiency or abnormality of factor VIII, affecting approximately 1 male in 10,000. A subgroup of the patients develops inhibitors against factor VIII during substitution therapy. Because a considerable percentage of all cases is thought to result from de novo mutations, it is likely that many different molecular lesions lead to hemophilia A. In order to understand the molecular basis of this disorder, we examined 160 patients with different clinical features using factor VIII gene probes. We could identify six different deletions and seven nonsense mutations within the factor VIII gene. Family analysis revealed that five of these mutations occurred de novo within two generations; two of them arose in the maternal grandfather and three in the mother. In one of these mothers we could identify a mitotic origin. Mapping of the deletions showed no deletion-prone region within the gene. Furthermore, we could not find any correlation between the particular gene defects and "inhibitor" phenotypes.

Base Sequence↗
PubMed1989

A beta-thalassemia gene caused by a 290-base pair deletion: analysis by direct sequencing of enzymatically amplified DNA.

The base composition around a recently detected deletion in the human beta-globin gene was determined by direct DNA sequencing of an enzymatically amplified DNA segment. The deletion removes 290 base pairs (bp), including the entire exon 1 and the mRNA cap site. In the vicinity of the deletion endpoints, the normal beta-globin gene contains direct and inverted repeats which may have taken part in generation of this deletion.

Base Sequence↗
PubMed1989

Validity of cytogenetic analyses from trophoblast tissue throughout gestation.

Cytogenetic findings in the Münster Chorionic Villi Sampling (CVS) program are presented after 1,184 first trimester transcervical samplings and 131 second and third trimester placentacenteses. In the first trimester series the abnormality rate is low (2.4%) in patients with only an age-dependent aneuploidy risk. In this group terminations were performed in only 1.6% because of aneuploidy. True mosaicism was found more frequently after CVS, and the risk of maternal cell contamination seems higher as compared to amniocentesis. There are no obvious differences in the overall rate of diagnostic errors after both procedures, when metaphases after direct preparation and chorionic cell cultures are analysed and doubtful findings such as mosaicism are adequately followed up by amniocentesis. The cytogenetic techniques also offer a very rapid approach to karyotyping in the second and third trimester. We found a high rate of aneuploidy (15%) when placentacentesis was performed after sonographic diagnosis of fetal abnormalities. We conclude that cytogenetic analysis from trophoblast tissue is an accurate diagnostic tool applicable from first to third trimester of pregnancy.

Amniocentesis↗
PubMed1989

Phenylketonuria: detection of a frequent haplotype 4 allele mutation.

By sequence analysis of 94 phenylketonuria (PKU) alleles using polymerase chain reaction (PCR) based techniques, we identified a G to A transition in exon 5 of the human phenylalanine hydroxylase gene. This base substitution predicts an Arg158----Glu158 amino acid exchange and is strongly associated with the mutant haplotype 4 PKU allele.

Alleles↗
PubMed1989

The molecular basis of beta thalassaemia in Bulgaria.

Bulgaria is in a geographical area where beta thalassaemia is relatively common. The frequency of carriers is 2 to 3% of the population. Data on the molecular characteristics of the disorder were obtained from the study of 33 homozygous patients and 57 beta thalassaemia carriers. As in other Mediterranean ethnic groups, haplotype I and the splicing mutation in IVS-1 nt 110 are the most common. Haplotype V is second in frequency and is associated with three different mutations. The second most common mutation, beta null 39, is found in association with haplotype II in 80% of cases. A rare haplotype, possibly resulting from a crossover between a haplotype II and a haplotype V chromosome, was found in two thalassaemia carriers in association with frameshift 6. Altogether four mutations (IVS-1 nt 110, beta null 39, frameshift 6, and IVS-1 nt 6) account for 67% of the thalassaemia chromosomes. Their detection would permit direct fetal DNA analysis in 84% of the families studied (45% fully informative). RFLP analysis (haplotype plus AvaII psi beta) is 100% informative in 79% of the high risk families.

Base Sequence↗
PubMed1989

Identification of a single nucleotide C-to-T transition and five different deletions in patients with severe hemophilia B.

DNA of 70 unrelated hemophilia B patients, including three inhibitor patients, was analyzed by using various restriction enzymes and was hybridized with both a factor IX cDNA and 3'- and 5'-flanking probes. When the gene was mapped this way, six patients all afflicted with severe hemophilia B were shown to have a deviating hybridization pattern. One inhibitor patient showed a partial deletion of about 9 kb that removes exons a-c. A partial deletion of at least 11 kb that removed exon a and that had a maximum size of 35 kb in the 5'-flanking region could be identified in a patient of unknown status. In another three noninhibitor patients a complete deletion of the factor IX gene and two partial deletions could be observed. The partial deletions are of approximately 8 kb and approximately 1.5 kb, removing exons d and e and exon g, respectively. As detected by oligonucleotide probing, a C-to-T transition at amino acid 338 gave rise to an altered TaqI restriction pattern that could be observed in a sixth patient. The other 64 hemophilia B patients, including two inhibitor patients, showed a hybridization pattern indistinguishable from a normal one.

Chromosome Deletion↗
PubMed1988

Rapid karyotyping for prenatal diagnosis in the second and third trimesters of pregnancy.

Direct chromosome preparations were performed on placental villi obtained by ultrasound-guided needle aspiration between 18 and 37 weeks of pregnancy in 53 patients. The sampling yielded a sufficient amount of tissue with a maximum of two, and in most cases one, insertions. Placental biopsy is easily performed in cases of severe oligohydrammnios, where fetal blood sampling is usually more difficult. Direct karyotyping of placental villi is faster than chromosome analysis from fetal blood or application of the pipette method on amniotic fluid cells, and currently represents the most rapid approach to prenatal diagnosis of chromosomal abnormalities from the first to the third trimester of pregnancy.

Biopsy, Needle↗