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Biomedical subjects

J Horst

Publications and source records attributed to J Horst.

At least 109 records · Page 6Linked to original sources
PubMed1991

Mosaicism and accuracy of prenatal cytogenetic diagnoses after chorionic villus sampling and placental biopsies.

Discrepant chromosome findings in placenta and fetus (false negative and false positive) after chorionic villus sampling (CVS) are mainly due to confined mosaicism. Non-mosaic normal or abnormal chromosome counts after direct preparation and culture nearly always correctly reflect the fetal chromosome constitution. False-negative results have almost exclusively been restricted to cytotrophoblast cells not representing a fetal chromosome abnormality. Diagnosis of placental mosaicism definitely requires an adequate follow-up by amniocentesis, fetal blood sampling, or sonography before a pregnancy is terminated. When direct preparations and cultured cells are used for cytogenetic diagnoses and placental mosaicism is not taken as proof for a chromosomal abnormality in the fetus, CVS is an accurate diagnostic tool.

Amniocentesis↗
PubMed1991

Recurrent nonsense mutation in exon 7 of the phenylalanine hydroxylase gene.

A new mutation (CGA to TGA) in codon 261 of exon 7 of the phenylalanine hydroxylase gene transforms Arg261 to a stop codon in two unrelated patients of German and Turkish origin. The different ethnic backgrounds and the different polymorphic characteristics of the two mutant alleles suggest an independent origin of the mutation. This is the second defect detected in codon 261 of the phenylalanine hydroxylase gene, a codon that thus appears to be a mutation hot spot.

Arginine↗
PubMed1991

A frameshift mutation in exon 2 of the phenylalanine hydroxylase gene linked to RFLP haplotype 1.

A deletion of a single base in codon 55 (exon 2) of the phenylalanine hydroxylase (PAH) gene has been identified by direct DNA sequencing of 94 phenylketonuria (PKU) chromosomes. This mutation alters the reading frame so that a stop signal (TAA) is generated in codon 60 of the PAH gene. Haplotype analysis revealed that all PKU alleles showing the codon 55 frameshift mutation exhibited haplotype 1. In our panel of DNA probes 13% of all mutant haplotype 1 alleles carry this particular mutation. Patients who were compound heterozygotes for this deletion and R408W in exon 12, or the splice mutation in intron 12, were affected by severe PKU. Thus, the clinical data provide additional evidence that haplotype 1 PKU alleles carry molecular defects which confer a null phenotype. In addition, we were able to show that the newly detected mutation occurs on alleles of different ethnic background.

Amino Acid Sequence↗
PubMed1991

Geographical distribution gradients of the major PKU mutations and the linked haplotypes.

Analysis of 81 phenylketonuria families from Bulgaria, Lithuania and eastern Germany demonstrated a high frequency of haplotype 2 and the associated Arg408----Trp408 substitution. Haplotype 3 and the splicing mutation in intron 12 are rare or absent in the groups studies. Pooling the data on European populations suggests a Balto-Slavic origin of the defect in codon 408 of the phenylalanine hydroxylase gene and a geographical gradient in the distribution of both major PKU mutations which may contribute to the higher incidence of classic PKU in northern Europeans.

Bulgaria↗
PubMed1991

Molecular analysis of PKU haplotypes in the population of southern Poland.

Out of a population of 138,598 infants born in southern Poland between 1987 and 1989, and screened for phenylketonuria (PKU), 28 cases were ascertained probands and their parents were isolated and eight polymorphic restriction sites were analyzed within the phenylalanine hydroxylase gene region. Twenty-one different haplotypes (HT) were revealed, five of them representing new categories. The most common haplotypes among those carrying normal alleles were: HT1 (27.3%) and HT4 (11.4%). Within the group of haplotypes with mutant alleles the most frequent was HT2 (56.8%), whereas the frequency of this haplotype in other European populations, such as French, Danish and German, ranged from 12% to 24%. HT3, being the most common in Danish (38%), and relatively frequent in the other western European (13-14%) populations, appeared to be very rare in our sample (2.3%). The mutation of codon 408 (exon 12, C----T, Arg----Trp), which has been described to be tightly linked to HT2, was tested on amplified DNA by dot-blot hybridization. This mutation was found in 25 out of 44 proband chromosomes. In one case it was linked to HT5, in the remaining 24 to HT2. Our results confirm molecular heterogeneity of PKU haplotypes, as well as their significant interpopulation variation.

Alleles↗
PubMed1991

Phenylketonuria in Poland: 66% of PKU alleles are caused by three mutations.

In order to investigate the molecular basis of phenylketonuria (PKU) in the Polish population, we screened 44 mutant chromosomes from PKU probands for six known mutations, frequently occurring in western European countries, by polymerase chain reaction amplification of their genomic DNA and hybridization with allele-specific oligonucleotides. Our results show that the majority (66%) of all PKU alleles are characterized by three different mutations: in codon 408 (56.8%), codon 158 (6.8%) and codon 261 (2.27%). Of the mutant haplotype 2 alleles, 96% were linked to the mutation in codon 408. Out of five mutant haplotype 4 alleles, three showed the codon 158 mutation, and out of four mutant haplotype 1 alleles, one had the codon 261 mutation. In two families, MspI digests revealed an additional 13.5-kb band similar in length to that previously reported. However, analysis of exon 9 excluded the presence of the T to C transition originally described, indicating a new MspI variant in the Polish population.

Alleles↗
PubMed1991

Aberrant splicing of phenylalanine hydroxylase mRNA: the major cause for phenylketonuria in parts of southern Europe.

We report a mutation within the phenylalanine hydroxylase (PAH) gene that causes aberrant splicing of the mRNA and that is in tight association with chromosomal haplotypes 6, 10, and 36. Because of the high frequency of these particular haplotypes in Bulgaria, Italy, and Turkey, it appears to be one of the more frequent defects in the PAH gene causing classical phenylketonuria in this part of Europe. The mutation is a G to A transition at position 546 in intron 10 of the PAH gene, 11 bp upstream from the intron 10/exon 11 boundary. It activates a cryptic splice site and results in an in-frame insertion of 9 nucleotides between exon 10 and exon 11 of the processed mRNA. Normal amounts of liver PAH protein are present in homozygous patients, but no catalytic activity can be detected. This loss of enzyme activity is probably caused by conformational changes resulting from the insertion of three additional amino acids (Gly-Leu-Gln) between the normal sequences encoded by exon 10 and exon 11.

Base Sequence↗
PubMed1991

Phenylalanine hydroxylase gene: novel missense mutation in exon 7 causing severe phenylketonuria.

By direct sequence analysis of 94 mutant phenylalanine hydroxylase alleles using polymerase chain reaction-based techniques, we identified a C to T transition in exon 7 of the human phenylalanine hydroxylase gene that is associated with RFLP haplotypes 1 and 4. A leucine for proline substitution at position 281 can be predicted from the nucleotide sequence of the mutant codon. Expression analysis in cultured mammalian cells after site-directed mutagenesis proved that the base substitution is a disease causing gene lesion. Dot-blot hybridization analysis using allele-specific oligonucleotides revealed that 25% of all mutant haplotype 1 alleles in the German population bear this mutation. In addition, this mutation could be detected on one mutant haplotype 4 allele. The fact that this mutation is associated with only 25% of all mutant haplotype 1 alleles suggests that multiple mutations may be associated with this haplotype. The occurrence of several different mutations would be in agreement with the clinical heterogeneity observed in the group of patients whose PKU alleles belong to haplotype 1.

Animals↗
PubMed1991

[Prenatal chromosome findings in sonographically conspicuous fetuses].

A retrospective evaluation of 463 prenatal chromosome analyses in a total of 375 patients with suspicious ultrasound findings, revealed a high rate of severe chromosomal abnormalities (16%). The highest risk for an abnormal karyotype was found after sonographic detection of hygroma colli. Abnormal chromosome counts were also frequently found in fetuses with omphaloceles, duodenal atresia and hydrops fetalis, as well as in presence of intrauterine growth retardation and/or anomalies of the amniotic fluid volume. The anomalies mentioned above are, therefore, an urgent indication for a prenatal chromosome analysis. The technical improvements of ultrasound machines and growing experience of operators will lead to an increasing importance of sonography as a method for the identification of pregnancies, that are at high risk for chromosomal abnormalities.

Adolescent↗
PubMed1991

[Prenatal diagnosis with chorionic villi and placenta puncture biopsy in the 1st to 3d trimester of pregnancy: diagnostic value of chromosome studies].

Chorionic villus sampling and placental biopsies became established diagnostic alternatives to amniocentesis worldwide during the 80's. Safety and accuracy are the most important criteria for the evaluation of these newer techniques as compared to amniocentesis. We report on our experience with more than 3400 chromosome analyses between 1985 and 1990 from first to third trimester of pregnancy in a single centre. Most obvious is the higher frequency of mosaicism, which is often, but not always confined to the placenta. Mosaicism accounts for the overwhelming majority of all discrepant (so-called false negative or false positive) cytogenetic findings. The most important prerequisites for diagnostic accuracy of chromosome analyses are meticulous separation of villi immediately after the sampling procedure as well as simultaneous use of direct preparation and cell culture. If mosaicism is not taken as sound evidence for foetal aneuploidy, the accuracy of cytogenetic diagnoses after chorionic villus sampling and placental biopsies is in the same range as the one after amniocentesis.

Adult↗
PubMed1991

Silent mutations in the phenylalanine hydroxylase gene as an aid to the diagnosis of phenylketonuria.

Direct sequencing of the phenylalanine hydroxylase (PAH) gene indicated the existence of silent mutations in codons 232, 245, and 385, linked to specific RFLP haplotypes in several Caucasian populations, namely Germans, Bulgarians, Italians, Turks, and Lithuanians. All three mutations create a new restriction site and can be easily detected on PCR amplified DNA. The usefulness of the silent mutations for diagnostic purposes depends on the haplotype distribution in the target population. The combined analysis of these markers and one or two PKU mutations forms a simple panel of diagnostic tests with full informativeness in a large proportion of PKU families, which helps to avoid the problems of genetic heterogeneity and of prenatal genomic Southern blot analysis.

Base Sequence↗
PubMed1990

Hb D Los Angeles (D-Punjab) and Hb Presbyterian: analysis of the defect at the DNA level.

Amplification of the beta-globin gene by the polymerase chain reaction (PCR) and direct sequencing were used for a fast and reliable identification of the beta-globin variant Hb D Los Angeles and revealed the predicted G----C substitution in codon 121. The same method showed the molecular defect in Hb Presbyterian to be a C----G substitution in codon 108; this eliminates a MaeII restriction site.

Base Sequence↗
PubMed1990

Molecular basis of beta-thalassemia in Turkey: detection of rare mutations by direct sequencing.

Using restriction endonuclease analysis, oligonucleotide hybridization, and direct sequencing of amplified genomic DNA, we characterized 11 different mutations in the DNA of 26 patients from Turkey homozygous for beta-thalassemia. We found that mutations IVS-1 nt110, IVS-1 nt6, and the frameshift at codon 8 were the most frequent. By direct sequencing we characterized two very rare mutations not previously reported in the Turkish population: a frameshift +1 at codons 9/10 and a nonsense mutation at codon 15.

DNA↗
PubMed1990

Molecular data on cystic fibrosis in Bulgaria.

A group of 42 cystic fibrosis (CF) patients and 80 heterozygote carriers was analysed for determining the prevalent CF haplotypes and the frequency of delta F508. The "high-risk" haplotype B (XV2c-KM19/1 2) was found in 66% of CF chromosomes. The prevalent normal haplotypes were A (1 1) and B (2 1). The deletion was detected in 54 CF chromosomes (56%), homozygotes constituting 35% of all CF patients. In 88% of cases the mutation was linked to haplotype B, and in 12% to haplotype D (2 2). Chromosomes that did not have delta F508 were found to be evenly distributed among all four XV2c-KM19 haplotypes. The use of restriction fragment length polymorphisms and direct detection of the mutation makes 94% of CF families fully informative for prenatal analysis.

Bulgaria↗
PubMed1990

Benefits of placental biopsies for rapid karyotyping in the second and third trimesters (late chorionic villus sampling) in high-risk pregnancies.

In a total of 301 placental biopsies in the second and third trimesters, 225 were performed because of suspicious ultrasonographic findings. In this group there was a high rate of aneuploidies (20%). As opposed to the alternative methods for rapid karyotyping, placental biopsies can easily be performed even in pregnancies with abnormal amounts of amniotic fluid. Oligohydramnios and polyhydramnios were key ultrasonographic findings in 38% of cases and were found to be associated with 22% of abnormal chromosomal findings. Suggestive ultrasonographic findings seem to justify the exclusive use of direct preparation.

Amniotic Fluid↗