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Biomedical subjects

B Steinmann

Publications and source records attributed to B Steinmann.

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

Missense mutations associated with RFLP haplotypes 1 and 4 of the human phenylalanine hydroxylase gene.

We report missense mutations associated with haplotype 1 and haplotype 4 alleles of the human phenylalanine hydroxylase (PAH) gene. Individual exon-containing regions were amplified by polymerase chain reaction from genomic DNA of a PKU patient who was a haplotype 1/4 compound heterozygote. The amplified DNA fragments were subcloned into M13 for sequence analysis. Missense mutations were observed in exons 5 and 7, resulting in the substitution of Arg by Gln at residues 158 and 261 of the enzyme, respectively. Expression analysis in heterozygous mammalian cells after site-directed mutagenesis demonstrated that the Arg158-to-Gln158 mutation is a PKU mutation, whereas the Arg261-to-Gln261 mutation is apparently silent in the assay system. Hybridization analysis using allele-specific oligonucleotide probes demonstrated that the Arg158-to-Gln158 mutation is present in two of six mutant haplotype 4 alleles among the Swiss and constitutes about 40% of all mutant haplotype 4 alleles in the European population. The mutation is not present in normal alleles or in any mutant alleles of other haplotypes. The results provide conclusive evidence that there is linkage disequilibrium between mutation and haplotype in the PAH gene and that multiple mutations have occurred in the PAH gene of a prevalent haplotype among Caucasians.

Base Sequence↗
PubMed1989

Temperature-dependent expression of a collagen splicing defect in the fibroblasts of a patient with Ehlers-Danlos syndrome type VII.

In this article we report the characterization of the molecular lesion in a patient with Ehlers-Danlos syndrome Type VII and provide evidence that a de novo substitution of the last nucleotide of exon 6 in one allele of the pro-alpha 2(I) collagen gene produces normally spliced mRNA and transcripts from which exon 6 sequences have been outspliced as well. Unexpectedly, the expression of the alternative splicing was found to be temperature-dependent, for missplicing in cellula is effectively abolished at 31 degrees C and gradually increases to 100% at 39 degrees C. In contrast, in a similar patient harboring a substitution in the obligatory GT dinucleotide of the 5' splice site of intron 6, complete outsplicing of exon 6 sequences was found at all temperatures.

Amino Acid Sequence↗
PubMed1989

Decreased thermal denaturation temperature of osteogenesis imperfecta mutant collagen is independent of post-translational overmodifications of lysine and hydroxylysine.

Fibroblasts from many patients with osteogenesis imperfecta (OI) synthesize and secrete Type I collagen which is both overmodified and exhibits a decreased thermal denaturation temperature. We have examined the relationship between overmodification and decreased melting temperature in several favorable OI mutants by selectively inhibiting lysyl hydroxylase activity with the drug Minoxidil and comparing the melting profiles of the resultant undermodified collagen with untreated control. Minoxidil treatment causes an appreciable decrease in hydroxylysine with compensatory increases in lysine content, and the delayed sodium dodecyl sulfate-polyacrylamide gel electrophoretic mobility of the overmodified collagen chains becomes normal. However, the decreased melting temperature was unchanged from untreated OI control. When unhydroxylated collagen produced by normal control and OI fibroblasts incubated with alpha,alpha'-dipyridyl was examined, mutant OI molecules melted at a lower temperature than control. These data indicate that the decreased thermal denaturation temperature of OI mutant collagen is independent of post-translational overmodification of lysine or hydroxylysine. Presumably, substitutions for glycine in the Gly-X-Y structural motif distort the helix and produce lower melting temperatures by presently unknown mechanisms.

Collagen↗
PubMed1989

Ehlers-Danlos syndrome type IV: a subset of patients distinguished by low serum levels of the amino-terminal propeptide of type III procollagen.

Serum levels of procollagen type III aminopropeptide (P-III-NP), a peptide released during conversion of type III procollagen to collagen, were abnormally low in six of 10 patients with Ehlers-Danlos syndrome (EDS) type IV (arterial-ecchymotic type) and low-normal in 4. The serum P-III-NP levels correlated with the amount of type III procollagen secreted by the patients' cultured fibroblasts. Serum P-III-NP determination is a simple test that identifies a major subgroup of patients with this life-threatening, dominantly inherited connective tissue disorder and may be especially helpful in making the diagnosis in children.

Adolescent↗
PubMed1989

Molecular defects of type III procollagen in Ehlers-Danlos syndrome type IV.

Fibroblasts from most patients with Ehlers-Danlos syndrome (EDS) type IV, a disorder characterized by fragility of skin, blood vessels, and internal organs, secrete reduced amounts of type III procollagen. In 7 of 8 cell strains analyzed, we found evidence of structural defects in half of the type III procollagen chains synthesized, such as deletions or bona fide amino acid substitutions, which cause delayed formation and destabilization of the collagen triple helix and, as a consequence, reduced secretion of the molecule. The data suggest that EDS type IV is often caused by heterozygosity for mutations at the COL3A1 locus, which affect the structure of type III procollagen. The triple-helical region of the molecule, like the homologous region of type I procollagen, appears to be particularly vulnerable.

DNA↗
PubMed1989

Hyperprolinaemia type I and white matter disease: coincidence or causal relationship?

We describe a 10-year-old boy with hyperprolinaemia type I and severe neurological abnormalities (mental retardation, cerebral palsy, epilepsy, nystagmus). Magnetic resonance imaging showed diffuse white matter involvement and electroretinography confirmed tapetoretinal degeneration. In view of reports in the literature, hyperprolinaemia type I may not be a benign condition, as usually assumed, but may lead to marked neurological abnormalities, particularly in affected males.

Brain Diseases↗
PubMed1989

Ehlers-Danlos syndrome type VI with normal lysyl hydroxylase activity cannot be explained by a defect in cellular uptake of ascorbic acid.

The uptake of ascorbic acid by cultured skin fibroblasts from two siblings with Ehlers-Danlos syndrome type VI, in extracts of which there is no deficit in lysyl hydroxylase activity, was found to be normal. Decreased availability of ascorbic acid to lysyl hydroxylase in cellula cannot, therefore, provide an explanation for the disorder in these patients, the cause of which remains obscure.

Adolescent↗
PubMed1989

Clinical variability of osteogenesis imperfecta linked to COL1A2 and associated with a structural defect in the type I collagen molecule.

We report a family in which dominant osteogenesis imperfecta segregates with a COL1A2 haplotype and is associated with a structural defect in the helical region of the type I procollagen molecule. All affected subjects had short stature, dentinogenesis imperfecta, and myopia; however, great differences were observed in the number of fractures and in the degree of bone deformity. Identical biochemical changes were found in the type I collagen molecules synthesised by fibroblasts of subjects with severe or minimal bone fragility. These results confirm that mutations in the triple helical region of alpha 2(I) chains produce a milder phenotype than analogous mutations in the alpha 1(I) chains, but indicate that, in addition to defects in the type I collagen molecule, other factors may modulate the degree of bone involvement in osteogenesis imperfecta.

Adult↗
PubMed1989

Haplotype distribution of the human phenylalanine hydroxylase locus in Scotland and Switzerland.

RFLP haplotypes at the phenylalanine hydroxylase (PAH) locus were determined in 45 nuclear Caucasian families from Switzerland and Scotland. The RFLPs at the PAH locus are highly informative, and prenatal diagnosis is possible in 85% of the families studied. The data were combined with the profiles previously observed in the Danish population, in order to study the variation in RFLP haplotype distribution among European populations. A total of 22 different haplotypes were observed in Denmark, Switzerland, and Scotland. Fifteen and 19 haplotypes are associated with the normal (non-PKU) and with the mutant chromosomes, respectively. The haplotype distribution and the allele frequency of normal chromosomes remain constant between Denmark, Switzerland, and Scotland. However, both the haplotype distribution and allele frequencies of mutant chromosomes show significant variation between the three countries. Our results suggest there may be additional mutations in the PAH gene that cause PKU.

Alleles↗
PubMed1988

The structure of human collagen type IX and its organization in fetal and infant cartilage fibrils.

Human collagen type IX was isolated from the media of organ cultures of fetal or infant hyaline cartilage. It consisted of three distinct, disulfide-bonded polypeptides of 115, 84, and 72 kDa, respectively. Digestion with chondroitinase ABC reduced the apparent molecular mass of the 115-kDa chain to about 65 kDa demonstrating that also human collagen type IX is a proteoglycan. In the electron microscope, the molecule had a rigid rod-like structure with characteristic kinks and with a globular domain at one end. Digestion of human collagen type IX with pepsin leads to somewhat heterogeneous fragments. Affinity-purified antibodies to the mixture of fragments specifically reacted with the fragment HMW without cross-reaction with chicken HMW. LMW of both species were recognized to the same low extent. Mechanically generated fibril fragments from human fetal cartilage were heterogeneous in diameter. Significantly, they could be immunostained for collagen type IX in a D-periodic pattern and regardless of the fibril diameter. Some fibrils were poorly labeled, again independently of the diameter. Therefore, the role of collagen type IX in cartilage probably is not to control directly the lateral growth during fibrillogenesis but rather to stabilize the fibril network.

Animals↗
PubMed1988

Identification of a mutation that causes exon skipping during collagen pre-mRNA splicing in an Ehlers-Danlos syndrome variant.

Recent biochemical studies have shown that the fibroblasts from a patient with Ehlers-Danlos Syndrome Type VIIB produce nearly equal amounts of normal and shortened pro-alpha 2(I) collagen chains (Wirtz, M.K., Glanville, R. W., Steinmann, B., Rao, V. H., and Hollister, D. (1987) J. Biol. Chem. 262, 16376-16385). Compositional and sequencing studies of the abnormal pro-alpha 2(I) chain identified an interstitial deletion of 18 residues corresponding to the N-telopeptide of the collagen molecule. Since this region is encoded by a 54-base pair exon, number 6, the protein defect could have been caused by gene deletion, abnormal pre-mRNA splicing, or both. Here, in order to elucidate the molecular nature of this mutation we have analyzed the sequences of pro-alpha 2(I) collagen cDNA and genomic clones obtained from RNA and DNA of the patient's fibroblasts. Using oligomer-specific cloning we identified a cDNA that contains a 54-base pair deletion corresponding precisely to the sequence of exon 6. Identification of the normal gene was based on the finding of an identical sequence polymorphism in a normal cDNA and in the genomic clone derived from one of the two collagen alleles. The other gene, instead, displayed a base substitution (T to C) in the obligatory GT dinucleotide of the 5' splice-site sequence of intron 6. Analysis of nearly 100 base pairs immediately 5' to exons 5, 6, and 7, and 3' to exons 5 and 7 did not reveal any additional change. Therefore, the data strongly suggest that the observed GT-to-GC transition at the splice donor site of intron 6 generates an abnormally spliced mRNA in which the sequence of exon 5 is joined to the sequence of exon 7. Since skipping of exon 6 does not interfere with the coding frame of the mRNA, the resulting shortened polypeptide, albeit utilized in the assembly of a procollagen trimer, ultimately causes the Ehlers-Danlos Syndrome Type VII phenotype.

Alleles↗
PubMed1988

Ehlers-Danlos syndrome type IV: a multi-exon deletion in one of the two COL3A1 alleles affecting structure, stability, and processing of type III procollagen.

We have studied a patient with severe, dominantly inherited Ehlers-Danlos syndrome type IV. The results indicate that this patient carries a deletion of 3.3 kilo-base pairs in the triple helical coding domain of one of the two alleles for the pro-alpha-chains of type III collagen (COL3A1). His cultured skin fibroblasts contain equal amounts of normal length mRNA and of mRNA shortened by approximately 600 bases, and synthesize both normal and shortened pro-alpha 1(III)-chains. In procollagen molecules containing one or more shortened chains, a triple helix is formed with a length of only about 780 amino acids. The mutant procollagen molecules have decreased thermal stability, are less efficiently secreted, and are not processed as their normal counterpart. The deletion in this family is the first mutation to be described in COL3A1.

Adult↗
PubMed1988

Impaired secretion of type III procollagen in Ehlers-Danlos syndrome type IV fibroblasts: correction of the defect by incubation at reduced temperature and demonstration of subtle alterations in the triple-helical region of the molecule.

The amount of type III procollagen secreted by fibroblasts from two patients with type IV Ehlers-Danlos syndrome is reduced to 25% and 20%, respectively, of that of control cells after incubation at 37 degrees C, but reverts to 70% and 110% when cells are incubated at 32 degrees C. The type III procollagen molecules secreted only at the lower temperature are of normal size but apparently contain different mutations which disrupt the triple-helical region and lower the thermal stability of the molecule. These data suggest that subtle mutations in the pro alpha 1(III)-chains produce Ehlers-Danlos syndrome type IV by disrupting the triple-helical region of the molecule, lowering its thermal stability, and thus impairing its secretion. At the lower temperature, stabilization of the defective molecules result in more efficient secretion. This approach may be useful for the characterization of other unstable collagens.

Cell Line↗
PubMed1988

Lethal osteogenesis imperfecta: abnormal collagen metabolism and biochemical characteristics of hypophosphatasia.

We have examined collagen from a patient with the rare type IIC form of perinatally lethal osteogenesis imperfecta, in whom biochemical characteristics of hypophosphatasia were also apparent. In addition to normal alpha 1(I) and alpha 2(I) chains, there were chains overmodified along their lengths. Unexpectedly, the thermal stability of molecules containing these chains was normal. This suggests the existence of a structural mutation causing delayed triple helix formation, situated in either the alpha 1(I) or alpha 2(I) C-terminal propeptide. Since collagen synthesised by fibroblasts from each of the patient's parents was normal, the mutation was probably newly arising and dominant. In contrast to other reported cases of lethal osteogenesis imperfecta, not only was the secretion of collagen by cultured fibroblasts considerably retarded, but that of non-collagenous proteins was also severely impaired.

Alkaline Phosphatase↗
PubMed1988

The neonatal pseudo-hydrocephalic progeroid syndrome (Wiedemann-Rautenstrauch). Report of a new patient and review of the literature.

A boy with the pseudo-hydrocephalic progeroid syndrome (McKusic 26409) is presented and compared to five previously reported children. The boy presented with major skeletal abnormalities, which receded during the first few months of life. Special investigations like studies on collagen, electron microscopy, and growth studies of fibroblasts did not contribute to our knowledge of the pathogenesis of this rare disease.

Collagen↗