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Biomedical subjects

B Steinmann

Publications and source records attributed to B Steinmann.

At least 91 records · Page 5Linked to original sources
PubMed1994

Changes of liver metabolite concentrations in adults with disorders of fructose metabolism after intravenous fructose by 31P magnetic resonance spectroscopy.

A novel 31P magnetic resonance spectroscopy procedure allows the estimation of absolute concentrations of certain phosphorus-containing compounds in liver. We have validated this approach by measuring ATP, phosphomonesters, and inorganic phosphate (Pi) during fasting and after an i.v. fructose bolus in healthy adults and in three adults with disorders of fructose metabolism and by comparing results with known metabolic concentrations measured chemically. During fasting, the ATP concentration averaged 2.7 +/- 0.3 (SD, n = 9) mmol/L, which, after due correction for other nucleoside triphosphates, was 2.1 mmol/L and corresponded well with known concentrations. Fructose-1-phosphate (F-1-P) could not be measured during fasting; its concentration after fructose was calculated from the difference of the phosphomonester signals before (2.9 +/- 0.2 mmol/L) and after fructose. Pi was 1.4 +/- 0.3 mmol/L and represented the one fourth of Pi visible in magnetic resonance spectra. In the three healthy controls after fructose (200 mg/kg, 20% solution, 2.5 min), the fructokinase-mediated increase of F-1-P was rapid, reaching 4.9 mmol/L within 3 min, whereas the uncorrected ATP decreased from 2.7 to 1.8 mmol/L and the Pi from 1.4 to 0.3 mmol/L. The subsequent decrease of F-1-P, mediated by fructaldolase, was accompanied by an overshooting rise of Pi to 2.7 mmol/L. In the patient with essential fructosuria, the concentrations of F-1-P, ATP, and Pi remained unchanged, confirming that fructokinase was indeed inactive. In the patient with hereditary fructose intolerance, initial metabolic changes were the same as in the controls, but baseline concentrations were not yet reestablished after 7 h, indicating weak fructaldolase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1994

Prenatal diagnosis of collagen disorders by direct biochemical analysis of chorionic villus biopsies.

We have developed a method for early prenatal diagnosis of molecular disorders of collagens I and III. The method takes advantage of the fact that isolated chorionic villi contain significant amounts of collagens in their extracellular matrix (stroma) and that they synthesize collagens in vitro. After metabolic labeling of chorion villus biopsies in toto with radioactive amino acids, collagens are extracted and analyzed by SDS-PAGE. Direct staining of the gel shows collagens synthesized in vivo, whereas autoradiofluorography identifies collagens synthesized during incubation in vitro. Unlike collagens synthesized by cultured amniotic fluid cells, collagens extracted from chorionic villi are not overmodified and thus allow better identification of molecular defects. Results are available within 3 to 5 d after biopsy. Using this method, we have correctly excluded Ehlers-Danlos syndrome type IV in two pregnancies, Ehlers-Danlos syndrome type VII in one pregnancy, and lethal osteogenesis imperfecta in four pregnancies. In addition, we correctly predicted a healthy fetus and an embryo affected with lethal osteogenesis imperfecta in consecutive pregnancies from a couple in which the asymptomatic mother was a somatic mosaic for a COL1A1 G-to-A transition (Gly355Asp). Direct collagen analysis of chorion villus biopsies labeled in toto is rapid and reliable and may become the method of choice for the prenatal diagnosis of selected collagen disorders.

Adult↗
PubMed1993

Mutations in the human Ca(2+)-sensing receptor gene cause familial hypocalciuric hypercalcemia and neonatal severe hyperparathyroidism.

We demonstrate that mutations in the human Ca(2+)-sensing receptor gene cause familial hypocalciuric hypercalcemia (FHH) and neonatal severe hyperparathyroidism (NSHPT), two inherited conditions characterized by altered calcium homeostasis. The Ca(2+)-sensing receptor belongs to the superfamily of seven membrane-spanning G protein-coupled receptors. Three nonconservative missense mutations are reported: two occur in the extracellular N-terminal domain of the receptor; the third occurs in the final intracellular loop. One mutated receptor identified in FHH individuals was expressed in X. laevis oocytes. The expressed wild-type receptor elicited large inward currents in response to perfused polyvalent cations; a markedly attenuated response was observed with the mutated protein. We conclude that the mammalian Ca(2+)-sensing receptor "sets" the extracellular Ca2+ level and is defective in individuals with FHH and NSHPT.

Amino Acid Sequence↗
PubMed1993

Long-term follow-up of two sibs with Larsen syndrome possibly due to parental germ-line mosaicism.

Larsen syndrome is a heterogeneous (autosomal dominant or recessive) disorder of characteristic facial changes, multiple joint dislocations, and bone deformities. Few data on the adult presentation of the recessive form of this disorder have been reported; thus, we set out to describe two sibs thought to be affected with autosomal recessive Larsen syndrome who were evaluated as infants and later as adults. Aside from secondary joint changes and the presence of cataracts, changes described in children with autosomal recessive Larsen syndrome were noted. Three years after evaluation, the sister gave birth to a daughter with Larsen syndrome. This occurrence raises the possibility of germ-line mosaicism as the mode of inheritance in this family. Thus, germ-line mosaicism must be considered in the genetic counseling of families with Larsen syndrome in which neither parent appears affected. These patients also illustrate that despite the severe skeletal and joint deformities, the prognosis can be good with careful orthopedic management.

Abnormalities, Multiple↗
PubMed1993

Ehlers-Danlos syndrome type VIIB. Morphology of type I collagen fibrils formed in vivo and in vitro is determined by the conformation of the retained N-propeptide.

Previously we showed that fibrils generated from collagen and pNcollagen-ex6 from fibroblasts of an individual with Ehlers-Danlos syndrome (EDS) type VIIB were hieroglyphic in cross-section and all N-propeptides were located at the fibril surface. Hieroglyphs were resolved to near-cylindrical fibrils (that were similar in appearance to the fibrils seen in the tissues of individuals with EDS type VIIB) by treatment with N-proteinase which cleaved the pN alpha 1(I) chains but not the pN alpha 2(I)-ex6 chains (Watson, R. B., Wallis, G. A., Holmes, D. F., Viljoen, D., Byers, P. H., and Kadler, K. E. (1992) J. Biol. Chem. 267, 9093-9100). Here, quantitative scanning transmission electron microscopy (STEM) showed that N-propeptides in hieroglyphs were in a "bent-back" conformation and thus located exclusively in the overlap zone of the fibril D-period (D = 67 nm). In contrast, STEM of fibrils from the dermis of an individual with EDS type VIIB showed that partially cleaved N-propeptides (in which cleaved pN alpha 1(I) remained in noncovalent association with pN alpha 2(I)-ex6 chains) were distributed equally between the gap and overlap zones of the fibrils. Comparison of experimental data with theoretical mass distributions of the fibril based on amino acid sequence data gave a consistent value of 33 nm for the total axial extent for the N-propeptides in hieroglyphic and tissue fibrils irrespective of the location of N-propeptides to the gap or overlap zone. These data exclude the possibility that N-propeptides adopt a random configuration, but rather, that they locate to specific sites in the gap and overlap zones. The results demonstrated that cleavage of pN alpha 1(I) chains in vivo releases the N-propeptides from the constraints of the bent-back conformation. Co-distribution of partially cleaved N-propeptides between gap and overlap zones allows a higher surface packing density of N-propeptides and explains how circularity of large diameter fibrils can be achieved despite the retention of N-propeptides in tissues of individuals with EDS type VIIB.

Animals↗
PubMed1993

Decreased extracellular deposition of fibrillin and decorin in neonatal Marfan syndrome fibroblasts.

Abnormalities of the microfibrillar protein fibrillin (Fib) have been reported in Marfan syndrome (MFS). The so-called neonatal Marfan syndrome (nMFS) is a lethal phenotype displaying features that are not seen in classical MFS. We have therefore studied the biosynthesis and extracellular deposition of Fib and decorin in fibroblasts from a patient with nMFS and controls. Immunofluorescence of the patient's cell cultures showed an almost complete absence of Fib and a marked reduction of decorin in the extracellular matrix (ECM). The nMFS skin revealed Fib on subbasal microfibrillar bundles in the papillary dermis, and Fib associated with elastic fibers in the reticular dermis; the bundles and fibers were fragmented and thinner than normal. Pulse-chase labeling of cells with [35S]Met/Cys revealed moderately reduced secretion, but a diminished deposition of Fib in the ECM; this was more apparent at a longer chase time. Fib mRNA and synthesis appeared to be normal, whereas both decorin mRNA and biosynthesis were reduced. We therefore assume a structural Fib defect in this patient causing reduced deposition into and/or enhanced removal from the ECM, whereas the reduced decorin biosynthesis may be a secondary regulatory phenomenon. The clinical relevance of this remains unclear. Our findings imply that Fib defects may be responsible for the severe, complex phenotype of nMFS.

Blotting, Northern↗
PubMed1993

SSCP detection of a Gly565Val substitution in the pro alpha 1(I) collagen chain resulting in osteogenesis imperfecta type II.

A patient with perinatal lethal osteogenesis imperfecta (OI) type II has been studied in order to identify the causative mutation. By analysis of the type I collagen produced by cultured fibroblasts from the patient, the defect was mapped to alpha 1 cyanogen bromide peptide 7, a region corresponding to 271 amino acid residues of either the alpha 1(I) or alpha 2(I) collagen chains. Polymerase chain reaction (PCR) amplification of the corresponding region of the alpha 1(I) mRNA followed by single-strand conformation polymorphism analysis of restriction enzyme digestions of the PCR products allowed further mapping of the mutation to a small region of COL1A1. A heterozygous transversion of G to T within the last glycine codon of exon 32 was identified by DNA sequence analysis. This resulted in the substitution of glycine-565 by a valine residue, disrupting the repeating Gly-Xaa-Yaa sequence that is obligatory for correct formation of the collagen molecule. The mutation was shown to have occurred de novo and is thought to result in the OI phenotype.

Base Sequence↗
PubMed1993

Pearson bone marrow-pancreas syndrome with insulin-dependent diabetes, progressive renal tubulopathy, organic aciduria and elevated fetal haemoglobin caused by deletion and duplication of mitochondrial DNA.

We report a patient with a clinical picture consisting of small birth weight, connatal hypoplastic anaemia, vacuolised bone marrow precursors, failure to thrive, and, subsequently, by insulin-dependent diabetes, renal Fanconi syndrome, lactic acidosis, complex organic aciduria, and elevation of haemoglobin F and of adenosine deaminase activity. The clinical course was progressive and death occurred at age 19 months. A high proportion of mitochondrial (mt) DNA molecules with a deletion of nucleotides 9238 to 15575 were identified in several tissues; about half of the shortened mtDNA molecules were concatenated to form circular dimers. The clinical and laboratory findings support recent conclusions that Pearson syndrome is not confined to bone marrow and pancreas, as originally described, but is a multi-organ disorder associated with deletions in part of the mtDNA molecules. The tissue distribution and the relative proportions of the abnormal mtDNA molecules apparently determine the phenotype and clinical course.

Acidosis, Lactic↗
PubMed1993

Homozygosity mapping of the gene for alkaptonuria to chromosome 3q2.

Alkaptonuria, the first human disorder recognized by Garrod as an inborn error of metabolism, is a rare recessive condition that darkens urine and causes a debilitating arthritis termed ochronosis. We have studied two families with consanguineous parents and four affected children in order to map the gene responsible for alkaptonuria. Coinheritance of either neonatal severe hyperparathyroidism or sucrase-isomaltase deficiency and alkaptonuria provided a candidate location for the mutated genes on chromosome 3. Homozygosity mapping with polymorphic loci identified a 16 centiMorgan region on chromosome 3q2 that contains the alkaptonuria gene. Analysis of two additional nonconsanguineous families supports linkage of alkaptonuria to this single locus (combined lod score = 4.3, theta = 0).

Adult↗
PubMed1993

Nonketotic hyperglycinemia: clinical and electrophysiologic effects of dextromethorphan, an antagonist of the NMDA receptor.

A 10-week-old girl with nonketotic hyperglycinemia was treated with increasing amounts of dextromethorphan, an NMDA receptor antagonist. She improved neurologically; at 35 mg/kg/d, seizures ceased and EEG normalized. Dextromethorphan withdrawal resulted in a dramatic clinical deterioration coinciding with epileptic and high-voltage slow activity in the EEG. After reintroduction of dextromethorphan (35 mg/kg/d), recovery occurred within 24 hours.

Amino Acid Metabolism, Inborn Errors↗
PubMed1993

Normal production, nature, and extent of intracellular degradation of newly synthesized collagen in fibroblasts from a patient with prolidase deficiency.

We have examined the extent of intracellular degradation of newly synthesized collagen occurring in fibroblasts from a patient with prolidase deficiency, a rare, autosomal recessively inherited disorder, in which a lack of prolidase, which normally cleaves imidodipeptides with a C-terminal Pro or Hyp residue, results in hyperimidodipeptiduria. The main clinical feature of the condition is chronic, intractable ulceration of the skin, and the suggestion has been made that it represents a specific disorder of collagen metabolism. Although most of the hydroxy-[14]proline derived from the intracellular degradation of newly synthesized collagen in prolidase-deficient fibroblasts occurred in imidodipeptides, with a similar chromatographic profile to those occurring in the patient's urine, the proportion of collagen undergoing such degradation was as in control cells. No abnormality was found in other parameters of collagen metabolism studied, and the results confirm that, although the pathogenesis of its clinical manifestations remains unclear, the disorder is one of protein degradation in general.

Carbon Radioisotopes↗
PubMed1993

An intronic deletion leading to skipping of exon 21 of COL1A2 in a boy with mild osteogenesis imperfecta.

A mild form of osteogenesis imperfecta was diagnosed in a 5-year-old boy with short stature, osteoporosis, blueish sclerae, dentinogenesis imperfecta, hyperextensible joints and bruisable skin. His skin fibroblasts synthesized both normal and shortened pro-alpha 2(I) collagen chains. Procollagen I molecules containing the shortened pro-alpha 2 chains were unstable and thus virtually excluded from secretion at 37 degrees C. Secretion was only partially restored at 30 degrees C. Cyanogen bromide mapping confined the defect to peptide alpha 2(I)CB4. PCR amplification of cDNA showed that the 108 nucleotides corresponding to exon 21 (coding for residues 274 to 309 of the helical domain) were missing in about half of the COL1A2 mRNA. Genomic DNA analysis showed that both exons 21 of COL1A2 were intact, but nucleotides +2 to +40 in intron 21 were deleted on one allele. The intronic deletion altered the conserved nucleotides at position +2 and +5 of the splicing donor site and apparently caused skipping of exon 21 during mRNA splicing. The mild phenotype associated with this COL1A2 mutation may be explained by very poor secretion of the structurally defective procollagen I molecules, which minimizes their deleterious effects on extracellular matrix formation.

Alleles↗
PubMed1992

Genetic linkage of the Marfan syndrome, ectopia lentis, and congenital contractural arachnodactyly to the fibrillin genes on chromosomes 15 and 5. The International Marfan Syndrome Collaborative Study.

BACKGROUND: The large glycoprotein fibrillin is a structural component of elastin-containing microfibrils found in many tissues. The Marfan syndrome has been linked to the fibrillin gene on chromosome 15, but congenital contractural arachnodactyly, which shares some of the physical features of the syndrome, has been linked to the fibrillin gene on chromosome 5. METHODS: Using specific markers for the fibrillin genes, we performed genetic linkage analysis in 28 families with the Marfan syndrome and 8 families with four phenotypically related disorders--congenital contractural arachnodactyly (3 families), ectopia lentis (2), mitral-valve prolapse syndrome (2), and annuloaortic ectasia (1). RESULTS: Genetic linkage was established between the Marfan syndrome and only the fibrillin gene on chromosome 15, with a maximum lod score of 25.6 (odds for linkage, 10(25.6):1). Ectopia lentis was also linked to the fibrillin gene on chromosome 15, whereas congenital contractural arachnodactyly was linked to the fibrillin gene on chromosome 5. There was no linkage of mitral-valve prolapse to the fibrillin gene on chromosome 5; studies of chromosome 15 were not informative. Annuloaortic ectasia was not linked to either fibrillin gene. CONCLUSIONS: The Marfan syndrome appears to be caused by mutations in a single fibrillin gene on chromosome 15. Diagnosis of the Marfan syndrome by genetic linkage and analysis is now feasible in many families.

Base Sequence↗
PubMed1992

A homozygous stop codon in the lysyl hydroxylase gene in two siblings with Ehlers-Danlos syndrome type VI.

Ehlers-Danlos syndrome (EDS) is characterized by joint hypermobility, alterations in the skin and additional signs of connective tissue involvement. EDS type VI was the first connective tissue disorder for which a specific defect in collagen metabolism was identified, namely a deficiency of lysyl hydroxylase activity. We now report a homozygous single basepair substitution converting the CGA codon (Arg319) to a TGA termination codon in two siblings with EDS type VI. The healthy parents, who are first cousins, and two of the three healthy siblings of the patients are heterozygous. The mutation leads to an almost complete absence of lysyl hydroxylase activity in extracts derived from fibroblasts of the patients.

Adolescent↗
PubMed1992

Essential fructosuria: increased levels of fructose 3-phosphate in erythrocytes.

Erythrocytes of 3 adult siblings with essential fructosuria contained 45-200 mumol/l fructose 3-phosphate (Fru-3-P), i.e. 3-15 times the concentration in normal controls. Sorbitol 3-phosphate was also increased, but to a lesser degree. An oral load with 50 g of fructose produced an additional 40 mumol/l increase of erythrocyte Fru-3-P after 5 h. The rate of Fru-3-P formation by red cells in vitro was normal. HbA1 and HbA1c were normal. The suspected pathogenetic role of Fru-3-P in diabetic complications is questioned.

Adult↗