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Biomedical subjects

B Steinmann

Publications and source records attributed to B Steinmann.

At least 73 records · Page 4Linked to original sources
PubMed1996

Ehlers-Danlos syndrome type IV caused by Gly400Glu, Gly595Cys and Gly1003Asp substitutions in collagen III: clinical features, biochemical screening, and molecular confirmation.

Three patients with Ehlers-Danlos syndrome type IV (EDS IV) and biochemical evidence of structural defects in collagen III were investigated for mutations within the collagen III gene (COL3A1). Single strand conformation polymorphism analysis of alpha 1 (III) cDNA indicated the presence of different heterozygous sequence changes in each of the patients. Nucleotide sequencing revealed mutations leading to the substitution of glycine 400 with glutamic acid, glycine 595 with cysteine, and glycine 1003 with aspartic acid. EDS IV is a life-threatening disorder which, as the clinical histories of our patients and their families show, still often escapes diagnosis. Biochemical and molecular studies can clarify the diagnosis and help provide appropriate management and counselling.

Adult↗
PubMed1996

The deletion of six amino acids at the C-terminus of the alpha 1 (II) chain causes overmodification of type II and type XI collagen: further evidence for the association between small deletions in COL2A1 and Kniest dysplasia.

We have identified an 18 bp deletion in exon 49 of the type II procollagen gene (COL2A1) in a patient with Kniest dysplasia. The deletion is located at the very C-terminus of the helical domain and removes two of three Gly-Pro-Pro triplets at positions 1007-1012, which are thought to be involved in helix formation and stability. Morphological investigation of an iliac crest biopsy showed large inclusions in the endoplasmic reticulum of chondrocytes, reflecting impaired secretion of type II collagen. Electrophoretic analysis of collagens extracted from cartilage or synthesised by cultured chondrocytes showed that type II and also type XI procollagen molecules containing mutant alpha 1 (II) chains showed post-translational overmodification. These observations provide further evidence for the general association of Kniest dysplasia with small deletions in the helical domain of type II collagen.

Amino Acid Sequence↗
PubMed1996

Gly802Asp substitution in the pro alpha 2(I) collagen chain in a family with recurrent osteogenesis imperfecta due to paternal mosaicism.

A proband with osteogenesis imperfecta (OI) type III/IV was born to clinically normal parents, who subsequently had two pregnancies terminated because of OI in the fetuses. Cultured fibroblasts from the proband, one fetus and the father produced abnormal collagen I. Cyanogen bromide mapping localised the defect to the region of the alpha 1(I)CB7 peptide. Sequencing revealed a G to A transition at nucleotide 2814 in COL1A2 in the proband, the fetus, and the father, which resulted in a Gly802Asp substitution in the pro alpha 2(I) collagen chain. About 25% of the paternal alleles from fibroblasts and leucocytes and 40% of paternal alleles from spermatocytes carried the mutation consistent with somatic and germinal mosaicism. For genetic counselling, parental mosaicism must be considered in all sporadic cases of OI.

Aspartic Acid↗
PubMed1996

Mutations and phenotype in isolated glycerol kinase deficiency.

We demonstrate that isolated glycerol kinase (GK) deficiency in three families results from mutation of the Xp21 GK gene. GK mutations were detected in four patients with widely differing phenotypes. Patient 1 had a splice-site mutation causing premature termination. His general health was good despite absent GK activity, indicating that isolated GK deficiency can be silent. Patient 2 had GK deficiency and a severe phenotype involving psychomotor retardation and growth delay, bone dysplasia, and seizures, similar to the severe phenotype of one of the first described cases of GK deficiency. His younger brother, patient 3, also had GK deficiency, but so far his development has been normal. GK exon 17 was deleted in both brothers, implicating additional factors in causation of the severe phenotype of patient 2. Patient 4 had both GK deficiency with mental retardation and a GK missense mutation (D440V). Possible explanations for the phenotypic variation of these four patients include ascertainment bias; metabolic or environmental stress as a precipitating factor in revealing GK-related changes, as has previously been described in juvenile GK deficiency; and interactions with functional polymorphisms in other genes that alter the effect of GK deficiency on normal development.

Abnormalities, Multiple↗
PubMed1996

Osteoporosis-pseudoglioma syndrome, a disorder affecting skeletal strength and vision, is assigned to chromosome region 11q12-13.

Osteoporosis-pseudoglioma syndrome (OPS) is an autosomal recessive disorder characterized by severe juvenile-onset osteoporosis and congenital or juvenile-onset blindness. The pathogenic mechanism is not known. Clinical, biochemical, and microscopic analyses suggest that OPS may be a disorder of matrix homeostasis rather than a disorder of matrix structure. Consequently, identification of the OPS gene and its protein product could provide insights regarding common osteoporotic conditions, such as postmenopausal and senile osteoporosis. As a first step toward determining the cause of OPS, we utilized a combination of traditional linkage analysis and homozygosity mapping to assign the OPS locus to chromosome region 11q12-13. Mapping was accomplished by analyzing 16 DNA samples (seven affected individuals) from three different consanguineous kindreds. Studies in 10 additional families narrowed the candidate region, supported locus homogeneity, and did not detect founder effects. The OPS locus maps to a 13-cM interval between D11S1298 and D11S971 and most likely lies in a 3-cM region between GSTP1 and D11S1296. At present, no strong candidate genes colocalize with OPS.

Alleles↗
PubMed1995

Truncated profibrillin of a Marfan patient is of apparent similar size as fibrillin: intracellular retention leads to over-N-glycosylation.

We studied profibrillin-1 (proFib) synthesis and microfibril formation in cultured fibroblasts from an individual with severe Marfan syndrome harboring a premature stop codon (W2756ter) in one FBN1 allele. Rotary shadowing analysis of extracellular matrix produced by these cells revealed the presence of only a very few intact microfibrils which showed marked disorganisation within the interbeaded domains. Metabolic pulse-chase studies identified intracellularly a population of truncated proFib molecules which were secreted more slowly than the normal proFib derived from the normal allele. Culture media contained strikingly reduced amounts of wild-type proFib in comparison to fibrillin (Fib). Our findings imply that (1) the truncated proFib is secreted and disturbs microfibril assembly; (2) the mutation is probably close to a putative cleavage site in the proFib C terminus necessary for the conversion of proFib to Fib; (3) the truncated proFib is over-N-glycosylated due to intracellular retention rather than incomplete cleavage of proFib with persistence of N-glycosylated sites; (4) not all potential N-glycosylation sites in proFib seem to be normally used, since we could produce over-N-glycosylated proFib in normal cells by brefeldin A mediated intracellular captivation and subsequent appearance of over-glycosylated Fib in culture medium upon removal of the compound. It is conceivable that post-translational over-modification might be important for modulating the phenotype of FBN1 mutations in Marfan syndrome.

Actin Cytoskeleton↗
PubMed1995

A glycine 375-to-cysteine substitution in the transmembrane domain of the fibroblast growth factor receptor-3 in a newborn with achondroplasia.

Achondroplasia, the most common form of chondrodysplasia, has been associated with mutations in the gene of the fibroblast growth factor receptor-3 (FGFR-3) on chromosome 4p. All 39 achondroplasia alleles studied so far carried point mutations which caused the same amino acid exchange, a substitution of glycine by arginine at position 380 (G380R) in the transmembrane domain of the receptor. We report on a newborn with achondroplasia who does not carry a G380R mutation but has a mutation causing substitution of a nearby glycine with a cysteine (G375C). This observation indicates allelic heterogeneity and confirms the role of mutations in the transmembrane domain of FGFR-3 in the pathogenesis of achondroplasia.

Achondroplasia↗
PubMed1995

Genetic counselling on brittle grounds: recurring osteogenesis imperfecta due to parental mosaicism for a dominant mutation.

UNLABELLED: Osteogenesis imperfecta (OI), a dominantly inherited connective tissue disorder, is usually caused by defects in collagen I. There is growing evidence for parental mosaicism that results in affected children born to unaffected parents. This situation poses a difficult task for the geneticist because a mosaic parent may appear clinically healthy while carrying the mutation in a fraction of her or his gonadal cells. To illustrate this problem, we report a Swiss couple whose first child was affected with severe OI. The unexpected recurrence of the disorder in the second child raised the suspicion of a recessive trait or, rather, of parental mosaicism. We identified the responsible collagen mutation in the COL1A2 gene (Gly688Ser in the alpha 2(I)-chain) in both children and demonstrated the father to be a somatic mosaic for this mutation and to have subtle clinical signs such as soft skin and short stature that may be a result of his mosaic state. CONCLUSION: After the birth of a child affected with OI the possibility of parental mosaicism should be considered and options for prenatal diagnosis discussed.

Adult↗
PubMed1994

Analyses of truncated fibrillin caused by a 366 bp deletion in the FBN1 gene resulting in Marfan syndrome.

We studied fibrillin synthesis in cultured fibroblasts from 11 members of a three-generation family with Marfan syndrome, caused by a large in-frame deletion in FBN1 (the fibrillin gene) leading to a loss of 366 bases in the corresponding fibrillin mRNA. Metabolic labelling with [35S]Met/Cys and SDS/PAGE allowed unequivocal identification of normal and truncated fibrillin in all cell strains harbouring the deletion. In culture medium, fibrillin and its truncated counterpart were predominant, whereas their respective larger precursors were found only in traces. This proportion, however, was markedly shifted towards the normal and truncated precursors by EGTA and reversed by the addition of calcium, which confirmed the existence of profibrillin and its probably calcium-dependent conversion into fibrillin. Tunicamycin caused increased electrophoretic mobility of normal and truncated molecules without changing their apparent size differences. Intracellularly, only profibrillin was found; in the mutant cells truncated and normal profibrillin molecules were present in similar amounts and both populations were secreted and deposited simultaneously into the extracellular matrix; there, however, truncated profibrillin only became easily detectable after treatment of cells with dextran sulphate, which increased the amount of extractable profibrillin. Immunofluorescence microscopy in patients' cultures identified fibrillin-containing microfibrils which appeared to be moderately reduced both in amount and diameter. Ultrastructural analysis by rotary-shadowing and immunogold electron microscopy demonstrated the presence of numerous beaded domains reacting with fibrillin antibodies, but no intact fibrillin microfibrils in patient's cell-layer extracts, in contrast with the extensive microfibrils elaborated by control cultures. Our findings suggest, that in the patients' cell cultures all microfibrils contained the truncated fibrillin molecules.

Actin Cytoskeleton↗
PubMed1994

Delayed triple helix formation of mutant collagen from patients with osteogenesis imperfecta.

The kinetics of triple helix formation of procollagen I were measured in normal human fibroblast cultures and cell strains from six patients with osteogenesis imperfecta (OI), a heritable connective tissue disorder. After a 4-minute pulse-labelling with [35S]methionine, the appearance of protease-resistant and thus helical collagen molecules was followed for variable chase times. In control cells, 50% of the molecules were fully triple-helical after 14 minutes. In the six OI cell strains harbouring a single Gly-->Cys substitution at positions 94, 223, 526, 691 and 988 in the helical domain of the alpha 1(I)-chain, formation of full-length protease-resistant molecules containing two mutant alpha 1(I)-chains as judged by the appearance of disulphide-linked alpha 1(I)-dimers was delayed by 5 to 60 minutes. The delay inversely correlated with the thermal stability of abnormal collagen molecules containing alpha 1(I)-dimers. Folding time and melting temperature of procollagen I in the sixth cell strain with a Gly-->Cys substitution at position 1017, outside the triple helical region in the C-terminal telopeptide, were normal. Here, we demonstrate the hitherto postulated delay in the zipper-like folding of collagen molecules harbouring Gly-->Cys substitutions in the alpha 1(I)-chain affecting the helical part of the molecule.

Amino Acid Sequence↗
PubMed1994

Ultrastructural analysis of skin and aorta from a patient with Menkes disease.

Ultrastructural studies of the skin and aorta of a patient with Menkes disease, an X-linked recessive disorder of copper metabolism, are described. Dermal thickness was normal, while dermal collagen fibrils exhibited a heterogeneous size range, with a mean diameter smaller than normal. Long-spacing collagen was often observed near fibroblasts, the plasma membranes of which were decorated by aggregates of interwoven filaments. Dermal elastin fibers were scarce and consisted of thin strands of amorphous elastin associated with numerous microfibrils. In the aorta, the amount of collagen was normal, although the fibrils displayed a broader range of diameters than normal, with a slightly smaller mean. Elastin fibers showed considerable disruption, appearing fragmented and wider than normal, and displaying irregular contours. The inclusion of cationic dyes during tissue fixation gave rise to numerous electron-dense precipitates within the elastin fibers, suggesting the presence there of glycosaminoglycans or proteoglycans, among which unsulfated and sulfated chondroitins were demonstrated by immunoelectron microscopy to be prominent. Heparan sulfate, observed to be a constituent of normal elastin fibers, was much reduced in amount. Elastin was also found associated with glycosaminoglycans in the soluble matrix of the aortic wall.

Aorta↗
PubMed1994

Three unrelated individuals with perinatally lethal osteogenesis imperfecta resulting from identical Gly502Ser substitutions in the alpha 2-chain of type I collagen.

In general, osteogenesis imperfecta is caused by heterozygous mutations in either of the genes encoding the alpha 1 or alpha 2 chains of type I collagen (COL1A1 and COL1A2, respectively). Usually, these mutations are unique to the affected individual or individuals within a family. In this study, single-strand conformation polymorphism mapping analysis has been coupled with sequence analysis to identify a single base mutation in the alpha 2(I) gene of type I collagen; this mutation is identical in three unrelated individuals with perinatal lethal osteogenesis imperfecta. The heterozygous G to A transition at a CpG dinucleotide results in a Gly502Ser substitution in the alpha 2 chain of type I collagen.

Base Sequence↗
PubMed1994

Molecular basis of essential fructosuria: molecular cloning and mutational analysis of human ketohexokinase (fructokinase).

Essential fructosuria is one of the oldest known inborn errors of metabolism. It is a benign condition which is believed to result from deficiency of hepatic fructokinase (ketohexokinase, KHK, E.C.2.7.1.3). This enzyme catalyses the first step of metabolism of dietary fructose, conversion of fructose to fructose-1-phosphate. Despite the early recognition of this disorder, the primary structure of human KHK and the molecular basis of essential fructosuria have not been previously defined. In this report, the isolation and sequencing of full-length cDNA clones encoding human ketohexokinase are described. Alternative mRNA species and alternative KHK isozymes are produced by alternative polyadenylation and splicing of the KHK gene. The KHK proteins show a high level of sequence conservation relative to rat KHK. Direct evidence that mutation of the KHK structural gene is the cause of essential fructosuria was also obtained. In a well-characterized family, in which three of eight siblings have fructosuria, all affected individuals are compound heterozygotes for two mutations Gly40Arg and Ala43Thr. Both mutations result from G-->A transitions, and each alters the same conserved region of the KHK protein. Neither mutation was seen in a sample of 52 unrelated control individuals. An additional conservative amino acid change (Val49IIe) was present on the KHK allele bearing Ala43Thr.

Alternative Splicing↗
PubMed1994

Intracellular accumulation of collagen VII in cultured keratinocytes from a patient with dominant dystrophic epidermolysis bullosa.

Expression of collagen VII, a candidate molecule for dystrophic epidermolysis bullosa, was analyzed in cultured keratinocytes from a patient with generalized dominant dystrophic epidermolysis bullosa (DEBD) of the Pasini subtype. Double immunofluorescence revealed an increased intracellular staining of collagen VII that co-localized with protein disulfide isomerase, a marker of the rough endoplasmic reticulum. Ultrastructural analysis of cultured DEBD cells showed dilated cisternae of the rough endoplasmic reticulum and numerous residual bodies, both of which contained abundant collagen VII as detected by immunoelectron microscopy. Immunoblotting of keratinocyte extracts indicated an increased ratio of cell-associated versus secreted soluble collagen VII in DEBD cells. Collagen VII mRNA was of normal size in the DEBD cells, but present in excessive amounts. The data suggest a mutation in the collagen VII gene that leads to intracellular accumulation and degradation of this collagen, and thus to a reduced number of anchoring fibrils at the dermo-epidermal junction, and subsequently to blistering of the skin in this family.

Adult↗
PubMed1994

Clinical, ultrastructural and biochemical studies in two sibs with Ehlers-Danlos syndrome type VI-B-like features.

Two Turkish sibs with clinical features of Ehlers-Danlos syndrome type VI-B are presented. The hydroxylysine contents of dermis and gel electrophoresis of type I and type III collagen produced by fibroblasts were normal. Ultrastructural studies of skin collagen and elastic fibers showed discrete abnormalities. Other syndromes with similar clinical, biochemical and ultrastructural features are discussed.

Child, Preschool↗
PubMed1994

Familial hypocalciuric hypercalcemia and neonatal severe hyperparathyroidism. Effects of mutant gene dosage on phenotype.

Neonatal severe hyperparathyroidism is a rare life-threatening disorder characterized by very high serum calcium concentrations (> 15 mg/dl). Many cases have occurred in families with familial hypocalciuric hypercalcemia, a benign condition transmitted as a dominant trait. Among several hypothesized relationships between the two syndromes is the suggestion that neonatal severe hyperparathyroidism is the homozygous form of familial hypocalciuric hypercalcemia. To test this hypothesis, we refined the map location of the gene responsible for familial hypocalciuric hypercalcemia on chromosome 3q. Analyses in 11 families defined marker loci closely linked to the gene responsible for familial hypocalciuric hypercalcemia. These loci were then analyzed in four families with parental consanguinity and offspring with neonatal severe hyperparathyroidism. Each individual who was homozygous for loci that are closely linked to the gene responsible for familial hypocalciuric hypercalcemia had neonatal severe hyperparathyroidism. The calculated odds of linkage between these disorders of > 350,000:1 (lod score = 5.56). We conclude that dosage of the gene defect accounts for these widely disparate clinical phenotypes; a single defective allele causes familial hypocalciuric hypercalcemia, while two defective alleles causes neonatal severe hyperparathyroidism.

Chromosome Mapping↗