Characterization of Point Mutations in the Collagen COL1A1 and COL1A2 Genes Causing Lethal Perinatal Osteogenesis Imperfecta

The triple helix of collagens - an ancient protein structure that enabled animal multicellularity and tissue evolution

The cellular microenvironment, characterized by an extracellular matrix (ECM), played an essential role in the transition from unicellularity to multicellularity in animals (metazoans), and in the subsequent evolution of diverse animal tissues and organs. A major ECM component are members of the collagen superfamily -comprising 28 types in vertebrates - that exist in diverse supramolecular assemblies ranging from networks to fibrils. Each assembly is characterized by a hallmark feature, a protein structure called a triple helix. A current gap in knowledge is understanding the mechanisms of how the triple helix encodes and utilizes information in building scaffolds on the outside of cells. Type IV collagen, recently revealed as the evolutionarily most ancient member of the collagen superfamily, serves as an archetype for a fresh view of fundamental structural features of a triple helix that underlie the diversity of biological activities of collagens. In this Opinion, we argue that the triple helix is a protein structure of fundamental importance in building the extracellular matrix, which enabled animal multicellularity and tissue evolution.

Osteoporosis and Bone Mass Disorders: From Gene Pathways to Treatments

Genomic technologies have evolved rapidly contributing to the understanding of diseases. Genome-wide association studies (GWAS) and whole-exome sequencing have aided the identification of the genetic determinants of monogenic and complex conditions including osteoporosis and bone mass disorders. Overlap exists between the genes implicated in monogenic and complex forms of bone mass disorders, largely explained by the clustering of genes encoding factors in signaling pathways crucial for mesenchymal cell differentiation, skeletal development, and bone remodeling and metabolism. Numerous of the remaining discovered genes merit functional follow-up studies to elucidate their role in bone biology. The insight provided by genetic studies is serving the identification of biomarkers predictive of disease, redefining disease, response to treatment, and discovery of novel drug targets for skeletal disorders.

Investigation of the human disease osteogenesis imperfecta: a research-based introduction to concepts and skills in biomolecular analysis

A blended approach encompassing problem-based learning (PBL) and structured inquiry was used in this laboratory exercise based on the congenital disease Osteogenesis imperfecta (OI), to introduce commonly used techniques in biomolecular analysis within a clinical context. During a series of PBL sessions students were presented with several scenarios involving a 2 year old child, who had experienced numerous fractures. Key learning goals related to both the theory and practical aspects of the course, covering biomolecular analysis and functional genomics, were identified in successive PBL sessions. The laboratory exercises were conducted in 3 hour blocks over six weeks, focused firstly on protein analysis, followed by nucleic acids. Students isolated collagen from normal and OI affected fibroblast cultures. Analysis by SDS-PAGE demonstrated α1 and α2 of collagen Type I chains at approximately 95 kDa and 92 kDa, respectively. Subtle differences in protein mobility between the control and OI samples were observed by some students, but most considered it inconclusive as a diagnostic tool. The nucleic acid module involved isolation of RNA from OI affected fibroblasts. The RNA was reverse transcribed and used as template to amplify a 354 bp COL1A1 fragment. Students were provided with the sequence of the OI affected COL1A1 PCR product aligned with the normal COL1A1 sequence, allowing identification of the mutation, as the substitution of Arg for Gly(976) of the triple helical region. Our experience with student cohorts over several years is that presentation of this laboratory exercise within a relevant clinical context, and the opportunity for active engagement with the experimental procedures via PBL sessions, supported the learning of basic theory and practical techniques of biomolecular analysis.

In vivo cellular adaptation to ER stress: survival strategies with double-edged consequences

Disturbances to the balance of protein synthesis, folding and secretion in the endoplasmic reticulum (ER) induce stress and thereby the ER stress signaling (ERSS) response, which alleviates this stress. In this Commentary, we review the emerging idea that ER stress caused by abnormal physiological conditions and/or mutations in genes that encode client proteins of the ER is a key factor underlying different developmental processes and the pathology of diverse diseases, including diabetes, neurodegeneration and skeletal dysplasias. Recent studies in mouse models indicate that the effect of ERSS in vivo and the nature of the cellular strategies induced to ameliorate pathological ER stress are crucial factors in determining cell fate and clinical disease features. Importantly, ERSS can affect cellular proliferation and the differentiation program; cells that survive the stress can become 'reprogrammed' or dysfunctional. These cell-autonomous adaptation strategies can generate a spectrum of context-dependent cellular consequences, ranging from recovery to death. Secondary effects can include altered cell-extracellular-matrix interactions and non-cell-autonomous alteration of paracrine signaling, which contribute to the final phenotypic outcome. Recent reports showing that ER stress can be alleviated by chemical compounds suggest the potential for novel therapeutic approaches.

Variation of nanomechanical properties of bone by gene mutation in the zebrafish

Significant variations of nanomechanical properties and fracture morphology between gene-mutated liliput(dtc232) (lil/lil) zebrafish skeletal bone and wild-type bone have been observed. Nanoindentation measurement disclosed that lil/lil bone has 36% lower nanohardness and 32% lower elastic modulus. The standard deviations of hardness and elastic modulus of lil/lil bone were both much higher than those of wild-type bone. SEM morphology of fracture surfaces further revealed that in bones after gene mutation, formative microcracks make the performance reduction and the increasing of brittleness. What is more, the plywood-like structure of the normal bone does not exist in the lil/lil bone.

Sequence of normal canine COL1A1 cDNA and identification of a heterozygous alpha1(I) collagen Gly208Ala mutation in a severe case of canine osteogenesis imperfecta

The sequence of canine COL1A1 cDNA was determined from four overlapping COL1A1 RT-PCR products generated from canine fibroblast RNA. In the translated region, nucleotide identity between canine and human COL1A1 cDNA was 93.2%, although the canine sequence lacked nucleotides 204 to 215 in the region coding for the N-propeptide. Amino acid identity was 97.7%. Total RNA and type I collagen were collected from cultured skin fibroblasts of a 12-week-old male golden retriever with pathologic fractures suggestive of osteogenesis imperfecta (OI) and dentinogenesis imperfecta. Sequential, overlapping approximately 1,000-bp fragments of COL1A1 and COL1A2 cDNA were each amplified by RT-PCR using primers containing 5' T7 polymerase sites. These PCR products were transcribed with T7 RNA polymerase, hybridized into RNA duplexes, and cleaved at mismatch sites with RNase. The proband had an unique cleavage pattern for the fragment of COL1A1 mRNA spanning nucleotides 709 to 1,531. Sequence analysis identified a G to C point mutation for nucleotide 1,276, predicting a codon change from glycine (GGA) to alanine (GCA) for amino acid 208. This change disrupts the normal Gly-X-Y pattern of the collagen triple helix. Restriction enzyme digestion of the RT-PCR product was consistent with a heterozygous COL1A1 mutation. Type I collagen was labeled with 3H-proline, salt precipitated, and analyzed by SDS-PAGE. Pepsin digested alpha chains were over-hydroxylated, and procollagen processing was delayed. Thus, canine and human OI appear homologous in terms of clinical presentation, etiology, and pathogenesis.

(G586V) substitutions in the alpha 1 and alpha 2 chains of collagen I: effect of alpha-chain stoichiometry on the phenotype of osteogenesis imperfecta?

Osteogenesis imperfecta (OI) is a congenital disease of connective tissue, most often caused by single amino acid substitutions of glycine residues within the triple helical region of collagen I. Collagen I consists of two alpha 1 chains and one alpha 2 chain. Thus, a substitution in the alpha 1(I) chain is thought to affect the function of the collagen molecule more than would a similar substitution in the alpha 2(I) chain, thereby causing more severe OI. Theoretically this hypothesis may be tested by comparing patients with identical substitutions in different alpha-chains. We present a Gly586Val substitution in the alpha 1(I) chain, and compare our findings to those resulting from Gly586Val substitutions in the alpha 2(I) chain (Forlino et al., 1994; Bateman et al., 1991). Our proband had lethal OI type II. Most alpha-chains of collagen I produced by his cultured fibroblasts were overmodified. The denaturation temperature of the abnormal collagen was 1.5 degrees C below normal. Cyanogen bromide cleavage and subsequent sequencing revealed a G-to-T base substitution at nucleotide 2420 of COL1A1, resulting in a Gly586Val substitution. The collagen findings were almost identical to those reported by Bateman et al. (1991) and Forlino et al. (1994), but the clinical phenotypes were different: the patients with the alpha 2(I) substitutions had OI type IV and III and not the lethal OI type II of our proband. It is known that identical biochemical aberrations in the same chain may have different phenotypic effects, both within families and between non-related patients. This must be taken into account in our cautious proposal that substitutions in the alpha 1(I) chain may have more serious consequences than similar substitutions in the alpha 2(I) chain.

Destabilization of osteogenesis imperfecta collagen-like model peptides correlates with the identity of the residue replacing glycine

Mutations resulting in replacement of one obligate Gly residue within the repeating (Gly-Xaa-Yaa)(n) triplet pattern of the collagen type I triple helix are the major cause of osteogenesis imperfecta (OI). Phenotypes of OI involve fragile bones and range from mild to perinatal lethal. In this study, host-guest triple-helical peptides of the form acetyl-(Gly-Pro-Hyp)(3)-Zaa-Pro-Hyp-(Gly-Pro-Hyp)(4)-Gly-Gly-amide are used to isolate the influence of the residue replacing Gly on triple-helix stability, with Zaa = Gly, Ala, Arg, Asp, Glu, Cys, Ser, or Val. Any substitution for Zaa = Gly (melting temperature, T(m) = 45 degrees C) results in a dramatic destabilization of the triple helix. For Ala and Ser, T(m) decreases to approximately 10 degrees C, and for the Arg-, Val-, Glu-, and Asp-containing peptides, T(m) < 0 degrees C. A Gly --> Cys replacement results in T(m) < 0 degrees C under reducing conditions but shows a broad transition (T(m) approximately 19 degrees C) in an oxidizing environment. Addition of trimethylamine N-oxide increases T(m) by approximately 5 degrees C per 1 M trimethylamine N-oxide, resulting in stable triple-helix formation for all peptides and allowing comparison of relative stabilities. The order of disruption of different Gly replacements in these peptides can be represented as Ala </= Ser < CPO(red) < Arg < Val < Glu </= Asp. The rank of destabilization of substitutions for Gly in these Gly-Pro-Hyp-rich homotrimeric peptides shows a significant correlation with the severity of natural OI mutations in the alpha1 chain of type I collagen.

Disrupted growth plates and progressive deformities in osteogenesis imperfecta as a result of the substitution of glycine 585 by valine in the alpha 2 (I) chain of type I collagen

The skeleton of a child with osteogenesis imperfecta type III, resulting from the substitution of glycine 586 by valine in the triple helical domain of the alpha 2 (I) chain of type I collagen, was severely porotic but contained lamellar bone and Haversian systems. From early childhood, structural failure of the bone resulted in the disruption of growth plates, progressive bone deformities, and severe growth retardation.

Arachnoid cyst and chronic subdural haematoma in a child with osteogenesis imperfecta type III resulting from the substitution of glycine 1006 by alanine in the pro alpha 2(I) chain of type I procollagen

The features of a child with osteogenesis imperfecta type III (OI III) resulting from the heterozygous substitution of glycine 1006 by alanine in the pro alpha 2(I) chain of type I procollagen were studied. He was born at term with the clinical features of severe OI, including deep grey-blue sclerae. He had severe osteopenia and all long bones were smaller than normal with cortical thinning, metaphyseal expansion, poor metaphyseal modelling, and multiple fractures. However, the vertebrae, pelvis, and shoulder girdle were of normal shape and there were few rib fractures. Histological examination of the calvarium and tibial shaft showed woven bone without lamellar bone or Haversian systems. The shafts of the long bones were widened owing to repeated fractures. Progressive enlargement of the calvarium occurred between 3 and 4.5 months of age owing to bilateral chronic subdural haematomata and a large arachnoid cyst in the Sylvian fissure. The cyst was probably developmental in origin while the subdural collections were probably the result of perinatal skull trauma. The cyst and the subdural collections resolved following drainage but ventricular dilatation with normal cerebrospinal fluid pressure followed. The proband is the first reported case of OI with a glycine substitution by alanine in the pro alpha 2(I) chain of type I procollagen.

Gly85 to Val substitution in pro alpha 1(I) chain causes mild osteogenesis imperfecta and introduces a susceptibility to protease digestion

In this paper we describe a mild moderate form of osteogenesis imperfecta caused by a point mutation in COL1A1 which converted glycine 85 to valine. The valine substitution introduced into the triple-helical domain of type-I collagen a conformational perturbation causing susceptibility to digestive proteases. In fact, SDS/PAGE of pepsin-treated collagen showed the presence of a faint band, migrating between alpha 1(I) and alpha 2(I), both in the medium and in the cell layer. On trypsin digestion the band, a shortened form of alpha 1(I), had a melting temperature of 39.5 degrees C. If the triple-helical collagen was obtained after trypsin or chymotrypsin digestion of procollagen, two shortened bands were identified; the enzymes cleaved about 40% of the trimers. The mutant procollagen was normally secreted and processed in the extracellular matrix at a normal rate. When native type-I collagen was formed after dextran-sulfate incubation, only chains of normal length were found, suggesting that the fibroblast proteases did not recognize the alteration introduced by the mutation. The effects of glycine 85 to valine substitution are compared with those produced by a previously described arginine substitution of the same residue (Deak et al., 1991).

The use of chemical reagents in the detection of DNA mutations

As the analysis of the human genome proceeds at an ever-increasing pace, many genes have been identified which are the site for mutations responsible for inherited diseases. The identification of the mutations within these genes has become a major application of molecular biology technologies, and to this end a number of mutation detection systems have been developed for use in diagnostic and research laboratories. The uses of these mutation detection systems are in the diagnosis of inherited disease (both prenatal and neonatal) and in an understanding of the function of the affected protein by cataloguing the range of mutations. Two of these mutation detection systems are reviewed here. Both rely on chemical modification of mismatched nucleotides, by either carbodiimide or hydroxylamine and osmium tetroxide. The methods are termed the carbodiimide (CDI) and the Chemical Cleavage of Mismatch (CCM) methods. The history and evolution of the methods is tracked, illustrating the way in which they developed, both as suitable technology became available (for example, the polymerase chain reaction) and as a result of a specific need. The current methodologies are briefly discussed, followed by a discussion of their applications, especially in the realm of disease mutation detection.

Osteogenesis imperfecta and type-I collagen mutations. A lethal variant caused by a Gly910-->Ala substitution in the alpha 1 (I) chain

In this study we describe a new dominant point mutation in COL1A1 causing a lethal form of Osteogenesis imperfecta (type II B). Dermal cultured fibroblasts from the proband were shown to produce both normal and heavily overmodified type-I collagen. The mutation introduced a local conformational perturbation, which causes abnormal exposure of arginine residues; the triple helical domain was susceptible to trypsin digestion even at 30 degrees C. The chains bearing the point mutation were poorly secreted and short-term pulse experiments showed that the extensive intracellular retention of mutant trimers also impaired the secretion of normal chains. The molecular defect was localized in a COL1A1 allele by cloning and sequencing a cDNA region corresponding to the CB6 peptide. A G to C transversion which causes the substitution in the triple helical region of Gly910 with alanine was found. The mutation also causes the disappearance of a MspI-recognition site at nucleotide 3263 of the pro alpha 1 (I) coding sequence. Restriction analysis, along with the biochemical screening of collagens, allowed us to perform prenatal diagnosis on cells from chorionic-villus sampling and to exclude the recurrence of the mutation in the sibling.

Moderately severe osteogenesis imperfecta associated with substitutions of serine for glycine in the alpha 1(I) chain of type I collagen

We have examined the type I collagen protein, RNA, and cDNA of 2 children with moderately severe (type IV) osteogenesis imperfecta (OI). They have in common a non-lethal form of OI with ambulatory potential, overmodification of type I collagen protein, and a substitution of serine for glycine in the collagen chain produced by one alpha 1(I) allele. The first child (Marini et al.: J Biol Chem 264:11893-11900, 1989) is now 7 years old, with the height of a 3-year-old. Her course includes significant remodeling of lower long bones and 4 femur fractures. She walks independently. A mishmatch was detected in her alpha 1(I) mRNA using RNA/RNA hybrids; it was demonstrated to be due to a G-->A point mutation in one allele of alpha 1(I), resulting in the substitution of serine for glycine 832. The second child is now 6 1/2 years old, with the height of 1 1/2-year-old. Her history includes significant bowing of femurs and tibias, 6 femur fractures, S-curve scoliosis, compression of all lumbar vertebrae, and limited short-distance walking with braces. Her alpha 1(I) mRNA has also been studied by RNA hybrid analysis; there is a single G-->A change in one alpha 1(I) allele causing the substitution of serine for gly 352. Both children have moderately severe OI. However, the serine substitution at gly 352 is associated with a more severe phenotype then is the serine substitution at gly 832. Compared to substitutions described in other cases of OI, the serine 352 is located in the middle of a cluster of cysteine substitutions associated with non-lethal OI.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemical cleavage method for the detection of RNA base changes: experience in the application to collagen mutations in osteogenesis imperfecta

We discuss the definition of mutations in osteogenesis imperfecta (OI) using a chemical cleavage method for detecting mismatched bases in patient mRNA: control cDNA heteroduplexes. The method is based on the increased chemical modification of cytosines (Cs) by hydroxylamine and thymines (Ts) by osmium tetroxide when they are not paired with their complementary base. The DNA is then cleaved at the modified base with piperidine and the use of radioactively labeled DNA probes allows the position of the mismatched base to be determined by electrophoresis of the cleavage-product. The precise mutations are then determined by specific amplification and sequencing of the region containing the mismatched base. In perinatally lethal OI (OI type II) mismatches have been detected in all 17 cases studied; 12 of these have been fully characterized. In 7 of these 12 cases the mismatches were point mutations in the genes for pro alpha 1(I) or pro alpha 2(I) which resulted in glycine substitutions in the triple helical region of the protein. Sequence variation was detected in addition to the glycine substitutions in 2 cases. In 2 cases the RNA mismatch resulted from changes in the amino acid sequence of the C-propeptide domain. In the 3 remaining cases the mismatch resulted from silent nucleotide sequence variants. In the less severe forms of OI we have studied, mismatches have been detected and characterized in 8 of 12 cases. In 4 of these 8 cases the mismatch resulted from presumably neutral sequence variation and in the other 4 cases mutations have been defined.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of expression of the type I collagen genes

The identification and functional analysis of DNA-protein interactions in the intronic and 5' flanking regions of the type I collagen genes has begun to define a series of cis-elements and trans-acting factors which regulate transcription of these genes. Studies such as these will eventually be expected to elucidate the mechanisms responsible for coordinate transcription of the alpha 1 and alpha 2 genes, a question which remains central to the field of collagen research. Although it is relatively straightforward to define sites of DNA-protein binding, interpretation of the functional importance of such interactions can be extremely complex. Furthermore, while mutation or deletion of a particular binding site may alter the functional activity of a construct transfected into cultured cells, there is no guarantee that a similar change will have the same effect in vivo, where the entire gene locus is present in its native chromosomal context. Nevertheless, these kinds of in vitro studies offer the best current approach to defining and isolating transcription factors that control expression of the alpha 1 and alpha 2 genes. Ultimately, it will be necessary to test the activity of such factors (and their respective cis-elements) in defined systems in vivo.

Paternal mosaicism for a COL1A1 dominant mutation (alpha 1 Ser-415) causes recurrent osteogenesis imperfecta

We describe a dominant point mutation in the COL1A1 gene causing extremely severe osteogenesis imperfecta (OI type II/III) which was detected in the dermal fibroblasts of a proband, diagnosed by ultrasonography at 24 weeks of gestation. Type I collagen secretion was reduced and pro alpha 1(I) chains were overmodified. The mutation was localised in one COL1A1 allele by chemical cleavage of mismatched bases in normal cDNA/proband's mRNA heteroduplexes, and identified by cloning and sequencing. A G-to-A transition which causes the substitution of Gly-415 with serine in the alpha 1(I) triple helical domain was found. The same mutation was detected in the father's spermatozoa and lymphocytes. Mosaicism in the father's germline explains the occurrence in the family of two additional OI pregnancies, which were documented by X-ray and ultrasound investigations.

The clinicopathological features of three babies with osteogenesis imperfecta resulting from the substitution of glycine by valine in the pro alpha 1 (I) chain of type I procollagen

The features of three babies with perinatal lethal osteogenesis imperfecta (OI II) resulting from substitutions of glycine by valine in the triple helical domain of the alpha 1(I) chain of type I collagen were studied. The babies were heterozygous for this substitution at residue 1006 in case 1 (OI35), 973 in case 2 (OI59), and 256 in case 3 (OI7B). OI35 had the most severe clinical form, OI IIC, with premature rupture of membranes, severe antepartum haemorrhage, stillbirth, severe short limbed dwarfism, and extreme osteoporosis. OI59 was a better formed baby but was also born prematurely as a result of premature rupture of membranes and severe antepartum haemorrhage. She had the radiographic features of OI IIA. OI7B was born at term and also had the radiographic features of OI IIA. Pathological examination of the skeletons of OI35 and OI59 showed grossly deficient intramembranous and endochondral ossification. Trabecular bone was sparse in the long bones and vertebrae. The trabeculae contained a cartilage core and an overlying layer of woven bone or osteoid. The diaphyses lacked cortical bone. The periosteal fibroblasts of OI35 contained grossly distended rough endoplasmic reticulum consistent with the 53% reduction in collagen secretion by cultured dermal fibroblasts. The aorta, skin, and lungs were hypoplastic in OI35 and OI59. The findings in this study show that glycine substitutions by valine in Gly-X-Y triplets, from glycine 256 to glycine 1006, of the triple helical domain of alpha 1(I) chains produce the OI II phenotype. The phenotype was most severe in the baby with the most carboxy-terminal substitution.

Complete mutation detection using unlabeled chemical cleavage

We have developed a strategy for the complete detection of point mutations, small insertions and deletions by chemical cleavage based on the methodology of Cotton et al. (1988). The technique was extended by the development of a nonisotopic cleavage product detection system using silver staining after gel electrophoresis. The complete mutation detection was achieved by use of mutant and wild-type DNAs in equimolar quantities in duplex formation, thus any mismatches that are resistant to chemical cleavage (e.g., some T.G mismatches) are easily detected by cleavage of the complementary heteroduplex (e.g., A.C mismatch). With such a strategy mutant DNAs can be screened for mutations and polymorphisms. The advantages of complete unlabeled mutation detection are considerable.

Lethal perinatal osteogenesis imperfecta due to a type I collagen alpha 2(I) Gly to Arg substitution detected by chemical cleavage of an mRNA:cDNA sequence mismatch

A single base mismatch was detected by a chemical cleavage method in heteroduplexes formed between patient mRNA and a control collagen alpha 2(I) cDNA probe in a case of osteogenesis imperfecta type II. The region of the mRNA mismatch was amplified using the polymerase chain reaction, cloned and sequenced. A heterozygous point mutation of G to C at base pair 1,774 of the collagen alpha 2(I) mRNA resulted in the substitution of glycine with arginine at amino acid position 457 of the helix. Type I collagen of alpha 1(I)- and alpha 2(I)-chains from the patient migrated slowly on electrophoresis due to increased levels of posttranslational modification of lysine. The parents' fibroblast collagen did not contain the mRNA mismatch and the collagens showed normal electrophoretic behaviour. Two-dimensional electrophoresis of the CNBr peptides from the patient's collagen confirmed the excessive posttranslational modification of the alpha 1(I)- and alpha 2(I)-chains in the CNBr peptides N-terminal to the mutation due to disruption of the obligatory Gly-X-Y triplet repeat of the helix. The mutation led to reduced procollagen secretion and helix destabilization as evidenced by a decreased thermal stability. These data lend further support to the accumulating evidence that type I collagen alpha 2(I) glycine substitution mutations result in the same spectrum of clinical severity as those in the alpha 1(I)-chain.(ABSTRACT TRUNCATED AT 250 WORDS)

Substitution of cysteine for glycine at residue 415 of one allele of the alpha 1(I) chain of type I procollagen in type III/IV osteogenesis imperfecta

We have examined the type I collagen in a patient with type III/IV osteogenesis imperfecta. Two forms of alpha 1(I) chain were produced, one normal and the other containing a cysteine residue within the triple helical domain of the molecule. Cysteine is not normally present in this domain of type I collagen. Peptide mapping experiments localised the mutation to peptide alpha 1(I)CB3 which spans residues 403 to 551 of the triple helix. Subsequent PCR amplification of cDNA covering this region followed by sequencing showed a G to T single base change in the GGC codon for glycine 415 generating TGC, the codon for cysteine. The effect of the mutation on the protein is to delay secretion from the cell, reduce the thermal stability of the molecule by 2 degrees C, and cause excessive post-translational modification of all chains in molecules containing one or more mutant alpha 1(I) chains. The clinical phenotype observed in this patient and the position of the mutation conform to the recent prediction of Starman et al that Gly----Cys mutations in the alpha 1(I) chain have a gradient of severity decreasing from the C-terminus to the N-terminus.

Characterisation of a glycine to valine substitution at amino acid position 910 of the triple helical region of type III collagen in a patient with Ehlers-Danlos syndrome type IV

We have studied a patient with Ehlers-Danlos syndrome type IV. Protein mapping studies of her type III collagen had indicated that cyanogen bromide fragment 9 contained the site of the mutation. Here we describe the mapping of this region for a single base mutation using a chemical modification and cleavage technique. Sequence analysis of cDNA showed a G to T mutation resulting in the substitution of glycine 910 by valine. This was confirmed by allele specific oligonucleotide hybridisation to the proband's genomic DNA.

Osteogenesis imperfecta: translation of mutation to phenotype

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Collagens as multidomain proteins

The number of proteins known to contain collagen-like triple helical domains is rapidly increasing. The functions of these domains are to provide molecular rods that separate spatially non-triple helical domains with varied properties and structures and to permit lateral interactions between molecules. Two-thirds of the amino acids of the triple helical domains have their side-chains at the surface of the protein. The triple helix is also a structure that is easily predictable from the primary structure. The structure of several recently discovered collagens are discussed in terms of domains and functions. The triple helical domains have sizes varying from 33 to over 1,000 amino acid residues. The longest uninterrupted triple helices are involved in the formation of the classical quarter-staggered fibrils. Other triple helical domains permit varied molecular aggregates. A very broad spectrum of non-triple helical or globular domains are interspersed by triple helices. Only those located at the extremities of the molecules are large in size, sometimes several hundred kDa, while the domains separating 2 triple helices are small (less than 50 amino acids) and provide the molecules with hinges, proteolytic cleavage sites or other specialized functions like a glycosaminoglycan attachment site. If the assembly of the 3 chains required for the triple helix formation can be controlled in vitro, collagen-like molecules offer an as yet unexploited potential for protein engineering.

Segmental amplification of the entire helical and telopeptide regions of the cDNA for human alpha 1 (I) collagen

Type I collagen is the site of several common genetic diseases and therefore, the diagnosis of mutational defects occurring therein is of considerable importance. By the polymerase chain reaction amplification of a series of seven overlapping segments, we show that the entire helical and telopeptide regions of the human alpha 1 (I) collagen cDNA can be cloned for sequencing. Unlike all other means of identifying collagen mutations, including protein sequencing and electrophoretic analysis, RNase A hybrid analysis and chemical cleavage of DNA or RNA heteroduplexes, the technique presented is capable of identifying all mutations and polymorphisms without false negative results.

Clinical applications of the polymerase chain reaction

The polymerase chain reaction (PCR) is a technique that allows a million-fold, or greater, amplification of defined regions of DNA or RNA. It is potentially capable of detecting a single copy of a gene, present only once in 105 eukaryotic cells. This remarkable level of sensitivity has allowed the development of many diagnostic assays for human pathogens and disease states. These include: the detection of viral, bacterial and protozoal agents; diagnosis and genetic analysis of inherited diseases such as β-thalassaemia, sickle cell disease, haemophilia, Tay-Sachs disease and many others; diagnosis and analysis of neoplastic disorders such as, chronic myelogenous leukaemia (CML), acute lymphocytic lymphoma (ALL), follicular lymphomas and various other cancers, including the detection of activated oncogenes; prenatal and pre-implantation diagnosis; and the development of genetic risk prediction.

The PCR can greatly simplify diagnostic processes that were previously difficult to perform, particularly where the initial amounts of biological material were very limited. In other cases, PCR provides the only method available for detection and diagnosis. However, although simple in theory, the PCR technique remains, for routine clinical diagnostic purposes, currently in the domain of the specialist laboratory. This is because of its sensitivity to nucleic acid contamination from other sources that can cause misleading results. Procedures and precautions are being developed to minimize this problem and there is little doubt that, in many instances, the PCR will be the diagnostic method of choice within the next few years.