Perinatal lethal osteogenesis imperfecta

Adult-Onset Transcriptomic Effects of Developmental Exposure to Benzene in Zebrafish (Danio rerio): Evaluating a Volatile Organic Compound of Concern

Urban environments are afflicted by mixtures of anthropogenic volatile organic compounds (VOCs). VOC sources that drive human exposure include vehicle exhaust, industrial emissions, and oil spillage. The highly volatile VOC benzene has been linked to adverse health outcomes. However, few studies have focused on the later-in-life effects of low-level benzene exposure during the susceptible window of early development. Transcriptomic responses during embryogenesis have potential long-term consequences at levels equal to or lower than 1 ppm, therefore justifying the analysis of adult zebrafish that were exposed during early development. Previously, we identified transcriptomic alteration following controlled VOC exposures to 0.1 or 1 ppm benzene during the first five days of embryogenesis using a zebrafish model. In this study, we evaluated the adult-onset transcriptomic responses to this low-level benzene embryogenesis exposure (n = 20/treatment). We identified key genes, including col1a2 and evi5b, that were differentially expressed in adult zebrafish in both concentrations. Some DEGs overlapped at the larval and adult stages, specifically nfkbiaa, mecr, and reep1. The observed transcriptomic results suggest dose- and sex-dependent changes, with the highest impact of benzene exposure to be on cancer outcomes, endocrine system disorders, reproductive success, neurodevelopment, neurological disease, and associated pathways. Due to molecular pathways being highly conserved between zebrafish and mammals, developmentally exposed adult zebrafish transcriptomics is an important endpoint for providing insight into the long term-effects of VOCs on human health and disease.

NGS analysis of collagen type I genes in Polish patients with Osteogenesis imperfecta: a nationwide multicenter study

Osteogenesis imperfecta (OI) is a rare genetic disorder of the connective tissue. It presents with a wide spectrum of skeletal and extraskeletal features, and ranges in severity from mild to perinatal lethal. The disease is characterized by a heterogeneous genetic background, where approximately 85%-90% of cases have dominantly inherited heterozygous pathogenic variants located in the COL1A1 and COL1A2 genes. This paper presents the results of the first nationwide study, performed on a large cohort of 197 Polish OI patients. Variants were identified using a next-generation sequencing (NGS) custom gene panel and multiplex ligation probe amplification (MLPA) assay. The following OI types were observed: 1 (42%), 2 (3%), 3 (35%), and 4 (20%). Collagen type I pathogenic variants were reported in 108 families. Alterations were observed in α1 and α2 in 70% and 30% of cases, respectively. The presented paper reports 97 distinct causative variants and expands the OI database with 38 novel pathogenic changes. It also enabled the identification of the first glycine-to-tryptophan substitution in the COL1A1 gene and brought new insights into the clinical severity associated with variants localized in "lethal regions". Our results contribute to a better understanding of the clinical and genetic aspects of OI.

Novel Mutations Within Collagen Alpha1(I) and Alpha2(I) Ligand-Binding Sites, Broadening the Spectrum of Osteogenesis Imperfecta - Current Insights Into Collagen Type I Lethal Regions

Osteogenesis imperfecta (OI) is a rare genetic disorder demonstrating considerable phenotypic and genetic heterogeneity. The extensively studied genotype-phenotype correlation is a crucial issue for a reliable counseling, as the disease is recognized at increasingly earlier stages of life, including prenatal period. Based on population studies, clusters in COL1A1 and COL1A2 genes associated with the presence of glycine substitutions leading to fatal outcome have been distinguished and named as "lethal regions." Their localization corresponds to the ligand-binding sites responsible for extracellular interactions of collagen molecules, which could explain high mortality associated with mutations mapping to these regions. Although a number of non-lethal cases have been identified from the variants located in lethal clusters, the mortality rate of mutations has not been updated. An next generation sequencing analysis, using a custom gene panel of known and candidate OI genes, was performed on a group of 166 OI patients and revealed seven individuals with a causative mutations located in the lethal regions. Patients' age, ranging between 3 and 25 years, excluded the expected fatal outcome. The identification of non-lethal cases caused by mutations located in lethal domains prompted us to determine the actual mortality caused by glycine substitutions mapping to lethal clusters and evaluate the distribution of all lethal glycine mutations across collagen type I genes, based on records deposited in the OI Variant Database. Finally, we identified six glycine substitutions located in lethal regions of COL1A1 and COL1A2 genes, of which four are novel. The review of all mutations in the dedicated OI database, revealed 33 distinct glycine substitutions in two lethal domains of COL1A1, 26 of which have been associated with a fatal outcome. Similarly, 109 glycine substitutions have been identified in eight lethal clusters of COL1A2, of which 51 have been associated with a fatal manifestation. An analysis of all glycine substitutions leading to fatal phenotype, showed that their distribution along collagen type I genes is not regular, with 17% (26 out of 154) of mutations reported in COL1A1 and 64% (51 out of 80) in COL1A2 corresponding to localization of the lethal regions.

What is new in genetics and osteogenesis imperfecta classification?

OBJECTIVE

Literature review of new genes related to osteogenesis imperfecta (OI) and update of its classification.

SOURCES

Literature review in the PubMed and OMIM databases, followed by selection of relevant references.

SUMMARY OF THE FINDINGS

In 1979, Sillence et al. developed a classification of OI subtypes based on clinical features and disease severity: OI type I, mild, common, with blue sclera; OI type II, perinatal lethal form; OI type III, severe and progressively deforming, with normal sclera; and OI type IV, moderate severity with normal sclera. Approximately 90% of individuals with OI are heterozygous for mutations in the COL1A1 and COL1A2 genes, with dominant pattern of inheritance or sporadic mutations. After 2006, mutations were identified in the CRTAP, FKBP10, LEPRE1, PLOD2, PPIB, SERPINF1, SERPINH1, SP7, WNT1, BMP1, and TMEM38B genes, associated with recessive OI and mutation in the IFITM5 gene associated with dominant OI. Mutations in PLS3 were recently identified in families with osteoporosis and fractures, with X-linked inheritance pattern. In addition to the genetic complexity of the molecular basis of OI, extensive phenotypic variability resulting from individual loci has also been documented.

CONCLUSIONS

Considering the discovery of new genes and limited genotype-phenotype correlation, the use of next-generation sequencing tools has become useful in molecular studies of OI cases. The recommendation of the Nosology Group of the International Society of Skeletal Dysplasias is to maintain the classification of Sillence as the prototypical form, universally accepted to classify the degree of severity in OI, while maintaining it free from direct molecular reference.

ER stress-mediated apoptosis in a new mouse model of osteogenesis imperfecta

Osteogenesis imperfecta is an inherited disorder characterized by increased bone fragility, fractures, and osteoporosis, and most cases are caused by mutations affecting the type I collagen genes. Here, we describe a new mouse model for Osteogenesis imperfecta termed Aga2 (abnormal gait 2) that was isolated from the Munich N-ethyl-N-nitrosourea mutagenesis program and exhibited phenotypic variability, including reduced bone mass, multiple fractures, and early lethality. The causal gene was mapped to Chromosome 11 by linkage analysis, and a C-terminal frameshift mutation was identified in the Col1a1 (procollagen type I, alpha 1) gene as the cause of the disorder. Aga2 heterozygous animals had markedly increased bone turnover and a disrupted native collagen network. Further studies showed that abnormal proα1(I) chains accumulated intracellularly in Aga2/+ dermal fibroblasts and were poorly secreted extracellularly. This was associated with the induction of an endoplasmic reticulum stress-specific unfolded protein response involving upregulation of BiP, Hsp47, and Gadd153 with caspases-12 and −3 activation and apoptosis of osteoblasts both in vitro and in vivo. These studies resulted in the identification of a new model for Osteogenesis imperfecta, and identified a role for intracellular modulation of the endoplasmic reticulum stress-associated unfolded protein response machinery toward osteoblast apoptosis during the pathogenesis of disease.

Osteogenesis imperfecta (OI) is a heterogeneous collection of connective tissue disorders typically caused by mutations in the COL1A1/2 genes that encode the chains of type I collagen, the principle structural protein of bone. Phenotypic expression in OI depends on the nature of the mutation, causing a clinical heterogeneity ranging from a mild risk of fractures to perinatal lethality. Here, we describe a new OI mouse model with a dominant mutation in the terminal C-propeptide domain of Col1a1 generated using the N-ethyl-N-nitrosourea (ENU) mutagenesis strategy. Heterozygous animals developed severe-to-lethal phenotypes that were associated with endoplasmic reticulum stress, and caspases-12 and −3 activation within calvarial osteoblasts. We provide evidence for endoplasmic reticulum stress–associated apoptosis as a key component in the pathogenesis of disease.

PRENATAL DIAGNOSIS OF SKELETAL DYSPLASIAS

Skeletal anomalies occur with a frequency of around 1:500 and can present a diagnostic challenge when detected prenatally. Increasingly more sophisticated imaging such as MRI or CT may elucidate features more easily interpreted by postnatal radiologists. The aetiology of these anomalies is varied and includes aneuploidy, genetic syndromes, skeletal dysplasias, teratogens, disruption and maternal disease, making a multidisciplinary approach to the diagnosis essential. The estimated prevalence of skeletal dysplasias varies from 2–3/10,000 to 4–7/10,000 and diagnosis may require biochemical, cytogenetic, molecular genetic or haematological investigation. Clinical genetic input is often required as the family history or parental examination may yield valuable clues to the diagnosis. This review will briefly describe the normal embryology and sonographic appearances of fetal limb development and go on to suggest a systematic approach to the diagnosis of fetal skeletal dysplasias.

Genetic aspects of birth defects: new understandings of old problems

Over the past two decades, combined advances in genetics, developmental biology and biochemistry have transformed the study of human birth defects. This review describes the importance of genome architecture, parent of origin effects (imprinting), molecular pathophysiology, developmental pathways, mosaicism and cancer predisposition syndromes in the understanding of birth defects. This knowledge can be applied to improve diagnostic accuracy, prognostic information, counselling and sometimes even treatment of these conditions.

Myostatin dominant negative allele products interact positively with wild type monomers

Myostatin is an extracellular negative regulator of muscle growth with an important role in bovine muscular hypertrophy. It belongs to the transforming growth factor beta (TGFbeta) superfamily, and has structural and functional characteristics similar to those of its other, members. Based on these characteristics, we designed three gene constructs in order to create a series of dominant negative (DN) alleles for murine myostatin. As a first requirement for any DN strategy, we first showed that each of the three mutant DN monomers were able to interact with wild type mature myostatin (wt-Mstn), both in a pull-down and a mammalian two-hybrid assay. In addition, the degree of DN-Mstn/wt-Mstn interaction was similar to that of wt-Mstn/wt-Mstn. These results suggest that the three designed alleles are good candidates for use in a DN-based strategy for generating muscular hypertrophy in cattle.

Syndromes with congenital brittle bones

Background

There is no clear definition of osteogenesis imperfecta (OI). The most widely used classification of OI divides the disease in four types, although it has been suggested that there may be at least 12 forms of OI. These forms have been named with numbers, eponyms or descriptive names. Some of these syndromes can actually be considered congenital forms of brittle bones resembling OI (SROI).

Discussion

A review of different syndromes with congenital brittle bones published in the literature is presented. Syndromes are classified in "OI" (those secondary to mutations in the type I pro-collagen genes), and "syndromes resembling OI" (those secondary to mutations other that the type I pro-collagen genes, identified or not). A definition for OI is proposed as a syndrome of congenital brittle bones secondary to mutations in the genes codifying for pro-collagen genes (COL1A1 and COL1A2).

Summary

A debate about the definition of OI and a possible clinical and prognostic classification are warranted.

[Lethal osteogenesis imperfecta. Prenatal diagnosis]

INTRODUCTION

Osteogenesis imparfecta (OI) comprises a group of disorders principally affecting type I collagen, which result in increased bone fragility. Lethal forms are rare and are characterised by micromelia with malformation of the limbs.

CASE REPORT

A prenatal diagnosis of lethal OI was made by ultrasonography at 18 weeks of gestation and therapeutic abortion was indicated.

COMMENTS

Molecular biology and genetic studies offer new possibilities of prenatal diagnosis, but ultrasonography remains the investigation of choice. It confirms the diagnosis by revealing an increase in bone transparency.

Osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a rare congenital disorder of collagen production that results in brittle bones and affects other body systems containing collagen. This article reviews the current body of knowledge about OI and the management of infants with the disorder. Relieving pain, reducing the incidence of new fractures, establishing adequate follow-up, and connecting parents with community resources are the goals of management during the neonatal period. A case study illustrates management and the discharge process.

Advances in osteogenesis imperfecta

Considerable progress has been made in many aspects of osteogenesis imperfecta. The international Sillence classification of osteogenesis imperfecta is being expanded to include a greater range of subgroups of patients. Attempts are being made to identify the genes causing forms of osteogenesis imperfecta and related syndromes that are not caused by mutations of the Type I collagen genes. In medium-term studies, bisphosphonate treatment has been shown to be the first method of treatment to improve the clinical course of the disease significantly. Somatic cell therapy, using allogeneic bone marrow and mesenchymal stromal cell transplantation, are in their early phases of development for use in humans with osteogenesis imperfecta. Somatic gene therapy, which aims to inactivate the mutation, is being evaluated in laboratory and animal studies.

A light and electron microscopic study of osteogenesis imperfecta bone samples, with reference to collagen chemistry and clinical phenotype

A detailed morphological study was carried out using light and electron microscopy on 36 bone specimens from patients suffering from osteogenesis imperfecta (OI) and 20 age- and site-matched control bone specimens. The findings were grouped into the clinical types of OI according to the Sillence classification. The morphological and ultrastructural alterations observed in OI bone correlate well with clinical severity. Thus, OI type I, the mildest type, showed the least abnormalities in bone ultrastructure. OI type IV closely resembled type I, with only minor abnormalities in the bone cells and osteoid. OI type III showed abnormalities in the structure and distribution of osteoid collagen fibrils, whilst OI type II, the lethal form, revealed many varied abnormalities such as thin cortical bone, sparse trabecular bone, increased numbers of osteoclasts and osteocytes, thin osteoid with thin collagen fibrils, and patchy mineralization.

Prenatal diagnosis of a novel COL1A1 mutation in osteogenesis imperfecta type I carried through full term pregnancy

Prenatal diagnosis was performed in a family where the father has osteogenesis imperfecta (OI) type I, with a novel mutation in the COL1A1 gene: a C to T change at position c3076 (c.3076C-->T) leading to a change of arginine at codon 848 to a stop codon (R848X). Prenatal diagnosis by chorionic villous sampling (CVS) was performed during the fourth pregnancy, and revealed that the fetus is a carrier of the same COL1A1 mutation. The possibility of phenotypic variability was discussed with the parents. They elected to carry the pregnancy to term, and a male child with mild OI was born. This is the first reported case where OI was diagnosed prenatally, and the parents opted to carry the pregnancy to term. It illustrates the potential use of DNA-based analysis for early prenatal diagnosis of OI, and the complexities of genetic counselling.

Bone material elasticity in a murine model of osteogenesis imperfecta

To investigate the source of bone brittleness in the disease osteogenesis imperfecta (OI), biomechanical properties have been measured in the femurs from a homozygous (oim/oim) mutant mouse model of OI, its heterozygous littermates, and wild-type animals. The novel technique of ultrasound critical-angle reflectometry (UCR) was used to determine bone material elasticity matrix from measurements of the pressure and shear wave velocity at different orientations about selected points of the bone specimens. This nondestructive method is the only available means for obtaining measurements of this nature from a single surface. The ultrasound pressure wave velocity showed an increased isotropy in the homozygous compared to the wild-type specimens. This was reflected in a significant decrease in the principal elastic modulus measured along the length of the oim/oim bones (E33) while the modulus along the width (E11) did not change significantly, compared to wild-type specimens. The Poisson's ratio, v12, also had a significantly increased value in oim/oim bones. Measurements of these parameters in heterozygous animals generally fell between those from homozygous and control mice. The differences in the elasticity components in oim/oim bones indicate an altered stress distribution and a modified elastic response to loads, compared to normal bone.

A disease-associated glycine substitution in BP180 (type XVII collagen) leads to a local destabilization of the major collagen triple helix

BP180 is a homotrimeric transmembrane protein with a carboxy-terminal ectodomain that forms an interrupted collagen triple helix. Null type mutations in the BP180 gene produce a recessive subepidermal blistering disease, non-Herlitz junctional epidermolysis bullosa. Like the null mutations, a glycine substitution (G627V) within the longest BP180 collagenous domain (COL15) is also associated with the recessive skin disease; however, unlike the null mutations, this glycine substitution appears to act in a dominant fashion to give rise to a novel form of random pitting dental enamel hypoplasia. The dominant effects of this mutation were thought to be due to alterations in the assembly and/or stability of this BP180 collagenous region. To further investigate this issue, a structural analysis was performed on recombinant forms of the wild type and G627V mutant BP180 ectodomain. Both proteins were found to form collagen-like triple helices with very similar Stokes radii and melting temperatures and exhibited very similar rates of synthesis, secretion and turn-over. Tryptic digestion analysis revealed that the mutant G627V-sec180e contains an additional highly sensitive proteolytic site that maps within the region of the mutation. Thus, the disease-associated G627V mutation in BP180 does not grossly alter protein structure, but causes a local destabilization of the triple-helix that exposes sensitive residues to the in vitro effects of trypsin and possibly affects its structure-function in vivo.

Four new cases of lethal osteogenesis imperfecta due to glycine substitutions in COL1A1 and genes. Mutations in brief no. 152. Online

Perinatal lethal osteogenesis imperfecta is the result of heterozygous mutations of the COL1A1 and COL1A2 genes. Here we describe the molecular defects responsible for four case of lethal OI. Two glycine substitutions within the COL1A1 gene (G478S, G994D) and two glycine substitutions within the COLIA2 gene (G319V, G697C) were identified. The mutation sites were localized in proalpha2(I) and proalpha2(I)mRNA molecules, respectively, by chemical cleavage of mismatch in hereteroduplex nucleic acids. Subsequent reverse transcription PCR amplification, cloning and sequencing, led to mutation identification. The aminoacid substitutions were due to two G-->A transitions in COL1A1(cases 1,2), to a G-->T transversion in COL1A2 (case 3), and to two contiguous point mutations in COL1A2 (case 4). All five nucleotide changes appeared to be fresh mutations. COLIA1(accession number Z74615) and COL1A2(accession number Z74616) wild type coding sequences (cDNA) were deduced from the EMBL DNA sequence database. The mutations described here can also be found in the human type I collagen mutation database at the web site:http://www.le.ac.uk/genetics/collagen.

Abnormalities in central nervous system development in osteogenesis imperfecta type II

Osteogenesis imperfecta (OI) type II is a perinatally lethal condition resulting from mutations in type I collagen genes. In addition to characteristic skeletal anomalies, OI type II has recently been shown to be associated with neuropathological alterations, specifically perivenous microcalcifications, and impaired neuroblast migration. In light of these findings, and because type I collagen promotes neuritic maturation both in vitro and in vivo, we sought to determine if additional central nervous system (CNS) developmental anomalies could be found in previously autopsied OI type II cases, and if specific abnormalities correlate with OI subtypes. We retrospectively studied brains of nine patients diagnosed with OI. Of these, seven were OI type II: five were OI type IIA, one was type IIB, and one was type IIC. One OI type I specimen and one OI type III brain were included for comparison, as well as five controls. The IIC brain showed hippocampal malrotation, agyria, abnormal neuronal lamination, diffuse hemorrhage, and periventricular leukomalacia (PVL). The IIB brain had white matter gliosis, PVL, and perivascular calcifications, but was normally developed. Of the five type IIA brains, two showed migrational defects with coexisting PVL and gliosis, two were normally developed with similar white matter injuries, and one was grossly normal. These findings support the contention that collagen mutations might negatively impact CNS development.

Family studies of infantile visceral myopathy: a congenital myopathic pseudo-obstruction syndrome

We conducted family studies of a rare congenital myopathic pseudo-obstruction to provide recurrence risks to families of affected children. This infantile visceral myopathy (IVM) involves the smooth muscles of the digestive tract and frequently the urinary bladder. Family and pregnancy histories from 16 families were evaluated to identify possible environmental or genetic components. The families were ethnically and geographically diverse within the United States. Eleven of the children were alive, four had died, and the status of one was unknown. The sex ratio was 5 females to 11 males. The pregnancy histories provided no evidence of a teratogenic cause. In one family, the disorder passed from parent to child. There were no consanguineous matings, no similarly affected sibs, and except for one case, the family histories did not suggest affected relatives. We suspect a new dominant mutation may be responsible for some cases of IVM, whereas in others, IVM may be caused from a dominant gene with variable expressivity and incomplete penetrance. Therefore, we predict the recurrence risk of severely affected children is much less than the 25 or 50% risk sometimes given families based on the assumption of autosomal recessive or autosomal dominant inheritance. When counseling IVM families, a thorough family history is essential. Subsequent pregnancies should be monitored by ultrasound for megacystis that was detected prenatally in seven of these cases.

Transparent Bone and Concave Ribs

Osteogenesis imperfecta (OI), a rare connective tissue deformity, can be classified into four categories, one of which (type II) is lethal. Lethal OI can be detected with the use of ultrasound prenatally. The authors studied nine OI cases, seven type II OI cases, and two nonlethal cases. All seven type II OI cases had very short limbs. In six of the seven cases, the back wall of the limb bone was visible (transparent bone sign). In four of the seven cases, concave ribs were visualized in the transverse plane. An incidental finding, beaking of the anterior portion of the skull, was noted in five cases. The transparent bone sign and concave ribs were not observed in the two nonlethal cases of OI.

Mutations in fibroblast growth-factor receptor 3 in sporadic cases of achondroplasia occur exclusively on the paternally derived chromosome

More than 97% of achondroplasia cases are caused by one of two mutations (G1138A and G1138C) in the fibroblast growth factor receptor 3 (FGFR3) gene, which results in a specific amino acid substitution, G380R. Sporadic cases of achondroplasia have been associated with advanced paternal age, suggesting that these mutations occur preferentially during spermatogenesis. We have determined the parental origin of the achondroplasia mutation in 40 sporadic cases. Three distinct 1-bp polymorphisms were identified in the FGFR3 gene, within close proximity to the achondroplasia mutation site. Ninety-nine families, each with a sporadic case of achondroplasia in a child, were analyzed in this study. In this population, the achondroplasia mutation occurred on the paternal chromosome in all 40 cases in which parental origin was unambiguous. This observation is consistent with the clinical observation of advanced paternal age resulting in new cases of achondroplasia and suggests that factors influencing DNA replication or repair during spermatogenesis, but not during oogenesis, may predispose to the occurrence of the G1138 FGFR3 mutations.

Osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a genetically determined disorder of connective tissue characterized by bone fragility. The disease state encompasses a phenotypically and genotypically heterogeneous group of inherited disorders that result from mutations in the genes that code for type I collagen. The disorder is manifest in tissues in which the principal matrix protein is type I collagen (mainly bone, dentin, sclerae, and ligaments). Musculoskeletal manifestations are variable in severity along a continuum ranging from perinatal lethal forms with crumpled bones to moderate forms with deformity and propensity to fracture to clinically silent forms with subtle osteopenia and no deformity. The differential diagnosis includes other entities with multiple fractures, deformities, and osteopenia. Classification is based on the timing of fractures or on multiple clinical, genetic, and radiologic features. Molecular genetic studies have identified more than 150 mutations of the COL1A1 and COL1A2 genes, which encode for type I procollagen. Various systemic treatments have been attempted; however, these interventions have been ineffective or inconclusive or are still experimental. Gene therapy has the potential to increase the synthesis of type I collagen in mild variants and to correct mutations in severe variants, but there are a great number of technical difficulties to overcome. The goals of treatment of OI are to maximize function, minimize deformity and disability, maintain comfort, achieve relative independence in activities of daily living, and enhance social integration. Attainment of these goals requires a team approach to tailor treatment needs to the severity of the disease and the age of the patient. Nonoperative management is the mainstay of orthopaedic treatment, with the goals of preventing and treating fractures and enhancing locomotion. Operative intervention is indicated for recurrent fractures or deformity that impairs function.

The Human Genome Project: implications for the treatment of musculoskeletal disease

The ultimate goal of the Human Genome Project is the determination of the molecular sequence of the entire human chromosomal complement. Realization of this goal will include characterization of all the genes that cause or predispose to disease, which will most certainly lead to the development of powerful new tools for diagnosis, prevention, and treatment in all medical fields, including orthopaedics. The authors review the fundamentals of human genetics and gene mapping, summarize the progress of the Human Genome Project thus far, and discuss the implications of this research as it relates to the treatment of musculoskeletal diseases.

The human type I collagen mutation database

Type I collagen is the most abundant and ubiquitously distributed of the collagen family of proteins. It is a heterotrimer comprising two alpha1(I) chains and one alpha2(I) chain which are encoded by the unlinked loci COL1A1 and COL1A2 respectively. Mutations at these loci result primarily in the connective tissue disorders osteogenesis imperfecta and Ehlers-Danlos syndrome types VIIA and VIIB. Two instances of osteoporosis and a single instance of Marfan syndrome are also the result of mutations at these loci. The mutation data are accessible on the world wide web at http://www.le.ac.uk/depts/ge/collagen/collagen.html

The phenotypic features of osteogenesis imperfecta resulting from a mutation of the carboxyl-terminal pro alpha 1 (I) propeptide that impairs the assembly of type I procollagen and formation of the extracellular matrix

The features of a baby with lethal perinatal osteogenesis imperfecta (OI-II), resulting from the substitution of tryptophan 94 by cysteine in the carboxyl-terminal propeptide of pro alpha 1 (I) chains of type I procollagen, were studied. The limbs and torso were of normal length, shape, and proportion. Similarly, all bones were of relatively normal shape and the long bones showed normal metaphyseal modelling. These clinical and radiographic features were similar to those observed in another baby with OI-II resulting from a mutation of the carboxy-terminal propeptide of pro alpha 1 (I) chains but dissimilar from those reported in babies with OI-II resulting from helical mutations of type I collagen.

Mutations, malformations and mortality

Although DNA replication is a very accurate process, a small number of new mutations are generated at every cell division. The generation of a new mutation during the formation of an ovum or sperm cell can cause an early miscarriage or birth defect. The generation of new mutations during embryogenesis can cause a variety of localized birth defects. The molecular delineation of these errors in somatic and gonadal cells has clarified the basis of some birth defects, and has both refined and complicated genetic counselling for a number of paediatric conditions. The processes responsible for these new mutations are present in all cells. For this reason new mutations accumulate in all cells throughout life and contribute to the ageing process. Thus the molecular events that cause many miscarriages and birth defects are the same as those that ultimately lead to death.