Recurrence risks and prognosis in severe sporadic osteogenesis imperfecta

A Dyadic Nosology for Osteogenesis Imperfecta and Bone Fragility Syndromes 2024

In 2023 following extensive consultation with key stakeholders, the expert Nosology Working Group of the International Skeletal Dysplasia Society (ISDS) published the new Dyadic Nosology for Genetic Disorders of the Skeleton. Some 770 entities were delineated associated with 552 genes. From these entities, over 40 genes resulting in distinct forms of Osteogenesis Imperfecta (OI) and Bone Fragility and/or Familial Osteoporosis were identified. To assist clinicians and lay stake holders and bring the considerable body of knowledge of the matrix biology and genomics to people with OI as well as to clinicians and scientists, a dyadic nosology has been recommended. This combines a genomic co-descriptor with a phenotypic naming based on the widely used Sillence nosology for the OI syndromes and the many other syndromes characterized in part by bone fragility.This review recapitulates and explains the evolution from the simple Congenita and Tarda subclassification of OI in the 1970 nosology, which was replaced by the Sillence types I-IV nosology which was again replaced in 2009 with 5 clinical groups, type 1 to 5. Qualitative and quantitative defects in type I collagen polypeptides were postulated to account for the genetic heterogeneity in OI for nearly 30 years, when OI type 5, a non-collagen disorder was recognized. Advances in matrix biology and genomics since that time have confirmed a surprising complexity both in transcriptional as well as post-translational mechanisms of collagens as well as in the many mechanisms of calcified tissue homeostasis and integrity.

Co-occurrence of heterozygous mutations in COL1A1 and SERPINF1 in a high-risk pregnancy complicated by osteogenesis imperfecta

Mutations in several genes, including SERPRINF1 and COL1A1, have been associated with the development of osteogenesis imperfecta (OI). Here, we reported the co-occurrence of a rare heterozygous variant (c.167C>G p.Ala56Gly) in SERPRINF1 and a novel heterozygous mutation (c.1634G>A p.Gly545Asp) in COL1A1 in a foetus with a severe form of OI. Bioinformatics modelling revealed that the effect of the mutation on SPERINF1 is neutral. In contrast, the mutation in COL1A1 is deleterious. It is predicted to cause distortion of the α (1) chain of the type I collagen and results in structural instability of the protein. Therefore, a novel dominant variant of COL1A1 likely underlies the severe foetal pathology observed, although we do not exclude the possibility that the heterozygous mutations in SERPINF and COL1A1 may interact and co-ordinately cause pathogenesis. This novel COL1A1 mutation is recommended to be included in the diagnostic panels for OI.

Osteogenesis imperfecta IIC caused by a novel heterozygous mutation in the C-propeptide region of COL1A1

Osteogenesis imperfecta IIC (OI IIC), which is a rare variant of lethal OI that has been considered to be an autosomal recessive trait, is characterized by twisted, slender long bones with dense metaphyseal margins. Here, we report a typical case of OI IIC caused by a novel heterozygous mutation in the C-propeptide region of COL1A1. OI IIC seems to be caused by a dominant mutation of COL1A1.

A novel mutation in LEPRE1 that eliminates only the KDEL ER- retrieval sequence causes non-lethal osteogenesis imperfecta

Prolyl 3-hydroxylase 1 (P3H1), encoded by the LEPRE1 gene, forms a molecular complex with cartilage-associated protein (CRTAP) and cyclophilin B (encoded by PPIB) in the endoplasmic reticulum (ER). This complex is responsible for one step in collagen post-translational modification, the prolyl 3-hydroxylation of specific proline residues, specifically α1(I) Pro986. P3H1 provides the enzymatic activity of the complex and has a Lys-Asp-Glu-Leu (KDEL) ER-retrieval sequence at the carboxyl terminus. Loss of function mutations in LEPRE1 lead to the Pro986 residue remaining unmodified and lead to slow folding and excessive helical post-translational modification of type I collagen, which is seen in both dominant and recessive osteogenesis imperfecta (OI). Here, we present the case of siblings with non-lethal OI due to novel compound heterozygous mutations in LEPRE1 (c.484delG and c.2155dupC). The results of RNA analysis and real-time PCR suggest that mRNA with c.2155dupC escapes from nonsense-mediated RNA decay. Without the KDEL ER- retrieval sequence, the product of the c.2155dupC variant cannot be retained in the ER. This is the first report of a mutation in LEPRE1 that eliminates only the KDEL ER-retrieval sequence, whereas other functional domains remain intact. Our study shows, for the first time, that the KDEL ER- retrieval sequence is essential for P3H1 functionality and that a defect in KDEL is sufficient for disease onset.

CRTAP mutations in lethal and severe osteogenesis imperfecta: the importance of combining biochemical and molecular genetic analysis

Autosomal recessive lethal and severe osteogenesis imperfecta (OI) is caused by the deficiency of cartilage-associated protein (CRTAP) and prolyl-3-hydroxylase 1 (P3H1) because of CRTAP and LEPRE1 mutations. We analyzed five families in which 10 individuals had a clinical diagnosis of lethal and severe OI with an overmodification of collagen type I on biochemical testing and without a mutation in the collagen type I genes. CRTAP mutations not described earlier were identified in the affected individuals. Although it seems that one important feature of autosomal recessive OI due to CRTAP mutations is the higher consistency of radiological features with OI type II-B/III, differentiation between autosomal dominant and autosomal recessive OI on the basis of clinical, radiological and biochemical investigations proves difficult in the affected individuals reported here. These observations confirm that once a clinical diagnosis of OI has been made in an affected individual, biochemical testing for overmodification of collagen type I should always be combined with molecular genetic analysis of the collagen type I genes. If no mutations in the collagen type I genes are found, additional molecular genetic analysis of the CRTAP and LEPRE1 genes should follow. This approach will allow proper identification of the genetic cause of lethal or severe OI, which is important in providing prenatal diagnosis, preimplantation genetic diagnosis and estimating recurrence risk.

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 collagen disorders and the impact on craniofacial development]

Extracellular matrix molecules provide to tissues their mechanical properties and constitute a reservoir of local or regional signals that regulate cellular function. Collagens, the major components of osseous and collagenous matrices, have structural similarities, but are encoded by different genes. We describe here osteogenesis imperfecta, a collagen I, the principal constituent of bone, genetic disease, and its craniofacial implications. By comparing it with genetic disorders of cartilage collagen (Kniest and Stickler syndromes) we try to clarify the respective influences of these matrix molecules upon craniofacial development.

Non-lethal Hallermann-Streiff syndrome with bone fracture: report of a case

The Hallermann-Streiff syndrome is characterized by bird-like face, micropthalmia, cataracts, micrognathia, beaked nose, abnormal dentition, hypotrichosis, cutaneous atrophy and proportional small stature. We present a 35-day-old patient with the classical signs except cutaneous atrophy, additionally he had a healing fracture at the proximal part of the left radius.

Initial experience using magnetic resonance imaging in prenatal diagnosis of osteogenesis imperfecta type II: a case report

We report a fetus with osteogenesis imperfecta (OI) first diagnosed by ultrasound in routine prenatal examination and further evaluated by magnetic resonance imaging (MRI). Fetal MRI was undertaken with a 1.5-T magnet using a body-phased array coil and an ultrafast imaging technique, half-Fourier single-shot turbo spin-echo (HASTE). Radiological examination shortly after birth and postmortem examination confirmed the prenatal diagnosis. In this case, fetal MRI provided excellent spatial and tissue resolution with multiplanar display. It revealed additional diagnostic information and improved imaging conspicuity. MRI complemented sonography for further differentiating clinical and sonographic findings.

Thrombocytopenia-absent radius syndrome: a clinical genetic study

The thrombocytopenia-absent radius (TAR) syndrome is a congenital malformation syndrome characterised by bilateral absence of the radii and a thrombocytopenia. The lower limbs, gastrointestinal, cardiovascular, and other systems may also be involved. Shaw and Oliver in 1959 were the first to describe this condition, but it was Hall et al in 1969 who reported the first major series of patients. Since then most reports have been based on single or small numbers of cases. We report the results of a clinical study looking at the phenotype of 34 patients with TAR syndrome. All cases had a documented thrombocytopenia and bilateral radial aplasia, 47% had lower limb anomalies, 47% cow's milk intolerance, 23% renal anomalies, and 15% cardiac anomalies. Congenital anomalies not previously described in association with TAR syndrome included facial capillary haemangiomata, intracranial vascular malformation, sensorineural hearing loss, and scoliosis. Karyotype analysis, chromosome breakage studies including premature centromeric separation and fluorescence in situ hybridisation studies looking for a deletion of chromosome 22q11 were undertaken. Two abnormal karyotypes were identified.

Excess paternal age in apparently sporadic osteogenesis imperfecta

The objective of this study was to examine whether parental age is associated with the occurrence of apparently sporadic osteogenesis imperfecta (OI). We compared parental age and the joint distribution of maternal and paternal age with expected distributions based on statutory birth records for each year and location of birth. The study included patients with OI based in the United Kingdom. The study was restricted to cases born in England, Wales, and Scotland between 1961 and 1998. Subgroup analysis was by clinical type [Sillence et al., 1979: J Med Genet 16:101-116] and apparent mode of inheritance based on pedigree analysis. Of 730 eligible cases, 357 were apparently sporadic. The mean age of fathers at birth of children with apparently sporadic OI was 0.87 years greater than expected (P = 0.010; 95% confidence interval = 0.21 to 1.54 years). The relative risk was 1.62 for fathers in the highest quintile of paternal age compared with fathers in the lowest quintile. The magnitude of the paternal age excess did not differ significantly between Sillence types (analysis of variance P = 0.534). In sporadic cases, paternal age was 0.51 years greater than expected, given maternal age, year, and location of birth (P = 0.033). In contrast, in familial cases, there was no significant paternal age excess, and paternal age was not significantly different from that expected given maternal age. Increased paternal age is a significant risk factor for sporadic OI. This effect is not accounted for by increasing maternal age. The magnitude of the paternal age excess is small in comparison with that in some other autosomal dominant disorders.

Clinical, genetical, radiological, and anatomopathological survey of 17 patients with lethal osteochondrodysplasias

Seventeen patients thought to have lethal osteochondrodysplasias were evaluated. Diagnosis was established through clinical evaluation, radiological studies and necropsy. Genetic counseling was provided to the affected patient's families. Specific diagnosis was confirmed in 16 cases. Nosologic diagnosis was done through clinical evaluation. However, the most efficient method for verifying the diagnosis was a skeletal radiological study. This fact corroborates the orientation of the International Classification of Osteochondrodysplasias (International Working Group on Constitutional Disease of Bone, 1992) in which a radiological criterion was adopted as the most relevant for classification of osteochondrodysplasias. An anatomopathological study was also done to detect internal anomalies, and was effective in identifying abnormalities in epiphyseal growth plate in a bone fragment study. This method had low specificity, but in two cases it was especially decisive for diagnostic differentiation.

Genetic counselling and prenatal diagnosis of osteogenesis imperfecta caused by paternal mosaicism

In a family with recurrent osteogenesis imperfecta (OI) caused by paternal mosaicism, prenatal diagnosis was made using restriction enzyme analysis for a mutation in COL1A2. Parental mosaicism is important to consider in genetic counselling for OI. Prenatal diagnosis of OI is available currently by means of collagen or gene analyses in the first trimester or by ultrasonography in the second trimester.

The surgical treatment of mandibular fractures in a child with osteogenesis imperfecta

The treatment of multiple mandibular fractures in an 8-year-old child suffering from osteogenesis imperfecta is described. The use of microplates is presented while some specific problems in relation to the disease are discussed.

Lethal syndrome of slender bones, intrauterine fractures, characteristics facial appearance, and cataracts, resembling Hallermann-Streiff syndrome in two sibs

We report on a family in which 1 males infant who died neonatally and 1 female fetus at 29 weeks of gestation had an identical condition resembling Hallermann-Streiff syndrome. The long bones were slender with a few fractures, the skull was underossified, and the face was characteristic of Hallermann-Streiff syndrome. Bilateral cataracts were identified in the male. We regard the condition in this family as a severe form of Hallermann-Streiff syndrome, which appears to have been lethal, at least in the liveborn male. This syndrome is usually sporadic. Recurrence in sibs suggests the possibility of autosomal-recessive inheritance, or of a dominant mutation with parental mosaicism.

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

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.

Defective pro alpha 2(I) collagen synthesis in a recessive mutation in mice: a model of human osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a heritable disorder of connective tissue associated with fractures, osteopenia, and short stature. OI results from mutations affecting the pro alpha 1 or pro alpha 2 gene of type I collagen. We describe a strain of mice with a nonlethal recessively inherited mutation (oim) that results in phenotypic and biochemical features that simulate moderate to severe human OI. The phenotype of homozygous oim mice includes skeletal fractures, limb deformities, generalized osteopenia, and small body size. Their femurs are smaller and demonstrate marked cortical thinning and fewer medullary trabeculae than those of wild-type mice. Breeding studies show the mutation is inherited in most crosses as a single recessive gene on chromosome 6, near the murine Cola-2 gene. Biochemical analysis of skin and bone, as well as isolated dermal fibroblast cultures, demonstrate that alpha 1(I) homotrimeric collagen accumulates in these tissues and is secreted by fibroblasts. Short labeling studies in fibroblasts demonstrate an absence of pro alpha 2(I) collagen chains. Nucleotide sequencing of the cDNA encoding the COOH-propeptide reveals a G deletion at pro alpha 2(I) nucleotide 3983; this results in an alteration of the sequence of the last 48 amino acids. The oim mouse will facilitate the study of type I collagen-related skeletal disease.

Non-invasive prenatal diagnosis of osteogenesis imperfecta

The main mode of non-invasive prenatal diagnosis of osteogenesis imperfecta (OI) is fetal imaging, either by radiography or detailed ultrasonography. Radiography is more of historical interest and ultrasonography is in practice virtually exclusively used for non-invasive second trimester diagnosis of OI. Both methods have also been reported later in pregnancy when diagnosis allows the most appropriate method of delivery to be planned. For example, a caesarean section can be avoided if the fetus is shown to have a form of OI associated with limited survival. Ultrasonography is useful mainly for prenatal diagnosis of the severe forms of OI, especially the perinatally lethal forms (Sillence type II) and to a lesser extent for the severe progressively deforming forms (Sillence types III and III/IV). For the milder varieties of OI (Sillence types I and IV), many cases will be missed by scans. Invasive methods of prenatal diagnosis of OI (principally chorion villous sampling) are used for families with the milder dominant forms of OI and in severe forms of OI in which the actual biochemical or molecular defect in type I collagen is known. Many cases of type II OI and a few of type III have now been reported which were detected by scans before 20 weeks gestation, the earliest being at 15 weeks, for type IIA OI. These include cases not only at genetic risk but also sporadic cases in which scans were done either routinely or for obstetric indications. The ultrasonic abnormalities which are found include reduced echogenicity, multiple fractures, and deformity of the long bones, ribs and skull.(ABSTRACT TRUNCATED AT 250 WORDS)

Approach to skeletal dysplasia

The mystique of skeletal dysplasias is gradually vanishing. Many more physicians are being taught about disorders of disproportionate shortness. The classification system is more practical, and the genetics of these individually uncommon disorders is better established. Metabolic studies will continue to identify the basic defect in these previously hard to get at disorders, allowing for prenatal diagnosis, carrier detection, and treatment. Advances such as bone marrow transplant, bone lengthening, and the encouraging positive effects of growth hormone therapy are exciting new interventions to aid the disproportionately short statured person. The scenario is set for clinicians to become effective participants in the realm of skeletal dysplasias, but it all starts with an accurate diagnosis.

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.

Osteogenesis imperfecta: a clinical study of the first ten years of life

One hundred twenty-seven children with osteogenesis imperfecta (O.I.) were studied during the first 10 years of life. According to Sillence, 40 patients were assigned to type I, 39 to type III, and 48 to type IV O.I. Centiles for height, weight, and the annual number of fractures could be established for the different types of O.I. The development of the skeletal changes could be documented for the different forms of the disease. At birth, the skeletal changes were significantly more severe in type III than in type IV patients. During the first 10 years of life the number of fractures, extent of skeletal deformities, and growth retardation did not differ between types III and IV. Only fracture nonunion, dentinogenesis imperfecta, and congenital cardiac malformations were more frequent in type III than in type IV. Papillary calcifications of the kidney and kidney stones were diagnosed in 4 type III and 2 type IV patients. Hemihypertrophy of the body developed in 2 type I patients. Although types III and IV patients suffered from severe short stature, serum insulin-like growth factor (IGF) I was in the normal range.

Substitution of cysteine for glycine-alpha 1-691 in the pro alpha 1(I) chain of type I procollagen in a proband with lethal osteogenesis imperfecta destabilizes the triple helix at a site C-terminal to the substitution

Skin fibroblasts from a proband with lethal osteogenesis imperfecta synthesized a type I procollagen containing a cysteine residue in the alpha 1(I) helical domain. Assay of thermal stability of the triple helix by proteinase digestion demonstrated a decreased temperature for thermal unfolding of the protein. Of special importance was the observation that assays of thermal stability by proteinase digestion revealed two bands present in a 2:1 ratio of about 140 and 70 kDa; the 140 kDa band was reducible to a 70 kDa band. Further analysis of the fragments demonstrated that the cysteine mutation produced a local unfolding of the triple helix around residue 700 and apparently exposed the arginine residue at position 704 in both the alpha 1(I) and alpha 2(I) chains. Analysis of cDNAs and genomic DNAs demonstrated a single-base mutation that changed the GGT codon for glycine-691 of the alpha 1(I) chain to a TGT codon for cysteine. The mutation was not found in DNA from either of the proband's parents. Since the proteinase assay of helical stability generated a fragment of 700 residues that retained disulphide-bonded cysteine residues at alpha 1-691, the results provide one of the first indications that glycine substitutions in type I procollagen can alter the conformation of the triple helix at a site that is C-terminal to the site of the substitution.

Changes in apatite crystal size in bones of patients with osteogenesis imperfecta

Apatite crystal size in compact bone of children (age less than 11 years) and adolescents (age greater than 12 years) with osteogenesis imperfecta (OI) was analyzed by X-ray diffraction. Eight type I, 4 type II, 11 type III, and 14 type IV OI patients were studied along with 9 controls. The crystal size was most significantly reduced in type II patients, all of whom had died at birth. Crystal size was also diminished in both children and adolescents with types III and IV, whereas with type I OI, crystal size was reduced in children only, returning to normal in adolescence. There was a trend toward increased bone crystal size with age in both OI patients and controls.

Prenatal counselling and diagnosis in progressively deforming osteogenesis imperfecta: a case of autosomal dominant transmission

A 21-year-old woman with progressively deforming or type III osteogenesis imperfecta (OI) presented for prenatal counselling and diagnosis at 10 weeks' gestation. Family history was non-contributory. At 14.8 weeks' gestation, ultrasonographic examination revealed fetal skeletal hypomineralization, easily compressible fetal cranium, and thickened long bones, indicating that the fetus was also affected. Confirmation of the prenatal diagnosis of OI type III was made following a Caesarean section birth of a male infant with multiple skeletal deformities and blue sclerae implying, in this case, autosomal dominant inheritance.

Recurrence risk of a new dominant mutation in children of unaffected parents

Extensions to models originally described by Hartl for predicting the recurrence risk of new dominant mutations are developed in this paper. Additions to the models are (1) possible somatic mosaicism in a parent in some families, (2) the possibility that the parental origin of the mutation may or may not be known, and (3) mutation rates which change as a function of sex and/or time. The models indicate that recurrence risks are most critically affected by (a) the amount of somatic mosaicism which can be tolerated in the parent without manifesting disease and (b) knowledge of the parental origin of the mutation. In addition, there is a moderate effect on recurrence risks if mutation rates increase in the father as a function of time. Recurrence risks are at least as large as the risk of trisomy 21 in a child of a mother of age 35 years or older, probably much higher (5%-10%) when the mutation is known to be of maternal origin or if substantial somatic mosaicism in the parent is compatible with a normal phenotype. The recurrence risk of a new mutation is high because of a very high ascertainment bias of families with substantial germ-line mosaicism.

Prenatal diagnosis of osteogenesis imperfecta by identification of the concordant collagen 1 allele

Dominantly inherited osteogenesis imperfecta is consistently linked to the two loci encoding the alpha 1 and alpha 2 subunits of collagen 1, the predominant bone collagen. We have performed several prenatal diagnoses based on identification of the segregating allele at the concordant locus in chorionic villus samples both in families where the linkage can be independently shown and in those where it cannot. Especially in the latter category, calculation of the final risk must incorporate an estimate of genetic heterogeneity within the OI population to give a prior probability of linkage. This figure can then be modified for each family by additional information from concordant meioses.

Prenatal diagnosis of severe osteogenesis imperfecta

The ultrasound findings in a series of 15 prenatally diagnosed cases of severe osteogenesis imperfecta types IIA, IIB, IIC, and III are described, eleven being detected on routine scans of women with no relevant history. As most cases of osteogenesis imperfecta type IIA are dominant sporadic mutations, the importance of prenatal diagnosis during routine scanning at a local level is emphasized. In addition to characteristic broad, shortened and fractured long bones, striking features of the chest and head are highlighted which may be encountered during a routine scan, prompting further assessment.

The clinical features of osteogenesis imperfecta resulting from a non-functional carboxy terminal pro alpha 1(I) propeptide of type I procollagen and a severe deficiency of normal type I collagen in tissues

The features of a baby with lethal perinatal osteogenesis imperfecta (OI II), owing to a frameshift mutation that resulted in the production of a truncated and functionless carboxy terminal propeptide of the pro alpha 1(I) chain of type I procollagen, were studied. The baby (OI26) was heterozygous for an insertion of a single uridine nucleotide after base pair 4088 of the prepro alpha 1(I) mRNA of type I procollagen. Only normal type I collagen was incorporated into the extracellular matrix of bone and dermis resulting in a type I collagen content of about 20% of control tissues. The baby was born at 35 weeks' gestation and died shortly afterwards. He was small and had the radiographical features most like those of OI IIB. The skeleton was poorly ossified. The ribs were discontinuously beaded and the femora were broad with multiple healed fractures of the diaphyses and metaphyses. Other long bones had broad metaphyses with overmodelled diaphyses. The calvarium contained many hundreds of wormian bones. Histological examination showed grossly deficient endochondral and intramembranous ossification. The bone was of a woven type without evidence of lamellar bone or Haversian systems and the osteoblasts did not mature into osteocytes. The cortex of the femur contained Haversian canals but they were surrounded by loose collagen fibres and a mosaic pattern of woven bone and islands of cartilage. We propose that OI IIB can be sub-classified into two groups, one with helical mutations and both normal and mutant type I collagen in the tissues, and the other with carboxy terminal propeptide mutations and a severe type I collagen deficiency, but without mutant collagen in the tissues.

Studies of type I collagen in osteogenesis imperfecta

We used the results of skin fibroblast type I collagen analysis to improve the accuracy of diagnosis and genetic counseling for six patients with osteogenesis imperfecta. The fibroblasts of two patients with osteogenesis imperfecta type I synthesized a reduced quantity of qualitatively normal type I procollagen. Another patient with osteogenesis imperfecta type I had two populations of type I collagen molecules, one apparently normal and the other with a substitution of cysteine for glycine in the triple helical domain. Three sporadic cases with osteogenesis imperfecta types II, III, and IV were studied; in each proband a normal and an abnormal overmodified population of type I collagen molecules were demonstrated, and parental collagens were normal in the two available patients. These results indicated that the probands were heterozygous for new dominant mutations and assisted our genetic counseling, especially in osteogenesis imperfecta types II and III, which were formerly believed to be inherited in an autosomal recessive fashion. The results could not exclude parental germ line mosaicism for a new dominant mutation, which has resulted in recurrence in siblings of some patients with osteogenesis imperfecta, so prenatal diagnosis was therefore offered for future pregnancies. Analysis of chorionic villus cell collagen may facilitate antenatal diagnosis in selected cases, and the study of a larger number of patients may allow correlation of the biochemical defects with the natural history and prognosis.

Segregation analysis of dominant osteogenesis imperfecta in Italy

We have performed linkage analysis in seven Italian families, in which mild osteogenesis imperfecta (OI) segregated as a dominant trait, by means of six DNA restriction fragment length polymorphisms (RFLPs) of type I collagen genes. OI type I was linked to the alpha 1(I) gene (COL1A1) in two families, and to the alpha 2(I) gene (COL1A2) in one family. OI type IV segregated with COL1A2 in two families. In two OI type I families, the molecular genetic data were insufficient for exclusion of one gene. Four DNA polymorphisms were particularly informative for cosegregation analysis of OI in Italian kindreds.

Analysis of cultured chorionic villi in a case of osteogenesis imperfecta type II: implications for prenatal diagnosis

We examined collagens produced by cultured cells from skin, chorionic villi, and placental membranes of a 32 week fetus with osteogenesis imperfecta (OI) type II. We observed that skin fibroblasts synthesized two populations of pro alpha 1(I) chains of type I procollagen; one population was normal, while the other population had excessive post-translational modification. The thermal stability of helices containing the overmodified chains was reduced 1-2 degrees C. Most significantly, the cells cultured from chorionic villi produced type I collagen chains with the same electrophoretic abnormalities as the skin collagen. This suggests that chorionic villus sampling (CVS) is a means of prenatal diagnosis for families with a previous type II or type IV OI infant.

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

The features of three babies with lethal perinatal osteogenesis imperfecta resulting from the substitution of glycine by arginine in the pro alpha 1(I) chain of type I procollagen were studied. The babies were heterozygous for this substitution at residue 391 in case 1 (0I24), 667 in case 2 (0I51), and 976 in case 3 (0I30). They were all small, term babies who died soon after birth. The ribs were broad and continuously beaded in 0I24, discontinuously beaded in 0I51, and slender with few fractures in 0I30. The overall radiographical classifications were type IIA in 0I24, IIA/IIB in 0I51, and IIB in 0I30. Histological examination confirmed that the long bones were misshapen and porotic. The calcified cartilage trabeculae were covered with an abnormally thin layer of osteoid and the bone trabeculae were thin and basophilic. There was no evidence of lamellar bone or Haversian systems. The osteoblasts remained relatively large and closely spaced. These babies shared many phenotypic features, but differences in the radiographical appearance of the ribs and long bones suggested that there was a gradient of bone modelling capacity from the slender and overmodelled bones in 0I30 to the absence of modelling in 0I24.

Radiological "metamorphosis" in a patient with severe congenital osteogenesis imperfecta

Congenital osteogenesis imperfecta (OI) was diagnosed by ultrasound in a 31-week-old fetus, and the diagnosis confirmed after delivery by caesarean section at week 36. The baby survived the neonatal period, but failed to thrive, had recurrent respiratory infections and ultimately died at 8 months. Cultured fibroblasts synthesized both normal type I collagen and unstable type I collagen harbouring a structural defect in the alpha 1 (I) cyanogen bromide-derived peptide number 8 (CB8) region of the molecule, indicating a heterozygous dominant mutation. At birth, the radiological picture was that of the "thin bone"-type of congenital OI (OI type IIB/III in the Sillence classification); at the age of 12 weeks ribs and long bones had undergone a marked expansion giving a very different picture, that of the "thick bone"-type congenital OI (OI type IIA). The mechanism responsible for this change in bone structure is not known, but fractures and callus formation are unlikely to be the only factors. Caution is needed in the interpretation of radiographs of newborns with OI for prognostic or genetic purposes.

Phenotypical features of an unique Irish family with severe autosomal recessive osteogenesis imperfecta

Severe Sillence type II/III Osteogenesis imperfecta (OI) is a lethal or severely crippling disease with either autosomal dominant or recessively inherited type I collagen mutations. Here we describe the detailed clinical features of a thin-ribbed OI variant with deformed limbs. The three consecutively affected children showed no genetic linkage with either of the two type I collagen genes, which implies that a novel mechanism causes this clinical phenotype. It can be prevented using ultrasound to diagnose affected foetuses.

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

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

Homozygous osteogenesis imperfecta unlinked to collagen I genes

In a consanguineous pedigree in which a severe type of osteogenesis imperfecta was segregating as an autosomal recessive trait, analysis of genetic markers for both collagen I structural loci COL1A1 and COL1A2 showed that the phenotype was unlinked to either locus.

Osteogenesis imperfecta

Major advances have occurred in the classification of OI and in the definition of underlying molecular defects. A clearer understanding of the pathogenesis of OI and of the relationships between the phenotypes and genotypes should emerge. The study of induced mutations in selected regions of the collagen genes with expression in cultured cells or transgenic mice should hasten this process. These advances will also provide a basis for studies into the large number of other genetically determined connective tissue disorders that are grouped together as the skeletal dysplasias. The results of recent studies in OI are providing a unique insight into many aspects of collagen and connective tissue biochemistry, physiology and pathology.

Perinatal lethal osteogenesis imperfecta: radiologic and pathologic evaluation of seven prenatally diagnosed cases

The radiologic and pathologic characteristics of 7 cases of lethal osteogenesis imperfecta (OI), diagnosed prenatally by ultrasound in the 15th to 34th week, are described. They include four variants of the Sillence classification: types IIA, IIB, IIC, and type III. The radiologic criteria that differentiate these types of OI are described. The histopathology of the bones differed only slightly in types IIA, IIB, and III; OI type IIC, however, differed markedly from the other types.