Osteogenesis imperfecta: mosaicism and refinement of the genotype-phenotype map in OI type III. Mutations in brief no. 242. Online

Non-lethal OI III (OMIM 259420) is caused by structural aberrations of collagen I. We report four novel glycine substitutions, one in the a1 (I) chain of collagen I (G688S) and three in the a2 (I) chain (G241D, G247C, G883V). In each of two families (G241D and G883V), we found parental mosaicism for the substitution explaining recurrence and intrafamilial variability of OI. The G247C and the G883V are the most N-terminally and C-terminally, respectively, placed cysteine and valine substitutions reported. The new substitutions add important information to the genotype-phenotype map and in particular the importance of a-chain stoichiometry is underlined. Data regarding the G688S substitution may suggest a different effect of the two a-chains in the development of dentinogenesis imperfecta (DI).

(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.

Metabolism of some radiolabeled essential fatty acids in isolated rat hepatocytes is affected by dietary ethanol

The metabolism of the essential fatty acids [1-14C]20:4n-6, [1-14C]20:5n-3 and [1-14C]22:6n-3 was studied in rat hepatocytes fed ethanol in two different diets. Using a diet with a low lipid content ethanol (1) reduced the elongation of eicosapentaenoic acid, (2) reduced the esterification of docosahexaenoic acid (DHA) in phospholipids (PL), (3) increased the oxidation of DHA, (4) increased the ratio of esterification of DHA in phosphatidylethanolamine (PE) compared to phosphatidylcholine (PC) (PE/PC ratio), (5) altered the formation of PL molecular species, and (6) induced a decrease in the endogenous content of the hepatocytes of arachidonic acid and linoleic acid and an increase in oleic acid, 20:3n-9 and DHA. Using a high lipid diet, only the above-mentioned effect (4) was induced by ethanol, not the effects (1)-(3) and (5)-(6).

[Child abuse and osteogenesis imperfecta. How do we distinguish?]

Osteogenesis imperfecta is a hereditary connective tissue disorder. Typical manifestations are fragile bones with multiple bone fractures and bone deformities. A history of minimal or no trauma and recurrent fractures is a feature of OI, but is also typical of non-accidental injury (NAI). OI and NAI are relevant differential diagnoses when a child presents with unexplained fractures. The differential diagnostic problems are reviewed, all of which are important for the child both in terms of treatment and for prognosis, socially and medicolegally. We conclude that comprehensive clinical evaluation is adequate for differential diagnosis and that both OI and NAI can be diagnosed by positive anamnestic and objective signs. Mild OI IV without other signs than fracture(s) is very rare and the new entity temporary brittle bone disease is hypothetical; the diagnosis of these two clinical pictures is unacceptable in small children. Routine analysis of collagens should not be performed.

Bone mineral content and collagen defects in osteogenesis imperfecta

Whole-body and spine dual-energy X-ray absorptiometry was done in 63 patients with osteogenesis imperfecta aged 5 to 63 y, and the results were compared with OI types and collagen defects. Bone mineral content (BMC)-for-age, bone area (BA)-for-age, bone mineral density (BMD)-for-age, and BMC-for-BA were reduced, especially in patients with OI III/IV and/or in those with a qualitative collagen defect. BA-for-height was normal. Some patients with OI I and/or a quantitative collagen defect had BMD at or above -2 z-scores. We conclude (i) that both BMC and BMD differ significantly between OI types and collagen defects, (ii) that reduced BMC-for-age in OI patients is due mainly to reduced height ("short bones") and reduced BMC-for-BA ("light bones"), whereas BA-for-height ("bone width") is normal, (iii) that most OI patients have lower than average BMC, but in some mildly affected patients brittleness may exist with only small reductions in BMC.

Co-existence of osteogenesis imperfecta and hyperparathyroidism

Osteogenesis imperfecta (OI) and hyperparathyroidism (HTP) are disorders affecting the skeletal system and calcium metabolism not evidently related to one another. We report a case in which both OI and HPT were present. Our female patient presented with hypercalcaemia (S-Ca2+ 1.59 mmol/l; normal range 1.15-1.30) and 4-gland parathyroid hyperplasia at 30 years of age. Since her first year she had fractures, blue sclera, hypermobile joints, short stature (height 1.51 m, weight 49.5 kg) but normal hearing, and dentiogenesis imperfecta (tooth disease caused by defective formation of dentin) was absent. This patient bears many similarities with the 5 patients reported previously but it is the only patient, to our knowledge, with OI and early onset of HPT (30 year old female). We have found the OI to be type 1. A minor improvement of the rate of bone turnover 10 months after parathyroidectomy indicates the HPT to be primary and suggests the OI type 1 and pHPT to be two different calcium metabolic diseases incidentally occurring in the same patient.

Anthropometry of patients with osteogenesis imperfecta

Standing height, sitting height, armspan, subischial leg length, head circumference, and growth hormone-insulin-like growth factor I (IGF-I) axis were determined in 86 patients with osteogenesis imperfecta. The aim of this study was to determine standing height and body proportions and their variability among osteogenesis imperfecta types and collagen defects. Mean standing height was reduced in all groups of patients, to the greatest extent and variability in osteogenesis imperfecta type III/IV and in those with qualitative collagen defects. The mean standing height of patients with osteogenesis imperfecta was lower than that of their unaffected first degree family members. Truncal height of patients with osteogenesis imperfecta was reduced; head size was increased, and this was more pronounced in patients with osteogenesis imperfecta type III/IV and qualitative collagen defects than in patients with osteogenesis imperfecta type I and quantitative collagen defects. Mean concentrations of IGF-I and IGF binding protein 3 (IGFBP-3) were low, but most values were within age specific reference values. The reduction of standing height appears to correlate with osteogenesis imperfecta type and the type of collagen defect. A relatively short trunk is typical and head circumference and body length are disproportionate.

[Shaken baby syndrome]

Shaken baby syndrome is a serious form of physical child abuse, which is frequently overlooked. It should be suspected in all children younger than one year of age, who present with drowsiness, coma, seizures or apnoea. A combination of subdural haematomas and retinal haemorrhages with minimal or no trauma and no coagulopathy is almost pathognomonic of the syndrome. The findings are caused by shaking with or without impact. Physical signs of violence are often absent and the syndrome may easily be mistaken for serious infection or seizure disorder. Many cases are fatal or lead to severe disability including blindness, cerebral palsy, mental retardation or epilepsy in about 60% of the children. There are many unresolved problems regarding diagnosis, pathophysiology, treatment, prognosis, prophylaxis and legal actions. We discuss these problems and in addition present eleven children with shaken baby syndrome.

Collagen-derived markers of bone metabolism in osteogenesis imperfecta

Markers of bone formation [C-terminal and N-terminal propeptides of procollagen I (PICP, PINP), osteocalcin and alkaline phosphatase] and bone resorption [C-terminal cross-linked telopeptide of collagen I (ICTP) and hydroxypyridinium cross-links, pyridinoline (Pyr) and deoxypyridinoline (Dpyr)] were measured in 78 osteogenesis imperfecta (OI) patients to investigate bone metabolism in vivo and relate marker concentrations to phenotype and in vitro collagen I defects, as shown by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). PICP and PINP were generally low, and the serum levels were lower in all children and adults with mild OI and a quantitative collagen defect than in patients with severe OI and a qualitative collagen I defect. ICTP, Pyr and Dpyr were generally normal or reduced, but elevated in severely affected adults with a qualitative collagen I defect. The in vivo findings correlated with in vitro results of collagen I SDS-PAGE. Bone turnover is reduced in OI children and mildly affected OI adults, whereas bone resorption is elevated in severely affected adults. These findings may prove helpful for diagnosis and decision-making regarding therapy in OI.

Atraumatic loss of a kidney in a patient with alpha1-antitrypsin deficiency

Alpha1-Antitrypsin (alpha1AT) deficiency is characterized by a high risk of developing pulmonary emphysema and liver disease. Arteriopathy may be associated with alpha1AT deficiency. We present a patient with only one kidney and alpha1AT deficiency, but only mild pulmonary symptoms and no signs of liver disease, and atraumatic loss of the remaining kidney. Histological examination of the renal artery showed desposits of a mucoid ground substance in the arterial media, as has been demonstrated in other patients with alpha1AT deficiency. After dialysis treatment for 15 months, the patient underwent an uneventful kidney transplantation. The case draws attention to the awareness of complications of alpha1AT deficiency even in cases with only mild pulmonary manifestations of the disorder. To our knowledge, atraumatic loss of a kidney in a patient with alpha1AT deficiency has not previously been reported.

Dental manifestations of osteogenesis imperfecta and abnormalities of collagen I metabolism

The in vitro protein-chemical features and the molecular background of osteogenesis imperfecta (OI), a heritable disorder of collagen I metabolism, have been elucidated in recent years. The aim of our study was to find the prevalence of dentinogenesis imperfecta (DI) and other dental anomalies in 88 patients with OI, to compare clinical with radiologic abnormalities, and to correlate these clinical/radiologic findings with the results of gel electrophoresis and molecular studies of collagen I. Twenty-eight percent of OI patients had DI. Most patients with DI had radiologic abnormalities, but some patients had radiologic signs compatible with DI, but no clinical signs of DI. OI type I patients with DI were more severely affected by OI than those without DI. In OI type III and IV, in contrast, there was no difference in overall severity between patients with and without DI. DI was not associated with any particular molecular aberration in any OI type. If defining DI from the presence of both clinical and radiologic signs, collagen I produced by cultured fibroblasts was qualitatively abnormal from all OI patients with DI. Some OI patients had dental abnormalities not resembling DI. A qualitative collagen abnormality could not be found in any of these patients. Denticles, i.e., calcifications within the pulpal cavity, were found more frequently in OI patients than in control subjects.

Osteogenesis imperfecta: clinical, cephalometric, and biochemical investigations of OI types I, III, and IV

The aim of the study was to analyze craniofacial development in 54 patients with osteogenesis imperfecta (OI), who were classified into OI types I, III, and IV according to clinical criteria, and to relate the findings to the abnormalities in collagen I production. In 33 patients, analysis of radioactively labelled procollagen was performed. Cephalometric radiographs, facial photographs, and CT-scans (a single case) were analyzed and mean facial diagrams for lateral and frontal films were produced based on registration of 221 reference points. Radiographs of 102 male and 51 female Danish students served as control material. In OI type I, size of the skull and jaws was generally slightly reduced, but morphology was within normal limits. In OI type IV and especially type III more severe abnormalities were found; the cranial base was flattened, the maxilla posteriorly inclined, and nearly all size-measurements were reduced. In OI type III the sagittal jaw relations were reduced and a mandibular overjet recorded. Three OI type I patients, whose fibroblasts produced structurally abnormal collagen I, had the stature and several features in the craniofacial region, which corresponded to those recorded for the OI type IV group. Also, in three OI type IV patients whose fibroblasts produced a reduced amount of normal collagen I, craniofacial morphology showed several features resembling type I patients. We conclude that structural abnormalities of collagen I generally give rise to more severe alterations of the craniofacial features than a quantitative defect of collagen I. OI type I patients are only slightly affected in their craniofacial region, while patients with OI type IV and especially type III are moderately to severely affected. The combined cephalometric and biochemical findings suggest that future classification of patients with osteogenesis imperfecta should be based on biochemical/molecular and radiological analyses in combination with clinical criteria rather than on clinical features alone.

Parental mosaicism and autosomal dominant mutations causing structural abnormalities of collagen I are frequent in families with osteogenesis imperfecta type III/IV

Protein-chemical and molecular studies were conducted on all osteogenesis imperfecta (OI) type III/IV patients referred to our hospital during the last 15 y. Of a total of 16 OI type III/IV patients studied, 15 patients were heterozygous for a mutation in one of the two genes coding for collagen I, COL1A1 or COL1A2. Cultured fibroblasts from these 15 patients produced both normal and abnormal collagen I molecules, pointing to a dominant-negative effect of the mutation. Nine mutations had not been described previously. Parental mosaicism was demonstrated in three families. In the 16th child the causative mutation was not found. In conclusion, OI type III/IV in most patients of Western European ancestry is caused by dominant mutations in the genes for collagen I, and recurrence of OI is caused in most cases by parental gonadal mosaicism.

Variable clinical expression in a family with OI type IV due to deletion of three base pairs in COL1A1

We have studied a family with autosomal dominant osteogenesis imperfecta (OI) type IV. Electrophoresis of collagen produced by cultured fibroblasts revealed a slower migrating population of collagen I. Cyanogen bromide peptide mapping localised the structural defect to the area of the alpha 1(1)CB3 peptide. Subsequent sequencing revealed a deletion of nucleotides 1964-1966 in exon 27 of COL1A1. By means of restriction enzyme analysis, the deletion could be detected in all affected family members. This in-frame deletion resulted in the removal of alanine-438 and Glu437Asp substitution in the pro alpha 1(I) collagen chain. Clinical variation was considerable among affected family members. The most consistent clinical features were reduced height and extraosseous manifestations of OI.

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.

Osteogenesis imperfecta and malignant hyperthermia. Is there a relationship?

We describe a patient with osteogenesis imperfecta who developed tachycardia, metabolic and respiratory acidosis (pH 7.14, PCO2 8.4 kPa, BE -8.5 mmol.l-1) and hyperthermia up to 40 degrees C during anaesthesia with barbiturates, fentanyl, pancuronium, and nitrous oxide. Malignant hyperthermia was suspected and the patient treated accordingly. Two years later the in-vitro contracture test for malignant hyperthermia was completely normal. We conclude that hypermetabolism in patients with osteogenesis imperfecta is due to unknown mechanisms other than malignant hyperthermia.

Deletion of a Gly-Pro-Pro repeat in the pro alpha2(I) chain of procollagen I in a family with dominant osteogenesis imperfecta type IV

We have investigated one member of a family with dominant osteogenesis imperfecta type IV through three generations. In protein-chemical studies of cultured fibroblasts derived from the proband, collagen I was overmodified, with normal processing of procollagen I, normal thermal stability, and a cyanogen bromide peptide map that suggested a C-terminal location of the structural abnormality in the collagen triple helix. Sequencing of the gene encoding the alpha2(I) chain of collagen I (COL1A2) indicated a nine base-pair deletion of nucleotides 3418-3426. When a polymerase chain reaction product containing the nucleotides in question was electrophoresed in a 12% polyacrylamide gel, two bands with a difference in size of nine base pairs could be shown. Sequencing of the molecular weight band confirmed the deletion of the nine base pairs involving codons 1003-1006 of COL1A2. The deletion introduced a SfiI restriction site that was used for confirmation of the deletion in genomic DNA from the proband. The deletion resulted in the removal of three amino acids (Gly-Pro-Pro), but this did not disrupt the Gly-X-Y sequence of the collagen triple helix, as is often the case in the more common glycine substitutions. We discuss the ways in which this deletion could result in osteogenesis imperfecta.

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

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

Phospholipid molecular species with eicosapentaenoic acid (20:5(n-3)) are less stable than species with arachidonic acid (20:4(n-6)) in isolated rat liver cells

We have studied the incorporation of [1-14C]20:5(n-3) and [1-14C]20:4(n-6) in the molecular species of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) in isolated rat liver cells. These two fatty acids are present in very different amounts in endogenous phospholipids, with 20:4 as one of the major fatty acids and 20:5 as a minor and very diet-dependent constituent. The main phospholipid species formed from 20:4(n-6) were 16:0-20:4 and 18:0-20:4. When formed, they were stable during incubations of liver cells for 2-3 h. The main species formed from 20:5(n-3) were 16:0-20:5 and 18:0-20:5. After formation, 16:0-20:5 and to a lesser degree 18:0-20:5 were, however, degraded during 1-2 h of incubation, especially in PC. Only small amounts of 22:5(n-3) and very little 22:6(n-3) were formed from 20:5(n-3) and small amounts of 22:4(n-6) were produced from 20:4(n-6). With 20:4(n-6) and 20:5(n-3) as substrates, 20:4-20:4 and 20:5-20:5 molecular species respectively were initially formed in PC and PE but both species were rapidly degraded.

Assignment of congenital cataract Volkmann type (CCV) to chromosome 1p36

Congenital cataract, type Volkmann (McKusick no 115665, gene symbol CCV) is an autosomal dominant eye disease. The disease is characterized by a progressive, central and zonular cataract, with opacities both in the embryonic, fetal and juvenile nucleus and around the anterior and posterior Y-suture. We examined blood samples from 91 members of a Danish pedigree comprising 426 members, by using highly informative short tandem repeat polymorphisms and found the closest linkage of the disease gene (CCV) to a (CA)n dinucleotide repeat polymorphism at locus D1S243 (Zmax = 14.04 at theta M = 0.025 theta F = 0.000), at a penetrance of 0.90. Using two additional chromosome 1 markers, we were able to map the CCV gene in the sequence 1pter-(CCV, D1S243)-D1S468-D1S214. The (enolase 1) gene has been mapped to this area; however, a mutation described in this gene did not give eye disease.

[Neurofibromatosis type 1 in children]

We describe the clinical findings in 75 children with neurofibromatosis type 1 (NF-1, von Recklinghausen disease) diagnosed by the National Institute of Health criteria. The children were on average three years old at the time of their diagnosis. In 12 children complications of NF-1 were noted before diagnosis of their underlying condition, and half of the children had a serious complication, including intracranial tumour, optic glioma, scoliosis, pseudarthrosis tibiae, or mental handicap. Most complications of NF-1 occur before the age of ten. Therefore, and because of its severity and multifaceted presentation, children with NF-1 might benefit from follow-up in a multidisciplinary, specialized clinic.

Osteogenesis imperfecta in Holstein-Friesian calves

Eight calves with osteogenesis imperfecta were born in a Danish Holstein-Friesian herd during a two-year period. In total 92 calves were born (84 normal), and all were sired by a clinically normal Holstein-Friesian bull. The defect was probably due to a de novo dominant mutation present as a gonadal mosaicism in the bull. Affected calves were characterised by multiple fractures, congenital bone deformations, general joint laxity, dentinogenesis imperfecta, and light blue sclerae. The skin seemed normal. Electron microscopical studies revealed slightly decreased average diameter of cutaneous collagen fibrils, while the diameter of collagen fibrils in tendons and ligaments was severely reduced. Abnormalities of collagen type I from skin and compact bone were not detected by biochemical analyses.