Osteogenesis Imperfecta, Type Ii

A number sign (#) is used with this entry because osteogenesis imperfecta type II (OI2) is caused by heterozygous mutation in the COL1A1 gene (120150) or the COL1A2 gene (120160).

Description

Osteogenesis imperfecta type II constitutes a disorder characterized by bone fragility, with many perinatal fractures, severe bowing of long bones, undermineralization, and death in the perinatal period due to respiratory insufficiency (Sillence et al., 1979; Barnes et al., 2006).

Also see osteogenesis imperfecta type VII (610682), an autosomal recessive form of lethal OI caused by mutation in the CRTAP gene (605497).

Clinical Features

Morphologically there appear to be 2 forms of OI congenita, a thin-boned and a broad-boned type. The latter is well illustrated by the male and female sibs reported by Remigio and Grinvalsky (1970). The diagnosis is in question, however, because one had dislocated lenses, aortic coarctation, and basophilic and mucoid changes in the connective tissue of the heart valves and aorta, while the other had less pronounced changes of the same nature in the aorta. Parental consanguinity was denied. Shapiro et al. (1982) suggested that the sibs reported by Remigio and Grinvalsky (1970) may have had another variant because of conspicuous extraskeletal features. The broad-bone type is also illustrated in Figure 8-3 by McKusick (1972) and the thin-bone type in Figure 8-5. The 'broad-bone' form of osteogenesis imperfecta and type IA achondrogenesis (200600) bear similarities. In the latter condition the ribs are thin and prone to fractures but the long bones of the limbs are severely shortened and bowed.

In a study in Australia, Sillence et al. (1979) encountered a seemingly recessively inherited lethal perinatal OI with radiologically crumpled femora and beaded ribs--the 'broad-bone' type.

By scanning electron microscopy, Levin et al. (1982) found no abnormality of the teeth in a case of OI congenita with death from pneumonia at age 10 months. Since abnormalities have been described in reported cases, these results may reflect heterogeneity in OI congenita. Levin et al. (1982) suggested that the case best fits OI type III of Sillence et al. (1979). They agreed with Sillence et al. (1979) that the term 'congenita' has limited usefulness since it merely indicates that fractures were present at birth--a feature that may occur in type I (166200), II, or III (259420).

Elejalde and Mercedes de Elejalde (1983) observed a family in which the fourth child had OIC and died a few hours after birth, and OIC was diagnosed at 17 weeks' gestation in the fifth pregnancy by ultrasonography. Diagnosis was based on low echogenic properties of all bones, abnormally shaped skull and rib cage, distally thinned ribs, and short, deformed long bones with wide metaphyses and thin diaphyses.

Radiographically the disorder reported by Buyse and Bull (1978) in 3 sibs (see 259410) was indistinguishable from Sillence's group A (see HISTORY), and chondroosseous histopathology was also identical; however, low birth weight, microcephaly, and cataracts were also present. The patients may, of course, have been homozygous for 2 separate but linked mutations or for a small chromosomal aberration.

Byers et al. (2006) published practice guidelines for the genetic evaluation of suspected OI.

Inheritance

Autosomal recessive inheritance of osteogenesis imperfecta had been proposed, but in most well-studied cases the diagnosis was found to be in error or a parent was mosaic for a heterozygous mutation in a collagen I gene. Smars et al. (1961), McKusick (1962), Awwaad and Reda (1960), and others described families with 2 or more sibs thought to have OIC but with ostensibly normal parents. Such is probably to be expected of a dominant trait with wide expressivity and does not require a recessive explanation. Hanhart (1951), however, described an inbred kindred with affected members in 5 sibships. Here germinal mosaicism is not a satisfactory explanation. In all such studies, care must be taken not to confuse hypophosphatasia (e.g., 241500) for osteogenesis imperfecta.

Kaplan and Baldino (1953) described a kindred derived from an inbred, Arabic-speaking, polygamous sect called the Mozabites, living in southern Algeria. Nine cases occurred in 4 sibships among the descendants. Kaplan et al. (1958) and Laplane et al. (1959), in a follow-up of the same kindred, described 19 cases. Parental consanguinity was noted by several authors, including Freund and Lehmacher (1954) and Rohwedder (1953); the latter described a case in which the parents were brother and sister.

Meyer (1955) reported 'atypical osteogenesis imperfecta' in several of the 11 offspring of a mentally defective woman by her own father. Manifestations were spontaneous fractures, generalized osteoporosis, and Wormian bones in the area of the lambdoidal sutures. Blue sclerae and deafness were not present.

Young and Harper (1980) concluded that autosomal recessive inheritance is unlikely to apply to most cases of OIC, including the 'thick boned' variety. They had information on 79 cases with multiple fractures present at birth. In only 3 families was more than 1 affected child born to normal parents and only 1 of the 79 families had consanguineous parents. The empiric recurrence risk figure is probably closer to 3% than 25%.

Thompson et al. (1987) thought that recessive inheritance was likely for Sillence subclassification group B of type II OI (see HISTORY) because of the frequency of parental consanguinity and multiple affected sibs. On the other hand, the evidence for dominant inheritance was strong in the case of group A (Young et al., 1987). Young et al. (1987) ascertained 30 cases of radiologically proven type II osteogenesis imperfecta of the Sillence group A subclassification. All were isolated cases, with 19 unaffected foreborn and 19 unaffected afterborn sibs. Two sets of parents, both Asian, were consanguineous. Paternal age effect was observed.

Byers et al. (1988) collected family data and radiographs for 71 probands with the perinatal lethal form of OI and analyzed the collagens synthesized by dermal fibroblasts cultured from 43 of the probands, 19 parental pairs, and single parents of each of 4 additional probands. In 65 families for which there were complete data, there was recurrence of OI II in 5 families such that 6 (8.6%) of 70 sibs were affected. In 2 families with recurrence, the radiographic phenotype was milder than that for the remainder; and 1 of those families was consanguineous, suggesting autosomal recessive inheritance. In the remaining 3 families there was no evidence of consanguinity, but in one of them gonadal mosaicism in the mother was suspected because 3 affected children were born of 2 different fathers. Biochemical studies indicated that the OI II phenotype is basically heterogeneous, that most cases result from new dominant mutations in the genes encoding type I collagen, and that some recurrences can be accounted for by gonadal mosaicism in one of the parents.

Daw et al. (1990) reported a remarkable family in which lethal OI of the thin-boned type occurred in 6 sibs with normal, unrelated parents. Daw et al. (1990) suggested that this was an instance of gonadal mosaicism for a dominant mutation.

Bonadio et al. (1990) described an infant apparently homozygous for a point mutation in the COL1A1 gene (120150.0039), a G-to-A transition at the +5 position within the spliced donor site of intron 14. In both parents, who were normal and unrelated, Bonadio et al. (1990) found absence of the mutation in all cells studied. They found evidence for uniparental disomy for chromosome 17 (Bonadio, 1990), however. This mutation, combined with uniparental disomy, may be responsible for the functionally homozygous state of the mutation in this infant. Bonadio (1992) had not had an opportunity to study the possibility further.

What one might call pseudorecessive inheritance has been observed in lethal OI congenita, which, as noted earlier, is almost always a new autosomal dominant mutation. Cohn et al. (1990) and Edwards et al. (1992) observed 2 offspring with lethal OI and demonstrated mosaicism in 1 parent. In the first case, the mutation was in the COL1A1 gene (120150.0016) and the mother had the mosaicism and was mildly affected. In the second case, the mutation was in the COL1A2 gene (120160.0019) and it was the father who was mosaic. His only manifestations of OI were shorter stature than his unaffected male relatives and mild dentinogenesis imperfecta.

In an investigation of paternal age in 106 cases of nonfamilial osteogenesis imperfecta compared with matched controls, Orioli et al. (1995) found only slightly elevated mean paternal age in a South American collaboration and no increase in an Italian collaboration. This was in contrast to the findings in 78 achondroplasia (100800) patients, in which a mean paternal age was greatly increased, and in 64 cases of thanatophoric dysplasia (see 187600), in which it was less strikingly elevated.

Cole and Dalgleish (1995) estimated the recurrence rate at 7%, owing to germline mosaicism in 1 parent.

From molecular genetic studies of 39 cases from a series totaling 65 (40M; 25F), Tsipouras et al. (1985) concluded that most cases of OI II are the result of new dominant mutation. They observed no parental age effect.

Horwitz et al. (1985) presented evidence that maternal gonadal mosaicism was responsible for 3 infants with OI II with 2 different fathers.

Biochemical Features

In a deceased 4-day-old infant with OIC, Trelstad et al. (1977) found that the collagen of bone had twice normal content of hydroxylysine and cartilage collagen, a 55% increase. The levels of covalently bound glucose and galactose were proportionately increased. Francis et al. (1981) found increased ratio of alpha-1(I) to alpha-2(I) and of alpha-1(III) to alpha-2(I) in both clinically normal parents of a child with severe OI.

Barsh and Byers (1981) restudied the cultured cells from a multiply studied patient from the Johns Hopkins Hospital with perinatal lethal osteogenesis imperfecta. This case was the basis of the report by Penttinen et al. (1975) which provided evidence that one form of OIC has a defect in synthesis of type I collagen. The clinical findings in this case were reported by Heller et al. (1975) and the cultured fibroblasts were also studied by Delvin et al. (1979), Steinmann et al. (1979), and Turakainen et al. (1980). Barsh and Byers (1981) found that the cells produced 2 distinct pro-alpha-1 chains of type I collagen, which were synthesized at the same rate. Analysis of cyanogen bromide peptides indicated that the 2 chains differed in their primary structures. Thus, structural abnormalities of type I procollagen prevented this molecule from being secreted normally, resulting in an anomalously low ratio of type I procollagen to other extracellular matrix molecules. In 4 phenotypically identical patients, a defect in secretion of type I procollagen was demonstrated. Thus, although lethal OI congenita is probably heterogeneous, one form may be autosomal dominant new mutational in nature and have a defect in secretion of type I collagen.

Byers et al. (1984) gave an update based on new biochemical information.

Molecular Genetics

In studies of material from the patient of Penttinen et al. (1975) and Heller et al. (1975), Williams and Prockop (1983) found deletion of about 500 bp in the gene for pro-alpha-1(I). See also Chu et al. (1983). This was probably the first characterization of a collagen gene defect. The deletion left coding sequences in register on either side. As a result, the mutant allele was expressed and half the pro-alpha-1 chains synthesized by fibroblasts were shortened by about 80 amino acids. Three-fourths of the procollagen trimers synthesized by fibroblasts contained either 1 or 2 shortened pro-alpha chains. The shortening was such that the presence of even 1 of the mutant pro-alpha-1 chains in a procollagen molecule prevented it from folding into a triple-helical configuration. Trimers containing 1 or 2 mutant pro-alpha-1 chains were rapidly degraded. Prockop (1984) called this 'protein suicide.' In further studies Chu et al. (1985) showed that the deletion eliminated 3 exons of the triple helical domain. The termini of the rearrangement were located within 2 short inverted repeats, suggesting that the self-complementary nature of these DNA elements favored formation of an intermediate that was the basis of the deletion. The patient's fibroblasts contained elevated type III collagen (120180) mRNA. The severity of the clinical presentation (with avulsion of the head and an arm during delivery) is explained. A null allele for pro-alpha-2 chains had much less deleterious effect (de Wet et al., 1983).

Steinmann et al. (1982) and Steinmann et al. (1984) studied material from a male newborn with the lethal perinatal form of OI (and avulsion of an arm). The mother had the Marfan syndrome, as did several other members of the kindred including 2 sibs of the OI proband. The father was healthy and young. The infant's dermis was thinner and collagen fibrils were smaller in diameter than normal and fibroblasts showed dilated endoplasmic reticulum filled with granular material. Cultured fibroblasts synthesized 2 different species of pro-alpha-1(I) chains in about equal amounts. One chain was normal; the other contained cysteine in the triple-helical portion of the COOH-terminal cyanogen bromide peptide alpha-1(I)CB6. Collagen molecules that contained 2 copies of the mutant chain formed alpha-1(I)-dimers linked through interchain disulfide bonds. Molecules containing either 1 or 2 mutant chains were delayed in secretion and underwent excessive posttranslational modification with resulting increased lysyl hydroxylation and hydroxylysyl glycosylation. Delay in triple-helix formation seemed to be responsible for the increased modification. Neither parent had a demonstrable abnormality of collagen. The authors suspected a point mutation with substitution of cysteine for glycine. This may have been the first known example of a point mutation in a collagen gene (Steinmann, 1983). The role of the mother's Marfan syndrome is unclear; the molecular defect underlying the Marfan syndrome in this family had not been determined and it was not known whether the infant inherited the Marfan gene from the mother. The triple-helical domain of type I collagen contains no cysteine. It is made up of repeating triplets of amino acids Gly-X-Y where X and Y are any amino acid except tryptophan, tyrosine, and cysteine and most commonly proline and hydroxyproline, respectively. The fact that type III collagen contains cysteine (and tyrosine) in its triple-helical domain may indicate that its substitution for X or Y in type I collagen would not have as disruptive effects as observed here. In the lethal case thought by Steinmann et al. (1984) to represent a point mutation, Cohn et al. (1986) indeed found substitution of cysteine for glycine at position 988 of the triple-helical portion of half of the alpha-1(I) chains of type I collagen (120150.0018). The mutation disrupted the (G-X-Y)n pattern necessary for formation of the triple helix. This experiment of nature established the minimal mutation capable of producing lethal disease, and the lethality indicated the selective mechanism for stringent maintenance of collagen gene structure. A possibly high mutation rate for the OI II phenotype, which may be at least as frequent as 1 in 60,000 births, can be explained, even if most of them are dominants of the type described here. The COL1A1 gene may present a large target for lethal mutations because any change in the first 2 positions of the repeated GGN-NNN-NNN nucleotide sequence that encodes the triple-helical tripeptide Gly-X-Y is likely to be lethal if it occurs in the part of the gene encoding the carboxy-terminal half of the triple helix.

Since the substitution of cysteine for glycine at position 988 of COL1A1 (120150.0018) was in the critical first position of the G-X-Y triplet, the mutation in the heterozygous state caused a lethal clinical picture. Sequence data confirmed that the mutation was a single base G-to-T change (Cohn et al., 1986). Conversely, Steinmann et al. (1986) found that the substitution of cysteine in the same domain of the alpha-1 chain in another family resulted in mild autosomal dominant OI (166200). The difference resulted from the fact that the substitution of cysteine was for X or Y rather than for G in the G-X-Y triplet.

Genotype/Phenotype Correlations

Bodian et al. (2009) screened DNA samples from 62 unrelated individuals with the perinatal lethal form of OI and identified COL1A1 or COL1A2 mutations in 59 samples and CRTAP or LEPRE1 (610339) mutations in 3 samples. The authors identified 61 distinct heterozygous mutations in the COL1A1 and COL1A2 genes, including 5 nonsynonymous rare variants of unknown significance. Sixty SNPs in the COL1A1 gene (including 17 novel variants) and 82 SNPs in COL1A2 (including 18 novel variants) were reported. Their findings suggested a frequency of 5% for CRTAP and LEPRE1 recessive mutations in severe/lethal OI. A computer model for predicting the outcome of glycine substitutions within the triple-helical domain of COL1A1 chains predicted lethality with 90% accuracy (26 of 29 mutations).

Takagi et al. (2011) studied 4 Japanese patients, including 2 unrelated patients with what the authors called 'classic OI IIC' (see HISTORY) and 2 sibs with features of 'OI IIC' but less distortion of the tubular bones (OI dense bone variant). No consanguinity was reported in their parents. In both sibs and 1 sporadic patient, they identified heterozygous mutations in the C-propeptide region of COL1A1 (120150.0069 and 120150.0070, respectively), whereas no mutation in this region was identified in the other sporadic patient. Familial gene analysis revealed somatic mosaicism of the mutation in the clinically unaffected father of the sibs, whereas their mother and healthy older sister did not have the mutation. Histologic examination in the 2 sporadic cases showed a network of broad, interconnected cartilaginous trabeculae with thin osseous seams in the metaphyseal spongiosa. Thick, cartilaginous trabeculae (cartilaginous cores) were also found in the diaphyseal spongiosa. Chondrocyte columnization appeared somewhat irregular. These changes differed from the narrow and short metaphyseal trabeculae found in other lethal or severe cases of OI. Takagi et al. (2011) concluded that heterozygous C-propeptide mutations in the COL1A1 gene may result in OI IIC with or without twisting of the long bones and that OI IIC appears to be inherited as an autosomal dominant trait.

Nomenclature

The autosomal recessive form of lethal OI designated OI VII (610682) had previously been designated OI IIB (OI2B). For a short time, the autosomal dominant form of lethal OI (OI II; OI2) was designated OI IIA (OI2A).

History

Sillence et al. (1984) reviewed 48 cases of the perinatal lethal form of OI (OI type II) and subclassified them into 3 categories on the basis of radiologic features: group A (38 cases)--short, broad, 'crumpled' long bones, angulation of tibias and continuously beaded ribs; group B (6 cases)--short, broad, crumpled femurs, angulation of tibias but normal ribs or ribs with incomplete beading; and group C (4 cases)--long, thin, inadequately modeled long bones with multiple fractures and thin beaded ribs. Information for segregation analysis was available on 33 families. Two or more sibs were affected in 6 of the families; 3 of these 6 families were examined by the authors and found to fall into group A, 2 into group B, and 1 into group C. The parents were related in 1 family of type A and 1 family of type C. Mean paternal age was not increased. For all these reasons, Sillence et al. (1984) concluded that most cases of OI II represent an autosomal recessive disorder. There is, however, clearly an autosomal dominant form as indicated by biochemical evidence provided by the studies of Barsh and Byers (1981) that there are 2 types of collagen I alpha-1 chains synthesized by fibroblasts.

Commenting on the paper of Sillence et al. (1984), Spranger (1984) stated that 'Type IIC poses no major nosologic problems' because of the radiologic distinctiveness.

On radiographic grounds, Tsipouras et al. (1985) suggested that 5 types of type II OI could be distinguished. Five patients in 3 families appeared to have type 5, the least severe form. The parents of these 5 patients were consanguineous, and Tsipouras et al. (1985) suggested that the inheritance of type 5 may be autosomal recessive.

Heterogeneity

Aitchison et al. (1988) studied a child with type II OI of Sillence subclassification B who was the product of consanguineous Pakistani parents. A brother and sister of the proband's mother, also the product of a consanguineous mating, had died with OI in the perinatal period. The proband was heterozygous for COL1A1 and COL1A2 genotypes, suggesting that the mutation causing the disease in this child was not at either of the structural genes for type I collagen.

Animal Model

Stacey et al. (1988) reproduced the OI II phenotype in transgenic mice carrying a mutant alpha-1(I) collagen gene into which specific glycine substitutions had been engineered. The experiments reproduced the findings in patients in whom a single point mutation resulted in OIC: substitution of glycine by arginine at position 391 (Bateman et al., 1987) or substitution of glycine by cysteine at position 988 (Cohn et al., 1986). Constantinou et al. (1989) described a lethal variant of OI in which a G-to-T substitution converted glycine to cysteine at position 904 of the COL1A1 gene. In addition, the proband may have inherited a second mutation from her asymptomatic mother that produced an overmodified and thermally unstable species of type I procollagen. Her mother was somewhat short and had slightly blue sclerae. Lamande et al. (1989) used the method of Cotton et al. (1988) to identify single base changes in the subunits of type I collagen in 5 patients with OIC. In 4 cases, the substitution was found in the alpha-1 subunit, and in 1 it was located in the alpha-2 chain. In all 5 cases, the first glycine in the amino acid triplet was replaced: gly-973 and gly-1006 to val, gly-928 to ala, and gly-976 to arg in the alpha-1 chain and gly-865 to ser in the alpha-2 chain. These mutations emphasize the importance of the Gly-X-Y repeating amino acid triplet for normal collagen helix formation and function. The method of Cotton et al. (1988) exploits the increased chemical modification of cytosines by hydroxylamine and of thymines by osmium tetroxide, when they are not paired with their complementary base. The DNA chain is then cleaved at the modified bases with piperidine. The use of radioactively end-labeled DNA probes allows the position of the mismatched cytosines and thymines in the probe to be determined by electrophoresis of the cleavage products. Cole et al. (1992) described the occurrence of premature birth in OIC due to precocious rupture of membranes and antepartum hemorrhage.