A familial case of achondrogenesis type II caused by a dominant COL2A1 mutation and "patchy" expression in the mosaic father

Achondrogenesis type II (ACG2) is the most severe disorder that can be produced by dominant mutations in COL2A1. We report on four pregnancies of an apparently healthy, nonconsanguineous young couple. The father had scoliosis as a child, and has slight body disproportion with short trunk. The first child was born at 32 weeks and died neonatally. In the second pregnancy, short limbs and fetal hygroma were noted on ultrasound at 17 weeks' gestation. Similar findings were observed in the third fetus. Clinical, radiological, and histological evaluation of the fetuses after termination of the pregnancies showed findings consistent with ACG2. Molecular analysis of genomic DNA extracted from amniotic cells of the second and third fetuses revealed heterozygosity for a 10370G > T missense mutation (G346V) in the COL2A1 gene. This mutation was also found in the father, as a mosaic. The couple had a fourth pregnancy, and at 11 weeks fetal hydrops with a septated cystic hygroma were obvious. DNA from CVS demonstrated the same COL2A1 mutation.     

A specific collagen type II gene (COL2A1) mutation presenting as spondyloperipheral dysplasia

We report on a patient with a skeletal dysplasia characterized by short stature, spondylo-epiphyseal involvement, and brachydactyly E-like changes. This condition has been described as spondyloperipheral dysplasia and the few published cases suggest autosomal dominant inheritance with considerable clinical variability. We found our sporadic case to be due to a collagen type II defect resulting from a specific COL2A1 mutation. This mutation is the first to be located at the C-terminal outside the helical domain of COL2A1. A frameshift as consequence of a 5 bp duplication in exon 51 leads to a stop codon. The resulting truncated C-propeptide region seems to affect helix formation and produces changes of chondrocyte morphology, collagen type II fibril structure and cartilage matrix composition. Our case with its distinct phenotype adds another chondrodysplasia to the clinical spectrum of type II collagenopathies. © 1996 Wiley-Liss, Inc.     

Localization of human type II procollagen gene (COL2A1) to chromosome 12

DNA was prepared from 39 humanmouse somatic cell hybrid lines, and mouse and human parental cell lines. The DNA was digested to completion with EcoRI and Southern filters were prepared. These filters were hybridized at high stringency conditions to the human genomic subclone phHCo1 (II)A which corresponds to the human 1 (type II) procollagen gene (COL2A1). The mouse DNA yielded a single band at >10 kb, whereas the human DNA had the expected single band at 4.8kb. Analyses of these human-mouse cell hybrids demonstrated that the human 1(type II) procollagen gene segregates with chromosome 12.     

Osteoarthritis in children associated with a mutation in the type II procollagen gene (COL2A1).

A single-base mutation resulting in an arginine-519-cysteine (R519C) mutation of type II procollagen (COL2A1) has been shown to result in precocious osteoarthritis with mild spinal chondrodysplasia without severe foreshortening (OMIM 604864). The nature of childhood disease among affected individuals has not been described. The recent presentation of four children with this mutation allows us to provide clinical correlation. This form of premature osteoarthritis may present in childhood and should be considered in the differential diagnosis of childhood arthropathy presenting in the context of a positive family history.     

Stickler syndrome and the vitreous phenotype: mutations in COL2A1 and COL11A1

Stickler syndrome is a dominantly inherited disorder affecting the fibrillar type II/XI collagen molecules expressed in vitreous and cartilage. Mutations have been found in COL2A1, COL11A1 and COL11A2. It has a highly variable phenotype that can include midline clefting, hearing loss, premature osteoarthritis, congenital high myopia and blindness through retinal detachment. Although the systemic phenotype is highly variable, the vitreous phenotype has been used successfully to differentiate between patients with mutations in these different genes. Mutations in COL2A1 usually result in a congenital membranous vitreous anomaly. In contrast mutations in COL11A1 result in a different vitreous phenotype where the lamellae have an irregular and beaded appearance. However, it is now apparent that a new sub‐group of COL2A1 mutations is emerging that result in a different phenotype with a hypoplastic vitreous that fills the posterior chamber of the eye, and is either optically empty or has sparse irregular lamellae. Here we characterise a further 89 families with Stickler syndrome or a type II collagenopathy, and correlate the mutations with the vitreous phenotype. We have identified 57 novel mutations including missense changes in both COL2A1 and COL11A1 and have also detected two cases of complete COL2A1 gene deletions using MLPA. ©2010 Wiley‐Liss, Inc.     

Osteogenesis imperfecta type III: mutations in the type I collagen structural genes, COL1A1 and COL1A2, are not necessarily responsible.

Most forms of osteogenesis imperfecta are caused by dominant mutations in either of the two genes, COL1A1 and COL1A2, that encode the pro alpha 1(I) and pro alpha 2(I) chains of type I collagen, respectively. However, a severe, autosomal recessive form of OI type III with a comparatively high frequency has been recognised in the black populations of southern Africa. We preformed linkage analyses in eight OI type III families using RFLPs associated with the COL1A1 and COL1A2 loci to determine whether mutations in the genes for type I collagen were responsible for this form of OI. Recombination between the OI phenotype and polymorphic markers at both loci was shown in three of the eight families investigated. The combined lod scores for the eight families were -10.6 for COL1A1 and -11.2 for COL1A2. Further, we examined the type I procollagen produced by skin fibroblast cultures derived from 15 affected and 12 unaffected subjects from the above eight families plus one further family. We found no evidence for defects in the synthesis, structure, secretion, or post-translational modification of the chains of type I procollagen produced by any of the family members. These results suggest that mutations within or near the type I collagen structural genes are not responsible for this form of OI.     

The human type II collagen gene (COL2A1) assigned to 12q14.3

A cosmid clone containing the entire human type II α1 collagen gene ( COL2A1 ) was used as probe in the Southern analysis of DNA from a panel of human/hamster somatic cell hybrids containing different portions of human chromosome 12. Two of the hybrids exhibited a similar terminal deletion q14.3→qter, but one was positive for the gene while the other was negative. Therefore, the gene must reside in the region q14.3.     

The phenotypic spectrum of COL2A1 mutations

Heterozygous mutations of COL2A1 create several clinical entities collectively termed type II collagenopathies. These disorders not only impair skeletal growth but also cause ocular and otolaryngological abnormalities. The classical phenotypes include the spondyloepiphyseal dysplasia (SED) spectrum with variable severity, Stickler dysplasia type I (STD-I), and Kniest dysplasia (KND). Most COL2A1 mutations occur in the triple helical region of alpha 1(II) chains: the SED spectrum is mostly attributed to missense mutations that substitute bulky amino acids for glycine residues, STD-I to haploinsufficiency of truncation mutations, and KND to exon skipping due to splice-site mutations. To further elucidate the genotype-phenotype relationship of type II collagenopathies, we examined COL2A1 mutations in 56 families that were suspected of having type II collagenopathies, and found 38 mutations in 41 families. Phenotypes for all 22 missense mutations and one in-frame deletion in the triple helical region fell along the SED spectrum. Glycine to serine substitutions resulted in alternating zones that produce severer and milder skeletal phenotypes. Glycine to nonserine residue substitutions exclusively created more severe phenotypes. The gradient of the SED spectrum did not necessarily correlate with the occurrence of extraskeletal manifestations. All nine truncation or splice-site mutations in the triple helical or N-propeptide region caused STD-I or KND, and extraskeletal changes were inevitable in both phenotypes. All six C-propeptide mutations produced a range of atypical skeletal phenotypes and created ocular, but not otolaryngological, changes.     

The phenotypic spectrum in patients with arginine to cysteine mutations in the COL2A1 gene

Background

The majority of COL2A1 missense mutations are substitutions of obligatory glycine residues in the triple helical domain. Only a few non‐glycine missense mutations have been reported and among these, the arginine to cysteine substitutions predominate.

Objective

To investigate in more detail the phenotype resulting from arginine to cysteine mutations in the COL2A1 gene.

Methods

The clinical and radiographic phenotype of all patients in whom an arginine to cysteine mutation in the COL2A1 gene was identified in our laboratory, was studied and correlated with the abnormal genotype. The COL2A1 genotyping involved DHPLC analysis with subsequent sequencing of the abnormal fragments.

Results

Six different mutations (R75C, R365C, R519C, R704C, R789C, R1076C) were found in 11 unrelated probands. Each mutation resulted in a rather constant and site‐specific phenotype, but a perinatally lethal disorder was never observed. Spondyloarthropathy with normal stature and no ocular involvement were features of patients with the R75C, R519C, or R1076C mutation. Short third and/or fourth toes was a distinguishing feature of the R75C mutation and brachydactyly with enlarged finger joints a key feature of the R1076C substitution. Stickler dysplasia with brachydactyly was observed in patients with the R704C mutation. The R365C and R789C mutations resulted in classic Stickler dysplasia and spondyloepiphyseal dysplasia congenita (SEDC), respectively.

Conclusions

Arginine to cysteine mutations are rather infrequent COL2A1 mutations which cause a spectrum of phenotypes including classic SEDC and Stickler dysplasia, but also some unusual entities that have not yet been recognised and described as type II collagenopathies.     

Thirty-three novel COL1A1 and COL1A2 mutations in patients with osteogenesis imperfecta types I-IV

Osteogenesis imperfecta (OI) is a heritable disease of bone characterized by low bone mass and bone fragility. Six different types of OI have been described to date, based on clinical phenotype and histological findings. The genetic defect in many patients with OI types I-IV is due to mutations in the genes encoding type I collagen, while patients with OI types V and VI show no evidence of mutations in the COL1A1/COL1A2 genes. Here we report thirty-three novel mutations in patients with types I-IV OI. Sixteen mutations were in COL1A1 and seventeen were in COL1A2. Most mutations resulted in substitutions for glycine: one of these, a doublet GG>CC transversion, created a unique Gly-->Pro missense mutation in the triple helical domain of COL1A2. Two rare triple helical Gly-->Glu substitutions in COL1A2 are also described. In addition, there were six single-base deletion mutations resulting in frameshifts, seven splice junction mutations, and a 9-bp triple helix insertion associated with a severe (OI II) phenotype. The variety of mutations described in the COL1A1/COL1A2 genes giving rise to an OI phenotype is in accordance with the clinical heterogeneity of the disease. Hum Mutat 17:434, 2001.     

Autosomal dominant spondylarthropathy due to a type II procollagen gene(COL2A1) point mutation

Osteoarthrosis represents a very common disease with heterogeneous etiology. In some pedigrees linkage of the condition with the type II collagen gene (COL2A1) has been established, but information on the underlying gene defect is still incomplete as only one mutation causing this phenotype has been identified. We analyzed the COL2A1 gene in a 27-year-old woman and her 47-year-old mother presenting with severe premature osteoarthrosis and X-ray signs compatible with mild spondyloepiphyseal dysplasia. Examination of the complete gene in both patients was done by amplification of all 54 exons, screening of the PCR products by SSCP-analysis, and subsequent sequencing. In mother and daughter a G to A transition at the 5′-end of exon 21 was detected, leading to a substitution of serine for glycine at position 274 of the triple helical domain. The mutation was not present in unaffected family members or in healthy control individuals. The autosomal dominant spondylarthropathies may represent the less severe entities of the clinical spectrum of type II collagenopathies. © 1994 Wiley-Liss, Inc.     

Absence of mutations in the promoter of the COL1A1 gene of type I collagen in patients with osteogenesis imperfecta type I.

Osteogenesis imperfecta type I results from decreased production of structurally normal type I collagen as a result of a COL1A1 "null" allele. Steady state amounts of COL1A1 mRNA are reduced in both the nucleus and cytoplasm of dermal fibroblasts from most affected subjects. Mutations involving key regulatory sequences in the COL1A1 promoter, such as the TATAAA and CCAAAT boxes, could alter steady state levels of mRNA, and therefore lead to this phenotype. To determine the frequency of such mutations in OI type I cell strains, we used PCR amplified genomic DNA in conjunction with denaturing gradient gel electrophoresis (DGGE) and SSCP, to screen the 5' untranslated domain, exon 1, and a small portion of intron 1 of the COL1A1 gene. In addition, direct sequence analysis was performed on an amplified genomic DNA fragment that included the TATAAA and CCAAAT boxes. Forty unrelated probands with OI type I, in whom no causative mutation was known, were included in the study. No mutations were included in the study. No mutations were identified in either the TATAAA or CCAAAT boxes in any of the affected people. In addition, there was little evidence of sequence diversity among any of the 40 subjects. These data suggest that mutations in the COL1A1 promoter do not play a significant role in the aetiology of OI type I.     

Structural and segregation analysis of the type II collagen gene (COL2A1) in some heritable chondrodysplasias.

Seventy-seven persons with a variety of heritable chondrodysplasias were screened for gross rearrangements of the structural gene encoding the major cartilage collagen, collagen II. None was found. Segregation of the locus (COL2A1) was studied in 19 pedigrees using three restriction site dimorphisms (shown by PvuII, HindIII, and BamHI) and a length polymorphism as linkage markers. Discordant segregation between COL2A1 and the mutant locus was seen in pedigrees with multiple epiphyseal dysplasia, autosomal recessive spondyloepiphyseal dysplasia tarda, hypochondroplasia, pseudoachondroplasia, diaphyseal aclasis, and trichorhinophalangeal syndrome. One pedigree with diastrophic dysplasia was weakly concordant. Autosomal dominant spondyloepiphyseal dysplasia tarda and metaphyseal chondrodysplasia (type Schmid) were not informative. We conclude that mutations of the collagen II gene are not a common feature of the heritable chondrodysplasias. Since the chondrocyte binding protein, chondrocalcin, is also encoded at COL2A1 our conclusions apply equally to this gene.     

Evidence against the structural gene encoding type II collagen (COL2A1) as the mutant locus in achondroplasia.

The structure of the locus encoding the major cartilage collagen gene (COL2A1) was studied in a total of 19 cases of achondroplasia. No gross rearrangements were seen. The segregation of COL2A1 was examined in three affected kindreds using restriction site and length variants as genetic markers. In two kindreds discordant segregation between the achondroplasia and COL2A1 loci was demonstrated. Paternity/maternity was confirmed using a 'minisatellite' core sequence probe which reveals cross hybridising polymorphic loci.     

Ehlers-Danlos syndrome type VIIA and VIIB result from splice-junction mutations or genomic deletions that involve exon 6 in the COL1A1 and COL1A2 genes of type I collagen

Ehlers-Danlos syndrome (EDS) type VII results from defects in the conversion of type I procollagen to collagen as a consequence of mutations in the substrate that alter the protease cleavage site (EDS type VIIA and VIIB) or in the protease itself (EDS type VIIC). We identified seven additional families in which EDS type VII is either dominantly inherited (one family with EDS type VIIB) or due to new dominant mutations (one family with EDS type VIIA and five families with EDS type VIIB). In six families, the mutations alter the consensus splice junctions, and, in the seventh family, the exon is deleted entirely. The COL1A1 mutation produced the most severe phenotypic effects, whereas those in the COL1A2 gene, regardless of the location or effect, produced congenital hip dislocation and other joint instability that was sometimes very marked. Fractures are seen in some people with EDS type VII, consistent with alterations in mineral deposition on collagen fibrils in bony tissues. These new findings expand the array of mutations known to cause EDS type VII and provide insight into genotype/phenotype relationships in these genes. Am. J. Med. Genet. 72:94–105, 1997. © 1997 Wiley-Liss, Inc.