Melanie Pepin

Clinical and Genetic Features of Ehlers–Danlos Syndrome Type IV, the Vascular Type

Background Ehlers–Danlos syndrome type IV, the vascular type, results from mutations in the gene for type III procollagen (COL3A1). Affected patients are at risk for arterial, bowel, and uterine rupture, but the timing of these events, their frequency, and the course of the disease are not well documented. Methods We reviewed the clinical and family histories of and medical and surgical complications in 220 index patients with biochemically confirmed Ehlers–Danlos syndrome type IV and 199 of their affected relatives. We identified the underlying COL3A1 mutation in 135 index patients. Results Complications were rare in childhood; 25 percent of the index patients had a first complication by the age of 20 years, and more than 80 percent had had at least one complication by the age of 40. The calculated median survival of the entire cohort was 48 years. Most deaths resulted from arterial rupture. Bowel rupture, which often involved the sigmoid colon, accounted for about a quarter of complications but rarely l...

Homozygosity for a Missense Mutation in SERPINH1, which Encodes the Collagen Chaperone Protein HSP47, Results in Severe Recessive Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) is characterized by bone fragility and fractures that may be accompanied by bone deformity, dentinogenesis imperfecta, short stature, and shortened life span. About 90% of individuals with OI have dominant mutations in the type I collagen genes COL1A1 and COL1A2. Recessive forms of OI resulting from mutations in collagen-modifying enzymes and chaperones CRTAP, LEPRE1, PPIB, and FKBP10 have recently been identified. We have identified an autosomal-recessive missense mutation (c.233T>C, p.Leu78Pro) in SERPINH1, which encodes the collagen chaperone-like protein HSP47, that leads to a severe OI phenotype. The mutation results in degradation of the endoplasmic reticulum resident HSP47 via the proteasome. Type I procollagen accumulates in the Golgi of fibroblasts from the affected individual and a population of the secreted type I procollagen is protease sensitive. These findings suggest that HSP47 monitors the integrity of the triple helix of type I procollagen at the ER/cis-Golgi boundary and, when absent, the rate of transit from the ER to the Golgi is increased and helical structure is compromised. The normal 3-hydroxylation of the prolyl residue at position 986 of the triple helical domain of proalpha1(I) chains places the role of HSP47 downstream from the CRTAP/P3H1/CyPB complex that is involved in prolyl 3-hydroxylation. Identification of this mutation in SERPINH1 gives further insight into critical steps of the collagen biosynthetic pathway and the molecular pathogenesis of OI.

CRTAP AND LEPRE1 MUTATIONS IN RECESSIVE OSTEOGENESIS IMPERFECTA

Autosomal dominant osteogenesis imperfecta (OI) is caused by mutations in the genes (COL1A1 or COL1A2) encoding the chains of type I collagen. Recently, dysregulation of hydroxylation of a single proline residue at position 986 of both the triple‐helical domains of type I collagen α1(I) and type II collagen α1(II) chains has been implicated in the pathogenesis of recessive forms of OI. Two proteins, cartilage‐associated protein (CRTAP) and prolyl‐3‐hydroxylase‐1 (P3H1, encoded by the LEPRE1 gene) form a complex that performs the hydroxylation and brings the prolyl cis‐trans isomerase cyclophilin‐B (CYPB) to the unfolded collagen. In our screen of 78 subjects diagnosed with OI type II or III, we identified three probands with mutations in CRTAP and 16 with mutations in LEPRE1. The latter group includes a mutation in patients from the Irish Traveller population, a genetically isolated community with increased incidence of OI. The clinical features resulting from CRTAP or LEPRE1 loss of function mutations were difficult to distinguish at birth. Infants in both groups had multiple fractures, decreased bone modeling (affecting especially the femurs), and extremely low bone mineral density. Interestingly, “popcorn” epiphyses may reflect underlying cartilaginous and bone dysplasia in this form of OI. These results expand the range of CRTAP/LEPRE1 mutations that result in recessive OI and emphasize the importance of distinguishing recurrence of severe OI of recessive inheritance from those that result from parental germline mosaicism for COL1A1 or COL1A2 mutations. Hum Mutat 0, 1–8, 2008.

WNT1 Mutations in Families Affected by Moderately Severe and Progressive Recessive Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) is a heritable disorder that ranges in severity from death in the perinatal period to an increased lifetime risk of fracture. Mutations in COL1A1 and COL1A2, which encode the chains of type I procollagen, result in dominant forms of OI, and mutations in several other genes result in recessive forms of OI. Here, we describe four recessive-OI-affected families in which we identified causative mutations in wingless-type MMTV integration site family 1 (WNT1). In family 1, we identified a homozygous missense mutation by exome sequencing. In family 2, we identified a homozygous nonsense mutation predicted to produce truncated WNT1. In family 3, we found a nonsense mutation and a single-nucleotide duplication on different alleles, and in family 4, we found a homozygous 14 bp deletion. The mutations in families 3 and 4 are predicted to result in nonsense-mediated mRNA decay and the absence of WNT1. WNT1 is a secreted signaling protein that binds the frizzled receptor (FZD) and the coreceptor low-density lipoprotein-receptor-related protein 5 (LRP5). Biallelic loss-of-function mutations in LRP5 result in recessive osteoporosis-pseudoglioma syndrome with low bone mass, whereas heterozygous gain-of-function mutations result in van Buchem disease with elevated bone density. Biallelic loss-of-function mutations in WNT1 result in a recessive clinical picture that includes bone fragility with a moderately severe and progressive presentation that is not easily distinguished from dominant OI type III.

The 2017 international classification of the Ehlers-Danlos syndromes.

The Ehlers–Danlos syndromes (EDS) are a clinically and genetically heterogeneous group of heritable connective tissue disorders (HCTDs) characterized by joint hypermobility, skin hyperextensibility, and tissue fragility. Over the past two decades, the Villefranche Nosology, which delineated six subtypes, has been widely used as the standard for clinical diagnosis of EDS. For most of these subtypes, mutations had been identified in collagen‐encoding genes, or in genes encoding collagen‐modifying enzymes. Since its publication in 1998, a whole spectrum of novel EDS subtypes has been described, and mutations have been identified in an array of novel genes. The International EDS Consortium proposes a revised EDS classification, which recognizes 13 subtypes. For each of the subtypes, we propose a set of clinical criteria that are suggestive for the diagnosis. However, in view of the vast genetic heterogeneity and phenotypic variability of the EDS subtypes, and the clinical overlap between EDS subtypes, but also with other HCTDs, the definite diagnosis of all EDS subtypes, except for the hypermobile type, relies on molecular confirmation with identification of (a) causative genetic variant(s). We also revised the clinical criteria for hypermobile EDS in order to allow for a better distinction from other joint hypermobility disorders. To satisfy research needs, we also propose a pathogenetic scheme, that regroups EDS subtypes for which the causative proteins function within the same pathway. We hope that the revised International EDS Classification will serve as a new standard for the diagnosis of EDS and will provide a framework for future research purposes.

Mutations in PPIB (cyclophilin B) delay type I procollagen chain association and result in perinatal lethal to moderate osteogenesis imperfecta phenotypes

Recessive mutations in the cartilage-associated protein (CRTAP), leucine proline-enriched proteoglycan 1 (LEPRE1) and peptidyl prolyl cis-trans isomerase B (PPIB) genes result in phenotypes that range from lethal in the perinatal period to severe deforming osteogenesis imperfecta (OI). These genes encode CRTAP (encoded by CRTAP), prolyl 3-hydroxylase 1 (P3H1; encoded by LEPRE1) and cyclophilin B (CYPB; encoded by PPIB), which reside in the rough endoplasmic reticulum (RER) and can form a complex involved in prolyl 3-hydroxylation in type I procollagen. CYPB, a prolyl cis-trans isomerase, has been thought to drive the prolyl-containing peptide bonds to the trans configuration needed for triple helix formation. Here, we describe mutations in PPIB identified in cells from three individuals with OI. Cultured dermal fibroblasts from the most severely affected infant make some overmodified type I procollagen molecules. Proα1(I) chains are slow to assemble into trimers, and abnormal procollagen molecules concentrate in the RER, and bind to protein disulfide isomerase (PDI) and prolyl 4-hydroxylase 1 (P4H1). These findings suggest that although CYPB plays a role in helix formation another effect is on folding of the C-terminal propeptide and trimer formation. The extent of procollagen accumulation and PDI/P4H1 binding differs among cells with mutations in PPIB, CRTAP and LEPRE1 with the greatest amount in PPIB-deficient cells and the least in LEPRE1-deficient cells. These findings suggest that prolyl cis-trans isomerase may be required to effectively fold the proline-rich regions of the C-terminal propeptide to allow proα chain association and suggest an order of action for CRTAP, P3H1 and CYPB in procollagen biosynthesis and pathogenesis of OI.

Studies of collagen synthesis and structure in the differentiation of child abuse from osteogenesis imperfecta

OBJECTIVE To determine whether analysis of collagen synthesized by dermal fibroblasts could identify children with osteogenesis imperfecta (OI) among those suspected to have been abused. METHODS We reviewed biochemical studies and clinical findings for all children who were referred to us to distinguish OI from abuse during a 4-year period. RESULTS Cells from 6 of 48 children tested to distinguish OI from abuse had biochemical evidence of OI. In five of the six children with abnormal results on collagen studies, clinical signs of OI in addition to fractures were present on examination by a physician familiar with the condition. In those five cases, the diagnosis of OI was strongly suspected. CONCLUSIONS OI can be diagnosed by biochemical studies in some cases of suspected abuse, but clinical evaluation by experienced physicians is usually sufficient to do so. When diagnostic uncertainty persists in cases of suspected child abuse, biochemical studies may be a useful adjunct, but routine biopsy for children suspected to have been abused is unwarranted.

STRATEGIES AND OUTCOMES OF PRENATAL DIAGNOSIS FOR OSTEOGENESIS IMPERFECTA: A REVIEW OF BIOCHEMICAL AND MOLECULAR STUDIES COMPLETED IN 129 PREGNANCIES

We completed prenatal diagnostic studies from 129 pregnancies at risk for osteogenesis imperfecta (OI). Studies in 107 pregnancies were completed by analysis of collagen synthesized by cells cultured from chorionic villus biopsies and the remaining 22 used direct mutation identification or analysis of polymorphic restriction sites in the COL1A1 gene of type I collagen. The vast majority of studies (n=113) were obtained to identify fetuses with OI type II (the perinatal lethal form) and some fetuses affected with OI type III or IV (the deforming varieties). Of the 50 couples who had had one previous affected pregnancy with the lethal form of OI, one had a second affected pregnancy, a rate of 2 per cent. Two of the seven unaffected couples (28 per cent) who had had two previous affected pregnancies with OI type II had a third affected pregnancy; none of the three with two previous pregnancies with OI type III had a third. Pregnancies at risk for OI type I could not be ascertained reliably by biochemical analysis of cultured CVS cells but were identified by direct analysis of the causative mutation or the use of linked markers in families. All prenatal diagnostic studies were undertaken only after earlier diagnostic studies (biochemical or molecular) had been completed on the proband, a necessary strategy for accurate results. In all pregnancies at risk for OI type II, OI type III, and OI type IV studied with biochemical strategies and in pregnancies at risk for OI type I studied with molecular techniques, there were neither false‐negative nor false‐positive results. Diagnostic information can be obtained within 20–30 days of biopsy using biochemical techniques and within 10–14 days when molecular strategies are used.

Survival is affected by mutation type and molecular mechanism in vascular Ehlers-Danlos syndrome (EDS type IV)

Purpose:We sought to characterize the natural history of vascular Ehlers–Danlos syndrome in individuals with heterozygous COL3A1 mutations.Methods:We reviewed clinical records for details of vascular, bowel, and organ complications in 1,231 individuals (630 index cases and 601 relatives).Results:Missense and splice-site mutations accounted for more than 90% of the 572 alterations that we had identified in COL3A1. Median survival was 51 years but was influenced by gender (lower in men) and by the type of mutation.Conclusion:Although vascular Ehlers–Danlos syndrome appears to be genetically homogeneous, allelic heterogeneity is marked, and the natural history varies with gender and type of mutation in COL3A1. These findings indicate that when counseling families, confirmation of the presence of a COL3A1 mutation and its nature can help evaluate the risks of complications. These data are also important ingredients in both the selection and allocation of individuals to appropriate arms in clinical trials to assess the effects of interventions.Genet Med 16 12, 881–888.

COL3A1 haploinsufficiency results in a variety of Ehlers-Danlos syndrome type IV with delayed onset of complications and longer life expectancy.

Purpose: To characterize the clinical outcome of heterozygosity for COL3A1 null mutations in Ehlers-Danlos syndrome type IV, the vascular type.Methods: We identified mutations that produced premature termination codons and resulted in nonsense-mediated messenger RNA decay in 19 families. We reviewed the clinical and family histories and medical complications in 54 individuals from these families with COL3A1 null mutations.Results: Compared with individuals with missense or exon-skipping mutations, we found that life span was extended, the age of first complication was delayed by almost 15 years, and major complications were limited to vascular events. The families were ascertained after a complication in a single individual, but only 28% of relatives, some of whom had reached their seventies or eighties without incidents, had a complication and only 30% had minor clinical features of Ehlers-Danlos syndrome type IVConclusion: Null mutations have reduced penetrance compared with missense and splicing mutations, and the phenotype seems to be limited almost entirely to vascular events.