Analysis of the COL1A1 and COL1A2 genes by PCR amplification and scanning by conformation-sensitive gel electrophoresis identifies only COL1A1 mutations in 15 patients with osteogenesis imperfecta type I: identification of common sequences of null-allele mutations

Effectiveness of whole exome sequencing analyses in the molecular diagnosis of osteogenesis imperfecta

OBJECTIVES

Osteogenesis imperfecta (OI) is a group of phenotypically and genetically heterogeneous connective tissue disorders that share similar skeletal anomalies causing bone fragility and deformation. This study aimed to investigate the molecular genetic etiology and to determine the relationship between genotype and phenotype in OI patients with whole exome sequencing (WES).

METHODS

Multiplex-Ligation dependent Probe Amplification (MLPA) analysis of COL1A1 and COL1A2 and WES were performed on cases between the ages of 0 and 18 whose genetic etiology could not be determined before using a targeted next-generation sequencing panel, including 13 genes (COL1A1, COL1A2, IFITM5, SERPINF1, CRTAP, P3H1, PPIB, SERPINH1, FKBP10, SP7, BMP1, MBTPS2, PLOD2) responsible for OI.

RESULTS

Twelve patients (female/male: 4/8) from 10 different families were included in the study. In 6 (50 %) families, consanguineous marriage was noted. The clinical typing based on Sillence classification; 3 (25 %) patients were considered to be type I, 7 (58.3 %) type III, and 2 (16.7 %) type IV. Deletion/duplication wasn't detected in the COL1A1 and COL1A2 genes in the MLPA analysis of the patients. Twelve patients were molecularly analyzed by WES, and in 6 (50 %) of them, a disease-causing variant in three different genes (FKBP10, P3H1, and WNT1) was identified. Two (33.3 %) detected variants in all genes have not been previously reported in the literature and were considered deleterious based on prediction tools. In 6 cases, no variants were detected in disease-causing genes.

CONCLUSIONS

This study demonstrates rare OI types' clinical and molecular features; genetic etiology was determined in 6 (50 %) 12 patients with the WES analysis. In addition, two variants in OI genes have been identified, contributing to the literature.

Pregnancy complicated by severe osteogenesis imperfecta poses a challenge for the anaesthetist: A case report

Pregnant women with severe osteogenesis imperfecta (OI) are uncommon, and there are limited data regarding anaesthesia for caesarean section in these high-risk individuals. The presence of anatomical and physiological abnormalities can pose technical challenges for the anaesthetist. This report describes the successful implementation of epidural anaesthesia in a parturient with severe OI. To our knowledge, this is the first documented use of ultrasound-assisted neuraxial anaesthesia and wrist blood pressure monitoring in such patients undergoing caesarean section. Understanding the pathophysiological changes associated with OI is crucial for ensuring safe administration of anaesthesia to these women.

Self-Assembling Triple-Helix Recombinant Collagen Hydrogel Enriched with Tyrosine

The self-assembly of collagen within the human body creates a complex 3D fibrous network, providing structural integrity and mechanical strength to connective tissues. Recombinant collagen plays a pivotal role in the realm of biomimetic natural collagen. However, almost all of the reported recombinant collagens lack the capability of self-assembly, severely hindering their application in tissue engineering and regenerative medicine. Herein, we have for the first time constructed a series of self-assembling tyrosine-rich triple helix recombinant collagens, mimicking the structure and functionality of natural collagen. The recombinant collagen consists of a central triple-helical domain characterized by the (Gly-Xaa-Yaa)n sequence, along with N-terminal and C-terminal domains featuring the GYY sequence. The introduction of GYY has a negligible impact on the stability of the triple-helical structure of recombinant collagen while simultaneously promoting its self-assembly into fibers. In the presence of [Ru(bpy)3]Cl2 and APS as catalysts, tyrosine residues in the recombinant collagen undergo covalent cross-linking, resulting in a hydrogel with exceptional mechanical properties. The recombinant collagen hydrogel exhibits outstanding biocompatibility and bioactivity, significantly enhancing the proliferation, adhesion, migration, and differentiation of HFF-1 cells. This innovative self-assembled triple-helix recombinant collagen demonstrates significant potential in the fields of tissue engineering and medical materials.

Expanding the genetic and clinical spectrum of osteogenesis imperfecta: identification of novel rare pathogenic variants in type I collagen-encoding genes

Introduction

Osteogenesis imperfecta (OI) is a clinically and genetically heterogeneous skeletal disorder. The majority of affected cases are attributed to autosomal dominant pathogenic variants (PVs) found in the COL1A1 and COL1A2 genes, which encode type I collagen. However, PVs in other genes involved in collagen posttranslational modification, processing, crosslinking, osteoblast differentiation, and bone mineralization have also been associated with OI.

Methods

In this study, we present the results of next-generation sequencing (NGS) analysis using a custom panel of 11 genes known to be associated with OI. This clinical study enrolled a total of 10 patients, comprising 7 male and 3 female patients from 7 families, all from the Puglia Region in South Italy, providing a detailed overview of their age, gender, family history, OI type, and non-skeletal features.

Results

The genetic analysis revealed 5 PVs in the COL1A1 gene and 2 PVs in the COL1A2 gene. Importantly, three of these PVs have not been previously reported in the literature. These include two novel heterozygous frameshift PVs in COL1A1 (c.2890_2893del and c.3887del) and one novel heterozygous missense PV in COL1A2 (c.596G>T).

Discussion

The identification of these previously unreported PVs expands the variant spectrum of the COL1A1 and COL1A2 genes and may have implications for accurate diagnosis, genetic counselling, and potential therapeutic interventions in affected individuals and their families.

Effectiveness of zebrafish models in understanding human diseases-A review of models

Understanding the detailed mechanism behind every human disease, disorder, defect, and deficiency is a daunting task concerning the clinical diagnostic tools for patients. Hence, a closely resembling living or simulated model is of paramount interest for the development and testing of a probable novel drug for rectifying the conditions pertaining to the various ailments. The animal model that can be easily genetically manipulated to suit the study of the therapeutic motive is an indispensable asset and within the last few decades, the zebrafish models have proven their effectiveness by becoming such potent human disease models with their use being extended to various avenues of research to understand the underlying mechanisms of the diseases. As zebrafish are explored as model animals in understanding the molecular basis and genetics of many diseases owing to the 70% genetic homology between the human and zebrafish genes; new and fascinating facts about the diseases are being surfaced, establishing it as a very powerful tool for upcoming research. These prospective research areas can be explored in the near future using zebrafish as a model. In this review, the effectiveness of the zebrafish as an animal model against several human diseases such as osteoporosis, atrial fibrillation, Noonan syndrome, leukemia, autism spectrum disorders, etc. has been discussed.

Clinical and molecular features of patients with COL1-related disorders: Implications for the wider spectrum and the risk of vascular complications

Abnormalities in type I procollagen genes (COL1A1 and COL1A2) are responsible for hereditary connective tissue disorders including osteogenesis imperfecta (OI), specific types of Ehlers-Danlos syndrome (EDS), and COL1-related overlapping disorder (C1ROD). C1ROD is a recently proposed disorder characterized by predominant EDS symptoms of joint and skin laxity and mild OI symptoms of bone fragility and blue sclera. Patients with C1ROD do not carry specific variants for COL1-related EDS, including classical, vascular, cardiac-valvular, and arthrochalasia types. We describe clinical and molecular findings of 23 Japanese patients with pathogenic or likely pathogenic variants of COL1A1 or COL1A2, who had either OI-like or EDS-like phenotypes. The final diagnoses were OI in 17 patients, classical EDS in one, and C1ROD in five. The OI group predominantly experienced recurrent bone fractures, and the EDS group primarily showed joint hypermobility and skin hyperextensibility, though various clinical and molecular overlaps between OI, COL1-related EDS, and C1ROD as well as intrafamilial phenotypic variabilities were present. Notably, life-threatening vascular complications (vascular dissections, arterial aneurysms, subarachnoidal hemorrhages) occurred in seven patients (41% of those aged >20 years) with OI or C1ROD. Careful lifelong surveillance and intervention regarding bone and vascular fragility could be required.

Osteogenesis Imperfecta: Search for Mutations in Patients from the Republic of Bashkortostan (Russia)

Osteogenesis imperfecta (OI) is an inherited disease of bone characterized by increased bone fragility. Here, we report the results of the molecular architecture of osteogenesis imperfecta research in patients from Bashkortostan Republic, Russia. In total, 16 mutations in COL1A1, 11 mutations in COL1A2, and 1 mutation in P3H1 and IFIMT5 genes were found in isolated states; 11 of them were not previously reported in literature. We found mutations in CLCN7, ALOX12B, PLEKHM1, ERCC4, ARSB, PTH1R, and TGFB1 that were not associated with OI pathogenesis in patients with increased bone fragility. Additionally, we found combined mutations (c.2869C>T, p. Gln957* in COL1A1 and c.1197+5G>A in COL1A2; c.579delT, p. Gly194fs in COL1A1 and c.1197+5G>A in COL1A2; c.2971G>C, p. Gly991Arg in COL1A2 and c.212G>C, p.Ser71Thr in FGF23; c.-14C>T in IFITM5 and c.1903C>T, p. Arg635* in LAMB3) in 4 patients with typical OI clinic phenotypes.

Restoration of Osteogenesis by CRISPR/Cas9 Genome Editing of the Mutated COL1A1 Gene in Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) is a genetic disease characterized by bone fragility and repeated fractures. The bone fragility associated with OI is caused by a defect in collagen formation due to mutation of COL1A1 or COL1A2. Current strategies for treating OI are not curative. In this study, we generated induced pluripotent stem cells (iPSCs) from OI patient-derived blood cells harboring a mutation in the COL1A1 gene. Osteoblast (OB) differentiated from OI-iPSCs showed abnormally decreased levels of type I collagen and osteogenic differentiation ability. Gene correction of the COL1A1 gene using CRISPR/Cas9 recovered the decreased type I collagen expression in OBs differentiated from OI-iPSCs. The osteogenic potential of OI-iPSCs was also recovered by the gene correction. This study suggests a new possibility of treatment and in vitro disease modeling using patient-derived iPSCs and gene editing with CRISPR/Cas9.

Genetic analysis in Japanese patients with osteogenesis imperfecta: Genotype and phenotype spectra in 96 probands

BACKGROUND

Osteogenesis imperfecta (OI) is a rare connective-tissue disorder characterized by bone fragility. Approximately 90% of all OI cases are caused by variants in COL1A1 or COL1A2. Additionally, IFITM5 variants are responsible for the unique OI type 5. We previously analyzed COL1A1/2 variants in 22 Japanese families with OI through denaturing high-performance liquid chromatography screening, but our detection rate was low (41%).

METHODS

To expand the genotype-phenotype correlations, we performed a genetic analysis of COL1A1/2 and IFITM5 in 96 non-consanguineous Japanese OI probands by Sanger sequencing.

RESULTS

Of these individuals, 54, 41, and 1 had type 1 (mild), type 2-4 (moderate-to-severe), and type 5 phenotypes, respectively. In the mild group, COL1A1 nonsense and splice-site variants were prevalent (n = 30 and 20, respectively), but there were also COL1A1 and COL1A2 triple-helical glycine substitutions (n = 2 and 1, respectively). In the moderate-to-severe group, although COL1A1 and COL1A2 glycine substitutions were common (n = 14 and 18, respectively), other variants were also detected. The single case of type 5 had the characteristic c.-14C>T variant in IFITM5.

CONCLUSION

These results increase our previous detection rate for COL1A1/2 variants to 99% and provide insight into the genotype-phenotype correlations in OI.

Osteogenesis imperfecta and combined orthodontics and orthognathic surgery: a case report on two siblings

Osteogenesis imperfecta is a heterogeneous group of connective tissue diseases that is predominantly characterized by bone fragility and skeletal deformity. Two siblings with undiagnosed type I osteogenesis imperfecta underwent orthognathic surgery for the treatment of facial asymmetry and mandibular prognathism. The authors report two cases of combined orthodontics and orthognathic surgery in patients with type I osteogenesis imperfecta, mandibular prognathism, and facial asymmetry.

An in vitro model to evaluate the properties of matrices produced by fibroblasts from osteogenesis imperfecta and Ehlers-Danlos Syndrome patients

AIM OF THE STUDY

Osteogenesis imperfecta and Ehlers Danlos syndrome are hereditary disorders caused primarily by defective collagen regulation. Osteogenesis imperfecta patients were divided to haploinsufficient and dominant negative depending on the effect of COL1A1 and COL1A2 mutations whereas Ehlers Danlos syndrome patients had a mutation in PLOD1. Although collagen abnormalities have been extensively studied in monolayer cultures, there are no reports about 3D in vitro models which may reflect more accurately the dynamic cell environment. This is the first study presenting the structural and mechanical characterization of a 3D cell-secreted model using primary patient fibroblasts.

MATERIALS AND METHODS

Fibroblasts from patients with osteogenesis imperfecta and Ehlers Danlos syndrome were cultured with ascorbic acid for 5 weeks. The effect of mutations on cytosolic and secreted collagen was tested by electrophoresis following incubation with radiolabeled ¹⁴C proline. Extracellular matrix was studied in terms of collagen fiber orientation, stiffness, as well as glycosaminoglycan and collagen content.

RESULTS AND CONCLUSIONS

Osteogenesis imperfecta patients with haploinsufficient mutations had higher percentage of anisotropic collagen fibers alignment compared to other patient groups; all patients had a lower percentage of anisotropic samples compared to healthy controls. This correlated with higher average stiffness in the control group. Glycosaminoglycan content was lower in the control and haploinsufficient groups. In cells with PLOD1 mutations, there were no differences in PLOD2 expression. This proof of concept study was able to show differences in collagen fiber orientation between different patient groups which can potentially pave the way towards the development of 3D models aiming at improved investigation of disease mechanisms.

COL1-related overlap disorder: A novel connective tissue disorder incorporating the osteogenesis imperfecta/Ehlers-Danlos syndrome overlap

The 2017 classification of Ehlers-Danlos syndromes (EDS) identifies three types associated with causative variants in COL1A1/COL1A2 and distinct from osteogenesis imperfecta (OI). Previously, patients have been described with variable features of both disorders, and causative variants in COL1A1/COL1A2; but this phenotype has not been included in the current classification. Here, we expand and re-define this OI/EDS overlap as a missing EDS type. Twenty-one individuals from 13 families were reported, in whom COL1A1/COL1A2 variants were found after a suspicion of EDS. None of them could be classified as affected by OI or by any of the three recognized EDS variants associated with COL1A1/COL1A2. This phenotype is dominated by EDS-related features. OI-related features were limited to mildly reduced bone mass, occasional fractures and short stature. Eight COL1A1/COL1A2 variants were novel and five recurrent with a predominance of glycine substitutions affecting residues within the procollagen N-proteinase cleavage site of α1(I) and α2(I) procollagens. Selected variants were investigated by biochemical, ultrastructural and immunofluorescence studies. The pattern of observed changes in the dermis and in vitro for selected variants was more typical of EDS rather than OI. Our findings indicate the existence of a wider recognizable spectrum associated with COL1A1/COL1A2.

Osteogenesis imperfecta in Brazilian patients

Osteogenesis Imperfecta (OI) is a heterogeneous genetic disorder characterized by bone fragility and fracture. Mutations in 20 distinct genes can cause OI, and therefore, the genetic diagnosis of OI is frequently difficult to obtain because of the great number of genes that can be related with this disease. Studies that report the most frequently mutated genes in OI patients can help to improve molecular strategies for diagnosis of the disease. In order to characterize the mutation profile of OI in Brazilian patients, we analyzed 30 unrelated patients through SSCP screening, NGS gene panel, and/or Sanger sequencing for the 11 most frequently mutated genes in the database of mutations, including COL1A1, COL1A2, P3H1, CRTAP, PPIB, SERPINH1, SERPINF1, FKBP10, SP7, WNT1 and IFITM5. Disease-causing variants were identified in COL1A1, COL1A2, FKBP10, P3H1, and IFITM5. A total of 28 distinct mutations were identified, including seven novel changes. Our data show that the analysis of these five genes is able to detect at least 95% of causative mutations in OI disorder from Brazilian population. However, it has to be taken into considerations that distinct populations can have different frequencies of disease-causing variants. Hence, it is important to replicate this study in other groups.

Zebrafish and medaka as models for biomedical research of bone diseases

The identification of disease-causing mutations has in recent years progressed immensely due to whole genome sequencing approaches using patient material. The task accordingly is shifting from gene identification to functional analysis of putative disease-causing genes, preferably in an in vivo setting which also allows testing of drug candidates or biotherapeutics in whole animal disease models. In this review, we highlight the advances made in the field of bone diseases using small laboratory fish, focusing on zebrafish and medaka. We particularly highlight those human conditions where teleost models are available.

A Case of Osteogenesis Imperfecta Type II With Additional Balanced Translocation t(1;20)(p13;p11.2)

BACKGROUND

Osteogenesis imperfect (OI) type II is a genetic disorder of bone characterized by bone fragility, multiple fractures, severe bowing and shortening of long bones, and perinatal death due to respiratory insufficiency. It is mainly caused by mutations in the COL1A1 or COL1A2 genes, inherited in an autosomal dominant manner.

CASE REPORT

A fetal form of this disorder that included brachydactyly, macrocephaly, frontal bossing, soft calvarium, saddle nose, micrognathia, low set ears, and narrow thoracic cavity is described. A postmortem skeletal survey revealed multiple fractures, unossified skull, and long crumpled bones. The fetal karyotype revealed a balanced translocation t(1;20)(p13;p11.2). DNA sequencing detected a c.3065G > T transversion in exon 42 of the COL1A1 gene, a mutation associated with OI type II.

CONCLUSION

Although the balanced translocation t(1:20)(p13;p11.2) appears to be incidental in our case, identification of the specific mutation and translocation is important for estimation of genetic risk for another afflicted child.

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 Due to Combined Heterozygous Mutations in Both COL1A1 and COL1A2, Coexisting With Pituitary Stalk Interruption Syndrome

Osteogenesis imperfecta (OI) is a hereditary connective tissue disorder, characterized by reduced bone content, fractures and skeletal malformation due to abnormal synthesis or dysfunction of type I collagen protein. Pituitary stalk interruption syndrome (PSIS) is usually associated with environmental and hereditary factors. Here, we report a rare case of OI and PSIS co-occurrence. A 19-year-old male patient sought treatment for growth delay and absent secondary sexual characteristics. Hormone measurements indicated the presence of hypopituitarism (secondary hypothyroidism, growth hormone deficiency, ACTH-cortisol hormone deficiency, hypogonadotropic hypogonadism). Pituitary magnetic resonance imaging indicated reduced morphology of the anterior lobe, absence of the pituitary stalk, and ectopic displacement of the posterior lobe to the infundibulum, supporting a diagnosis of PSIS. In addition, the patient, his monozygotic twin brother (no evidence of PSIS), and their mother all presented blue sclera and susceptibility to bone fractures before adulthood. Next-generation sequencing demonstrated that the family had compound heterozygous mutations in COL1A1 and COL1A2, with no known mutations related to PSIS, pituitary hormone deficiency (PHD), or holoprosencephaly (HPE). The mother experienced breech and natural delivery of the patient and his brother, respectively. Thus, we deduced that the patient's PSIS might have resulted from breech delivery. Although we cannot exclude the possibility that the proband might have an undetected genetic abnormality causing PSIS or increasing his susceptibility to damage to the hypothalamic-pituitary region due to the limitation of exome sequencing, this rare case suggests that breech delivery in the newborn with OI might be related to PSIS.

Special form of osteoporosis in a 53-year-old man

Male osteoporosis often remains unrecognised. Osteoporotic fractures occur approximately 10 years later in men than in women due to higher peak bone mass. However, 30% of all hip fractures occur in men. Risk factors of osteoporotic fractures can be grouped into primary and secondary causes. We present the case of a 53-year-old man, who suffered a compression fracture of a lumbar vertebra after a generalised seizure and an atraumatic rib fracture 5 months later. We could exclude secondary causes of bone mineral loss such as primary hyperparathyroidism, glucocorticoid use and hypogonadism. However, a heterozygous missense mutation of the COL1A1 gene in exon 48 in further search of a secondary cause was found. Therapy was changed from bisphosphonate treatment to teriparatide. Considering the lack of other osteogenesis imperfecta (OI) symptoms and signs, the patient's illness can be classified as mild. OI should be considered as differential diagnosis in unexplained cases with osteoporosis.

Responsiveness to pamidronate treatment is not related to the genotype of type I collagen in patients with osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a heritable disorder characterized by increased bone fragility, low bone mass, dentinogenesis imperfecta, and blue sclerae. Most patients with OI have a mutation in either COL1A1 or COL1A2, which encode type I collagen. We screened these genes in Japanese patients with OI and compared their genotype and phenotype, focusing on the clinical response to treatment with pamidronate. Sequencing analysis of the genes in 19 families revealed 15 mutations, of which ten were missense mutations, thee were nonsense mutations, and two were frameshift mutations. Each of the 15 mutations was found in unrelated families, even though the patients were from a contiguous region surrounding our hospital. Substitutions of serine for glycine were the commonest mutation in both genes; notably, dentinogenesis imperfecta and fractures at birth were detected with higher frequencies in patients with this substitution when compared with other genotypes. The Z score of the bone mineral density of patients with this substitution was also lower than that of patients with other genotypes. Pamidronate treatment significantly increased the Z score in all patients, and increases in the Z score did not correlate with the OI types, causative genes, or genotype. In conclusion, the efficacy of pamidronate treatment does not seem to be related to the genotype of type I collagen in patients with OI.

Adults with osteogenesis imperfecta: Clinical characteristics of 151 patients with a focus on bisphosphonate use and bone density measurements

An expert center for adults with Osteogenesis Imperfecta (OI) has been founded at the Isala Hospital in Zwolle, the Netherlands to achieve optimal care for adults with OI. Clinical data such as patient history, Dual Energy X-ray Absorptiometry measurements and laboratory findings are collected with patient consent. This study provides an overview of clinical characteristics of the patients who visited the clinic during its first 5 years, a total of 151 patients. In this study, we focus on bisphosphonate use and bone density measurements at time of presentation at the expert center. As such, insight into the natural history of OI in adults will be increased. Analysing the data of a large group of adults with this rare disorder within a national expert center will allow detailed exploration of the course of OI over time.

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The reported cohort of 151 adult individuals with OI is one of the largest adult cohorts described in the literature.

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45/145 patients (31%) had a 25OH-vitamin D levels <50 nm/L. Only a small group reported calcium and vitamin D use.

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Men with OI type 1 aged <50 years had significantly lower Z-scores of the lumbar spine compared to women.

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T- and Z-scores were lower when measured at the LS compared to PF in type 1 and 4 OI patients.

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BP use was variable; of OI type 1, 3 and 4 patients respectively 46.7%, 27.8% and 59.1% had never used BP.

Temporomandibular disorders and psychosocial status in osteogenesis imperfecta - a cross-sectional study

Background

Osteogenesis Imperfecta (OI) is characterized by a number of deviations in the orofacial region. The aims of the present study were to investigate the occurrence of temporomandibular disorders, to evaluate the psychosocial status, and to assess the dental occlusion in a population of adult OI patients.

Methods

Participants (n = 75) were classified with mild OI, type I (n = 56), or moderate-severe OI, type III and IV (n = 19). OI patients were examined according to the Research Diagnostic Criteria for Temporomandibular Disorders (axis I and II).

Results

Temporomandibular disorders and functional limitations in the orofacial region were rare and did not differ between patients with mild and moderate-severe OI (P > 0.050). No significant differences between Graded Chronic Pain Scale grades 0, 1, and 2 were found in mild OI vs. moderate-severe OI (P > 0.160). Few patients (16%) had signs of depression, but close to half (48%) had signs of somatization. Patients with moderate-severe OI had a lower mean number of teeth compared to patients with mild OI (P <  0.050). In general, malocclusions were prevalent, and mandibular overjet and posterior cross-bite were found more often in moderate-severe OI compared with mild (P <  0.050).

Conclusions

Patients with moderate-severe OI had more malocclusions than patients with mild OI. The psychosocial status of OI patients was remarkably healthy considering the severity of this disabling systemic disorder. The bodily pain complaints frequently reported in OI patients were not largely reflected in the orofacial area as painful temporomandibular disorders.

Confirmation of the pathogenicity of a mutation p.G337C in the COL1A2 gene associated with osteogenesis imperfecta

Mutation analysis as the gold standard is particularly important in diagnosis of osteogenesis imperfecta (OI) and it may be preventable upon early diagnosis. In this study, we aimed to analyze the clinical and genetic materials of an OI pedigree as well as to confirm the deleterious property of the mutation.A pedigree with OI was identified. All family members received careful clinical examinations and blood was drawn for genetic analyses. Genes implicated in OI were screened for mutation. The function and structure of the mutant protein were predicted using bioinformatics analysis.The proband, a 9-month fetus, showed abnormal sonographic images. Disproportionately short and triangular face with blue sclera was noticed at birth. She can barely walk and suffered multiple fractures till 2-year old. Her mother appeared small stature, frequent fractures, blue sclera, and deformity of extremities. A heterozygous missense mutation c.1009G>T (p.G337C) in the COL1A2 gene was identified in her mother and her. Bioinformatics analysis showed p.G337 was well-conserved among multiple species and the mutation probably changed the structure and damaged the function of collagen.We suggest that the mutation p.G337C in the COL1A2 gene is pathogenic for OI by affecting the protein structure and the function of collagen.

Next-Generation Sequencing Reveals One Novel Missense Mutation in COL1A2 Gene in an Iranian Family with Osteogenesis imperfecta

BAckground

Osteogenesis imperfecta (OI) is a clinically and genetically heterogeneous disorder characterized by bone loss and bone fragility. The aim of this study was to investigate the variants of three genes involved in the pathogenesis of OI.

Methods

Molecular genetic analyses were performed for COL1A1, COL1A2, and CRTAP genes in an Iranian family with OI. The DNA samples were analyzed by next-generation sequencing (NGS) gene panel and Sanger sequencing.

Results

Five different variants were identified in COL1A1 and COL1A2, including two variants in COL1A1 and three variants in COL1A2. Among the five causative COL1A1 and COL1A2 variants, one novel variants, c.1081 G>A, was found in COL1A2, which was identified in two siblings.

Conclusion

Our finding extends the variant spectrum of the COL1A2 gene and has important implications for genetic counseling of families. The NGS is a powerful molecular diagnostic strategy for OI, a heterogeneous disorder.

Osteogenesis imperfecta: new genes reveal novel mechanisms in bone dysplasia

Osteogenesis imperfecta (OI) is a skeletal dysplasia characterized by fragile bones and short stature and known for its clinical and genetic heterogeneity which is now understood as a collagen-related disorder. During the last decade, research has made remarkable progress in identifying new OI-causing genes and beginning to understand the intertwined molecular and biochemical mechanisms of their gene products. Most cases of OI have dominant inheritance. Each new gene for recessive OI, and a recently identified gene for X-linked OI, has shed new light on its (often previously unsuspected) function in bone biology. Here, we summarize the literature that has contributed to our current understanding of the pathogenesis of OI.

DNA sequence analysis in 598 individuals with a clinical diagnosis of osteogenesis imperfecta: diagnostic yield and mutation spectrum

We detected disease-causing mutations in 585 of 598 individuals (98 %) with typical features of osteogenesis imperfecta (OI). In mild OI, only collagen type I encoding genes were involved. In moderate to severe OI, mutations in 12 different genes were found; 11 % of these patients had mutations in recessive genes.

INTRODUCTION

OI is usually caused by mutations in COL1A1 or COL1A2, the genes encoding collagen type I alpha chains, but mutations in at least 16 other genes have also been associated with OI. It is presently unknown what proportion of individuals with clinical features of OI has a disease-causing mutation in one of these genes.

METHODS

DNA sequence analysis was performed on 598 individuals from 487 families who had a typical OI phenotype. OI type I was diagnosed in 43 % of individuals, and 57 % had moderate to severe OI, defined as OI types other than type I.

RESULTS

Disease-causing variants were detected in 97 % of individuals with OI type I and in 99 % of patients with moderate to severe OI. All mutations found in OI type I were dominant and exclusively affected COL1A1 or COL1A2. In moderate to severe OI, dominant mutations were found in COL1A1/COL1A2 (77 %), IFITM5 (9 %), and P4HB (0.6 %). Mutations in one of the recessive OI-associated gene were observed in 12 % of individuals with moderate to severe OI. The genes most frequently involved in recessive OI were SERPINF1 (4.0 % of individuals with moderate to severe OI) and CRTAP (2.9 %).

CONCLUSIONS

DNA sequence analysis of currently known OI-associated genes identifies disease-causing variants in almost all individuals with a typical OI phenotype. About 20 % of individuals with moderate to severe OI had mutations in genes other than COL1A1/COL1A2.

Molecular Mechanisms of Stress-Responsive Changes in Collagen and Elastin Networks in Skin

Collagen and elastin networks make up the majority of the extracellular matrix in many organs, such as the skin. The mechanisms which are involved in the maintenance of homeostatic equilibrium of these networks are numerous, involving the regulation of genetic expression, growth factor secretion, signalling pathways, secondary messaging systems, and ion channel activity. However, many factors are capable of disrupting these pathways, which leads to an imbalance of homeostatic equilibrium. Ultimately, this leads to changes in the physical nature of skin, both functionally and cosmetically. Although various factors have been identified, including carcinogenesis, ultraviolet exposure, and mechanical stretching of skin, it was discovered that many of them affect similar components of regulatory pathways, such as fibroblasts, lysyl oxidase, and fibronectin. Additionally, it was discovered that the various regulatory pathways intersect with each other at various stages instead of working independently of each other. This review paper proposes a model which elucidates how these molecular pathways intersect with one another, and how various internal and external factors can disrupt these pathways, ultimately leading to a disruption in collagen and elastin networks.

Next-generation sequencing of common osteogenesis imperfecta-related genes in clinical practice

Next generation sequencing (NGS) is a rapidly developing area in genetics. Utilizing this technology in the management of disorders with complex genetic background and not recurrent mutation hot spots can be extremely useful. In this study, we applied NGS, namely semiconductor sequencing to determine the most significant osteogenesis imperfecta-related genetic variants in the clinical practice. We selected genes coding collagen type I alpha-1 and-2 (COL1A1, COL1A2) which are responsible for more than 90% of all cases. CRTAP and LEPRE1/P3H1 genes involved in the background of the recessive forms with relatively high frequency (type VII and VIII) represent less than 10% of the disease. In our six patients (1–41 years), we identified 23 different variants. We found a total of 14 single nucleotide variants (SNV) in COL1A1 and COL1A2, 5 in CRTAP and 4 in LEPRE1. Two novel and two already well-established pathogenic SNVs have been identified. Among the newly recognized mutations, one results in an amino acid change and one of them is a stop codon. We have shown that a new full-scale cost-effective NGS method can be developed and utilized to supplement diagnostic process of osteogenesis imperfecta with molecular genetic data in clinical practice.

Decreased fracture rate, pharmacogenetics and BMD response in 79 Swedish children with osteogenesis imperfecta types I, III and IV treated with Pamidronate

BACKGROUND

Osteogenesis imperfecta (OI) is an inherited heterogeneous bone fragility disorder, usually caused by collagen I mutations. It is well established that bisphosphonate treatment increases lumbar spine (LS) bone mineral density (BMD), as well as improves vertebral geometry in severe OI; however, fracture reduction has been difficult to prove, pharmacogenetic studies are scarce, and it is not known at which age, or severity of disease, treatment should be initiated.

MATERIALS AND METHODS

COL1A1 and COL1A2 were analyzed in 79 children with OI (type I n=33, type III n=25 and type IV n=21) treated with Pamidronate. Data on LS BMD, height, and radiologically confirmed non-vertebral and vertebral fractures were collected prior to, and at several time points during treatment.

RESULTS

An increase in LS BMD Z-score was observed for all types of OI, and a negative correlation to Δ LS BMD was observed for both age and LS BMD Z-score at treatment initiation. Supine height Z-scores were not affected by Pamidronate treatment, The fracture rate was reduced for all OI types at all time points during treatment (overall p<0.0003, <0.0001 and 0.0003 for all OI types I, III and IV respectively). The reduced fracture rate was maintained for types I and IV, while an additional decrease was observed over time for type III. The fracture rate was reduced also in individuals with continued low BMD after >4yrs Pamidronate. Twice as many boys as girls with OI type I were treated with Pamidronate, and the fracture rate the year prior treatment was 2.2 times higher for boys (p=0.0236). Greater Δ LS BMD, but smaller Δ fracture numbers were observed on Pamidronate for helical glycine mutations in COL1A1 vs. COL1A2. Vertebral compression fractures did not progress in any individual during treatment; however, they did not improve in 9%, and these individuals were all >11years of age at treatment initiation (p<0.0001).

CONCLUSION

Pamidronate treatment in children with all types of OI increased LS BMD, decreased fracture rate, and improved vertebral compression fractures. Fracture reduction was prompt and maintained during treatment, irrespective of age at treatment initiation and collagen I mutation type.

Osteogenesis Imperfecta Diagnosed from Mandibular and Lower Limb Fractures: A Case Report

Osteogenesis imperfecta (OI) is a congenital disease characterized by bone fragility and low bone mass. Despite the variety of its manifestation and severity, facial fractures occur very infrequently. Here, we report a case of an infant diagnosed with OI after mandibular and lower limb fractures. A boy aged 1 year and 3 months was brought to his neighboring hospital with a complaint of facial injury. He was transferred to our hospital to undergo operation 3 days later. Computed tomography images revealed multiple mandibular fractures including complete fracture in the symphysis and dislocated condylar fracture on the right side. Open reduction and internal fixation with absorbable implants was performed 7 days after injury. He fractured his right lower limb 2 months later. He was diagnosed with OI type IA by an orthopedist. He will be administered bone-modifying agents if he suffers from frequent fractures.

Mutations in COL1A1 Gene Change Dentin Nanostructure

Although many studies have attempted to associate specific gene mutations with dentin phenotypic severity, it remains unknown how the mutations in COL1A1 gene influence the mechanical behavior of dentin collagen and matrix. Here, we reported one osteogenesis imperfecta (OI) pedigree caused by two new inserting mutations in exon 5 of COL1A1 (NM_000088.3:c.440_441insT;c.441_442insA), which resulted in the unstable expression of COL1A1 mRNA and half quantity of procollagen production. We investigated the morphological and mechanical features of proband's dentin using atomic force microscope (AFM), scanning electron microscope, and transmission electron microscope. Increased D-periodic spacing, variably enlarged collagen fibrils coating with fewer minerals were found in the mutated collagen. AFM analysis demonstrated rougher dentin surface and sparsely decreased Young's modulus in proband's dentin. We believe that our findings provide new insights into the genetic-/nano- mechanisms of dentin diseases, and may well explain OI dentin features with reduced mechanical strength and a lower crosslinked density.

Structure-mechanics relationships of collagen fibrils in the osteogenesis imperfecta mouse model

The collagen molecule, which is the building block of collagen fibrils, is a triple helix of two α1(I) chains and one α2(I) chain. However, in the severe mouse model of osteogenesis imperfecta (OIM), deletion of the COL1A2 gene results in the substitution of the α2(I) chain by one α1(I) chain. As this substitution severely impairs the structure and mechanics of collagen-rich tissues at the tissue and organ level, the main aim of this study was to investigate how the structure and mechanics are altered in OIM collagen fibrils. Comparing results from atomic force microscopy imaging and cantilever-based nanoindentation on collagen fibrils from OIM and wild-type (WT) animals, we found a 33% lower indentation modulus in OIM when air-dried (bound water present) and an almost fivefold higher indentation modulus in OIM collagen fibrils when fully hydrated (bound and unbound water present) in phosphate-buffered saline solution (PBS) compared with WT collagen fibrils. These mechanical changes were accompanied by an impaired swelling upon hydration within PBS. Our experimental and atomistic simulation results show how the structure and mechanics are altered at the individual collagen fibril level as a result of collagen gene mutation in OIM. We envisage that the combination of experimental and modelling approaches could allow mechanical phenotyping at the collagen fibril level of virtually any alteration of collagen structure or chemistry.

Genetic epidemiology, prevalence, and genotype-phenotype correlations in the Swedish population with osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a rare hereditary bone fragility disorder, caused by collagen I mutations in 90% of cases. There are no comprehensive genotype-phenotype studies on >100 families outside North America, and no population-based studies determining the genetic epidemiology of OI. Here, detailed clinical phenotypes were recorded, and the COL1A1 and COL1A2 genes were analyzed in 164 Swedish OI families (223 individuals). Averages for bone mineral density (BMD), height and yearly fracture rate were calculated and related to OI and mutation type. N-terminal helical mutations in both the α1- and α2-chains were associated with the absence of dentinogenesis imperfecta (P<0.0001 vs 0.0049), while only those in the α1-chain were associated with blue sclera (P=0.0110). Comparing glycine with serine substitutions, α1-alterations were associated with more severe phenotype (P=0.0031). Individuals with type I OI caused by qualitative vs quantitative mutations were shorter (P<0.0001), but did not differ considering fractures or BMD. The children in this cohort were estimated to represent >95% of the complete Swedish pediatric OI population. The prevalence of OI types I, III, and IV was 5.16, 0.89, and 1.35/100 000, respectively (7.40/100 000 overall), corresponding to what has been estimated but not unequivocally proven in any population. Collagen I mutation analysis was performed in the family of 97% of known cases, with causative mutations found in 87%. Qualitative mutations caused 32% of OI type I. The data reported here may be helpful to predict phenotype, and describes for the first time the genetic epidemiology in >95% of an entire OI population.

Interferon-Induced Transmembrane Protein 5 Mutation Causing Type-V Osteogenesis Imperfecta: A Case Report

CASE

We report a case of heterozygous mutation of c.-14C>T in the 5'-untranslated region of the interferon-induced transmembrane protein 5 in a nine-year-old girl. She was diagnosed with type-V osteogenesis imperfecta based on the classic features of bone fragility, radial head dislocation, forearm interosseous membrane calcification, limited forearm rotation, hyperplastic callus formation, and radiodense metaphyseal bands, as well as absent blue sclerae, absence of hearing loss, and absence of dentinogenesis imperfecta.

CONCLUSION

Although the differential diagnosis may include infantile cortical hypertrophy, child abuse, or a malignant tumor (e.g., osteosarcoma), the presence of typical clinical and radiographic features and characteristic gene mutation helps confirm the diagnosis of type-V osteogenesis imperfecta.

The collagenopathies: review of clinical phenotypes and molecular correlations

Genetic defects of collagen formation (the collagenopathies) affect almost every organ system and tissue in the body. They can be grouped by clinical phenotype, which usually correlates with the tissue distribution of the affected collagen subtype. Many of these conditions present in childhood; however, milder phenotypes presenting in adulthood are increasingly recognized. Many are difficult to differentiate clinically. Precise diagnosis by means of genetic testing assists in providing prognosis information, family counseling, and individualized treatment. This review provides an overview of the current range of clinical presentations associated with collagen defects, and the molecular mechanisms important to understanding how the results of genetic testing affect medical care.

Nonsense-mediated decay in genetic disease: friend or foe?

Eukaryotic cells utilize various RNA quality control mechanisms to ensure high fidelity of gene expression, thus protecting against the accumulation of nonfunctional RNA and the subsequent production of abnormal peptides. Messenger RNAs (mRNAs) are largely responsible for protein production, and mRNA quality control is particularly important for protecting the cell against the downstream effects of genetic mutations. Nonsense-mediated decay (NMD) is an evolutionarily conserved mRNA quality control system in all eukaryotes that degrades transcripts containing premature termination codons (PTCs). By degrading these aberrant transcripts, NMD acts to prevent the production of truncated proteins that could otherwise harm the cell through various insults, such as dominant negative effects or the ER stress response. Although NMD functions to protect the cell against the deleterious effects of aberrant mRNA, there is a growing body of evidence that mutation-, codon-, gene-, cell-, and tissue-specific differences in NMD efficiency can alter the underlying pathology of genetic disease. In addition, the protective role that NMD plays in genetic disease can undermine current therapeutic strategies aimed at increasing the production of full-length functional protein from genes harboring nonsense mutations. Here, we review the normal function of this RNA surveillance pathway and how it is regulated, provide current evidence for the role that it plays in modulating genetic disease phenotypes, and how NMD can be used as a therapeutic target.

Osteogenesis imperfecta type I: A case report

A 15-year-old male patient was admitted to hospital having experienced repeated fractures over the previous three years, predominantly due to falling down or overexertion. The clinical signs and radiological features, such as recurrent fractures, blue sclera and low bone mineral density (BMD) level, all led to the diagnosis of a mild form of osteogenesis imperfecta (OI) type I. The patient began treatment with a regular intake of calcium (1,000 mg/day), an adequate intake of vitamin D (800 U/day) and intravenous pamidronate (60 mg). Following four months of treatment, the symptoms and quality of life of the patient improved. This patient appears to be a rare case of OI type I.

A novel mild variant of osteogenesis imperfecta type I caused by a Gly1088Glu mutation in COL1A1

Osteogenesis imperfecta (OI), also known as brittle bone disease, characterized by multiplicative osteopsathyrosis, blue sclera, dentinogenesis imperfecta and mild audition, is a rare inherited connective tissue disease. There are seven types of OI, I to VII, among which type I-IV are relatively common and associated with type I collagen. Defects in type I collagen synthesis or structure are responsible for the majority of clinical OI cases since collagen is the major matrix protein of all connective tissues. Type I collagen consists of two pro-α1 chains and one pro-α2 chain, which are encoded by two genes, COL1A1 and COL1A2, respectively. The two subunits have a Gly-X-Y repeat domain, of which glycine is highly conserved in the majority of species. Point mutations on these sites appear to trigger OI. In the current study, a heterozygous mutation, c.3263G>A, p.Gly1088Glu, was identified in the Gly-X-Y domain of type I collagen in an affected individual with type I OI. A lethal phenotype with the p.Gly1088Ala mutation was observed at the same site as the current findings. This suggests that variant characteristics of the substitution for Gly may trigger a varying degree of OI from lethal to mild, even when the mutation occurs at the same site. It is hypothesized that the study may provide insight into the phenotype-genotype association and may assist, not only in the clinical diagnosis, but also in investigating the mechanism of collagen-associated diseases.

Mineral particle size in children with osteogenesis imperfecta type I is not increased independently of specific collagen mutations

Osteogenesis imperfecta (OI) type I represents the mildest form of OI and is usually caused by two classes of autosomal dominant mutations in collagen type I: haploinsufficiency leading to a reduced quantity of structurally normal collagen (quantitative mutation), or sequence abnormalities generating structurally aberrant collagen chains (qualitative mutation). An abnormally high bone matrix mineralization has been observed in all OI cases investigated so far, independently of mutation type. This raises the question whether the increased amount of mineral is due to mineral particles growing to larger sizes or to a higher number of more densely packed particles. For this reason, we revisit the problem by investigating the mineral particle size in cancellous bone from two subsets of the previously analyzed biopsies (patient's age: 2-4.2 and 7.6-11years) comparing OI quantitative mutations (n=5), OI qualitative mutations (n=5) and controls (n=6). We used a combined small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) setup with a beam diameter of 10μm of synchrotron radiation, which allows the determination of mineral particle characteristics in 10μm thick sections at the same positions where the matrix mineralization density was previously determined. The thickness parameter of mineral particles (T) was obtained from SAXS data and the mineral volume fraction was calculated from the mean calcium content of the bone matrix determined by quantitative back-scattered electron imaging (qBEI). The combination of these two quantities allowed calculating the true particle width (W) of the plate-like mineral crystals. T was larger in the older than in the younger age-group independently of genotype (p<0.004) and was larger in the controls than in each OI group. The qBEI results showed that the mineral volume fraction increased from 32.45wt.% in controls to 36.44wt.% in both OI groups (corresponding to a 12% increase in relative terms). Combining these data, we find that also W was larger in the older than in the younger age-group (p<0.002), but stayed equal or smaller in both OI genotypes (controls: 2.3nm±0.04, OI qualitative: 2.2±0.05; OI quantitative 2.3±0.04, mean±SEM). A linear regression analysis even suggests a slower increase of W in qualitative OI as compared to quantitative OI and controls, where the particle sizes stayed similar at all ages. We thus conclude that the high mineral density in human OI is not due to increased particle size but rather to increased particle packing density. The lack of an observed difference between the two classes of mutations suggests the occurrence of a bone cell defect downstream of the collagen mutation.

Copper deficiency in patients with cystinosis with cysteamine toxicity

OBJECTIVES

To assess whether copper deficiency plays a role in the recently described cysteamine toxicity in patients with cystinosis, and to examine whether polymorphisms in copper transporters, lysyl oxidase, and/or type I procollagen genes could be responsible for the occurrence of cysteamine toxicity in a small subset of patients with cystinosis.

STUDY DESIGN

Thirty-six patients with cystinosis were included: 22 with Fanconi syndrome (including 7 with cysteamine toxicity), 12 after renal transplantation, 1 receiving hemodialysis, and 1 with ocular cystinosis. Serum copper and ceruloplasmin levels and urinary copper/creatinine ratio were measured. Genes ATP7A and CTR1 (encoding copper transporters), LOX (encoding lysyl oxidase), and COL1A1 and COL1A2 (encoding type I procollagen) were analyzed in patients with (n = 6) and without (n = 5) toxicity. Fibroblast (pro)collagen synthesis was compared in patients with (n = 3) and those without (n = 2) cysteamine toxicity.

RESULTS

All 22 patients with Fanconi syndrome had increased urinary copper excretion. Serum copper and ceruloplasmin levels were decreased in 9 patients, including all 7 patients with cysteamine toxicity. No specific sequence variations were associated with toxicity. All fibroblasts exhibited normal (pro)collagen synthesis.

CONCLUSION

Patients with cystinosis with cysteamine toxicity demonstrate copper deficiency. This can cause decreased activity of lysyl oxidase, the enzyme that generates the aldehydes required for collagen cross-linking. Thus, copper supplementation might prevent cysteamine toxicity.

Skeletal clinical characteristics of osteogenesis imperfecta caused by haploinsufficiency mutations in COL1A1

COL1A1 haploinsufficiency mutations lead to the mildest form of osteogenesis imperfecta (OI), OI type I. The skeletal clinical characteristics resulting from such mutations have not been characterized in detail. In this study we assessed 86 patients (36 male, 50 female; mean age 13.3 years; range, 0.6 to 54 years) with COL1A1 haploinsufficiency mutations, of whom 70 were aged 21 years or less ("pediatric" patients). Birth history was positive for fracture or long-bone deformity in 12% of patients. The average rate of long-bone fracture (femur, tibia/fibula, humerus, radius/ulna) in pediatric patients was 0.62 fractures per year, one-half of which affected the tibia/fibula. Long-bone fracture rate was negatively associated with age and lumbar spine areal bone mineral density. Vertebral compression fractures were observed in 71% of the 58 pediatric patients who had lateral spine radiographs. The median number of vertebral fractures was higher for females (median 4; range, 0 to 14) than for males (median 1; range, 0 to 8) (p = 0.03). Lumbar spine areal bone mineral density was negatively associated with the severity of vertebral compression fractures, as reflected in the spine deformity index. Scoliosis was present in about 30% of pediatric patients but the Cobb angle was <30 degrees in all cases. The average final height Z-score was -1.1, representing a deficit of 8 to 10 cm compared to the general population. In summary, OI patients with COL1A1 haploinsufficiency mutations have high rates of significant skeletal involvement. Systematic follow-up of growing patients with COL1A1 haploinsufficiency mutations including radiographic screening for vertebral compression fractures and scoliosis is warranted.

Osteogenesis imperfecta type I: second-trimester diagnosis and incidental identification of a dominant COL1A1 deletion mutation in the paucisymptomatic father

OBJECTIVE

To present second-trimester ultrasound and molecular diagnosis for osteogenesis imperfecta (OI) type I in a female fetus and incidental identification of a dominant COL1A1 deletion mutation in her paucisymptomatic father.

CASE REPORT

A 30-year-old, primigravid woman was referred for genetic counseling in the second trimester because of bowing of the fetal lower limbs. She and her husband were non-consanguineous, and there was no family history of skeletal dysplasias. Prenatal ultrasound at 22 weeks of gestation revealed short and curved right femur and left tibia, and a short left fibula. The lengths of other long bones were normal. The husband was 158 cm tall, had blue sclerae, a history of habitual subluxation and dislocation of bilateral elbows and left knee, and an episode of left ulna fracture, and was not aware of his being affected with OI type I. The woman underwent amniocentesis. Cytogenetic analysis revealed a karyotype of 46,XX. Molecular analysis of the amniocytes revealed a heterozygous deletion mutation of c.1064_1068delCTGGT in exon 17 of the COL1A1 gene. By genetic testing the husband was found to carry the same mutation. Despite counseling of favorable outcome for OI type I with the parents, the woman elected to terminate the pregnancy. Postnatal skeletal X-ray findings were consistent with OI type I.

CONCLUSION

Prenatal ultrasound diagnosis of mild forms of OI should include molecular analysis of type I collagen genes in both fetus and parents. Molecular genetic analysis of the family may incidentally identify a collagen gene mutation in the paucisymptomatic affected parent.

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.

Osteogenesis Imperfecta: A Review with Clinical Examples

Osteogenesis imperfecta (OI) is characterized by susceptibility to bone fractures, with a severity ranging from subtle increase in fracture frequency to prenatal fractures. The first scientific description of OI dates from 1788. Since then, important milestones in OI research and treatment have, among others, been the classification of OI into 4 types (the 'Sillence classification'), the discovery of defects in collagen type I biosynthesis as a cause of most cases of OI and the use of bisphosphonate therapy. Furthermore, in the past 5 years, it has become clear that OI comprises a group of heterogeneous disorders, with an estimated 90% of cases due to a causative variant in the COL1A1 or COL1A2 genes and with the remaining 10% due to causative recessive variants in the 8 genes known so far, or in other currently unknown genes. This review aims to highlight the current knowledge around the history, epidemiology, pathogenesis, clinical/radiological features, management, and future prospects of OI. The text will be illustrated with clinical descriptions, including radiographs and, where possible, photographs of patients with OI.

A novel DHPLC-based procedure for the analysis of COL1A1 and COL1A2 mutations in osteogenesis imperfecta

Approximately 90% of patients with osteogenesis imperfecta (OI) exhibit dominant COL1A1 or COL1A2 mutations; however, molecular analysis is difficult because these genes span 51 and 52 exons, respectively. We devised a PCR-denaturing high-performance liquid chromatography (DHPLC) procedure to analyze the COL1A1 or COL1A2 coding regions and validated it using 130 DNA samples from individuals without OI, 25 DNA samples from two cells to investigate the procedure's potential for preimplantation diagnosis, and DNA samples from 10 patients with OI. Three novel intronic variants in vitro were expressed using a minigene assay to assess their effects on splicing. The procedure is rapid, inexpensive, and reproducible. Analysis of samples from individuals without OI revealed six novel and some known polymorphisms useful for linkage diagnosis because of high heterozygosity. Analysis of two-cell samples confirmed the known genotype in 24 of 25 experiments; DNA failed to amplify in only one case. No incidence of allele dropout was recorded. DHPLC revealed six novel mutations, three of which were intronic, in all patients with OI, and these results were confirmed by means of COL1A1 and COL1A2 direct sequencing. Expression of intronic mutations demonstrated that variant 804 + 2_804 + 3delTG in intron 11 disrupts normal splicing, thereby leading to formation of two alternative products. Variants c.3046-4_3046-5dupCT (COL1A1) and c.891 + 77A>T (COL1A2) did not affect splicing. The described DHPLC protocol combined with the minigene assay may contribute to molecular diagnosis in OI. Moreover, this protocol will aid in counseling about prenatal and preimplantation diagnosis.

EMQN best practice guidelines for the laboratory diagnosis of osteogenesis imperfecta

Osteogenesis imperfecta (OI) comprises a group of inherited disorders characterized by bone fragility and increased susceptibility to fractures. Historically, the laboratory confirmation of the diagnosis OI rested on cultured dermal fibroblasts to identify decreased or abnormal production of abnormal type I (pro)collagen molecules, measured by gel electrophoresis. With the discovery of COL1A1 and COL1A2 gene variants as a cause of OI, sequence analysis of these genes was added to the diagnostic process. Nowadays, OI is known to be genetically heterogeneous. About 90% of individuals with OI are heterozygous for causative variants in the COL1A1 and COL1A2 genes. The majority of remaining affected individuals have recessively inherited forms of OI with the causative variants in the more recently discovered genes CRTAP, FKBP10, LEPRE1,PLOD2, PPIB, SERPINF1, SERPINH1 and SP7, or in other yet undiscovered genes. These advances in the molecular genetic diagnosis of OI prompted us to develop new guidelines for molecular testing and reporting of results in which we take into account that testing is also used to ‘exclude' OI when there is suspicion of non-accidental injury. Diagnostic flow, methods and reporting scenarios were discussed during an international workshop with 17 clinicians and scientists from 11 countries and converged in these best practice guidelines for the laboratory diagnosis of OI.