Inter- and Intrafamilial Phenotypic Variability in Individuals with Collagen-Related Osteogenesis Imperfecta

Genetic Evaluation for Monogenic Disorders of Low Bone Mass and Increased Bone Fragility: What Clinicians Need to Know

PURPOSE OF REVIEW

The purpose of this review is to outline the principles of clinical genetic testing and to provide practical guidance to clinicians in navigating genetic testing for patients with suspected monogenic forms of osteoporosis.

RECENT FINDINGS

Heritability assessments and genome-wide association studies have clearly shown the significant contributions of genetic variations to the pathogenesis of osteoporosis. Currently, over 50 monogenic disorders that present primarily with low bone mass and increased risk of fractures have been described. The widespread availability of clinical genetic testing offers a valuable opportunity to correctly diagnose individuals with monogenic forms of osteoporosis, thus instituting appropriate surveillance and treatment. Clinical genetic testing may identify the appropriate diagnosis in a subset of patients with low bone mass, multiple or unusual fractures, and severe or early-onset osteoporosis, and thus clinicians should be aware of how to incorporate such testing into their clinical practices.

Caution with noninvasive prenatal screening for single gene disorders: A case report of a COL1A1 variant in osteogenesis imperfecta

What is already known?

What does this study add?

The IMPACT survey: a mixed methods study to understand the experience of children, adolescents and adults with osteogenesis imperfecta and their caregivers

BACKGROUND

Osteogenesis imperfecta (OI) is a rare, heritable connective tissue disorder associated with a variety of symptoms, that affect individuals' quality of life (QoL) and can be associated with increased healthcare resource use. While some aspects of OI are well studied, others remain poorly understood. Therefore, the IMPACT survey aimed to elucidate the humanistic, clinical and economic burden of OI on individuals with OI, their families, caregivers and wider society.

METHODS

We developed an international mixed methods online survey in eight languages (fielded July-September 2021), aimed at adults (aged ≥ 18 years) or adolescents (aged ≥ 12-17 years) with OI, caregivers (with or without OI) of individuals with OI and other close relatives. All respondents provided data on themselves; caregivers additionally provided data on individuals in their care by proxy. Data were cleaned, coded, and analysed using the pandas Python software package and Excel.

RESULTS

IMPACT collected 2208 eligible questionnaires (covering 2988 individuals of whom 2312 had OI) including 1290 non-caregiver adults with OI, 92 adolescents with OI, 150 caregiver adults with OI, 560 caregivers for individuals with OI, 116 close relatives and 780 proxy care-recipients with OI. Most individuals with OI (direct or proxy) described their OI as moderate (41-52% across populations) and reported OI type 1 (33-38%). Pain (72-82%) was the most reported clinical condition experienced in the past 12 months and was also most frequently rated as severely or moderately impactful. Further, among adults, 67% reported fatigue, 47% scoliosis, and 46% sleep disturbance; in adolescents, fatigue affected 65%, scoliosis and other bone problems 60%, and mental health problems 46%; in children, fractures were common in 67%, fatigue in 47%, and dental problems in 46%.

CONCLUSION

IMPACT has generated an extensive dataset on the experience of individuals with OI, their caregivers and relatives. We found that, irrespective of age, individuals with OI experience numerous and evolving symptoms that affect their QoL; however, pain and fatigue are consistently present. Upcoming analyses will provide further insights into the economic impact, healthcare journey and caregiver wellbeing, aiming to contribute to improved treatment and care for the OI community.

Osteogenesis imperfecta: a cross-sectional study of skeletal and extraskeletal features in a large cohort of Italian patients

Introduction

The present study aims to describe a large cohort of Italian patients affected by osteogenesis imperfecta, providing a picture of the clinical bony and non-bony features and the molecular background to improve knowledge of the disease to inform appropriate management in clinical practice.

Methods

A total of 568 subjects (from 446 unrelated Italian families) affected by osteogenesis imperfecta who received outpatient care at Istituto Ortopedico Rizzoli from 2006 to 2021 were considered in the present study.

Results

Skeletal and extraskeletal features were analyzed showing a lower height (mean z-scores equal to -1.54 for male patients and -1.47 for female patients) compared with the general Italian population. Half of the patient population showed one or more deformities, and most of the patients had suffered a relatively low number of fractures (<10). An alteration in the sclera color was identified in 447 patients. Similarly, several extraskeletal features, like deafness, dental abnormalities, and cardiac problems, were investigated. Additionally, inheritance and genetic background were evaluated, showing that most of the patients have a positive family history and the majority of pathogenic variants detected were on collagen genes, as per literature.

Conclusion

This study supports the definition of a clear picture of the heterogeneous clinical manifestations leading to variable severity in terms of skeletal and extra-skeletal traits and of the genetic background of an Italian population of osteogenesis imperfecta patients. In this perspective, this clearly highlights the crucial role of standardized and structured collection of high-quality data in disease registries particularly in rare disease scenarios, helping clinicians in disease monitoring and follow-up to improve clinical practice.

Novel pathogenic variants in SPARC as cause of osteogenesis imperfecta: Two case reports

Pathogenic variants in SPARC cause a rare autosomal recessive form of osteogenesis imperfecta (OI), classified as OI type XVII, which was first reported in 2015. Only six patient cases with this specific form of OI have been reported to date. The SPARC protein plays a crucial role in the calcification of collagen in bone, synthesis of the extracellular matrix, and the regulation of cell shape. In this case report, we describe the phenotype of two patients with SPARC-related OI, including a patient with two novel pathogenic variants in the SPARC gene. Targeted Next Generation Sequencing revealed new compound heterozygous variants (c.484G > A p.(Glu162Lys)) and c.496C > T p.(Arg166Cys)) in one patient and a homozygous nonsense pathogenic variant (c.145C > T p.(Gln49*)) in the other. In line with previously reported cases, the two OI patients presented delayed motor development, muscular weakness, scoliosis, and multiple fractures. Interestingly, our study reports for the first time the occurrence of dentinogenesis imperfecta. The study also reports the effectiveness of bisphosphonate treatment for OI type XVII. This article enhances the genetic, clinical, therapeutic, and radiological understanding of SPARC-related OI.

Preimplantation genetic testing for recurrent autosomal dominant osteogenesis imperfecta associated with paternal gonosomal mosaicism

Research Question: How to prevent the transfer of a mutation causing osteogenesis imperfecta (OI) to offspring in a couple with recurrent adverse pregnancy outcomes, when the male partner is a gonosomal mosaic carrier.

Design: High-throughput sequencing and first-generation DNA sequencing were performed using the tissues from an aborted fetus and its parents. Regions 2 Mb upstream and downstream of the COL1A1 gene were subjected to multiplex PCR to identify single nucleotide polymorphisms (SNPs) and family haplotypes associated with the disease-causing mutation. Single-cell whole-genome amplification and sequencing were performed on trophoblasts cultured in vitro for 5–6 days to construct embryonic SNP haplotypes, and first-generation sequencing was used for pathogenic locus verification and aneuploidy screening. Preimplantation genetic testing for monogenic disorders (PGT-M) was also performed.

Results: The aborted fetus was heterozygous for the COL1A1 mutation c.1454G>A (chr17-48272089, p.Gly485Asp) suspected to cause OI. The variant was also detected in the peripheral blood cells and sperm of the male partner, who appeared to be a gonosomal mosaic carrier of the mutation. Three morphologically usable blastocysts were obtained in vitro and successfully expanded after a trophectoderm biopsy. Two blastocysts were unusable owing to aneuploidy; however, one was euploid and did not carry the paternal mutation. Post-transfer gestation was confirmed by systematic B-scan ultrasound, and amniocentesis findings were consistent with the PGT-M results.

Conclusion: Parental gonadal mosaicism was the cause of recurrent terminated pregnancies due to fetal skeletal dysplasia. Using PGT-M to select embryos without the paternal pathogenic mutation prevented the vertical transmission of OI in this family, and a successful pregnancy was achieved.

Hub Genes and Long Noncoding RNAs That Regulates It Associated with the Prognosis of Esophageal Squamous Cell Carcinoma Based on Bioinformatics Analysis

Objective

Through bioinformatics analysis methods, the public databases GEO and TCGA were used to research mRNA and squamous cell carcinoma of the esophagus, construct a lncRNA-mRNA network, and screen hub genes and lncRNAs related to prognosis.

Method

Download esophageal squamous cell carcinoma-related mRNA and lncRNA datasets GEO and TCGA public datasets, as well as clinical data, use bioinformatic tools to perform gene differential expression analysis on the datasets to obtain differentially expressing mRNA (DEmRNA) and lncRNA (DElncRNA), and plot volcano plots and cluster heatmaps. The differential intersection of differentially expressed DEmRNA and DElncRNA was extracted by Venn diagram and imported into CytoScape software, a regulatory network visualization software, to construct a lncRNA-mRNA network and use cytoHubba and MCODE plug-ins to screen hub genes and key lncRNAs. The DEmRNA in the network was imported into the Gene and Protein Interaction Retrieval Database (STRING), gene-encoded protein-protein interactions (PPI) network maps were created, and the genes in the PPI network maps were submitted to GO functional annotation and pathway enrichment analysis using Kyoto Encyclopedia of Gene Genomes (KEGG) (KEGG). The link between hub gene and prognosis was studied using the clinical data collected by TCGA.

Result

Retrieve the datasets GSE23400 and GSE38129 from the GEO database and the esophageal squamous cell carcinoma-related mRNAs from TCGA databases and then obtain intersection. Differentially regulated genes revealed a correlation of 326 (up) with 191 (down) in terms of the differential intersection; for this study, we need to collect the GSE130078 dataset from GEO, as well as the lncRNAs from TCGA databases that are connected to esophageal squamous cell cancer. There were 184 differentially up- and downregulated genes in the differential intersection. A differential intersection network of the differential intersection lncRNA-mRNA network allowed us to identify the hub genes, including COL5A2 (COL3A1), COL1A1 (COL1A1), CTD-2171N6.1 (CTD-2171N6.1), and RP11-863P13.3 (RP11-863P13.3). The extracellular matrix, which is important in protein digestion and absorption, was shown to be the primary site of functional enrichment, as shown by GO/KEGG analysis. Squamous cell carcinoma of the mouth and throat is associated with a poor prognosis because of a change in the extracellular matrix structure caused by specific long noncoding RNA (lncRNA) regulatory upregulation.

Conclusion

For the purpose of predicting the prognosis of cancer of the esophagus, researchers studied the esophageal squamous cell carcinoma-related hub genes and important noncoding RNAs (ncRNAs).

Prenatal Cases Reflect the Complexity of the COL1A1/2 Associated Osteogenesis Imperfecta

Introduction: Osteogenesis imperfecta (OI) is a rare mendelian skeletal dysplasia with autosomal dominant or recessive inheritance pattern, and almost the most common primary osteoporosis in prenatal settings. The diversity of clinical presentation and genetic etiology in prenatal OI cases presents a challenge to counseling yet has seldom been discussed in previous studies. Methods: Ten cases with suspected fetal OI were enrolled and submitted to a genetic detection using conventional karyotyping, chromosomal microarray analysis (CMA), and whole-exome sequencing (WES). Sanger sequencing was used as the validation method for potential diagnostic variants. In silico analysis of specific missense variants was also performed. Results: The karyotyping and CMA results of these cases were normal, while WES identified OI-associated variants in the COL1A1/2 genes in all ten cases. Six of these variants were novel. Additionally, four cases here exhibited distinctive clinical and/or genetic characteristics, including the situations of intrafamilial phenotypic variability, parental mosaicism, and “dual nosogenesis” (mutations in collagen I and another gene). Conclusion: Our study not only expands the spectrum of COL1A1/2-related OI, but also highlights the complexity that occurs in prenatal OI and the importance of clarifying its pathogenic mechanisms.

Dissecting the phenotypic variability of osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a heterogeneous family of collagen type I-related diseases characterized by bone fragility. OI is most commonly caused by single-nucleotide substitutions that replace glycine residues or exon splicing defects in the COL1A1 and COL1A2 genes that encode the α1(I) and α2(I) collagen chains. Mutant collagen is partially retained intracellularly, impairing cell homeostasis. Upon secretion, it assembles in disorganized fibrils, altering mineralization. OI is characterized by a wide range of clinical outcomes, even in the presence of identical sequence variants. Given the heterotrimeric nature of collagen I, its amino acid composition and the peculiarity of its folding, several causes may underlie the phenotypic variability of OI. A deep analysis of entries regarding glycine and splice site collagen substitution of the largest publicly available patient database reveals a higher risk of lethal phenotype for carriers of variants in α1(I) than in α2(I) chain. However, splice site variants are predominantly associated with lethal phenotype when they occur in COL1A2. In addition, lethality is increased when mutations occur in regions of importance for extracellular matrix interactions. Both extracellular and intracellular determinants of OI clinical severity are discussed in light of the findings from in vitro and in vivo OI models. Combined with meticulous tracking of clinical cases via a publicly available database, the available OI animal models have proven to be a unique tool to shed light on new modulators of phenotype determination for this rare heterogeneous disease.

Phenotypic Variation in Vietnamese Osteogenesis Imperfecta Patients Sharing a Recessive P3H1 Pathogenic Variant

Osteogenesis imperfecta (OI) is a syndromic disorder of bone fragility with high variation in its clinical presentation. Equally variable is molecular aetiology; recessive forms are caused by approximately 20 different genes, many of which are directly implicated in collagen type I biosynthesis. Biallelic variants in prolyl 3-hydroxylase 1 (P3H1) are known to cause severe OI by affecting the competence of the prolyl 3-hydroxylation—cartilage associated protein—peptidyl-prolyl cis-trans isomerase B (P3H1-CRTAP-CyPB) complex, which acts on the Pro986 residue of collagen type I α 1 (COL1A1) and Pro707 collagen type I α 2 (COL1A2) chains. The investigation of an OI cohort of 146 patients in Vietnam identified 14 families with P3H1 variants. The c.1170+5G>C variant was found to be very prevalent (12/14) and accounted for 10.3% of the Vietnamese OI cohort. New P3H1 variants were also identified in this population. Interestingly, the c.1170+5G>C variants were found in families with the severe clinical Sillence types 2 and 3 but also the milder types 1 and 4. This is the first time that OI type 1 is reported in patients with P3H1 variants expanding the clinical spectrum. Patients with a homozygous c.1170+5G>C variant shared severe progressively deforming OI type 3: bowed long bones, deformities of ribcage, long phalanges and hands, bluish sclera, brachycephaly, and early intrauterine fractures. Although it remains unclear if the c.1170+5G>C variant constitutes a founder mutation in the Vietnamese population, its prevalence makes it valuable for the molecular diagnosis of OI in patients of the Kinh ethnicity. Our study provides insight into the clinical and genetic variation of P3H1-related OI in the Vietnamese population.

Phenotypic Spectrum and Molecular Basis in a Chinese Cohort of Osteogenesis Imperfecta With Mutations in Type I Collagen

Osteogenesis imperfecta (OI) is a rare inherited connective tissue dysplasia characterized with skeletal fragility, recurrent fractures and bone deformity, predominantly caused by mutations in the genes COL1A1 or COL1A2 that encode the chains of type I collagen. In the present study, clinical manifestations and genetic variants were analysed from 187 Chinese OI patients, majority of whom are of southern Chinese origin. By targeted sequencing, 63 and 58 OI patients were found carrying mutations in COL1A1 and COL1A2 respectively, including 8 novel COL1A1 and 7 novel COL1A2 variants. We validated a novel splicing mutation in COL1A1. A diverse mutational and phenotypic spectrum was observed, coupling with the heterogeneity observed in the transcriptomic data derived from osteoblasts of six patients from our cohort. Missense mutations were significantly associated (χ²p = 0.0096) with a cluster of patients with more severe clinical phenotypes. Additionally, the severity of OI was more correlated with the quality of bones, rather than the bone mineral density. Bone density is most responsive to bisphosphonate treatment during the juvenile stage (10–15 years old). In contrast, height is not responsive to bisphosphonate treatment. Our findings expand the mutational spectrum of type I collagen genes and the genotype-phenotype correlation in Chinese OI patients. The observation of effective bisphosphonate treatment in an age-specific manner may help to improve OI patient management.

Collagen transport and related pathways in Osteogenesis Imperfecta

Osteogenesis Imperfecta (OI) comprises a heterogeneous group of patients who share bone fragility and deformities as the main characteristics, albeit with different degrees of severity. Phenotypic variation also exists in other connective tissue aspects of the disease, complicating disease classification and disease course prediction. Although collagen type I defects are long established as the primary cause of the bone pathology, we are still far from comprehending the complete mechanism. In the last years, the advent of next generation sequencing has triggered the discovery of many new genetic causes for OI, helping to draw its molecular landscape. It has become clear that, in addition to collagen type I genes, OI can be caused by multiple proteins connected to different parts of collagen biosynthesis. The production of collagen entails a complex process, starting from the production of the collagen Iα1 and collagen Iα2 chains in the endoplasmic reticulum, during and after which procollagen is subjected to a plethora of posttranslational modifications by chaperones. After reaching the Golgi organelle, procollagen is destined to the extracellular matrix where it forms collagen fibrils. Recently discovered mutations in components of the retrograde transport of chaperones highlight its emerging role as critical contributor of OI development. This review offers an overview of collagen regulation in the context of recent gene discoveries, emphasizing the significance of transport disruptions in the OI mechanism. We aim to motivate exploration of skeletal fragility in OI from the perspective of these pathways to identify regulatory points which can hint to therapeutic targets.

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.

RNA sequencing analysis reveals increased expression of interferon signaling genes and dysregulation of bone metabolism affecting pathways in the whole blood of patients with osteogenesis imperfecta

BACKGROUND

Osteogenesis imperfecta (OI) is a rare genetic disorder in which the patients suffer from numerous fractures, skeletal deformities and bluish sclera. The disorder ranges from a mild form to severe and lethal cases. The main objective of this pilot study was to compare the blood transcriptional landscape of OI patients with COL1A1 pathogenic variants and their healthy relatives, in order to find out different gene expression and dysregulated molecular pathways in OI.

METHODS

We performed RNA sequencing analysis of whole blood in seven individuals affected with different OI severity and their five unaffected relatives from the three families. The data was analyzed using edgeR package of R Bioconductor. Functional profiling and pathway analysis of the identified differently expressed genes was performed with g:GOSt and MinePath web-based tools.

RESULTS

We identified 114 differently expressed genes. The expression of 79 genes was up-regulated, while 35 genes were down-regulated. The functional analysis identified a presence of dysregulated interferon signaling pathways (IFI27, IFITM3, RSAD12, GBP7). Additionally, the expressions of the genes related to extracellular matrix organization, Wnt signaling, vitamin D metabolism and MAPK-ERK 1/2 pathways were also altered.

CONCLUSIONS

The current pilot study successfully captured the differential expression of inflammation and bone metabolism pathways in OI patients. This work can contribute to future research of transcriptional bloodomics in OI. Transcriptional bloodomics has a strong potential to become a major contributor to the understanding of OI pathological mechanisms, the discovery of phenotype modifying factors, and the identification of new therapeutic targets. However, further studies in bigger cohorts of OI patients are needed to confirm the findings of the current work.