Recessive Osteogenesis Imperfecta Research Articles

Osteogenesis imperfecta type XVII: expansion of the phenotype

BackgroundBiallelic variants in SPARC are extremely rare, and have been reported in only a few cases of autosomal recessive osteogenesis imperfecta (OI) type XVII. Here, we describe an individual with a SPARC homozygous missense variant (c.787G > A; p.Glu263Lys) and expand on the phenotype.Case presentationThe proband had a history of multiple fractures, osteopenia, severe thoracolumbar levoscoliosis, rib fusion, global hypotonia, conductive hearing loss, and was non-ambulatory. Several of his features were similar to previously described cases, such as early neuromuscular concerns, scoliosis, long bone and vertebral compression fractures, and delayed motor milestones, suggesting these are consistent across SPARC-related osteogenesis imperfecta (OI). However, the proband sustained fractures at a younger age with a more severe course compared to most previous reports. He also had bony fusion of several ribs and hearing loss, which have not been reported in SPARC-related OI.ConclusionsOverall, the proband supports the current phenotype of SPARC-related OI, but also expands the phenotypic variability.

Genetic analysis, phenotype spectrum and functional study of rare osteogenesis imperfecta caused by CRTAP Variants.

Deficiency of cartilage-associated protein (CRTAP) can cause extremely rare autosomal recessive osteogenesis imperfecta (OI) type VII. We investigated the pathogenic mechanisms of CRTAP variants through functional studies on OI patient-derived bones. Two nonconsanguineous families with CRTAP mutations were included, and their phenotypes and genotypes were evaluated. Bone specimens were obtained from one OI patient and a normal control during orthopedic surgery. The impacts of the novel variant on the CRTAP transcript were confirmed. The expression levels of CRTAP mRNA and CRTAP protein were analyzed. The quantification of prolyl 3-hydroxylation in the α1 chain of type I collagen was evaluated. Patients with OI type VII had early-onset recurrent fractures, severe osteoporosis, and bone deformities. The c.621 + 1G > A and c.1153-3C > G mutations were identified in CRTAP in the OI patients. The c.621 + 1G > A variant was a novel mutation that could impair mRNA transcription, leading to a truncated CRTAP protein. In a patient with c.621 + 1G > A and c.1153-3C > G mutations in CRTAP, the mRNA and protein levels of CRTAP in osteoblasts were significantly decreased, and the osteoid volume and osteoblast numbers were markedly reduced compared with those in the normal control individual. This was simultaneously accompanied by significantly reduced prolyl 3-hydroxylation of Pro986 in the α1 chain of type I collagen and invisible active bone formation in bone. The novel c.621 + 1G > A mutation in CRTAP expands the genotypic spectrum of type VII OI. Biallelic mutations of c.621 + 1G > A and c.1153-3C > G in CRTAP can lead to reduced CRTAP mRNA and deficient CRTAP protein in osteoblasts, which reduces 3-hydroxylation in Pro986 of the α1 chain of type I collagen and impairs bone formation, thus contributing to severe OI type VII.

Atypical cell death and insufficient matrix organization in long-bone growth plates from Tric-b-knockout mice

TRIC-A and TRIC-B proteins form homotrimeric cation-permeable channels in the endoplasmic reticulum (ER) and nuclear membranes and are thought to contribute to counterionic flux coupled with store Ca2+ release in various cell types. Serious mutations in the TRIC-B (also referred to as TMEM38B) locus cause autosomal recessive osteogenesis imperfecta (OI), which is characterized by insufficient bone mineralization. We have reported that Tric-b-knockout mice can be used as an OI model; Tric-b deficiency deranges ER Ca2+ handling and thus reduces extracellular matrix (ECM) synthesis in osteoblasts, leading to poor mineralization. Here we report irregular cell death and insufficient ECM in long-bone growth plates from Tric-b-knockout embryos. In the knockout growth plate chondrocytes, excess pro-collagen fibers were occasionally accumulated in severely dilated ER elements. Of the major ER stress pathways, activated PERK/eIF2α (PKR-like ER kinase/ eukaryotic initiation factor 2α) signaling seemed to inordinately alter gene expression to induce apoptosis-related proteins including CHOP (CCAAT/enhancer binding protein homologous protein) and caspase 12 in the knockout chondrocytes. Ca2+ imaging detected aberrant Ca2+ handling in the knockout chondrocytes; ER Ca2+ release was impaired, while cytoplasmic Ca2+ level was elevated. Our observations suggest that Tric-b deficiency directs growth plate chondrocytes to pro-apoptotic states by compromising cellular Ca2+-handling and exacerbating ER stress response, leading to impaired ECM synthesis and accidental cell death.

A Founder Intronic Variant in P3H1 Likely Results in Aberrant Splicing and Protein Truncation in Patients of Karen Descent with Osteogenesis Imperfecta Type VIII.

One of the most important steps in post-translational modifications of collagen type I chains is the hydroxylation of carbon-3 of proline residues by prolyl-3-hydroxylase-1 (P3H1). Genetic variants in P3H1 have been reported to cause autosomal recessive osteogenesis imperfecta (OI) type VIII. Clinical and radiographic examinations, whole-exome sequencing (WES), and bioinformatic analysis were performed in 11 Thai children of Karen descent affected by multiple bone fractures. Clinical and radiographic findings in these patients fit OI type VIII. Phenotypic variability is evident. WES identified an intronic homozygous variant (chr1:43212857A > G; NM_022356.4:c.2055 + 86A > G) in P3H1 in all patients, with parents in each patient being heterozygous for the variant. This variant is predicted to generate a new "CAG" splice acceptor sequence, resulting in the incorporation of an extra exon that leads to a frameshift in the final exon and subsequent non-functional P3H1 isoform a. Alternative splicing of P3H1 resulting in the absence of functional P3H1 caused OI type VIII in 11 Thai children of Karen descent. This variant appears to be specific to the Karen population. Our study emphasizes the significance of considering intronic variants.

A progeroid syndrome caused by a deep intronic variant in TAPT1 is revealed by RNA/SI-NET sequencing.

Exome sequencing has introduced a paradigm shift for the identification of germline variations responsible for Mendelian diseases. However, non-coding regions, which make up 98% of the genome, cannot be captured. The lack of functional annotation for intronic and intergenic variants makes RNA-seq a powerful companion diagnostic. Here, we illustrate this point by identifying six patients with a recessive Osteogenesis Imperfecta (OI) and neonatal progeria syndrome. By integrating homozygosity mapping and RNA-seq, we delineated a deep intronic TAPT1 mutation (c.1237-52 G>A) that segregated with the disease. Using SI-NET-seq, we document that TAPT1's nascent transcription was not affected in patients' fibroblasts, indicating instead that this variant leads to an alteration of pre-mRNA processing. Predicted to serve as an alternative splicing branchpoint, this mutation enhances TAPT1 exon 12 skipping, creating a protein-null allele. Additionally, our study reveals dysregulation of pathways involved in collagen and extracellular matrix biology in disease-relevant cells. Overall, our work highlights the power of transcriptomic approaches in deciphering the repercussions of non-coding variants, as well as in illuminating the molecular mechanisms of human diseases.

Dominant osteogenesis imperfecta with low bone turnover caused by a heterozygous SP7 variant.

Mutations in SP7 (encoding osterix) have been identified as a rare cause of recessive osteogenesis imperfecta ('OI type XII') and in one case of dominant juvenile Paget's disease. We present the first description of young adult siblings with OI due to a unique heterozygous mutation in SP7. The phenotype was characterized by fragility fractures (primarily of the long bone diaphyses), poor healing, scoliosis, and dental malocclusion. Both siblings had very low cortical volumetric bone mineral density on peripheral quantitative computed tomography of the radius (z-scores -6.6 and-6.7 at the diaphysis), porous cortices, and thin cortices at the radial metaphysis. Histomorphometry demonstrated thin cortices and low bone turnover with reduced osteoblast function. Both siblings were heterozygous for a missense variant affecting a highly conserved zinc finger domain of osterix (c.1019A>C; p.Glu340Ala) on DNA sequencing. Co-transfection of plasmids carrying the SP7 mutation with DLX5 and a luciferase reporter demonstrated that this variant impacted gene function (reduced transcription co-activation compared to wild-type SP7). The low cortical density and cortical porosity seen in our patients are consistent with previous reports of individuals with SP7 mutations. However, the low bone turnover in our patients contrasts with the high turnover state seen in previously reported patients with SP7 mutations. This report indicates that dominant variants in SP7 can give rise to OI. The predominant feature, low cortical density, is common in patients with other SP7 mutations, however other features appear to depend on the specific variant.

Tendon and motor phenotypes in the Crtap-/- mouse model of recessive osteogenesis imperfecta.

Osteogenesis imperfecta (OI) is characterized by short stature, skeletal deformities, low bone mass, and motor deficits. A subset of OI patients also present with joint hypermobility; however, the role of tendon dysfunction in OI pathogenesis is largely unknown. Using the Crtap-/- mouse model of severe, recessive OI, we found that mutant Achilles and patellar tendons were thinner and weaker with increased collagen cross-links and reduced collagen fibril size at 1- and 4-months compared to wildtype. Patellar tendons from Crtap-/- mice also had altered numbers of CD146+CD200+ and CD146-CD200+ progenitor-like cells at skeletal maturity. RNA-seq analysis of Achilles and patellar tendons from 1-month Crtap-/- mice revealed dysregulation in matrix and tendon marker gene expression concomitant with predicted alterations in TGF-β, inflammatory, and metabolic signaling. At 4-months, Crtap-/- mice showed increased αSMA, MMP2, and phospho-NFκB staining in the patellar tendon consistent with excess matrix remodeling and tissue inflammation. Finally, a series of behavioral tests showed severe motor impairments and reduced grip strength in 4-month Crtap-/- mice - a phenotype that correlates with the tendon pathology.

Detection of a Recurrent TMEM38B Gene Deletion Associated with Recessive Osteogenesis Imperfecta.

Osteogenesis imperfecta is a clinically and genetically group of heterogeneous disorders associated with decreased bone density, brittle bones, bone deformity, recurrent fractures, and growth retardation. Osteogenesis imperfecta is commonly associated with mutations of the genes encoding for type I collagen (COL1A1/COL1A2). Mutations in other genes, some associated with type I collagen post-translational processing, have also been identified as the cause of osteogenesis imperfecta. Mutations in the transmembrane protein 38B (TMEM38B) gene have been reported in a rare autosomal recessive form of osteogenesis imperfecta.  TMEM38B encodes TRIC-B - a trimeric intracellular cation channel type B which is essential to modulate intracellular calcium signaling. In this study, we are reporting a case of osteogenesis imperfecta type XIV from a Saudi consanguineous family. Our patient was an eight-month-old child with short limbs, club feet, and lower limb deformities with developmental delay. Radiological findings were consistent with the evidence of osteogenesis imperfecta. There was no evidence of impaired hearing or blue sclera and based on the clinical assessment, we classified our patient as a non-syndromic osteogenesis imperfecta. A pathogenic deletion in the chromosome 9q31.2 region, partially encompassing the TMEM38B gene, was detected using chromosomal microarray analysis. This study expands our knowledge about the rare type of osteogenesis imperfecta in our consanguineous population. Besides, it emphasizes the use of genomic medicine in clinical practices to formulate early interventions to clinically improve the patient’s condition.

A novel P3H1 mutation is associated with osteogenesis imperfecta type VIII and dental anomalies

Our objective was to investigate the molecular etiology of osteogenesis imperfecta type VIII and dental anomalies in 4 siblings of a Karen tribe family. Four patients and their unaffected parents were studied by clinical and radiographic examination. In situ hybridization of P3h1 during early murine tooth development, whole-exome sequencing, and Sanger direct sequencing were performed. A novel homozygous missense P3H1 mutation (NM_001243246.1; c.2141A>G; NP_001230175.1; p.Lys714Arg) was identified in all patients. Their unaffected parents were heterozygous for the mutation. The mutation is hypothesized to belong to isoform c of P3H1. Mutations in P3H1 are associated with autosomal recessive osteogenesis imperfecta type VIII. Hypodontia, a mesiodens, and single-rooted permanent second molars found in our patients have never been reported in patients with P3H1 mutations. Single-rooted second permanent molars or failure to form multiple roots implies effects of the P3H1 mutation on root development. We report a novel P3H1 mutation as the underlying cause of osteogenesis imperfecta type VIII with dental anomalies. Our study suggests that isoform c of P3H1 is also a functional isoform of P3H1. We report, for the first time, to our knowledge, the association of P3H1 mutation and osteogenesis imperfecta type VIII with dental anomalies.

Over-Representation of Recessive Osteogenesis Imperfecta in Asian Indian Children.

Several genes are implicated in the etiology of early onset osteogenesis imperfecta (OI). The various genes causing severe OI include WNT1 , SERPINF1 , P3H1 , CREB3L1 , and CRTAP , although glycine substitutions in COL1A1chains have also been predicted to cause perinatal lethal OI . Patients with early onset OI present decreased mobility, recurrent rib fractures, bony deformities, and chest infections that lead to an early death. We reported our experience in children with OI in Asian Indian families, which includes two patients with SERPINF1 pathogenic variants; and another two patients with severe OI and antenatal fractures caused by pathogenic variants in the CRTAP gene, identified by next generation sequencing (NGS). For one affected fetus, medical termination of pregnancy was done. The other baby was started on zoledronate therapy just after birth and is now 3 years old. Prenatal diagnosis was subsequently done on chorionic villus sample in the latter family.

Genotypic and Phenotypic Analysis in Chinese Cohort With Autosomal Recessive Osteogenesis Imperfecta.

Osteogenesis imperfecta (OI) is a rare heritable skeletal disorder which is mainly caused by defected type I collagen. Autosomal recessive OI (AR-OI) is caused by mutations of genes that are responsible for type I collagen modification and folding, and is often associated with more severe phenotypes. Due to the limited number of recessive OI patients, it has been difficult to study the mutation spectrum as well as the correlation of genotype and phenotype. This study recruited a Chinese cohort of 74 AR-OI families, aiming to establish the mutation spectrum and to examine the genotypic and phenotypic correlation. We identified 82 variants including 25 novel variants and 57 HGMD reported variants in these AR-OI patients, using whole exome sequencing/panel sequencing combined with Sanger sequencing. Pathogenic mutations were found at WNT1 (n = 30, 40.54%), SERPINF1 (n = 22, 29.73%), FKBP10 (n = 10, 13.51%), CRTAP (n = 3, 4.05%), P3H1 (n = 3, 4.05%), SERPINH1 (n = 2, 2.70%), SEC24D (n = 3, 4.05%), and PLOD2 (n = 1, 1.35%) respectively. Thus, WNT1 represents the most frequent pathogenic gene of AR-OI in Chinese population. The most common clinical manifestations of AR-OI patients include walking problem (72.86%), scoliosis (65.28%) and frequent fractures (fractures ≥2/year) (54.05%). Interestingly, ptosis represents a unique phenotype of patients carrying WNT1 variants, and it was rare in patients harboring other pathogenic genes. Our study expanded the mutation spectrum of AR-OI and enriched the knowledge of genotypic and phenotypic correlation in Chinese cohort with AR-OI.

Homozygous Loss-of-Function Mutations in CCDC134 Are Responsible for a Severe Form of Osteogenesis Imperfecta.

Osteogenesis imperfecta (OI) is a primary bone fragility disorder with an estimated prevalence of 1 in 15,000 births. The majority of OI cases are inherited in an autosomal-dominant manner, while 5% to 10% have recessive or X-linked inheritance. Up to now, approximately 5% of OI cases remain without mutation demonstrated, supporting the involvement of other genes in the disease spectrum. By whole-exome sequencing, we identified a homozygous variant (c.2T>C) in CCDC134 gene in three patients from two unrelated families with severe bone fragility that did not respond to bisphosphonate treatment, short stature, and gracile long bones with pseudarthroses but no dentinogenesis imperfecta. CCDC134 encodes a secreted protein widely expressed and implicated in the regulation of some mitogen-activated protein kinases (MAPK) signaling pathway. Western blot and immunofluorescence analyses confirmed the absence of CCDC134 protein in patient cells compared with controls. Furthermore, we demonstrated that CCDC134 mutations are associated with increased Erk1/2 phosphorylation, decreased OPN mRNA and COL1A1 expression and reduced mineralization in patient osteoblasts compared with controls. These data support that CCDC134 is a new gene involved in severe progressive deforming recessive osteogenesis imperfecta (type III). © 2020 American Society for Bone and Mineral Research.

Development of Craniofacial Biomineralization in Mice with Osteogenesis Imperfecta (OI)

Osteogenesis imperfecta (OI), or “brittle bone disease,” is a rare autosomal dominant disorder characterized by mutations in the genes that encode the alpha 1 (COL1A1) and alpha 2 (COL1A2) chains of type I collagen, a significant component of bone. Misfolding of the mutated collagen polypeptides interfere with proper assembly of collagen chains, or the triple helical structures, leading to extreme skeletal fragility. OI manifests in a variety of types, with type I being the most mild and most common, and type III, the subject of this study, being more severe and more rare. Clinical manifestations of OI type III generally include a short stature, low bone mineral density (BMD), dental problems, hearing loss, and blue sclerae. In this study, we use a mouse model of OI type III to examine how mutations in type I collagen synthesis impact craniofacial biomineralization during postnatal growth.The homozygous recessive osteogenesis imperfecta murine (OIM) is a model of OI type III and is characterized by increased skeletal fractures, low postcranial BMD, osteopenia, progressive skeletal deformities, and small body size. Wild type mice (WT) and OIM littermates (n≥3/genotype) were micro‐CT scanned at weaning (4 weeks) and adulthood (16 weeks). BMD at three regions of interest (ROI) within the mouse skull was measured using Bruker CTAnalyzer software. ROIs were chosen based on the amount of load during mastication, and included the temporomandibular joint (TMJ), the parietal bone (1mm from the sagittal suture), and the anterior maxilla at the incisal alveolus. Mann‐Whitney U‐tests (α=0.05) were used to compare BMD values between the genotypes for each ROI.At weaning, OIM mice had significantly lower BMD values (g.cm−3 CaHA) than their wild type littermates at the TMJ (0.39 vs 0.58), parietal bone (0.35 vs 0.64), and anterior maxilla (0.53 vs 0.85). These statistical differences persist into adulthood. This decrease in BMD reflects decreased deposition of CaHA due to an abnormal collagen framework in the craniofacial skeleton of OIM mice. Ongoing efforts will expand this analysis to quantify the development of BMD at additional regions within the craniofacial skeleton.Support or Funding InformationThis research was supported by an Indiana University Collaborative Research Grant and the Ralph W. and Grace Showalter Trust.

Fracture Healing in Collagen-Related Preclinical Models of Osteogenesis Imperfecta.

Osteogenesis imperfecta (OI) is a genetic bone dysplasia characterized by bone deformities and fractures caused by low bone mass and impaired bone quality. OI is a genetically heterogeneous disorder that most commonly arises from dominant mutations in genes encoding type I collagen (COL1A1 and COL1A2). In addition, OI is recessively inherited with the majority of cases resulting from mutations in prolyl-3-hydroxylation complex members, which includes cartilage-associated protein (CRTAP). OI patients are at an increased risk of fracture throughout their lifetimes. However, non-union or delayed healing has been reported in 24% of fractures and 52% of osteotomies. Additionally, refractures typically go unreported, making the frequency of refractures in OI patients unknown. Thus, there is an unmet need to better understand the mechanisms by which OI affects fracture healing. Using an open tibial fracture model, our study demonstrates delayed healing in both Col1a2 G610c/+ and Crtap -/- OI mouse models (dominant and recessive OI, respectively) that is associated with reduced callus size and predicted strength. Callus cartilage distribution and chondrocyte maturation were altered in OI, suggesting accelerated cartilage differentiation. Importantly, we determined that healed fractured tibia in female OI mice are biomechanically weaker when compared with the contralateral unfractured bone, suggesting that abnormal OI fracture healing OI may prime future refracture at the same location. We have previously shown upregulated TGF-β signaling in OI and we confirm this in the context of fracture healing. Interestingly, treatment of Crtap -/- mice with the anti-TGF-β antibody 1D11 resulted in further reduced callus size and predicted strength, highlighting the importance of investigating dose response in treatment strategies. These data provide valuable insight into the effect of the extracellular matrix (ECM) on fracture healing, a poorly understood mechanism, and support the need for prevention of primary fractures to decrease incidence of refracture and deformity in OI patients. © 2020 American Society for Bone and Mineral Research.

Cardiac valvular Ehlers-Danlos syndrome is a well-defined condition due to recessive null variants in COL1A2.

Cardiac valvular Ehlers-Danlos syndrome (EDS) is a rare EDS subtype, caused by specific recessive variants in the gene encoding pro-α2-chain of type I collagen (COL1A2). Cardiac valvular EDS is mainly characterized by generalized/peripheral joint hypermobility, moderate-severe cardiac valvular disease, skin hyperextensibility and other minor soft tissues features. Only five molecularly confirmed patients have been reported to date. Here, we describe two additional affected sisters, who share the homozygous c.3601G>T nonsense variant in COL1A2. Clinical data and literature review allowed to better define the clinical spectrum of cardiac valvular EDS which now emerges as a more recognizable EDS variant with progressive heart valve disease firstly affecting the mitral valve. Possibly distinguishing features include bilateral flatfeet with hindfoot pronation, lower eyelid ptosis and hypoplasia of the interphalangeal creases. The absence of bone fragility in our patients indicates that cardiac valvular EDS is also separated from patients with autosomal recessive osteogenesis imperfecta and variants in COL1A2, as well as from individuals with autosomal dominant osteogenesis imperfecta and severe cardiac valvular disease.

A homozygous pathogenic missense variant broadens the phenotypic and mutational spectrum of CREB3L1-related osteogenesis imperfecta.

The cyclic adenosine monophosphate responsive element binding protein 3-like 1 (CREB3L1) gene codes for the endoplasmic reticulum stress transducer old astrocyte specifically induced substance (OASIS), which has an important role in osteoblast differentiation during bone development. Deficiency of OASIS is linked to a severe form of autosomal recessive osteogenesis imperfecta (OI), but only few patients have been reported. We identified the first homozygous pathogenic missense variant [p.(Ala304Val)] in a patient with lethal OI, which is located within the highly conserved basic leucine zipper domain, four amino acids upstream of the DNA binding domain. In vitro structural modeling and luciferase assays demonstrate that this missense variant affects a critical residue in this functional domain, thereby decreasing the type I collagen transcriptional binding ability. In addition, overexpression of the mutant OASIS protein leads to decreased transcription of the SEC23A and SEC24D genes, which code for components of the coat protein complex type II (COPII), and aberrant OASIS signaling also results in decreased protein levels of SEC24D. Our findings therefore provide additional proof of the potential involvement of the COPII secretory complex in the context of bone-associated disease.

Splicing defect in FKBP10 gene causes autosomal recessive osteogenesis imperfecta disease: a case report

BackgroundOsteogenesis imperfecta (OI) is a group of connective tissue disorder caused by mutations of genes involved in the production of collagen and its supporting proteins. Although the majority of reported OI variants are in COL1A1 and COL1A2 genes, recent reports have shown problems in other non-collagenous genes involved in the post translational modifications, folding and transport, transcription and proliferation of osteoblasts, bone mineralization, and cell signaling. Up to now, 17 types of OI have been reported in which types I to IV are the most frequent cases with autosomal dominant pattern of inheritance.Case PresentationHere we report an 8- year- old boy with OI who has had multiple fractures since birth and now he is wheelchair-dependent. To identify genetic cause of OI in our patient, whole exome sequencing (WES) was carried out and it revealed a novel deleterious homozygote splice acceptor site mutation (c.1257-2A > G, IVS7-2A > G) in FKBP10 gene in the patient. Then, the identified mutation was confirmed using Sanger sequencing in the proband as homozygous and in his parents as heterozygous, indicating its autosomal recessive pattern of inheritance. In addition, we performed RT-PCR on RNA transcripts originated from skin fibroblast of the proband to analyze the functional effect of the mutation on splicing pattern of FKBP10 gene and it showed skipping of the exon 8 of this gene. Moreover, Real-Time PCR was carried out to quantify the expression level of FKBP10 in the proband and his family members in which it revealed nearly the full decrease in the level of FKBP10 expression in the proband and around 75% decrease in its level in the carriers of the mutation, strongly suggesting the pathogenicity of the mutation.ConclusionsOur study identified, for the first time, a private pathogenic splice site mutation in FKBP10 gene and further prove the involvement of this gene in the rare cases of autosomal recessive OI type XI with distinguished clinical manifestations.

Novel mutations of the SERPINF1 and FKBP10 genes in Chinese families with autosomal recessive osteogenesis imperfecta.

The aim of the present study was to characterize the clinical manifestations and identify the mutations of Serpin family F member1 (SERPINF1) and FK506 binding protein10 (FKBP10) genes in Chinese patients with osteogenesis imperfecta (OI). Using whole‑exome sequencing in the first and third probands, a novel mutation was identified in SERPINF1 and a novel compound heterozygous mutation was revealed in FKBP10. Using Sanger sequencing, an additional novel mutation in SERPINF1 was identified in a probandof family2. In family1, the probandpresented with a novel homozygous missense mutation of the SERPINF1 gene, c.1067T>A (V356E). In family2, the probandhad a novel homozygous deletion mutation of the SERPINF1 gene, c.283+473_643+104del (p.Ala96_Gly215del). Serum pigment‑epithelium‑derived factor concentration was not detected in probands with OI typeVI. For both families, the proband's father was demonstrated to have a heterozygous mutation of SERPINF1, whereas no mutations was detected in the probands' mothers. An assessment of allelic copy numbers revealed a deletion of SERPINF1 in the mother of family1. The results of the present study demonstrate that patients may have mild symptoms of OI with a large fragment deletion in the SERPINF1 gene. Thus, the phenotypeof Chinese patients with typeVI OI is milder than that of Caucasian and Korean patients. In family3, the probanddisplayed a novel compound heterozygous mutation in FKBP10, c.813_814delGA (p.Glu271AspfsX101) and c.831delC (p.Gly278AlafsX20), and did not have Bruck syndrome. Codon 831 of the FKBP10 gene may represent a mutation hotspot for human OI. These results extend both the phenotypic and the genotypic contents of OI patients with SERPINF1 or FKBP10 mutations.

FAM46A mutations are responsible for autosomal recessive osteogenesis imperfecta

BackgroundStüve-Wiedemann syndrome (SWS) is characterised by bowing of the lower limbs, respiratory distress and hyperthermia that are often responsible for early death. Survivors develop progressive scoliosis and spontaneous fractures. We...

An ENU-induced splice site mutation of mouse Col1a1 causing recessive osteogenesis imperfecta and revealing a novel splicing rescue

GU-AG consensus sequences are used for intron recognition in the majority of cases of pre-mRNA splicing in eukaryotes. Mutations at splice junctions often cause exon skipping, short deletions, or insertions in the mature mRNA, underlying one common molecular mechanism of genetic diseases. Using N-ethyl-N-nitrosourea, a novel recessive mutation named seal was produced, associated with fragile bones and susceptibility to fractures (spine and limbs). A single nucleotide transversion (T → A) at the second position of intron 36 of the Col1a1 gene, encoding the type I collagen, α1 chain, was responsible for the phenotype. Col1a1seal mRNA expression occurred at greatly reduced levels compared to the wild-type transcript, resulting in reduced and aberrant collagen fibers in tibiae of seal homozygous mice. Unexpectedly, splicing of Col1a1seal mRNA followed the normal pattern despite the presence of the donor splice site mutation, likely due to the action of a putative intronic splicing enhancer present in intron 25, which appeared to function redundantly with the splice donor site of intron 36. Seal mice represent a model of human osteogenesis imperfecta, and reveal a previously unknown mechanism for splicing “rescue.”