Osteogenesis imperfecta: Ultrastructural and histological findings on examination of skin revealing novel insights into genotype-phenotype correlation

© 2016 Taylor & Francis. Osteogenesis imperfecta (OI) is a heterogeneous group of inherited disorders of bone formation, resulting in low bone mass and an increased propensity to fracture. Over 90% of patients with OI have a mutation in COL1A1/COL1A2, which shows an autosomal dominant pattern of inheritance. In-depth phenotyping and in particular, studies involving manifestations in the skin connective tissue have not previously been undertaken in OI. The aims of the study were to perform histological and ultrastructural examination of skin biopsies in a cohort of patients with OI; to identify common and distinguishing features in order to inform genotype-phenotype correlation; and to identify common and distinguishing features between the different subtypes of OI. As part of the RUDY (Rare Diseases in Bone, Joints and/or Blood Vessels) study, in collaboration with the NIHR Rare Diseases Translational Research Collaboration, we undertook a national study of skin biopsies in patients with OI. We studied the manifestations in the skin connective tissue and undertook in-depth clinical and molecular phenotyping of 16 patients with OI. We recruited 16 patients: analyses have shown that in type 1 collagen mutation positive patients (COL1A1/ COL1A2) (n-4/16) consistent findings included: variable collagen fibril diameter (CFD) and presence of collagen flowers. Histological examination in these patients showed an increase in elastic fibers that are frequently fragmented and clumped. These observations provide evidence that collagen flowers and CFD variability are consistent features in OI due to type 1 collagen defects and reinforce the need for accurate phenotyping in conjunction with genomic analyses

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

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

Mutations in FKBP10 can cause a severe form of isolated Osteogenesis imperfecta

<p>Abstract</p> <p>Background</p> <p>Mutations in the <it>FKBP10 </it>gene were first described in patients with Osteogenesis imperfecta type III. Two follow up reports found <it>FKBP10 </it>mutations to be associated with Bruck syndrome type 1, a rare disorder characterized by congenital contractures and bone fragility. This raised the question if the patients in the first report indeed had isolated Osteogenesis imperfecta or if Bruck syndrome would have been the better diagnosis.</p> <p>Methods</p> <p>The patients described here are affected by severe autosomal recessive Osteogenesis imperfecta without contractures.</p> <p>Results</p> <p>Homozygosity mapping identified <it>FKBP10 </it>as a candidate gene, and sequencing revealed a base pair exchange that causes a C-terminal premature stop codon in this gene.</p> <p>Conclusions</p> <p>Our study demonstrates that <it>FKBP10 </it>mutations not only cause Bruck syndrome or Osteogenesis imperfecta type III but can result in a severe type of isolated Osteogenesis imperfecta type IV with prenatal onset. Furthermore, it adds dentinogenesis imperfecta to the spectrum of clinical symptoms associated with <it>FKBP10 </it>mutations.</p

Generalized Connective Tissue Disease in Crtap-/- Mouse

Mutations in CRTAP (coding for cartilage-associated protein), LEPRE1 (coding for prolyl 3-hydroxylase 1 [P3H1]) or PPIB (coding for Cyclophilin B [CYPB]) cause recessive forms of osteogenesis imperfecta and loss or decrease of type I collagen prolyl 3-hydroxylation. A comprehensive analysis of the phenotype of the Crtap-/- mice revealed multiple abnormalities of connective tissue, including in the lungs, kidneys, and skin, consistent with systemic dysregulation of collagen homeostasis within the extracellular matrix. Both Crtap-/- lung and kidney glomeruli showed increased cellular proliferation. Histologically, the lungs showed increased alveolar spacing, while the kidneys showed evidence of segmental glomerulosclerosis, with abnormal collagen deposition. The Crtap-/- skin had decreased mechanical integrity. In addition to the expected loss of proline 986 3-hydroxylation in α1(I) and α1(II) chains, there was also loss of 3Hyp at proline 986 in α2(V) chains. In contrast, at two of the known 3Hyp sites in α1(IV) chains from Crtap-/- kidneys there were normal levels of 3-hydroxylation. On a cellular level, loss of CRTAP in human OI fibroblasts led to a secondary loss of P3H1, and vice versa. These data suggest that both CRTAP and P3H1 are required to maintain a stable complex that 3-hydroxylates canonical proline sites within clade A (types I, II, and V) collagen chains. Loss of this activity leads to a multi-systemic connective tissue disease that affects bone, cartilage, lung, kidney, and skin

Quality of life in caregivers of children and adolescents with Osteogenesis Imperfecta

Background: Osteogenesis imperfecta (OI) is a group of genetic disorders of collagen biosynthesis, characterized by low bone density leading to fractures. Most patients exhibit functional impairment and require the aid of a caregiver. The aim of this study is to assess the quality of life (QoL) of caregivers of patients with OI. Methods: In this cross-sectional study, a convenience sampling strategy was used to enroll adult caregivers of children and adolescents with OI who attended a referral center in southern Brazil. The WHOQOL-BREF instrument was used to assess QoL. Results: Twenty-four caregivers of 27 patients (10 with type I, 4 with type III, and 13 with type IV OI) were included in the study. Eighteen caregivers were the patients’ mothers, two had OI, and 22 cared for only one patient. Mean WHOQOL-BREF scores were 14.59 for the physical health domain, 13.80 for the psychological domain, 15.19 for the social relationships domain, and 12.87 for the environmental domain; the mean total QoL score was 14.16. QoL scores did not differ significantly according to patients’ OI type or number of fractures. Economic status was not correlated significantly with QoL scores. Conclusions: QoL appears to be impaired in caregivers of patients with OI. Additional studies are required to confirm these findings and to ascertain which factors account for this phenomenon

Small Vessel Ischemic Disease of the Brain and Brain Metastases in Lung Cancer Patients

Brain metastases occur commonly in patients with lung cancer. Small vessel ischemic disease is frequently found when imaging the brain to detect metastases. We aimed to determine if the presence of small vessel ischemic disease (SVID) of the brain is protective against the development of brain metastases in lung cancer patients.A retrospective cohort of 523 patients with biopsy confirmed lung cancer who had received magnetic resonance imaging of the brain as part of their standard initial staging evaluation was reviewed. Information collected included demographics, comorbidities, details of the lung cancer, and the presence of SVID of the brain. A portion of the cohort had the degree of SVID graded. The primary outcome measure was the portion of study subjects with and without SVID of the brain who had evidence of brain metastases at the time of initial staging of their lung cancer.109 patients (20.8%) had evidence of brain metastases at presentation and 345 (66.0%) had evidence of SVID. 13.9% of those with SVID and 34.3% of those without SVID presented with brain metastases (p<0.0001). In a model including age, diabetes mellitus, hypertension, hyperlipidemia, and tobacco use, SVID of the brain was found to be the only protective factor against the development of brain metastases, with an OR of 0.31 (0.20, 0.48; p<0.001). The grade of SVID was higher in those without brain metastases.These findings suggest that vascular changes in the brain are protective against the development of brain metastases in lung cancer patients

Rib Cage Deformities Alter Respiratory Muscle Action and Chest Wall Function in Patients with Severe Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) is an inherited connective tissue disorder characterized by bone fragility, multiple fractures and significant chest wall deformities. Cardiopulmonary insufficiency is the leading cause of death in these patients.Seven patients with severe OI type III, 15 with moderate OI type IV and 26 healthy subjects were studied. In addition to standard spirometry, rib cage geometry, breathing pattern and regional chest wall volume changes at rest in seated and supine position were assessed by opto-electronic plethysmography to investigate if structural modifications of the rib cage in OI have consequences on ventilatory pattern. One-way or two-way analysis of variance was performed to compare the results between the three groups and the two postures. compared to predicted values, on condition that updated reference equations are considered. In both positions, ventilation was lower in OI patients than control because of lower tidal volume (p<0.01). In contrast to OI type IV patients, whose chest wall geometry and function was normal, OI type III patients were characterized by reduced (p<0.01) angle at the sternum (pectus carinatum), paradoxical inspiratory inward motion of the pulmonary rib cage, significant thoraco-abdominal asynchronies and rib cage distortions in supine position (p<0.001).In conclusion, the restrictive respiratory pattern of Osteogenesis Imperfecta is closely related to the severity of the disease and to the sternal deformities. Pectus carinatum characterizes OI type III patients and alters respiratory muscles coordination, leading to chest wall and rib cage distortions and an inefficient ventilator pattern. OI type IV is characterized by lower alterations in the respiratory function. These findings suggest that functional assessment and treatment of OI should be differentiated in these two forms of the disease