Determination of a new collagen type I alpha 2 gene point mutation which causes a Gly640 Cys substitution in osteogenesis imperfecta and prenatal diagnosis by DNA hybridisation

Whole Exome Sequencing Aids the Diagnosis of Fetal Skeletal Dysplasia

Skeletal dysplasia is a complex group of bone and cartilage disorders with strong clinical and genetic heterogeneity. Several types have prenatal phenotypes, and it is difficult to make a molecular diagnosis rapidly. In this study, the genetic cause of 16 Chinese fetuses with skeletal dysplasia were analyzed, and 12 cases yielded positive results including one deletion in DMD gene detected by SNP-array and 14 variants in other 6 genes detected by whole exome sequencing (WES). In addition, somatic mosaicism was observed. Our study expanded the pathogenic variant spectrum and elucidated the utilization of WES in improving the diagnosis yield of skeletal dysplasia.

Intracellular and Extracellular Markers of Lethality in Osteogenesis Imperfecta: A Quantitative Proteomic Approach

Osteogenesis imperfecta (OI) is a heritable disorder that mainly affects the skeleton. The inheritance is mostly autosomal dominant and associated to mutations in one of the two genes, COL1A1 and COL1A2, encoding for the type I collagen α chains. According to more than 1500 described mutation sites and to outcome spanning from very mild cases to perinatal-lethality, OI is characterized by a wide genotype/phenotype heterogeneity. In order to identify common affected molecular-pathways and disease biomarkers in OI probands with different mutations and lethal or surviving phenotypes, primary fibroblasts from dominant OI patients, carrying COL1A1 or COL1A2 defects, were investigated by applying a Tandem Mass Tag labeling-Liquid Chromatography-Tandem Mass Spectrometry (TMT LC-MS/MS) proteomics approach and bioinformatic tools for comparative protein-abundance profiling. While no difference in α1 or α2 abundance was detected among lethal (type II) and not-lethal (type III) OI patients, 17 proteins, with key effects on matrix structure and organization, cell signaling, and cell and tissue development and differentiation, were significantly different between type II and type III OI patients. Among them, some non-collagenous extracellular matrix (ECM) proteins (e.g., decorin and fibrillin-1) and proteins modulating cytoskeleton (e.g., nestin and palladin) directly correlate to the severity of the disease. Their defective presence may define proband-failure in balancing aberrances related to mutant collagen.

4-PBA ameliorates cellular homeostasis in fibroblasts from osteogenesis imperfecta patients by enhancing autophagy and stimulating protein secretion

The clinical phenotype in osteogenesis imperfecta (OI) is attributed to the dominant negative function of mutant type I collagen molecules in the extracellular matrix, by altering its structure and function. Intracellular retention of mutant collagen has also been reported, but its effect on cellular homeostasis is less characterized. Using OI patient fibroblasts carrying mutations in the α1(I) and α2(I) chains we demonstrate that retained collagen molecules are responsible for endoplasmic reticulum (ER) enlargement and activation of the unfolded protein response (UPR) mainly through the eukaryotic translation initiation factor 2 alpha kinase 3 (PERK) branch. Cells carrying α1(I) mutations upregulate autophagy, while cells with α2(I) mutations only occasionally activate the autodegradative response. Despite the autophagy activation to face stress conditions, apoptosis occurs in all mutant fibroblasts. To reduce cellular stress, mutant fibroblasts were treated with the FDA-approved chemical chaperone 4-phenylbutyric acid. The drug rescues cell death by modulating UPR activation thanks to both its chaperone and histone deacetylase inhibitor abilities. As chaperone it increases general cellular protein secretion in all patients' cells as well as collagen secretion in cells with the most C-terminal mutation. As histone deacetylase inhibitor it enhances the expression of the autophagic gene Atg5 with a consequent stimulation of autophagy. These results demonstrate that the cellular response to ER stress can be a relevant target to ameliorate OI cell homeostasis.

Prenatal diagnosis and management of intrauterine fracture

Intrauterine fracture is an extremely rare finding, but can occur as the result of maternal trauma, osteogenesis imperfecta (OI), or theoretically other metabolic/structural abnormalities. Increased clinical awareness of the diagnosis and optimal management of these cases can lead to more positive outcomes for the patient and her child. Blunt abdominal trauma late in gestation increases the risk of fetal skull fracture, while a known diagnosis of OI or other abnormalities leading to decreased fetal bone density creates concern for long bone fracture. Biochemical and genetic tests can aid in the prenatal diagnosis of OI, while ultrasound is the best overall imaging modality for identifying fetal fracture of any etiology. When fetal fracture is diagnosed radiologically, specific management is recommended to promote optimal outcomes for mother and fetus, with special consideration given to the mother with OI. With the exception of fetal fractures due to lethal conditions, cesarean delivery is recommended in most cases, especially when fetal or maternal well-being cannot be assured. When a patient presents with risk factors for intrauterine fracture, careful evaluation via thorough history-taking, ultrasonography of the entire fetal skeleton, and laboratory tests should be performed. Heightened awareness of intrauterine fracture allows better postpartum management, whether for simple fracture care or for long-term care of patients with OI or genetic/metabolic abnormalities.

TARGET AUDIENCE

Obstetricians & Gynecologist, Family Physicians.

LEARNING OBJECTIVES

After completion of this educational activity, the reader will be able to compare x-ray, ultrasound modalities and MRI and their utility in diagnosing fetal fracture. Formulate a differential diagnosis for fetal fracture. Propose a delivery plan for a patient whose fetus has a prenatally diagnosed fetal fracture.

Prenatal diagnosis of a novel COL1A1 mutation in osteogenesis imperfecta type I carried through full term pregnancy

Prenatal diagnosis was performed in a family where the father has osteogenesis imperfecta (OI) type I, with a novel mutation in the COL1A1 gene: a C to T change at position c3076 (c.3076C-->T) leading to a change of arginine at codon 848 to a stop codon (R848X). Prenatal diagnosis by chorionic villous sampling (CVS) was performed during the fourth pregnancy, and revealed that the fetus is a carrier of the same COL1A1 mutation. The possibility of phenotypic variability was discussed with the parents. They elected to carry the pregnancy to term, and a male child with mild OI was born. This is the first reported case where OI was diagnosed prenatally, and the parents opted to carry the pregnancy to term. It illustrates the potential use of DNA-based analysis for early prenatal diagnosis of OI, and the complexities of genetic counselling.