Prenatal ultrasound findings and prenatal diagnosis of fetal skeletal dysplasia.

OBJECTIVE: To analyze the value of prenatal ultrasound and molecular testing in diagnosing fetal skeletal dysplasia (SD). METHODS: Clinical data, prenatal ultrasound data, and molecular results of pregnant women with fetal SD were collected in the ultrasound department of our clinic from May 2019 to December 2021. RESULTS: A total of 40 pregnant women with fetal SD were included, with 82.5% exhibiting short limb deformity, followed by 25.0% with central nervous system malformations, 17.50% with facial malformations, 15% with cardiac malformations, and 12.5% with urinary system malformations. The genetic testing positive rate was 70.0% (28/40), with 92.8% (26/28) being single-gene disorders due to mutations in FGFR3, COL1A1, COL1A2, EVC2, FLNB, LBR, and TRPV4 genes. The most common SD subtypes were osteogenesis imperfecta (OI), thanatophoric dysplasia (TD), and achondroplasia (ACH). The gestational age (GA) at initial diagnosis for TD, OI, and ACH was 16.6, 20.9, and 28.3 weeks, respectively (p < 0.05), with no significant difference in femoral shortening between the three groups (p > 0.05). Of the OI cases, 5 out of 12 had a family history. CONCLUSION: Short limb deformity is the most prevalent phenotype of SD. When fetal SD is suspected, detailed ultrasound screening should be conducted, combined with GA at initial diagnosis, family history, and molecular evidence, to facilitate more accurate diagnosis and enhance prenatal counseling and perinatal management.

Mesomelic dysplasias associated with the HOXD locus are caused by regulatory reallocations.

Human families with chromosomal rearrangements at 2q31, where the human HOXD locus maps, display mesomelic dysplasia, a severe shortening and bending of the limb. In mice, the dominant Ulnaless inversion of the HoxD cluster produces a similar phenotype suggesting the same origin for these malformations in humans and mice. Here we engineer 1 Mb inversion including the HoxD gene cluster, which positioned Hoxd13 close to proximal limb enhancers. Using this model, we show that these enhancers contact and activate Hoxd13 in proximal cells, inducing the formation of mesomelic dysplasia. We show that a secondary Hoxd13 null mutation in-cis with the inversion completely rescues the alterations, demonstrating that ectopic HOXD13 is directly responsible for this bone anomaly. Single-cell expression analysis and evaluation of HOXD13 binding sites suggests that the phenotype arises primarily by acting through genes normally controlled by HOXD13 in distal limb cells. Altogether, these results provide a conceptual and mechanistic framework to understand and unify the molecular origins of human mesomelic dysplasia associated with 2q31.

Combined deletions of IHH and NHEJ1 cause chondrodystrophy and embryonic lethality in the Creeper chicken.

The Creeper (Cp) chicken is characterized by chondrodystrophy in Cp/+ heterozygotes and embryonic lethality in Cp/Cp homozygotes. However, the genes underlying the phenotypes have not been fully known. Here, we show that a 25 kb deletion on chromosome 7, which contains the Indian hedgehog (IHH) and non-homologous end-joining factor 1 (NHEJ1) genes, is responsible for the Cp trait in Japanese bantam chickens. IHH is essential for chondrocyte maturation and is downregulated in the Cp/+ embryos and completely lost in the Cp/Cp embryos. This indicates that chondrodystrophy is caused by the loss of IHH and that chondrocyte maturation is delayed in Cp/+ heterozygotes. The Cp/Cp homozygotes exhibit impaired DNA double-strand break (DSB) repair due to the loss of NHEJ1, resulting in DSB accumulation in the vascular and nervous systems, which leads to apoptosis and early embryonic death.

Fetal magnetic resonance imaging of skeletal dysplasias.

BACKGROUND: Fetal magnetic resonance imaging (MRI) is obtained for prenatal diagnosis and prognostication of skeletal dysplasias; however, related literature is limited. OBJECTIVE: The purpose of this study was to define the utility of fetal MRI for skeletal dysplasias and to report MRI findings associated with specific diagnoses. MATERIALS AND METHODS: This retrospective study was approved by the institutional review board; informed consent was waived. Women referred for suspected fetal skeletal dysplasia who underwent MRI between January 2003 and December 2018 were included. Definitive diagnoses were determined by genetic testing, autopsy, physical examination and/or postnatal/postmortem imaging. Fetal MRI examinations and reports were reviewed. Descriptive statistics were used to summarize imaging findings. RESULTS: Eighty-nine women were referred for fetal MRI for possible skeletal dysplasia. Forty-three (48%) were determined to have a diagnosis other than skeletal dysplasia and nine were excluded for lack of specific skeletal dysplasia diagnosis. Thirty-seven cases of skeletal dysplasia with available fetal MRI and specific diagnosis were included for analysis. Diagnoses included achondrogenesis (n=2), achondroplasia (n=5), Boomerang dysplasia (n=1), campomelic dysplasia (n=2), Jeune syndrome (n=1), Kniest dysplasia (n=1), osteogenesis imperfecta (n=15) and thanatophoric dysplasia (n=10). A specific skeletal dysplasia diagnosis was mentioned in 17/37 (46%) of MRI imaging reports and correct for 14/17 (82%). MRI findings were reported for each specific skeletal dysplasia diagnosis. CONCLUSION: Fetal MRI is a useful diagnostic tool for skeletal dyplasias and excluded the diagnosis in nearly half of referred pregnancies. In addition to providing fetal lung volumes, fetal MRI demonstrates findings of the brain in achondroplasia and thanatophoric dysplasia, of the spine in achondroplasia and achondrogenesis, of the calvarium in osteogenesis imperfecta and thanatophoric dysplasia, and of the cartilage in Kniest dysplasia.

Honeycomb sterna: an unusual case of a developmental abnormality in the sternum.

This report details an unusual case of a human sternal developmental abnormality of an anatomical specimen part of the skeletal collection curated by University College London, Anthropology Department skeletal collection. This rarely reported developmental abnormality is caused by the non-fusion of lateral ossification centres in the sternebrae, resulting in the mesosternum having a honeycomb-like appearance. Sternal defects are typically underreported in the clinical literature as many cases being asymptomatic that they are typically diagnosed incidentally, as such there is a dearth in our current understanding of the development and anatomical variants of the sternum. Although in recent years, large-scale CT studies have investigated the prevalence of sternal developmental abnormalities, these studies have not reported sternal defects similar to the individual presented in this report. While most sternal defects are clinically uneventful, the lack of awareness of these variants can result in misinterpretation of radiological and pathological findings as such an understanding of anatomical variants even when asymptomatic is vital.

Prenatal diagnosis of skeletal dysplasias using a targeted skeletal gene panel.

OBJECTIVE: This study aimed to perform an accurate and precise diagnosis for fetuses with suspected skeletal anomalies based on an incomplete and limited ultrasound phenotype. METHODS: Proband-only targeted skeletal gene panel sequencing was performed on 12 families who had fetuses with suspected skeletal anomalies based on ultrasound evaluations at a mean gestational age of 24 weeks and 3 days. The fetuses all had normal standard genetic testing yield (karyotyping and microarray). RESULTS: In 10 of 12 fetuses, panel sequencing provided a diagnosis or possible diagnosis with identification of variants in the following genes: FGFR3, COL1A2, IHH, COL2A1, and DYNC2H1. Two cases revealed novel variants in COL2A1 and DYNC2H1. CONCLUSIONS: Our study suggests that targeted skeletal gene panel sequencing is highly sensitive for prenatal diagnosis of fetuses presenting with unexpected ultrasound findings suggestive of a skeletal dysplasia.

Ultra-Low-Dose Fetal CT With Model-Based Iterative Reconstruction: A Prospective Pilot Study.

OBJECTIVE: Prenatal diagnosis of skeletal dysplasia by means of 3D skeletal CT examination is highly accurate. However, it carries a risk of fetal exposure to radiation. Model-based iterative reconstruction (MBIR) technology can reduce radiation exposure; however, to our knowledge, the lower limit of an optimal dose is currently unknown. The objectives of this study are to establish ultra-low-dose fetal CT as a method for prenatal diagnosis of skeletal dysplasia and to evaluate the appropriate radiation dose for ultra-low-dose fetal CT. SUBJECTS AND METHODS: Relationships between tube current and image noise in adaptive statistical iterative reconstruction and MBIR were examined using a 32-cm CT dose index (CTDI) phantom. On the basis of the results of this examination and the recommended methods for the MBIR option and the known relationship between noise and tube current for filtered back projection, as represented by the expression SD = (milliamperes)-0.5, the lower limit of the optimal dose in ultra-low-dose fetal CT with MBIR was set. The diagnostic power of the CT images obtained using the aforementioned scanning conditions was evaluated, and the radiation exposure associated with ultra-low-dose fetal CT was compared with that noted in previous reports. RESULTS: Noise increased in nearly inverse proportion to the square root of the dose in adaptive statistical iterative reconstruction and in inverse proportion to the fourth root of the dose in MBIR. Ultra-low-dose fetal CT was found to have a volume CTDI of 0.5 mGy. Prenatal diagnosis was accurately performed on the basis of ultra-low-dose fetal CT images that were obtained using this protocol. The level of fetal exposure to radiation was 0.7 mSv. CONCLUSION: The use of ultra-low-dose fetal CT with MBIR led to a substantial reduction in radiation exposure, compared with the CT imaging method currently used at our institution, but it still enabled diagnosis of skeletal dysplasia without reducing diagnostic power.

miR-21 is involved in skeletal deficiencies of zebrafish embryos exposed to polychlorinated biphenyls.

Polychlorinated biphenyl (PCB) exposure increases the incidence and severity of skeletal diseases, but little is known about the mechanisms that mediate this relationship. We exposed zebrafish embryos to PCB1254 and assessed the changes in bone morphology protein receptor II (BMPRII), which is involved in bone formation and embryonic development, miRNA-21, for which BMPRII is a known target, and calcium metabolism. PCB1254 upregulated the expression of miR-21 and suppressed BMPRII expression. The inhibition of miR-21 reversed the downregulation of BMPRII and alleviated the PCB1254-induced loss of calcium. These findings suggest new biomarkers of developmental defects of the skeleton caused by PCBs.

Tomografía computarizada fetal de baja dosis para diagnosticar displasias óseas / Low-dose computed tomography to diagnose fetal bone dysplasias

Presentamos un caso de displasia cleidocraneal diagnosticado en la semana 25 de gestación mediante tomografía computarizada (TC) de baja dosis fetal. La sospecha era de displasia ósea grave debido al percentil bajo en los huesos largos y la apariencia ecográfica de craneosinostosis. La TC no demostró alteraciones incompatibles con la vida. La dosis efectiva de la prueba fue de 5 mSv, dentro del rango recomendado para estas exploraciones. La TC de baja dosis fetal es una técnica emergente que permite estudiar estructuras óseas con precisión a partir del segundo trimestre de gestación. En España, es legalmente posible interrumpir el embarazo en caso de malformación grave del feto incluso si se sobrepasa la semana 22 de gestación. Por tanto, ante la sospecha de una displasia ósea grave, el radiólogo debe conocer las estrategias para disminuir la dosis manteniendo una calidad diagnóstica suficiente, y conocer las estructuras óseas que debe evaluar (AU)

We present a case of cleidocranial dysplasia diagnosed by low-dose fetal computed tomography (CT) in the 25th week of gestation. Severe bone dysplasia was suspected because of the fetus’ low percentile in long bones length and the appearance of craniosynostosis on sonography. CT found no abnormalities incompatible with life. The effective dose was 5 mSv, within the recommended range for this type of examination. Low-dose fetal CT is a new technique that makes precision study of the bony structures possible from the second trimester of pregnancy. In Spain, abortion is legal even after the 22nd week of gestation in cases of severe fetal malformations. Therefore, in cases in which severe bone dysplasia is suspected, radiologists must know the strategies for reducing the dose of radiation while maintaining sufficient diagnostic quality, and they must also know which bony structures to evaluate (AU)

Approach to the diagnosis of skeletal dysplasias: Experience at a center with limited resources.

PURPOSE: A fetus with skeletal disorder poses diagnostic challenges in a resource-poor setting with limited management options. The objective of the study was to develop a step-by-step approach for the diagnosis of skeletal dysplasia in light of the limited resources available. METHODS: An algorithmic approach was used. The assessment for lethality was the first step, followed by the evaluation for fractures. In cases without evidence of fracture, severe constriction of thorax or associated polydactyly were searched for. In cases without severe thoracic constriction, the severity of micromelia was evaluated. After delivery, fetal examination was done to ascertain the etiology. RESULTS: During the 6-year period, 41 cases with shortened long bones were fully evaluated. Lethality was suspected in 30 cases. Fracture and beading were present in eight cases, and severe thoracic constriction with polydactyly was observed in seven cases. Mild micromelia was seen in 19 cases and severe micromelia in 7 cases. Among lethal skeletal dysplasias, thanatophoric dysplasia was most common (six cases). Among nonlethal skeletal dysplasias, achondroplasia was seen in eight cases. CONCLUSIONS: Lethality of skeletal dysplasia could be predicted on prenatal ultrasound with 100% accuracy. The step-by-step approach was helpful to characterize skeletal dysplasias. © 2016 Wiley Periodicals, Inc. J Clin Ultrasound 44:529-539, 2016.

Prenatal diagnosis of proximal focal femoral deficiency: Literature review of prenatal sonographic findings.

Proximal focal femoral deficiency (PFFD) is a rare musculoskeletal malformation that occurs in 0.11-0.2 per 10,000 live births. This congenital anomaly involves the pelvis and proximal femur with widely variable manifestations, from mild femoral shortening and hypoplasia to the absence of any functional femur and acetabular aplasia. Prenatal diagnosis of PFFD is still a challenge, but early recognition of this malformation could provide useful information to both parents and physicians concerning management and therapeutic planning. For this review, we analyzed all the cases of prenatally diagnosed PFFD that were reported in the literature from 1990 to 2014 and provide a description of the most common prenatal sonographic findings.

Signaling Pathways in Craniofacial Development: Insights from Rare Skeletal Disorders.

In the developing embryo, signaling pathways define how the mesenchymal precursors of bone form individual skeletal elements with the proper size, shape, orientation, and integration. Disruptions to these signaling processes lead to a large variety of congenital conditions categorized as skeletal dysplasias. While individually these skeletal disorders are rare, collectively they represent a significant cause of disability in the United States. Here, we discuss how the study of these rare events in human development reveal novel and unexpected insights into signaling mechanisms that regulate normal skeletal development and, in the process, advance novel molecular-based therapies for treatment of rare and common bone diseases alike.

Use of low dose computed tomography with 3D reconstructions for the prenatal evaluation of suspected skeletal dysplasia.

BACKGROUND: Sonographic evaluation of congenital skeletal dysplasias is often challenging. Ultrasound may be limited in demonstrating the skeleton and may overlook specific signs of skeletal abnormality. Computed tomography (CT) with 3D reconstruction was proposed as an aid in the diagnosis of skeletal dysplasias. OBJECTIVES: To describe our experience with 3D-CT imaging for the evaluation of suspected skeletal dysplasias. METHODS: The study group comprised 20 pregnant women carrying 22 fetuses, referred for further evaluation by CT following sonographic suspicion of fetal skeletal dysplasia at 17-39 weeks of gestation. Examinations were performed using various CT protocols. Radiation exposure was decreased during the study period, with eventual lowering of the dose to 1-3 mSv. Meticulous review of the skeleton and long bone measurements were performed on 3D reconstructions. For cases of pregnancy termination, the postmortem diagnosis was compared retrospectively with the CT findings. RESULTS: Very low dose CT protocols provided excellent diagnostic images. Of 22 fetuses suspected of having skeletal dysplasia on ultrasound, 8 were found by CT to be dysplastic and in 7 the pregnancy was terminated. Postmortem findings, when available, concurred with the CT diagnosis. The remaining 14 fetuses within this cohort were found to be normal according to CT and were carried to term. CONCLUSIONS: 3D-CT may be a valuable complimentary imaging tool to ultrasound for the diagnosis of skeletal dysplasias. With low dose protocols, this examination is relatively safe, and in the appropriate clinical context may assist in making difficult decisions prenatally.

Imaging in the diagnosis of rare diseases.

A disease is considered rare if it affects no more than 5 in 10,000 people. More than six thousand rare diseases have been detected so far and they affect 6-8% of the population which equals 2.3-3 million people in Poland. Some of the rare diseases are already diagnosed in utero, e.g. skeletal dysplasias on ultrasonography or central nervous system diseases on magnetic resonance imaging (MRI). Many cases are finally diagnosed after radiologist's suggestion in a radiological report. Although diagnostic imaging cannot be considered as a basis for diagnosis of most of rare diseases, these studies represent an important element in the diagnostic chain. The complicated and long process of diagnosis may be significantly shortened by suggestions of the radiologist, based on the observation of these elements of radiological appearance of the lesions that are characteristic for a particular group of diseases, or even for a particular disease entity. However, the absolute condition for success is the close clinical-radiological cooperation, with clinicians providing the radiologists with their knowledge of patient's history, clinical manifestations, and the results of other investigations.

Radiation dose reduction at MDCT with iterative reconstruction for prenatal diagnosis of skeletal dysplasia: preliminary study using normal fetal specimens.

OBJECTIVE: The purpose of this study was to investigate to what degree the radiation dose can be reduced without affecting the ability to evaluate normal fetal bones at MDCT with iterative reconstruction. MATERIALS AND METHODS: Fifteen normal fetal specimens immersed in containers (30- and 35-cm diameter) were scanned with a 64-MDCT scanner, with tube voltage of 100 kVp and tube current of 600, 300, 150, 100, and 50 mA. Images were subjected to adaptive statistical iterative reconstruction (ASIR). The fetal dose was measured using glass dosimeters. We calculated the relative ratio of the dose at 600 mA. Image quality was evaluated on maximum-intensity-projection and volume-rendering images. Two radiologists recorded the visualization scores of five regions. Images at 600 mA were considered to be standard. RESULTS: With the 30-cm-diameter container, the fetal dose was 10.15 mGy (relative ratio, 100%) at a tube current of 600, 51% at 300, 25% at 150, 17% at 100, and 9% at 50 mA. With the 35-cm-diameter container the fetal dose was 10.01 mGy (relative ratio, 100%) at 600, 47% at 300, 24% at 150, 17% at 100, and 8% at 50 mA. Visual evaluation showed that in both containers, with ASIR 90%, there was a statistically significant difference between 50-and 600-mA images (p<0.01) but not between 600-mA images and those acquired at 100, 150, and 300 mA (p=0.08-1.00). CONCLUSION: The fetal radiation dose for the evaluation of normal fetal bones can be reduced by 83% with ASIR 90%.

Fetal skeletal computed tomography: when? How? Why?

PURPOSE: To study the additional role of fetal skeletal computed tomography in suspected prenatal bone abnormalities. MATERIALS AND METHODS: Two centers included in a retrospective study all fetuses who benefited from skeletal computed tomography for a suspected constitutional bone disease or focal dysostosis. RESULTS: A total of 198 patients were included. CT was performed in 112 patients (56%) for an isolated short femur below the third percentile (group A), in 15 patients (8%) for bowed or fractured femur (group B), in 23 patients (12%) for biometric discrepancy between a short femur and increased head circumference (group C) and in 48 patients (24%) for suspected focal dysostosis (group D). CT was interpreted as normal in 126 cases (64%), i.e. 87% in group A, 0% in group B, 65% in group C and 25% in group D. When including only cases with postnatal or postmortem clinical and/or radiological confirmation was available, CT provided additional and/or more accurate information than ultrasound in 20% of cases in group A, 66% in group B, 30% in group C and 72% in group D. Sixty-seven percent of patients in whom CT was interpreted as normal were lost to follow-up. CONCLUSION: In isolated short femur, fetal skeletal CT is normal in the great majority of cases although protocolized follow-up of these babies is absolutely compulsory, as a large proportion is lost to follow-up. Fetal skeletal CT can confirm or improve imaging for the suspected diagnosis in suspected focal dysostosis or constitutional bone disease.

Follistatin in chondrocytes: the link between TRPV4 channelopathies and skeletal malformations.

Point mutations in the calcium-permeable TRPV4 ion channel have been identified as the cause of autosomal-dominant human motor neuropathies, arthropathies, and skeletal malformations of varying severity. The objective of this study was to determine the mechanism by which TRPV4 channelopathy mutations cause skeletal dysplasia. The human TRPV4(V620I) channelopathy mutation was transfected into primary porcine chondrocytes and caused significant (2.6-fold) up-regulation of follistatin (FST) expression levels. Pore altering mutations that prevent calcium influx through the channel prevented significant FST up-regulation (1.1-fold). We generated a mouse model of the TRPV4(V620I) mutation, and found significant skeletal deformities (e.g., shortening of tibiae and digits, similar to the human disease brachyolmia) and increases in Fst/TRPV4 mRNA levels (2.8-fold). FST was significantly up-regulated in primary chondrocytes transfected with 3 different dysplasia-causing TRPV4 mutations (2- to 2.3-fold), but was not affected by an arthropathy mutation (1.1-fold). Furthermore, FST-loaded microbeads decreased bone ossification in developing chick femora (6%) and tibiae (11%). FST gene and protein levels were also increased 4-fold in human chondrocytes from an individual natively expressing the TRPV4(T89I) mutation. Taken together, these data strongly support that up-regulation of FST in chondrocytes by skeletal dysplasia-inducing TRPV4 mutations contributes to disease pathogenesis.