Arterial dysgenesis and limb defects: Clinical and experimental examples

Embryonic Vascular Dysgenesis: The Origin of Proximal Femoral Focal Deficiency

BACKGROUND

Proximal Femoral Focal Deficiency (PFFD) is the most proximal manifestation of a syndrome involving Congenitally Shortened lower Limbs (CSL), which also affects the fibula and midline metatarsals. This pattern of congenital human long bone deficiencies corresponds, in a time dependent manner, to the failed ingrowth pathways of new blood vessels of the growing embryonic limb. The distal femoral condyles are, in contrast, served by an alternative vascular supply from around the knee joint, and so remain resistant to the CSL deficiency.

AIM

We hypothesize that embryonic vascular dysgenesis causes PFFD, as well as the cardinal features of the Femoral, Fibular and midline Metatarsal deficiencies (FFM) syndrome.

RESULTS

Arteriography of CSL with PFFD reveals diminution or failed formation of the Femoral Artery (FA), which corresponds to downstream skeletal reductions. It may also reveal preservation of the primitive Axial Artery (AA) of the embryonic limb. The combination of missing and retained primitive vessels inform the time, place, and nature of the etiologic vascular events. This suggests that PFFD is the visible expression of a normally prefigured cartilaginous scaffold of the femur, which develops in conformity with the available pattern of blood vessels present. The teratogen thalidomide, known to affect the forming embryonic vasculature, also produces PFFD indistinguishable from the naturally occurring entity.

CONCLUSION

The entire spectrum of PFFD, including phocomelia, fibular, and metatarsal dystrophisms, should thus be regarded as downstream skeletal results of embryonic arterial dysgeneses.

Embryonic development grand challenge: crosslinking advances

Research on embryonic development is entering into a new era. As a traditionally descriptive discipline within anatomy, embryologists have formed international consortia and digitized important histological collections for preservation and open access. Embryonic development has recently received a wider attention in context with temporo-spatial transcriptomics at single cell level. These can be expected to fuel the realization of the transdisciplinary significance of efforts to decipher embryonic development. Addressing its complexities encompasses a wealth of challenges that intersect across the domains of science, society, and politics underlining its outstanding importance as well as its inherently interdisciplinary nature. The challenges of this field are by no means confined to understanding the intricate biological mechanisms but also have humanitarian implications. To fully appreciate the mechanisms underlying human development, principles of embryogenesis have predominantly been analyzed employing animal models which allow us to broaden our view on developmental processes. As a result of recent pioneering work and technical progress centered around stem cell-based 3D approaches, we are entering into a historical new phase of learning about mammalian embryonic development. In vertebrates, a growing concern now focuses the reduction of animal experimentation. This perspective article outlines the major challenges in this amazing field that offer an enormous potential for basic biomedical sciences as well as related translational approaches if they are tackled in a multidisciplinary discourse.

Limb reduction in an Esco2 cohesinopathy mouse model is mediated by p53-dependent apoptosis and vascular disruption

Roberts syndrome (RBS) is an autosomal recessive disorder with profound growth deficiency and limb reduction caused by ESCO2 loss-of-function variants. Here, we elucidate the pathogenesis of limb reduction in an Esco2fl/fl;Prrx1-CreTg/0 mouse model using bulk- and single-cell-RNA-seq and gene co-expression network analyses during embryogenesis. Our results reveal morphological and vascular defects culminating in hemorrhage of mutant limbs at E12.5. Underlying this abnormal developmental progression is a pre-apoptotic, mesenchymal cell population specific to mutant limb buds enriched for p53-related signaling beginning at E9.5. We then characterize these p53-related processes of cell cycle arrest, DNA damage, cell death, and the inflammatory leukotriene signaling pathway in vivo. In utero treatment with pifithrin-α, a p53 inhibitor, rescued the hemorrhage in mutant limbs. Lastly, significant enrichments were identified among genes associated with RBS, thalidomide embryopathy, and other genetic limb reduction disorders, suggesting a common vascular etiology among these conditions.

Teratogenicity and Reactive Oxygen Species after transient embryonic hypoxia: Experimental and clinical evidence with focus on drugs causing failed abortion in humans

Teratogenicity and Reactive Oxygen Species after transient embryonic hypoxia: Experimental and clinical evidence with focus on drugs with human abortive potential. Reactive Oxygen Species (ROS) can be harmful to embryonic tissues. The adverse embryonic effects are dependent on the severity and duration of the hypoxic event and when during organongenesis hypoxia occurs. The vascular endothelium of recently formed arteries in the embryo is highly susceptible to ROS damage. Endothelial damage results in vascular disruption, hemorrhage and maldevelopment of organs, which normally should have been supplied by the artery. ROS can also induce irregular heart rhythm in the embryo resulting in alterations in blood flow and pressure from when the tubular heart starts beating. Such alterations in blood flow and pressure during cardiogenesis can result in a variety of cardiovascular defects, for example transpositions and ventricular septal defects. One aim of this article is to review and compare the pattern of malformations produced by transient embryonic hypoxia of various origins in animal studies with malformations associated with transient embryonic hypoxia in human pregnancy due to a failed abortion process. The results show that transient hypoxia and compounds with potential to cause failed abortion in humans, such as misoprostol and hormone pregnancy tests (HPTs) like Primodos, have been associated with a similar spectrum of teratogenicity. The spectrum includes limb reduction-, cardiovascular- and central nervous system defects. The hypoxia-ROS related teratogenicity of misoprostol and HPTs, is likely to be secondary to uterine contractions and compression of uterinoplacental/embryonic vessels during organogenesis.

Congenital Limb Defects: A Retrospective Cohort Study and Overview of the Literature

PURPOSE

Congenital limb defects are common malformations that are often associated with other organ defects and genetic disorders. Since prenatal detection is challenging and classification is often complex, the aim of this study was to describe a large cohort of fetuses with congenital limb defects and to identify characteristics that are essential for prenatal evaluation, counselling, and management.

MATERIALS AND METHODS

In this retrospective cohort study, all cases of confirmed fetal limb defects from two centers for prenatal ultrasound between 2001 and 2021 were evaluated. Cases with skeletal dysplasia were excluded from this study. Demographic data, association with genetic disorders, and correlation with maternal parameters were analyzed statistically.

RESULTS

170 fetuses were included in this study. 60% were diagnosed with a reduction anomaly and 40% with a duplication anomaly. The majority of fetuses were male, and in 73.5% of all cases, additional malformations were present. Among the genetic causes, trisomy 13 and 18 were the most common in this cohort.

CONCLUSION

Congenital limb malformations are important markers for complex fetal disorders that warrant referral to specialists in prenatal ultrasound. To improve prenatal detection, care should be taken to visualize all fetal extremities already in early pregnancy.

Thalidomide upper limb embryopathy - pathogenesis, past and present management and future considerations

This review article provides a comprehensive overview of thalidomide upper limb embryopathy including updates about its pathogenesis, a historical account of the management of the paediatric thalidomide patient, experience with management of the adult patient, as well as creating awareness about early onset age-related changes associated with limb differences. Despite its withdrawal from the market in November 1961, novel discoveries have meant thalidomide is licensed again and currently still in use to treat a variety of conditions, including inflammatory disorders and some cancers. Yet, if not used safely, thalidomide still has the potential to cause damage to the embryo. Recent work identifying thalidomide analogues that retain clinical benefits yet without the harmful effects are showing great promise. Understanding the problems thalidomide survivors face as they age can allow surgeons to support their unique healthcare issues and translate these principles of care to other congenital upper limb differences.

Genetic overview of postaxial polydactyly: Updated classification

Polydactyly or polydactylism, also known as a hyperdactyly, is a congenital limb defect with various morphologic phenotypes. Apart from physical and functional impairments, the presence of polydactyly is an indication of an underlying syndrome in the newborn. Usually, it follows as an autosomal dominant/recessive inheritance pattern with defects in the limb development's anteroposterior patterning. Although mutations in several genes have been associated with polydactyly; however, the exact underlying cause, pathways, and disease mechanisms are still unexplored, thus making it of multi-factorial origin. Polydactyly is divided into three subtypes; radial, ulnar, and central polydactyly. So far, 11 loci (PAPA1-PAPA11) and seven human genes have been reported to cause non-syndromic postaxial polydactyly in humans, including the ZNF141, GLI3, IQCE, GLI1, FAM92A1, KIAA0825, and DACH1. In this review, we discuss emerging evidences of clinical and molecular characterization of polydactyly types in term of the involvement of newly associated genes and loci for non-syndromic postaxial polydactyly, and how these might impact our understanding of the genetic mechanisms and molecular etiology involved in the cause of polydactyly.

Vanadium(IV) oxide affects embryonic development in mice

Vanadium(V) and vanadium(IV) are the predominant redox forms present in the environment, and epidemiological studies have reported that prenatal vanadium exposure is associated with restricted fetal growth and adverse birth outcomes. However, data about the toxic effects of vanadium(IV) oxide (V₂ O₄ ) on the development of mammals are still limited. Therefore, in this work, 4.7, 9.4, or 18.7 mg/kg body weight/injection/day V₂ O₄ was administered through an intraperitoneal (ip) injection to pregnant mice from gestational days 6 to 16. The results showed that V₂ O₄ produced maternal and embryo-fetal toxicity and external abnormalities in the offspring, such as malrotated and malpositioned hind limbs, hematomas and head injuries. Moreover, the skeletons of the fetuses presented reduced ossification of the cranial bones, including the frontal and parietal bones, corresponding to head injuries observed in the external assessment of the fetuses. These results demonstrate that administration of V₂ O₄ to pregnant females in the organogenesis period adversely affects embryonic development.

From the Farm to the Lab: How Chicken Embryos Contribute to the Field of Teratology

Congenital anomalies and its causes, particularly, by external factors are the aim of the field called teratology. The external factors studied by teratology are known as teratogens and can be biological or environmental factors for example, chemicals, medications, recreational drugs, environmental pollutants, physical agents (e.g., X-rays and maternal hyperthermia) and maternal metabolic conditions. Proving the teratogenicity of a factor is a difficult task requiring epidemiology studies as well as experimental teratology evidence from the use of animal models, one of which is the chicken embryo. This model in particular has the advantage of being able to follow development live and in vivo, with rapid development hatching around 21 days, is cheap and easy to manipulate and to observe development. All this allows the chicken embryo to be used in drug screening studies, teratogenic evaluation and studies of mechanisms of teratogenicity. The chicken embryo shares morphological, biochemical and genetic similarities with humans as well as mammalian species, making them ideal to ascertain the actions of teratogens, as well as screen drugs to test for their safety. Pre-clinical trials for new drugs are carried out in rodents and rabbits, however, chicken embryos have been used to screen new compounds or analogs of thalidomide as well as to investigate how some drugs can lead to congenital malformations. Indeed, the chicken embryo has proved valuable in understanding how many congenital anomalies, seen in humans, arise following teratogen exposure. The aim of this review is to highlight the role of the chicken embryo as an experimental model for studies in teratology, exploring its use in drug screening studies, phenotypic evaluation and studies of teratogenic mechanisms of action. Here, we discuss many known teratogens, that have been evaluated using the chicken embryo model including some medicines, such as, thalidomide, valproic acid; recreational drugs including alcohol; environmental influences, such as viruses, specifically ZIKV, which is a newly discovered human teratogen. In addition, we discuss how the chicken embryo has provided insight on the mechanisms of teratogenesis of many compounds and also how this impact on drug safety.

Embryology of the lower limb demonstrates that congenital absent fibula is a radiologic misnomer

The congenitally shortened limb (CSL) with fibular deficiency or absence has historically been graded by plain radiography, while associated cartilaginous and arterial soft tissue anomalies have been comparatively neglected. Consistent pathological evidence of remnant cartilaginous bodies in place of the fibula presupposes earlier existence of a preformed cartilaginous template of the fibula. In complete fibular radiographic absences, often associated with midline metatarsal deficiencies, the two usual nutrient arteries to the fibula fail to form, as they normally would have, around the (16-18 mm stage) sixth embryonic week. The histopathology of fallow persisting fibular anlagen, in association with missing arteries and retained primitive arteries, suggests the anlage is a dystrophic, but otherwise normally prefigured, cartilaginous scaffold of the fibula. Thus, the widely employed term absent fibula, which has been grounded in plain radiography, is a misnomer. Additionally, since the metatarsals missing in congenitally shortened limb are midline, the related term, fibular hemimelia, is similarly inaccurate. A new taxonomy, based on embryological principles rather than radiographic appearance alone, will promote limb dystrophism as a more accurate term combining arrested embryonic vascular development and congenitally shortened limb of the lower extremity.

The vascular origins of antero-medial tibial bowing in congenital fibular deficiency

Anteromedial bowing and shortening of the tibia are intrinsic features of limbs with congenital fibular deficiency (CFD). Tibial bowing occurs more frequently when the fibula is radiographically absent rather than deficient. The bowing has been attributed to rapid longitudinal growth of the tibial anlage coupled with anteromedial tibial bending moments of the posterior crural and lateral peroneal musculature unopposed in the absence of a fibular strut. Eccentric mechanical loading results in asymmetric mineral deposition and thickening of the diaphyseal cortex. Skeletogenesis depends upon an intimate interplay between the normally prefigured tibial cartilage anlage and beginning muscular contractile actions during initial vascularization of the anlage, while the embryonic limb vasculature is undergoing a series of transitions. A diaphyseal periosteal collar normally forms at the site of nutrient artery invasion and stabilizes the growing anlage. In CFD however, arteriography consistently reveals anomalous tibial nutrient arterial branches, which originate from a primitive axial artery rather than from the usual posterior tibial artery. These anomalous nutrient arteries enter the tibial shaft at the posterior aspect of the proximal metaphysis, establishing an eccentric bone collar. The developing vasculature of the embryonic limb is responsive to the then most metabolically active tissues. Disruption of the reciprocal relationship between the transitioning vasculature and the developing long bones is pivotal in producing the diverse skeletal malformations of the congenital short limb (CSL). Embryonic vascular dysgenesis contributes not only to the well-recognized congenital tibial and fibular shortenings but also predisposes to congenital anteromedial bowing of the tibia.

Missing Midline Metatarsals Conform to Plantar Arterial Arch Dysgenesis

Midline metatarsal ray deficiencies, which occur in approximately half of congenital short limbs with fibular deficiency, provide the most distal and compelling manifestation of a fluid spectrum of human lower-extremity congenital long bone reductions; this spectrum syndromically affects the long bone triad of the proximal femur, fibula, and midline metatarsals. The bony deficiencies correspond to sites of rapid embryonic arterial transitioning. Long bones first begin to ossify because of vascular invasions of their respective mesenchymal/cartilage anlagen, proceeding in a proximal-to-distal sequence along the forming embryonic limb. A single-axis artery forms initially in the embryonic lower limb by means of vasculogenesis. Additional arteries evolve in overlapping transitional waves, in proximity to the various anlagen, during the sixth and seventh weeks after fertilization. An adult pattern of vessels presents by the eighth week. Arterial alterations, in the form of retained primitive embryonic vessels and/or reduced absent adult vessels, have been observed clinically at the aforementioned locations where skeletal reductions occur. Persistence of primitive vessels in association with the triad of long bone reductions allows a heuristic estimation of the time, place, and nature of such coupled vascular and bony dysgeneses. Arterial dysgenesis is postulated to have occurred when the developing arterial and skeletal structures were concurrently vulnerable to teratogenic insults because of embryonic arterial instability, a risk factor during arterial transition. It is herein hypothesized that flawed arterial transitions subject the prefigured long bone cartilage models of the rapidly growing limb to the risk of teratogenesis at one or more of the then most rapidly growing sites. Midline metatarsal deficiency forms the keystone of this developmental concept of an error of limb development, which occurs as a consequence of failed completion of the medial portion of the plantar arch. Therefore, the historical nomenclature of congenital long bone deficiencies will benefit from modification from a current reliance on empirical physical taxonomies to a developmental foundation.

Congenital fibular dystrophisms conform to embryonic arterial dysgenesis

The congenital short limb (CSL) with fibular deficiency has traditionally been graded by plain radiography. The most popular orthopedic classification sorts the fibular dysmorphologies into three radiographic groupings: IA (thinned), IB (proximally truncated), or II (absent). In contrast, the soft tissues have been relatively neglected. Since bone formation of the fibula progresses from the anlage, a scaffolding cartilage mold intermediate, cartilage transformation to bone is dependent upon timely embryonic arterial invasion. Absences of the requisite arteries predicate specific skeletal dysmorphologies. The usual arterial supply of the fibula is comprised primarily of the anterior tibialis artery (ATA), which uniquely supplies the proximal portion of the fibula, and also joins the peroneal artery (PA) in supplying the mid to distal fibular shaft. Combinations of the two nutrient arteries allow four potential variations of fibular vascular supply, among which the ATA and PA conjoin to supply the normal fibula and variably supply the three dysmorphic fibular models. The IA and IB deformities conform, respectively, to the absences of the PA and the ATA. Combined ATA and PA absences present in the radiographically "absent" fibula. Thus, each of the four fibular (dys)morphologies conforms to a specific embryonic pattern of arterial development. The term "dystrophism" most accurately characterizes such malformed long bones.

Effect on the offspring of pregnant females CD-1 mice treated with a single thallium(I) application

Thallium (Tl) is a highly toxic metal for human beings; higher amounts found in diverse fluids of pregnant women are associated with low birth weight and preterm birth. However, experimental data concerning their effects on the embryonic development of mammalian organisms are limited. Hence, in the present work, TI(I) acetate of 0, 4.6, 9.2, or 18.5 mg/kg body weight were administered by intraperitoneal injection to groups of 10 pregnant CD-1 mice on the 7th gestational day, and animals were sacrificed on day 18 of gestation. The fetuses obtained showed some variations, such as trunk bent over (18.5 mg/kg), tail variations (all doses), forelimbs malrotation and hind limbs (all doses). Skeletal examination of the fetuses showed a delay in the ossification of skull bones, ribs, and limbs (all doses). In conclusion, the Intraperitoneal injection of Tl(I) acetate to pregnant mice induced morphological variations and a delay of the fetus ossification.

Vascular anomalies of the upper limb

Vascular anomalies are common in the upper extremities, but there continues to be a relative paucity of information about them in publications dealing with surgery in the hands and upper limbs. The wide spectrum of pathology and an inconsistent use of terminology make vascular anomalies susceptible to incorrect diagnosis and as a result, to misdirected management. This article aims to provide an update on vascular anomalies relevant to the upper limbs, focusing on significant advances in pathogenesis and genetics, classification systems, diagnosis and treatment.

The teratogenic effects of thalidomide on limbs

Thalidomide remains notorious as a result of the damage it caused to children born to mothers who used it to treat morning sickness between 1957 and 1961. The re-emergence of the drug to treat a range of conditions including erythema nodosum leprosum (a complication of leprosy) has led to a new generation of thalidomide damaged children being born in Brazil. Although thalidomide affects most of the developing tissues and organs of the body, the damage to the limbs is striking. Indeed phocomelia, the severe reduction or loss of the proximal long bones with retention of the distal hand/foot plate remains the stereotypical image of thalidomide. This review focuses on the type and range of damage thalidomide caused to the limbs, reviews current understanding of the mechanisms underlying thalidomide-induced limb malformations and outlines some of the challenges remaining in elucidating its teratogenicity.

Expression analysis of limb element markers during mouse embryonic development

Background: While data regarding expression of limb element and tissue markers during normal mouse limb development exist, few studies show expression patterns in upper and lower limbs throughout key limb development stages. A comparison to normal developmental events is essential when analyzing development of the limb in mutant mice models. Results: Expression patterns of the joint marker Gdf5, tendon and ligament marker Scleraxis, early muscle marker MyoD1, and blood vessel marker Cadherin5 (Cdh5) are presented during the most active phases of embryonic mouse limb patterning. Anti‐neurofilament staining of developing nerves in the fore‐ and hindlimbs and cartilage formation and progression also are described. Conclusions: This study demonstrates and describes a range of key morphological markers and methods that together can be used to assess normal and abnormal limb development. Developmental Dynamics 247:1217–1226, 2018. © 2018 The Authors. Developmental Dynamics published by Wiley Periodicals, Inc. on behalf of American Association of Anatomists

Expression patterns of molecular markers throughout both fore‐ and hindlimb development ‐ which can be used to assess normal and abnormal development.

Detailled description of innervation during fore‐ and hindlimb development confirming innervation first seen after limb patterning events have begun.

Description of cartilage development and progression indicates alizarin red staining not seen until E15.5 in both fore‐ and hindlimbs.

Hindlimb lags behind forelimb molecularly and morphologically until E14.5.

Detailled description of methods used to study fore‐ and hindlimb development.

Vertebrate embryos as tools for anti-angiogenic drug screening and function

The development of new angiogenic inhibitors highlights a need for robust screening assays that adequately capture the complexity of vessel formation, and allow for the quantitative evaluation of the teratogenicity of new anti-angiogenic agents. This review discusses the use of screening assays in vertebrate embryos, specifically focusing upon chicken and zebrafish embryos, for the detection of anti-angiogenic agents.

"The legacy of thalidomide" - A multidisciplinary meeting held at the University of York, United Kingdom, on September 30, 2016

BACKGROUND

Between 1957 and 1962 thalidomide was used as a nonaddictive, nonbarbiturate sedative that also was successful in relieving the symptoms of morning sickness in early pregnancy. Infamously, thousands of babies were subsequently born with severe birth defects. The drug is used again, today, to successfully treat leprosy, and tragically, there is a new generation of thalidomide damaged children in Brazil. While the outward damage in babies has been documented, the effects of the damage upon the survivors as they grow up, the lifestyle changes and adaptations required to be made, as well as studies into ageing in survivors, has received little attention and remains understudied.

METHODS

A unique multidisciplinary meeting was organized at the University of York bringing together thalidomide survivors, clinicians, scientists, historians, and social scientists to discuss the past, the current and the future implications of thalidomide.

RESULTS

There is still much to learn from thalidomide, from its complex history and ongoing impact on peoples' lives today, to understanding its mechanism/s to aid future drug safety, to help identify new drugs retaining clinical benefit without the risk of causing embryopathy.

CONCLUSION

For thalidomide survivors, the original impairments caused by the drug are compounded by the consequences of a lifetime of living with a rare disability, and early onset age-related health problems. This has profound implications for their quality of life and need for health and social care services. It is vital that these issues are addressed in research, and in clinical practice if thalidomide survivors are to "age well". Birth Defects Research 109:296-299, 2017. © 2017 Wiley Periodicals, Inc.

A new mammalian model system for thalidomide teratogenesis: Monodelphis domestica

From 1957 to 1962, thalidomide caused birth defects in >10,000 children. While the drug was pulled from the market, thalidomide is currently prescribed to treat conditions including leprosy. As a result, a new generation of babies with thalidomide defects is being born in the developing world. This represents a serious problem, as the mechanisms by which thalidomide disrupts development remain unresolved. This lack of resolution is due, in part, to the absence of an appropriate mammalian model for thalidomide teratogenesis. We test the hypothesis that opossum (Monodelphis domestica) is well suited to model human thalidomide defects. Results suggest that opossum embryos exposed to thalidomide display a range of phenotypes (e.g., heart, craniofacial, limb defects) and penetrance similar to humans. Furthermore, all opossums with thalidomide defects exhibit vascular disruptions. Results therefore support the hypotheses that opossums make a good mammalian model for thalidomide teratogenesis, and that thalidomide can severely disrupt angiogenesis in mammals.