Detection of G1138A Mutation of the FGFR3 Gene in Tooth Material from a 180-Year-Old Museological Achondroplastic Skeleton

Contains fulltext : 189828.pdf (publisher's version ) (Open Access

Two is a Crowd Two is a Crowd: On the Enigmatic Etiopathogenesis of Conjoined Twinning

In this article, we provide a comprehensive overview of multiple facets in the puzzling genesis of symmetrical conjoined twins. The etiopathogenesis of conjoined twins remains matter for ongoing debate and is currently cited—in virtually every paper on conjoined twins—as partial fission or secondary fusion. Both theories could potentially be extrapolated from embryological adjustments exclusively seen in conjoined twins. Adoption of these, seemingly factual, theoretical proposals has (unconsciously) resulted in crystallized patterns of verbal and graphic representations concerning the enigmatic genesis of conjoined twins. Critical evaluation on their plausibility and solidity remains however largely absent. As it appears, both the fission and fusion theories cannot be applied to the full range of conjunction possibilities and thus remain matter for persistent inconclusiveness. We propose that initial duplication of axially located morphogenetic potent primordia could be the initiating factor in the genesis of ventrally, laterally, and caudally conjoined twins. The mutual position of two primordia results in neo-axial orientation and/or interaction aplasia. Both these embryological adjustments result in conjunction patterns that may seemingly appear as being caused by fission or fusion. However, as we will substantiate, neither fission nor fusion are the cause of most conjoined twinning types; rather what is interpreted as fission or fusion is actually the result of the twinning process itself. Furthermore, we will discuss the currently held views on the origin of conjoined twins and its commonly assumed etiological correlation with monozygotic twinning. Finally, considerations are presented which indicate that the dorsal conjunction group is etiologically and pathogenetically different from other symmetric conjoined twins. This leads us to propose that dorsally united twins could actually be caused by secondary fusion of two initially separate monozygotic twins. An additional reason for the ongoing etiopathogenetic debate on the genesis of conjoined twins is because different types of conjoined twins are classically placed in one overarching receptacle, which has hindered the quest for answers. Clin. Anat. 2019. © 2019 Wiley Periodicals, Inc

Pectus excavatum and carinatum

Pectus excavatum and carinatum are the most common morphological chest wall abnormalities. For both pectus excavatum and carinatum the pathogenesis is largely unknown although various hypotheses exist. Usually, exclusion of an underlying syndromal or connective tissue disorder is the reason for referral for genetic evaluation. A detailed anamnesis and family history are needed as well as a complete dysmorphological physical examination. If no features of an underlying disorder are detected, then the pectus excavatum/carinatum can be considered as an isolated abnormality and no further genetic studies seem indicated. Although cases of non-syndromal pectus excavatum/carinatum with a positive family history fitting Mendelian inheritance have been described, it is possible that these pedigrees represent multifactorial inheritance, as no genetic cause for familial isolated pectus excavatum/carinatum has been described yet. The recurrence risk for a non-familial iolated pectus excavatum/carinatum is unknown, but thought to be low. If other symptoms are found then appropriate further diagnostic studies are indicated as pectus excavatum/carinatum can be part of many syndromes. However, the most important and most frequently observed monogenic syndromes with pectus excavatum/carinatum are Marfan Syndrome and Noonan Syndrom

The development of the human notochord

The notochord is a major regulator of embryonic patterning in vertebrates and abnormal notochordal development is associated with a variety of birth defects in man. Proper knowledge of the development of the human notochord, therefore, is important to understand the pathogenesis of these birth defects. Textbook descriptions vary significantly and seem to be derived from both human and animal data whereas the lack of references hampers verification of the presented data. Therefore, a verifiable and comprehensive description of the development of the human notochord is needed. Our analysis and three-dimensional (3D) reconstructions of 27 sectioned human embryos ranging from Carnegie Stage 8 to 15 (17-41 days of development), resulted in a comprehensive and verifiable new model of notochordal development. Subsequent to gastrulation, a transient group of cells briefly persists as the notochordal process which is incorporated into the endodermal roof of the gut while its dorsal side attaches to the developing neural tube. Then, the notochordal process embeds entirely into the endoderm, forming the epithelial notochordal plate, which remains intimately associated with the neural tube. Subsequently, the notochordal cells detach from the endoderm to form the definitive notochord, allowing the paired dorsal aortae to fuse between the notochord and the gut. We show that the formation of the notochordal process and plate proceeds in cranio-caudal direction. Moreover, in contrast to descriptions in the modern textbooks, we report that the formation of the definitive notochord in humans starts in the middle of the embryo, and proceeds in both cranial and caudal directions