2011 William Allan Award: development and evolution

Evolution in the clinic: Maladaptive units and "minor anomalies"

It is here argued that the application of the term "minor anomalies" is often imprecise and likely outdated. In the past, the designation was used indiscriminately to refer to a great variety of unrelated morphogenetic phenomena. Also, the term does not discriminate between mild qualitative defects of development (mild malformations) and quantitative variants of normal structure. The human face was formed by natural and sexual selection. Morphological and morphogenetic analyses have shown that the human face with its skin, muscles, nerves, arteries, veins, glands, and lymphatics is a complex structure made up of progeny of ectoderm and mesoderm. Holoprosencephaly demonstrates graphically how these embryonic derivatives fit together sequentially. These derivatives are the adaptive units of the human organism, the result of stringent evolutionary forces uniting essential function to a minimum of structure. Before an "unusual" facial appearance is diagnosed as "abnormal", phenotype analysis is required to determine if there is a family resemblance or if it is a pleiotropic structure. The facial structures of chimps and humans are homologous by virtue of descent from a common ancestor (Darwin, 1859). Differences in the appearance of these species reflect adaptive divergence over some 6-7 million years of evolution while retaining over 98-99% genetic identity. Both species may develop Down syndrome, evidence of similarly retained developmental plasticity. It has occurred to us that Dobzhansky's axiom ("Nothing in biology makes sense except in the light of evolution") applies not only to genetics, but to all of medicine.

An evolutionary and developmental biology approach to gastroschisis

Recent advances have now made it possible to speak of gastroschisis narrowly in morphogenetic terms invoking the Rittler-Beaudoin (R-B) model. This proceeds from the appreciation of gastroschisis as a congenital intestinal herniation (without cover or liver) within the primordial umbilical ring, mostly to the right side of a normally formed umbilical cord. Presently, it is unresolved whether this visceral prolapse represents failure of ring closure before return of the physiological hernia into the abdomen or rupture of the delicate amniotic/peritoneal membrane at the ring's edge to the right of the cord. Animal observations and experiments will be required to address this question effectively. If gastroschisis is, in fact, a primary malformation with the primordial umbilical ring as the developmental field involved, then homology implies potential gastroschisis in all amniotes with corresponding nourishment from yolk sac (aka omphalomesenteric) vessels going into the embryo and excretory products out via the ancient umbilical connection. It also implies homology of corresponding morphogenetic signal transduction cascades. We review the history of gastroschisis, its presumed pathogenesis, and the developmental biology of the amniotic umbilical ring from this perspective. Therefore, based on the animal and human evidence to date, we propose that gastroschisis is a primary midline malformation that involves the umbilical canal from amniotic to peritoneal space and its primordial umbilical ring, either through nonclosure or rupture of the membrane covering the area, mostly to the right, between the cord and the edge of the ring.

Annals of morphology fields and prepatterns. Editorial Festschrift for John C. Carey, MD, MPH

The investigation of mammalian malformations began to approach human needs in the 19th century with, for example, Meckel's dissection of sibs with the "Meckel" syndrome, his intimation of Heredität as cause of the condition, his conclusion as to the common causal origin of this specific combination of congenital anomalies, the clear enunciation of the concept of primary malformations, the recognition that many human malformations are normal developmental states in other animals, and that some were normal anatomical states in remote ancestors and now still normal in collateral descendants (atavisms, Darwin's "reversions"; for example, four wings in dipterans, normal in dragonflies and their common ancestor). Later in the century, Wilhelm His Sr. had proposed a schematic map of "organ-forming districts" for prospective chick development, a concept that did not sit well with early workers in developmental biology (e.g., Boveri) until methods became available for a direct experimental "attack" on the embryo. This approach was pioneered by Spemann and Mangold through interspecies transplantation of embryonic rudiments with the spectacular result that set the research stage in developmental biology for the next many years. But it was not until mid-century that the late, great geneticist, Curt Stern, made the His model of chick development more intellectually and experimentally approachable with his meticulous analysis of cuticular appendages of Drosophila, one bristle and one bristle group (field) at a time, in mosaics or gynandromorphs, leading to the ingenious concept of prepatterns. As a basic scientist, Stern did not broaden prepatterns into medicine or to human malformations where it has now found a most gratifying application. This contribution to the Carey Festschrift is to summarize, briefly, field and prepattern theory. © 2016 Wiley Periodicals, Inc.

ADAM "sequence" part II: hypothesis and speculation

Noted for centuries in humans, a relatively hairless mammal [e.g., Hallero, 1766; Hohl, 1828 in Klunker, 2003], the so-called amniotic deformities, adhesions, mutilations (ADAM) sequence remains causally and pathogenetically incognito. In 1930 Streeter stated " apodictically" that no evidence has been found that intra-uterine amputation is due to amniotic bands or adhesions …" and that his 16 cases provided (histological) evidence for a "germinal origin." He concluded that an amniotic cord was "not an adhesion or inflammatory product but … an anomalous developmental structure and present from the outset." In survivors the "traces" of damaged limb-buds "reveal the scars of poor germ-plasm." In 1958, Willis, in dismissing the amniotic origin of the ADAM defects (or "Streeter" or "Simonart" bands) quoted Keith [1940] to the effect that "(a)mniotic adhesions … are always produced by … the fetus – as a result of dysplasia in foetal tissues. They are the result, not the cause, of foetal malformations." Streeter [1930] mentions a potential familial case (56-year-old man and his mother), not controlled by photographs or other records and concluded "that the (ADAM) deformity is not easily transmissible," but "due to the constitution of the germ-plasm." Torpin [1968] concluded, as apodictically as Streeter and Willis, that "… proof of amnion rupture without damage to the chorionic sac is no longer "in question." Considering Torpin's decades-long study of the ADAM phenomenon and review of 494 references (missing many) it is surprising that he does not discuss the relationship between the apparent ADAM defects and other, internal anomalies that maybe present in an affected fetus or infant not evidently caused by the amniotic disruptions, adhesions or mutilations, unless his mind was made up. Our review of these internal and other presumed primary malformations in ADAM is ongoing. However, on a preliminary basis, it seems likely to us that: (1) there is an increased prevalence of such primary anomalies in the ADAM condition confirming the view and experience of others, for example Czeizel et al. [1993]; (2) these malformations (e.g., heterotaxy) may arise as early as gastrulation; (3) that, given the ADAM phenomenon is exclusively ascertained as the ADAM phenotype in fetuses and infants, that is, that its cause and ascertainment are completely congruent, then the apparent amniotic defect must also be regarded as a malformation; (4) that in such a case the ADAM phenomenon with associated primary malformation(s) is a form of syndromal pleiotropy due to one cause yet to be elucidated. To that end we recommend archiving DNA from all affected fetuses coming to autopsy and their parents and placentas and surgical tissues of all viable affected infants for ultimate exome or genome sequencing perhaps with special attention to the syncytin genes.

Historical perspective on developmental concepts and terminology

In their ontogeny and phylogeny all living beings are historical entities. The revolution in biology of the 18th and 19th centuries that did away with the scala naturae according to which we humans, the acme of creation, "made a little lower than the angels," also led to the gradual realization that a humble one-celled protist ("protoctist"), such as Entamoeba histolytica of ill repute [Margulis and Chapman, ] has the same 4-billion-year phylogeny as that of Homo sapiens, vivid testimony to common ancestry and the relatedness of all living beings on earth. The group of medical geneticists who assembled at the NIH, Bethesda, MD this January to address terms pertaining to human ontogeny, did so in the long tradition of Sydenham, Linnaeus, Meckel, Geoffroy St-Hilaire père et fils, Wilhelm His and so many others before who had over the previous two centuries wrestled as earnestly as they could with concepts of "classification" and nomenclature of developmental anomalies. The prior massive need for classification per se in medical morphology has diminished over the years in favor of ever more sophisticated understanding of pathogenesis and cause through experimental biology and genetics; however, in the winter of 2013 it was still found prudent to respect terminological precedent on general terms while recognizing recent advances in developmental pathology requiring clarification and definition of special terms. Efforts along similar lines instigated by the German Society of Anatomists at their first meeting in Leipzig in 1887 culminated, after intense years of work by hundreds of experts and consultants under the goad of Wilhelm His, in the Basel Nomina Anatomica [BNA, His (1895)]. His, himself, stated prefatorily that the BNA had no legislative weight, only an evanescent consensus of many to be amended in the future as needed and indicated. Without hubris, no one before or after will do the same. The more substantial the consensus the more permanent the structure. After some 120 years the BNA is alive and flourishing. Now retitled Terminologia Anatomica, it has been amended and added to many times, is still in Latin but now with synonyms in English, the new lingua franca of science, for every anatomical, histological and embryological term. May our successors be equally effective.

Annals of morphology. Atavisms: phylogenetic Lazarus?

Dedication: with highest respect and affection to Prof. Giovanni Neri on the eve of his official administrative retirement as Chair of the Institute of Medical Genetics of the Università Cattolica of Rome for leadership in medical genetics and medical science and friendship for decades. The concept "atavism," reversion, throwback, Rückschlag remains an epistemological challenge in biology; unwise or implausible over-interpretation of a given structure as such has led some to almost total skepticism as to its existence. Originating in botany in the 18th century it became applied to zoology (and humans) with increasing frequency over the last two centuries such that the very concept became widely discredited. Presently, atavisms have acquired a new life and reconsideration given certain reasonable criteria, including: Homology of structure of the postulated atavism to that of ancestral fossils or collateral species with plausible soft tissue reconstructions taking into account relationships of parts, obvious sites of origin and insertion of muscles, vascular channels, etc. Most parsimonious, plausible phylogenetic assumptions. Evident rudimentary or vestigial anatomical state in prior generations or in morphogenesis of a given organism. Developmental instability in prior generations, that is, some closely related species facultatively with or without the trait. Genetic identity or phylogenomic similarity inferred in ancestors and corroborated in more or less closely related species. Fluctuating asymmetry may be the basis for the striking evolutionary diversification and common atavisms in limbs; however, strong selection and developmental constraints would make atavisms in, for example, cardiac or CNS development less likely. Thus, purported atavisms must be examined critically in light of the above criteria.