Rudimentary Limbs Research Articles

MS21.01 Surgery and its Evolution

MS21.01 Surgery and its Evolution

Covering the Cover

Covering the Cover

Three-dimensionally preserved minute larva of a great-appendage arthropod from the early Cambrian Chengjiang biota

A three-dimensionally preserved 2-mm-long larva of the arthropod Leanchoilia illecebrosa from the 520-million-year-old early Cambrian Chengjiang biota of China represents the first evidence, to our knowledge, of such an early developmental stage in a short-great-appendage (SGA) arthropod. The larva possesses a pair of three-fingered great appendages, a hypostome, and four pairs of well-developed biramous appendages. More posteriorly, a series of rudimentary limb Anlagen revealed by X-ray microcomputed tomography shows a gradient of decreasing differentiation toward the rear. This, and postembryonic segment addition at the putative growth zone, are features of late-stage metanauplii of eucrustaceans. L. illecebrosa and other SGA arthropods, however, are considered representative of early chelicerates or part of the stem lineage of all euarthropods. The larva of an early Cambrian SGA arthropod with a small number of anterior segments and their respective appendages suggests that posthatching segment addition occurred in the ancestor of Euarthropoda.

Acardius-myelacephalus: management of a misdiagnosed case of twin reversed arterial perfusion sequence with tense polyhydramnios

Abstract Background: Twin reversed arterial perfusion (TRAP) sequence is the most severe form of twin to twin transfusion syndrome. Survival of the pump twin is threatened by extreme prematurity from polyhydramnios and cardiac failure, necessitating interventions. Rarely, interventions are indicated as a result of maternal life-threatening complications. The management of an acardiac-myelacephalus variant of TRAP sequence, complicated by severe maternal respiratory distress from tense polyhydramnios is presented in this report. Case presentation: A 29-year-old G3P2, Alive2 was referred to the Perinatal Unit on account of ultrasound diagnosed twin gestation with demise of one twin at an estimated gestational age (EGA) of 29 weeks. She was in severe respiratory distress with central cyanosis, and grossly distended abdomen. Ultrasonography revealed twin gestation with cardiac activity in only one twin and polyhydramnios. The second twin had no recognizable human body structure and retrograde umbilical arterial flow. TRAP sequence with tense polyhydramnios was diagnosed. The respiratory distress was relieved with serial reductive amniocentesis, and she was managed conservatively until an EGA of 34 weeks, when she delivered a live twin that weighed 2.05 kg, and an amorphous twin with a rudimentary limb that weighed 1.82 kg following spontaneous rupture of membranes. Monochorionic placentation was confirmed at delivery. The pump twin was discharged in a satisfactory state after a period of observation. Conclusion: TRAP sequence may be easily misdiagnosed due to its rarity, with adverse consequences. Accurate diagnosis of the condition, and the provision of basic facilities for in utero interventions when indicated are necessary for fetal salvage.

Phocomelia – A case study

Background: Phocomelia syndrome is a rare birth defect especially of the upper limbs. The bones of the upper arm and in some cases other appendages may be extremely shortened and even absent. In rare cases, there is absence of the upper bones of both the arms and legs so that the hands and feet appear attached directly to the body. Here we present a rare case of phocomelia. Case Presentation: A newly born female infant was brought to the orphanage in our city in very weak condition. She had pansystolic murmur in parasternal region and was diagnosed with ventricular septal defect. Both upper limbs showed single forearm with rudimentary phalyngeal bones. Lower limbs shows rudimentary phalyngeal bones with long femur, spine normal. The child did not survive and died shortly after presentation. Autopsy was done within 24 hours of the death of the female infant, and no significant abnormality other than rudimentary upper and lower limbs was noted. Evidence of bronchopneumonia was observed in both lungs. Cause of death was attributed to bronchopneumonia. Conclusion: The present case had only deformity of the upper and lower limbs with acyanotic heart disease with small muscular ventricular septal defect. The case highlights the morphological defect in such individuals and challenges that may exist due to the neglect of such a child by their parents and the need for special care for such individuals having congenital defects if they survives.

Fetus-in-fetu: a pediatric rarity.

Fetus-in-fetu (FIF) is a rare entity resulting from abnormal embryogenesis in diamniotic monochorionic twins, being first described by Johann Friedrich Meckel (1800s). This occurs when a vertebrate fetus is enclosed in a normally growing fetus. Clinical manifestations vary. Detection is most often in infancy, the oldest reported age being 47. We report the case of a 4-day-old girl who was referred postnatally following a prenatal fetal scan which had revealed the presence of a multi-loculated retroperitoneal mass lesion with calcifications within. A provisional radiological diagnosis of FIF was made. Elective laparotomy revealed a well encapsulated retroperitoneal mass containing among other structures a skull vault and rudimentary limb buds. Recovery was uneventful. Here we discuss the difference between FIF and teratomas, risks of non-operative therapy and the role of serology in surveillance and detection of malignant change.

Sacrococcygeal Fetiform Teratoma Altman Type 1: A Rare Case Report in a 11 Year Old Girl

Fetiform teratoma (homunculus) is a rare but distinct entity, characterized by presence of more organoid differentiation than the classical teratoma but not enough to classify as fetus-in-fetu. Presence of rudimentary limbs in presence/absence of axial skeleton is often reported as an important differentiating feature. Sacrococcygeal location has been reported in a few case reports but in neonates only. This is a rare case of sacrococcygeal fetiform teratoma (Altman type 1) in an 11-year-old girl presenting as a gluteal mass.

Amphibia of Enspel (Late Oligocene, Germany)

Amphibia from the Late Oligocene (MP 28) locality Enspel, Germany are represented by two caudates: a hyperossified salamandrid Chelotriton paradoxus and an indeterminate salamandrid different from Chelotriton in proportions of vertebral column. Anurans are represented by two forms of the genus Palaeobatrachus, one of which is nearly as large as P. gigas (now synonymized with P. grandipes). Pelobates cf. decheni, represented in this locality by three nearly complete adult skeletons and a large number of tadpoles, is the earliest record for the genus. Compared with later representatives of the genus, it does not yet possess specializations for burrowing. Ranidae are represented by two rather fragmentary and incomplete skeletons referred to as Rana sp. A comparatively large series of tadpoles was assigned to the Pelobatidae on the basis of tripartite frontoparietal complex. Most of them are premetamorphic larvae, and a few older ones are postmetamorphic, but they do not exceed Gossner stage 42. One specimen is a large premetamorphic tadpole (no rudimentary limbs) with a total body length of 147 mm. Anatomically, it can be equally assigned to Pelobates or to Eopelobates; the second possibility was excluded only on the basis of absence of adult Eopelobates in this locality.

Foetus in fetu with common bile duct injury: a case report and review of literature

Six-month-old female child presented with history of abdominal lump of 2 months duration. There was an intra-abdominal mass of about 15 × 10 cm on the right side of the abdomen and laboratory investigations were normal. Roentgenogram showed calcified mass in the region of lumbar vertebrae. Ultrasound of the abdomen revealed a retroperitoneal mass of mixed echogenicity with calcifications. Computerized tomography (CT) scan showed an encapsulated mass with fat densities and rudimentary limbs (Fig. 1). Based on these imaging findings provisional diagnosis of foetus in fetu (FIF) was made preoperatively. Computerized tomography scan image of tumour showing heterogenous mass in upper retroperitonium and showing fat densities and calcifications and early organogenesis. During surgery, the mass was crossing the midline. The duodenum was densely adherent to the mass. During separation of the duodenum, common bile duct thinned out because stretching by the tumour was seen merely as a fold of peritoneum and hence was cut. Single-layer end-to-end anastomosis of the common bile duct was done using vicryl 5-0 and keeping all the knots outside after placing 5 fr infant feeding tube as a stent across the anastomosis (Fig. 2). The feeding tube was cut open along its axis for about 6 cm and one end of the tube was put into distal common bile duct and duodenum and the other end was brought out from the anterior abdominal wall. Complete tumour excision was done. On macroscopic examination, the mass was showing head, trunk and rudimentary limb-like structure (Fig. 3). Histopathology of the specimen confirmed it to be FIF. Common bile duct anastomosed over 5 fr infant feeding tube. Excised specimen showing skull, body and rudimentary limbs of the foetus. Tube cholangiogram was performed on day 14 post-op, and contrast was seen entering into the duodenum without any extravasations. Tube was removed. Hippuran imino diacetic acid scan was performed after 6 weeks showed prompt gut activity. Patient at present is under regular follow-up for the last 1 year and having normal abdominal ultrasound findings. Her liver functions are within normal range and is doing well. Foetus in fetu is a malformed monozygotic diamniotic twin found inside the body of a living child.1-3 Now with CT scan commonly being used, preoperative diagnosis is not difficult. In this case, the common bile duct was so much stretched because of the tumour that it appeared like a thin fold of peritoneum, and it was injured. Once the injury was identified immediately, options were roux – en-y choledocho jejunostomy, choledocho duodenostomy and end-to-end bile duct anastomosis with or without stenting by T tube or by infant feeding tube or cholecystostomy along with common bile duct anastomosis.4 But the placing of stents was difficult because of the small diameter of the bile duct. Same was the reason for not doing other procedures: because of technical difficulties and a high rate of complications of such bilio-enteric anastomosis. Hence, decision for using no. 5 infant feeding tube as a stent and for perfoming end-to-end bile duct repair was made, and it gave us a good result. Literature on such bile duct injury in children was reviewed. Most of the paediatric bile duct injuries are traumatic or iatrogenic but are rare. Transection injury requires surgical repair. Partial tear, avulsion or injuries because of physical trauma can be managed by endoscopic stenting with good results.5 Our case becomes different not only because of its uncommon pathology but also because of management of the complication in such a technically difficult situation and necessitates the importance of versatility of surgical technique.

Giant retroperitoneal fetus-in-fetu: An unusual cause of respiratory distress

Fetus-in-fetu (FIF) is a rare congenital condition in which a vertebrate fetus is incorporated within its host, a newborn or an infant. We report an interesting case of FIF presenting as an abdominal mass with respiratory distress in a 4-month-old girl, and review the existing literature. An ultrasound abdomen showed a right sided cystic mass containing multiple calcifications. Laparotomy revealed a well-encapsulated right retroperitoneal mass above the right kidney with two rudimentary limbs attached to an amniotic bag by an umbilical cord. Excision of the capsule revealed a yellowish fluid and an incompletely developed fetus covered by vernix caseosa. Pathologic examination showed an irregular fetiforme mass, weighing 1200 gm, with two rudimentary limbs, encephalus, stomach, duodenum, bowel, bone, cartilage, bone marrow, upper and lower respiratory tissue, and spleen. Complete excision of the FIF was performed. The postoperative period was uneventful and the patient was discharged on the seventh postoperative day.

Is Palaeospondylus gunni a fossil larval lungfish? Insights from Neoceratodus forsteri development

The enigmatic Devonian fossil Palaeospondylus gunni was identified as a larval form, metamorphosing into the lungfish Dipterus valenciennesi. Morphological features used to identify P. gunni as a larval lungfish include enlarged cranial ribs, rudimentary limb girdles, and absence of teeth. However, this combination of features does not characterize the extant lungfish Neoceratodus forsteri, even at very young stages, nor early stages of Devonian and younger fossil lungfish. Absence of teeth is problematic because early ontogenetic stages of fossil and living lungfish possess full dentitions including marginal teeth. Also problematic are cranial ribs as a defining character of lungfish, as these also occur in certain actinopterygians. It is argued that Neoceratodus is an obligate neotene (reproductively mature larva), with the implication that metamorphosis was a feature of the ontogeny of early lungfish. Pedomorphic characters have been recognized in Neoceratodus and other post-Devonian lungfish, including large cells and correspondingly large genome size; these latter characters correlate with neoteny in salamanders. Small cells preserved in fossil bone suggest that Devonian lungfish had a smaller genome than post-Devonian lungfish, implying that they were not neotenic. As fossil lungfish cell sizes (and genomes) increased in the late Paleozoic, the diversity of lungfish morphologies decreased, so that taxa like Sagenodus and Conchopoma show morphological similarity to Neoceratodus, marking a point in phylogeny at which metamorphosis was potentially lost. Since ancestral larval characters are retained in neotenic adults, we predict that Devonian larvae should resemble these post-Devonian taxa, a prediction which Palaeospondylus does not fulfill.

Establishment of a clonal human mesenchymal cell line that retains multilineage differentiation capacity from a spinal hamartoma.

We isolated a single-cell-derived cell line from a spinal hamartoma, a which occurred in a newborn boy and was associated with a rudimentary limb. The maternal cells (HHC-7) differentiated into osteoblasts, chondrocytes, adipocytes, and skeletal muscles when they were cultured in differentiation-inducing media specific to each mesenchymal cell. We isolated a single-cell-derived clonal cell line (Clone K) after transfection with SV40 T antigen. These cells expressed CD73 and CD117, while being negative for expression of CD45. Clone K cells cultured in an osteogenic differentiation medium increased ALP activity and expressed mRNAs for Runx2 and osteocalcin. Treatment with rhBMP-2 induced Clone K cells to differentiate into both osteoblasts and chondrocytes. These cells expressed mRNAs for Sox9 and aggrecan in addition to osteogenic markers. Culture in an adipogenic differentiation medium induced Clone K cells to differentiation into adipocytes, which expressed mRNAs for PPARgamma2 and a2P. Clone K cells cultured in a serum-depleted medium generated desmin-positive cells and expressed MyoD1 mRNA. Clone K cells exhibited numerous alpha-smooth muscle actin-positive cells; however, treatment with rhBMP-2 decreased their number. Clone K cells, transplanted with a carrier containing rhBMP-2 into the muscles of SCID mice, generated ectopic endochondral bone formation. In these tissues, several osteoblasts and chondrocytes expressed SV40 T antigen, indicating their Clone K cell origin. Thus, Clone K cells are useful tools for analyzing the characteristics of human multipotential mesenchymal progenitors.

Fetus in fetu—diagnostic criteria and differential diagnosis—a case report and literature review

Fetus-in-fetu (FIF) is a rare congenital condition in which a vertebrate fetus is incorporated within its twin. The authors report the case of a newborn boy with prenatal ultrasonographic diagnosis of intraabdominal mass, provoking compression of the left kidney. Plain abdominal radiography, ultrasonography, and computer tomography showed a cystic mass containing multiple calcifications. Pathologic examination showed an irregular fetiforme mass, weighing 8 g, attached to an amniotic sac by a rudimentary umbilical cord with 2 rudimentary limbs, vertebral bodies, encephalus, coroidal plexus, stomach, duodenum, bowel, adrenal glands, upper and lower respiratory tissue, spleen, lymphoid tissue, single cavity heart, and kidney. Molecular analysis using an informative genetic marker, for uniparental isodisomy of chromosomes 14 and 15 showed no genetic difference between the host infant and the fetiform mass. Serum alpha-fetoprotein was ≤ 16.000 UI/mL (reference values for age, 4 to 18.9904 UI/mL) before surgery and 8.364 UI/mL after surgery.

Roles of insulin-like growth factor-I (IGF-I) and IGF-I binding protein-2 (IGFBP2) and -5 (IGFBP5) in developing chick limbs.

Insulin-like growth factor-I (IGF-I) and the IGF-I binding proteins (IGFBPs) which modulate IGF-I action have been implicated in the development of the vertebrate limbs and skeleton. We have examined the distribution of IGF-I, IGFBP2 and IGFBP5 in developing chick limb buds and have investigated their functional roles and relationships during chick limb development. IGF-I and IGFBP2 are co-expressed throughout the lateral plate from which limbs form, although IGFBP2, unlike IGF-I, does not promote formation of rudimentary limb buds from non-limb-forming flank regions in vitro. During limb outgrowth, IGF-I is present in non-AER limb ectoderm, but little IGF-I is present in the AER itself, suggesting that restriction of endogenous IGF-I activity may be required for proper AER function. Consistent with this possibility, the ectoderm of mutant limbless and wingless wing buds, which fail to form an AER, continues to express IGF-I. We also found that the AER contains abundant IGFBP2 but that IGFBP2 is not present in limb subridge mesoderm. In contrast, IGFBP2 is present in the distal mesoderm of mutant limbless or wingless limb buds, which fail to grow out. This suggests that attenuation of IGFBP2 expression is controlled by the AER and that cessation of IGFBP2 expression may be necessary for the proliferation and suppression of differentiation of subridge mesoderm that is required for limb outgrowth to occur. Consistent with this possibility, we found that exogenous IGFBP2 inhibits the anti-differentiative activity of the AER in vitro. We also found that regions of cell death in the limb contain abundant IGF-I-immunoreactive cells, consistent with a role for IGF-I in apoptosis. During skeletogenesis, IGF-I and IGFBP2 are co-localized to the condensing central core of the limb, implicating these factors as potential regulators of the onset of chondrogenic differentiation. Intriguingly, we found that IGF-I and IGFBP2 have opposing effects on chondrogenesis, as IGF-I stimulates but IGFBP2 inhibits accumulation of cartilage matrix by micromass cultures in vitro. Long [R(3)] IGF-I, an analog of IGF-I that cannot bind IGFBPs, is more effective than IGF-I in stimulating matrix accumulation, consistent with a negative role for IGFBP2 in chondrogenesis. As the chondrocytes of the limb mature, IGF-I is present only in terminal hypertrophic chondrocytes, which undergo programmed cell death, while IGFBP2 becomes localized to prehypertrophic and hypertrophic chondrocytes, suggesting involvement in chondrocyte maturation. Consistent with this possibility, we found that exogenous IGFBP2 induces precocious expression of Indian hedgehog, a marker of prehypertrophy, in maturing chondrocytes in vitro. IGF-I and IGFBP2 are also present in the osteoblasts, clasts and nascent matrix of the long bones, consistent with roles in endochondral bone formation. Unlike in rodent limbs, IGFBP5 is not expressed by chick limb ectoderm or AER. IGFBP5 expression is highly localized to developing limb musculature and, later, to the developing skeletal elements where it is expressed by osteoblast precursers and osteoblasts. The results of this study suggest potential novel roles for IGF-I and IGFBP2 in several aspects of limb development including limb outgrowth and AER activity, programmed cell death, chondrogenesis and chondrocyte maturation.

Somites et prolongements somitiques impliqués dans la formation des membres chez les reptiles. L'amélie chez les serpents

Summary A new study was carried out on an increased number of young embryos of Reptile taxa either with well developed limbs or limbless to complete the previous observations devoted to the relationships between the somatic extensions and the formation of limb buds. Results are summarized in table I. In the embryos of Reptiles, the somites involved in limb formation send ventral processes in the somatopleural territory of the future limb and the limb develops only in front of these somatic extensions. In lizards with well developed limbs, there are always eight somites (S6–S13, S1 being the first postotic somite) which send ventral processes in the somatopleure and are thus involved in anterior limb formation. In serpentiform lizards such as Anguis fragilis, Ophisaurus apodus, Scelotes brevipes, only four or five somites (S6–S9 or S6–S10) form ventral extensions; the limb bud develops only in front of these somites, and its size is thus reduced from this early stage. Macroscopic and histological studies of young embryos belonging to four species of snakes (Natrix natrix, Natrix tessellata, Natrix maura and Vipera aspis) shows that none of the thoracic somites of the series S6–S13 form ventral extensions. Several observations suggest that in Reptiles with well developed limbs, the somitic extensions may initiate limb development by liberating a growth factor of the FGF family. In snake embryos, which are devoid of somitic extensions, no growth factor would be liberated and thus no anterior limb would develop. In some species, some pelvian somites form short extensions, which induce a feeble pelvian thickening or a rudimentary posterior limb bud (e.g. Boidae). It is an embryonic mechanism which is responsible for the limbless condition in Snakes.

Hensen's Node Provides an Endogenous Limb-Forming Signal

Acquisition of limb-forming ability by discrete regions of the lateral plate of the chick embryo is thought to depend on a signaling cascade moving sequentially from the area of Hensen's node to the somitic mesoderm, the intermediate mesoderm, and then to the prospective limb-forming regions of the lateral plate (Stephenset al.,1991). In the present study it is demonstrated that grafts of Hensen's node can induce the formation of supernumerary rudimentary limbs from the non-limb-forming flank region of the lateral plate of stage 9–15 chick embryos. The rudimentary limbs that form from the flank in response to Hensen's node grafts often contain elongated, jointed cartilaginous elements arranged in three distinct proximodistal segments resembling the developing stylopod, zeugopod, and autopod and express the limb-characteristic genesMsx-2andBMP-4.However, the rudimentary limbs are incomplete and nonpolarized in that they do not form girdles or paired skeletal elements and fail to expresssonic hedgehog, FGF-4,andFGF-8,signaling molecules that have been implicated in regulating the patterning of the developing limb bud. These results indicate that Hensen's node can provide a limb-forming signal to the lateral mesoderm, but that other signals are necessary to promote the expression of genes required for the complete patterning and morphogenesis of the limb.

On the development of Cetacean extremities: I. Hind limb rudimentation in the Spotted dolphin (Stenella attenuata).

The Cetacea are group of animals which have completely lost their hind limbs during the course of evolution as a result of their entirely aquatic mode of life. It is known, however, that during their embryonal period, the hind limb buds are temporarily present. The control mechanisms of this regression are not yet understood, and vestigial limbs can sometimes be found in adults. The aim of the present study is to describe the course of hind limb rudimentation during prenatal development of Stenella attenuata (Spotted dolphin) at tissue and cell levels and compare the results with other natural or experimentally induced amelias. Hind limb buds of dolphin embryos, CRL 10-30 mm, were examined histologically. Before total disappearance, they show histodifferentiation comparable with other mammals. Initially, they form the apical ectodermal ridge, which soon regresses. The mesenchyme undergoes the process of condensation to form anlagens of prospective skeletal elements. These condensations are surrounded by vascular plexuses. During the course of rudimentation, some mesenchymal cells die, while the others are incorporated into the body wall. Nerve ingrowth into rudimentary limb buds was also detected. The temporary presence of hind limb rudiments in cetacean embryos can be regarded as a good example of recapitulation of phylogenesis in ontogenesis.

IGF-I and Insulin in the Acquisition of Limb-Forming Ability by the Embryonic Lateral Plate

Acquisition of limb-forming ability by discrete regions of the lateral plate of the chick embryo is dependent on a medial–lateral inductive signaling cascade moving sequentially from the area of Hensen's node to the somitic mesoderm, the intermediate mesoderm, and then to the prospective limb-forming regions of the lateral plate. IGF-I and insulin are expressed by medial tissues as they are influencing the prospective limb-forming regions of the lateral plate. Here we report that IGF-I and insulin, but not FGF-2 or FGF-4, induce the formation of limb bud-like structuresin vitrofrom prospective limb regions before they have acquired the ability to form limbs independent of medial tissues, and also induce the formation of limb bud-like structures from the prospective flank. The limb bud-like structures induced by IGF-I and insulin possess a thickened cap of ectoderm along their distal tips that resembles the apical ectodermal ridge (AER) and this thickened distal apical ectoderm expresses the AER-characteristic homeobox-containing geneMsx-2.Like in normal limb buds, a population of highly proliferating cells which express the homeobox-containing geneMsx-1are localized in the mesoderm directly subjacent to the thickened AER-like structures induced by IGF-I and insulin. However, the limb bud-like structures induced by IGF-I and insulin do not expresssonic hedgehog,which encodes a secreted signaling molecule that has been implicated in regulating the anteroposterior patterning of the developing limb bud. IGF-I- and insulin-treated prospective limb explants give rise to rudimentary limbs containing identifiable skeletal elements when grafted into the coelom or to somites of host embryos. Overall, these results suggest that IGF-I and insulin may be endogenous signals produced by medial tissues that are involved in conferring limb-forming ability to the lateral plate and may promote the initial outgrowth of limb buds and possibly induce the AER. However, other signals are necessary to promote the expression of genes such assonic hedgehogthat regulate the patterning of the developing limb.

Congenital abnormalities associated with limb deficiency defects: a population study based on cases from the Hungarian Congenital Malformation Registry (1975-1984).

Limb deficiency defects (LD) occurring among 1,575,904 births in Hungary during 1975-1984 were reviewed. The overall birth prevalence of LD was 1 in 1,816. This paper discusses the nature and distribution of the limb and other defects in the 275 (32%) children who had structural malformations in other systems. Two main forms of classification were used: morphologic and causal. Additional malformations were most commonly seen in infants with amelia, rudimentary limb (RL), radial/tibial (RT), intercalary or central axis (CA) LD and rarely in those with terminal transverse (TT) or ulnar/fibular (UF) defects. Upper limbs (81%) were involved significantly more often than lower limbs (42%) and there were more right-sided defects (83% vs. 71%) due to an excess of right arm involvement especially with radial ray and split hand anomalies. Single limb involvement was relatively common with amelia (88%), UF (82%), RT (50%), and TT (50%) defects. With other LD, multimelic involvement was more characteristic. This was usually symmetric with intercalary and RL defects but asymmetric with CA anomalies and digital deficiencies (DD). From a causal perspective, 17% of cases had genetic disorders, 52% had recognized associations, anomalies, sequences, environmental causes or patterns of unknown origin, and 31% had unknown patterns of malformations. The commonest entities were amnion disruption sequence (16% of cases) and VACTERL association (8%). Both of these disorders showed unusual temporal distribution. As anticipated, patterns of malformations differed with the type of LD. Amelia and digital amputations were often seen with body wall defects, atypical anencephaly or encephalocele, and cleft lip reflecting amnion disruption. Rudimentary limb was seen with anencephaly, omphalocele, renal agenesis, aberrant genitalia, and imperforate anus, reflecting defects of blastogenesis including the cloacal exstrophy and caudal regression sequences and Schisis association. Radial/tibial defects were associated with different patterns depending on whether the limb defects were unilateral or bilateral. Unilateral defects occurred with anomalies suggesting VACTERL association or the facio-auriculo-vertebral anomaly, while bilateral defects occurred more often in genetic or potentially genetic disorders including VACTERL with hydrocephalus. Central axis defects showed three main patterns of association: one reflecting the ectrodactyly-ectodermal dysplasia-clefting syndrome; one with tongue anomalies representing a variant of oro-mandibular-limb (Hanhart) anomaly, and the last with hydronephrosis indicating a group of "acro-renal" syndromes. Strong associations with other anomalies were not seen in the groups with TT, UF, or intercalary defects.

Developmental expression of the alpha receptor for platelet-derived growth factor, which is deleted in the embryonic lethal Patch mutation.

The alpha receptor of PDGF (Pdgfra) is expressed in primitive endoderm and mesoderm derivatives throughout embryogenesis. In the early primitive streak stage the gene is transcribed in the visceral and parietal endoderm. Later it is expressed in the presomitic mesoderm, yolk sac and amnion. During somitogenesis its transcription localizes to the heart and the somites. Subsequently, it is transcribed in the dermatome, the sclerotome, the developing limb and in various mesenchymal tissues of visceral organs. Its wild-type expression pattern correlates well with the phenotype of homozygous mutant Patch (Ph) embryos, where the Pdgfra gene is deleted. The Ph phenotype is first detectable at the primitive streak stage with convoluted and hypertrophic visceral yolk sac, deformed neural plate and disorganized or missing mesoderm. Most Ph/Ph embryos die before the 11th day of gestation. Those that survive till early organogenesis are very small, have hypertrophic yolk sacs, small and undifferentiated somites, convoluted neural tubes, large heart and pericardium, rudimentary limb buds and branchial arches. Our observations together suggest that the alpha PDGF receptor may be required for the normal development of visceral endoderm and mesoderm derivatives.