Mesonephros has a role in limb development and is related to thalidomide embryopathy

Terminal transverse limb defects with "nubbins"

BACKGROUND

A terminal transverse limb defect with absence of the forearm and hand or just the hand is an uncommon limb deformity in an otherwise healthy newborn. Most of the affected infants also have tiny digit-like nubbins on the stump of the affected limb, a finding that could represent an attempt at regeneration following vascular obstruction in early limb development.

METHODS

One hundred ninety-four newborn infants with a limb deficiency were identified among 289,365 births in an active malformations surveillance program at Brigham and Women's Hospital in Boston, MA from 1972 to 2012. Twenty-eight infants with terminal transverse limb defects were identified.

RESULTS

Twenty-four had tiny digit-like nubbins (0.5 cm in length) on the stump at one of three levels: the proximal portion of the forearm, the wrist or the forefoot. The examination of the placentas of eight affected infants showed no evidence of amnion rupture. Three of these 28 infants had associate chromosome abnormalities: trisomy 21, chromosome 11q deletion and the deletion of 22q11.2.

CONCLUSION

Terminal transverse limb defects reflect failure of early limb development. Awareness of this phenotype at birth, or when identified by ultrasound screening, can provide more accurate counseling than occurs with the more common misdiagnosis of "amniotic band syndrome."

The effect of thalidomide in chicken embryos

Early in the history of the thalidomide disaster, chick embryos were "eliminated" as useful in the study of thalidomide. One reason for that conclusion was that many of the early experiments were flawed. We employed a number of experiments to expose chick embryos to thalidomide. Our data show that thalidomide does cause limb reduction defects in chick embryos as long as the embryos are directly exposed to the drug. The most useful techniques are implanting thalidomide-soaked beads into the embryo immediately adjacent to the limb territory or soaking presumptive chick limb territories in thalidomide and then grafting the explants to a host embryo celom. Thalidomide affects the chick limb grafted to a host embryo in a dose response fashion. Furthermore, S-thalidomide and S-EM12 are more teratogenic than R-thalidomide and R-EM12.

The short toes mutation of the axolotl

The axolotl mutant strain, short toes (s/s), can regenerate spinal cord and tail, but not limbs. This makes s/s potentially very useful for limb regeneration studies. This mutant merits a new examination that integrates the original description of the mutant, existing experimental studies, new data and current thinking about stem cells and regeneration. There are still major gaps in information about this mutant; the gene(s) causing the defects has not yet been discovered, and even the histological description is incomplete, especially regarding muscle abnormalities. In the short toes limb, MyHC (myosin heavy chain)-1, MyHC-2b and pax7 are down-regulated. In particular, all three MyHC genes and pax7 are highly expressed in the normal limb, but almost lost in the s/s limb. MyHC genes are one of the main components of skeletal muscle, and Pax7 is the skeletal muscle satellite cell marker. Histological experiments confirm that severe s/s has lost most skeletal muscle and myosin. These results suggest that skeletal muscle, which includes satellite cells, could play an important role in axolotl limb regeneration.

Induction and prepatterning of the zebrafish pectoral fin bud requires axial retinoic acid signaling

Vertebrate forelimbs arise as bilateral appendages from the lateral plate mesoderm (LPM). Mutants in aldh1a2 (raldh2), an embryonically expressed gene encoding a retinoic acid (RA)-synthesizing enzyme, have been used to show that limb development and patterning of the limb bud are crucially dependent on RA signaling. However, the timing and cellular origin of RA signaling in these processes have remained poorly resolved. We have used genetics and chemical modulators of RA signaling to resolve these issues in the zebrafish. By rescuing pectoral fin induction in the aldh1a2/neckless mutant with exogenous RA and by blocking RA signaling in wild-type embryos, we find that RA acts as a permissive signal that is required during the six- to eight-somite stages for pectoral fin induction. Cell-transplantation experiments show that RA production is not only crucially required from flanking somites, but is sufficient to permit fin bud initiation when the trunk mesoderm is genetically ablated. Under the latter condition, intermediate mesoderm alone cannot induce the pectoral fin field in the LPM. We further show that induction of the fin field is directly followed by a continued requirement for somite-derived RA signaling to establish a prepattern of anteroposterior fates in the condensing fin mesenchyme. This process is mediated by the maintained expression of the transcription factor hand2, through which the fin field is continuously posteriorized, and lasts up to several hours prior to limb-budding. Thus, RA signaling from flanking somites plays a dual early role in the condensing limb bud mesenchyme.

Thalidomide: dermatological indications, mechanisms of action and side-effects

Thalidomide was first introduced in the 1950s as a sedative but was quickly removed from the market after it was linked to cases of severe birth defects. However, it has since made a remarkable comeback for the U.S. Food and Drug Administration-approved use in the treatment of erythema nodosum leprosum. Further, it has shown its effectiveness in unresponsive dermatological conditions such as actinic prurigo, adult Langerhans cell histiocytosis, aphthous stomatitis, Behçet's syndrome, graft-versus-host disease, cutaneous sarcoidosis, erythema multiforme, Jessner-Kanof lymphocytic infiltration of the skin, Kaposi sarcoma, lichen planus, lupus erythematosus, melanoma, prurigo nodularis, pyoderma gangrenosum and uraemic pruritus. This article reviews the history, pharmacology, mechanism of action, clinical uses and adverse effects of thalidomide.

Renal defects and limb deficiencies in 197 infants: is it possible to define the "acrorenal syndrome"?

Dieker and Opitz in 1969 described the simultaneous occurrence of limb deficiencies (LDs) and renal anomalies (RAs) in three patients. Curran and Curran introduced in 1972 the term "acrorenal syndrome." Since then, the term "acrorenal syndrome" is used occasionally, but a well-circumscribed definition has never been established. On the other hand, the concept of an acrorenal polytopic developmental field defect was postulated by Opitz and others to explain the association between RAs and LDs. We undertook this study to investigate whether this acrorenal "syndrome" could be identified in a large group of cases with congenital RAs and a limb deficiency. Eleven birth defect registries that are part of the International Clearinghouse for Birth Defects Monitoring (i.e., registries of ICBDMS in Finland, France [Paris and Strasbourg], Israel, Italy [IPIMC and Emilia Romagna], Mexico, Northern Netherlands, South America, Spain, and the United States [Atlanta]) provided data on 815 infants who had a LD and at least one other major congenital anomaly. These 815 cases were ascertained among 5,163,958 births. We selected the 197 cases who had both a limb deficiency and a renal or urinary tract anomaly. In about 50% of these cases a diagnosis or a recognized phenotype was reported, with chromosomal aberrations and VACTERL being most frequent. In the group with no diagnosis or recognized phenotype (95 cases), we looked for (a) clustering of specific types of LDs and RAs, and (b) for clustering of associated anomalies, in order to find evidence for and be able to define better the term "acrorenal syndrome." Our data suggest that an association exists between LDs and RAs, possibly explained by the concept of the acrorenal polytopic developmental field defect. However, our dataset does not yield evidence for the existence of one distinct "syndrome," defined as a pattern of causally related multiple anomalies. Therefore, use of the term "acrorenal syndrome" should be avoided.

Difficulties in the study of adverse fetal and neonatal effects of drug therapy during pregnancy

This article reviews the difficulties in studying adverse effects of drugs during pregnancy on the fetus and newborn. A study design should strive for prospective recording of drug intake during pregnancy, comparison to appropriate control groups adjusted for inherited traits, and single drug exposures for evaluation of specific syndromic causation, such as the Fetal Hydantoin Syndrome. Animal models are best used in mechanistic study of adverse drug effects on the fetus rather than for screening for adverse effects. Careful conclusions about causation of drug-induced adverse effects are needed to avoid false associations while providing appropriate safeguards to the fetus and newborn.

Limb development: molecular dysmorphology is at hand!

We present a review of limb development integrating current molecular information and selected genetic disorders to illustrate the advances made in this field over the last few years. With this knowledge, clinical geneticists can now begin to consider molecular mechanisms and pathways when investigating patients with limb malformation syndromes.

Limb initiation and development is normal in the absence of the mesonephros

With rapid progress in understanding the genes that control limb development and patterning interest is becoming focused on the factors that permit the emergence of the limb bud. The current hypothesis is that FGF-8 from the mesonephros induces limb initiation. To test this, the inductive interaction between the Wolffian duct and intermediate mesoderm was blocked rostral to the limb field, preventing mesonephric differentiation while maintaining the integrity of the limb field. The experimental outcome was monitored by following expression of cSim1 and Lmx1, molecular markers for the duct and the mesonephros, respectively. Evidence is presented that the intermediate mesoderm undergoes apoptosis when the inductive interaction with the Wolffian duct is blocked. fgf-8 expression was undetectable in the mesonephric area of embryos with confirmed absence of mesonephros; nevertheless, limb buds formed and limb development was normal. The mesonephros in general, and specifically its fgf-8 expression, was shown to be unnecessary for limb initiation and development; the hypothesis linking the mesonephros and limb development is not supported. Further studies of axial influences on limb initiation should now concentrate on medial structures such as Hensen's node and paraxial mesoderm; the alternative that no axial influences are required should also be examined.