Embryology of the upper limb: the molecular orchestration of morphogenesis

The Story of the Hand

This review describes the Story of the Human Hand. It traces the functional needs that led to evolution of the human hand as well as its embryological development. The various in utero stages of formation of the human hand are covered along with a description of the various molecular and genetic factors that control this process.

A multidisciplinary review of triphalangeal thumb

Despite being a rare congenital limb anomaly, triphalangeal thumb is a subject of research in various scientific fields, providing new insights in clinical research and evolutionary biology. The findings of triphalangeal thumb can be predictive for other congenital anomalies as part of an underlying syndrome. Furthermore, triphalangeal thumb is still being used as a model in molecular genetics to study gene regulation by long-range regulatory elements. We present a review that summarizes a number of scientifically relevant topics that involve the triphalangeal thumb phenotype. Future initiatives involving multidisciplinary teams collaborating in the field of triphalangeal thumb research can lead to a better understanding of the pathogenesis and molecular mechanisms of this condition as well as other congenital upper limb anomalies.

Classification of congenital upper limb anomalies: towards improved communication, diagnosis, and discovery

Recently the International Federation of Societies for Surgery of the Hand replaced the Swanson scheme for classifying congenital upper limb anomalies with the Oberg, Manske, Tonkin (OMT) classification. This review explores the reasons for this change after nearly 50 years of using the Swanson classification. In particular, it documents the state of our understanding regarding genetics and limb development at the time Swanson generated his classification. It also describes the continued progress in clinical genetics and developmental biology. Such progress drives the need to embrace and incorporate these changes within a new classification scheme; one that will improve communication, diagnosis, and support further discovery of the pathogenesis of congenital hand anomalies.

The Duplicated Thumb: A Review

Preaxial polydactyly is a common, often sporadic, congenital anomaly that must be addressed surgically early in life. Ideally, the surgeon seeks to accomplish three goals: construction of a thumb that is adequate in size, preservation of pinch function, and reconstruction of all components in one procedure. Although each case is unique, several classification systems attempt to describe the various types. In this article, the authors discuss the various classification systems, procedures, and outcomes after surgery for pediatric thumb duplication.

Altered localization of gene expression in both ectoderm and mesoderm is associated with a murine strain difference in retinoic acid-induced forelimb ectrodactyly

BACKGROUND

Defects in digit number or fusion as a teratogenic response are well documented in humans and intensively studied in various mouse models. Maternal exposure to excess levels of all-trans-retinoic acid (RA) at gestational day 9.5 induces postaxial ectrodactyly (digit loss) in the murine C57BL/6N strain but not in the SWV/Fnn strain.

METHODS

Whole-mount in situ hybridization was used to examine the differential expression of limb patterning genes at the transcriptional level between the two mouse strains following the maternal exposure to a teratogenic level of RA. The detection of a gene with altered expression was followed by either the evaluation of other genes that were synexpressed or with an assessment of downstream genes.

RESULTS

In the C57BL/6N limb bud following maternal RA administration, gene-specific perturbations were observed within hours of the RA injection in the posterior pre-AER (apical ectodermal ridge) (Fgf8, Dlx3, Bmp4, Sp8, but not Dlx2 or p63), whereas these genes were normally expressed in the SWV/Fnn limb bud. Furthermore, although RA caused comparable reductions of Shh expression between the strains in the 12 h after administration, some Shh downstream genes were differentially expressed (e.g., Gli1, Ptc, and Hoxd13), whereas others were not (e.g., Fgf4, Bmp4, and Gremlin).

CONCLUSIONS

It is proposed that altered gene expression in both pre-AER and mesoderm is involved in the pathogenesis of postaxial digit loss, and that because the alterations in the pre-AER occur relatively early in the temporal sequence of events, those changes are candidates for an initiating factor in the malformation.