Current Molecular Medicine - Volume 2, Issue 1, 2002

Gestational trophoblastic disease (GTD) encompasses a diverse group of lesions with specific pathogenesis, morphological characteristics and clinical features. The modified World Health Organization-classification of GTD includes complete and partial hydatidiform mole, invasive mole, choriocarcinoma, placental site trophoblastic tumor, epithelioid trophoblastic tumor, exaggerated placental site, and placental site nodule. The various forms of gestational trophoblastic disease can be defined and related to discrete pathologic aberrations occurring at different stages of trophoblastic differentiation. Some of these lesions are true neoplasms, whereas others represent abnormally formed placentas with a predisposition for neoplastic transformation of the trophoblast. Except hydatidiform moles in which the cytogenetic studies have been extensively reported, the pathogenesis of other trophoblastic lesions is poorly understood. Recent studies have shed light on the molecular mechanisms of trophoblastic function, especially as it relates to trophoblastic disease. This review will focus on these advances with special emphasis on the pathogenesis of each specific form of GTD. In addition, the morphology and clinical behavior of each of these entities will be briefly discussed.

Homeobox genes encode transcriptional regulators of embryonic development. Many genetic disorders affecting multiple organ systems have been associated with a diverse array of mutations in one or another of at least 27 different members of this gene family. We briefly describe the affected genes and the major phenotypes presented by the patients that carry the mutations. Although cause-and-effect relationships are difficult to prove in human genetics, there is little doubt that the observed mutations play a crucial role in the etiology of the associated disorders. The impressive wealth of collected data greatly benefits genetic counseling and stimulates efforts to develop novel avenues of targeted therapy

Mammalian sex differentiation involves the action of a cascade of genes. Discovery of the sex-determining region of the Y chromosome (SRY) marked the beginning of the delineation of the genes in the cascade. Studies of the genetics of mammalian sex reversal and the embryogenesis of the mice are essential in this endeavor. A number of genes involved in the pathway have been identified and all except one of these genes have a putative role in male sex differentiation. Besides SRY being the master switch in male sex differentiation the hierarchical relationship of the genes identified are far from being understood. Similarly, our knowledge of the genetic regulation of female sex differentiation is minimal. Differential screening and gene expression profiling bring a new dimension to the pursuit with the identification of a number of genes previously unknown to be involved in sex differentiation. Wider application of functional genomic techniques and introduction of proteomic analyses are expected to shed light to our understanding of this complicated developmental process.

Despite an externally symmetric body plan, the internal viscera of all vertebrates are asymmetric with respect to the left-right body axis. Determination of the handedness of this asymmetry is nonrandom and highly conserved among vertebrates. Errors in patterning along the left-right axis, which occur in about 1 in 10,000 human births, may result in significant morbidity and mortality. During early embryonic development, midline structures, in particular the node, coordinate patterning of the three main embryonic axes: anterior-posterior, dorsal-ventral, and left-right. A current model for specification of the handedness of left-right axis asymmetry invokes the activity of embryonic cilia in the node that create a net leftward flow of extraembryonic fluid. This flow is proposed to provide a signal for subsequent asymmetric gene expression. Signaling from the node defines patterns of asymmetric gene expression on the left and right sides of the embryo. These signals for “left” and “right” are ultimately interpreted by organ primordia during later development. Complex activating and inhibiting interactions involving TGF-β family members, as well as homeobox transcription factors, mediate these asymmetric patterns of gene expression. The identification of the genes regulating left-right axis patterning in model organisms has resulted in the characterization of human mutations associated with left-right axis malformations.

The development of the gastrointestinal (GI) tract and its associated parenchymal organs depends on Hedgehog signals from the endoderm to the surrounding mesoderm. During development, Hedgehog signaling is essential for patterning the GI tract along anterior-posterior (A-P), dorsal-ventral (D-V), and radial axes, as well as in maintenance of stem cells. Our knowledge about these roles for Hedgehog signaling is derived from studies of developmental defects that result from disrupted or activated Hedgehog signaling in model organisms including mouse, chick, and frog. These studies provide evidence for distinct roles of specific Hedgehog ligands in GI development. Studies in model organisms have also elucidated how Hedgehog signaling may function in development and function of the GI tract in humans. Several diseases and congenital syndromes are known to result from genetic defects in Hedgehog signaling components, and this pathway may ultimately prove to be an important target for future diagnostic and therapeutic tools.

Most lysosomal storage diseases (LSD) exhibit neurological symptoms and there has been limited success in their treatment. Innovative treatments employing novel therapy or gene therapy may offer the prospect of improvement. Recent attempts to treat the neurological forms of LSD include neural stem cell therapy, mesenchymal stem cell therapy, hematopoietic stem cell therapy and gene therapy. Additional approaches have included substrate deprivation / chaperone therapy for the treatment of LSD. This article reviews these new technologies, discusses recent progress, and suggests their possible application.