Teratogensis: Caudal Dysgenesis (Sirenomelia)

Teratogensis: Caudal Dysgenesis ( sirenomelia)
The third week of development is the period of greatest sensitivity for teratogensis (Sadler 2010). In caudal dysgenesis (sirenomelia) genetic abnormalities and toxins disrupt normal gastrulation. A more common name for sirenomelia is the mermaid syndrome. Sirenomelia is characterized by insufficient mesoderm formed in the caudalmost region of the embryo. The mesoderm contributes to the formation of the lower limbs, urogenital system and the lumbosacral vertebrate. Defect varies from simple cutaneous fusion of the limbs to absence of all long bones but one femur. The defect of the feet is proportional to the defect of the long bones, with cutaneous defect commonly presenting a double fused foot
Formation of the neural tube first occurs on day 22 at the level of somite 3; fusion precedes and the neural tube is closed by day 26, whereas lower limb buds are recognizable between 28-32 days of developments. From an embryological point of view, a condition that combines cephalic (craniospinal rachischisis) and caudal defects (fused lower limbs along with pelvic, lower vertebrae and genitourinary organ anomalies), as in this case, are considered to be an example of axial mesodermal dysplasia sequence. A primary disturbance in the axial mesodermal system may impair formation, elevation and approximation of neural folds leading to craniospinal rachischisis (Haider et al 2001). The caudal eminence is an active seat of cell proliferation which contributes to the formation of notochord, vertebrae, lower limb buds, perineum, neural plate, neural cord, hind gut and blood vessels. Although an extensive disturbance of axial mesoderm is likely to occur in the formation of neural tube defect, a milder alteration of neuroectoderm cannot be excluded in most sirenomelia, as defect occurs in coordinated process of cell proliferation, migration and cell to cell adhesion (Haider et al
Although many theories have been presented on etiology, there is none known and genetic factors are not considered with this teratogen. Many cofactors are involved with sirenomelia that include oligohydramnios, renal agenesis, hypoplasia and in some cases maternal diabetes. Most of the embryos that develop sirenomelia are discovered by the 27th week using a sonogram. Low amniotic fluid and the fusion of the lower limbs are the factors that physicians use to diagnosis sirenomelia. Most cases result in termination of the pregnancy. Other pregnancies result in still birth and in rare cases individuals survive birth but die within