The exact cause of the condition is unknown. Although various theories indicate incomplete separation of monozygotic twins as an etiological factor, abnormal adherence between the ectoderm and endoderm during gastrulation, polytopic primary developmental field defects, somatic and germ line mutations in developmental genes, and damage to the<unk>  cell mass and posterior gut have also been linked to cause structural anomalies in the<unk>  region. It is speculated that the condition is related to the HOX gene, namely HOX10 and HOX11. Normally coding for the mammalian appendicular and axial skeleton, misexpression of the genetic factors could lead to abnormal proliferation of the<unk>  mesenchyme. Embryology is suggested to have an intimate association with the development of<unk>  syndrome. At day 15 after fertilisation, the notochord grows from the primitive knot, in which it invaginates and forms the notochord canal within. Progressively, on day 20, the ventral wall of the notochord dissolves, while communications are formed between the amniotic and yolk sac. One such connection is the Kovalevsky’s canal. From the 23rd to 25th day of gestation, the spinal cord develops except for its distal-most aspect where the notochord and neural tube are joined to form the<unk>  cell mass. The canal of Kovalevsky crosses the<unk>  cell mass, while endoderm located anteriorly to the cell mass develops into the hindgut, various insults towards the cell mass and hindgut during the stage of development may lead to the development of<unk>  anomalies, one of which is<unk>  syndrome. The incomplete regression of Kovalevsky’s canal may also lead to formations of fibrous bands joining the hindgut to the spinal canal, possibly leading to the onset of diastemetaomyelia. These bands may divide the notochord, developing into<unk> s of the lower spine and spinal cord, the adjacent mesoderm is also divided, resulting in duplicates of GI and GU tracts. Subsequently, the<unk> s can also lead to the presence of a range of anomalies including dorsal enteric fistulas, enteric cysts, spina bifida, malformed or duplicated colon, bladder, sacrum, and lower spinal cord. Moreover, a midline pelvic mass defect during gestation could be an obstacle to<unk>  migration of paramesonephric structures (Müllerian duct), which could lead to<unk>  of the genital tract. Whilst failures of migration or fusion of those structures is one of the more prevalent embryological theories for<unk>  of lower genitourinary organs such as the bladder. Intestinal<unk> s extending into the rectum or anus is often rare. However, if the<unk>  cell mass is divided early,<unk> s of the distal bowel may still occur. In gastrointestinal abnormalities, a mechanism known as<unk>  twinning” is proposed in which during the 23rd to 25th day of gestation, the intestinal tract is filled by rapid proliferation of endothelial cells, as the gut increases in size, vacuoles appear within the cell masses to constitute a single lumen. However, in abnormal cases where a vacuole is pinched off, a second lumen is created. The second lumen is then proposed to magnify in size in proportion to the growth of the colon, effectively<unk> g all<unk>  structures distal from the point of separation.
Caudal duplication
Isodisomy
Robertsonian translocation
Genomic imprinting
Bromism
Trisomy
Germline mosaicism
Uniparental disomy