Situs ambiguus or situs ambiguous (the former spelling is more correct etymologically, but the latter spelling is very common), also known as heterotaxy or heterotaxia, is a rare congenital defect in which the major visceral organs are distributed abnormally within the chest and abdomen.
The normal position of the organs is known as situs solitus; situs inversus is a condition in which the usual positions of the organs are reversed from left to right as a mirror image of the normal condition. If these are the two extreme positions on a continuum of asymmetric thoracic and abdominal organ formation, situs ambiguus covers everything in between.
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Classically, it comprises:
More rarely, vascular abnormalities are found, including interrupted inferior vena cava, bilateral superior or inferior venae cavae, intrahepatic interruption of the inferior vena cava with connection to the azygos or hemiazygos veins, and aberrant portal veins.
Although its etiology is poorly understood, it has been found to be linked to maternal diabetes mellitus,[1][2] family history of malformations, and maternal cocaine use,[3] suggesting both genetic and environmental[4] factors play a role.
Genetic associations of heterotaxy include:
Type | OMIM | Gene | Locus |
---|---|---|---|
HTX1 | 306955 | ZIC3 | Xq26.2 |
HTX2 | 605376 | CFC1 | 2q21.1 |
HTX3 | 606325 | PA26 | 6q21 |
HTX4 | 613751 | ACVR2B | 992 |
HTX5 | 270100 | NODAL | 10q22.1 |
Side | Left | Both | Right |
---|---|---|---|
General | Ambidexterity | ||
In cognitive abilities | Geschwind–Galaburda hypothesis | ||
In brain | Brain asymmetry · Dual brain theory · Bicameralism | ||
In eyes | Ocular dominance | ||
In hands | Left-handedness | Cross-dominance | Right-handedness |
Handedness in boxing | Southpaw stance | Orthodox stance | |
Handedness in people | Musicians · US presidents | ||
Handedness related to | Sex · Maths | ||
Handedness measurement | Edinburgh Handedness Inventory | ||
Handedness genetics | LRRTM1 | ||
In heart | Levocardia | Dextrocardia | |
In major viscera | Situs solitus | Situs ambiguus | Situs inversus |
In feet | Footedness |