Situs ambiguus

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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. Both individuals with situs solitus and those with situs inversus generally have no functional impairments in their organ systems. In contrast, the mixing of organ asymmetries found in situs ambiguus often leads to severe and potentially fatal complications, usually of the heart or lungs. [1]


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 [2][3] to family history of malformations, and maternal cocaine use,[4] suggesting both genetic and environmental factors play a role.[5]

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

See also[edit]


  1. ^ Belmonte, Juan Carlos (June 1999). "How the Body Tells Left from Right". Scientific American: 46–48. 
  2. ^ Martínez-Frías ML (March 2001). "Heterotaxia as an outcome of maternal diabetes: an epidemiological study". American journal of medical genetics 99 (2): 142–6. doi:10.1002/1096-8628(2000)9999:999<00::AID-AJMG1139>3.0.CO;2-Z. PMID 11241474. 
  3. ^ Maeyama K, Kosaki R, Yoshihashi H, Casey B, Kosaki K (March 2001). "Mutation analysis of left-right axis determining genes in NOD and ICR, strains susceptible to maternal diabetes". Teratology 63 (3): 119–26. doi:10.1002/tera.1022. PMID 11283968. 
  4. ^ Kuehl KS, Loffredo C (November 2002). "Risk factors for heart disease associated with abnormal sidedness". Teratology 66 (5): 242–8. doi:10.1002/tera.10099. PMID 12397632. 
  5. ^ Kuehl KS, Loffredo CA (March 2003). "Population-based study of l-transposition of the great arteries: possible associations with environmental factors". Birth defects research. Part A, Clinical and molecular teratology 67 (3): 162–7. doi:10.1002/bdra.10015. PMID 12797457. 

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