Lateralization disorders are divided into complete (ie, situs inversus totalis) and incomplete (ie, heterotaxy); the word heterotaxy is derived from the Greek heteros, meaning “other” and taxis, meaning “arrangement.” The disorders have been recognized since at least 1933 (complete)
and 1826 (incomplete).
Only relatively recently have genetic alterations responsible for their occurrence in humans been identified. The discovery of kindreds in which both heterotaxy and situs inversus totalis occur strongly suggests that these are not truly separate diseases.
At least 12% of primary ciliary dyskinesia (PCD) patients have heterotaxy.
Because PCD is present in about a quarter of situs inversus totalis patients and due to the fact that situs inversus totalis is present in nearly half of individuals with PCD, this article covers both heterotaxy syndrome and PCD. Moreover, because asplenia and polysplenia can occur in the same family,
a patient’s splenic phenotype should be viewed as merely one phenotypic aspect of an underlying laterality disorder, even though many prior reviews of heterotaxy syndrome have divided patients into two groups based on only splenic phenotype.