Heterotaxy Heterotaxy ('heter' meaning 'other' and 'taxy' meaning 'arrangement'), or situs ambiguus, is a developmental condition characterized by randomization of the placement of visceral organs, including the heart, lungs, liver, spleen, and stomach. The organs are oriented randomly with respect to the left-right axis and with respect to one another (Srivastava, 1997). Heterotaxy is a clinically and genetically heterogeneous disorder. Multiple Types of Congenital Heart Defects Congenital heart defects (CHTD) are among the most common congenital defects, occurring with an incidence of 8/1,000 live births. The etiology of CHTD is complex, with contributions from environmental exposure, chromosomal abnormalities, and gene defects. Some patients with CHTD also have cardiac arrhythmias, which may be due to the anatomic defect itself or to surgical interventions (summary by van de Meerakker et al., 2011). Reviews Obler et al. (2008) reviewed published cases of double-outlet right ventricle and discussed etiology and associations. Genetic Heterogeneity of Visceral Heterotaxy See also HTX2 (605376), caused by mutation in the CFC1 gene (605194) on chromosome 2q21; HTX3 (606325), which maps to chromosome 6q21; HTX4 (613751), caused by mutation in the ACVR2B gene (602730) on chromosome 3p22; HTX5 (270100), caused by mutation in the NODAL gene (601265) on chromosome 10q22; HTX6 (614779), caused by mutation in the CCDC11 gene (614759) on chromosome 18q21; HTX7 (616749), caused by mutation in the MMP21 gene (608416) on chromosome 10q26; HTX8 (617205), caused by mutation in the PKD1L1 gene (609721) on chromosome 7p12; HTX9 (618948), caused by mutation in the MNS1 gene (610766) on chromosome 15q21; HTX10 (619607), caused by mutation in the CFAP52 gene (609804) on chromosome 17p13; HTX11 (619608), caused by mutation in the CFAP45 gene (605152) on chromosome 1q23; and HTX12 (619702), caused by mutation in the CIROP gene (619703) on chromosome 14q11. Genetic Heterogeneity of Multiple Types of Congenital Heart Defects An X-linked form of CHTD, CHTD1, is caused by mutation in the ZIC3 gene on chromosome Xq26. CHTD2 (614980) is caused by mutation in the TAB2 gene (605101) on chromosome 6q25. A form of nonsyndromic congenital heart defects associated with cardiac rhythm and conduction disturbances (CHTD3; 614954) has been mapped to chromosome 9q31. CHTD4 (615779) is caused by mutation in the NR2F2 gene (107773) on chromosome 15q26. CHTD5 (617912) is caused by mutation in the GATA5 gene (611496) on chromosome 20q13. CHTD6 (613854) is caused by mutation in the GDF1 gene (602880) on chromosome 19p13. CHTD7 (618780) is caused by mutation in the FLT4 gene (136352) on chromosome 5q35. CHTD8 (619657) is caused by mutation in the SMAD2 gene (601366) on chromosome 18q21. CHTD9 (620294) is caused by mutation in the PLXND1 gene (604282) on chromosome 3q22.

Heterotaxy ('heter' meaning 'other' and 'taxy' meaning 'arrangement'), or situs ambiguus, is a developmental condition characterized by randomization of the placement of visceral organs, including the heart, lungs, liver, spleen, and stomach. The organs are oriented randomly with respect to the left-right axis and with respect to one another (Srivastava, 1997). Heterotaxy is a clinically and genetically heterogeneous disorder. For a discussion of the genetic heterogeneity of visceral heterotaxy, see HTX1 (306955).

Heterotaxy ('heter' meaning 'other' and 'taxy' meaning 'arrangement'), or situs ambiguus, is a developmental condition characterized by randomization of the placement of visceral organs, including the heart, lungs, liver, spleen, and stomach. The organs are oriented randomly with respect to the left-right axis and with respect to one another (Srivastava, 1997). Heterotaxy is a clinically and genetically heterogeneous disorder. For a discussion of genetic heterogeneity of visceral heterotaxy, see HTX1 (306955).

Weiss-Kruszka syndrome is characterized by metopic ridging or synostosis, ptosis, nonspecific dysmorphic features, developmental delay, and autistic features. Brain imaging may identify abnormalities of the corpus callosum. Developmental delay can present as global delay, motor delay, or speech delay. Affected individuals may also have ear anomalies, feeding difficulties (sometimes requiring placement of a gastrostomy tube), and congenital heart defects. There is significant variability in the clinical features, even between affected members of the same family.

Multiple types of congenital heart defects-8 (CHTD8) is characterized by cardiac septal defects, double-outlet right ventricle, unbalanced complete atrioventricular canal, and valvular anomalies, as well as vascular anomalies including dextroposition of the great arteries, anomalous pulmonary venous return, and superior vena cava to left atrium defect. Patients may also exhibit laterality defects, including dextrocardia, atrial isomerism, dextrogastria, left-sided gallbladder, and intestinal malrotation (Zaidi et al., 2013; Granadillo et al., 2018).

Visceral heterotaxy-12 (HTX12) is an embryonic developmental disorder characterized by defects in the asymmetric positioning of visceral organs across the left-right axis, known as laterality defects. The phenotype is highly variable, ranging from complete organ reversal (situs inversus totalis) to selective misarrangement of organs (situs ambiguus) such as the liver, spleen, and pancreas. The disorder is often associated with dextrocardia or variable complex congenital heart defects. Early death may occur in the most severe cases (summary by Szenker-Ravi et al., 2022). For a discussion of the genetic heterogeneity of visceral heterotaxy, see HTX1 (306955).

Neurodevelopmental disorder with intention tremor, pyramidal signs, dyspraxia, and ocular anomalies (NEDITPO) is an autosomal recessive multiple congenital anomaly syndrome characterized by mild to moderate intellectual disability, dysmorphic facial features, intention tremor, dyspraxia, and vertical strabismus (Rahikkala et al., 2022).