Primary ciliary dyskinesia-40 (CILD40) is an autosomal recessive disorder with a relatively mild respiratory phenotype compared to other CILDs. Patients present in childhood with mild upper respiratory symptoms and infections, but typically do not develop serious lung disease. Nitric oxide levels are low-normal or normal. All reported patients have had situs inversus, including several with severe congenital cardiac malformations, but left-right body asymmetry is still theoretically random and would occur in 50% of patients (summary by Loges et al., 2018). For a discussion of genetic heterogeneity of primary ciliary dyskinesia and Kartagener syndrome, see CILD1 (244400).

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).