CT image showing situs inversus. The liver is normally on the right side of the body and the spleen on the left, they are switched in this patient with situs inversus. This condition is genetically inherited. Structures that make up the cilia, including inner and/or outer dynein arms, central apparatus, radial spokes, etc. are missing or dysfunctional and thus the axoneme structure lacks the ability to move. Axonemes are the elongated structures that make up cilia and flagella. Additionally, there may be chemical defects that interfere with<unk>  function in the presence of adequate structure. Whatever the underlying cause, dysfunction of the cilia begins during and impacts the embryologic phase of development. Axial CT image showing dextrocardia with the IVC and morphologic right ventricle on the left and the left ventricle on the right. Specialised monocilia known as nodal cilia are at the heart of this problem. They lack the central-pair microtubules of ordinary motile cilia and so rotate clockwise rather than beat; in the primitive node at the anterior end of the primitive streak in the embryo, these are angled posteriorly such that they describe a D-shape rather than a circle. This has been shown to generate a net leftward flow in mouse and chick embryos, and sweeps the protein to the left, triggering normal asymmetrical development. However, in some individuals with<unk> , mutations thought to be in the gene coding for the key structural protein left-right dynein (lrd) result in monocilia which do not rotate. There is therefore no flow generated in the node, Shh moves at random within it, and 50% of those affected develop situs inversus, which can occur with or without dextrocardia, where the laterality of the internal organs is the mirror-image of normal. Affected individuals therefore have Kartagener syndrome. This is not the case with some<unk> -related genetic mutations: at least 6% of the<unk>  population have a condition called situs ambiguus or heterotaxy, where organ placement or development is neither typical (situs solitus) nor totally reversed (situs inversus totalis) but is a hybrid of the two. Splenic abnormalities such as polysplenia, asplenia and complex congenital heart defects are more common in individuals with situs ambiguus and<unk> , as they are in all individuals with situs ambiguus. The genetic forces linking failure of nodal cilia and situs issues and the relationship of those forces to<unk>  are the subject of intense research interest. However, knowledge in this area is constantly advancing. Relation to other rare genetic disorders Recent findings in genetic research have suggested that a large number of genetic disorders, both genetic syndromes and genetic diseases, that were not previously identified in the medical literature as related, may be, in fact, highly related in the genetypical root cause of the widely varying, phenotypically-observed disorders. Thus,<unk>  is a ciliopathy. Other known ciliopathies include Bardet–Biedl syndrome, polycystic kidney and liver disease, nephronophthisis, Alström syndrome, Meckel–Gruber syndrome and some forms of retinal degeneration.
Primary ciliary dyskinesia
Cystic fibrosis
Eustachian tube dysfunction
MOG antibody disease
Goldenhar syndrome
Oculopharyngeal muscular dystrophy
Adventitial cystic disease
Wolfram syndrome