SITUS-INVERSUS AND CILIARY ABNORMALITIES - WHAT IS THE CONNECTION

The finding of men with living but immotile sperm tails has initiated a search for the cause of the disorder. The sperm tails were found to lack dynein arms or to have some other ultrastructurally visible defec t and the cilia were found to have the same defects. The disorder was hence named the immotile-cilia syndrome. Two more groups with the same clinical symptoms were later found, characterized by ciliary dysmotil ity or ciliary aplasia. In each group there are several subgroups. Man y of the affected persons have situs inversus totalis; in some subgrou ps the incidence of situs inversus is probably 50%; there is, thus, a random determination of visceral asymmetry. Five hypotheses have been forwarded that attempt to explain the connection between ciliary defec ts and loss of laterality control. Support for, or evidence against, t hese five hypotheses have been sought in some animal models of the syn drome. Whereas immotile-cilia syndrome in dogs and pigs is very simila r to the human one, an animal model in the rat differs from the human syndrome in that mainly the males are affected. Two animal models in t he mouse differ in that one has ciliary defects but no increased incid ence of situs inversus and the other has a random determination of vis ceral laterality and no ciliary defects. The connection between ciliar y defects and random determination of laterality remains enigmatic.