Medical genetics of ciliopathies.

Neither of us had heard about the existence of cilia during biology or genetics courses in high school or university. Nonetheless, these evolutionarily conserved, antenna-shaped organelles of the cell appear to be essential for human development and proper functioning of our organs. Inheritance plays an important role, because genetic defects causing disruption of cilia or ciliary signaling pathways have been shown to result in more than twenty human disorders, collectively known as ciliopathies. While these disorders are each individually rare, many pediatricians and geneticists encounter patients with a ciliary disorder in the clinic. It is therefore important to educate clinicians about cardinal signs of ciliopathies, ciliary disease genes and molecular disease mechanisms. After reading this special ciliopathies issue, specialists should have a good perspective on how to diagnose, manage and treat ciliary disorders occurring in the pediatric clinic in a multidisciplinary team. The disorders that are discussed in this issue are quite diverse, but can be categorized in two groups based on the occurrence of two types of cilia, i.e. motile (actively moving) cilia and immotile (sensory or primary) cilia. The differences in function and ultrastructure between motile and immotile cilia are discussed in detail in the first review. With respect to disease, the majority of ciliopathies result from defects