Ellis–Van Creveld syndrome (also called mesoectodermal dysplasia but see 'Nomenclature' section below) is a rare genetic disorder of the skeletal dysplasia type. Signs and symptoms It involves numerous anomalies including: Post-axial polydactyly Congenital heart defects (most commonly an atrial septal defect producing a common atrium, occurring in 60% of affected individuals) Teeth present at birth (natal teeth) Fingernail dysplasia Short-limbed dwarfism, mesomelic pattern Short ribs Cleft palate Malformation of the wrist bones (fusion of the hamate and capitate bones). Genetics Ellis–Van Creveld syndrome often is the result of founder effects in isolated human populations, such as the Amish and some small island inhabitants. Although relatively rare, this disorder does occur with higher incidence within founder-effect populations due to lack of genetic variability. Observation of the inheritance pattern has illustrated that the disease is autosomal recessive, meaning that both parents have to carry the gene in order for an individual to be affected by the disorder. Ellis–Van Creveld syndrome is caused by a mutation in the EVC gene, as well as by a mutation in a nonhomologous gene, EVC2, located close to the EVC gene in a head-to-head configuration. The gene was identified by positional cloning. The EVC gene maps to the chromosome 4 short arm (4p16). The function of a healthy EVC gene is not well understood at this time. Relation to other rare disorders: genetic ciliopathy Until recently, the medical literature did not indicate a connection among many genetic disorders, both genetic syndromes and genetic diseases, that are now being found to be related. As a result of new genetic research, some of these are, in fact, highly related in their root cause despite the widely varying set of medical symptoms that are clinically visible in the disorders. Ellis–Van Creveld syndrome is one such disease, part of an emerging class of diseases called ciliopathies. The underlying cause may be a dysfunctional molecular mechanism in the primary cilia structures of the cell, organelles which are present in many cellular types throughout the human body. The cilia defects adversely affect "numerous critical developmental signaling pathways" essential to cellular development and thus offer a plausible hypothesis for the often multi-symptom nature of a large set of syndromes and diseases. Known ciliopathies include primary ciliary dyskinesia, Bardet–Biedl syndrome, polycystic kidney and liver disease, nephronophthisis, Alström syndrome, Meckel–Gruber syndrome and some forms of retinal degeneration. Weyers acrofacial dysostosis is due to another mutation in