Acrocallosal syndrome is a rare, heterogeneous autosomal recessive disorder first discovered by Albert Schinzel in a 3-year-old boy. To inherit ACLS, one gene copy from each parent must contain a mutation somewhere in the KIF7 gene and be passed on to the child. Characteristics of this syndrome include absence or poor development of the area connecting the left and right parts of the brain, an abnormally large head, increased distance between facial features, poor motor skills, mental retardation, extra fingers and toes, many facial deformities, and cleft palate. This is considered a rare disorder and is placed on the NIH Office of Rare Diseasesrare disease list. Lifespan may range from stillbirth to normal expectancy depending on pregnancy complications and severity of the disorder. In mild cases, the subjects have been shown to live relatively normal lives, but with developmental delays.
Pathology
Acrocallosal syndrome is a rare, heterogeneous, autosomalrecessive disorder. The heterogeneity of this condition refers to the multiple genes that may function to contribute to varying degrees of this syndrome and is often linked to consanguinity. Characteristics of this syndrome include agenesis of the corpus, macrocephaly, hypertelorism, polydactyly, mental and motor retardation, craniofacial dysmorphism, hallux duplication, and sometimes palatal clefting. It has also been reported that there are many similar signs and symptoms between ACLS, Greig cephalopolysyndactyly, and hydrolethalus syndrome, although there is little evidence to support common genetic causation at this point.
Mechanism
Recent studies by, have indicated that the mutations responsible for ACLS are located in the KIF7 protein. KIF7 is a 1343 amino acid protein with a kinesin motor, coiled coil, and Gli-binding domains. Its functions are largely associated with ciliary motor function, and is a key factor in the Sonic Hedgehog transduction pathways that are crucial during embryogenesis. Therefore, mutations in Hedgehog signaling components may lead to cilia based pathologies and ultimately defects in the brain and other areas associated with ACLS and related disorders. More specifically, mutations observed by, in the GLI3 gene have yielded similar characteristics to ACLS, but further evidence is needed since the corpus callosum is usually present in these cases. Other studies have also indicated that KIF7 interacts with Gli transcription factors, so mutations in the KIF7 gene may be upstream effectors of GLI3. Further understanding about the functionality of ACLS and its underlying mechanisms opens new doors to pharmacological manipulation and other forms of molecular therapy.
