Acrocallosal Syndrome, Schinzel Type

The acrocallosal syndrome is an autosomal recessive mental retardation syndrome with brain abnormalities such as corpus callosum agenesis and/or Dandy-Walker malformation as well as dysmorphic features, postaxial polydactyly of the hands, and preaxial polydactyly of the feet ({28:Schinzel and Schmid, 1980}). It is considered a ciliopathy ({21:Putoux et al., 2011}). Joubert syndrome-12 is a disorder with an overlapping phenotype characterized by the hallmark finding of the molar tooth sign (MTS) on brain MRI. For a phenotypic description and a discussion of genetic heterogeneity of Joubert syndrome, see {213300}. Hydrolethalus-2 (HLS2; {614120}) is an allelic disorder with a more severe phenotype and death in utero.