Cerebellum cerebellum may be absent. The inherited neurological disorders Machado–Joseph disease, ataxia telangiectasia, and Friedreich's ataxia cause progressive neurodegeneration linked to cerebellar loss. Congenital brain malformations outside the cerebellum can, in turn, cause herniation of cerebellar tissue, as seen in some forms of Arnold–Chiari malformation. Other conditions that are closely linked to cerebellar degeneration include the idiopathic progressive neurological disorders multiple system atrophy and Ramsay Hunt syndrome type I, and the autoimmune disorder paraneoplastic cerebellar degeneration, in which tumors elsewhere in the body elicit an autoimmune response that causes neuronal loss in the cerebellum. Cerebellar atrophy can result from an acute
Medulla (hair) The medulla's presence in human hair and its patterns differ both from person to person and from strand to strand on a single person's head. One hair may have an absent medulla while another from the same person may have a complete or fragmented medulla. For this reason, medulla patterns are not very useful as forensic evidence and are typically only used for determining the species of the subject. The medulla contains large amounts of mitochondrial (as opposed to nuclear) DNA. Mitochondrial DNA is passed from the mother to her offspring. As such, mtDNA may be of forensic value. Medulla