Transmissible spongiform encephalopathies (TSEs) are a group of progressive and fatal conditions that are associated with prions and affect the brain and nervous system of many animals, including humans, cattle, and sheep. According to the most widespread hypothesis, they are transmitted by prions, though some other data suggest an involvement of a Spiroplasma infection. Mental and physical abilities deteriorate and many tiny holes appear in the cortex causing it to appear like a sponge when brain tissue obtained at autopsy is examined under a microscope. The disorders cause impairment of brain function, including memory changes, personality changes and problems with movement that worsen chronically.TSEs of humans include Creutzfeldt–Jakob disease, Gerstmann–Sträussler–Scheinker syndrome, fatal familial insomnia, kuru, as well as the recently discovered variably protease-sensitive prionopathy and familial spongiform encephalopathy. Creutzfeldt-Jakob disease itself has four main forms, the sporadic (sCJD), the hereditary/familial (fCJD), the iatrogenic (iCJD) and the variant form (vCJD). These conditions form a spectrum of diseases with overlapping signs and symptoms. TSEs in non-human mammals include scrapie in sheep, bovine spongiform encephalopathy (BSE) in cattle – popularly known as "mad cow disease" – and chronic wasting disease (CWD) in deer and elk. The variant form of Creutzfeldt–Jakob disease in humans is caused by exposure to bovine spongiform encephalopathy prions.Unlike other kinds of infectious disease, which are spread by agents with a DNA or RNA genome (such as virus or bacteria), the infectious agent in TSEs is believed to be a prion, thus being composed solely of protein material.
When the condition is heritable, each pregnancy with the same partners has the same risk of passing the mutated genes to offspring. New mutations (de novo) can also occur causing NM and de novo mutations have been most often found to occur in the ACTA1 gene. MYPN is the last found gene related to NM The risk of all cases of nemaline myopathy is the same in males and females. The physical capabilities of a given person with NM do not correlate well either with genotype or with muscle pathology as observed in the biopsy. Mechanism
Muscle cells contract in complex mechanical and chemical processes. If any part of the process or structure is disrupted, dysfunction will likely result, as in the case of those with genetic variations. In those with nemaline myopathy, muscle contraction is adversely affected. At the electron microscopic level, rod-shaped components can often be seen in some of the muscle cells, and when seen, are diagnostic for the condition called nemaline rod myopathy. The presence of these rods is not itself causing muscle weakness; rather they appear as a result of something going wrong within the muscle fiber. There is no connection between the number of rods found in the muscle cells and the amount of weakness a person has. All of the different gene mutations leading to the condition called nemaline myopathy that have been found so far are in genes that encode different components of the sarcomere.