Central Nervous System
All of the following diseases show abnormal folding of proteins except (AIIMS Nov 2013)
Disorders caused by misfolding of proteins are
• Alzheimer's disease and other neurodegenerative diseases
• Transmissible prion diseases like CID
• Some genetic disease caused by mutations that lead to misfolding of protein and loss of function, such as certain of the cystic fibrosis mutations.
Prions are infectious proteins that cause degeneration of the central nervous system (CNS) Prion diseases are disorder of protein conformation, the most common of which in humans is called Creutzfeldt-Jakob disease (CJD). CJD typically presents with dementia and myoclonus, is relentlessly progressive, and generally causes death within a year of onset. Four new concepts have emerged from studies of prions:
• Prions are the only known infectious pathogens that are devoid of nucleic acid; composed of either RNA or DNA that direct the synthesis of their progeny.
• Prion diseases may manifest as infectious, genetic, and sporadic disorders; no all other infectious agents possess genolres other group of illnesses with a single etiologry
presents with such a wide spectrum of clinical manifestations'
• Prion diseases result from the accumulation of PrPS", the conformation of which differs substantially from that of its precursor, PrPc-
• prp& can exist in a variety of different conformations, each of which seems to specify a particular dlsglse phenotype' How 3 specific
conformation of a prps" molecule is imparted to PrPc during Prion replication to produce nascent with the same conformaticn is unknown. Additionally, it is unclear what factors determine where in the CNS a particular PrPsc molecule will be deposited.