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(BQ) Part 2 book "Harrison's neurology in clinical medicine" presents the following contents: Diseases of the nervous system, chronic fatigue syndrome, psychiatric disorders, alcoholism and drug dependency. Invite you to consult. | SECTION III DISEASES OF THE NERVOUS SYSTEM CHAPTER 25 MECHANISMS OF NEUROLOGIC DISEASES Stephen L. Hauser M. Flint Beal The human nervous system is the organ of consciousness cognition ethics and behavior as such it is the most intricate structure known to exist. More than one-third of the 23 000 genes encoded in the human genome are expressed in the nervous system. Each mature brain is composed of 100 billion neurons several million miles of axons and dendrites and 1015 synapses. Neurons exist within a dense parenchyma of multifunctional glial cells that synthesize myelin preserve homeostasis and regulate immune responses. Measured against this background of complexity the achievements of molecular neuroscience have been extraordinary. This chapter reviews selected themes in neuroscience that provide a context for understanding fundamental mechanisms that underlie neurologic disorders. NEUROGENETICS The landscape of neurology has been transformed by modern molecular genetics. More than 350 different disease-causing genes have been identified and 1000 neurologic disorders have been genetically mapped to various chromosomal locations. Several hundred neurologic and psychiatric disorders now can be diagnosed through genetic testing http uwu .ncbi.nlm.nih.gov sites GeneTests db GeneTests . The vast majority of these disorders represent highly penetrant mutations that cause rare neurologic disorders alternatively they represent rare monogenic causes of common phenotypes. Examples of the latter include mutations of the amyloid precursor protein in familial Alzheimer s disease the microtubule-associated protein tau MAPT in frontotemporal dementia and a-synuclein in Parkinson s disease. These discoveries have been profoundly important because the mutated gene in a familial disorder often encodes a protein that is also pathogenetically involved although not mutated in the typical sporadic form. The common mechanism involves disordered processing and ultimately aggregation
