Multiple sclerosis and Tay-Sachs disease are degenerative disorders of the myelin sheath. In multiple sclerosis (MS), the oligodendrocytes and myelin sheaths of the CNS deteriorate and are replaced by hardened scar tissue, especially between the ages of 20 and 40. Nerve conduction is disrupted with effects that depend on what part of the CNS is involved—double vision, blindness, speech defects, neurosis, tremors, and numbness. Patients experience variable cycles of milder and worse symptoms until they eventually become bedridden. Most die from 7 to 32 years after the onset of the disease. The cause of MS remains uncertain; most theories suggest that it results from an immune disorder triggered by a virus in genetically susceptible individuals. There is no cure.
Tay-Sachs24 disease is a hereditary disorder seen mainly in infants of Eastern European Jewish ancestry. It results from the abnormal accumulation of a glycolipid called GM2 (ganglioside) in the myelin sheath. GM2 is normally decomposed by a lysosomal enzyme, but this enzyme is lacking from people who are homozygous recessive for the Tay-Sachs allele. As GM2 accumulates, it disrupts the conduction of nerve signals and the victim typically suffers blindness, loss of coordination, and dementia. Signs begin to appear before the child is a year old and most victims die by the age of three or four. Asymptomatic adult carriers can be identified by a blood test and advised by genetic counselors on the risk of their children having the disease.
24Warren Tay (1843-1927), English physician; Bernard Sachs (1858-1944), American neurologist
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.