How
does a faulty gene trigger disease?
 A
healthy body depends on the continuous interaction of thousands
of proteins, reacting in just the correct proportions and in just
the right places; Every correctly functioning protein is the product
of an undamaged gene. The most common gene error or mutation involves
a single changed base in the DNA. Other alterations include the
loss or gain of a base. Sometimes long segments of DNA are multiplied
or disappear. Some mutations are silent; they affect neither the
structure of the encoded protein nor its function. Other mutations
result in an altered protein. In some instances, the protein is
normal enough to function, but not well; this is the case of the
flawed hemoglobin the oxygen-carrying protein in the blood that
causes sickle-cell anemia. In other instances, the protein can
be totally disabled. The outcome of a particular mutation depends
not only on how it alters a protein's function but also on how
vital that particular protein is to survival.
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