A variety of metabolic diseases are now known to be caused by
deficiencies or malfunctions of enzymes. Albinism, for example,
is often caused by the absence of tyrosinase, an enzyme
essential for the production of cellular pigments. The
hereditary lack of phenylalanine hydroxylase results in the
disease phenylketonuria (PKU) which, if untreated, leads to
severe mental retardation in children. Sections in this article:
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