Encyclopedia of Health and Medicine

porphyria 137
phenylalanine. Phenylalanine is common in all
foods that contain protein (such as meats, dairy
products, fish, and legumes) and in artificial
sweeteners such as aspartame. Avoiding foods that
contain phenylalanine, which means following a
strict low-protein diet, prevents phenylalanine
accumulations and the resultant damage that
affects primarily the NERVOUS SYSTEM. The most
significant consequence of undiagnosed PKU is
irreversible, and usually severe, intellectual
impairment.
Symptoms and Diagnostic Path
Early symptoms of PKU appear soon after birth and
include restlessness, irritability, stunted growth,
and a characteristic musty smell to the breath. The
appearance of symptoms means neurologic damage
is already occurring, however. Newborn screening
to identify PKU before symptoms appear is essential
to prevent intellectual impairment. Hospitals in the
United States routinely screen newborns, typically
within two days of birth, to detect elevated levels of
phenylalanine in the blood. Further testing can
confirm the diagnosis, and immediate dietary
restrictions can prevent the disorder from causing
permanent damage.
Treatment Options and Outlook
Treatment is stringent restriction of dietary phenylalanine,
which includes BREAST milk. Infants
require special phenylalanine-free formulas.
Dietary restrictions are lifelong. Many food products
contain labeling information that states their
phenylalanine content, and a number of food
manufacturers produce low-phenylalanine versions
of popular foods such as cereals as well as
phenylalanine-free protein substitutes. Fruits, vegetables,
breads, and pastas contain very low
amounts of phenylalanine. In the United States
foods that contain aspartame must state on the
label that they contain phenylalanine.
Women who have PKU can safely carry a PREG-
NANCY to term though must be especially diligent to
maintain a low phenylalanine diet because excessive
phenylalanine in the mother’s BLOOD circulation
also affects the developing FETUS and can cause
permanent neurologic and other damage before
birth. Because the inheritance pattern for PKU is
autosomal recessive, women who have PKU will
pass the disorder to their children only if the father
carries the mutated gene or also has PKU.
Risk Factors and Preventive Measures
PKU is an autosomal recessive, single-GENE mutation.
Both parents must carry the PKU mutation
for a child to have the disorder. However, PKU
carriers often do not know they have the mutated
gene because they do not show any indications of
the disorder. People who know they are PKU carriers
or who have PKU should consider GENETIC
COUNSELING as an element of their FAMILY PLANNING.
See also CARRIER; GENETIC DISORDERS; INHERITANCE
PATTERNS; NUTRITIONAL NEEDS; PORPHYRIA.
porphyria The collective term for a group of eight
inherited GENETIC DISORDERS of METABOLISM in which
deficiencies of certain enzymes block the production
of heme and allow the accumulation of porphyrins.
Heme is an iron-containing pigment
normally present in nearly all tissues in the body,
notably as a component of HEMOGLOBIN in the BLOOD
and of electron transport proteins called
cytochromes. The LIVER produces cytochromes,
which are essential for metabolizing numerous
drugs, hormones, NUTRIENTS, and other substances.
Heme synthesis occurs in a sequence of eight steps,
each occurring through the actions of a particular
enzyme. Each of the eight forms of porphyria represents
the absence of one of these enzymes.
Symptoms and Diagnostic Path
Symptoms vary with the type of porphyria and may
be neurologic (affect the NERVOUS SYSTEM), dermatologic
(affect the SKIN), hepatic (involve the liver), or
erythropoietic (involve the BONE MARROW and
blood). Typically symptoms are episodic, occurring
as attacks that last for days to weeks and sometimes
longer. Symptoms vary widely in appearance,
severity, and duration and may include
• eruptive skin rashes (bullae)
• PHOTOSENSITIVITY
• severe ABDOMINAL PAIN
• NAUSEA, VOMITING, and DIARRHEA
• MUSCLE weakness and possibly PARALYSIS
• agitation and hallucinations