Facts on File Encyclopedia of Health and Medicine

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 pheny-
lalanine, which includes BREAST milk. Infants
require special phenylalanine-free formulas.
Dietary restrictions are lifelong. Many food prod-
ucts contain labeling information that states their
phenylalanine content, and a number of food
manufacturers produce low-phenylalanine ver-
sions of popular foods such as cereals as well as
phenylalanine-free protein substitutes. Fruits, veg-
etables, 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-
NANCYto term though must be especially diligent to
maintain a low phenylalanine diet because exces-
sive phenylalanine in the mother’s BLOODcircula-
tion also affects the developing FETUSand 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-GENEmuta-

tion. 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 car-

riers or who have PKU should considerGENETIC

COUNSELINGas 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 DISORDERSof METABOLISMin which

deficiencies of certain enzymes block the produc-

tion of heme and allow the accumulation of por-

phyrins. Heme is an iron-containing pigment

normally present in nearly all tissues in the body,

notably as a component of HEMOGLOBINin 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 rep-

resents 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), dermato-

logic (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, andDIARRHEA


• MUSCLEweakness and possibly PARALYSIS


• agitation and hallucinations

porphyria 137