C–D

cystinuria An inherited genetic disorder in
which the KIDNEYSdo not properly reabsorb amino
acids collectively called cystine. The excessive
excretion of cystine to the URINEcauses crystalline
calcifications, commonly called stones, to form in
the kidneys, ureters, and BLADDER. Most people
learn they have the GENE MUTATION, which is auto-
somal recessive, during analysis of the calcifica-
tions. Doctors have known of cystine calcifications
in the bladder since the early 1800s. Researchers
identified cystinuria as hereditary in the early
1900s and discovered the first effective medication
to reduce the formation of cystine calcifications,
penicillamine, in the early 1960s. In the late 1990s
researchers identified the mutated genes as
SLC3A1 on CHROMOSOME2 and SLC7A9 on chro-
mosome 19.
Pain in the side or back, often on only one side,
is the typical symptom of an occlusive (blocking)
calcification. The urine may also smell of sulfur
(rotten eggs) The diagnostic path may include
ULTRASOUND, COMPUTED TOMOGRAPHY (CT) SCAN, or
MAGNETIC RESONANCE IMAGING(MRI) of the abdomen
to visualize the calcifications. Laboratory analysis
of fragments filtered from the urine identifies their
composition as cystine, confirming the diagnosis.
Most of the time the stones pass on their own,
though the process often is painful. Doctors usu-
ally prescribe ANALGESIC MEDICATIONSfor PAINrelief
during the time a stone is passing. Occasionally
treatments such as EXTRACORPOREAL SHOCK WAVE
LITHOTRIPSY (ESWL), which uses high-frequency
sound waves to break the calcification into frag-
ments, or surgery (percutaneous nephrolitho-
tomy) are necessary to remove an obstructive and
impacted stone.
Because there are as yet no treatments to cor-
rect the gene mutation, the cystine calcifications

recur throughout life. Penicillamine, which binds

with cystine in the urine to form a compound that

easily dissolves in water, remains the medication

urologists most often prescribe to reduce the for-

mation of stones. The urologist may also prescribe

medications to increase the alkalinity of the urine,

such as potassium citrate, which helps dissolve

cystine. It is important for people who have

cystinuria to drink enough water to maintain good

urine output, which dilutes the concentration of

cystine and pass it from the body before it forms

calcifications. Other lifestyle modifications include

decreasing dietary sodium and protein consump-

tion (protein is the source of the cystine).

See alsoENDOSCOPY; FANCONI’S SYNDROME; GENE

THERAPY; HYPEROXALURIA; INHERITANCE PATTERNS;

NEPHROLITHIASIS; SURGERY BENEFIT AND RISK ASSESS-

MENT; UROLITHIASIS.

cystitis INFLAMMATIONof the BLADDER. The most

common cause of cystitis is bacterial INFECTION,

called URINARY TRACT INFECTION (UTI). Other

pathogens, such as fungi (yeasts) and viruses, also

can cause infectious cystitis. Nonpathogenic causes

of cystitis include irritation of the lining of the blad-

der, which may occur with excessive consumption

of irritating substances such as CAFFEINE, high-acid

foods, or certain medications. Cigarette smoking is

a significant bladder irritant. RADIATION THERAPY,

CHEMOTHERAPY, and AUTOIMMUNE DISORDERSalso may

cause cystitis. Interstitial cystitis is a chronic condi-

tion the hallmark of which is inflammation of the

bladder along with a constellation of symptoms for

which there are no clearly identifiable causes.

Symptoms and Diagnostic Path

The symptoms of cystitis may include

• DYSURIA(burning or PAINwith URINATION)

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