Webster's New World Medical Dictionary

tumor suppressor gene
A protective gene that
normally limits the growth of tumors. When a tumor
suppressor gene is mutated (altered), it may fail to
keep a cancer from growing. BRCA1, an example of
a tumor suppressor gene, was the first breast can-
cer gene to be identified; mutated forms of this gene
are responsible for some cases of inherited breast
cancer.
tunica albuginea
The whitish membrane within
the penis that surrounds the spongy chambers (cor-
pora cavernosa). The tunica albuginea helps to trap
the blood in the corpora cavernosa, thereby sustain-
ing erection of the penis.
tunnel
Any passageway in the body that traverses
solid tissue and is completely enclosed except for
the ends, which are open and permit entrance to
and exit from the tunnel. An example of a tunnel is
the carpal tunnel.
TUR
Transurethral resection.
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TUR
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turbinate
A bone in the nose that is situated along
the side wall of the nose and is covered by mucous
membrane.
Turcot syndrome
A genetic disease character-
ized by polyps in the colon (large intestine) in addi-
tion to tumors in the brain. The polyps in the colon
tend to become malignant. The brain tumors are
also malignant. Skin abnormalities can also occur.
Turcot syndrome is inherited in an autosomal reces-
sive manner and can result from mutations in either
the adenomatous polyposis coli (APC) gene or the
mismatch repair genes underlying the syndrome of
hereditary nonpolyposis colon cancer (HNPCC).
Turner syndrome
The most common sex chro-
mosome disorder in females, characterized by short
stature, webbed neck, broad shield-like chest, wide-
spaced nipples, increased carrying angle at the
elbow (cubitus valgus), short fourth finger, and mal-
formations of the heart and aorta. The intelligence of
those with Turner syndrome is usually within the
normal range. Girls with Turner syndrome at the
time of puberty do not experience the development
of secondary sex characteristics such as breast
enlargement. As women, they are infertile due to
ovarian failure. The ovaries typically contain no folli-
cles and look like streaks of fibrous tissue. The diag-
nosis of Turner syndrome is confirmed with
chromosome analysis (karyotype). Turner syndrome
is due to the presence of only one normal X chro-
mosome and no other normal sex chromosome. A
second sex chromosome may be present, but it is
not structurally and functionally normal. However,
the most frequent karyotype in Turner syndrome is
45, X, which is sometimes referred to as XO. The
overwhelming majority of pregnancies with Turner
syndrome conceptions result in miscarriages.