Webster's New World Medical Dictionary

fracture, transverse
A fracture in which the
break is across a bone, at a right angle to the long
axis of the bone.
fracture, Y
A fracture with a Y-like shape that
occurs at the end of a bone.
fragile site
A point on a chromosome where
gaps and breaks tend to occur, which can be passed
on from one generation to another.
fragile X chromosome
An X chromosome that
has a fragile site and is associated with a common
form of mental retardation. Fragile X chromosome
is due to a mutation (a trinucleotide repeat) in the
DNA at that spot. Not all people who inherit the frag-
ile site have the fragile X syndrome, and it is not yet
known what genetic or environmental factors cause
the breaks or deletions at this fragile site. Also
known as FRAXA (as is fragile X syndrome). See
also 
fragile X syndrome.
fragile X syndrome
The most common herita-
ble form of mental retardation. Fragile X syndrome
is due to a dynamic mutation (a trinucleotide
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fragile X syndrome
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repeat) at an inherited fragile site on the X chromo-
some; therefore, it is an X-linked disorder.
Characteristics of fragile X syndrome in boys may
include, in addition to mental impairment, promi-
nent or long ears, a long face, delayed speech,
hyperextensible joints, hyperactivity, tactile defen-
siveness, gross motor delays, and autistic-like
behaviors. Boys are typically more severely affected
than girls with fragile X syndrome. Only about half
of all females who carry the genetic mutation for
fragile X syndrome have symptoms themselves.
Because the mutation is dynamic, it can vary in
length and hence in severity of its effects from gen-
eration to generation, from person to person, and
even within a given individual. The diagnosis of the
syndrome is confirmed by molecular genetic testing.
Also known as FRAXA (as is the fragile X chromo-
some itself) and Martin-Bell syndrome.