Families and Fragile X Syndrome

Fragile X syndrome (also called Fragile X) is
the most common inherited form of mental
retardation.* It results from a change, or
mutation, in a single gene, which can be passed
from one generation to the next. Fragile X appears
in families of every ethnic group and income level.
Symptoms of Fragile X syndrome occur
because the mutated gene cannot produce
enough of a protein that is needed by the
body’s cells, especially cells in the brain,
to develop and function normally. The
amount and usability of this protein, in
part, determine how severe the effects of
Fragile X are.
The most noticeable and consistent effect of Fragile X
is on intelligence. More than 80 percent of males
with Fragile X have an IQ (intelligence quotient) of
75 or less.1 The effect of Fragile X on intelligence is
more variable in females. Some females have mental
impairment, some have learning disabilities, and
some have a normal IQ.