The fragile X syndrome is an X linked, semidominant mental retardation
disorder caused by the amplification of a CGG repeat in the 5' UTR of
the FIMR1 gene. Nineteen fragile X families in which the mutated FIMR
1 gene segregated were evaluated. The implications of the diagnosis fo
r the parents and family were studied through pedigree information, in
terviews, and questionnaires. Information about the heredity of fragil
e X syndrome was only disseminated by family members to a third (124/3
66) of the relatives with an a priori risk of being a carrier of the f
ragile X syndrome. Twenty-six percent (94/366) of the relatives were t
ested. Transmission of information among first degree relatives seemed
satisfactory but dropped off sharply with increasing distance of the
genetic relationship, leaving 66% uninformed. This is particularly dis
advantageous in an X linked disease. Of those subjects tested, 42% (39
/94) had a premutation and 18% (17/94) had a full mutation. On average
, in each family one new fragile X patient and two new carriers were f
ound. When people have the task of transmitting genetic information to
their relatives, they usually feel responsible and capable; however,
reduced acquaintance and contact with more distant relatives severely
reduces the effectiveness of such transfer of information in fragile X
families.