Fragile X syndrome is the leading inherited form of
mental retardation, and second only to
Down's syndrome as a cause of
mental retardation attributable to an identifiable genetic abnormality.
Fragile X syndrome is caused by a defect in the fragile X
mental retardation 1 gene (FMR1), located near the end of the long arm of the X chromosome. FMR1 normally synthesises the fragile X
protein (FMRP), but mutations in FMR1 lead to a lack of FMRP synthesis, resulting in
fragile X syndrome. While the specific function of FMRP is not yet fully understood, the
protein is known to be important for normal brain development. The physical, cognitive and behavioural features of individuals with
fragile X syndrome depend on gender (females have two X chromosomes, one active and one inactive) and the molecular status of the mutation (premutation, full mutation or mosaic). Features of the behavioural profile of individuals with
fragile X syndrome include
hypersensitivity to stimuli, overarousability, inattention, hyperactivity and (mostly in men)
explosive and aggressive behaviour to others or self. Social anxiety, other
anxiety disorders, depression, impulse control disorder and
mood disorders are the most common
psychiatric disorders diagnosed in individuals with
fragile X syndrome, although no formal studies have been undertaken. There have been very few psychopharmacological studies of the treatment of behaviours associated with
fragile X syndrome. These limited studies and surveys of
psychotropic drugs used in individuals with
fragile X syndrome suggest that stimulants are helpful for hyperactivity, that alpha(2)-adrenoceptor agonists and
beta-adrenoceptor antagonists help to control overarousability, impulsivity and aggressiveness, and that
SSRIs can control anxiety, impulsivity and irritability, alleviate depressive symptoms and decrease aggressive and self-injurious behaviour. Typical and atypical
antipsychotics in combination with other psychotropics have been used for control of
psychotic disorders and severe aggressive behaviours. Mood stabilisers have been found to be useful when mood dysregulation or
mood disorders are present with or without aggressive behaviour.
Folic acid and L-
acetylcarnitine (levacecarnine) have not been found to improve deficits or behaviours. As there is no specific
psychotropic drug for any of the deficits or behaviours associated with
fragile X syndrome, clinicians are advised to diagnose any psychiatric syndromes or disorders present and treat them with the appropriate
psychotropic drug. If no
psychiatric disorder can be diagnosed and the patient's challenging behaviours cannot be controlled with environmental manipulation or behaviour modification techniques, the most benign
psychotropic drug should be used.
Antipsychotics should be reserved for
psychotic disorders, for
impulse control disorders (used in combination with other psychotropics), or when challenging behaviours constitute an emergency. In the future, new medications targeting molecules implicated in the modulation of anxiety, fear and fear responding will be useful for treating the social anxiety and overarousability exhibited by individuals with
fragile X syndrome.