Fragile X syndrome is an inherited condition that can cause
learning disabilities in sufferers. The condition is cause by a mutation to the
FMR1 gene on the X chromosome. Because of this it is more prevalent in males
(who only inherit one X chromosome, from their mother, so if it is faulty, will
have the condition) however, it can also be inherited by females. Fragile X is
also the largest genetic cause of autism accounting for 5% of cases. Around 1
in 4000 males and less than 1 in 6000 females are estimated to suffer from
fragile X.
The FMR1 gene codes for a protein known as FMRP (fragile X
mental retardation protein). This protein is involved in the formation of
dendritic spines. Dendritic spines are developed by neurons (nerve cells) and
are used to help transmit electrical signals and to increase the number of
connections between neurons. Without this protein, people can have severe intellectual
impairment, including a decline in memory with age, and children often learn
55% slower than their unaffected peers; however, some people with fragile X
have a normal IQ.
Fragile X sufferers often have a characteristic phenotype,
including large protruding ears, a long face, hyperextensible fingers and
thumbs, flat feet, low muscle tone (hypertonia), macroorchidism (large testes
in post-pubescent men) and a single palm crease. Fragile X also has an effect
on vision and common problem include strabismus (lazy eye) or refractive
errors. Sufferers are also at risk of suffering from seizures, but these can be
treated with medication.
Fragile X syndrome can also affect emotions and behaviour in
addition to IQ, sufferers can also have social anxieties such as poor eye
contact and difficulties forming per relationships. Up to 75% of male sufferers
where categorised as having excessive shyness, and many suffered from panic
attacks. This is thought to be due to challenges that sufferers have with recognising
faces of people they have met and also due to hypersensitivity to noise (so a
dislike of crowds). Obsessive or anxiety based behaviours are also common such
as hand flapping or biting(self-injury), perseveration (repeating an action
even when a stimulus has been removed), self-talk and aggression. Most males
and around 30% of females with the full mutation for fragile X have ADHD so
display symptoms such as hyperactivity and inattentiveness.
Associated disorders of fragile X syndrome include autism,
FXTAS and FXPOI. FXTAS is fragile X associated tremor/ataxia syndrome, which is
an adult onset disorder which can lead to dementia, mood instability, cognitive
decline and memory loss, tremors, ataxia (loss of balance) and symptoms of
Parkinson’s disease such as shuffling movement. FXPOI is fragile X associated
primary ovarian insufficiency, and includes symptoms similar to menopause such
as hot flushes, unusual menstruation, FXPOI can lead to decreased fertility or
infertility, and occurs in around 20% of women with fragile X or carriers of
fragile X.
We can screen for fragile X in pregnancy by testing the amniotic
fluid or CVS (chorionic villus sampling), however this cannot accurately determine
whether a child will develop any of the associated disorders.
There is no cure for fragile X at the moment, however, with
educational and emotional support, many affected people are able to cope with
related disorders, and some medications or therapies can help alleviate certain
symptoms. Other options could include gene therapy to demethylate genes using
drugs or blocking receptors for mGluR5 a protein which, when FMRP is missing,
causes over-activity of the brain, and by inhibition can reduce seizures and
learning delays.
Base pairs, are found as part of the nucleotides in DNA, A-adenine
which pairs with T-thymine and C-cytosine with G-guanine.
Nucleotides, the molecules which make up DNA and are made
from a phosphate group, 5-carbon sugar and an organic base (see base pairs)
Phenotype, is the observable, physical and behavioural characteristics
of an organism.
No comments:
Post a Comment