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MOLECULAR GENETICS TESTS - RETT SYNDROME |
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Background:
Rett syndrome is a severe progressive neurological condition that
develops in early childhood and affects only girls. Andreas Rett first
described Rett syndrome in 1966, but recognition of the syndrome outside
Europe did not occur until the early 1980s. With an estimated incidence
of 1 in 10,000, Rett syndrome is the second most common cause (after
Down syndrome) of mental retardation in females.
Girls with Rett syndrome have normal growth and development during the
first few months of life. The clinical features begin to develop between
6 months and 3 years of life. Over a period of months to years there is
a progressive loss of previously acquired motor skills, regression in
language and communication skills and the onset of stereotypical hand
movements. The clinical course for girls with classical Rett Syndrome is
a progression through several stages of global neurologic decline
accompanied by poor head growth and growth failure. Ultimately girls
affected with this condition become totally dependent and the majority
will die in late adolescence or early adulthood.
The diagnosis of Rett syndrome is made according to a set of diagnostic
criteria, but several clinical variants have been described and there is
clinical overlap with other neuro-developmental conditions such as
Angelmans syndrome. MeCP2 mutations have been found in ~5% of atypical
Angelman syndrome cases. In addition there are many cases of
developmental regression in girls where, after extensive investigation,
no definitive diagnosis is made. Since the MeCP2 gene is involved in a
very fundamental biologic process it is possible that some girls with
unexplained developmental regression may have mutations in this gene.
More recently there have been other cases where MeCP2 mutations have
been found, including some X-linked mental retardation pedigrees where
there are retarded males with mutations in the gene.
About 75% of girls with Rett syndrome have mutations in MeCP2. Some rare
pedigrees have affected girls and cases of males with a severe neonatal
severe encephalopathy. These boys have also have MeCP2 mutations
confirming the X linked dominant genetics, and demonstrating unique
sex-limited disease phenotypes.
Analysis:
- Exon by exon sequencing of exons 2 - 4.
Indications for Testing:
- Diagnosis of Rett syndrome.
- Presymtomatic testing for individuals with a family history of Rett
syndrome.
- Prenatal testing for Rett syndrome when there is a known familial mutation.
Speciment Requirements:
Blood: 3 x 4.0mL whole blood into EDTA tubes . Invert several times to
mix. Forward within 24-48 hours at ambient temperature.
Paediatric Samples: Minimum of 3mL whole blood in EDTA tubes.
Prenatal Samples:
- Chorionic Villus: Obtain 20mg chorionic villus sample (CVS) and
transfer to a vial containing transport medium.
- Amniotic Fluid: A minimum of 20mL amniotic fluid required. Bloody
specimens may reflect extensive contamination with maternal cells. Such a
specimen may not be suitable for testing.
NOTE:
- Maternal cell contamination is a potential problem when analysing DNA
from CVS samples or cultured amniotic cells. To rule out the presence of
maternal cell contamination a peripheral blood specimen in EDTA from the
mother must be sent with the prenatal sample (minimum 3ml whole blood in
EDTA required).
Referral reason plus adequate information and family history must be
submitted with the specimen. Pedigree must be included where appropriate.
Usual test turnaround time:
6 weeks once patient sample/s is received.
Cost of test:
Please contact the laboratory for the latest price on this test.
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