The importance of Clinical Details
Clinical details are very important when providing genetic
analysis. The more clinical information that is available (e.g.
details of ultrasound information, phenotypic features or family
history) the better the service we can provide. Failure to provide
this information for cytogenetic studies may result in an
inaccurate analysis.
CYTOGENETICS
Cytogenetic analysis is performed according to the
Professional Guidelines for the Association of Clinical
Cytogeneticists and the recommendations provided are dependent
on the clinical indications given for
each case.
Clinical details inform the investigation at all stages:
- Prior to analysis, clinical details may indicate, for example,
that specialist procedures such as chromosome breakage or leukaemic
studies are required, which must be referred to a specialist
centre.
- During analysis they may indicate that extra cells should be
screened to investigate the possibility of mosaicism, for example
in a diagnosis of suspected Turner syndrome, or that particular
chromosomes must be targeted for high-resolution study, for example
chromosome 8 in suspected Langer-Giedion syndrome.
- When the analysis has been completed they may help to provide
an accurate interpretation of the findings and in some instances
prompt further investigations, for example FISH or molecular
genetic studies.
When clinical details are not available a routine analysis
will be performed and a conditional report issued.
MOLECULAR GENETICS
Clinical details can be extremely important for clinical
interpretation of a molecular genetic test.
For example, the clinical comments accompanying a cystic
fibrosis screening report will vary depending
on whether the patient is a potential gamete donor or a person
exhibiting a cystic fibrosis phenotype.
Similarly, the interpretative comment accompanying Factor II
and V studies may vary depending on
whether the investigation is prompted by a history of
recurrent miscarriage or the need to determine a
thrombotic risk.
It may also be crucial, where a mutation has already been
shown to be segregating in a family, to be
provided with information concerning the mutation and a family
pedigree to ensure the correct analysis
is performed and reliable risk figures calculated.
Notes for Cytogenetics
As cytogenetic studies require living cells, please ensure
that samples reach the laboratory quickly. If a delay before
despatch is unavoidable, samples may be stored in a refrigerator
(4°C) but they must not be frozen.
Information concerning packaging, transportation, and
labelling of samples is provided on the inside cover of our
TDL Genetics Request Form Pad.
On completion of analyses, fixed cell suspensions are stored
for a minimum of three months and are available for additional
follow-up studies (for example, FISH), if necessary.
Requesting additional tests
Any further tests not requested at the time of sample receipt
must be requested within:
- 2 weeks for DNA testing
- 2 weeks for cell culture testing
- 3 months for FISH testing
Samples can be stored for longer periods if specifically
requested at the time of sample receipt.
Postnatal Diagnosis (Blood Culture)
Reasons for analysis: Chromosome studies are requested where
problems that may have a cytogenetic
basis are suspected, e.g. babies with birth defects; children
with developmental delay and physical handicaps, or adults
with fertility problems. Additionally, prospective gamete donors
are screened to detect carriers of balanced chromosome
rearrangements.
Sample requirements: Lithium heparin whole blood specimens are
required - gently mixed to prevent clotting and must not be
frozen. Sample volumes may be reduced for children (2-4ml) and
neonates (1-2ml).
Turnaround time: The usual turnaround time is 2-3 weeks
however the laboratory will endeavour to respond to urgent
requests. Where a major trisomy is suspected, a rapid PCR screen
may be performed to provide an urgent provisional
result.
Notes
a) Rarely, blood samples fail to culture (
b) The culture may yield chromosomes of insufficient quality.
This will be indicated on the report and a repeat study
suggested;
c) The laboratory should be informed if the patient has
recently received a blood transfusion.
Leukaemic Studies (Bone Marrow)
Sample requirements: 5-10ml bone marrow in preservative free
heparin and RPMI medium. This can be supplied by the
laboratory.
Clinical information: Please complete the Leukaemic Studies
Request form at the back of the laboratory guide, including WBC,
reason for referral, stages of disease/treatment and analysis
required i.e. karyotype and/or FISH.
Prenatal diagnosis
Reasons for analysis: Chromosome studies are requested where
pregnancies are identified as being at risk of a cytogenetic
abnormality e.g. advanced maternal age; positive maternal serum
screening; fetal abnormalities found on ultrasound; or where a
parent is a known carrier of a chromosome anomaly.
Sample requirements:
a) amniotic fluid - 10ml+ in a plain sterile, leak-proof
container. Suitable containers can be provided by the laboratory.
The specimen must not be frozen.
b) chorionic villus - 5mg+ in sterile transport medium.
Suitable containers containing medium can be provided by the
laboratory. The specimen must not be frozen.
c) fetal blood - 1-2ml LITHIUM HEPARIN whole blood, gently
mixed to prevent clotting.
The specimen must not be frozen.
Turnaround time: This is dependant on the rate of cell growth,
however, the usual turnaround time is approximately two weeks.
Fetal blood results will usually be reported within 7 days.
Notes
a) Maternal contamination, and mosaicism may complicate the
analysis and may lead to the suggestion that a second invasive test
is performed.
b) Rarely, cultures fail to grow (overall
c) Very small chromosome abnormalities may not be detected
(this is why the phrase 'No trisomies or major chromosome
abnormalites detected...' is used in our reports).
Solid Tissue
Reasons for analysis: Fibroblast cultures may be used in
addition to blood cultures, for example where tissue specific
mosaicism is suspected, or where blood samples cannot be obtained.
Analysis may be requested for early spontaneous miscarriages,
stillbirths, or to confirm a prenatal diagnosis.
Sample requirements: All specimens should be placed in a
sterile container, preferably containing transport medium.
This can be supplied by the laboratory. Sterile normal saline can
be used if transport medium is not available. Samples must not
be placed in formaldehyde or other preservative and must not be
frozen.
Turnaround time: This is dependant on the rate of cell growth,
however, the usual turnaround time is
approximately 4 weeks.
Notes
a) Material from miscarriages has a relatively high culture
failure rate (around 20%)
b) If no villus or fetal parts are identified in supposedly
POC material and a normal female chromosome result is found, this
may indicate that maternal tissue has been cultured (this will be
noted on our report)
c) Disposal of material from miscarriages will be by
incineration. Other arrangements can be made if requested at the
time of sample receipt
Fluorescence In Situ Hybridisation (FISH)
Where FISH studies for specific microdeletion syndromes are
required this must be indicated on the request form.
Note: FISH studies for a prenatal aneuploidy screen have now
been superceded in our laboratory by multiplex-PCR technology and
subtelomeric screens are now performed by an MLPA assay.