Molecular Genetics

The Bristol Genetics Laboratory (BGL) provides testing for a large number of genetic disorders. We operate as part of a consortium called SCOBEC (Salisbury, Cardiff, Oxford, Bristol, Exeter and Cambridge) and the United Kingdom Genetic Testing Network (UKGTN)  to ensure access to the full range of genetic tests available nationally. The referring clinician is responsible for funding testing carried out on submitted samples.

Reasons for Molecular Genetic Analysis:

  • to confirm a clinical diagnosis in an affected individual
  • to determine carrier status in a relative of an affected individual
  • to carry out prenatal diagnosis
  • to carry out prenatal exclusion testing
  • to determine the risk of an individual developing symptoms of a late onset disorder
  • for prognosis/therapeutic decision making in cancer 

Samples that can be used for DNA analysis are:

  • lymphocytes taken from whole blood
  • chorionic villus biopsies
  • cultured amniotic cells
  • cultured fibroblasts
  • fresh or frozen tissue
  • buccal cells (contact laboratory to discuss before referral)
  • paraffin embedded tissue (contact laboratory before referral)

Sample Requirements:
Whole Blood
At least 3ml in EDTA tube (mixed well to avoid clotting) or 1-2ml for paediatric samples. Blood should be kept at room temperature or at 4°C. The sample must not be frozen before diespatch. Samples should be sent via 1st class post or equivalent.
Clinicians are encouraged to send samples to their nearest laboratory for extraction. An aliquot of DNA can be sent to a laboratory for genetic analysis if a clinical letter of referral has been provided or other appropriate details given on the referral form.

Chorionic Villus Samples (CVS)
Please contact both the Molecular Genetic and Cytogenetics sections when the clinical appointment is confirmed. Samples should be sent in appropriate transport medium to the Cytogenetics section to be received in the laboratory the same day they are taken.
Prenatal results are usually available within 3-10 days provided appropriate information regarding the pathological mutation in the family is already available.

Buccal Cells, Mouthwashes, Brushes, Tissue Samples (not including CVS) by arrangement with the laboratory – please contact Bristol Genetics Laboratory.

Restrictions and Limitations:
DNA extraction and banking is generally available for disorders that clearly have a genetic basis. Where a test is not available, or when it is not obvious which locus is being investigated, the laboratory will store the DNA until further information is forthcoming. In these circumstances consent must be obtained to store the DNA indefinitely.

Late onset neurological disorders

Diagnostic Testing
For late onset neurological disorders such as Huntington disease, molecular analysis is carried out to confirm a diagnosis in a patient showing clinical signs. The laboratory will require signed, informed consent from the proband before analysis is undertaken. The consent form should state that the individual and other family members understand the implications of a positive test result. If the proband is not able to provide a signature the laboratory will accept the signature of another family member or the main carer. We also require the signature of the specialist clinician. We are able to provide consent forms, pleasecontact us for details.

Predictive Testing
Predictive testing for late onset neurological disorders such as Huntington disease (that is, when the individual is at risk because of a family history but is not showing clinical symptoms) will be undertaken only after appropriate genetic counselling. The laboratory follows the guidelines laid down by the UK Consortium for Predictive Testing in Huntington disease. The result is given only to the clinician or the genetics nurse specialist who had requested the test. Patients requesting such a test should be referred to the local Clinical Genetics Services.
General Practitioners wishing to arrange testing for Huntington disease can contact the local Clinical Genetics Services directly to refer patients.

Testing children for carrier status of an X-linked or autosomal recessive disorder
In some circumstances a parent or grandparent, knowing that there is a genetic disorder in the family, may request that their child be tested for carrier status even though that child is not at risk of developing the disorder. The laboratory follows the guidelines of the British Society of Human Genetics regarding genetic testing in children which protect a child’s right to privacy of his/her own genetic status and the right of an individual to make informed decisions about genetic testing for themselves. We reserve the right to withhold molecular analysis of a child’s DNA until the child is able to provide his/her own informed consent for genetic testing.

Samples from non-specialist clinicians
The genetics laboratories at Bristol Genetics Laboratory adopt the policy that the majority of genetic tests are usually undertaken only at the request of a specialist clinician. Samples from a General Practitioner are usually stored until further clinical information is provided by a specialist clinician.

Private referrals including those for Fertility Studies
If samples from private patients are taken by a General Practitioner on behalf of a private clinic, the name and address of the private clinic/specialist consultant should be provided for reporting purposes, when forwarding to the laboratory.

Non-specific requesting
Molecular genetic analysis is time-consuming and frequently expensive. Samples are often sent to the laboratory supported by non-specific clinical information and a request for testing a large number of disorders, some of which follow different patterns of inheritance. In order to rationalise time and effort the laboratory may store the DNA and withhold testing until more specific clinical information has been received from the requesting clinician.

Last updated: 13/07/2011