Molecular genetics

Last updated: Tuesday, 23, March, 2004

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Molecular genetics techniques allow the detection of specific sequences in the nuclear or mitochondrial genome of a patient or the genome of a micro-organism.

Molecular genetics contributes to diagnosis in the following main areas:

  1. Identification of affected individuals or carriers of genetic disorders; characterisation of the specific genetic abnormality causing the disorder.
    See Molecular genetics - genetic disorders and Molecular genetics - individual genetic disorders.
  2. Identification of neoplastic cells; characterisation of the gene abnormalities arising in neoplastic tissue.
    See Molecular genetics - neoplasia.
  3. Establishment of the identity of an individual eg paternity testing, criminal investigation.
    See Molecular genetics - forensic.
  4. Detection and identification of specific micro-organisms.
    See Molecular genetics - microbial.
Item Process
Method

  1. Direct microscopic detection of a specific DNA sequence eg, FISH;
  2. Family associations by linkage analysis using DNA polymorphisms;
  3. Analysis of the DNA or RNA sequences and mutation detection (usually by PCR).

The sequence may be identified by determination of the size of the DNA fragment after digestion with a restriction endonuclease and/or binding of a non-specific fluorescent probe or a specific DNA probe labelled with a detection system eg, radio-isotopic, chemiluminescent, fluorescent or enzymatic detection methods.

If a number of mutations can give rise to the genetic disease in question, nucleotide sequencing or linkage analysis may be necessary.
The sequence targeted for identification may be the normal sequence, a polymorphism, or a disease-causing mutation.
Deletions, duplications or variable repeat sequences can also be targeted.

Testing is performed in relatively few laboratories so specimens may have to be referred.

The pathologist should be consulted prior to organising specimen collection.

Reference

Trent RJ. Molecular Medicine: an introductory text. 2nd ed. Churchill Livingstone 1997.

Elles R ed. Molecular diagnosis of genetic diseases. Methods in Molecular Medicine. Humana Press 1996.