The ligase chain reaction (LCR) is a method of DNA amplification. While the better-known PCR carries out the amplification by polymerizing nucleotides, LCR instead amplifies the nucleic acid used as the probe. For each of the two DNA strands, two partial probes are ligated to form the actual one; thus, LCR uses two enzymes: a DNA polymerase

DNA polymerase

A DNA polymerase is an enzyme that helps catalyze in the polymerization of deoxyribonucleotides into a DNA strand. DNA polymerases are best known for their feedback role in DNA replication, in which the polymerase "reads" an intact DNA strand as a template and uses it to synthesize the new strand....

 and a DNA ligase

DNA ligase

In molecular biology, DNA ligase is a specific type of enzyme, a ligase, that repairs single-stranded discontinuities in double stranded DNA molecules, in simple words strands that have double-strand break . Purified DNA ligase is used in gene cloning to join DNA molecules together...

. Each cycle results in a doubling of the target nucleic acid molecule. A key advantage of LCR is greater specificity as compared to PCR..

Target conditions

It has been widely used for the detection of single base mutation

Point mutation

A point mutation, or single base substitution, is a type of mutation that causes the replacement of a single base nucleotide with another nucleotide of the genetic material, DNA or RNA. Often the term point mutation also includes insertions or deletions of a single base pair...

s, as in genetic diseases.

LCR and PCR may be used to detect gonorrhea

Gonorrhea

Gonorrhea is a common sexually transmitted infection caused by the bacterium Neisseria gonorrhoeae. The usual symptoms in men are burning with urination and penile discharge. Women, on the other hand, are asymptomatic half the time or have vaginal discharge and pelvic pain...

 and chlamydia, and may be performed on first-catch urine samples, providing easy collection and a large yield of organisms. Endogenous inhibitors limit the sensitivity

Sensitivity and specificity

Sensitivity and specificity are statistical measures of the performance of a binary classification test, also known in statistics as classification function. Sensitivity measures the proportion of actual positives which are correctly identified as such Sensitivity and specificity are statistical...

, but if this effect could be eliminated, LCR and PCR would have clinical advantages over any other methods of diagnosing gonorrhea and chlamydia.

General reading

• Walker, J. M., & Rapley, R. (2005). Medical biomethods handbook. Totowa, N.J.: Humana Press. ISBN 9781592598700