QF-PCR: what is it and what is it used for in prenatal diagnosis?

Prenatal diagnosis is performed during pregnancy to determine if there is any alteration in the development of the foetus. Approximately 3% of live newborns have some type of chromosomal abnormality. In order to detect them prenatally, different techniques have been developed in recent years that have helped to improve diagnosis. QF-PCR, is a technique widely used in prenatal diagnosis due to its ease and speed. In this article we explain what it consists of and why it is very useful in this area.

What is QF-PCR?

QF-PCR stands for Quantitative Fluorescent Polymerase Chain Reaction. It is a molecular biology technique mainly used for rapid prenatal diagnosis of the most common chromosomal aneuploidies.

This technique has its origins in 1993, and was developed with the aim of providing a rapid result in cases where Down syndrome is suspected, as the diagnostic technique par excellence, karyotyping, requires around 2 weeks to obtain the results.

PCR is a laboratory technique whose name comes from the acronym “Polymerase Chain Reaction”. It has recently become one of the most well-known diagnostic techniques worldwide as it is used for the diagnosis of SARS-CoV2 (COVID-19) infection, although it is a technique that has numerous applications.

PCR is a laboratory technique used to exponentially increase the genetic material present in the sample to be studied. When we obtain a biological sample, the amount of DNA, as you can imagine, is small and if we want to study only a small fragment, the percentage will be even smaller. For this reason, a PCR is often performed to amplify the fragment to be studied in order to be able to analyse it.

How does QF-PCR work?

QF-PCR allows the detection of chromosomal alterations such as trisomies and monosomies, by amplifying specific DNA sequences. These sequences are known as STRs (Short Tandem Repeats) and are highly polymorphic, i.e. they have a high variability and are distributed throughout the DNA, making them an excellent specific marker for each chromosome we wish to study.

On the one hand, QF-PCR allows us to exponentially increase the DNA fragments we need to study and also to mark them with fluorochromes. Fluorescence makes it possible to easily detect the amplified and labelled STRs of each chromosome. The amount of amplified product will be proportional to the number of chromosomes in the sample, so if there is more of a chromosome, it will be reported as a trisomy, while if less than expected is detected, we will speak of a monosomy.

Its application in prenatal diagnosis is mainly aimed at detecting the most frequent chromosomal alterations, which is why QF-PCR amplifies STRs of:

• Chromosome 21: for the detection of Down’s Syndrome
• Chromosome 18: for the detection of Edwards’ Syndrome
• Chromosome 13: for the detection of Patau’s syndrome.
• Sex chromosomes X and Y: for the detection of Turner Syndrome or anomalies in the sex chromosomes such as trisomies, for example, XXY, XXX, among others.

It should be noted that this is a technique with a high sensitivity and specificity for detecting this type of anomalies, which is why it is of great clinical use.

Furthermore, although its main objective is to analyse the anomalies mentioned above, it is also possible to detect other anomalies such as triploidy (presence of three copies of each chromosome) or uniparental disomy (when the two copies of a chromosome come from the same parent).

Advantages of QF-PCR

Rapid diagnosis

This technique does not require cell culture, which allows results to be reported more quickly, in fact, they can be available within 24-48 hours once the sample is obtained. In all prenatal diagnostic tests, it is essential to know the results as soon as possible to reduce parental anxiety and to know the final diagnosis in order to make informed decisions.

Sample requirements

To perform the test it is necessary to obtain a sample of foetal origin, either amniotic fluid or chorionic villus biopsy. Unlike other techniques, QF-PCR can be used with very small amounts of DNA, as an amplification process is performed. For this reason, it allows results to be obtained even when other techniques have previously failed due to sample shortage.

Versatility

QF-PCR can also be used in the case of multiple pregnancies. It has the ability to identify zygosity, i.e. to identify whether the two foetuses come from the same zygote (monozygotic, i.e. identical twins) or from different ones (twins).

At Veritas Intercontinental we are committed to proactive health care from the first moments of life and therefore also during the prenatal stage. For this reason, we offer the specialist our portfolio of prenatal medicine services, focusing on both screening and diagnosis. Find here more info about our perinatal genetic services.