What is the primary application of Fragile X testing using PCR?

The primary application of Fragile X testing using PCR is to detect repeat number variations in the FMR1 gene, which is critical for diagnosing Fragile X syndrome. PCR (polymerase chain reaction) is particularly effective at amplifying specific DNA sequences, making it suitable for assessing the number of CGG repeats in the FMR1 gene.

In Fragile X syndrome, the number of CGG repeats can range from a normal range (5 to 44 repeats) to a premutation range (55 to 200 repeats), and to a full mutation (over 200 repeats), which leads to gene silencing and clinical phenotypes associated with the syndrome. While initial repeat size assessment can be performed using PCR, if the results indicate a premutation or a full mutation, follow-up testing with Southern blot analysis is often conducted to obtain more precise and quantitative data regarding the repeat size and the methylation status of the gene.

This context highlights the strength of PCR in the primary detection of repeat number variations, which acts as a precursor to more detailed testing, such as Southern blotting, for thorough confirmation and analysis. The other options, while related to genetic testing and analysis, do not accurately describe the primary role of PCR in the context of