Scientists Develop Quick, Accurate Diagnostic Test for Angelman and Prader-Willi Syndromes

Researchers have developed a new quick and accurate molecular diagnostic test for patients with either Angelman and Prader-Willi syndrome.

Their study, “A rapid and accurate methylation‐sensitive high‐resolution melting analysis assay for the diagnosis of Prader Willi and Angelman patients,” was published in Molecular Genetics & Genomic Medicine.

Prader-Willi (PWS) and Angelman (AS) syndromes are two rare genetic disorders caused by imprinting defects in the same region of chromosome 15. While PWS is associated with loss of function of paternal genes, Angelman is caused by loss of function of maternal genes. Genomic imprinting is the process by which one copy of a gene, either the maternal or paternal copy, is silenced by a chemical DNA modification called methylation.

“The laboratory diagnosis of PWS and AS is a challenge and demands several molecular and cytogenetic [the study of chromosomes] methods to elucidate the genetic mechanism that leads to the development of the syndrome,” the investigators wrote.

Analyses of DNA methylation patterns in a specific region of chromosome 15 — known as the SNURF‐SNRPN locus by methylation‐specific polymerase chain reaction (MS‐PCR, a technique that detects changes in DNA methylation in specific regions of a DNA sequence) — allows researchers to diagnose and distinguish patients with PWS from those with AS.

“Even though DNA sequencing is considered the ‘gold standard’ for mutation screening, this methodology remains relatively expensive, laborious, and time‐consuming,” the researchers wrote.

In this study, scientists developed a method based on high-resolution melting (HRM, a technique that allows researchers to distinguish between normal and mutated DNA sequences based on their melting profile). It’s a simple, fast, sensitive, specific, and low-cost alternative to DNA sequencing to diagnose and distinguish PWS and AS patients.

To test and validate the new MS-HRM method, the researchers first isolated DNA from blood samples of 43 patients suspected of having either PWS or AS. They then performed and compared results from the standard MS-PCR to the new MS-HRM method.

The test results showed that MS-HRM and MS-PCR were in agreement in all cases, identifying 19 (44%) patients with PWS, three (7%) with AS, and 21 (49%) with no alterations.

Subsequent fluorescence in situ hybridization (FISH, a technique that allows researchers to visualize specific regions of chromosomes labeled with a fluorescent probe) performed on 19 (44%) patients detected four cases of PWS caused by a deletion (where part of the DNA sequence of a gene is lost) in chromosome 15.

The MS‐HRM “does not need additional techniques such as agarose gel electrophoresis [which allows researchers to separate and distinguish DNA sequences with different sizes], reducing the time taken to obtain an accurate result and reducing the risks of cross‐contamination between samples,” the researchers wrote.

“The sensitivity of MS‐HRM allows the detection of a tiny fraction of sample [and] is important in the analysis of samples, which are difficult to obtain especially from newborn hypotonic [low muscle tone] infants. Besides, high reproducibility of HRM makes this method suitable for both research and diagnostic applications in the study of PWS and AS syndromes,” they added.

“A quick and accurate diagnosis of PWS or AS allows effective medicament intervention, avoiding several characteristics of these disorders, providing a better quality of life,” they concluded.