[Quick diagnosis of Prader-Willi and Angelman syndromes by means of methylation test by PCR]

Angelman (AS) and Prader-Willi (PWS) syndromes are two different neurogenetic diseases caused by a deficiency of maternal (AS) or paternal (PWS) contributions of the region 15q11-13. Molecular diagnosis of these pathologies can be accomplished by several techniques: DNA polymorphism (microsatellite) analysis, cytogenetic techniques of fluorescent in situ hybridization (FISH) and methylation test by Southern blot (SB), with the latter being the most reliable. Recently, a new technique, based on the study of methylation through treatment with sodium bisulphite and subsequent polymerase chain reaction (PCR), has become available. We have evaluated this technique, comparing the results with those previously obtained by SB in a group of patients suspected of having PWS or AS.

Genomic DNA from 70 patients with suspected PWS or AS was used. Methylation testing by SB was carried out using the probe PW71B labeled with radioactivity. For methylation testing by PCR the DNA was treated with sodium bisulphite and hydroquinone and PCR preformed using specific primers for the maternal and paternal alleles.

Of the 70 patients studied by PCR, 45 were normal, 17 and 8 showed altered molecular patterns that were compatible with PWS and AS, respectively. The concordance with the results obtained previously with SB was 100%.

These data suggest that the reliability of this new technique is very good and it has advantages compared to SB, since it requires a smaller quantity of DNA and can be applied for diagnosis in newborns.