RESUMEN
BACKGROUND: Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are distinctive diseases with severe impairment of psychomotoric development and behaviour. Both syndromes are caused by the loss of paternal (PWS) or maternal (AS) gene expression of chromosomal region 15q11-13. The work reveals the various causes of this loss. The choice of the most suitable method for screening of the genome mutations in the patients suspected of PWS and AS is another purpose of the work. METHODS AND RESULTS: The methyl specific analysis (MS PCR) in locus SNRPN, short tandem repeat (STR) analysis and fluorescent in situ hybridization (FISH) were used. In the group of 55 patients tested for PWS and AS only maternal allele was present in 11 patients and only paternal allele was present in 1 patient in the locus SNRPN: 10 microdeletions 15q11-13, 1 UPD(15)mat and 1 UPD(15)pat. CONCLUSIONS: MS PCR seems to be the most profitable method for the first step of selection of PWS patients. In positive cases is inevitable to use also additional tests of molecular diagnosis to distinguish the particular mechanism leading to the disorders. In AS patients is also MSPCR recommended as the first step although it is necessary to exclude mutation in UBE3A gene in case of MS PCR negativity.