Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are two different multisystem neurogenetic disorders linked by chromosomal region 15q11-q13. The part of DNA is significant by containing some genes whose regulation of expression is under the influence of genomic imprinting. These syndromes are caused by the absence of inherited region 15q11-q13; either by paternal (PWS) or maternal region (AS). The absence of gene expression arises due to deletions, uniparental disomies, mutations in imprinting centre and mutations in UBE3A gene. There are lots of diagnostic tools used in laboratories detecting causal mutations based on cytogenetics, molecular-cytogenetics and molecular genetics. This article has presented particularly the techniques confirming PWS/AS clinic diagnoses, their effectiveness, differentiation ability, advantages and disadvantages. Our objective is to point out the importance of combining the methods to determine and specify the absence of inherited material with the aim to confirm diagnoses effectively, to compare genotype with phenotype, and to estimate the recurrence risks in a proband’s family. The article has been based on long-term routine as well as research experience, and has summarized the progression of methods used in our laboratory.

        Key words: PWS, AS, chromosomal region 15q11-q13, FISH, STR analysis, methylation analysis