A Case of Mosaicism in Prader-Willi Syndrome:Detection Using Fluorescent in Situ Hybridization / 대한소아내분비학회지

ABSTRACT

Prader-Willi syndrome is caused by absence of paternal contribution of chromosome region 15q11-q13. PWS is clinically suspected and can be confirmed by laboratory tests. It is accepted that DNA methylation analysis is very useful screening test and FISH with specific probe can be used for deletion detection for PWS. In clinically suspected PWS patients, we conducted two genetic tests, FISH with SNRPN probe and SNRPN expression study with RT-PCR. We found discordance in one patient. This PWS male presented with severe obesity, hypogonadism and typical appearance with the history of neonatal hypotonia and feeding problems. The FISH showed the microdeletion in 15q11-q13 as expected, but the result of SNRPN expression was positive. We reviewed FISH and observed normal cells without deletion. Methylation analysis is not sensitive enough to identify cases of mosaic PWS. So, when the molecular screening is negative, precise clinical examination is essential and other cytogenetic analysis like FISH should be combined.