[Prader-Willi syndrome and genomic imprinting].
OBJECTIVE
Prader-Willi syndrome (PWS) is an example of a human genetic disorder that involves imprinting genes on the proximal long arm of chromosome 15 and SNRPN gene as a candidate gene for this syndrome. The purpose of this study was to show the molecular genetic defects and genomic imprinting basis in Chinese PWS patients and to evaluate the clinical applications of a differential diagnostic test for PWS.


METHODS
Fluorescence in situ hybridization (FISH) and methylation-specific PCR (MSPCR) techniques were applied for 4 clinically suspected PWS patients. Using three probes, including SNRPN probe for identification of the critical locus in PWS region, D15Z1 and PML control probes for identification of the 15p arm and 15q arm, the authors detected the deletions 15q in PWS. MSPCR was based on sodium bisulfite treatment of DNA and PCR primers specific for the maternal and paternal allele.


RESULTS
When hybridized with mixed probes, it was found in 2 patients that the central specific signal was absent, but both the flanking control signals were retained, indicating SNRPN gene deletion of chromosome 15q11-13. Bisulfite-modified DNA from all PWS children amplified with methylated allele-specific primer pair showed only maternal 131bp PCR product, indicating the maternal uniparental disomy (UPD15).


CONCLUSIONS
Genomic imprinting plays an important role in the molecular pathogenesis of PWS that caused by paternal microdeletions of 15q11-q13 or maternal UPD of chromosome 15. The basic defect seemed to be an absence of function of PWS genes that are normally expressed only from the paternal chromosome 15. MSPCR is a rapid and simple PCR-based assay compared with other cyto-molecular tests and its results were consistent with the clinical diagnosis of PWS, so it seems to be a reliable diagnostic method for PWS patients who show abnormal methylation at SNRPN. The genetic differential tests for PWS are important in determining familial recurrence risk.
Wang
Wei
W
Department of Pediatrics, Ruijin Hospital, Shanghai Second Medical University, Shanghai 200025, China.
Wang
De-fen
DF
Cui
Yi-fen
YF
Ni
Ji-hong
JH
Dong
Zhi-ya
ZY
Fu
Man-fen
MF
Fu
Hong-mei
HM
Lu
Guo-qiang
GQ
Chen
Feng-sheng
FS
D000293:Adolescent; D001324:Autoantigens; D002872:Chromosome Deletion; D002884:Chromosomes, Human, Pair 15 / Q000235:genetics; D017353:Gene Deletion; D018392:Genomic Imprinting / Q000235:genetics*; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008297:Male; D016133:Polymerase Chain Reaction / Q000379:methods; D011218:Prader-Willi Syndrome / Q000235:genetics*; D017411:Ribonucleoproteins, Small Nuclear / Q000235:genetics; D055517:snRNP Core Proteins
D001324:Autoantigens; D017411:Ribonucleoproteins, Small Nuclear; C526417:SNRPN protein, human; D055517:snRNP Core Proteins