Molecular Diagnosis of Prader-Willi Syndrome

SUTHIPONG PANGKANON, MD*

Affiliation : * Genetic Unit, Queen Sirikit National Institute of Child Health, Bangkok 10400, Thailand.

AbstractBackground : Prader-Willi syndrome (PWS) is characterized by neonatal hypotonia and feed ing problems in infancy, developmental delay, hyperphagia with obesity, short stature, hypogonadism, characteristic facial appearance, and behavior problems. The diagnosis of PWS is based on clinical findings that change with age. PWS has proved to be a difficult condition to recognize with the diag nosis often being delayed until later childhood or even adulthood. Therefore, a molecular testing for PWS is needed to confirm the diagnosis.
Objective : To study the clinical features of Prader-Willi syndrome patients and confirm diagnosis by molecular testing.
Materials and Methods : Eighteen Prader-Willi syndrome patients who were diagnosed be tween March, 1997 and February, 2002 at the Genetic Unit, Queen Sirikit National Institute of Child Health, Bangkok. Peripheral blood lymphocytes were obtained and cultured using the standard tech nique for chromosome analysis. For fluorescence in situ hybridization (FISH) studies, the specific DNA probes for loci small nuclear ribonucleoprotein polypeptide N (SNRPN) were used to detect deletion. Non-deleted cases were confirmed to have PWS by methylation analysis.
Results : The diagnosis of eighteen PWS patients was confirmed by FISH using DNA probes for loci SNRPN demonstrating a deletion of chromosome 15q 11-q 13 in fourteen cases (77% ). Four cases (23%) were confirmed to have PWS resulting from maternal uniparental disomy by demonstrating exclusively maternal specific DNA methylation patterns.
Conclusion : The clinical diagnosis of PWS should be confirmed by molecular testing espe cially in the infancy period to avoid needless invasive diagnostic testing.

Keywords : Prader-Willi Syndrome, Fluorescence in Situ Hybridization, Uniparental Disomy, Methy lation Study

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