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A molecular and cytogenetic study in Finnish Prader-Willi patients
H Kokkonen1, M Kähkönen, J Leisti
1Dept. of Clinical Genetics, Oulu University Central Hospital, Finland.
Insights
Prader-Willi syndrome (PWS) diagnosis can be challenging. Molecular testing, particularly methylation analysis, is crucial for identifying deletions or uniparental disomy in chromosome 15q11-q13, confirming PWS in most affected individuals.
Area of Science:
- Genetics
- Developmental Biology
- Molecular Diagnostics
Background:
- Prader-Willi syndrome (PWS) is a complex genetic developmental disorder.
- It results from a deficiency in paternal gene contributions within the 15q11-q13 chromosomal region.
- Causes include deletions, maternal uniparental disomy, or imprinting defects.
Purpose of the Study:
- To evaluate the diagnostic yield of cytogenetic and molecular techniques for Prader-Willi syndrome.
- To assess the effectiveness of specific molecular probes in PWS diagnosis.
Main Methods:
- Studied 41 patients with suspected PWS and their parents.
- Employed cytogenetic and molecular analyses.
- Utilized methylation testing with probes PW71 (D15S63) and hN4HS (SNRPN).
Main Results:
- Identified molecular deletions in 85% of clinically typical PWS patients (23 out of 27).
- Cytogenetic methods detected only 71% of these deletions (15 out of 23).
- Maternal uniparental heterodisomy was found in four cases; other patients lacked detectable molecular defects.
Conclusions:
- Methylation testing with specific probes is highly effective for PWS diagnosis.
- This method reliably distinguishes between deletions and uniparental disomy.
- Molecular diagnostics offer superior sensitivity compared to cytogenetics for PWS detection.
Abstract:
The Prader-Willi syndrome (PWS) is a developmental disorder caused by a deficiency of paternal contributions, arising from differently sized deletions, uniparental disomy or rare imprinting mutations, in the chromosome region 15q11-q13. We studied 41 patients with suspected PWS and their parents using cytogenetic and molecular techniques. Of the 27 clinically typical PWS patients, 23 (85%) had a molecular deletion that could be classified into four size categories. Only 15 of them (71%) could be detected cytogenetically. Maternal uniparental heterodisomy was observed in four cases. The rest of the patients showed no molecular defects including rare imprinting mutations. In our experience, the use of the methylation test with the probe PW71 (D15S63), together with the probe hN4HS (SNRPN), which distinguishes between a deletion and uniparental disomy, is the method of choice for the diagnosis of PWS.