Tests
1st tests to order
DNA methylation testing
Test
Organize DNA methylation testing if Prader-Willi syndrome (PWS) is suspected, which will confirm the diagnosis in >99% of patients.[1][3]
In general, key features that should prompt DNA methylation testing in an infant are hypotonia, difficulty feeding, and/or hypogonadism.[2] A full list of clinical features by age that can help guide which patients should undergo DNA methylation testing has been proposed. See Criteria.
DNA methylation testing does not identify the specific genotype (deletion, maternal uniparental disomy of chromosome 15, or imprinting defect) of PWS; this requires further genetic testing by a medical geneticist.[3]
If there are existing genetic test results, repeat testing is not recommended unless there is uncertainty about the existing result, e.g., the result is inconsistent with the patient’s clinical presentation or the test methodology has changed.[27]
Result
no paternal allele at 15q11-q13
Tests to consider
further genetic testing
Test
Refer the patient to a medical geneticist for further genetic testing if Prader-Willi syndrome is confirmed on DNA methylation testing, in order to determine the specific genotype.[3][25] Further genetic testing may include:[25]
Methylation-specific multiplex ligation-dependent probe amplification[41]
Fluorescence in situ hybridization[41]
Chromosome microarray (CMA)
CMA-SNP (single-nucleotide polymorphism-based chromosomal microarray analysis) array
DNA polymorphism analysis
DNA sequence analysis.
If there are existing genetic test results, repeat testing is not recommended unless there is uncertainty about the existing result, e.g., the result is inconsistent with the patient’s clinical presentation or the test methodology has changed.[27]
Result
determination of genotype (deletion, maternal uniparental disomy, or imprinting defect)
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