Investigations

1st investigations to order

DNA methylation testing

Test
Result
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]

Result

no paternal allele at 15q11-q13

Investigations to consider

further genetic testing

Test
Result
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[40]

  • Fluorescence in situ hybridisation[40]

  • Chromosome microarray (CMA)

  • CMA-SNP (single-nucleotide polymorphism-based chromosomal microarray analysis) array

  • DNA polymorphism analysis

  • DNA sequence analysis.

Result

determination of genotype (deletion, maternal uniparental disomy, or imprinting defect)

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