Genetic mechanisms giving rise to Angelman syndrome
| Class | Mechanism | Methylation analysis* | Other diagnostic tests | Frequency |
|---|---|---|---|---|
| Ia | De novo deletion | Abnormal Paternal band only | High resolution cytogenetics FISH | 70% |
| Ib | Deletion owing to chromosome rearrangement | Abnormal Paternal band only | High resolution cytogenetics FISH | <1% |
| II | Uniparental paternal disomy | Abnormal Paternal band only | RFLP analysis | 2% |
| IIIa | Imprinting defect owing to imprinting centre mutation | Abnormal Paternal band only | Screening of IC for mutations is positive | 2% |
| IIIb | Imprinting defect without IC mutation | Abnormal Paternal band only | Screening of IC for mutations is negative | 2% |
| IIIc | Mosaic imprinting defect | Abnormal Faint maternal band | Screening of IC for mutations is usually negative | ? |
| IV | UBE3A mutation | Normal Both maternal and paternal bands | Screening of UBE3A for mutations | 5–10% |
| V | No genetic abnormality identified | Normal Both maternal and paternal bands | Consider other diagnoses | 12–15% |