Question

Explain what occurs on chromosome 15 in a patient with Angelman syndrome that DOES NOT have uniparental disomy.

Please be detailed!

Answer 1

Angelman syndrome (AS) is a rare neuro-genetic disorder. It is caused by a loss of function of the UBE3A gene in the 15th chromosome derived from the mother.

UBE3A :ubiquitin protein ligase E3A

There are FOUR ways that Angelman syndrome(AS) can occur.

1.Deletion positive

• most common
• 70% of cases of Angeman syndrome
• Deletion of UBE3A gene at Chromosome 15

2. Mutation:

• 11% of cases of AS
• mutation or alteration in the maternal copy of the UBE3A gene at Chromosome 15

3. Imprinting center(IC) Defect:

• 6% of cases of AS
• abnormality in the imprinting center of chromosome 15

4. Paternal Uniparental Disomy (UPD): 3% of cases of AS

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Approximately 90% of chromosome deletions initiate at BP1 or BP2 and terminate in region BP3 (class I and class II).

Approximately 10% of deletions are larger, typically spanning from BP1 to BP5.