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58 SECTION II BIOCHEmISTRY ``BIOCHEMISTRY—GENETICS BIOCHEmISTRY ``BIOCHEMISTRY—GENETICS
Disorders of imprinting Imprinting—one gene copy is silenced by methylation, and only the other copy is expressed
parent-of-origin effects.
Prader-Willi syndrome AngelMan syndrome
WHICH GENE IS SIlENT? Maternally derived genes are silenced Paternally derived UBE3A is silenced
Disease occurs when the Paternal allele is deleted Disease occurs when the Maternal allele is
or mutated deleted or mutated
SIGNS AND SYMPTOMS Hyperphagia, obesity, intellectual disability, Seizures, Ataxia, severe Intellectual disability,
hypogonadism, hypotonia inappropriate Laughter (“happy puppet”)
Set SAIL for Angel Island
CHROMOSOMES INVOlVED Chromosome 15 of paternal origin UBE3A on maternal copy of chromosome 15
NOTES 25% of cases are due to maternal uniparental 5% of cases are due to paternal uniparental
disomy disomy
Prader has no Dad (Paternal Deletion) MDs are angels (Maternal Deletion)
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