Imprinted genes are silenced genes, meaning they are not expressed, and can be a normal phenomenon. Humans have two sets of genes, from both their mother and father, and having one set of genes (alleles) imprinted is normally not an issue, as the other gene is present to express the given trait. However if a mutation occurs on the active allele while the other allele is imprinted, then there will no longer be a functional copy of the gene in that region. In Angelman syndrome, the paternal allele is imprinted, or silenced, at baseline. Disease then results if the maternal allele is mutated or deleted, since this results in no functional gene existing.
The affected genes are found on the long arm of chromosome 15, more specifically at the locus 15q11-13. Recall that “q” refers to the long arm of a chromosome, while “p” represents the short arm. A mutation on the maternal 15q allele, whether it be a deletion, inversion, etc., will lead to Angelman’s syndrome.
Although an outdated term, Angelman’s syndrome was once known as “Happy Puppet Syndrome” due to the personality and behavior of these individuals. They smile and laugh constantly and are easily excited.
Angelman’s patients are known for their uniquely and seemingly pleasant behavior of laughing and smiling, even if it can be at inappropriate times. They often have short attention spans as well.
A wide based gait due to poor motor control is characteristic of Angelman’s; these individuals also exhibit hypermotoric behavior with arm waving and hand flapping.
Because of the severe intellectual disability that accompanies Angelman’s syndrome, these patients are unable to live independently and will require lifelong care.
Seizures can be a concerning complication of Angelman’s syndrome. Parents should be educated about proper seizure care when caring for affected children.
After diagnosis of Angelman’s has been made, an EEG should be obtained for baseline evaluation. A notable finding with these patients are large-amplitude slow-spike waves, with or without documented seizure activity.
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