Genotypes

In the world of genetic disorders, the word also refers to the alleles or variants an individual carries in a particular gene or genetic location. (This is in contrast to one’s phenotype, which is the word used to describe observable characteristics or traits.)

Angelman syndrome is caused by a genetic problem on the UBE3A region of chromosome 15, but this problem can take different forms—which is why there are different kinds of AS genotypes. They are:

Deletion

These individuals AS are missing a piece of DNA in region 15q11‑13 on the maternal copy of chromosome 15. Go here to learn more, and connect with other Deletion families.

Mutation

These individuals have a small abnormality in the DNA in region 15q11‑13 on the maternal copy of chromosome 15. A mutation can happen anywhere on the gene. Go here to learn more, and connect with other Mutation families.

UPD/ICD

These two genotypes are technically different, but functionally the same. An individual with UPD has two copies of chromosome 15 from their father, both of which are silent, instead of one each from the father and mother. Those with ICD have a defect on their imprinting center. In these cases, the mother’s chromosome 15 is blank, and the center copies the father’s chromosome 15—thereby rendering both copies “silent.” Go here to learn more, and connect with other UPD/ICD families.

Mosaic

This is an extremely rare genotype of Angelman syndrome where a small proportion of the body’s cells are expressing UBE3A. A person with mosaicism has a mixture of fully expressing and non-expressing UBE3A DNA in the cells of the body. Go here to learn more, and connect with other Mosaic families.

In addition, there are also people whose testing for Angelman syndrome is normal, but who still meet the diagnostic criteria for AS. These individuals may have as yet unrecognized mutations that affect UBE3A or genomic imprinting on Chromosome 15. (It’s also important to note that there are several other syndromes that present like AS. Visit this page for more information.)