Types of 15q Duplications

There are several types of chromosome 15q duplications. Each involves different symptoms and risk for recurrence.

CHROMOSOME 15Q11.2-13.1 DUPLICATION SYNDROME

Chromosome 15q11.2-13.1 duplication syndrome (dup15q) is a clinically identifiable syndrome which results from duplications of chromosome 15q11.2-q13.1. Chromosome 15q duplications are associated with autism spectrum disorders, developmental delay, learning disabilities/cognitive delays, and seizures/epilepsy.

Clinicians should suspect this syndrome in any infant/child with early central hypotonia, minor dysmorphic features, significant developmental delay, autistic behaviors, infantile spasms or who subsequently develops hard to control seizures/epilepsy.

Chromosome 15q duplications most commonly occur in one of two forms, either as an extra isodicentric 15 chromosome or as an interstitial duplication of chromosome 15q.

Isodicentric 15

Isodicentric chromosome 15, abbreviated idic(15), is diagnosed in individuals who have 47 chromosomes (or sometimes more) instead of the typical 46 chromosomes. The extra chromosome is made up of a portion of chromosome 15 that has been duplicated and "inverted," so that there are two copies of part of chromosome 15q attached to one another that appear to be mirror images. Because of this arrangement, idic(15) used to be referred to as "inverted duplication chromosome 15." Most commonly, the region called 15q11-q13 is the portion of chromosome 15 duplicated. Sometimes the duplicated region is larger. The size of the idic(15) varies depending on the size of the region of chromosome 15 that is duplicated.

Interstitial Duplication 15 

People born with the typical 46 chromosomes, but who have a segment of duplicated material within chromosome 15, are said to have an interstitial duplication chromosome 15. Most often this is the same section (15q11-q13) that makes up the extra chromosome in idic(15). For this reason, people with interstitial duplications of 15q and those with idic(15) share similar characteristics. 

When the extra genetic material comes from the paternal chromosome, a child may have normal development. However, when the duplicated material comes from the maternal chromosome, developmental problems are often the result. In most cases of chromosome 15q11.2-13.1 duplication syndrome, the chromosome duplication is not inherited, but occurred as a random event during the formation of reproductive cells (eggs and sperm).

Please see the following pages for more details:

Isodicentric Chromosome 15 

Interstitial Duplication Chromosome 15

Mosaicism

Edge Duplications - 11.2 and 13.3