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Chromosome 15
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Chromosome

Chromosome 15

Chromosome 15, one of the 23 pairs in human cells, comprises over 3 percent of total DNA and is estimated to contain around 630 genes that provide instructions for various proteins.

Description

Humans normally have 46 chromosomes in each cell, divided into 23 pairs. Two copies of chromosome 15, one copy inherited from each parent, form one of the pairs. Chromosome 15 spans approximately 102 million DNA building blocks (nucleotides) and represents more than 3 percent of the total DNA in cells.

Researchers are continually improving their methods of genome sequencing and working to confirm the number of genes on each chromosome. Chromosome 15 is estimated to contain around 630 genes that provide instructions for making proteins. These proteins perform a variety of different roles in the body.

Health Conditions Related to Chromosomal Changes

The following chromosomal conditions are associated with changes in the structure or number of copies of chromosome 15.

15q11-q13 duplication syndrome

Duplication of a region of the long (q) arm of chromosome 15 can result in 15q11-q13 duplication syndrome (also called dup15q syndrome). The features of this condition can include weak muscle tone (hypotonia); intellectual disabilities; recurrent seizures (epilepsy); and characteristics typical of autism spectrum disorder, a developmental condition that affects communication and social interaction.

Dup15q syndrome is caused by the presence of at least one extra copy of a region of chromosome 15 called 15q11.2-q13.1. This region is also called the Prader-Willi/Angelman critical region (PWACR) because genetic changes in it are also involved in conditions called Prader-Willi syndrome and Angelman syndrome (described below). Individuals with a 15q11.2-q13.1 duplication will develop the signs and symptoms of dup15q syndrome only if the chromosome abnormality occurs on the copy of the chromosome that comes from the egg cell. During fertilization, the egg and the sperm each contribute one copy of each chromosome. However, some genes on chromosome 15, including some of those in the 15q11.2-q13.1 region, are turned on (active) only on the copy that came from the egg cell. This parent-specific gene activation results from a phenomenon called genomic imprinting.

The most common chromosome abnormality that leads to 15q11.2-q13.1 duplication, occurring in about 80 percent of people with dup15q syndrome, is called an isodicentric chromosome 15. An isodicentric chromosome contains mirror-image segments of genetic material and has two constriction points (centromeres), rather than the single centromere found in normal chromosomes. In people with an isodicentric chromosome 15, cells have the usual two copies of chromosome 15 plus the two duplicated copies of the segment of genetic material in the isodicentric chromosome, for a total of four copies of the duplicated segment.

In about 20 percent of cases of dup15q syndrome, the duplication occurs on the q arm of one of the two copies of chromosome 15 in each cell; this situation is called an interstitial duplication. In these cases, cells have two copies of chromosome 15, one of which has an extra copy of the segment of genetic material, for a total of three copies of the duplicated segment.

In all cases of dup15q syndrome, the duplicated genetic material results in extra copies of certain genes involved in development. This extra genetic material disrupts normal development, causing the characteristic features of this disorder. People with dup15q syndrome caused by an interstitial duplication often have milder signs and symptoms than those with an isodicentric chromosome 15.

15q13.3 microdeletion

A 15q13.3 microdeletion is a chromosomal change in which a small piece of chromosome 15 is deleted in each cell. The deletion occurs on the q arm of the chromosome at a position designated q13.3. Most people with a 15q13.3 microdeletion are missing a sequence of about 2 million DNA nucleotides, also written as 2 megabases (Mb). The exact size of the deleted region varies, but it typically contains at least six genes. It is unclear how a loss of these genes increases the risk of intellectual disabilities, seizures, behavioral problems, and psychiatric disorders in some individuals with a 15q13.3 micro

Frequently Asked Questions

The severity of symptoms varies significantly among individuals. While many face challenges with intellectual disability, seizures, and autism spectrum traits, early intervention therapies such as physical, occupational, and speech therapy can improve functional outcomes. Some individuals with milder duplications may achieve a higher level of independence with appropriate support systems.
ll three conditions involve genetic changes in the same region of chromosome 15, known as the Prader-Willi/Angelman critical region. However, the specific mechanism differs: duplication syndrome involves an extra copy of the region, while Prader-Willi and Angelman syndromes are caused by the loss of function of genes in that region, leading to distinct clinical profiles.
There is no single universal diet for all patients, but some clinicians may recommend the ketogenic diet if seizures are difficult to control with medication. Lifestyle management often includes maintaining a consistent sleep schedule, avoiding known seizure triggers, and regular neurological monitoring to adjust anticonvulsant therapy as the child grows.
Diagnosis typically begins with clinical observation of symptoms like hypotonia and developmental delays, followed by genetic testing such as chromosomal microarray analysis or fluorescence in situ hybridization (FISH). These tests can detect the extra copy of the 15q11.2-q13.1 region, which is often too small to be seen under a standard microscope.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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