Isodicentric 15
A chromosome abnormality linked to autism and developmental delays.
Isodicentric 15, also known as marker chromosome 15 syndrome, idic(15), partial tetrasomy 15q, or inverted duplication 15 (inv dup 15), is a chromosome abnormality in which a child is born with extra genetic material from chromosome 15. People with idic(15) are typically born with 47 chromosomes in their body cells instead of the normal 46, and the extra chromosome is a small supernumerary marker chromosome made up of a duplicated, mirror-image piece of chromosome 15. The syndrome is significant because it is the most frequently identified chromosome problem in individuals with autism, and its study may help locate autism-related genes.
- Field
- Genetics, Chromosome Abnormalities
- Known for
- Extra genetic material from chromosome 15 causing developmental delays, autism, and neurological symptoms
- Alternate names
- Marker chromosome 15 syndrome, idic(15), partial tetrasomy 15q, inv dup 15, Dup15q Syndrome
- Chromosome count
- Typically 47 chromosomes (instead of 46)
- Inheritance
- Usually de novo, not inherited; often maternal in origin
- Associated condition
- Autism spectrum disorder
Lore & Background
Diagnosis is made through chromosome analysis (karyotyping), confirmed by FISH to distinguish idic(15) from other marker chromosomes, and array CGH can determine gene content. There is no specific treatment to undo the chromosomal abnormality, but physical, occupational, and speech therapies, along with special education, can help individuals develop to their full potential. Medications, particularly SSRIs, should be used with caution due to potential sensitivity.
Reader's Guide
Isodicentric 15 is a key chromosome abnormality in the study of autism, as it is the most frequently identified chromosome problem in individuals with autism. The duplicated region 15q11.2-q13.1 contains the critical PWS/AS region and the Ube3a gene; introducing extra copies of Ube3a in mice produced autism-related behaviors, supporting a genetic link. The condition highlights how extra chromosomal material can disrupt neurodevelopment, and its study may lead to identifying specific autism-related genes. Management focuses on symptom-based therapies, with careful medication use. Genetic counseling is essential because the abnormality usually occurs de novo, but parental karyotyping is needed to rule out inheritance and guide future pregnancies. The variability in symptoms—from mild to severe—underscores the importance of individualized care and the need for further research into gene dosage effects.
Did You Know?
- People with idic(15) typically have 47 chromosomes instead of the normal 46.
- The extra chromosome is usually not inherited but occurs de novo, most often in the mother's egg cells.
- Mice with two extra copies of the Ube3a gene showed autism-related behavioral deficits.
More in Genetic disorders with no OMIM 1-24
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