Chromosome 3q duplication is a chromosome abnormality that occurs when there is an extra copy of genetic material on thelong arm (q) of chromosome 3. The severity of the condition and the signs and symptoms depend on the size and location of the duplication and which genes are involved. Features that often occur in people with chromosome 3q duplication include developmental delay, intellectual disability, behavioral problems and distinctive facial features. Chromosome 3q duplication can be de novo or inherited from a parent with a chromosomal rearrangement such as a balanced translocation. Treatment is based on the signs and symptoms present in each person. The disease is partial duplication of the long arm of chromosome 3 (MONDO_0016954). Also known as: partial duplication of chromosome 3q, partial duplication of the long arm of chromosome type 3, partial trisomy of chromosome 3q.