partial duplication of the long arm of chromosome 12 (MONDO_0042969, a Monarch Disease Ontology entry) can be described as follows. Chromosome 12q duplication is a chromosome abnormality that occurs when there is an extra copy of genetic material on the long arm (q) of chromosome 12. 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 12q duplication include developmental delay, intellectual disability, behavioral problems, growth delay, and distinctive facial features. Most cases are not inherited, but people can pass the duplication on to their children. Treatment is based on the signs and symptoms present in each person.