Chromosome 3q29 microduplication syndrome is a rare chromosome abnormality characterized by having an extra copy of material (duplication) on a specific part of the long arm of chromosome 3. The signs and symptoms vary among affected individuals, but the most common features include mild or moderate intellectual disability and microcephaly. The condition may occur for the first time in the affected individual (de novo) or it can be inherited from a mildly affected or apparently normal parent. Treatment is directed toward the specific signs and symptoms present in each individual.

The signs and symptoms of chromosome 3q29 microduplication syndrome appear to vary among affected individuals. This condition has reduced penetrance, which means that some individuals with this chromosome abnormality do not have any signs and symptoms and are clinically unaffected.Developmental delay, abnormally small head size (microcephaly) and ophthalmologic (eye-related) findings seem to be the most common features. Other signs and symptoms that have been reported in affected individuals include cardiac (heart) abnormalities; poor muscle tone (hypotonia); speech delay; craniosynostosis; high palate (roof of the mouth); dental abnormalities; conductive hearing loss (hearing loss due to mechanical problems in the outer or middle ear); musculoskeletal abnormalities; and seizures.

The prognosis for chromosome 3q29 microduplication syndrome varies depending on the presence and severity of signs and symptoms in each affected individual. Because microduplications have only more recently been diagnosed due to improving technology, it is not known with certainty what the long term affects are. Those who have no birth defects and are generally healthy likely will have a normal life expectancy, while individuals who are more severely affected may experience various complications.