Xq12-q13.3 duplication syndrome is a rare chromosomal anomaly that happens when a part of the long arm of the X chromosome is duplicated. This condition is characterized by global developmental delay, autistic behavior, microcephaly, and distinctive facial features. The facial features may include down-slanting palpebral fissures, a depressed nasal bridge, anteverted nares, a long philtrum, and down-slanting corners of the mouth. In some patients, seizures have also been reported. Overall, the syndrome affects several areas of development and appearance, making its clinical presentation variable among people with this condition.

Common symptoms associated with this syndrome include global developmental delay, autistic behavior, and microcephaly. People with this condition may also show distinctive facial dysmorphism such as down-slanting palpebral fissures, a depressed nasal bridge, anteverted nares, a long philtrum, and down-slanting corners of the mouth. In addition, seizures have been noted in some individuals.

Xq12-q13.3 duplication syndrome is caused by the partial duplication of the long arm of the X chromosome. This chromosomal anomaly leads to a range of developmental and physical differences. More detailed information about other potential risk factors or genetic causes is currently limited for this condition.