However, people with KdVS typically live at least into adulthood. For children with epilepsy, seizures may be hard to control.

17q21.31 microduplications. A 17q21. 31 microduplication is a rare genetic condition caused by an extra part of one of the body's 46 chromosomes – chromosome 17. For healthy development, chromosomes should contain just the right amount of genetic material (DNA) – not too much and not too little.

In many affected individuals, behavior is described as friendly, amiable, and cooperative, with or without frequent laughing. However, behavioral findings including attention-deficit/hyperactivity disorder have been reported [Koolen et al 2008, Tan et al 2009, Koolen et al 2016].

Males with Koolen-de Vries syndrome often have undescended testes (cryptorchidism). Defects in the walls between the chambers of the heart (septal defects) or other cardiac abnormalities, kidney problems, and skeletal anomalies such as foot deformities occur in some affected individuals.