From OMIM
The features of the chromosome 15q11-q13 duplication syndrome include autism, mental retardation, ataxia, seizures, developmental delays, and behavioral problems (Bundey et al., 1994; Burnside et al., 2011). See also chromosome 15q13.3 deletion syndrome (612001) and chromosome 15q11.2 deletion syndrome (615656). For a discussion of genetic heterogeneity of autism, see 209850.  http://www.omim.org/entry/608636

From MedlinePlus Genetics
15q11-q13 duplication syndrome (dup15q syndrome) is a developmental disorder; its signs and symptoms vary among affected individuals.

Poor muscle tone (hypotonia) is common in individuals with dup15q syndrome and contributes to delayed development and impairment of motor skills, including sitting and walking. Most affected children develop the ability to walk independently after age 2 or 3, and they typically have a wide-based or uncoordinated (ataxic) pattern of walking (gait). Babies with dup15q syndrome often have trouble feeding due to weak facial muscles that impair sucking and swallowing.

Intellectual disability also occurs in people with dup15q syndrome and can range from mild to profound; however, it is usually in the moderate to severe range. Speech and language development are particularly affected, with some individuals never developing functional speech. Most individuals with this disorder have autism spectrum disorder (ASD), and many have language problems associated with ASD such as repeating the words of others (echolalia) or repeating particular phrases (stereotypical utterances).

Behavioral difficulties are also associated with dup15q syndrome, including other features of ASD such as difficulty with changes in routine and problems with social interaction. Affected individuals may also experience hyperactivity, anxiety, and frustration leading to tantrums. Mood disorders and psychosis occur in some affected individuals.

More than half of people with dup15q syndrome have recurrent seizures (epilepsy). The seizures usually develop between the ages of 6 months and 9 years. Some people with dup15q syndrome have only focal seizures, which affect one part of the brain and usually do not cause a loss of consciousness. In other affected individuals, seizures begin with a type called infantile spasms (seizures that usually appear before the age of 1 and involve recurrent muscle contractions) and later include other types of seizures. In addition to focal seizures, these can include rapid uncontrolled muscle jerks (myotonic seizures); tonic-clonic (also called grand mal) seizures, which involve rigidity, convulsions, and loss of consciousness; and absence (also known as petit mal) seizures, which are brief episodes of impaired consciousness that look like staring spells. Affected individuals may develop complex, difficult-to-treat (intractable) seizure patterns such as Lennox-Gastaut syndrome. Seizures can lead to falls, loss of developmental milestones (developmental regression), and in a small minority of cases, sudden death during sleep (called sudden unexpected death in epilepsy, or SUDEP).

Hearing loss in childhood is common in dup15q syndrome and usually results from ear infections that cause fluid buildup in the middle ear. This hearing loss is often temporary. However, if ear infections are left untreated during early childhood, the hearing loss can interfere with language development and worsen the speech problems associated with dup15q syndrome.

About 30 percent of individuals with dup15q syndrome are born with eyes that do not look in the same direction (strabismus). Other unusual facial features that can occur in this condition include a low forehead; outside corners of the eyes that point downward (downslanting palpebral fissures); a flattened nasal bridge with a short, upturned nose; nostrils that open to the front rather than downward (anteverted nares); a long space between the nose and the upper lip (philtrum); a small lower jaw (micrognathia); a high-arched roof of the mouth (palate); full lips; low-set ears; and a flat back of the head (occiput). These features are typically subtle and may not be noticed during infancy.

Other problems associated with dup15q syndrome in some affected individuals include a reduced ability to feel pain; a spine that curves to the side (scoliosis); recurrent respiratory infections in childhood; a skin condition called eczema; early (precocious) puberty and, in females, menstrual irregularities; minor genital abnormalities in males such as undescended testes (cryptorchidism); overeating; and excessive weight gain.  https://medlineplus.gov/genetics/condition/15q11-q13-duplication-syndrome