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16p11.2 deletion syndrome

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Other Names: Chromosome 16p11.2 deletion syndrome; Del(16)(p11.2); Monosomy 16p11.2; Microdeletion 16p11.2 16p11.2 deletion syndrome is a condition caused by a missing piece (deletion) on a specific region of chromosome 16 designated as p11.2. People with 16p11.2 deletion syndrome usually have developmental delay and intellectual disability. Most also have at least some features of autism spectrum disorder.

Epidemiology

Most people tested for the 16p11.2 deletion have come to medical attention as a result of developmental delay or autistic behaviors. Other individuals with the 16p11.2 deletion have no associated health or behavioral problems, and so the deletion may never be detected. For this reason, the prevalence of this deletion in the general population is difficult to determine but has been estimated at approximately 3 in 10,000.

Cause

People with 16p11.2 deletion syndrome are missing a sequence of about 600,000 DNA building blocks (base pairs), also written as 600 kilobases (kb), at position p11.2 on chromosome 16. This deletion affects one of the two copies of chromosome 16 in each cell. The 600 kb region contains more than 25 genes, and in many cases little is known about their function. Researchers are working to determine how the missing genes contribute to the features of 16p11.2 deletion syndrome.

Inheritance

Autosomal dominant pattern, a 50/50 chance.

16p11.2 deletion syndrome is considered to have an autosomal dominant inheritance pattern because a deletion in one copy of chromosome 16 in each cell is sufficient to cause the condition. However, most cases of 16p11.2 deletion syndrome are not inherited. The deletion occurs most often as a random event during the formation of reproductive cells (eggs and sperm) or in early fetal development. Affected people typically have no history of the disorder in their family, although they can pass the condition to their children. Several examples of inherited 16p11.2 deletion have been reported. In inherited cases, other family members may be affected as well.

Signs and symptoms

People with 16p11.2 deletion syndrome usually have developmental delay and intellectual disability. Most also have at least some features of autism spectrum disorders. These disorders are characterized by impaired communication and socialization skills, as well as delayed development of speech and language. In 16p11.2 deletion syndrome, expressive language skills (vocabulary and the production of speech) are generally more severely affected than receptive language skills (the ability to understand speech). Some people with this disorder have recurrent seizures (epilepsy).

Some affected individuals have minor physical abnormalities such as low-set ears or partially webbed toes (partial syndactyly). People with this disorder are also at increased risk of obesity compared with the general population. However, there is no particular pattern of physical abnormalities that characterizes 16p11.2 deletion syndrome. Signs and symptoms of the disorder vary even among affected members of the same family. Some people with the deletion have no identified physical, intellectual, or behavioral abnormalities.

For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed.

80%-99% of people have these symptoms

  • Global developmental delay
  • Intellectual disability(Mental deficiency)
  • Language impairment

30%-79% of people have these symptoms

  • Autism
  • Broad forehead(Increased width of the forehead)
  • EEG abnormality
  • Macrocephaly(Increased size of skull)
  • Malar flattening(Zygomatic flattening)
  • Seizure

5%-29% of people have these symptoms

  • Anophthalmia(Absence of eyeballs)
  • Aortic regurgitation
  • Atrial septal defect(An opening in the wall separating the top two chambers of the heart)
  • Attention deficit hyperactivity disorder(Attention deficit)
  • Cleft palate(Cleft roof of mouth)
  • Congenital diaphragmatic hernia
  • Feeding difficulties(Feeding problems)
  • Gastroesophageal reflux
  • Acid reflux
  • Hand polydactyly(Extra finger)
  • Hemivertebrae(Missing part of vertebrae)
  • Hypertelorism(Wide-set eyes)
  • Micrognathia(Little lower jaw)
  • Microphthalmia(Abnormally small eyeball)
  • Muscular hypotonia(Low or weak muscle tone)
  • Myopia(Close sighted)
  • Obesity(Having too much body fat)
  • Optic nerve coloboma
  • Psychosis
  • Pyloric stenosis
  • Scoliosis
  • Strabismus(Cross-eyed)
  • Syringomyelia(Fluid-filled cyst in spinal cord)
  • Ventriculomegaly

1%-4% of people have these symptoms

  • Feeding difficulties in infancy
  • Motor delay

Diagnosis

Suggestive Findings The 16p11.2 recurrent microdeletion should be suspected in individuals with the following clinical findings:

  • Delayed language development (with expressive language typically more affected than receptive language) and abnormal speech articulation
  • Learning difficulties/intellectual disability
  • Social impairments with or without a diagnosis of autism spectrum disorder (ASD)
  • Macrocephaly
  • Chiari I/cerebellar tonsillar ectopia
  • Seizures/epilepsy
  • Vertebral anomalies
  • Obesity starting in adolescence, and in the setting of developmental delay

The 16p11.2 microdeletion is defined as the recurrent ~593-kb heterozygous deletion at the approximate position of 29.6-30.2 Mb in the reference genome (GRCh37/hg19). The microdeletion is identified by genomic testing that determines copy number of sequences, such as chromosomal microarray (CMA). This deletion cannot be detected by routine analysis of G-banded chromosomes or other conventional cytogenetic banding techniques. While FISH analysis is not appropriate for identification of the deletion in a proband, it may be used to test relatives of a proband who is known to have the deletion.

Treatment

Treatment should be targeted to the specific deficits identified. Full developmental assessment, including neuropsychological testing by a clinical psychologist, is strongly suggested to establish neurodevelopmental needs and treatment recommendations. Refer to a neurologist if seizures are suspected. Because of the high risk of obesity beginning in adolescence, encourage healthy eating habits with attention to portion size and an active lifestyle from a young age. Routine management of vertebral anomalies.

Prognosis

We are not aware of long-term follow-up data for people with 16p11.2 deletion syndrome. The long-term outlook (prognosis) for affected people likely depends on the specific features and severity in each person. Some affected people may have congenital abnormalities such as a heart defect, while others have no identifiable signs or symptoms.

NIH genetic and rare disease info

16p11.2 deletion syndrome is a rare disease.


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