Chromosome 16 Disorders - Duplications and Deletions

Duplications and Deletions

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Chromosomes are the structures that hold our genes, which provide instructions that guide the body's development and functioning. There are 46 chromosomes, occurring in 23 pairs, and containing thousands of genes. Within each pair, one is inherited from the mother and one from the father. While everyone should have 46 chromosomes in every cell of the body, chromosomes can be missing or duplicated, resulting in missing or extra genes.

These aberrations can cause problems in health and development. 

Chromosome 16

Like other chromosomes, chromosome 16 contains thousands of genes. The role of these genes is to guide protein production, which impacts a variety of functions in the body. Unfortunately, many genetic conditions are related to problems with the genes on chromosome 16. Changes in the structure or number of copies of a chromosome can cause problems with health and development. The following chromosomal conditions are associated with chromosome 16.

Trisomy 16

Instead of the normal pair, there are three copies of chromosome 16. Trisomy 16 is estimated to occur in more than 1 percent of pregnancies, making it the most common trisomy in humans. Unfortunately, this also makes trisomy 16 the most common chromosomal cause of miscarriages, as the condition is not compatible with life.

Trisomy 16 Mosaicism

Sometimes there may be three copies of chromosome 16, but not in all cells of the body (some have the normal two copies).

This is called mosaicism. Symptoms of trisomy 16 mosaicism include:

  • musculoskeletal anomalies
  • urethral opening too low (hypospadias) (7.6% of boys).

There is also an increased risk of premature birth for infants with trisomy 16 mosaicism.

16 P Minus (16p-)

In this disorder, part of the short (p) arm of chromosome 16 is missing. A disorder associated with 16p- is Rubinstein-Taybi syndrome.

16 P Plus (16p+)

The duplication of some or all of the short (p) arm of chromosome 16 may cause:

  • poor growth of the fetus during pregnancy and of the infant after birth
  • small round skull
  • scant lashes and eyebrows
  • round flat face
  • prominent upper jaw with small lower jaw
  • round low-set ears with deformities
  • thumb anomalies
  • severe mental impairment.

16 Q Minus (16q-)

In this disorder, part of the long (q) arm of chromosome 16 is missing. Some individuals with 16q- may have severe growth and developmental disorders, and anomalies of the face, head, internal organs, and musculoskeletal system.

16 Q Plus (16q+)

Duplication of some or all of the long (q) arm of chromosome 16 may produce the following symptoms:

  • poor growth
  • mental impairment
  • asymmetrical head
  • high forehead with short prominent or beaked nose and thin upper lip
  • Joint anomalies
  • genitourinary anomalies.

Other Disorders

There are many other combinations of deletions or duplications of parts of chromosome 16. More research needs to be done on all of the disorders of chromosome 16 to better understand their full implications for the individuals affected by them.

Sources:
Disorders of Chromosome 16 Foundation. A brief (and basic) overview of chromosome 16 disorders.
University of British Columbia. (2002). Trisomy 16 mosaicism. http://www.medgen.ubc.ca/wrobinson/mosiac/trisomy16.htm.
Watson, M. Chromosome 16. Specialty Laboratories  http://obstetrics.specialtylabs.com/books/display.asp?id=1183.

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