Posted October 30, 2008on:
Duplications and deletions may occur
Chromosome 16 normally occurs in cells as a pair of chromosomes, one inherited from each parent. But when it comes to chromosomes, as the old saw says, anything that can go wrong, will. Pieces of the chromosome can mistakenly be duplicated, or may break off and get lost, or there can be too many copies of the entire chromosome. Below are some of the disorders of chromosome 16.
Instead of the normal pair, there are three copies of chromosome 16. Trisomy 16 is estimated to occur in more than 1% 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:
- poor growth of the fetus during pregnancy
- congenital heart defects, such as ventricular septal defect (16% of individuals) or atrial septal defect (10% of individuals)
- unusual facial features
- underdeveloped lungs or respiratory tract problems
- 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
- asymetrical head
- high forehead with short prominent or beaked nose and thin upper lip
- Joint anomalies
- genitourinary anomalies.
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.
Information for this article was taken from:
– Disorders of Chromosome 16 Foundation. A brief (and basic) overview of chromosome 16 disorders.
– University of British Columbia. (2002). Trisomy 16 mosaicism. Accessed at http://www.medgen.ubc.ca/wrobinson/mosiac/trisomy16.htm.
– Watson, M. Chromosome 16. Specialty Laboratories, accessed at http://obstetrics.specialtylabs.com/books/display.asp?id=1183.