Chromosome 16 Disorders and Health

There are many genetic conditions related to problems with the genes on chromosome 16. It contains thousands of genes that guide protein production, which is needed for a variety of functions in the body.

Changes in the structure or number of copies of a chromosome can cause problems with health and development. For example, having an extra copy of the gene is called trisomy 16. The most common health effect of trisomy 16 is miscarriage.

Basics of Chromosomes

Chromosomes are the structures that hold your 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, in rare instances chromosomes can be missing or duplicated, resulting in missing or extra genes. These aberrations can cause problems in health and development.

The following chromosomal conditions are associated with abnormalities of chromosome 16. These can include an extra copy of chromosome 16, deletions (a section of the chromosome is missing) or duplications (extra portions of the chromosome are present).

Trisomy 16

In trisomy 16, instead of the normal pair, there are three copies of chromosome 16. Trisomy 16 is incompatible with life, and most pregnancies do not progress beyond the first trimester.

Trisomy 16 is estimated to occur in more than 1% of pregnancies, making it the most common trisomy in humans. It is also the second most common chromosomal cause of miscarriage, closely following X-chromosome monosomy (only one copy of the X or Y sex genes).

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.

Trisomy 16 mosaicism is compatible with life. Children born with this condition will develop many deformities as a result of the extra genetic material.

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
• Hypospadias (urethral opening too low) in 7.6% of boys

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

16p13.3 deletion syndrome (16p-)

In this disorder, part of the short (p) arm of chromosome 16 is missing. Deletion of 16p13.3 has been reported among individuals with tuberous sclerosis, Rubnstein-Taybi syndrome, and alpha-thalassemia.

16p11.2 duplication (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 the 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.

16p11.2 Deletion Syndrome

This is the deletion of a segment of the short arm of the chromosome of about 25 genes, affecting one copy of chromosome 16 in each cell. Individuals born with this syndrome often have delayed development, intellectual disability, and autism spectrum disorder.

However, some have no symptoms. They can pass this disorder to their children, who can have more severe effects.

16p11.2 Duplication

This is a duplication of the same 11.2 segment and may have similar symptoms as the deletion. However, more individuals with duplication have no symptoms.

As with the deletion syndrome, they can pass the abnormal chromosome to their children who may show more severe effects.

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.