Trisomy 8 causes Warkany syndrome 2, a human
chromosomal disorder caused by having three copies (
trisomy
A trisomy is a type of polysomy in which there are three instances of a particular chromosome, instead of the normal two. A trisomy is a type of aneuploidy (an abnormal number of chromosomes).
Description and causes
Most organisms that reprodu ...
) of
chromosome 8
Chromosome 8 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 8 spans about 145 million base pairs (the building material of DNA) and represents between 4.5 and 5.0% of the total DNA ...
. It can appear with or without
mosaicism
Mosaicism or genetic mosaicism is a condition in multicellular organisms in which a single organism possesses more than one genetic line as the result of genetic mutation. This means that various genetic lines resulted from a single fertilized ...
.
Characteristics
Complete trisomy 8 causes severe effects on the developing fetus and can be a cause of
miscarriage
Miscarriage, also known in medical terms as a spontaneous abortion and pregnancy loss, is the death of an embryo or fetus before it is able to survive independently. Miscarriage before 6 weeks of gestation is defined by ESHRE as biochemical lo ...
.
Complete trisomy 8 is usually an early lethal condition, whereas trisomy 8
mosaicism
Mosaicism or genetic mosaicism is a condition in multicellular organisms in which a single organism possesses more than one genetic line as the result of genetic mutation. This means that various genetic lines resulted from a single fertilized ...
is less severe and individuals with a low proportion of affected cells may exhibit a comparatively mild range of physical abnormalities and developmental delay. Individuals with trisomy 8 mosaicism are more likely to survive into childhood and adulthood, and exhibit a characteristic and recognizable pattern of developmental abnormalities. Common findings include stunted psychomotor development, moderate to severe intellectual disability, variable growth patterns which can result in either abnormally short or tall stature, an expressionless face, and many musculoskeletal, visceral, and eye abnormalities, as well as other
anomalies. A deep plantar furrow is considered to be pathognomonic of this condition, especially when seen in combination with other associated features. The type and severity of symptoms are dependent upon the location and proportion of trisomy 8 cells compared to normal cells.
Other conditions
Trisomy 8 mosaicism affects wide areas of chromosome 8 containing many genes, and can thus be associated with a range of symptoms.
* Mosaic trisomy 8 has been reported in rare cases of
Rothmund–Thomson syndrome
Rothmund–Thomson syndrome (RTS) is a rare autosomal recessive skin condition.
There have been several reported cases associated with osteosarcoma. A hereditary basis, mutations in the DNA helicase ''RECQL4'' gene, causing problems during initi ...
, a genetic disorder associated with the
DNA helicase
Helicases are a class of enzymes thought to be vital to all organisms. Their main function is to unpack an organism's genetic material. Helicases are motor proteins that move directionally along a nucleic acid phosphodiester backbone, separatin ...
RECQL4
ATP-dependent DNA helicase Q4 is an enzyme that in humans is encoded by the ''RECQL4'' gene.
Mutations in ''RECQL4'' are associated with the autosomal recessive disease Rothmund–Thomson syndrome, a disorder that has features of premature aging. ...
on chromosome 8q24.3. The syndrome is "characterized by
skin atrophy,
telangiectasia
Telangiectasias, also known as spider veins, are small dilated blood vessels that can occur near the surface of the skin or mucous membranes, measuring between 0.5 and 1 millimeter in diameter. These dilated blood vessels can develop anywhere on ...
,
hyper- and
hypopigmentation
Hypopigmentation is characterized specifically as an area of skin becoming lighter than the baseline skin color, but not completely devoid of pigment. This is not to be confused with depigmentation, which is characterized as the absence of all pi ...
,
congenital skeletal abnormalities, short
stature,
premature aging
Progeroid syndromes (PS) are a group of rare genetic disorders that mimic physiological aging, making affected individuals appear to be older than they are. The term ''progeroid syndrome'' does not necessarily imply progeria (Hutchinson–Gilford ...
, and increased risk of
malignant disease
Malignancy () is the tendency of a medical condition to become progressively worse.
Malignancy is most familiar as a characterization of cancer. A ''malignant'' tumor contrasts with a non-cancerous ''benign'' tumor in that a malignancy is not s ...
".
* Some individuals trisomic for chromosome 8 were deficient in production of
coagulation factor VII due to a factor 7 regulation gene (F7R) mapped to 8p23.3-p23.1.
* Trisomy and other rearrangements of chromosome 8 have also been found in
tricho–rhino–phalangeal syndrome.
* Small regions of chromosome 8 trisomy and monosomy are also created by
recombinant chromosome 8 syndrome Recombinant may refer to:
* Recombinant organism – an organism that contains a different combination of alleles from either of its parents.
* Recombinant DNA – a form of artificial DNA sequence
* Recombinant protein - artificially produced (and ...
(
San Luis Valley syndrome), causing anomalies associated with
tetralogy of Fallot
Tetralogy of Fallot (TOF), formerly known as Steno-Fallot tetralogy, is a congenital heart defect characterized by four specific cardiac defects. Classically, the four defects are:
*pulmonary stenosis, which is narrowing of the exit from the ri ...
, which results from recombination between a typical chromosome 8 and one carrying a parental
paracentric inversion.
* Trisomy is also found in some cases of
chronic myeloid leukaemia, potentially as a result of karyotypic instability caused by the
bcr:abl fusion gene A fusion gene is a hybrid gene formed from two previously independent genes. It can occur as a result of translocation, interstitial deletion, or chromosomal inversion. Fusion genes have been found to be prevalent in all main types of human neopla ...
.
Diagnosis
The simplest and easiest way to detect trisomy 8 is by a
karyotype
A karyotype is the general appearance of the complete set of metaphase chromosomes in the cells of a species or in an individual organism, mainly including their sizes, numbers, and shapes. Karyotyping is the process by which a karyotype is disce ...
, a photograph representing all chromosomes of a cell in an orderly manner.
Amniocentesis
Amniocentesis is a medical procedure used primarily in the prenatal diagnosis of genetic conditions. It has other uses such as in the assessment of infection and fetal lung maturity. Prenatal diagnostic testing, which includes amniocentesis, is ne ...
is also a technique for diagnosis. Samples from the amniotic fluid are taken from a fetus, cultured, then analyzed by a karyotype. If the photograph shows 3 copies of chromosome 8 instead of 2, then the individual has trisomy 8.
See also
*
Warkany syndrome 1
References
External links
U.S. National Library of Medicine: Warkany Syndrome 2{{Chromosomal abnormalities
Autosomal trisomies
Syndromes