Trisomy 8
Encyclopedia
Trisomy 8 is a human chromosomal disorder
caused by having three copies (trisomy
) of chromosome
8
. It can appear with or without mosaicism.
. Complete trisomy 8 is usually an early lethal condition, whereas trisomy 8 mosaicism
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 retarded psychomotor development, moderate to severe mental retardation, 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.
.
Genetic disorder
A genetic disorder is an illness caused by abnormalities in genes or chromosomes, especially a condition that is present from before birth. Most genetic disorders are quite rare and affect one person in every several thousands or millions....
caused by having three copies (trisomy
Trisomy
A trisomy is a type of polysomy in which there are three copies, instead of the normal two, of a particular chromosome. A trisomy is a type of aneuploidy .-Description and causes:...
) of chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
8
Chromosome 8 (human)
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 and represents between 4.5 and 5.0% of the total DNA in cells....
. It can appear with or without mosaicism.
Characteristics
Complete trisomy 8 causes severe effects on the developing fetus and can be a cause of miscarriageMiscarriage
Miscarriage or spontaneous abortion is the spontaneous end of a pregnancy at a stage where the embryo or fetus is incapable of surviving independently, generally defined in humans at prior to 20 weeks of gestation...
. Complete trisomy 8 is usually an early lethal condition, whereas trisomy 8 mosaicism
Mosaic (genetics)
In genetic medicine, a mosaic or mosaicism denotes the presence of two populations of cells with different genotypes in one individual who has developed from a single fertilized egg...
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 retarded psychomotor development, moderate to severe mental retardation, 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.
Synonym
Trisomy 8 with or without mosaicism is occasionally referred to by the eponym Warkany syndrome or Warkany syndrome 2Warkany syndrome
Two distinct congenital syndromes were named after Joseph Warkany, an Austrian-American geneticist and pediatrician, 1902-1992.- Warkany syndrome 1 :...
.
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 syndromeRothmund-Thomson syndromeRothmund–Thomson syndrome , also known as poikiloderma atrophicans with cataract or poikiloderma congenitale, is a rare autosomal recessive skin condition originally described by August von Rothmund in 1868. Matthew Sydney Thomson published further descriptions in 1936.There have been several...
, a genetic disorder associated with the DNA helicase RECQL4RECQL4ATP-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. There are two types of Rothmund Thomson syndrome and it is Type 2 that is caused by patients carrying...
on chromosome 8q24.3. The syndrome is "characterized by skin atrophy, telangiectasiaTelangiectasiaTelangiectasias /tɛ.læn.dʒiː'ɛk.teɪ.ʃi:ə/ are small dilated blood vessels near the surface of the skin or mucous membranes, measuring between 0.5 and 1 millimeter in diameter. They can develop anywhere on the body but are commonly seen on the face around the nose, cheeks, and chin...
, hyper-HyperpigmentationIn dermatology, hyperpigmentation is the darkening of an area of skin or nails caused by increased melanin.-Causes:Hyperpigmentation may be caused by sun damage, inflammation, or other skin injuries, including those related to acne vulgaris...
and hypopigmentationHypopigmentationHypopigmentation is the loss of skin color. It is caused by melanocyte or melanin depletion, or a decrease in the amino acid tyrosine, which is used by melanocytes to make melanin.-Treatments:...
, congenital skeletal abnormalities, short stature, premature aging, and increased risk of malignant disease".
- 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 (San Luis Valley syndrome), causing anomalies associated with tetralogy of FallotTetralogy of FallotTetralogy of Fallot is a congenital heart defect which is classically understood to involve four anatomical abnormalities...
, 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 geneFusion geneA fusion gene is a hybrid gene formed from two previously separate genes. It can occur as the result of a translocation, interstitial deletion, or chromosomal inversion...
.