Mosaic trisomy 8
Alternate names[edit | edit source]
Mosaic trisomy chromosome 8; Trisomy 8 mosaicism
Definition[edit | edit source]
Mosaic trisomy 8 is a chromosomal abnormality that can affect many parts of the body. In individuals with mosaic trisomy 8, some of the body's cells have three copies of chromosome 8 (trisomy), while other cells have the usual two copies of this chromosome.
Epidemiology[edit | edit source]
- Mosaic trisomy 8 is a rare condition which affects only 1 in every 25,000 to 50,000 liveborn babies.
- It affects males more often than females.
- More than 120 people with this condition have been reported in the medical literature.
Cause[edit | edit source]
- Most cases of mosaic trisomy 8 occur due to a random event during the formation of the reproductive cells (egg and sperm) or after fertilization has taken place.
- An error in cell division (called nondisjunction) may cause some eggs or sperm to have an abnormal number of chromosomes.
- If an egg or sperm with an extra chromosome 8 contributes to the genetic makeup of an embryo, the embryo will have an extra copy of chromosome 8 in each cell.
- As the embryo grows and divides, an attempt may be made to correct the mistake by eliminating one extra chromosome 8.
- In individuals with mosaic trisomy 8, this attempt may be partly successful, leaving some cells with an extra chromosome 8 and some cells with the extra chromosome deleted (the usual chromosome number).
- This correction process is called trisomy rescue.
- In other cases, the egg and sperm may have a normal number of chromosomes, but an error of cell division (nondisjunction) occurs when the fertilized egg is growing and dividing.
- If an error occurs during one of the divisions, it can cause some cells to have an abnormal number of chromosomes.
- In people affected by mosaic trisomy 8, some of the body's cells have the usual two copies of chromosome 8, and other cells have three copies of this chromosome (trisomy).
- The percentage of cells with trisomy 8 and which parts of the body are affected vary from person to person. This leads to variability in the range and severity of symptoms.
Inheritance[edit | edit source]
Most cases are not inherited; it often occurs sporadically as a random event during the formation of the reproductive cells (egg and sperm).
Signs and symptoms[edit | edit source]
The signs and symptoms of mosaic trisomy 8 vary but may include:
- Characteristic facial features such as elongation of the skull (scaphocephaly), prominent forehead, widely-spaced eyes, deeply set eyes, broad upturned nose, and micrognathia
- Brain malformations such as agenesis of the corpus callosum
- Highly arched or cleft palate
- Shortened neck with extra skin folds
- Long slim body with a narrow chest, shoulders, and pelvis
- Kidney and cardiac abnormalities
- Camptodactyly and stiff joints
- Absent malformed kneecap
- Vertebral malformations such as scoliosis
- Eye abnormalities
- Most individuals with mosaic trisomy 8 have moderate intellectual disabilities (IQ between 50 and 75), with some people having a normal intelligence. There is no known connection between the percentage of trisomic cells and the severity of the intellectual disability.
- Mosaic trisomy 8 also may increase the risk for infections, and seems to increase the risk for certain cancers such as Wilms tumor, myelodysplasia, and acute myeloid leukemia.
Clinical presentation[edit | edit source]
For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed.
80%-99% of people have these symptoms
- Intellectual disability, moderate(IQ between 34 and 49)
30%-79% of people have these symptoms
- Abnormality of the antihelix
- Abnormality of the ribs(Rib abnormalities)
- Broad nasal tip(Broad tip of nose)
- Camptodactyly of finger(Permanent flexion of the finger)
- Corneal opacity
- Deep palmar crease(Deep palm line)
- Deep plantar creases(Deep wrinkles in soles of feet)
- Deeply set eye(Deep set eye)
- Dolichocephaly(Long, narrow head)
- Frontal bossing
- Hydronephrosis
- Hypertelorism(Wide-set eyes)
- Limitation of joint mobility(Decreased joint mobility)
- Long face(Elongation of face)
- Macrotia(Large ears)
- Micrognathia(Little lower jaw)
- Narrow chest(Low chest circumference)
- Narrow pelvis bone
- Patellar aplasia(Absent kneecap)
- Protruding ear(Prominent ear)
- Scoliosis
- Strabismus(Cross-eyed)
- Vertebral segmentation defect
- Vesicoureteral reflux
- Wide nose(Broad nose)
5%-29% of people have these symptoms
- Abnormality of cardiovascular system morphology
- Agenesis of corpus callosum
- Arthrogryposis multiplex congenita
- Cleft palate(Cleft roof of mouth)
- Clinodactyly of the 5th finger(Permanent curving of the pinkie finger)
- Cryptorchidism(Undescended testes)
- Decreased testicular size(Small testes)
- Hearing impairment(Deafness)
- High palate(Elevated palate)
- Hypopigmented skin patches(Patchy loss of skin color)
- Short neck(Decreased length of neck)
- Short stature(Decreased body height)
- Tall stature(Increased body height)
Diagnosis[edit | edit source]
Diagnosis is based on analysis of chromosomes via genetic testing, such as karyotype.
Treatment[edit | edit source]
- Because mosaic trisomy 8 affects many different areas of the body, medical management often involves a team of doctors and other healthcare professionals. Treatment for mosaic trisomy 8 varies depending on the signs and symptoms present in each individual.
- For example, for individuals with delays in motor skills such as walking, physical therapy or occupational therapy may be helpful.
- Early intervention and special education may be recommended depending on the degree of intellectual disability.
- If present, cleft palate, cardiac malformations, and kidney malformations may need to be surgically repaired.
- Other surgeries and interventions may be needed depending on the nature and severity of the other features and their symptoms.
NIH genetic and rare disease info[edit source]
Mosaic trisomy 8 is a rare disease.
Mosaic trisomy 8 Resources | ||
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