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Trisomy 9 is a rare chromosomal disorder in which the entire 9th
chromosome appears three times (trisomy) rather than twice in some
cells of the body.
Other variations include:
- Trisomy 9 Mosaic (some cells have duplication and some don't)
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Trisomy 9p (the p-arm only is duplicated)
-
Tetrasomy 9p (the p-arm of the 9th chromosome appears 4 times rather than twice)
- Trisomy 9q (the q-arm only is duplicated)
- Monosomy 9 (the complete 9th chromosome only appears once rather than twice)
General information
Chromosome 9, Trisomy Mosaic, also
known as Trisomy 9 Mosaicism syndrome, is a rare chromosomal disorder
in which the entire 9th chromosome appears three times (trisomy) rather
than twice in some cells of the body. The term "mosaic" indicates that
some cells contain the extra chromosome 9, while others have the normal
chromosomal pair.
Associated symptoms and findings may vary greatly in range and
severity, depending on the percentage of cells with the extra
chromosome. However, common features include growth deficiency before
birth (intrauterine growth retardation); mental retardation; structural
malformations of the heart that are present at birth (congenital heart
defects); and/or distinctive abnormalities of the skull and facial
(craniofacial) region, such as a sloping forehead, a bulbous nose,
short eyelid folds (palpebral fissures), deeply set eyes, and/or
low-set, malformed ears. The syndrome may also be characterized by
musculoskeletal, genital, kidney (renal), and/or additional physical
abnormalities. Chromosome 9, Trisomy Mosaic may be caused by errors
during the division of a parent's reproductive cells (meiosis) or
during the division of body tissue cells (somatic cells) early in the
development of the embryo (mitosis).
Chromosome 9, Trisomy 9p is a rare chromosomal syndrome in
which a portion of the 9th chromosome appears three times (trisomy)
rather than twice in cells of the body. The trisomy may involve a
portion of the short arm (9p), the entire short arm, or the short arm
and a portion of the long arm (9q) of chromosome 9. (Each chromosome
contains a short arm known as "p" and a long arm designated as "q.")
Evidence suggests that, in many cases, associated symptoms and findings
may be relatively similar among affected infants despite differing
lengths of the trisomic (duplicated) segment of 9p. However, in those
with larger trisomies (e.g., extending to middle or end [distal]
regions of 9q), additional features may also be present that appear to
correlate with the extent of the duplication.
Virtually all individuals with Trisomy 9p are affected by mental
retardation and distinctive malformations of the skull and facial
(craniofacial) region. In some instances, additional physical
abnormalities may also be present, such as other skeletal defects,
structural malformations of the heart that are present at birth
(congenital heart defects), and/or other findings. In some cases, the
trisomy appears to result from a balanced chromosomal rearrangement in
one of the parents; in others, it is thought to arise from spontaneous
(de novo) errors very early in embryonic development that occur for
unknown reasons (sporadically).
Chromosome 9, Tetrasomy 9p is a very rare chromosomal disorder
in which the short arm of the ninth chromosome (9p) appears four times
(tetrasomy) rather than twice in all or some cells of the body.
Individuals with a normal chromosomal make-up (karyotype) have two 9th
chromosomes, both of which have a short arm ("9p") and a long arm
("9q"). However, in individuals with Chromosome 9, Tetrasomy 9p, four
short arms (9ps) are present in cells rather than the normal two.
The symptoms of Chromosome 9, Tetrasomy 9p may vary greatly in range
and severity from case to case. Associated abnormalities may include
mild growth retardation, moderate to severe delay in the attainment of
skills requiring the coordination of muscular and mental activities
(psychomotor retardation), and/or moderate to severe mental
retardation. In addition, the disorder may be characterized by various
physical abnormalities, such as malformations of the skull and facial
(craniofacial) region, abnormalities of the hands and fingers, skeletal
malformations, and/or heart (cardiac) defects. Chromosome 9, Tetrasomy
9p appears to result from spontaneous (de novo) errors very early in
embryonic development that occur for unknown reasons (sporadically).
National Organization of Rare Diseases
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Last Updated ( Saturday, 13 November 2004 )
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Trisomy 9 Info 
