Trisomy Disorders

Trisomy 9

Posted on: October 30, 2008

Syndrome chromosome 9 trisomy syndrome

Synonyms 9 trisomy trisomy 9 Summary Presence of an additional (third) chromosome in an otherwise diploid chromosome 9 with psychomotor retardation and multiple abnormalities of the craniofacial structures, heart, skeletal system, extremities, and other organs. Includes mosaic trisomy 9 syndrome.

Major Features

Head and neck: Microcephaly, prominent occiput micrognathia, wide cranial sutures and fontanels, craniosynostosis, facial cleft and cloverleaf skull.

Ears: Low-set malformed ears.

Eyes: Short and upslanting palpebral fissures, microphthalmia, coloboma, corneal clouding, hypertelorism, and deeply set eyes.

Nose: Bulbous tip.

Mouth and oral structures: Tongue abnormalities, ankyloglossia, cleft and protruding thin arched lip, and cleft or dysplastic palate.

Neck: Short and webbed.

Hand and foot: Dysplasia of hands and feet, rockerbottom feet, overlapping fingers, camptodactyly, abnormal hand positioning, and talipes. Dermatoglyphic changes include deep palmar and plantar creases.

Extremities: Hip dislocation, abnormally shaped long bones, limitation of joint movement, and short limbs.

Skin appendages: Hyperconvex nails.

Nervous system: Dandy-Walker cyst, subependymal cysts, and ventricular dilatation of the brain.

<FONTSIZE=4>Cardiovascular system: Ventricular septal defect, atrial septal defect, patent ductus arteriosus, valve defects, double outlet right ventricle, persistent left superior vena cava, and endocardial fibroelastosis.

Urogenital system: Hydronephrosis, duplication of collecting system, microcystic kidneys, dysplastic kidneys, cryptorchidism, small penis, hypospadias, and hypoplastic labia.

Temporal features: Most affected patients die during infancy or early childhood.

 Growth and development: Growth and mental retardation.

Behavior and performance: Failure to thrive.

Heredity: Trisomy 9 and trisomy 9 mosaicism have similar phenotype.

Trisomy 9




Trisomy 9 Home

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)
  • 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 heartthat 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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