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the presence of an additional (third) chromosome of one type in an otherwise diploid cell (2n +1). adj., adj triso´mic.
trisomy 8 syndrome a syndrome associated with an extra chromosome 8, usually mosaic (trisomy 8/normal), characterized by mild to severe mental retardation, prominent forehead, deep-set eyes, thick lips, prominent ears, and camptodactyly (abnormally flexed fingers).
trisomy 13 syndrome holoprosencephaly due to an extra chromosome 13, in which central nervous system defects are associated with mental retardation, cleft lip and palate, polydactyly (extra fingers or toes), and dermal pattern anomalies, as well as abnormalities of the heart, viscera, and genitalia. Called also Patau's syndrome. Information for families affected by this disorder can be obtained from the Support Organization for Trisomy 18, 13, and Related Disorders (S.O.F.T.), 2982 S. Union St., Rochester, NY 14624.
trisomy 18 syndrome a condition due to the presence of an extra chromosome 18, characterized by neonatal hepatitis, mental retardation, scaphocephaly or other skull abnormality, small receding mandible, blepharoptosis (drooping eyelids), low-set ears, corneal opacities, deafness, webbed neck, short digits, ventricular septal defects, Meckel's diverticulum, and other deformities. Called also Edwards' syndrome. Information for families affected by this disorder and professionals caring for affected individuals can be obtained from the Support Organization for Trisomy 18, 13, and Related Disorders (S.O.F.T.), 2982 S. Union St., Rochester, NY 14624.
trisomy 21 syndrome Down syndrome.
trisomy 22 syndrome a syndrome due to an extra chromosome 22, characterized typically by mental and growth retardation, undersized head, low-set or malformed ears, small receding mandible, long philtrum on the upper lip, preauricular skin tag or sinus, and congenital heart disease. In males, there is a small penis or undescended testes.