Medical term:

trisomy

[tri´so-me]

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.

tri·so·my

(trī'sō-mē),

The state of an individual or cell with an extra chromosome instead of the normal pair of homologous chromosomes; in humans, the state of a cell containing 47 normal chromosomes. For various types of trisomy syndrome, see entries under syndrome.

[tri- + (chromo)some]

Farlex Partner Medical Dictionary © Farlex 2012

trisomy

(trī-sō′mē, trī′sō′-)

n. pl. triso·mies

The condition of having three copies of a given chromosome in each somatic cell rather than the normal number of two.

tri′some′ n.

tri·so′mic adj.

tri·so·my

(trī'sō-mē)

The state of an individual or cell with an extra chromosome instead of the normal pair of homologous chromosomes; in humans, the state of a cell containing 47 normal chromosomes.

[tri- + (chromo)some]

Medical Dictionary for the Health Professions and Nursing © Farlex 2012

trisomy

The occurrence of an extra chromosome in one of the 23 matched and identifiable pairs so that there are three, instead of two, of a particular chromosome. This anomaly may cause a wide range of structural abnormalities or even early death of the fetus. Trisomy of chromosome 21 (trisomy 21) is the cause of DOWN'S SYNDROME.

Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005

trisomy

a state in which a DIPLOID (2) organism has three chromosomes of one type in a cell or in all cells. For example, DOWN'S SYNDROME individuals are trisomic for chromosome number 21, but have two of every other type of chromosome. See also EDWARDS’ SYNDROME and PATAU'S SYNDROME.

Trisomy

An abnormality in chromosomal development. Chromosomes are the structures within a cell that carry its genetic information. They are organized in pairs. Humans have 23 pairs of chromosomes. In a trisomy syndrome, an extra chromosome is present so that the individual has three of a particular chromosome instead of the normal pair. An extra chromosome 18 (trisomy 18) causes mental retardation.

Mentioned in: Down Syndrome, Edwards' Syndrome, Mental Retardation, Patau Syndrome, Polydactyly and Syndactyly

chromosome

One of the thread-like structures located within the cell nucleus composed of an extremely long, double-stranded DNA (deoxyribonucleic acid) helix tightly folded around proteins called histones. Each chromosome carries genes that contain the hereditary material that controls the growth and characteristics of the body. There are 46 chromosomes in each human somatic cell organized in 23 pairs, of which 22 pairs are similar in appearance but differ at the molecular level. They are called autosomal chromosomes or autosomes and are designated by a number (with chromosome 1 being the longest, followed by chromosome 2, etc.). The other pair, the sex chromosomes determines the sex of the individual. In mammals the two sex chromosomes of females are alike (homologous) and are referred to as X chromosomes. Males carry one X chromosome along with a much shorter chromosome, the Y chromosome. Each chromosome has a centromere that divides it into two arms, the short arm 'p' and the long arm 'q'. Disorders of chromosome number in which the number of chromosomes is above or below the normal (46) are called aneuploidy. Common forms of aneuploidy are trisomy in which there is one extra chromosome and monosomy in which there is one less, than the normal 46. They rarely cause specific eye diseases but affected individuals present ocular manifestations. Examples: Down's syndrome (trisomy of chromosome 21), Edwards' syndrome (trisomy 18), Turner's syndrome (monosomy 45 XO). There are other chromosome abnormalities such as translocation (one segment of a chromosome is transferred to another chromosome) as may occur in congenital anterior polar cataract, deletion (a loss of a piece of chromosome) as in aniridia, choroideremia, retinoblastoma, etc. Other cases involve damage of a chromosome (e.g. fragile X syndrome). See defective colour vision; gene; mitosis; mutation.

tri·so·my

(trī'sō-mē)

State of an individual or cell with an extra chromosome instead of normal pair of homologous chromosomes; in humans, the state of a cell containing 47 normal chromosomes.

[tri- + (chromo)some]

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