chromosomal disorder


chromosomal disorder
Syndrome caused by chromosome abnormality.

Normally, humans have 23 pairs of chromosomes, including one pair of sex chromosomes. Any variation from this pattern causes abnormalities. A chromosome may be duplicated (trisomy) or absent (monosomy); one or more extra full sets of chromosomes can be present (see ploidy); or part of a chromosome may be missing (deletion) or transferred to another (translocation). Resulting disorders include Down's syndrome, mental retardation, heart malformation, abnormal sexual development, malignancies, and sex-chromosome disorders (e.g., Turner's syndrome, Klinefelter's syndrome). Chromosomal disorders occur in 0.5% of births; many can now be diagnosed before birth by amniocentesis.

* * *

      any syndrome characterized by malformations or malfunctions in any of the body's systems, and caused by abnormal chromosome number or constitution.

      Normally, humans have 46 chromosomes arranged in 23 pairs; the pairs vary in size and shape and are numbered by convention. Twenty-two of the pairs are autosomes, and one pair, number 23, is the sex chromosomes. Any variation from this pattern causes abnormalities. A chromosome from any of the pairs may be duplicated (trisomy) or absent (monosomy); an entire set of 23 chromosome pairs can be duplicated three (triploidy) or more ( polyploidy) times; or one arm or part of one arm of a single chromosome may be missing (deletion). Part of one chromosome may be transferred to another (translocation), which has no effect on the person in which it occurs but generally causes a deletion or duplication syndrome in his or her children. Changes in chromosome number occur during sperm or egg formation or in the early development of the embryo. In the latter case, a mixture of cells, some normal (euploid) and some containing abnormal chromosome complements, may occur, a condition known as mosaicism. In either case, abnormalities of development occur because of the unusual genetic signals transmitted by the chromosomes. Some one of these chromosome imbalances occurs in 0.5 percent of all births.

       Down syndrome (mongolism), trisomy of chromosome 21, was the first chromosomal disorder identified (in 1959); it is the most common trisomy and the most common cause of mental retardation (intellectual disability). Mental retardation is perhaps the most common manifestation of chromosomal abnormalities, occurring to some extent in all major autosomal abnormalities. Several chromosomal abnormalities, including Down syndrome, have also been related to heart disease (congenital heart disease) or malformations. Other evidence of chromosome abnormalities include abnormal sexual development, behavioral disturbances, malignancy (e.g., the Philadelphia chromosome in chronic myelocytic leukemia), and spontaneous abortion.

      Sex chromosome abnormalities are more common and tend to have less-drastic effects than autosomal abnormalities. Normal females have two X chromosomes and males have an X and a Y; abnormalities in sex chromosome distribution produce Turner's syndrome (XO), Klinefelter's syndrome (XXY), and the so-called “supermale” (XYY). Turner's and Klinefelter's individuals have female and male genitalia, respectively, with retarded development of sexual characteristics. Supermales tend to be taller than average and to have learning disabilities. In addition, some studies have revealed that the percentage of XYY individuals in institutions for the criminally insane exceeds the incidence of supermaleness in newborn male populations. However, many XYY are socially well adjusted, and the link between supermaleness and criminal behaviour is highly debatable.

      Several chromosomal disorders can now be diagnosed before birth by examining cells obtained from the amniotic fluid. See also Down syndrome; cri-du-chat syndrome; trisomy 13; trisomy 18; Turner's syndrome; X-trisomy; Klinefelter's syndrome; XYY-trisomy.

* * *


Universalium. 2010.

Look at other dictionaries:

  • disorder — /dis awr deuhr/, n. 1. lack of order or regular arrangement; confusion: Your room is in utter disorder. 2. an irregularity: a disorder in legal proceedings. 3. breach of order; disorderly conduct; public disturbance. 4. a disturbance in physical… …   Universalium

  • chromosomal aberration — noun any change in the normal structure or number of chromosomes; often results in physical or mental abnormalities • Syn: ↑chromosomal anomaly, ↑chrosomal abnormality, ↑chromosonal disorder • Hypernyms: ↑aberrance, ↑aberrancy, ↑aberration, ↑ …   Useful english dictionary

  • chromosomal anomaly — noun any change in the normal structure or number of chromosomes; often results in physical or mental abnormalities • Syn: ↑chromosomal aberration, ↑chrosomal abnormality, ↑chromosonal disorder • Hypernyms: ↑aberrance, ↑aberrancy, ↑aberration, ↑ …   Useful english dictionary

  • disorder of sexual development — (DSD) a congenital condition in which development of chromosomal, gonadal, or phenotypic sex is atypical …   Medical dictionary

  • childhood disease and disorder — Introduction       any illness, impairment, or abnormal condition that affects primarily infants and children i.e., those in the age span that begins with the fetus and extends through adolescence.       Childhood is a period typified by change,… …   Universalium

  • Congenital disorder — Classification and external resources MeSH D009358 …   Wikipedia

  • immune system disorder — Introduction        Disorders of the immune systemany of various failures in the body s defense mechanisms against infectious organisms (see table (Disorders of the immune system)). Disorders of immunity include immune deficiency diseases, such… …   Universalium

  • congenital disorder — Structural abnormality (e.g., atresia, agenesis), functional problem (e.g., cystic fibrosis, phenylketonuria), or disease present at birth. Almost all are due to genetic factors (inherited or spontaneous mutations, chromosomal disorders),… …   Universalium

  • Bipolar disorder — Manic depression redirects here. For other uses, see Manic depression (disambiguation). Bipolar disorder Classification and external resources ICD 10 F …   Wikipedia

  • Attention-deficit hyperactivity disorder controversies — Methylphenidate (Ritalin) 10mg Pill (Ciba/Novartis), a drug commonly prescribed to treat ADHD The causes, diagnosis, and the treatment of attention deficit hyperactivity disorder (ADHD) have been the subject of active debate at least since the… …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.