Chromosomal Syndromes and Genetic Disease


The normal human chromosome complement consists of 46 chromosomes comprising 22 morphologically different pairs of autosomes and one pair of sex chromosomes. Variation in either chromosome number or structure frequently results in significant mental and/or clinical abnormalities. Chromosomal syndromes are associated with specific chromosomal abnormalities.

Keywords: chromosome abnormalities; chromosomal syndromes; maternal age effects; recurrence risks

Figure 1.

47,XX,+21 female Down syndrome karyotype demonstrating trisomy 21. (Karyotype prepared by Dave McDonald.)

Figure 2.

45,X Turner syndrome karyotype demonstrating monosomy X. (Karyotype prepared by Dave McDonald.)

Figure 3.

Chromosome structural rearrangements, described in the text. (a) Chromosome arm and numerical banding designations according to ISCN (1995). (b) Terminal deletion and (c) interstitial deletion, each with loss of acentric fragment. (d) Pericentric inversion and (e) paracentric inversion, each with rotation of segment between breaks. (f) Direct duplication and (g) inverted duplication. (h) Isochromosome generation for short and long arms. (i) Ring chromosome with two acentric fragments. (j) Insertion of segment from one chromosome into a nonhomologous chromosome. (k) Reciprocal translocation with exchange of segments between nonhomologous chromosomes. (l) Robertsonian translocation between two acrocentric chromosomes. (Illustration prepared by Dave McDonald.)


Further Reading

de Grouchy J and Turleau C (1984) Clinical Atlas of Human Chromosomes, 2nd edn. New York: Wiley.

Gelehrter TD, Collins FS and Ginsburg D (1998) Principles of Medical Genetics, 2nd edn. Baltimore, MD: Williams and Wilkins.

Harper PS (1988) Practical Genetic Counseling, 3rd edn. Boston, MA: Wright.

Hassold TJ (1986) Chromosome abnormalities in human reproductive wastage. Trends in Genetics 2: 105–110.

Mitelman F (ed.) (1995) An International System for Human Cytogenetic Nomenclature recommendations of the International Standing Committee on Human Cytogenetic Nomenclature, Memphis, Tennessee, USA, October 9–13, 1994 Basel, Switzerland: Karger.

Nora JJ, Clarke Fraser F, Bear J, Greenberg CR, Patterson D and Warburton D (1993) Medical Genetics: Principles and Practices, 4th edn. Philadelphia: Lea and Febiger.

Schreinemachers DM, Cross PK and Hook EB (1982) Rates of trisomies 21,18,13 and other chromosome abnormalities in about 20 000 prenatal studies compared with estimated rate in live births. Human Genetics 61: 318–324.

Therman E and Sulsman M (1992) Human Chromosomes: Structure, Behavior and Function, 3rd edn. New York: Springer.

Thompson MW, McInnis RR and Willard HF (1991) Genetics in Medicine, 5th edn. Philadelphia: WB Saunders.

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Luthardt, Frederick W, and Keitges, Elisabeth(Apr 2001) Chromosomal Syndromes and Genetic Disease. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1038/npg.els.0001446]