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Structural disorders

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Structural abnormalities are a consequence of chromosomal breakage. Once broken, there is the possibility that repair may join two unrelated sections of chromosome. The spontaneous mutation rate is 1 per 1000 gametes. Breakage is facilitated by ionizing radiation, mutatogenic chemicals and some rare inherited conditions.

A number of types of structural aberration are recognized:

  • translocation - the transfer of chromosomal material between chromosomes. Three subtypes are recognized according to which region of the chromosomes swap. Often, the carrier with a 'balanced translocation' is not affected, but offspring are affected.

  • deletion - where this occurs at both ends of a chromosome, a ring chromosome can result.

  • duplication - the presence of two copies of a segment of chromosome, often with little harmful consequences.

  • inversion - breakage at two ends of a chromosome with a rotation and rejoining of the part inbetween so that it lies the wrong way around. There is an increased risk of chromosomally imbalanced offspring. Carriers may appear normal.

  • isochrome - a chromosome which has deletion of one arm and duplication of the other.

  • centric fragments - small, remaining material left after translocations.

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The content herein is provided for informational purposes and does not replace the need to apply professional clinical judgement when diagnosing or treating any medical condition. A licensed medical practitioner should be consulted for diagnosis and treatment of any and all medical conditions.

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