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Inversion

A chromosomal rearrangement in which a segment of the chromosome breaks away from the chromosome and re-inserts into the chromosome 180 degrees relative to its previous orientation.
  Pericentric inversion

An inversion in which the breakpoints occur on both arms of a chromosome. The inverted segment includes the centromere
(
the constricted portion of the chromosome).

Inversion of chromosome 3 or 8 has been associated with an increased risk for abnormal offspring . Pericentric inversion of chromosome 9 appears to be a normal variant in humans, and occurs in approximately one percent of the population. Inversion of chromosome  9 does not appear to be associated with an increased risk of miscarriage or abnormal offspring.

46,X,inv (Y)(p11.2q11.2)
Pericentric inversion of the y chromosome is usually a familial variant of no known clinical significance occurring in 1 in 1000 males. A chromosome analysis of the father's blood may be performed  to determine if this Y chromosome is inherited ( 5 mL in a green top sodium heparin tube).

REFERENCES
Milunsky JM In Milunsky, A ed , Genetic Disorders of the Fetus, 5th edition Baltimore: The Johns Hopkins University Press 2004. P 322

 

  Paracentric inversion

An inversion in which the breakpoints occur on one arm of a chromosome. The inverted segment does NOT include the centromere
(
the constricted portion of the chromosome).
Because paracentric inversions do not change the arm ratio of the chromosome they are difficult to detect on routine chromosome analysis.

The risk of abnormal children for persons who have a paracentric inversion on one chromosome is low but increases with the finding of recurrent abortions or abnormal children or both in other carriers in the family.

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