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Home > D. General pathology > Genetic and developmental anomalies > Chromosomal diseases > Microdeletion syndromes > chromosomal deletions

chromosomal deletions

Monday 29 September 2003

Definition: A deletion is a loss of a portion of a chromosome. Most deletions are interstitial, but terminal deletions may occur rarely.

Interstitial deletions occur when there are two breaks within a chromosome arm, followed by loss of the chromosomal material between the breaks, and fusion of the broken ends.

One can specify in which region(s) and at what bands the breaks have occurred. For example, 46,XY,del(16)(p11.2p13.1) describes breakpoints in the short arm of chromosome 16 at 16p11.2 and 16p13.1 with loss of material between breaks.

Terminal deletions result from a single break in a chromosome arm, producing a fragment with no centromere, which is then lost at the next cell division. The broken chromosome end is protected by acquiring telomeric sequences.

Deletions are notated del(chromosome number) as del(1p) or del(7)(q21q31).


- 17p13.3 deletion (Miller-Dieker syndrome)