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Editor—In recent years the increased resolution that can be obtained with GTL banded prometaphase chromosomes has led to the recognition of abnormalities involving small regions of the karyotype. Some of these abnormalities involve deletion or duplication of only one or two chromosomal bands and are associated with a sufficiently mild phenotype as to be directly inherited. Nevertheless, directly inherited duplication of visible chromosomal material is an uncommon category of chromosomal abnormality that has been reported for a small number of specific regions of the karyotype, including 2q11.2-q21.1,1 6p23-pter,26q22-q24,3 7p12-p13,4 8p23.1,59p22-p24,6 14q13-q22,7 15q12,8and 18p.9 Some of these duplications are without apparent phenotypic effect,5 8 while in other cases there are mild phenotypic abnormalities.1 2 Genomic imprinting has been shown to have an effect on the phenotypic expression of dup(15)(q12)8 and also dup(6)(q24),3 and is a point for consideration in other small duplications.
Tandem duplications occur when a second copy of a chromosomal region is inserted adjacent to the original region. They have been reported for a number of chromosomal segments,2 9 although not previously for band 10p14. Microduplication and microdeletion of chromosomal material is presumed to occur as a meiotic event following uneven crossing over between short sequences of highly similar DNA inserted at two close, but not contiguous sites along the chromosome.10 11 Tandem duplication is generally de novo with rare cases reported of direct inheritance.3-6 8 9To be balanced, an intrachromosomal duplication would have to be associated with chromosomal deletion of the specific region in the other homologue and to have occurred postzygotically. To our knowledge, this type of balanced chromosomal rearrangement has not been reported as a constitutional abnormality. We describe here a previously unreported small …