Three cases with enlarged acrocentric p-arms and two cases with cryptic partial trisomies.

In three cases, banding analysis revealed a normal karyotype except for an enlarged short arm of one chromosome 13 or 15. To clarify whether this enlargement was due to a heteromorphism or to a cryptic chromosomal trisomy, so-called cenM-FISH probe sets containing a microdissection-derived probe specific for the acrocentric human p-arms were applied. The results enabled us to confirm in one case and to exclude in two cases that the enlargement on the suspect chromosome was due to a p-arm polymorphism. M-FISH and/or microdissection were used to resolve the nature of the rearrangements, i.e., partial trisomies 6 and 19.