IDENTIFICATION OF PARTIAL TRISOMY 13 SYNDROME BY DNA REPLICATION STUDIES

Abstract

The Giemsa stainability of chromosomal regions containing late replicating DNA can be suppressed or enhanced by incorporation of BUdR into the DNA at the end or beginning of the S period. A terminal pulse of BUdR reveals a uniquely informative pattern of chromosomal bands coupled with specific decondensation of late replicating regions. These techniques provide new information for the clinician and cytogeneticist in precise identification of heretofore undecipherable “de novo” structural chromosomal rearrangements with partial aneuploidy. Our patient was a one month old male with multiple congenital anomalies including postaxial polydactyly, heart defect and renal anomaly. Conventional chromosomal analysis revealed a 46, XY, Dq+ karyotype, while Trypsin G-banding suggested an inverted duplication of the distal long arm of chromosome 13 (i.e. 46, XY, inv dup (13q) (ql4→q34). Chromosomes of both parents are normal. Bands q21 and q31 of chromosome 13 are late replicating and would be included in the presumed duplication. Employing a modified “33258 Hoechst” Giemsa procedure, and chromosomes prepared for enhancement and suppression of stainability of late replicating regions, we observed the predicted four bands of late replication on the abnormal D group chromosome, thus allowing confirmation of the diagnosis of partial Trisomy 13 Syndrome.