Functional mosaic trisomy of 1q12-->1q21 resulting from X-autosome insertion translocation with random inactivation.

Cytogenetic studies of a 16-year-old female with behaviour and learning problems revealed that one X chromosome had additional material inserted at Xq21. Fluorescence in situ hybridization (FISH) analysis showed that the inserted segment contained heterochromatin and adjacent euchromatin of chromosome 1 origin. The karyotype of this patient was established as: 46,X,der(X)ins(X;?)(q21;?).ish der(X) ins(X;1)(q21;q12q21)(wcp1+). Chromosome replication studies demonstrated a random pattern of X inactivation, suggesting that the inserted material may be too 'small' to skew lyonization. The consequences of this abnormal X chromosome in relation to the clinical phenotype are discussed.