Two unbalanced segregation products due to a maternal t(7;16)inv(16)

We report a prenatal case of a maternally inherited abnormal chromosome 16, originally interpreted as a pericentric inversion only, but after family s tudies re-interpreted as a pericentric inversion (16) accompanied by an unb alanced (7;16) translocation. Because of the inversion 16 and an elder son with developmental delay and craniofacial dysmorphic features, in the past karyotyped as 46,XY, the chromosomes 16 of the mother and son were carefull y re-examined. Using a whole chromosome 16 paint and sub-telomere probes of 16p and 16q, the karyotype of the mother was shown to be 46,XXinv(16)(p11. 2q23.2).ish der(7:16)(q36 p13.3)inv(16). Subsequently one chromosome 16 of the elder son appeared to be a der(16)t(7:16)(q36,p13.3). This is probably the result of a meiotic crossover between the chromosomes 16 in the mother. The prenatal karyotype was finally interpreted as 46,XY,inv(16)(p11.2q23.2 ).ish der(16)t(7:16)(q36:p13.3)inv(16). This is the same cytogenetic imbala nce as his elder brother: a partial trisomy of chromosome 7 (q36 --> qter) and a partial monosomy of chromosome 16 (p13.3 --> pter). Copyright (C) 200 1 John Wiley & Sons, Ltd.