X-autosome translocation in normal mother and effectively 21-monosomic daughter

Abstract

A phenotypically normal mother carries a balanced X-21 translocation. Autoradiography of the mother's cells reveals that in all cells the normal X is late replicating. Her only pregnancy produced like-sex twins, one of whom is phenotypically and karyotypically normal. The co-twin is mentally retarded and has multiple anomalies. Her karyotype is 46,XX,der(21),t(X;21)(q11;p11?)mat. In the majority of informative cells from the daughter, one normal X and the entire X t replicate late. This maintains X dosage compensation, but results in effective monosomy 21. The phenotype of the infant is similar to others with 21q−.