DOWN-SYNDROME CONSEQUENT TO A CRYPTIC MATERNAL 12P-21Q-CHROMOSOME TRANSLOCATION

A 9-year-old, mildly mentally retarded girl presented with phenotypic manifestations of Down syndrome, G-banded chromosomal analyses of peri pheral blood lymphocytes from the patient and her parents, and skin fi broblasts from the patient, did not detect any abnormality, Molecular analysis of 15 highly polymorphic chromosome 21 dinucleotide repeat ma rkers demonstrated a partial duplication of the Down syndrome critical region (D21S55, subband 21q22.2) of maternal origin in the patient. T he segmental trisomy was confirmed by FISH analysis using the cosmid p robe D21S55. Further analysis demonstrated that the trisomy was due to segregation of an apparently balanced cryptic translocation from the mother, The patient's karyotype is 46,XX,-12, tder(12)t(12;21)(p13.l;q 22.2)mat. (C) 1995 Wiley-Liss, Inc.