INTRACHROMOSOMAL TRIPLICATION OF DISTAL 7P

A female infant who died at 2 years of age with growth and psychomotor retardation, wide anterior fontanelle, downward slanting palpebral fi ssures, large, simple ears, joint dislocation/contractures, recurrent infections, and severe pulmonary hypertension was found to have a de n ovo 7p+ chromosome. The G banding pattern was suggestive of a triplica tion of 7p21.3 and 7p22; results of fluorescence in situ hybridisation studies using a chromosome 7 specific Library, a subtelomeric 7p repe at (109A6), and yeast artificial chromosome clones 786g1 and 850al, wh ich are respectively associated with the (CA)n repeat markers D7S517 a nd D7S513, supported the cytogenetic interpretation and showed that th e middle repeat was inverted. The patient's phenotype was consistent w ith the 7p duplication syndrome, allowing for the effects of the extra burden introduced by the partial tetrasomy. The present rearrangement may have resulted from several meiotic events occurring at the four c hromatid stage, namely an unequal crossover or interhomologue transloc ation with points of exchange at 7p22 and 7p15 followed by the inverte d insertion of 7p21.3-->p21.2 at the former breakpoint junction; moreo ver, a further duplication including D7S517 within the terminal 7p22 b and is also required.