Interstitial tandem direct duplication of the long arm of chromosome 4 (q23-q27) and possible assignment of the structural gene encoding human aspartylglucosaminidase to this segment.

We report on a girl with a previously undescribed de novo direct tandem duplication 4q involving the segment q23----q27. Clinical manifestations included postnatal growth and psychomotor retardation, microcephaly, hirsute forehead, epicanthic folds, strabismus, depressed nasal bridge, long philtrum, small mouth, tetralogy of Fallot, and sacral dimple. Her phenotype is compared with that of previously reported cases of duplication 4q. An increased activity of the enzyme aspartylglucosaminidase (AGA) in cultured fibroblasts was demonstrated. This suggests possible assignment of the AGA gene to the chromosomal segment 4q23----4q27.