Syndromes associated with deletion of the long arm of chromosome 18[del(18q)].

We studied eight persons whose karyotypes demonstrated deletion of a portion of the long arm of chromosome 18. Seven of these persons who showed the typical del(18q) syndrome had a common deletion in band 18q21, most likely band q21.3, and in at least two persons the deletion was interstitial. Another mentally retarded child, dissimilar in appearance, had a more proximal deletion within band 18q12. Two different clinical syndromes resulted from deletions of these different segments of the long arm of chromosome 18.