The trisomy 9p syndrome.

Since the first description of trisomy 9p in 1970, there has been a rapidly increasing recognition and reporting of new cases. The physical and mental features of retarded growth and development, down-turned corners of the mouth, mildly globular nose, slightly wide-set and deep-set eyes with anti-Mongoloid slant, and unusual dermatoglyphics are distinctive enough to establish trisomy 9p as a clinical chromosomal entity--one which may prove to be the fourth most common autosomal syndrome (after trisomies 21, 13, and 18). This paper includes a review and tabulation of features seen in the 20 reported cases and photographs of the faces of ten of these children. A new case included in this survey demonstrates the practical application of four types of chromosome banding identification (C, G, Q, and R). The confirmation of the chromosomal aberration in this syndrome is dependent on the use of one or more of these special laboratory techniques. Most of the clinical characteristics distinctive of the trisomy 9p syndrome are seen also in other trisomies involving more or less of the number 9 chromosome. From these observations it is determined that the crucial determinants of the classical features of this syndrome lie within the distal half of the number 9 short arm.