DELINEATION OF SUPERNUMERARY MARKER CHROMOSOMES IN 38 PATIENTS

We present cytogenetic and clinical data on 38 patients with supernume rary marker chromosomes (SMCs), SMCs were characterized using a strate gy combining classical banding techniques and molecular cytogenetic st udies, Cases were ascertained prenatally, postnatally, and after fetal death. In 26 patients (68%), the SMC originated entirely from acrocen tric chromosomes, Among these, most patients carried a der(15), In 11 patients (29%), they were of nonacrocentric origin, including 9 autoso mal and 2 gonosomal marker chromosomes, In 1 patient the SMC was of pa rtially acrocentric origin. Patients with small derivatives of chromos ome 15 [der(15)] had a normal phenotype, Those with a larger der(15) s howed phenotypical abnormalities. Patients with supernumerary marker c hromosomes derived from chromosomes 13 or 21, and 14 appeared to have a low risk of abnormalities, Out of this group only 1 patient who carr ied an additional r(21) had physical anomalies, Patients with an SMC o riginating from chromosome 22 showed physical abnormalities in 2 out o f 6 cases, Supernumerary marker chromosomes identified as i(9p), i(12p ), and der(18) were all associated with an abnormal phenotype. Two of the derivatives of chromosome 20 analyzed were correlated with a norma l phenotype, while the carrier of the third one showed physical anomal ies and motor retardation, Of 2 patients with an extra der(X), 1 was n ormal and 1 showed an abnormal phenotype. (C) 1998 Wiley-Liss, Inc.