Recent studies have implicated alpha-satellite DNA as an integral part of the centromere, important for the normal segregation of human chromosomes. To explore the relationship between the normal functioning centromere and alpha-satellite DNA, we have studied eight accessory marker chromosomes in which fluorescence in-situ hybridization could detect neither pancentromeric nor chromosome-specific alpha-satellite DNA. These accessory marker chromosomes were present in the majority of or all cells analyzed and appeared mitotically stable, thereby indicating the presence of a functional centromere. FISH analysis with both chromosome-specific libraries and single-copy YACs, together with microsatellite DNA studies, allowed unequivocal identification of both the origin and structure of these chromosomes. All but one of the marker chromosomes were linear mirror image duplications, and they were present along with either two additional normal chromosomes or with one normal and one deleted chromosome. Indirect immunofluorescence analysis revealed that the centromere protein CENP-B was not present on these markers; however, both CENP-C and CENP-E were present at a position defining a 'neo-centromere'. These studies provide insight into a newly defined class of marker chromosomes that lack detectable alpha-satellite DNA. At least for such marker chromosomes, alpha-satellite DNA at levels detectable by FISH appears unnecessary for chromosome segregation or for the association of CENP-C and CENP-E at a functional centromere.

Deletions of the short arm of chromosome 6 are relatively rare, the main features being developmental delay, craniofacial malformations, hypotonia, and defects of the heart and kidney, with hydrocephalus and eye abnormalities occurring in some instances. We present the molecular cytogenetic investigation of six cases with 6p deletions and two cases with unbalanced translocations resulting in monosomy of the distal part of 6p. The breakpoints of the deletions have been determined accurately by using 55 well-mapped probes and fluorescence in situ hybridization (FISH). The cases can be grouped into two distinct categories: interstitial deletions within the 6p22-p24 segment and terminal deletions within the 6p24-pter segment. Characteristics correlating with specific regions are: short neck, clinodactyly or syndactyly, brain, heart and kidney defects with deletions within 6p23-p24; and corneal opacities/iris coloboma/Rieger anomaly, hypertelorism and deafness with deletions of 6p25. The two cases with unbalanced translocations presented with a Larsen-like syndrome including some characteristics of the 6p deletion syndrome, which can be explained by the deletion of 6p25. Such investigation of cytogenetic abnormalities of 6p using FISH techniques and a defined set of probes will allow a direct comparison of reported cases and enable more accurate diagnosis as well as prognosis in patients with 6p deletions.

Six human neuroblastomas were analyzed by Giemsa and fluorescence banding techniques to identify chromosomal aberrations. Two neuroblastomas were primary tumors from untreated children, and four were cell lines established from human neuroblastomas. Five of the six tumors studied were diploid or near diploid; one was near tetraploid. A lp-was found in three of the neuroblastomas examined. The Ip-was present in both primary tumors, and in one it was the only abnormality detected. This deletion was also found in the cells of an established line, in addition to other abnormalities. Giant markers of different origins were found in the four cell lines, and no double-minute chromosomes were found in the primaries or the cell lines studied. Thus, a 1 p-deletion was the most consistent abnormality found in the six human neuro-blastomas examined in this study. We attempt to correlate this finding with Knudson's hypothesis on the brigin of childhood cancer. Additional studies of primary tumors should clarify whether this specific chromosomal abnormality is related to the acquisition of malignant behavior in human neuroblastomas.

Recently, a new clinically recognizable syndrome resulting from a small interstitial deletion of 17p [del(17)(p11.2p11.2)] was described in ten unrelated patients. We have identified six additional patients with similar cytogenetic and phenotypic abnormalities. Consistent clinical manifestations include 1) brachycephaly with a broad face and nasal bridge, 2) flat midface, 3) short, broad hands, and 4) mental retardation associated with hyperactivity and often self-destructive behavior. The craniofacial and hand anomalies are reminiscent of several craniosynostosis syndromes. Most patients also had growth deficiency and several other (more variable) congenital malformations. Chromosome studies with special attention to 17 should be performed in any patient with a similar phenotype.

We describe a 7 1/2-year-old girl with mildly unusual phenotype and complex heart disease including ventricular myocardial noncompaction. She was found to have a distal 5q deletion, del(5)(q35.1q35.3). Fluorescent in situ hybridization showed that this deletion included the locus for the cardiac specific homeobox gene, CSX. This suggests that some instances of ventricular myocardial noncompaction may be caused by haploinsufficiency of CSX.