Large terminal fragments of human chromosomes 2p, 6p, 8q, 12q, and 18q were cloned using yeast artificial chromosomes (YACs). RecA-assisted restriction endonuclease (RARE) cleavage analysis of genomic DNA samples from II unrelated individuals using YAC-derived probes confirmed the telomeric localizations of the half-YACs studied. The cloned fragments provide telomeric closure of maps for the respective chromosome arms and will supply the reagents needed for analyzing and sequencing these distal subtelomeric regions.Close

We describe two sibs with the unbalanced translocation der(6)t(6;8)(p25.1;q24.23), making them monosomic for 6p25.1-->6pter and trisomic for 8q24.23-->8qter. The siblings both possess Axenfeld-Rieger Anomaly (ARA), hypertelorism, clinodactyly, and cardiac anomalies, but otherwise vary in the phenotypic manifestations of this unbalanced translocation. We compare them to previously described cases and a recently proposed syndrome of ARA, atrial septal defect, and sensorineural deafness.Close

We report two 46,XY female patients with two different de novo unbalanced translocations, each involving the chromosomal region 6p25. The patient with a 46,XY,der(6)t(X;6)(p21.2;p25) karyotype had a sex reversal phenotype. The patient with a 46,XY,der(13)t(6;13)(p25;q33) karyotype had a male pseudohermaphrodite phenotype. Multi-paint fluorescent in situ hybridization was performed to determine the origin of the derivative material on 6p and 13q. The association of abnormalities of the 6p25 region with either an Xp duplication or a 13q deletion is reported here for the first time.Close

Human chromosomes terminate with specialized telomeric structures including the simple tandem repeat (TTAGGG)n and additional complex subtelomeric repeats. Unique sequence DNA for each telomere is located 100-300 kilobases (kb) from the end of most chromosomes. A high concentration of genes and a number of candidate genes for recognizable syndromes are known to be present in telomeric regions. The human telomeric regions represent a major diagnostic challenge in clinical cytogenetics, because most of the terminal bands are G negative, and cryptic deletions and translocations in the telomeric regions are therefore difficult to detect by conventional cytogenetic methods. In fact, several submicroscopic chromosomal abnormalities in patients with undiagnosed mental retardation or multiple congenital anomalies have been identified by other molecular methods such as DNA polymorphism analysis. To improve the sensitivity for deletion detection and to determine whether such cryptic rearrangements represent a significant source of human pathology that has not been previously appreciated, it would be valuable to have specific FISH probes for all human telomeres. We report here the isolation and characterization of a complete set of specific FISH probes representing each human telomere. As most of these clones are at a known distance of within 100-300 kb from the end of the chromosome arm, this provides a 10-fold improvement in deletion detection sensitivity compared with high-resolution cytogenetics (2-3 Mb resolution). While testing these probes, we serendipitously identified a family with multiple members carrying a cryptic 1q;11p rearrangement in the balanced or unbalanced state.Close

Deletions of the short arm of chromosome 6 are relatively rare, only 16 cases having been described in the literature so far. Here we present a detailed investigation by fluorescence in situ hybridisation of two further cases with different but overlapping interstitial deletions involving 6p22, 6p23 and 6p24. The main features involved are craniofacial malformations, heart and kidney defects, mental retardation/developmental delay, hypotonia and hydrocephalus. By using 36 yeast artificial chromosome and cosmid clones from a contig covering 6p22.3-6p25 and other probes with defined cytogenetic locations within 6p21-6p22 we have precisely localised the breakpoints involved in each of the cases, estimated the sizes of the deleted regions and defined the region that is hemizygously deleted in both cases.Close

The FKHL7 gene has been implicated in the pathogenesis of glaucoma/autosomal dominant iridogoniodysgenesis (IGDA) (IRID1). This has been supported by mutations in some glaucoma and IGDA patients and the development of anterior eye chamber anomalies in patients with 6p deletions affecting the 6p25 region. We report a case with anterior eye chamber anomalies and an interstitial deletion of 6p24-p25 that does not include the FKHL7 gene, suggesting the possible additional involvement of another locus, within 6p24-6p25, in anterior eye chamber development. A candidate gene is AP-2alpha, which is contained within the deleted segment and plays a role in anterior eye chamber development.Close

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.Close

We report on a newborn boy with a congenital heart defect, severe pre- and postnatal growth retardation, feeding problems, facial anomalies and unilateral hydronephrosis. Cytogenetic analysis showed extra chromosomal material on the short arm of one chromosome 15 that at first sight could be mistaken for a chromosomal variant and could not be identified with conventional banding techniques. Chromosome analysis of the parents showed that both had a normal karyotype. Microdissection of five copies of the aberrant chromosome 15, amplification of the dissected chromosomal material by DOP-PCR and subsequent reverse painting was performed and disclosed that the patient had a de novo 46,XY,der(15)(6pter-->6p22.1::15p12-->15qter) karyotype with a "pure" trisomy of chromosome region 6p22.1-->6pter. The associated phenotypic anomalies are compared with other reported cases with a distal duplication of chromosome 6p. Copyright Wiley-Liss. Inc.Close

First described in 1971, partial trisomy 6p is uncommon and generally secondary to a familial reciprocal translocation. The proximal breakpoint of the reported cases varies from p11 to p25. We here report on a patient with moderate mental retardation, craniofacial and pigmentary anomalies, proteinuria, and hyperglycemia who was found to have a mosaic karyotype 46,X,add(Y)(q12)/45,X. Fluorescence in situ hybridization (FISH) enabled us to identify that the additional material on Yqh derived from 6p and to define the rearrangement as der(Y)t(Y;6)(q12;p22). To the best of our knowledge, this is the first case of trisomy 6p22-pter without an associated deleted segment; the second breakpoint of the rearrangement is in Yqh. Precise mapping of the centromeric breakpoint of the trisomic 6p segment allowed a more convincing correlation between partial 6p trisomy and clinical phenotype to be addressed. In particular, the proteinuria often observed in 6p trisomic patients could be assigned to the 6p22-6pter region.Close

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Telomere-specific clones are a valuable resource for the characterization of chromosomal rearrangements. We previously reported a first-generation set of human telomere probes consisting of 34 genomic clones, which were a known distance from the end of the chromosome ( approximately 300 kb), and 7 clones corresponding to the most distal markers on the integrated genetic/physical map (1p, 5p, 6p, 9p, 12p, 15q, and 20q). Subsequently, this resource has been optimized and completed: the size of the genomic clones has been expanded to a target size of 100-200 kb, which is optimal for use in genome-scanning methodologies, and additional probes for the remaining seven telomeres have been identified. For each clone we give an associated mapped sequence-tagged site and provide distances from the telomere estimated using a combination of fiberFISH, interphase FISH, sequence analysis, and radiation-hybrid mapping. This updated set of telomeric clones is an invaluable resource for clinical diagnosis and represents an important contribution to genetic and physical mapping efforts aimed at telomeric regions.Close

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The recent spreading of a subtelomeric region at nine different human chromosome ends was characterized by a combination of segregation analyses, physical mapping, junction cloning, and FISH investigations. The events occurred very recently in human genome evolution as demonstrated by sequence analysis of different alleles and the single location of the ancestral site at chromosome 17qter in chimpanzee and orangutan. The domain successfully colonized most 1p, 5q, and 6q chromosome ends and is also present at a significant frequency of 6p, 7p, 8p, 11p, 15q, and 19p ends. On 6qter, the transposed domain is immediately distal to the highly conserved, single-copy gene PDCD2.Close

Cryptic subtelomeric rearrangements are suspected to underlie a substantial portion of terminal chromosomal deletions. We have previously described two children, one with an unbalanced subtelomeric rearrangement resulting in deletion of 22q13-->qter and duplication of 1qter, and a second with an apparently simple 22q13-->qter deletion. We have examined two additional patients with deletions of 22q13-->qter. In one of the new patients presented here, clinical findings were suggestive of the 22q13 deletion syndrome and FISH for 22qter was requested. Chromosome studies suggested an abnormality involving the telomere of one 22q (46,XX,?add(22)(q13. 3)). FISH using Oncor D22S39 and Vysis ARSA probes confirmed a terminal deletion. A multi-telomere FISH assay showed a signal from 19qter on the deleted chromosome 22. Results were confirmed with 19qtel and 22qtel specific probes. The patient is therefore trisomic for 19qter and monosomic for 22qter. The patient's mother was found to have a translocation (19;22)(q13.42;q13.31). We also re-examined chromosomes from two patients previously diagnosed with 22q deletions who were not known to have a rearrangement using the multi-telomere assay. One of these patients was found to have a derivative chromosome 22 (der(22)t(6;22)(p25;q13)). No evidence of rearrangement was detected in the other patient. Thus we have found the 22q13 deletion to be associated with a translocation in three of four patients. This report illustrates the usefulness of examining patients with hypotonia, severe language delay, and mild facial dysmorphism for this syndrome and suggests that most of these deletions may be unbalanced subtelomeric rearrangements.Close

Partial trisomy 6p with duplications ranging from 6p21 to 6p25 is emerging as an established syndrome. A case of duplication of segment p22-p25 of the short arm of chromosome 6 as the result of a maternal t (1;6)(q44;p22.2) translocation in a mentally retarded girl with congenital anomalies is reported here. The associated phenotypic anomalies are compared with other reported cases of duplication 6p involving adjacent regions.Close

We report the prenatal diagnosis of a karyotype 46,XY,rec(6)dup p, inv(6) (p23q27) mat detected by fluorescence in situ hybridization using chromosome 6pter and 6qter specific DNA markers. This partial duplication-deletion (6p12-->pter; 6q27-->qter) emanated from a balanced pericentric inversion 46,XX inv(6) (p23q27)pat present in the mother. The phenotypes of two relatives with the same unbalanced anomaly are described. This report illustrates the sensitivity and specificity of fluorescence in situ hybridization (FISH) and its benefit in rapid and unequivocal prenatal diagnosis of subtle chromosomal rearrangements.Close