Loss of subtelomeric sequence associated with a terminal inversion duplication of the short arm of chromosome 4.

We report on a 4(1/2)-year-old girl, who presented with multiple minor anomalies consistent with trisomy for 4p. GTG-banding identified a de novo terminal inversion duplication of distal 4p, dup(4)(p16.3p15.3). Fluorescence in situ hybridization (FISH) with a wcp4 probe confirmed the chromosome 4 origin of the additional material. FISH with a 4p subtelomere probe, D4F26, showed no signal on the dup(4) chromosome identifying a deletion of this region. Molecular analysis of 4p STS loci confirmed the subtelomeric deletion and showed loss of the paternal allele in this region. The paternal origin of the deleted region and homozygosity for one of the two paternal alleles within the region of the duplication suggests that a sister chromatid rearrangement on the paternal chromosome 4 was involved in the formation of the dup(4) chromosome. To date, the best characterized mechanisms of formation of chromosome duplications are terminal inversion duplications of 8p, which were shown to be derived from rearrangements at maternal meiosis-I. Our data show that mechanisms other than a maternal meiosis-I rearrangement can lead to the formation of terminal inversion duplications. FISH analysis with the appropriate subtelomeric probes is warranted in terminal inversion duplications to check for associated deletions.

Molecular cytogenetic analysis of uterine leiomyoma and leiomyosarcoma by comparative genomic hybridization.

Uterine leiomyomata are among the most common of human neoplasms and are associated with abnormal uterine bleeding, infertility, and abdominal pain. Uterine leiomyosarcomata are presumed to be the malignant counterpart to uterine leiomyomata and are very rare. Transformation of uterine leiomyoma (ULM) into uterine leiomyosarcoma (ULMS) is yet to be conclusively confirmed, and each type of tumor may represent a distinct genetic entity. We used comparative genomic hybridization (CGH) to evaluate DNA sequence copy-number changes in 12 specimens of ULM and 8 of ULMS. CGH analysis of ULM demonstrated chromosomal imbalances in 8 of 12 (66. 7%) specimens. The most frequent ULM gains were observed at 9q34 (a novel finding) and on chromosome 19. Other ULM imbalances included gains and losses of chromosome 1p, losses on 7q, and gains on 12q. All ULMS specimens demonstrated chromosomal aberrations. Chromosome 1 imbalances were very prominent. The most frequent losses were detected on 14q and 22q. Losses on 14q are rarely seen in other types of leiomyo-sarcoma and may be a distinctive feature of ULMS. Gains on chromosomes 8, 17, and X were observed in half the cases and were accompanied by high-level amplification. Other chromosome arms overrepresented included 12q and 19p. The absence of specific anomalies common to all ULM and ULMS argues against their being benign-malignant counterparts.

Cloning and characterization of human PREB; a gene that maps to a genomic region associated with trisomy 2p syndrome.

We have isolated the human homolog of a novel rodent gene that may be involved in the regulation of pituitary gene transcription. The human PREB gene encodes a predicted protein of 417 amino acids, exhibiting several sequences characteristic of the WD-motif protein family. PREB transcripts were detected in every human fetal and adult tissue examined, although a great variation in levels of expression was observed. PREB was mapped to human Chromosome 2p23, a region of the genome associated with partial trisomy 2p syndrome. Although variable, the common duplication phenotype includes facial abnormalities, skeletal defects, growth and mental retardation, congenital heart and neural tube defects, and abnormalities of the genitalia. We propose that PREB has a role during human development and that abnormal dosage of this transcription factor may be involved in some of the developmental abnormalities observed in patients with partial trisomy 2p.

Jumping translocations in spontaneous abortions.

Chromosome translocations involving one donor chromosome and multiple recipient chromosomes have been referred to as jumping translocations (JTs). Acquired JTs are commonly observed in cancer patients, mainly involving chromosome 1. Constitutional forms of JTs mostly involve the acrocentric chromosomes and their satellites and have been reported in patients with clinical abnormalities. Recognizable phenotypes resulting from these events have included Down, Prader-Willi, and DiGeorge syndromes. The presence of JTs in spontaneous abortions has not been previously described. The breakpoints of all JTs occur in areas rich in repetitive DNA (telomeric, centromeric, and nucleolus organizing regions). We report two different unstable chromosome rearrangements in samples derived from spontaneous abortions. The first case involved a chromosome 15 donor. The recipient chromosomes were 1, 9, 15, and 21, and the respective breakpoints were in either the heterochromatic regions or the centromeres. FISH studies confirmed that the breakpoints of the jumping 15 rearrangement did not involve the Prader-Willi region but originated at the centromere or in the proximal short arm. A second case of instability was observed with a rearrangement resulting from a presumed de novo 8;21 translocation. Three JT cell lines were observed. They consisted of a deleted 8p chromosome, a dicentric 8;21 translocation, and an 8q isochromosome. The instability regions appeared to be at the pericentromeric region of chromosome 8 and the satellite region of chromosome 21. Both cases proved to be de novo events. The unstable nature of the JT resulting in chromosomal imbalance most likely contributed to the fetal loss. It appears that JT events may predispose to chromosomal imbalance via nondisjunction and chromosomal rearrangement and, therefore, may be an unrecognized cause of fetal loss.

Prenatal molecular cytogenetic diagnosis of partial tetrasomy 10p due to neocentromere formation in an inversion duplication analphoid marker chromosome.

Neocentromeres are fully functional centromeres found on rearranged or marker chromosomes that have separated from endogenous centromeres. Neocentromeres often result in partial tri- or tetrasomy because their formation confers mitotic stability to acentric chromosome fragments that would normally be lost. We describe the prenatal identification and characterization of a de novo supernumerary marker chromosome (SMC) containing a neocentromere in a 20-wk fetus by the combined use of comparative genomic hybridization (CGH) and fluorescence in situ hybridization (FISH). GTG-banding of fetal metaphases revealed a 47,XY,+mar karyotype in 100% of cultured amniocytes; parental karyotypes were both normal. Although sequential tricolor FISH using chromosome-specific painting probes identified a chromosome 10 origin of the marker, a complete panel of chromosome-specific centromeric satellite DNA probes failed to hybridize to any portion of the marker. The presence of a neocentromere on the marker chromosome was confirmed by the absence of hybridization of an all-human-centromere alpha-satellite DNA probe, which hybridizes to all normal centromeres, and the presence of centromere protein (CENP)-C, which is associated specifically with active kinetochores. Based on CGH analysis and FISH with a chromosome 10p subtelomeric probe, the marker was found to be an inversion duplication of the distal portion of chromosome 10p. Thus, the proband's karyotype was 47,XY,+inv dup(10)(pter-->p14 approximately 15::p14 approximately 15-->neo-->pter), which is the first report of partial tetrasomy 10p resulting from an analphoid marker chromosome with a neocentromere. This study illustrates the use of several molecular strategies in distinguishing centric alphoid markers from neocentric analphoid markers.

Clinical applications of comparative genomic hybridization.

PURPOSE: Comparative genomic hybridization (CGH) is a powerful DNA-based cytogenetic technique that allows the entire genome to be scanned for chromosomal imbalances without requiring the sample material to be mitotically active. During the past 2 years we received many requests from various medical centers around the country to use CGH to resolve the identity of aberrant chromosomal material. METHODS: We report the use of CGH for the evaluation of 12 clinical postnatal cases in which traditional cytogenetic analysis yielded ambiguous results. This series consisted of five marker chromosomes, five unbalanced translocations, and two intrachromosomal duplications. RESULTS: Identification and characterization of the additional unknown chromosomal material was achieved with use of CGH. All CGH findings were validated by traditional fluorescence in situ hybridization and other specialized staining techniques. CONCLUSLONS: These results demonstrate the effective use of CGH as a focused, single-step method for the identification of chromosomal material of unknown origin.

Paternal uniparental disomy for chromosome 14: a case report and review.

Uniparental disomy (UPD) for several chromosomes has been associated with disease phenotypes. Maternal UPD for chromosome 14 has been described and has a characteristic abnormal phenotype. Paternal UPD14 is rare and only three previous cases have been reported. We describe a new case of paternal UPD for chromosome 14 in an infant with a 45,XX,der(13q;14q) karyotype, which was confirmed by molecular analysis. The proposita had findings similar to those of the previous cases of patUPD14 and we conclude that there is a characteristic patUPD14 syndrome most likely due to imprinting effects. Couples with Robertsonian translocations involving chromosome 14 should be counseled as to the possibility of UPD14 and the option of prenatal diagnosis when indicated.

A transcript map of the newly defined 165 kb Wolf-Hirschhorn syndrome critical region.

Wolf-Hirschhorn syndrome (WHS) is a multiple malformation syndrome characterised by mental and developmental defects resulting from the absence of a segment of one chromosome 4 short arm (4p16.3). Due to the complex and variable expression of this disorder, it is thought that the WHS is a contiguous gene syndrome with an undefined number of genes contributing to the phenotype. In an effort to identify genes that contribute to human development and whose absence results in this syndrome, we have utilised a series of landmark cosmids to characterise a collection of WHS patient derived cell lines. Fluorescence in situ hybridisation with these cosmids was used to refine the WHS critical region (WHSCR) to 260 kb. The genomic sequence of this region is available and analysis of this sequence through BLAST detected several cDNA clones in the dbEST data base. A total of nine independent cDNAs, and their predicted translation products, from this analysis show no significant similarity to members of DNA or protein databases. Furthermore, these genes have been localised within the WHS critical region and reveal an interesting pattern of transcriptional organisation. A previously published report of a patient with proximal 4p- syndrome further refines the WHSCR to 165 kb defined by the loci D4S166 and D4S3327. This work provides the starting point to understand how multiple genes or other mechanisms can contribute to the complex phenotype associated with the Wolf-Hirschhorn syndrome.

Characterization of a de novo unbalanced chromosome rearrangement by comparative genomic hybridization and fluorescence in situ hybridization.

Fluorescence in situ hybridization (FISH) has proven useful for the identification of chromosomal material of unknown origin. More recently, comparative genomic hybridization (CGH) has been used to identify deletions and amplifications, particularly in neoplastic samples. Here, we describe the combined use of CGH and FISH to identify the origin of a de novo unbalanced translocation in a newborn with multiple congenital anomalies. GTG banding of metaphases from cultured lymphocytes showed an unbalanced karyotype, with extra material on a chromosome 5: 46,XX,add(5)(q35). Parental karyotypes were both normal. CGH revealed the additional material was from distal 11q (11q23-->'qter). This finding was confirmed by FISH with a whole chromosome paint for chromosome 11. Based on the CGH and FISH analyses, the proband's karyotype was therefore 46,XX,der(5)t(5;11)(q35.2; q23.2).ish der(5)(wcp11+). This case demonstrates the efficient use of CGH and confirmatory FISH for the identification of chromosomal material of unknown origin.

Localization and ordering of acid alpha-glucosidase (GAA) and thymidine kinase (TK1) by fluorescence in situ hybridization.

Genomic DNA clones of human acid alpha glucosidase (GAA) and thymidine kinase (TK1) were used to map the exact location and order of these genes on human chromosome 17. Both genes were localized to the 17q25-qter band (17q25.2-q25.3), with GAA distal to TK1. They were also shown to be, respectively, distal and proximal to an anonymous cosmid (cK17.71) previously mapped to this region.

Summary of the 1993 ASHG ancillary meeting "recent research on chromosome 4p syndromes and genes".

The following is a summary of presentations given during an ancillary meeting to the 1993 American Society of Human Genetics Meeting in New Orleans, LA. This ancillary meeting, entitled "Recent Research on Chromosome 4p Syndromes and Genes," reviewed the history of the Wolf-Hirschhorn syndrome (WHS), the natural history of patients with WHS, and the smallest region of deletion associated with the WHS. The proximal 4p deletion syndrome and the duplication 4p syndrome were also described and advice was offered regarding detection of chromosome 4p deletions, duplications, and rearrangements. The current status of the physical map of chromosome 4p with emphasis on the genes that map to the 4p16 region was presented along with a preliminary phenotypic map of 4p16. The goal of this format was to provide a comprehensive review of the clinical presentations, diagnostic capabilities, and genetic mapping advances involving chromosome 4p.

Long-term follow-up of two sibs with Larsen syndrome possibly due to parental germ-line mosaicism.

Larsen syndrome is a heterogeneous (autosomal dominant or recessive) disorder of characteristic facial changes, multiple joint dislocations, and bone deformities. Few data on the adult presentation of the recessive form of this disorder have been reported; thus, we set out to describe two sibs thought to be affected with autosomal recessive Larsen syndrome who were evaluated as infants and later as adults. Aside from secondary joint changes and the presence of cataracts, changes described in children with autosomal recessive Larsen syndrome were noted. Three years after evaluation, the sister gave birth to a daughter with Larsen syndrome. This occurrence raises the possibility of germ-line mosaicism as the mode of inheritance in this family. Thus, germ-line mosaicism must be considered in the genetic counseling of families with Larsen syndrome in which neither parent appears affected. These patients also illustrate that despite the severe skeletal and joint deformities, the prognosis can be good with careful orthopedic management.