Interphase cytogenetics

Molecular characterization of 21p- variant chromosome

Fortuitously, within a 1-month period, we were referred two individuals for routine cytogenetic amniocenteses involving one chromosome 21 from each patient, which had apparently lost the entire short arm and a major portion of the centromeric alphoid sequences in their amniocytes. Breakage may have occurred within alphoid sequences resulting in extreme variants. Variations of a similar nature were originally referred to as Christchurch (Ch1) chromosomes and have been wrongly determined to be abnormal. The 21p- chromosome variants were similar in both cases, though they are from unrelated individuals. These rare variants, whose origins were both maternal and have no clinical consequences, were characterized by the FISH-technique to provide a greater degree of certainty.

Correlation of numerical chromosome 11 and 17 imbalance with metastasis of primary breast cancer to lymph nodes

Abnormalities of chromosomes 11 and 17 have been widely reported in invasive carcinoma of the breast. Interphase cytogenetics using pericentromeric repeat probes allows the evaluation of numerical chromosomal aberrations in tumour cell populations. We have developed a method for interphase cytogenetics on fine needle aspirates taken from breast tumours and have applied it to the analysis of chromosomes 11 and 17 in 49 cases of invasive adenocarcinoma. Frequency distributions of signal number were generated for each case and no correlation was found between modal signal number and tumour size at presentation, nodal status or tumour differentiation. In 14 cases, two copies of each of chromosomes 11 and 17 were present, and in 14, the number of chromosomes 11 and 17 were equal but abnormal. In 14 cases, the chromosome 11 number was greater than chromosome 17 and in 7 cases, the chromosome 17 number was greater than chromosome 11. Chromosome inequality correlated with the presence of lymph node metastases or disseminated disease at presentation and the absence of in situ carcinoma. There was no relationship with the presence of vascular invasion. These data suggest that numerical chromosome 11 and 17 imbalance may indicate the ability of breast cancers to metastasize rather than invade vessels. The pattern of numerical chromosome abnormality described may define a subgroup of tumours with a greater tendency for metastasis.

Interphase cytogenetics: analysis of numerical chromosome aberrations in isolated cells

Probes which recognize pericentromeric repetitive sequences can be used to determine numerical chromosome aberrations in interphase nuclei. Under appropriate stringency conditions, these probes decorate only the chromosome from which they were derived. It has been assumed that abnormalities of signal number in interphase nuclei reflect aneuploidy rather than proliferation, but this has not been clearly demonstrated. In this paper, three alphoid probes (D3Z1, D11Z1, and DXZ1) were localized to the appropriate chromosomes and the factors governing the production of reproducible signal distributions from three aneuploid cervical carcinoma-derived epithelial cell lines were investigated. Abnormalities of signal number represent numerical chromosome aberrations rather than changes associated with proliferation. Using four simple rules of interpretation, reproducible results can be obtained with minimal technical variation and selection bias. These results demonstrate that pericentromeric repetitive probes can be used reproducibly to determine numerical chromosome aberrations independent of cell proliferation in interphase nuclei, a necessary prerequisite for the application of this approach to the analysis of human tumours.

Molecular cytogenetic analysis of monosomy 7 in pediatric patients with myelodysplastic syndrome

Monosomy 7 is a non-random cytogenetic abnormality that is frequently associated with myelodysplastic syndromes (MDS). Twenty-four bone marrow samples from five pediatric patients with MDS were analysed using both traditional and interphase cytogenetic analysis. The majority of the metaphases were monosomic for chromosome 7 while interphase cytogenetic analysis consistently detected a disomic cell population in nondividing cell populations. This suggests that the monosomy 7 cells have a distinct proliferative advantage compared to the disomic cell population. The results demonstrate that interphase cytogenetic analysis provides important cytogenetic information about non-dividing cell subpopulations, enhancing our understanding of the cell dynamics of normal and monosomy 7 cells in MDS.

Detection of confined placental mosaicism in trisomy 18 conceptions using interphase cytogenetic analysis

Fluorescence in situ hybridization provides a rapid and accurate technique for detecting chromosomal aneuploidy. It is an excellent method for identifying mosaicism in placental tissues following prenatal diagnosis. Mosaicism, in the form of confined placental mosaicism, occurs im approximately 1%-2% of viable pregnancies studied by chorionic villus sampling at 9-11 weeks of gestation. It has been detected in pregnancies with both diploid and trisomic fetuses and appears to have an important effect on the intrauterine fetal survival. Using both standard cytogenetic analysis and fluorescence in situ hybridization, we have studied 12 placentas from pregnancies with trisomy 18 for the presence of chromosomal mosaicism. These included 2 that were spontaneously aborted, 5 that were terminated after prenatal diagnosis, and 4 that were delivered as either stillborn or liveborn. Significant levels of mosaicism, confined exclusively to cytotrophoblast, were detected in 7 pregnancies. This study demonstrates the usefulness of interphase cytogenetic analysis of uncultured tissues as an alternative method for the detection of mosaicism.

Use of fluorescent in situ hybridization to detect trisomy 13 in archival tissues for cytogenetic diagnosis

The present report describes the use of molecular probes to investigate the chromosomal constitution of interphase nuclei of formalin-fixed, paraffin-embedded tissue from three infants with multiple congenital malformations and a provisional diagnosis of trisomy 13 in two. Fluorescent in situ hybridization with the probe for the 13 and 21 centromeric regions revealed five nuclear signals in two of the cases, indicating the presence of an extra chromosome, and only four nuclear signals in the other case. Only the two positive cases had phenotypic features consistent with trisomy 13. Routine cytogenetic analysis was performed on one child and confirmed an additional chromosome 13. The child without an extra chromosome had features consistent with Ivemark syndrome. This study demonstrates the utility of fluorescent DNA probes for the retrospective diagnosis of aneuploidies in archival material.

Variations in alphoid DNA sequences escape detection of aneuploidy at interphase by FISH technique

The advent of a new staining technique, termed fluorescence in situ hybridization (FISH), allows the rapid identification of the genomic constitution of an individual with aneuploidy even in interphase nuclei through the use of a series of chromosome-specific DNA probes, an approach termed "interphase cytogenetics." However, alphoid DNA sequences of every centromere are polymorphic (heteromorphic), and the number of targeted sequences may be below the detection level of a specific DNA probe, thus escaping detection and resulting in the imprecise identification of the chromosomal constitution at interphase. The limitations associated with the FISH technique have dire consequences which are emphasized here with an example in which the presence of an additional chromosome 21 in two siblings born consecutively with trisomy 21 (Down syndrome) was not detected by "interphase cytogenetics." The copy number of alphoid DNA sequences of one of the paternal chromosomes 21 was low and resulted in discordance between domain numbers at interphase and actual chromosome numbers at metaphase in both children. This is an isolated incident that could have led to a misdiagnosis if FISH were the only test employed. Although the advantages of this technology are undeniably enormous, the present finding has made it apparent that precise standards and reliability of the procedure must be established prior to its routine application.

Model system for optimising mRNA non-isotopic in situ hybridisation: riboprobe detection of lysozyme mRNA in archival gut biopsy specimens

The aim of this study was to optimise conditions for mRNA detection by nonisotopic in situ hybridisation (NISH) using biotinylated and digoxigenin labelled riboprobes. Because lysozyme gene transcripts are present at high concentrations in Paneth and other alimentary cells, archival gut biopsy specimens were chosen as a model system for these experiments. Most of the variables in NISH, from unmasking of mRNA, to its ultimate detection by peroxidase or alkaline phosphatase based detection systems, were examined in detail. The most important findings were that simultaneous heating of tissue targets and riboprobes at 95 degrees C for 15 minutes before hybridisation at 50 degrees C for two hours gave the most intense signal for lysozyme mRNA in Paneth cells, Brunner's glands, and lamina propria macrophages; digoxigenin labelled riboprobes gave a higher signal to noise ratio than their biotinylated counterparts, and probes 600 base pairs long were superior to shorter probes. It is concluded that the mRNA NISH method may be generally useful for detecting gene transcription in archival clinical biopsy specimens.

Interphase cytogenetics using biotin and digoxigenin labelled probes: III. Increased sensitivity and flexibility for detecting HPV in cervical biopsy specimens and cell lines

A monoclonal antibody to digoxin enabled sandwich techniques to be used for the detection of hybridised digoxigenin labelled probes in cultured cells and paraffin wax sections. This system has greater flexibility than alkaline phosphatase conjugated polyclonal antidigoxigenin antibody and permits the use of alternative detector enzymes, such as horseradish peroxidase and fluorescence labels. The APAAP detection system that does not require the use of biotin can also be used in situations where endogenous biotin is a problem. The low level of background staining combined with precise substrate deposition of the amplified peroxidase system gives higher sensitivity and resolution. This permits localisation of closely adjacent chromosomal loci in interphase nuclei. The most sensitive peroxidase based digoxigenin detection system visualises two and a half to 12 copies of human papillomavirus (HPV) per nucleus. This system is also suitable for the analysis of low copy number HPV infection of cervical tissues.