In situ hybridization analysis of isodicentric X-chromosomes with short arm fusion

Isodicentric X chromosome and mosaicism: report on two cases of 45,X/46,X,idic(Xq)/47,X,idic(Xq),idic(Xq) and review of the literature

We present 2 instances of Ullrich-Turner syndrome with mosaicism 45,X/46,X,idic(Xq)/47, X,idic(Xq),idic(Xq) and X-isochromosomes with 2 C-bands. The mosaicism with the 3 cell lines points to the presence of the isodicentric chromosome in the zygote and a subsequent nondisjunction event.

Identification of a supernumerary der(18) chromosome by a rational strategy for the cytogenetic typing of small marker chromosomes with chromosome-specific DNA probes

A case of a supernumerary der(18) marker chromosome is presented. The chromosomal origin of the marker chromosome was not evident by traditional chromosome analysis, but was determined by PRimed IN Situ labelling (PRINS) with chromosome specific centromere probes as primers for chain elongation in situ. For this purpose a strategy was developed which, in a few simple reactions, makes it possible unequivocally to determine the origin of any small marker chromosome. The approach does not require any hints about the origin of the chromosome prior to the analysis, since the chromosomal origin of the marker is established through PRINS reactions with pooled and single chromosome-specific centromere probes. Identification, mosaic screening and structural analysis require a total of 8-9 such reactions and may, due to the extreme speed of the PRINS reaction, be obtained within a single working day.

Prenatal identification of a 45,X/46,Xder(Y) mosaicism and confirmation by high resolution cytogenetics and fluorescence in situ hybridization

A 45,X/46,Xder(Y) mosaicism detected prenatally was shown to have a rare Y inversion-duplication or Y/Y translocation which can only be identified by a combination of high resolution cytogenetics and fluorescence in situ hybridization. The present data indicate the usefulness and importance of chromosome-specific probes in the identification and characterization of chromosome rearrangements.

An improved method for chromosome-specific labeling of alpha satellite DNA in situ by using denatured double-stranded DNA probes as primers in a primed in situ labeling (PRINS) procedure

An improved primed in situ labeling (PRINS) procedure that provides fast, highly sensitive, and nonradioactive cytogenetic localization of chromosome-specific tandem repeat sequences is presented. The PRINS technique is based on the sequence-specific annealing in situ of unlabeled DNA. This DNA then serves as primer for chain elongation in situ catalyzed by a DNA polymerase. If biotin-labeled nucleotides are used as substrate for the chain elongation, the hybridization site becomes labeled with biotin. The biotin is subsequently made visible through the binding of FITC-labeled avidin. Tandem repeat sequences may be detected in a few hours with synthetic oligonucleotides as primers, but specific labeling of single chromosomes is not easily obtained. This may be achieved, however, if denatured double-stranded DNA fragments from polymerase-chain-reaction products or cloned probes are used as primers. In the latter case, single chromosome pairs are stained with a speed and ease (1 h reaction and no probe labeling) that are superior to traditional in situ hybridization. Subsequent high-quality Q banding of the chromosomes is also possible. The developments described here extends the range of applications of the PRINS technique, so that it now can operate with any type of probe that is available for traditional in situ hybridization.

Identification of the origin of centromeres in whole-arm translocations using fluorescent in situ hybridization with alpha-satellite DNA probes

We detected 2 patients with whole-arm translocations resulting in a derivative chromosome consisting of 18q and 21q. Because the breakpoints were near the centromere, classical cytogenetic techniques could not determine the centromeric origin of the derivative chromosomes. Using nonradioactive in situ hybridization with a chromosome 18 alpha-satellite DNA probe (D18Z1), the centromeres in the abnormal chromosomes were determined to be from chromosome 18. The abnormality in one patient resulted in monosomy 18p with a karyotype 45,XX, -18, -21, + der(18)t(18;21) (p11;q11)mat complement. The second patient with a 46,XX, -21, + der(18)t(18;21)(p11;q11) de novo karyotype had complete trisomy of 18q. In both cases the appropriate phenotype was observed.

A simplified protocol for fluorescence in situ hybridization with repetitive DNA probes and its use in clinical cytogenetics

A method for chromosome-specific staining and its use in clinical cytogenetics is described. This fluorescence in situ hybridization protocol for repetitive DNA probes results in yellow-green fluorescent signals on orange-red stained chromosomes. Special characteristics are its simplicity, the use of digoxigenin-11-dUTP for labeling, and the combination of high stringency criteria for hybridization and low stringency for washing. The method is particularly advantageous in cases with structurally abnormal extra chromosomes (ESACs), marker chromosomes of gonosomal origin, and chromosomal mosaicism. It may also facilitate the screening of cases for fragile X. The chromosome-specific staining can be done within 1 working-day.

Application of fluorescence in situ hybridization techniques in clinical genetics: use of two alphoid repeat probes detecting the centromeres of chromosomes 13 and 21 or chromosomes 14 and 22, respectively

Two cloned DNA fragments, one derived from an alpha satellite subfamily common to chromosomes 13 and 21, and the other derived from a similar subfamily common to chromosomes 14 and 22, have been used as biotinylated probes in in situ hybridization studies. Under high stringency conditions, chromosome specific centromeric labelling can be obtained. The applications of this technique in clinical situations are illustrated on metaphases from a fetus with trisomy 21, a fetus with trisomy 13, and a child with clinical features of cat-eye syndrome.