I1307K Mutation Detection by Allele-Specific PCR in Familial Colorectal Cancer.

Familial colorectal cancer (FCC) is a hereditary form of colorectal cancer that accounts for 15-50% of all colorectal cancers (1,2). FCC patients generally have one or two family members affected with colon polyps or cancer. A mutation (I1307K) in the APC gene has been associated with colorectal cancer in Ashkenazi Jews (3). This specific mutation is detected in approx 6% of the Ashkenazic Jewish population. The frequency increases to about 28% in Ashkenazim with a family history of colorectal cancer. A person carrying this mutation will have a twofold increased risk, over the general Ashkenazic Jewish population, of developing colorectal cancer in his or her lifetime (3). This risk is estimated to be approx 18-30% (3). Screening for this mutation is therefore important preventative care in this high-risk population.

Rapid prenatal diagnosis of 14 cases of triploidy using fish with multiple probes.

Fluorescence in situ hybridization (FISH) of chromosome-specific probes to interphase nuclei can rapidly identify aneuploidies in uncultured amniotic fluid cells. Using DNA probe sets specific for chromosomes 13, 18, 21, X, and Y, we have identified 14 fetuses where the hybridization pattern was consistent with a triploid chromosome constitution. In each case, the identification of fetal abnormalities by ultrasound examination initiated a request for rapid determination of ploidy status via prenatal FISH analysis of uncultured amniocytes. FISH produced a three-signal pattern for the three autosomes in combination with signals indicating an XXX or XXY sex chromosome complement. This hybridization pattern was interpreted to be consistent with triploidy. Results were reported to the physician within 2 days of amniocentesis and subsequently confirmed by cytogenetics. These cases demonstrate the utility of FISH for rapid prenatal identification of triploidy, particularly when fetal abnormalities are seen with ultrasonographic examination.

Rapid prenatal diagnosis of chromosomal aneuploidies by fluorescence in situ hybridization: clinical experience with 4,500 specimens.

Detection of chromosome aneuploidies in uncultured amniocytes is possible using fluorescence in situ hybridization (FISH). We herein describe the results of the first clinical program which utilized FISH for the rapid detection of chromosome aneuploidies in uncultured amniocytes. FISH was performed on physician request, as an adjunct to cytogenetics in 4,500 patients. Region-specific DNA probes to chromosomes 13, 18, 21, X, and Y were used to determine ploidy by analysis of signal number in hybridized nuclei. A sample was considered to be euploid when all autosomal probes generated two hybridization signals and when a normal sex chromosome pattern was observed in greater than or equal to 80% of hybridized nuclei. A sample was considered to be aneuploid when greater than or equal to 70% of hybridized nuclei displayed the same abnormal hybridization pattern for a specific probe. Of the attempted analyses, 90.2% met these criteria and were reported as informative to referring physicians within 2 d of receipt. Based on these reporting parameters, the overall detection rate for aneuploidies was 73.3% (107/146), with an accuracy of informative results for aneuploidies of 93.9% (107/114). Compared to cytogenetics, the accuracy of all informative FISH results, euploid and aneuploid, was 99.8%, and the specificity was 99.9%. In those pregnancies where fetal abnormalities had been observed by ultrasound, referring physicians requested FISH plus cytogenetics at a significantly higher rate than they requested cytogenetics alone. The current prenatal FISH protocol is not designed to detect all chromosome abnormalities and should only be utilized as an adjunctive test to cytogenetics. This experience demonstrates that FISH can provide a rapid and accurate clinical method for prenatal identification of chromosome aneuploidies.

p82H identifies sequences at every human centromere.

A cloned alphoid sequence, p82H, hybridizes in situ to the centromere of every human chromosome. After washing under stringent conditions, no more than 8% of the grains are located on any specific chromosome. p82H thus differs from other centromeric sequences which are reported to be chromosome specific, because it detects sequences that are conserved among the chromosomes. Two experimental approaches show that the p82H sequences are closely associated with the centromere. First, p82H remains with the relocated centromeres in an inv(19) and an inv(6) chromosome. Second, p82H hybridizes at the centromere but not to the centromeric heterochromatin of chromosomes 1, 9 and 16 that have elongated 1qh, 9qh and 16qh regions produced by short growth in 5-azacytidine. The only noncentromeric site of hybridization is at the distal end of the 9qh region.

Placental changes in fetal triploidy syndrome.

The sonographic findings in fetal triploidy syndrome include intrauterine growth retardation, hydrocephalus, oligohydramnios, and hydropic changes of the placenta. Ultrasonography can establish the diagnosis only when placental findings coexist with a fetus. Although the majority of triploid conceptions abort spontaneously in the first trimester, occasionally they will progress further, but rarely to term. Six cases are presented in which the diagnosis was suspected by early ultrasound examinations, including one case in which there was an unusually large trophoblastic cyst. Determination of the karyotype is important for the management of a pregnancy with a live fetus, and has implications for genetic counseling of subsequent pregnancies.