Prenatal diagnosis using interphase fluorescence in situ hybridization (FISH): 2-year multi-center retrospective study and review of the literature.

Since 1993, the position of the American College of Medical Genetics (ACMG) has been that prenatal interphase fluorescence in situ hybridization (FISH) is investigational. In 1997, the FDA cleared the AneuVysion assay (Vysis, Inc.) to enumerate chromosomes 13, 18, 21, X and Y for prenatal diagnosis. Data is presented from the clinical trial that led to regulatory clearance (1379 pregnancies) and from retrospective case review on 5197 new pregnancies. These studies demonstrated an extremely high concordance rate between FISH and standard cytogenetics (99.8%) for specific abnormalities that the AneuVysion assay is designed to detect. In 29 039 informative testing events (6576 new and 22 463 cases in the literature) only one false positive (false positive rate = 0.003%) and seven false negative results (false negative rate = 0.024%) occurred. A historical review of all known accounts of specimens tested is presented (29 039 using AneuVysion and 18 275 specimens tested with other probes). These performance characteristics support a prenatal management strategy that includes utilization of FISH for prenatal testing when a diagnosis of aneuploidy of chromosome 13, 18, 21, X or Y is highly suspected by virtue of maternal age, positive maternal serum biochemical screening or abnormal ultrasound findings.

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.

Preliminary definition of a "critical region" of chromosome 13 in q32: report of 14 cases with 13q deletions and review of the literature.

We report on 14 patients with partial deletions of chromosome 13q. These patients exhibit a wide spectrum of phenotypes. Deletions limited to proximal bands q13-q31 are associated with growth retardation but not with major malformations. We review the literature since 1975 and summarize 13q deletion cases which have a phenotype involving one or more major malformations and mental retardation. Analysis of the breakpoints of these cases, as well as those reported by us, supports the hypothesis that only deletions involving at least part of band q32 are associated with major malformations and digital abnormalities. Patients with more distal deletions have severe mental retardation but do not have major malformations or growth retardation. A group of patients in whom the breakpoint is stated to be within q32 has had an intermediate phenotype. This suggests that it may be possible to define subregions within q32 whose deletion is associated with particular developmental defects.

Monochromosomal rodent-human hybrids from microcell fusion of human lymphoblastoid cells containing an inserted dominant selectable marker.

An improved system for the production of a series of rodent-human hybrids selectively retaining single human chromosomes marked in known locations is described. Such hybrids have significant applications in gene mapping and other genetic studies. Human lymphoblastoid lines were infected with the retroviral vector SP-1, which contains the bacterial his-D gene allowing mammalian cells to grow in the presence of histidinol. Microcell fusion of the infected lymphoblastoid cells with CHO cells was used to produce hybrids containing single human chromosomes retained by histidinol selection. Hybrids containing a single human chromosome 9 and a single human chromosome 19 are described. These have been characterized cytogenetically by G-banding, in situ hybridization, and Southern blot analysis.

The value of chromosome analysis in cases of neural tube defects: a case of anencephaly associated with fetal dup(2)(p24----pter).

A family is described in which two anencephalic fetuses were identified in two pregnancies. Autopsy revealed kidney anomalies in both fetuses. Chromosome analysis was performed only on the second fetus, which had a 46,XY,10q+ karyotype. Parental chromosome analysis showed the maternal karyotype to be 46,XX,t(2;10)(p24;q26) thus demonstrating that the fetus was carrying a duplication 2(p24----pter). Recurrence risks for anencephaly based on the cytogenetic abnormality were much higher than those which would be quoted for isolated anencephaly. This points out the necessity for complete diagnostic studies when a fetus with a neural tube defect is identified. The literature in regard to the 2p duplication phenotype is reviewed. It is possible that the duplication of the distal segment of 2p results in a neural tube defect/kidney anomaly phenotype.

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.