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Objective: To assess laboratory performance, use, and limitations in the joint College of American Pathologists and American College of Medical Genetics proficiency testing program for laboratories performing cytogenetic tests based on fluorescence in situ hybridization (FISH)., Data Sources: Eight proficiency surveys dealing with FISH detection of microdeletions or microduplications, aneuploidy in interphase cells, gene amplification, and neoplasm-specific translocations. Participating laboratories used their own DNA probes (commercial or home-brew), hybridization methods, and analytic criteria to answer clinical questions about cases represented by slides included in the survey materials. They also described their test results according to the International System for Human Cytogenetic Nomenclature (ISCN) and answered supplementary questions relating to their experience with the subject test systems., Data Extraction: In addition to evaluating diagnostic accuracy, we evaluated survey use, laboratory experience, variation in methodologic approach, and the practicality of using ISCN nomenclature for describing test results., Synthesis and Conclusions: With the exception of one challenge, at least 80% of the participants reached the correct diagnostic conclusion. In the sole exception, there was still a consensus of 91.7% of participants with the same (albeit erroneous) diagnostic conclusion. The overall outstanding performance of participating laboratories clearly shows the reliability of current FISH methods. Despite the fact that a large number of laboratories reported little or no experience with the specific test systems, the overwhelming majority performed very well. This result shows that the program's strategy of targeting classes of abnormalities (vs a single abnormality associated with a specific disease) did not put at a disadvantage participants who did not routinely perform all of the potential tests in the class. The extraordinary variation in ISCN descriptions submitted by participants showed that the existing system for human cytogenetic nomenclature is not suitable for facile communication of FISH test results.

Objective: To assemble and interpret karyotype data provided as part of the College of American Pathologists/American College of Medical Genetics Cytogenetics Proficiency Testing Program., Data Sources, Extraction, and Synthesis: The Cytogenetics Resource Committee requested data on all cells analyzed in a 1994 whole-blood specimen challenge. In that study, 287 participating laboratories analyzed a total of 14297 cells derived from a sample drawn from an adult donor with Turner syndrome. This individual had previously been found to have mosaicism, including cell lines with X structural anomalies along with monosomy X, making this an excellent challenge for a multicenter cytogenetic survey., Results and Conclusions: Analysis of the data from this extensive study revealed mosaicism of up to 10 different sex chromosome complements involving the X chromosome with and without a small ring X or a derivative X chromosome. In the routine cytogenetic analysis performed by the participating laboratories, cell lines observed, in decreasing order of prevalence, included 45,X (n = 8357 cells), 46,X,r(X) (n = 3597), 46,X,der(X)t(X;X) (n = 2237), 46,XX (n = 93), 47,X,r(X),r(X) (n = 5), 47,X,der (X)t(X;X),der(X)t(X;X) (n = 3), 47,XX,r(X) (n = 2), and one observation each of 47,XX,der(X)t(X;X), 47,X,der(X)t (X;X),r(X), and 47,XXX. Our molecular cytogenetic data, as well as detailed analysis of G-banded chromosomes, suggest the nomenclature for these 2 abnormal X chromosomes as r(X)(p11.3q21.3) and der(X)t(X;X)(p11.3;q21.3), and we discuss models for the concomitant formation of these 2 entities. Both the degree of analysis and the extensive mosaicism that was discovered in this study are exceptional, and similar reported cases as well as possible mechanisms for the observed X chromosome instability are reviewed.

Fluorescence in situ hybridization using chromosome-specific DNA probes is rapidly becoming part of clinical laboratory practice for certain congenital and neoplastic disorders. Current legislation requires proficiency testing for clinical laboratory studies. To evaluate the efficacy of fluorescence in situ hybridization proficiency testing, we invited 19 representative institutions to participate in three pilot studies. One study used probes for the X and Y chromosomes to evaluate metaphase spreads and interphase nuclei. Another study used probes for bcr and abl to detect bcr/abl fusion in interphase nuclei in chronic myelogenous leukemia. The third study used a D22S75 probe to detect microdeletions in metaphase spreads from a patient with velocardiofacial syndrome. The results of these studies demonstrate that proficiency testing with fluorescence in situ hybridization is attainable using either metaphase or interphase preparations, and that either microscope slides or fixed cell pellets are suitable.

In a large public urban hospital obstetrics service with > 123,000 deliveries in a 10-year period (1980-89), the frequencies (0.12%) of any type of chromosomal abnormality and of trisomy syndromes were analyzed for maternal age-related risk, by logistic regression. Focusing on very young gravidas, we found that in the study period there were 9,332 births (7.5% of all deliveries) to mothers < or = 16 years old. Estimated risks of chromosomal abnormalities among offspring associated with very young maternal age (9-16 years) were similar to those age-associated risks of mothers 20-29 years old. Risks of chromosomal abnormalities increase with advancing maternal age and are independent of ethnicity.

The cytogenetics of childhood neoplasms are reviewed. Chromosome abnormalities specific for various pediatric neoplasms can provide diagnostic, prognostic, and scientific information of value to the pathologist, clinician, and molecular biologist. Karyotypes of acute leukemia have independent prognostic significance. Chromosome aberrations associated with several of the small round blue-cell tumors of childhood can clarify the diagnosis. Recurring abnormalities in several tumors, such as hepatoblastomas, primitive neuroectodermal tumors, fibrosarcomas, and other tumor types, suggest interesting questions about pathogenesis and histogenetic relationships. Several tumor-specific chromosome aberrations, mostly in the acute leukemias, have been characterized at a molecular level.

The College of American Pathologists and the American Society of Human Genetics offer a proficiency testing program in clinical cytogenetics. Two hundred twenty-five laboratories now provide data for this survey, which was begun in 1986. Challenges have consisted of photographed metaphases, fixed lymphoblastoid cell suspensions, fresh peripheral blood, and disarranged karyotypes. The "correct" response was based on 80% or greater consensus among either the referees or the participants. Referee laboratories performed better than participants. More laboratories were able to report accurate recognition of abnormalities by using a coded list than could write the interpretation in standardized nomenclature. Deletions, unbalanced translocations, and inversions were more difficult challenges than balanced translocations or trisomies. Prenatal and lymphocyte challenges were more likely to result in consensus than were bone marrow challenges. Participants performed best on whole-blood challenges. Fixed cell suspensions were less satisfactory. Excellent quality case material is essential for a successful challenge. A grading system has been devised to separate artifacts of the survey process from proficiency variables.

Cytogenetic, immunocytochemical, and ultrastructural studies were performed on a large congenital fibrosarcoma. To our knowledge, this is the first report of a congenital fibrosarcoma characterized by all of these techniques. The findings of immunochemical and electron microscopic studies supported the suggestion that the tumor is of fibroblastic origin. The karyotype of the tumor (48,XY,+11,+20) is similar to that observed in previously reported cases and substantiates the hypothesis that congenital fibrosarcoma is characterized by nonrandom gain of chromosomes.

Ribonuclease inhibitor (RNH) is a protein that binds tightly to ribonucleases in cells and may be essential in the control of mRNA degradation and gene expression. The human RNH gene has been regionally localized to chromosome band 11p15 by in situ hybridization. A human placental cDNA was used to construct a 600-bp probe, which was then radiolabeled with tritium for in situ hybridization to human metaphase chromosomes. Localization of the RNH gene to 11p15, and possibly to 11p15.5, adds to a large number of genes assigned to this band, including 10 structural genes. This chromosomal region also represents an evolutionarily conserved syntenic group in the owl monkey, mouse, rat, and cow. Thus, regional assignment of RNH could facilitate the understanding of this gene and its association with ribonucleases, and perhaps extend a conserved syntenic region in mammalian genomes.

One of female MZ twins presented with muscular dystrophy. Physical examination, creatine phosphokinase levels, and muscle biopsy were consistent with Duchenne muscular dystrophy (DMD). However, because of her sex she was diagnosed as having limb-girdle muscular dystrophy. With cDNA probes to the DMD gene, a gene deletion was detected in the twins and their mother. The de novo mutation which arose in the mother was shown by novel junction fragments generated by HindIII, PstI, or TaqI when probed with cDNA8. Additional evidence of a large gene deletion was given by novel SfiI junction fragments detected by probes p20, J-Bir, and J-66 on pulsed-field gel electrophoresis (PFGE). Immunoblot analysis of muscle from the affected twin showed dystrophin of normal size but of reduced amount. Immunofluorescent visualization of dystrophin revealed foci of dystrophin-positive fibers adjacent to foci of dystrophin-negative fibers. These data indicate that the affected twin is a manifesting carrier of an abnormal DMD gene, her myopathy being a direct result of underexpression of dystrophin. Cytogenetic analysis revealed normal karyotypes, eliminating the possibility of a translocation affecting DMD gene function. Both linkage analysis and DNA fingerprint analysis revealed that each twin has two different X chromosomes, eliminating the possibility of uniparental disomy as a mechanism for DMD expression. On the basis of methylation differences of the paternal and maternal X chromosomes in these MZ twins, we propose uneven lyonization (X chromosome inactivation) as the underlying mechanism for disease expression in the affected female.

An 11-year-old patient with incomplete testicular feminization and a 47,XXY karyotype is described. The patient had female external genitalia, clitoromegaly, and some features of Klinefelter's syndrome, including speech delay and delayed intellectual development. DNA analysis using X chromosomal DNA sequences suggest that the supernumerary X chromosome in the patient resulted from maternal nondisjunction during meiosis II. The M II error thereby provides the basis for homozygosity of a mutation in the androgen receptor locus.

When the thymidine analog BrdU was incorporated into the DNA of a fibroblast cell line derived from the cactus mouse Peromyscus eremicus, a chromosome region with an increased frequency of gaps and breaks was observed. Nearly a third of the chromatid aberrations found at this site were associated with a sister-chromatid exchange (SCE) although this chromosome region showed no increase in sister-chromatid exchange in the absence of a gap or break. SCEs were significantly decreased in the remainder of the chromosome arm when it contained an aberration at the unstable site. This BrdU-sensitive region, unlike others reported, was found not to be late-replicating.--In this chromosome complement, the frequency of sister-chromatid exchange in C-band positive regions was significantly lower than that in C-band negative regions.

Incidence of malignancy among close relatives was used to evaluate the relationship of early age at diagnosis and familial cancer predisposition in a general population of cancer patients. The occurrence of cancer and other conditions in families of more than 1,350 randomly selected patients with a wide variety of malignancies was ascertained. Each patient was assigned to one of four study groups based on comparison of his age at diagnosis with the distribution of ages at diagnosis for his cancer site compiled by the Third National Cancer Survey. These groups consisted of patients whose ages at diagnosis were in: (1) the lowest decile, (2) the median decile, (3) above the median decile, and (4) between the lowest and median deciles. Person-years and calendar time at risk were calculated for first-degree relatives in each group. The numbers of cancers expected among these relatives were calculated using age- and time-specific incidence rates of a standard population. Statistical analysis of (1) the numbers of reported vs. expected cancers in relatives and (2) the numbers of families reporting cancer in parents or siblings of patients showed that a familial tendency to develop cancer exists in this randomly selected population of cancer patients, regardless of age at onset of malignancy in the proband. Conversely, early age at diagnosis of cancer may indicate genetic predisposition to malignancy only in exceptional cases.