Grandmaternal origin of an isochromosome 18p present in two maternal half-sisters.

The syndrome of tetrasomy 18p has been well documented in the literature. This is typically a result of a supernumerary isochromosome 18p, that has arisen during maternal meiosis II. This report presents clinical and molecular findings in two maternal half sisters with an isochromosome 18p. The isochromosome is inferred to have arisen during meiosis in the maternal grandmother and to have undergone mitotic and meiotic recombination in the mother of JJ and AT. The abnormal cell line may be restricted to the gonad in the mother as only normal 46,XX cells were detected by cytogenetic analysis of her blood or fibroblasts and physical examination revealed only normal findings. Thus, the isochromosome, although present at fertilization, must have been lost from the majority of embryonic precursor cells. This case raises important genetic counseling issues concerning recurrence risks.

Partial duplication of 3q (q25.1-->q26.1) without the Brachmann-de Lange phenotype.

Partial duplications of chromosome 3 have previously been reported to have phenotypic characteristics similar to Brachmann-de Lange syndrome (BDLS). We present the case of a 13-year-old girl with an apparent duplication in the 3q25.1-->q26.1 region but none of the manifestations commonly seen in BDLS. The chromosome 3 duplication was confirmed with a FISH painting probe of the involved region. These results suggest that the region critical for Brachmann-de Lange syndrome is not within the duplicated region of 3q25.1-->q26.1.

Characterization of an inversion duplication of the short arm of chromosome 8 by fluorescent in situ hybridization.

A de novo chromosome aberration in a woman with severe mental retardation and minor anomalies has been characterized cytogenetically. The patient's karyotype was described as 46, XX, inv dup (8)(p12-->p23.1). Previous Southern blot dosage studies with the marker locus D8S7 demonstrated that the patient was monosomic for this locus, suggesting that the rearrangement generated a duplication-deficiency chromosome. We have reinvestigated this patient using fluorescent in situ hybridization with chromosome 8 cosmids and an Alu-PCR product specific for 8p. These studies have confirmed directly that the duplicated chromosome also has undergone deletion.

Isolation and high-resolution mapping of new DNA markers from the pericentromeric region of chromosome 10.

The gene responsible for multiple endocrine neoplasia type 2A (MEN 2A) has been localized to the pericentromeric region of chromosome 10. Several markers that fail to recombine with MEN2A have been identified, including D10Z1, D10S94, D10S97, and D10S102. Meiotic mapping in the MEN2A region is limited by the paucity of critical crossovers identified and by the dramatically reduced rates of recombination in males. Additional approaches to mapping loci in the pericentromeric region of chromosome 10 are required. We have undertaken the generation of a detailed physical map by radiation hybrid mapping. Here we report the development of a radiation hybrid panel and its use in the mapping of new DNA markers in pericentromeric chromosome 10. The radiation-reduced hybrids used for mapping studies all retain small subchromosomal fragments that include both D10S94 and D10Z1. One hybrid was selected as the source of DNA for cloning. One hundred five human recombinant clones were isolated from a lambda library made with pp11A DNA. We have completed regional mapping of 22 of those clones using our radiation hybrid mapping panel. Seven markers have been identified and, when taken together with previously meiotically mapped markers, define eight radiation hybrid map intervals between D10S34 and RBP3. The identical order is found for a number of these using either the radiation hybrid mapping panel or the meiotic mapping panel. We believe that this combination cloning and mapping approach will facilitate the precise positioning of new markers in pericentromeric chromosome 10 and will help in refining further the localization of MEN2A.

X chromosome aneuploidy in lymphocyte cultures from women with recurrent spontaneous abortions.

Occasional metaphases with X chromosome aneuploidy can be detected in short-term lymphocyte cultures from women with recurrent abortions. The significance of this finding is unknown. It has been suggested that it may reflect a genetic tendency to nondisjunction that predisposes these women to an increased risk of producing aneuploid offspring. We have investigated prospectively the frequency of X chromosome aneuploidy in lymphocyte cultures from 104 women with a normal chromosome constitution and a history of recurrent pregnancy loss defined as 2 or more spontaneous abortions. Seventeen women (16%) had a significant number (2-10%) of X aneuploid cells in cultured lymphocytes but no evidence of constitutional chromosome mosaicism, based on analysis of fibroblast cultures. A control group of age-matched fertile women without a history of recurrent abortions showed a similar level of X chromosome aneuploidy in lymphocyte cultures. No increased risk for production of liveborn children with aneuploidy was found on retrospective analysis of the reproductive histories of these women. A significant effect of culture conditions on X chromosome gain or loss has been demonstrated by comparison of medium 199 with Dulbecco's modified Eagle medium.

Confined chorionic mosaicism in prenatal diagnosis.

Confined chorionic mosaicism, detected commonly on chorionic villus sampling (CVS) and occasionally in cultured amniotic fluid cells, is described in five pregnancies that showed confined chorionic mosaicism for trisomies 12, 13, 14, 17 and a marker chromosome. Cytogenetic findings in these pregnancies support the conclusion that within chorion some chromosomal mosaicism are confined to the trophectoderm derivatives while others to the extra-embryonic mesoderm. The etiology of confined chorionic mosaicism is discussed in relation to a significant role of multiple cell lineages contributing to the early development of placenta. The need is indicated for the use of both direct and long-term cultures in CVS prenatal diagnosis, and for the confirmatory testing of fetal blood or amniotic fluid in cases where mosaicism is detected in chorionic villi.

Inverted tandem duplication generates a duplication deficiency of chromosome 8p.

An adult female with sever mental retardation and dysmorphic features is described. A de novo chromosomal aberration involving 8p was found. The karyotype was 46, XX, inv dup (8) (p12----p23.1). Dosage studies with the DNA probe D8S7, which is located at 8p23----8pter, showed that the patient was monosomic for this marker. Thus the de novo rearrangement generated a duplication-deficiency chromosome. The possible mechanisms of formation of this abnormal chromosome are discussed.

Klinefelter's syndrome and acute leukemia.

Klinefelter's syndrome is associated with an increased risk of certain types of cancer. A small number of reports have documented the occurrence of acute leukemia in these patients. Our review of 1200 consecutive patients investigated cytogenetically for actual or suspected hematologic malignancy revealed only one patient with acute leukemia and the 47,XXY syndrome. This finding suggests that the risk of acute leukemia in Klinefelter's patients is no greater than that of the general population.

Infantile autism: an occasional manifestation of fragile (X) mental retardation.

Classical infantile autism occurs more frequently in males and has recently been noted in patients with the fragile (X) form of X-linked mental retardation (XLMR). In order to better understand this association and to determine whether fra(X) XLMR could account for the excess of autistic males, we investigated a group of institutionalized severely handicapped adults, 33 males and eight females, who were diagnosed as autistic using the DSM III diagnostic criteria of infantile autism. Chromosome studies using FUdR showed that three of the males had the Xq27 fragile site. We confirmed the association of autism and fra(X) XLMR, and showed that this extreme form of behaviour is part of the spectrum seen in the Martin-Bell syndrome. Two of the three autistic males with the Xq27 fragile site had a history of birth insults, which in combination with developmental deficits due to the fragile X gene, might have led to the behavioural disorder. Even though the fragile X cannot account for the excess of males with classical autism, it is an important X-linked factor in its cause. The diagnosis can allow more accurate counselling for this subset of autistic males.

Normal male carriers in the fra(X) form of X-linked mental retardation (Martin-Bell syndrome).

Evidence for the transmission of X-linked mental retardation through normal male carriers is reviewed in 6 kindreds. In these pedigrees we identified 15 unaffected males who likely had passed the gene on through their daughters. Fifty-one mentally retarded grandsons or great grandsons descended from these male carriers. In total, these males had 50 daughters with only 2 of them being of low intelligence. Two of the male carriers were recently identified through fra(X)- positive results in their mentally normal daughters. Among the sibs of these males, mentally retarded brothers were found in 3 families. This was unexpected since earlier observations suggested that the risk for mental retardation among sibs of nonmanifesting carriers is exceedingly low.

Chromosomal mosaicism confined to the placenta in human conceptions.

Placental and fetal tissues from 46 human pregnancies were cultured and cytogenetically analyzed in an attempt to document the existence of chromosomal mosaicism confined strictly to tissues of extraembryonic origin. In two gestations in which chromosomal mosaicism was found, it was expressed exclusively in placental chorionic cells and was not detected in cells derived from the embryo proper. This demonstration of confined chorionic mosaicism may have implications for the understanding of the fetoplacental unit and for prenatal diagnosis.

Fragile X chromosome and chromosome condensation.

The effect of chromosome condensation on the frequency of expression of the fragile X chromosome was examined. Chromosome decondensation substances were tested for their ability to elicit expression or improve frequencies of expression of the fragile X chromosome in five patients. The substances tested included the AT specific DNA ligands ethidium bromide, Hoechst 33258, and netropsin, and the GC specific substances actinomycin D and olivomycin. Under culture conditions appropriate for eliciting fragile X expression none of the decondensation compounds studied significantly altered frequencies of expression, nor did any of the substances elicit fragile X expression under conditions that normally suppress fragile X expression. The fragile X was found to be more frequently evident in less condensed chromosome preparations from fibroblasts. The implications of these findings with respect to the nature of fragile sites are discussed.

Triploidy in 40 human spontaneous abortuses: assessment of phenotype in embryos.

Forty human spontaneous abortuses were identified as triploid, 34 by karyotype and 6 by DNA measurement. Of the 40, 26 were embryos of 5 to 7 weeks' developmental age, 6 were intact empty sacs, 4 were early growth-disorganized embryos, and 4 were fetuses. In an attempt to determine the extent to which embryonic phenotype reveals triploid karyotype, the phenotypes of the 26 triploid embryos were compared with those of the 40 embryos of known nontriploid karyotype identified in larger study of consecutive spontaneous abortuses. Each embryo was scored for presence or absence of each of 4 abnormal phenotypic features: retarded limb development, facial dysplasia, subectodermal hemorrhage, and cystic chorionic villi. Whereas this combination of features was found in a few abortuses with normal or trisomic karyotype, it was both common and most frequent with triploidy. Approximately half (12 of 22) of the triploid embryos had at least 3 of the features. Conversely, among assessable embryos of known karyotype, four fifths (12 of 15) of those with at least 3 of the 4 abnormal features were triploid. Thus, while not definitive, such phenotypic information can be used with caution in counseling for subsequent pregnancies.

Further delineation of X-linked mental retardation.

Chromosomal, clinical, and psychological data are presented on members of six families with X-linked mental retardation. Affected males in three of these families express the fra(X)(q28) marker, while the retarded males in the other three do not. Similar variable physical and psychological characteristics, such a lop ears, large testes, and perseverative speech, are present in affected males in all six families. Preliminary analysis of the psychological data also shows that males with and without marker expression cannot be differentiated with certainty. On this basis we suggest that there is a type of X-linked mental retardation with many phenotypic features of marker-X mental retardation but without expression of the X chromosome fragile site.

Expression in fibroblast culture of the satellited-X chromosome associated with familial sex-linked mental retardation.

The satellited-X chromosome previously shown in lymphocyte culture to be associated with certain types of sex-linked mental retardation has, for the first time, been demonstrated in cultured skin fibroblasts and lymphocytes from two affected males and an obligate carrier female. These findings provide a basis for reliable diagnosis of female carriers and for the development of prenatal diagnosis.

Rapid determination of polyploidy in human chorionic tissue sections.

Chromosomal analysis from aborted tissue has become an important diagnostic aid. However, the necessary cultures are frequently unsuccessful due to the condition of the aborted tissue. Polyploidy, in particular triploidy, in the conceptus is a common cause of early pregnancy loss and unlike aneuploidy does not appear to be associated with an increased recurrence risk. The necessity to monitor a subsequent pregnancy with amniocentesis is therefore eliminated. Therefore, in cases where a chromosomal anomaly is probable, a fast simple method of identification of a polyploid karyotype would be valuable. In this presentation, we describe a method using a scanning light microscope and histologic tissue preparations. This method can accurately determine the ploidy of the aborted material in 5 days.