Redefining the risks of prenatally ascertained supernumerary marker chromosomes: a collaborative study

BACKGROUND

A marker chromosome is defined as a structurally abnormal chromosome that cannot be identified by routine cytogenetics. The risk for phenotypic abnormalities associated with a marker chromosome depends on several factors, including inheritance, mode of ascertainment, chromosomal origin, and the morphology, content, and structure of the marker.

METHODS

to understand the karyotype-phenotype relationship of prenatally ascertained supernumerary de novo marker chromosomes, we combined data from prenatal cases obtained from 12 laboratories with those from studies in the literature. We were able to obtain cytogenetic and phenotypic data from 108 prenatally ascertained supernumerary de novo marker chromosomes to refine the phenotypic risk associated with these markers. Because of the growing number of cases and because more techniques are available to delineate marker morphology, we have been able to group risk estimates into subcategories, such as by marker type and whether there are ultrasound abnormalities.

RESULTS

If a de novo supernumerary marker chromosome is found prenatally, our data suggest there is a 26% risk for phenotypic abnormality when there is no other information defining the marker (such as chromosomal origin or information about the existing phenotype). However, if high resolution ultrasound studies are normal, this risk reduces to 18%.

CONCLUSIONS

Our findings strongly support the value of additional genetic studies for more precisely defining the risk in individual cases involving marker chromosomes.

Real-time three-dimensional ultrasound methods for shape analysis and visualization

Real-time three-dimensional (RT3D) ultrasound is a relatively new imaging modality that uses a special ultrasound transducer consisting of a matrix array of elements. The array electronically steers an ultrasound beam to interrogate a 3D volume of tissue. The real-time nature of RT3D ultrasound differentiates it from reconstructed 3D ultrasound, in which a conventional ultrasound transducer is moved mechanically through the third dimension. RT3D ultrasound is considerably faster than reconstructed 3D ultrasound, making it suitable for capturing continuous rapid motion such as that of the beating heart. Although RT3D ultrasound has not yet found widespread clinical use, these scanners are presently employed in more than 20 locations worldwide, primarily for cardiac research. The author helped develop the RT3D ultrasound technology as well as specialized analysis and visualization methods for the resulting data. In developing such methods, it has been necessary to consider the physical and mathematical processes by which the ultrasound data are collected. Difficulties arise because of high noise, variation in contrast and intensity between scans, ultrasound's nonrectilinear coordinate system, and the anisotropic nature of the echoes themselves. This article reviews these specific difficulties and provides solutions that are applicable to generalized analysis and visualization of RT3D ultrasound data. Some of the methods presented can also be applied to other imaging modalities with nonrectilinear coordinates.

Partial trisomy 7p defined by analysis of a complex chromosome rearrangement using a BAC clone panel

PURPOSE

To illustrate the use of bacterial artificial chromosome (BAC) clone panels for molecular cytogenetic analysis of complex chromosome rearrangements (CCRs).

METHODS

High resolution cytogenetics followed by fluorescence in situ hybridization (FISH) analysis using chromosome band-specific BAC probes, in addition to commercially available probes.

RESULTS

High resolution cytogenetics in conjunction with FISH using commercially available probes proved inadequate to resolve problems in characterizing a balanced CCR in the mother of a patient who had inherited an unbalanced form of the CCR. Accurate interpretation of the CCR and the unbalanced rearrangement in the patient as trisomy 7p12.2-->p21.3 was accomplished only through use of the BAC clone panel.

CONCLUSION

Use of BAC clone panels can enhance the power of FISH analysis in defining chromosome rearrangements that cannot be resolved by high resolution chromosome analysis.

Non-mosaic trisomy 20 presenting at 21 weeks' gestation as a thoraco-abdominal mass

Non-mosaic trisomy 20 is rare in fetuses surviving beyond the first trimester. We report a case of a fetus with non-mosaic trisomy 20 in amniotic fluid cultures obtained during the prenatal evaluation of an unusual thoraco-abdominal mass which was found at autopsy to be pulmonary sequestration. Gross inspection and autopsy of the fetus revealed multiple anomalies.

Real-time volumetric echocardiography: the technology and the possibilities

The heart is a dynamic organ with complexities in its shape. As such, it places special demands on three-dimensional techniques for reconstruction. Real-time volumetric echocardiography, which is based on phased array and parallel processing principles to enhance line density within a scan volume, provides rapid image acquisition. We introduce the principle, potential clinical importance, current limitations, and future of volumetric imaging methods.

Human PRRX1 and PRRX2 genes: cloning, expression, genomic localization, and exclusion as disease genes for Nager syndrome

In this study, we extend our examination of the function of the Prrx1 (a.k.a Mhox, Prx1, K-2, and Pmx1) as well as Prrx2 (a.k.a. S8 and Prx2) genes by characterizing the expression of the human orthologs and their potential for causing specific human malformations. The expression pattern of PRRX2 and its close relative, PRRX1, were analyzed in human tissue by RT-PCR. Although the expression of these human genes is similar to their mouse orthologs, there are notable differences in expression. PRRX2 was detected in the human kidney and lung, whereas in mice and chickens neither of these tissues has been reported to express Prrx2. For PRRX1 the expression pattern was quite similar to other vertebrates, but the ratio of the two isoforms was reversed. To begin the search for the gene-disease connection, both genes were mapped to human chromosomes by FISH. The PRRX1 locus maps to 1q23, whereas the PRRX2 locus maps to 9q34.1. This localization, along with the recently described phenotypes of the gene-targeted Prrx1, Prrx2 and double mutant mice, enabled us to search the human disease databases for similar malformations. This examination suggested that mutations at the PRRX1 and/or PRRX2 loci could result in Nager Acrofacial Dysostosis (NAFD) syndrome. We obtained DNA samples from eight patients with NAFD, as well as two patients with Miller syndrome, and analyzed them for mutations in the PRRX1 and PRRX2 genes. The data excludes mutations in the presumed coding sequences of these genes from causing NAFD.

A cre-lox recombination system for the targeted integration of circular yeast artificial chromosomes into embryonic stem cells

The ability to produce embryonic stem (ES) cell lines containing different yeast artificial chromosomes (YACs) integrated into the same location in the genome provides a system for comparing the bio-logical effects of YAC transgenes without the confounding influences of integration site and copy number. A targeting system was developed for the directed integration of circular YACs into mouse ES cells. The system combines Cre-lox recombination technology, specifically a positive-selection integration system, with circular YAC lipofection technology to achieve single copy targeted integration of a transgene. Three independent germline competent ES cell lines [lox-containing ES lines (designated LES)] were created that contain a '-neo-lox' cassette integrated at different sites within the ES genome. A plasmid containing YAC vector sequences and a complementary '-neo-lox' cassette was used to circularize two linear YACs containing genomic DNA from human chromosome 21. The circularized YACs were then targeted to the lox sites of the LES cell lines. Polymerase chain reaction and Southern analysis demonstrated that 21% (5 of 24) of lox-recombinants contain a full-length intact YAC. This system will make the study of YAC transgenic mice more reliable and reproducible, allowing the potential for direct comparison of different transgenes expressed from the same site within the genome.

Common trisomy mosaicism diagnosed in amniocytes involving chromosomes 13, 18, 20 and 21: karyotype-phenotype correlations

Karyotype-phenotype correlations of common trisomy mosaicism prenatally diagnosed via amniocentesis was reviewed in 305 new cases from a collaboration of North American cytogenetic laboratories. Abnormal outcome was noted in 10/25 (40%) cases of 47,+13/46, 17/31 (54%) cases of 47,+18/46, 10/152 (6.5%) cases of 47,+20/46, and in 49/97 (50%) cases of 47,+21/46 mosaicism. Risk of abnormal outcome in pregnancies with less than 50% trisomic cells and greater than 50% trisomic cells were: 26% (4/15) versus 60% (6/10) for 47,+13/46, 52% (11/21) versus 75% (6/8) for 47,+18/46, 4.5% (6/132) versus 20% (4/20) 47,+20/46, and 45% (27/60) versus 59% (22/37) for 47,+21/46. Phenotypically normal liveborns were observed with mean trisomic cell lines of 9.3% for 47,+13/46, 8.6% for 47,+18/46, 27% for 47, +20/46, and 17% for 47,+21/46. Cytogenetic confirmation rates were 46% (6/13 cases) for 47,+13/46 mosaicism, 66% (8/12 cases) for 47, +18/46, 10% (10/97 cases) for 47,+20/46, and 44% (24/54 cases) for 47,+21/46. There were higher confirmation rates in pregnancies with abnormal versus normal outcome: 50% versus 44% for 47,+13/46 mosaicism, 100% versus 33% for 47,+18/46, 66% versus 7% for 47, +20/46, and 55% versus 40% for 47,+21/46. Repeat amniocentesis is not helpful in predicting clinical outcome. It may be considered when there is insufficient number of cells or cultures to establish a diagnosis. Fetal blood sampling may have a role in mosaic trisomy 13, 18, and 21 as the risk for abnormal outcome increases with positive confirmation: 1/5 (20%) normal cases versus 5/8 (62%) abnormal cases. High resolution ultrasound examination(s) is recommended for clinical correlation and to facilitate genetic counselling.

Molecular cytogenetic analysis and clinical findings in a newborn with prenatally diagnosed rec(7)dup(7q)inv(7)(p22q31.3)pat

We report prenatal and early postnatal findings in a newborn with a partial trisomy of chromosome 7 (7q31.3-qter), arising from meiotic recombination of a paternal pericentric inversion, inv(7)(p22q31.3). The inversion breakpoints were localized and the regions of duplication and deletion were defined by fluorescence in situ hybridization (FISH) analysis using a series of locus-specific and subtelomeric probes. To our knowledge, only three cases involving a recombinant 7 with duplication of 7q have been reported, two of these being first cousins. The clinical findings in our patient included skeletal abnormalities, facial dysmorphism, dilated cerebral ventricles, microretrognathia and short neck. These findings and some aspects of the neonatal course were consistent with the phenotype previously reported for duplication of distal 7q, without associated monosomy for sequences from another chromosome.

Integration of cytogenetic with recombinational and physical maps of mouse chromosome 16

To link the cytogenetic map for mouse chromosome 16 (Chr 16) to the more detailed recombinational and physical maps, multiple probes were mapped by fluorescence in situ hybridization (FISH). Sixteen large insert clones (YACs, BACs, and PACs) containing markers that have been assigned to the Chr 16 recombinational map were localized to a cytogenetic band or subband by high-resolution FISH. This linkage of the cytogenetic and recombinational maps provides a useful tool for assigning new probe locations and for defining breakpoints in mice with chromosomal rearrangements. A direct application of these probes is demonstrated by identifying mice trisomic for distal Chr 16 using FISH analysis of interphase nuclei.

Real-time, three-dimensional echocardiography: feasibility of dynamic right ventricular volume measurement with saline contrast

BACKGROUND

The asymmetry and complex shape of the right ventricle have made it difficult to determine right ventricular (RV) volume with 2-dimensional echocardiography. Three-dimensional cardiac imaging improves visualization of cardiac anatomy but is also complex and time consuming. A newly developed volumetric scanning system holds promise of obviating past limitations.

METHODS

Real-time, transthoracic 3-dimensional echocardiographic images of the right ventricle were obtained with a high-speed volumetric ultrasound system that uses a 16:1 parallel processing schema from a 2.5 MHz matrix phased-array scanner to interrogate an entire pyramidal volume in real time. The instrumentation was used to measure RV volume in 8 excised canine hearts; dynamic real-time 3-dimensional images were also obtained from 14 normal subjects.

RESULTS

Three-dimensional images were obtained in vitro and in vivo during intravenous hand-agitated saline injection to determine RV volumes. The RV volumes by real-time 3-dimensional echocardiography are well correlated with those of drained in vitro (y = 1.26x - 9.92, r = 0.97, P <.0001, standard error of the estimate = 3.26 mL). For human subjects, the end-diastolic and end-systolic RV volumes were calculated by tracing serial cross-sectional, inclined C scans; functional data were validated by comparing the scans with conventional 2-dimensional echocardiographic indexes of left ventricular stroke volume.

CONCLUSIONS

These data indicate that RV volume measurements of excised heart by real-time 3-dimensional echocardiography are accurate and that beat-to-beat RV quantitative measurement applying this imaging method is possible. The new application of real-time 3-dimensional echocardiography presents the opportunity to develop new descriptors of cardiac performance.

X-linked adrenoleukodystrophy: genes, mutations, and phenotypes

X-linked adrenoleukodystrophy (X-ALD) is a complex and perplexing neurodegenerative disorder. The metabolic abnormality, elevated levels of very long-chain fatty acids in tissues and plasma, and the biochemical defect, reduced peroxisomal very long-chain acyl-CoA synthetase (VLCS) activity, are ubiquitous features of the disease. However, clinical manifestations are highly variable with regard to time of onset, site of initial pathology and rate of progression. In addition, the abnormal gene in X-ALD is not the gene for VLCS. Rather, it encodes a peroxisomal membrane protein with homology to the ATP-binding cassette (ABC) transmembrane transporter superfamily of proteins. The X-ALD protein (ALDP) is closely related to three other peroxisomal membrane ABC proteins. In this report we summarize all known X-ALD mutations and establish the lack of an X-ALD genotype/phenotype correlation. We compare the evolutionary relationships among peroxisomal ABC proteins, demonstrate that ALDP forms homodimers with itself and heterodimers with other peroxisomal ABC proteins and present cDNA complementation studies suggesting that the peroxisomal ABC proteins have overlapping functions. We also establish that there are at least two peroxisomal VLCS activities, one that is ALDP dependent and one that is ALDP independent. Finally, we discuss variable expression of the peroxisomal ABC proteins and ALDP independent VLCS in relation to the variable clinical presentations of X-ALD.

Cloning and characterization of a secreted frizzled-related protein that is expressed by the retinal pigment epithelium

The Wnt/frizzled cell signaling pathway has been implicated in the determination of polarity in a number of systems, including the Drosophila retina. The vertebrate retina develops from an undifferentiated neuroepithelium into an organized and laminated structure that demonstrates a high degree of polarity at both the tissue and cellular levels. In the process of searching for molecules that are preferentially expressed by the vertebrate retinal pigment epithelium (RPE), we identified secreted frizzled-related protein 5 (SFRP5), a member of the SFRP family that appears to act by modulating Wnt signal transduction. SFRP5 is highly expressed by RPE cells, and is also expressed in the pancreas. Within the retina, the related molecule SFRP2 is expressed specifically by cells of the inner nuclear layer. Thus, photoreceptors are likely to be bathed by two opposing gradients of SFRP molecules. Consistent with SFRP5 's postulated role in modulating Wnt signaling in the retina, it inhibits the ability of Xwnt-8 mRNA to induce axis duplication in Xenopus embryos. The human SFRP5 gene consists of three coding exons and it maps to chromosome 10q24.1; human SFRP2 maps to 4q31.3. Based on the biology and complementary expression patterns of SFRP2 and SFRP5, we suggest that they may be involved in determining the polarity of photoreceptor, and perhaps other, cells in the retina.

Revised genomic organization of FBN1 and significance for regulated gene expression

FBN1 encodes fibrillin-1, an extracellular matrix protein that is defective in Marfan syndrome. This gene is divided into 65 exons and was previously reported to be approximately 110 kb in length. The existence of 3 exons upstream of the exon containing the putative initiating methionine left open the possibility of alternative fibrillin-1 isoforms that vary at their N-termini. Detailed examination of YACs containing human FBN1 reveal that the gene is 200 kb, almost twice as large as previously thought. Characterization of the porcine FBN1 cDNA and 5' flanking sequence demonstrates extreme conservation between the pig and the human predicted proteins and argues against the possibility of alternative amino-terminal coding sequence. These data further our understanding of the regulatory requirements for gene expression and establish a framework for recombinant expression of fibrillin-1.

Assessment of regional wall motion abnormalities with real-time 3-dimensional echocardiography

Accurate characterization of regional wall motion abnormalities requires a thorough evaluation of the entire left ventricle (LV). Although 2-dimensional echocardiography is frequently used for this purpose, the inability of tomographic techniques to record the complete endocardial surface is a limitation. Three-dimensional echocardiography, with real-time volumetric imaging, has the potential to overcome this limitation by capturing the entire volume of the LV and displaying it in a cineloop mode. The purpose of this study was to assess the feasibility of using real-time 3-dimensional (RT3D) echocardiography to detect regional wall motion abnormalities in patients with abnormal LV function and to develop a scheme for the systematic evaluation of wall motion by using the 3-dimensional data set. Twenty-six patients with high-quality 2-dimensional echo images and at least 1 regional wall motion abnormality were examined with RT3D echocardiography. For 2-dimensional echocardiography, wall motion was analyzed with a 16-segment model and graded on a 4-point scale from normal (1) to dyskinetic (4), from which a wall motion score index was calculated. Individual segments were then grouped into regions (anterior, inferoposterior, lateral, and apical) and the number of regional wall motion abnormalities was determined. The RT3D echocardiogram was recorded as a volumetric, pyramid-shaped data set that contained the entire LV. Digital images, consisting of a single cardiac cycle cineloop, were analyzed off-line with a computerized display of the apical projection. Two intersecting orthogonal apical projections were simultaneously displayed in cineloop mode, each independently tilted to optimize orientation and endocardial definition. The 2 planes were then slowly rotated about the major axis to visualize the entire LV endocardium. Wall motion was then graded in 6 equally spaced views, separated by 30 degrees, yielding 36 segments per patient. A higher percentage of segments were visualized with 2-dimensional versus RT3D echocardiography (97% vs 83%, respectively, P <.001). With the use of the 2-dimensional echocardiographic results as the standard, RT3D echocardiography detected 55 (96%) of 57 regional wall motion abnormalities. Analysis of the RT3D echocardiograms resulted in 3 false-negative and 5 false-positive findings. The total number of regional wall motion abnormalities was correctly classified by RT3D echocardiography in 19 (73%) of 26 patients. RT3D echocardiography detected 11 of 13 anterior, 19 of 20 inferoposterior, 9 of 9 lateral, and 15 of 15 apical wall motion abnormalities. An excellent correlation was found between the 2 techniques for assessment of the regional wall motion score index (r = 0.89, P <.001). This initial clinical study demonstrates the feasibility and potential advantages of RT3D echocardiography for the assessment of regional LV function. Compared with 2-dimensional echocardiography, this new method permits recording of the entire LV in a single beat, allowing the extent and location of the regional wall motion abnormalities to be determined.

Genomic structure of PEX13, a candidate peroxisome biogenesis disorder gene

The peroxisome biogenesis disorders (PBDs) are a set of lethal genetic diseases characterized by peroxisomal metabolic deficiencies, multisystem abnormalities, mental retardation, and premature death. These disorders are genetically heterogeneous and are caused by mutations in genes, termed PEX genes, required for import of proteins into the peroxisomal matrix. We have previously reported the identification of human PEX13, the gene encoding the docking factor for the PTS1 receptor, or PEX5 protein. As such, mutations in PEX13 would be expected to abrogate peroxisomal protein import and result in PBD phenotypes. We report here the structure of the human PEX13 gene. PEX13 spans approximately 11 kb on chromosome 2 and contains four exons, one more than previously thought. The corrected PEX13 cDNA is predicted to encode a protein product with a molecular mass of 44,312 Da. We examined the ability of PEX13 expression to rescue the peroxisomal protein import defects of fibroblast cells representing all known PBD complementation groups. No complementation was observed, suggesting that this gene is not mutated in any set of existing patients. However, given that complementation group assignments have been determined for only a subset of PBD patients, it is possible that PEX13-deficient patients may exist at a low frequency within our existing PBD patient population or within ethnic groups underrepresented in our patient pool.

Isolation and characterization of the human gene encoding Ito: further diversity by alternative mRNA splicing

The transient outward K+ current (Ito) in the heart is responsible for the initial phase of repolarization and for setting the plateau voltage of the ventricular action potential. Recently, Kv4.3 has emerged as the leading candidate alpha-subunit gene that underlies Ito in larger mammals such as dogs and humans. We have cloned the human Kv4.3 homolog and describe a carboxyl-terminal splice variant that inserts 19 amino acids with a consensus protein kinase C (PKC) phosphorylation site into the protein after the last membrane-spanning segment. The coding region of Kv4.3 is comprised of at least five exons and is located on chromosome 1p13.3. In the basal state the basic biophysical properties of both of the splice variants are identical.

Region-specific FISH probes used to identify and characterize an interstitial paracentric inv(21)(q22.1q22.3)

Region-specific probes developed for the diagnosis of specific syndrome, can be adapted to elucidate the exact nature of certain chromosomal structural anomalies. We describe the use of FISH probes in characterizing a prenatally diagnosed chromosome rearrangement. An abnormal chromosome 21 was detected during amniocentesis for maternal age indication, and a similar appearing chromosome 21 was found in the mother. The exact nature of the rearrangement was not immediately evident from G-banded karyotypes. FISH was performed using a whole chromosome painting probe, as well as the region-specific probes D21S65 (21q21-22.1), D21S55 (21q22.3) and D21S1219/D21S1220 (21q22.3-qter) (Oncor). Results showed an interstitial paracentric inversion, with breakpoints in bands 21q22.1 and 21q22.3, which was identical in the mother and the fetus: 46,XX,?inv(21)(q).ish inv(21)(q22.1q22.3)(wcp+.D21S65 mv, D21S55 mv, D21S1219/D21S1220 st). In this case, FISH using region-specific probes was helpful in characterizing the inversion and aided in the genetic counselling of risk assessment for the family.

Immunolocalization of CENP-A suggests a distinct nucleosome structure at the inner kinetochore plate of active centromeres

The trilaminar kinetochore directs the segregation of chromosomes in mitosis and meiosis. Despite its importance, the molecular architecture of this structure remains poorly understood [1]. The best known component of the kinetochore plates is CENP-C, a protein that is required for kinetochore assembly [2], but whose molecular role in kinetochore structure and function is unknown. Here we have raised for the first time monospecific antisera to CENP-A [3], a 17 kD centromere-specific histone variant that is 62% identical to the carboxy-terminal domain of histone H3 [4,5] and that resembles the yeast centromeric component CSE4 [6]. We have found by simultaneous immunofluorescence with centromere antigens of known ultrastructural location that CENP-A is concentrated in the region of the inner kinetochore plate at active centromeres. Because CENP-A was previously shown to co-purify with nucleosomes [7], our data suggest a specific nucleosomal substructure for the kinetochore. In human cells, these kinetochore-specific nucleosomes are enriched in alpha-satellite DNA [8]. However, the association of CENP-A with neocentromeres lacking detectable alpha-satellite DNA, and the lack of CENP-A association with alpha-satellite-rich inactive centromeres of dicentric chromosomes together suggest that CENP-A association with kinetochores is unlikely to be determined solely by DNA sequence recognition. We speculate that CENP-A binding could be a consequence of epigenetic tagging of mammalian centromeres.

Segregation of a familial balanced (12;10) insertion resulting in Dup(10)(q21.2q22.1) and Del(10)(q21.2q22.1) in first cousins

An interchromosomal insertion in 3 generations of a family was ascertained through two developmentally delayed first cousins. Cytogenetic analysis using G-banding and chromosome painting showed an apparently balanced direct insertion of chromosome 10 material into chromosome 12, ins(12;10)(q15;q21.2q22.1), in the mothers and grandfather of these children. The proposita inherited only the derivative 10 chromosome, resulting in deletion of 10q21.2 --> 22.1 while her cousin inherited only the derivative 12, resulting in duplication of 10q21.2 --> 22.1. A comparison of the proposita with published deletion cases suggests a pattern of anomalies attributable to deletion of the 10q21 --> q22 region: developmental delay, hypotonia, a heart murmur, telecanthus, broad nasal root and ear abnormalities. This is the first report of a nontandem duplication of the 10q21 --> q22 region. The phenotype of the cousin with the duplication does not overlap greatly with published tandem 10q duplications. Finally, this report reaffirms the importance of obtaining family studies of patients with interstitial chromosomal abnormalities.

A paternally derived inverted duplication of 7q with evidence of a telomeric deletion

We report on a de novo constitutional rearrangement involving the long arm of chromosome 7 in a second trimester fetus with the karyotype of 46,XX, inv dup del (7)(pter-q36::q36-q21.2:) pat. Both a large duplication (q21.2-q36) and a small deletion (within q36) were confirmed by FISH studies. DNA analysis on the family showed that the abnormal chromosome was derived from a single paternal homolog. A mechanism is proposed in light of this finding. The phenotype at autopsy was consistent with reported cases of similar duplications in chromosome 7 in that hydrocephalus, a depressed nasal bridge, low set ears, microretrognathia and a short neck were present.

Ambiguous genitalia in an elderly woman with a mosaic 45,X/46,X,dic(Y)(Q11.2) karyotype

A 66-year-old woman presented with clitoromegaly since childhood, primary amenorrhea, no breast development, and a large right inguinal hernia. A mosaic karyotype was identified containing a predominant 45,X cell line and a cell line with 46 chromosomes, one X chromosome, and a small dicentric Y chromosome with a breakpoint in band qII.2. The patient underwent hysterectomy, bilateral gonadectomy, inguinal hernia repair, clitoral recession, and formation of a neointroitus. A dysgerminoma was identified in the right dysgenetic gonad. This report demonstrates the natural history of untreated mixed gonadal dysgenesis and the importance of early evaluation and treatment, as well as the molecular characterization of a dicentric Y chromosome.

Incidence and significance of chromosome mosaicism involving an autosomal structural abnormality diagnosed prenatally through amniocentesis: a collaborative study

Among 179,663 prenatal diagnosis cases collected from ten institutions and two publications, 555 (0.3 per cent) were diagnosed as having chromosome mosaicism. Of these, 57 (10.3 per cent) were mosaic for an autosomal structural abnormality, 28 (5 per cent) for a sex chromosome structural abnormality, and 85 (15.3 per cent) were mosaic for a marker chromosome. Ninety-five cases of prenatally diagnosed mosaicism with a structural abnormality in an autosome and a normal cell line, and with a known phenotypic outcome, were collected for karyotype-phenotype correlations through our collaboration (40 cases), a prior survey (26 cases), and published reports (29 cases). They included 13 balanced reciprocal translocations, one unbalanced reciprocal translocation, four balanced Robertsonian translocations, four unbalanced Robertsonian translocations, four inversions, 17 deletions, three ring chromosomes, 19 i(20q), seven +i(12p), six other isochromosomes, and 17 partial trisomies resulting from a duplication or other rearrangement. All cases mosaic for a balanced structural rearrangement resulted in a normal phenotype. All cases of 46/46,i(20q) resulted in normal liveborns. Five of seven cases with 46/47,+i(12p) had an abnormal phenotype compatible with Killian-Pallister syndrome. The overall risk for an abnormal outcome for a mosaic case with an unbalanced structural abnormality, excluding 46/46,i(20q) and 46/47,+i(12p), is 40.4 per cent. In the same category, the study also suggested a correlation between the percentage of abnormal cells and an abnormal phenotype. For mosaicism involving a terminal deletion, the possibility of a familial fragile site should be considered.

Alterations of yeast artificial chromosome transgenic sequences in stretched embryonic stem-cell chromatin visualized by fluorescence in situ hybridization

Transgenic mice have been generated from embryonic stem (ES) cells carrying functional genes cloned within yeast artificial chromosomes (YACs). Information on the integrity and organization of the inserted sequences, including the number of copies and their orientation to each other, is still limited by current methods. We have applied fluorescence in situ hybridization to stretched chromatin preparations from YAC-transfected ES cells to analyze the organization and copy number of the integrated sequences.

TRPC1, a human homolog of a Drosophila store-operated channel

In many vertebrate and invertebrate cells, inositol 1,4,5-trisphospate production induces a biphasic Ca2+ signal. Mobilization of Ca2+ from internal stores drives the initial burst. The second phase, referred to as store-operated Ca2+ entry (formerly capacitative Ca2+ entry), occurs when depletion of intracellular Ca2+ pools activates a non-voltage-sensitive plasma membrane Ca2+ conductance. Despite the prevalence of store-operated Ca2+ entry, no vertebrate channel responsible for store-operated Ca2+ entry has been reported. trp (transient receptor potential), a Drosophila gene required in phototransduction, encodes the only known candidate for such a channel throughout phylogeny. In this report, we describe the molecular characterization of a human homolog of trp, TRPC1. TRPC1 (transient receptor potential channel-related protein 1) was 40% identical to Drosophila TRP over most of the protein and lacked the charged residues in the S4 transmembrane region proposed to be required for the voltage sensor in many voltage-gated ion channels. TRPC1 was expressed at the highest levels in the fetal brain and in the adult heart, brain, testis, and ovaries. Evidence is also presented that TRPC1 represents the archetype of a family of related human proteins.

Magnetic orientation of spiny lobsters in the ocean: experiments with undersea coil systems

The western Atlantic spiny lobster Panulirus argus undergoes an annual migration and is also capable of homing to specific dens in its coral reef environment. Relatively little is known, however, about the orientation cues that lobsters use to guide their movements. To determine whether lobsters can orient to the earth's magnetic field, divers monitored the orientation of lobsters tethered inside magnetic coil systems submerged offshore in the Florida Keys, USA. Each coil could be used to reverse either the horizontal or vertical component of the earth's field. Tethered lobsters walking inside the coils often established and maintained consistent courses towards specific directions. After a lobster had established a course, it was exposed to one of three conditions: (1) a reversal of the horizontal component of the earth's field; (2) a reversal of the vertical component of the earth's field; or (3) no change in the ambient field (controls). Lobsters subjected to the horizontal field reversal deviated significantly from their initial courses. In contrast, control lobsters and those subjected to the reversed vertical field did not. These results demonstrate that spiny lobsters possess a magnetic compass sense. Because inverting the vertical component of the earth's field had no effect on orientation, the results suggest that the lobster compass is based on field polarity and thus differs from the inclination compasses of birds and sea turtles. The magnetic compass of lobsters may function in homing behavior, in guiding the autumn migration or in both.

Molecular characterization of a deleted X chromosome (Xq13.3-Xq21.31) exhibiting random X inactivation

As a result of selection following random X chromosome inactivation in human females, X chromosomes with visible deletions are usually inactive in every somatic cell. We have studied a female with mental retardation and dysmorphic features whose karyotype includes an X chromosome with a visible interstitial deletion in the proximal long arm. Based on cytogenetic analysis, the proximal breakpoint appeared to be in band Xq13.1, and the distal one in band q21.3. However, molecular analyses show that less of the q13 band is missing than cytogenetic studies indicated, as the deletion includes only loci from the region Xq13.3 to Xq21.31. Unexpectedly, studies of chromosome replication show that the pattern of X inactivation is random. Whereas the deleted X chromosome is late replicating in some cells from all tissues studied, it is early replicating in the majority of blood lymphocytes and skin fibroblasts, and is the active X chromosome in many of the hybrids derived from skin fibroblasts. As this chromosome is able to inactivate, it must include those DNA sequences from the X-inactivation center (XIC) that are essential for cis X inactivation. Molecular studies show that the XIC region, at Xq13.2, is present, so it is unlikely that the lack of consistent inactivation of this chromosome is attributable to close proximity of the breakpoint to the XIC. Supporting this conclusion is the similarity of the breakpoints to those of the other chromosomes we studied, whose deletions clearly do not interfere with the ability to inactivate. Our results show that deletions distal to DXS441 in Xq13.2 do not interfere with cis X inactivation. We attribute the random pattern of X inactivation reported here to the fact that in the tissues studied, cells with this interstitial deletion are not at a selective disadvantage.

An accessory marker derived from chromosome 20 and its co-existence with a mosaic trisomy 20 cell line

We report a 16-month-old boy with delayed psychomotor development, dysmorphic features, and failure to thrive. He had a mosaic karyotype detected prenatally: mos 46,XY/47,XY, +r(20)/47,XY, +20. After birth, the abnormal cell lines were confirmed in a number of tissues. The small ring chromosome was identified using fluorescence in situ hybridization as derived from chromosome 20. We compared our patient with previously reported cases of mosaic trisomy 20 detected prenatally and associated with an abnormal phenotype. In an attempt to characterize an r(20) syndrome, we also compared our case with two similar reports in the literature.

Molecular analysis of a complex chromosomal rearrangement and a review of familial cases

A complex chromosome rearrangement (CCR) involving chromosomes 7, 8, and 13 was detected in a phenotypically normal woman ascertained through her mentally retarded son with abnormal phenotype. He had a karyotype with 47 chromosomes including an extra der(13). In initial banding studies the CCR in the mother was interpreted as a three-way translocation. Fluorescence in situ hybridization with whole chromosome libraries and a telomere-specific probe was used to better characterize the rearrangement. Combined data allowed us to reinterpret the CCR as a translocation and an insertion. A review of 35 familial CCRs involving at least three chromosomes led to the following observations: 1) familial CCRs tend to have fewer chromosomes involved and fewer break-points than do de novo CCRs; 2) familial transmission is mainly observed through female carriers although the origin of de novo cases is paternal; 3) an apparent excess of balanced female carriers among the offspring of index carriers was noted; and 4) meiotic segregation resulting in malformed liveborn infants is most frequently due to adjacent-1 segregation, followed by 4:2 segregation; no adjacent-2 segregation was observed.

Unilateral renal hypoplasia and contralateral renal agenesis: a new association with 45,X/46,XY mosaicism

The association of urinary anomalies with Turner's syndrome is well established. This report describes an unusual antenatal presentation of this cytogenetic disorder and the first reported case of unilateral renal hypoplasia and contralateral renal agenesis in a 45,X/46,XY fetus. The fetus presented with severe third trimester oligohydramnios and symmetrical intrauterine growth retardation at 29 weeks and 2 days' gestation. Chorionic villus cultures revealed a 45,X karyotype. A phenotypically male infant weighing 1833 g was delivered at 35 weeks and 2 days. Chromosomal analysis of the newborn showed a 45,X/46,XY mosaicism, and surgical exploration revealed absence of the left kidney and a hypoplastic right kidney. The infant died at 11 months of age from renal failure and peritonitis. This case demonstrates that monosomy X may be encountered in fetuses with marked growth delay and oligohydramnios. The etiology of the oligohydramnios in this case was a fetal renal malformation not previously described in Turner's syndrome. Antenatal cytogenetic findings should be confirmed postnatally, with a search for mosaicism, when monosomy X is encountered.

Nonrandom inactivation of the Y-bearing X chromosome in a 46,XX individual: evidence for the etiology of 46,XX true hermaphroditism

We previously reported a subject with 46,XX true hermaphroditism who had a 46,X,del(X) karyotype and Y-chromosomal sequences in genomic DNA. We hypothesized that the Y-chromosomal sequences were translocated to the deleted X chromosome and that the incomplete testis determination of this individual was the result of inactivation of the translocated X chromosome. In situ hybridization studies demonstrated that the Y-chromosomal sequences were located on the distal portion of the short arm of the deleted X chromosome. Investigation of the replication of the X chromosome, using a modified R-banding technique and localization of Y-chromosomal sequences by in situ hybridization, showed that the translocated X chromosome was late replicating in all 100 EBV-transformed lymphoblasts that were examined. By contrast, when cells from a subject with 46,XX maleness were studied, the translocated X chromosome was late replicating in only 21 of 47 cells. As the late-replicating X chromosome is presumed to be the inactive X chromosome, selection of cells in which the Y-bearing X chromosome has been inactivated may play a role in the incomplete testis determination in subjects with "Y-positive" 46,XX true hermaphroditism.

Prenatal cytogenetic analysis of the fetus

A number of different cell sources can be used for prenatal cytogenetic analysis, the most common being chorionic villi and amniotic fluid. Analysis can be done at any time between 9 weeks' gestation and term. Depending on the cell source and type of analysis required, the laboratory will take anywhere from 24 hours to 2 weeks to complete the study.

A complex chromosomal rearrangement detected prenatally and studied by fluorescence in situ hybridization

We report of case of a complex chromosomal rearrangement detected prenatally and studied with traditional banding methods and fluorescence in situ hybridization. The combination of these techniques showed that four chromosomes were involved in the translocation. Nine breakpoints were proposed to explain these results. Some of the findings could only be detected with fluorescence in situ hybridization, demonstrating the usefulness of this technique in characterizing chromosomal abnormalities that would otherwise be difficult to interpret correctly with classical cytogenetics alone.

Unbalanced translocation, t(18;21), detected by fluorescence in situ hybridization (FISH) in a child with 18q- syndrome and a ring chromosome 21

We report on an 8-year-old girl with minor anomalies consistent with 18q- syndrome and mild developmental delay. Initially cytogenetics showed a terminal deletion of chromosome 21 with mosaicism for a small ring chromosome 21 as the only apparent karyotypic abnormality: mos 45,XX,-21/46,XX,+r(21) (48%/52%). Further studies including FISH and DNA analysis demonstrated a de novo unbalanced translocation of chromosomes 18 and 21 with the likely breakpoints in 18q23 and 21q21.1. Most of 21q was translocated to the distal long arm of one chromosome 18, and this derivative 18 appeared to lack 18q23-qter. The small ring chromosome 21 [r(21)], present in only 52% of the patient's blood lymphocytes, did not appear to be associated with the abnormal phenotype since all 13 chromosome 21 markers that were examined in genomic DNA were present in 2 copies, and the phenotype of the patient was consistent with the 18q- syndrome. The karyotype was reinterpreted as mos 45,XX,-18,-21,+der(18) t(18;21) (q23;q21.1)/46,XX,-18,-21,+der(18) t(18;21) (q23;q21.1), +r(21) (p13q21.1) (48%/52%). These results demonstrate the power of FISH in conjunction with DNA analysis for examination of chromosome rearrangements that may be misclassified by traditional cytogenetic studies alone.

The role of the sex-determining region Y gene in the etiology of 46,XX maleness

The condition of 46,XX maleness is characterized by testicular development in subjects who have two X chromosomes but who lack a normal Y chromosome. Several etiologies have been proposed to explain 46,XX maleness: 1) translocation of the testis-determining factor from the Y to the X chromosome, 2) mutation in an autosomal or X chromosome gene which permits testicular determination in the absence of TDF, and 3) undetected mosaicism with a Y-bearing cell line. We evaluated 10 affected subjects who were ascertained for different reasons and who had several distinct phenotypes. Six subjects had inherited sequences from the short arm of the Y chromosome including the sex-determining region Y gene (SRY). Five of the subjects were pubertal at the time of evaluation and had a phenotype similar to that of Klinefelter syndrome with evidence of Sertoli cell and Leydig cell dysfunction. One subject had evidence from Southern blot analysis and in situ hybridization for the presence of an intact Y chromosome in approximately 1% of cells. Three subjects lacked Y sequences by Southern blot analysis and by polymerase chain reaction amplification of SRY. These subjects were ascertained in the newborn period because of congenital anomalies. One had multiple anomalies including cardiac abnormalities; one had cardiac anomalies alone; and one had ambiguous genitalia. Our data confirm the genetic heterogeneity of 46,XX maleness, in which some subjects have SRY while other subjects lack it. In addition, there is phenotypic heterogeneity among subjects who lack SRY suggesting that there is also genetic heterogeneity within this subgroup.

Fetal ascitic fluid: a new source of lymphocytes for rapid chromosomal analysis

BACKGROUND

The cells found in ascites can be processed like amniotic fluid for fetal karyotyping. We have characterized these cells and used them for a rapid cytogenetic result.

CASES

Three patients presented with massive fetal ascites detected by sonography. Samples of ascitic fluid were obtained at fetal paracentesis. Cells from the fluid were cultured using standard methods for fetal blood, and were compared with fetal blood lymphocytes and amniocytes. The length of time in culture, chromosome morphology, and mitotic index of ascitic fluid cells were equivalent to those of fetal blood. In the third case, we performed immunophenotyping on the ascitic fluid cells.

CONCLUSION

Ascitic fluid contains lymphocytes that permit rapid chromosomal analysis within 96 hours.

Isolated fetal ascites detected by sonography: an unusual presentation of Turner syndrome

The prenatal sonographic diagnosis of Turner syndrome usually depends upon the discovery of a cystic hygroma or nonimmune hydrops fetalis. This report describes isolated fetal ascites as a newly recognized presentation of the disorder. Intrapartum fetal paracentesis permitted atraumatic vaginal birth. The etiology of the ascites in this case was congenital intestinal lymphangiectasia, consistent with the generalized lymphatic hypoplasia previously described in Turner syndrome.

Analysis of reciprocal translocations by chromosome painting: applications and limitations of the technique

Fluorescent in situ hybridization with chromosome-specific DNA libraries (chromosome painting) is an important new method for assessing chromosome rearrangements. In the research presented in this paper, two familial reciprocal translocations have been studied in the balanced and unbalanced forms, using both traditional G-banding techniques and chromosome painting. Although for each case two chromosomes were involved in the rearrangement, we found that only one chromosome library was suitable for detecting the translocation. These findings illustrate both the potential and the limitations of chromosome painting as a diagnostic tool in cytogenetics.

Prenatal identification of small mosaic markers of different chromosomal origins

In situ hybridization using a series of alphoid DNA probes has demonstrated the origin of two small accessory mosaic marker chromosomes ascertained from 1079 amniocenteses. These markers appeared to be de novo, derived from acrocentric chromosomes, and identical by traditional cytogenetic staining (G, Q, C, AgNOR, Hoechst-distamycin). Molecular characterization showed that one marker had originated from chromosome 14, the other from chromosome 22. Clinical outcome in both cases was normal.