Blaschkolinear malformation syndrome in complex trisomy-7 mosaicism.

Results of repeated peripheral blood chromosome studies were normal in a boy with intrauterine growth retardation, short stature, moderate mental retardation, and multiple minor anomalies. At age 9 years it was recognized that the swirls of pigmentation/depigmentation on his trunk, linear streaks on his limbs, and body asymmetry were suggestive of chromosomal mosaicism. Four skin biopsies were obtained under anesthesia during a dental procedure. All showed mosaicism for a normal cell line, a line with an extra chromosome 7, and a cell line with an extra small ring. In one biopsy, there was a fourth cell line with an extra chromosome 7 and the ring. Fluorescence in situ hybridization (FISH) with a chromosome 7 paint confirmed trisomy 7 and the chromosome 7 derivation of the ring. This young man's intra-uterine and postnatal growth retardation is an aneuploidy effect, whereas his asymmetry reflects a mosaicism effect that should have aroused suspicion of tissue-limited mosaicism before the development of obvious Blaschkolinear skin pigmentary dysplasia.

A common molecular basis for rearrangement disorders on chromosome 22q11.

The chromosome 22q11 region is susceptible to rearrangements that are associated with congenital anomaly disorders and malignant tumors. Three congenital anomaly disorders, cat-eye syndrome, der() syndrome and velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS) are associated with tetrasomy, trisomy or monosomy, respectively, for part of chromosome 22q11. VCFS/DGS is the most common syndrome associated with 22q11 rearrangements. In order to determine whether there are particular regions on 22q11 that are prone to rearrangements, the deletion end-points in a large number of VCFS/DGS patients were defined by haplotype analysis. Most VCFS/DGS patients have a similar 3 Mb deletion, some have a nested distal deletion breakpoint resulting in a 1.5 Mb deletion and a few rare patients have unique deletions or translocations. The high prevalence of the disorder in the population and the fact that most cases occur sporadically suggest that sequences at or near the breakpoints confer susceptibility to chromosome rearrangements. To investigate this hypothesis, we developed hamster-human somatic hybrid cell lines from VCFS/DGS patients with all three classes of deletions and we now show that the breakpoints occur within similar low copy repeats, termed LCR22s. To support this idea further, we identified a family that carries an interstitial duplication of the same 3 Mb region that is deleted in VCFS/DGS patients. We present models to explain how the LCR22s can mediate different homologous recombination events, thereby generating a number of rearrangements that are associated with congenital anomaly disorders. We identified five additional copies of the LCR22 on 22q11 that may mediate other rearrangements leading to disease.

Quantification by flow cytometry of chromosome-17 deletions in Smith-Magenis syndrome patients.

We have used bivariate flow karyotyping to quantify the deletions involving chromosome 17 in sixteen patients with Smith-Magenis syndrome (SMS). The fluorescence intensities of mitotic chromosomes stained with Hoechst 33258 and chromomycin were quantified in a dual-beam flow cytometer. For each patient, the position of the peak representing the deleted chromosome 17 was compared to those of the normal homologs of an unaffected parent. The patients could be classified into four groups based on the size of their deletions. The deletions ranged from approximately 9-10 Mb (approximately 10-11% of the chromosome) to below the detection limit of the technique (2 Mb). Different deletion sizes were detected among patients whose high-resolution banding results were similar. Some deletions detected by banding were not detected by flow analyses. Deletion estimates are largely consistent with the results of molecular analyses. Patients with larger deletions that extend into band 17p 12 have abnormal electrophysiologic studies of peripheral nerves. Deletion size does not appear to correlate with the degree of mental retardation, presence of behavioral abnormalities, craniofacial anomalies or common skeletal findings in SMS. By identifying patients with varying deletion sizes, these data will aid the construction of a long-range deletion-based map of 17p11.2 and identification of the genes involved in this syndrome.

The mouse and human excitatory amino acid transporter gene (EAAT1) maps to mouse chromosome 15 and a region of syntenic homology on human chromosome 5.

The gene for human excitatory amino acid transporter (EAAT1) was localized to the distal region of human chromosome 5p13 by in situ hybridization of metaphase chromosome spreads. Interspecific back-cross analysis identified the mouse Eaat1 locus in a region of 5p13 homology on mouse chromosome 15. Markers that are linked with EAAT1 on both human and mouse chromosomes include the receptors for leukemia inhibitory factor, interleukin-7, and prolactin. The Eaat1 locus appears not to be linked to the epilepsy mutant stg locus, which is also on chromosome 15. The EAAT1 locus is located in a region of 5p deletions that have been associated with mental retardation and microcephaly.

Microphthalmia with linear skin defects (MLS) syndrome: clinical, cytogenetic, and molecular characterization.

The microphthalmia with linear skin defects (MLS) syndrome (MIM 309801) is a severe developmental disorder observed in XX individuals with distal Xp segmental monosomy. The phenotype of this syndrome overlaps with that of both Aicardi (MIM 304050) and Goltz (MIM 305600) syndromes, two X-linked dominant, male-lethal disorders. Here we report the clinical, cytogenetic, and molecular characterization of 3 patients with this syndrome. Two of these patients are females with a terminal Xpter-p22.2 deletion. One of these 2 patients had an aborted fetus with anencephaly and the same chromosome abnormality. The third patient is an XX male with Xp/Yp exchange spanning the SRY gene which results in distal Xp monosomy. The extensive clinical variability observed in these patients and the results of the molecular analysis suggest that X-inactivation plays an important role in determining the phenotype of the MLS syndrome. We propose that the MLS, Aicardi, and Goltz syndromes are due to the involvement of the same gene(s), and that different patterns of X-inactivation are responsible for the phenotypic differences observed in these 3 disorders. However, we cannot rule out that each component of the MLS phenotype is caused by deletion of a different gene (a contiguous gene syndrome).

Transient myeloproliferative disorder of the Down type in the normal newborn.

Two infants with congenital nonlymphoblastic leukemia were discovered to have mosaicism for trisomy 21. Both infants achieved durable spontaneous remissions. Trisomy was apparently restricted to the leukemic clone and could be detected in neither phytohemagglutinin-stimulated peripheral blood cells or bone marrow in either patient nor in myeloid progenitor cells from the second patient after resolution of the transient myeloproliferative disorder. We conclude that spontaneous remission of congenital leukemia is not confined to infants with partial or complete systemic trisomy 21 but can occur in genetically normal newborns whose leukemic cells contain a third chromosome 21.

Molecular definition of a region of chromosome 21 that causes features of the Down syndrome phenotype.

Down syndrome (DS) is a major cause of mental retardation and heart disease. Although it is usually caused by the presence of an extra chromosome 21, a subset of the diagnostic features may be caused by the presence of only band 21q22. We now present evidence that significantly narrows the chromosomal region responsible for several of the phenotypic features of DS. We report a molecular and cytogenetic analysis of a three-generation family containing four individuals with clinical DS as manifested by the characteristic facial appearance, endocardial cushion defect, mental retardation, and probably dermatoglyphic changes. Autoradiograms of quantitative Southern blots of DNAs from two affected sisters, their carrier father, and a normal control were analyzed after hybridization with two to six unique DNA sequences regionally mapped on chromosome 21. These include cDNA probes for the genes for CuZn-superoxide dismutase (SOD1) mapping in 21q22.1 and for the amyloid precursor protein (APP) mapping in 21q11.2-21.05, in addition to six probes for single-copy sequences: D21S46 in 21q11.2-21.05, D21S47 and SF57 in 21q22.1-22.3, and D21S39, D21S42, and D21S43 in 21q22.3. All sequences located in 21q22.3 were present in three copies in the affected individuals, whereas those located proximal to this region were present in only two copies. In the carrier father, all DNA sequences were present in only two copies. Cytogenetic analysis of affected individuals employing R and G banding of prometaphase preparations combined with in situ hybridization revealed a translocation of the region from very distal 21q22.1 to 21qter to chromosome 4q. Except for a possible phenotypic contribution from the deletion of chromosome band 4q35, these data provide a molecular definition of the minimal region of chromosome 21 which, when duplicated, generates the facial features, heart defect, a component of the mental retardation, and probably several of the dermatoglyphic changes of DS. This region may include parts of bands 21q22.2 and 21q22.3, but it must exclude the genes S0D1 and APP and most of band 21q22.1, specifically the region defined by S0D1, SF57 and D21S47.

Down syndrome: toward a molecular definition of the phenotype.

Down syndrome (DS) is a major cause of mental retardation and heart disease. Although it is usually caused by the presence of an extra chromosome 21, a subset of the diagnostic features may be caused by the presence of only band q22. Molecular and cytogenetic analysis of a family with 4 DS members has significantly narrowed the chromosomal region responsible for the DS phenotype: congenital heart disease, facial features, and possibly dermatoglyphics. Using high-resolution chromosome banding and in situ hybridization, we found the DS phenotype in the family is caused by a duplication of chromosome 21 material including a region of distal band q22.1 below the limit of cytogenetic resolution, in addition to bands q22.2-q22.3. By quantitative Southern blot analyses of DS members of the family, all random DNA sequences and expressed genes mapping in band q22.1 and proximal are found not to be duplicated. These include cDNA probes for the genes for superoxide dismutase (SOD1) mapping in 21q22.1 and for the amyloid precursor protein (APP) mapping in 21q21.05; D21S46 in 21q11.2-21.05; and D21S47 and SF57 in 21q22.1-q22.3. With one exception, DNA sequences mapping in band q22.3 are duplicated (D21S39, D21SD42, and D21S43). This analysis has now been extended to show that D21S17, previously mapped to band 21q22.3, is not duplicated. In conclusion, the genes SOD1 and APP have been excluded from a necessary role in generating the classical DS features, and the proximal border of the chromosomal region causing DS has been defined.

Physical linkage of the genes for platelet membrane glycoproteins IIb and IIIa.

The fibrinogen receptor on human platelets is a prototypic member of the integrin family and is composed of subunit glycoproteins IIb (gpIIb) and IIIa (gpIIIa) in a 1:1 stoichiometric ratio. We have isolated cDNA clones for gpIIb and gpIIIa and localized both genes to chromosome 17. In the current study, several approaches were used to localize and map the genes for gpIIb and gpIIIa. A preliminary evaluation of subchromosomal localization was performed by using a panel of mouse-human somatic cell hybrids that contain different amounts of the long arm of human chromosome 17. Southern hybridization to the DNA of these hybrids shows that both genes map near the thymidine kinase gene. In situ hybridization to intact human chromosomes localized both genes to the 17q21-22 region. To better define the physical distance between the two genes, we examined the genomic hybridization pattern of each cDNA probe to high molecular weight restriction fragments separated by pulsed-field gel electrophoresis. Serial hybridizations of the same filter have allowed construction of long-range Mlu I and Sfi I restriction maps spanning more than 500 kilobases. Finally, nonoverlapping portions of the cDNAs for both gpIIb and gpIIIa were used to probe Sfi I digests of genomic DNA separated by field-inversion gels. This confirmed that the genes are physically linked within the same 260-kilobase Sfi I fragment and suggests that the gene for gpIIb is located on the 3' side of the gene for gpIIIa. These results suggest that coordinate expression of gpIIb and gpIIIa may depend on physical proximity.

The genes coding for human pro alpha 1(IV) collagen and pro alpha 2(IV) collagen are both located at the end of the long arm of chromosome 13.

We have isolated and characterized a cDNA clone containing DNA sequences coding for the noncollagenous carboxy-terminal domain of human pro alpha 2(IV) collagen. Using this cDNA clone in both Southern blot analysis of DNA isolated from human-mouse somatic-cell hybrids and in situ hybridization of normal human metaphase chromosomes, we have demonstrated that the gene coding for human pro alpha 2(IV) collagen is located at 13q33----34, in the same position on chromosome 13 as the pro alpha 1(IV) collagen gene.

A somatic cell hybrid panel for localizing DNA segments near the Huntington's disease gene.

Thirty-four random DNA probes from the terminal half of the human chromosome 4 short arm were further localized within 4pter----p15.1. A panel of somatic cell hybrid lines defining six chromosomal regions within 4pter----p15.1 was constructed using human cell lines containing translocation or deletion chromosomes. The vast majority of the DNA sequences, 32 of 34 or 94%, mapped to the three most proximal regions comprising 4p16.1----4p15.1. Only two probes were localized distal to 4p16.1: one in the region 4p16.3----4p16.1 and one in 4p16.3. D4S10, a polymorphic DNA marker linked to the Huntington's disease defect, has previously been mapped to the terminal region of 4p with conflicting assignments to 4p16.1 and 4p16.3. Analysis of restriction fragment length polymorphisms demonstrated hemizygosity for D4S10 in a patient with Wolf-Hirschhorn syndrome resulting from an unbalanced translocation t(4;8)(p16.3;p23.1), supporting the 4p16.3 localization. Our panel of somatic cell hybrids provides a rapid method for mapping new probes to the same vicinity as that of D4S10. However, the relative paucity of such DNA segments identified here suggests that a more directed approach may be required to generate additional markers near the HD gene.

Comparison of maternal and fetal chromosome heteromorphisms to monitor maternal cell contamination in chorionic villus samples.

Maternal cell contamination (MCC) presents a potential problem in the analysis of chorionic villus sampling (CVS) preparations for early prenatal diagnosis by chromosomal, biochemical and molecular methods. Through the comparison of fluorescent chromosome variants from CVS and maternal cells, we found three out of 50 samples to have MCC. One of these was observed on a direct preparation. Routine chromosome heteromorphism analysis is suggested as a reliable method for monitoring MCC in CVS specimens.

The single copy gene coding for human alpha 1 (IV) procollagen is located at the terminal end of the long arm of chromosome 13.

Using dual-laser sorted chromosomes and spot-blot analysis, we have previously assigned genomic DNA sequences coding for human alpha 1 (IV) procollagen to chromosome 13 (Pihlajaniemi et al. 1985). By in situ hybridization to normal chromosomes and chromosomes with 13q deletions, we now report the localization of this gene to the terminal end of the long arm of chromosome 13. In addition, Southern and slot blot hybridization analysis clearly show that these genomic sequences are present only once per haploid genome.

Interstitial deletion of (17)(p11.2p11.2) in nine patients.

We describe a new and distinct syndrome involving an interstitial deletion of short arm of chromosome 17 in nine unrelated patients (six males; three females) ranging in age from 3 months to 65 years. In eight patients, a deletion of a portion of band 17p11.2 was associated with a striking similar phenotype including brachycephaly, midface hypoplasia, prognathism, hoarse voice, and speech delay with or without hearing loss, psychomotor and growth retardation, and behavior problems. The one patient with a complete deletion of band 17p11.2 was more severely affected with facial malformations, cleft palate, and major anomalies of cardiac, skeletal, and genitourinary systems; the patient died at age 6 months. Careful cytogenetic analysis including high-resolution techniques will be important for the further identification of patients with this previously unrecognized deletion syndrome.

Characterization of the supernumerary chromosome in cat eye syndrome.

Most individuals with cat eye syndrome (CES) have a supernumerary bisatellited chromosome which, on the basis of cytogenetic evidence, has been reported to originate from either chromosome 13 or 22. To resolve this question, a single-copy DNA probe, D22S9, was isolated and localized to 22q11 by in situ hybridization to metaphase chromosomes. The number of copies of this sequence was determined in CES patients by means of Southern blots and densitometry analysis of autoradiographs. In patients with the supernumerary chromosome, four copies were found, whereas in one patient with a duplication of part of chromosome 22, there were three copies. Therefore, the syndrome results from the presence of either three or four copies of DNA sequences from 22q11; there is no evidence that sequences from other chromosomes are involved. This work demonstrates how DNA sequence dosage analysis can be used to study genetic disorders that are not readily amenable to standard cytogenetic analysis.

Translocation X;10 in a case of congenital acute monocytic leukemia.

Unusual cytogenetic findings were noted in the leukemic cells from a patient with congenital acute monocytic leukemia (AMol or M5, according to the FAB classification), whereas, the chromosomes of cultured skin fibroblasts were normal. G-banded karyotypes of leukemic cells showed an X-autosome translocation, 46,X,t(X;10)(Xpter----q13::10q11.2----qter)(10pter---- q11.2::Xq28----q13:: Xq28----qter). Review of reported cases of acute nonlymphocytic leukemia (ANLL) with rearrangements involving chromosomes #10 or X showed a high frequency of abnormalities of the short arm of #10 in myelomonocytic (M4) and monocytic (M5) leukemias, particularly in patients less than 2-yr-of-age. Although previously reported cases of ANLL in infants are predominantly of these types, the translocation observed in this case is unique. Fragile sites known to exist on chromosomes #10 and X are not associated with neoplasia and, except for Xq27-28, were not at the breakpoints of the case presented. The precise location of a human cellular oncogene recently identified on the X chromosome remains unknown.

Bone marrow transplantation for severe combined immune deficiency in an infant with chimerism due to intrauterine-derived maternal lymphocytes: donor engraftment documented by chromosomal marker studies.

Chromosomal heteromorphisms defined by the quinacrine banding technique were used to identify the maternal origin of 46,XX lymphocytes present in the blood of a male infant with severe combined immune deficiency disease. These chromosomal markers were also used to document the engraftment by donor lymphocytes from the sister and the concurrent disappearance of maternal lymphocytes after a successful bone marrow transplantation. Donor lymphocytes were detected by this technique 6 days after transplantation, earlier than is usually possible with other marker systems and before definite evidence of immunoreconstitution. Maternal lymphocytes persisted in the patient's peripheral blood for a prolonged period of time, being detectable 172 days after transplantation. Analysis of T-lymphocyte- and B-lymphocyte-enriched populations after transplantation documented lymphoid chimerism with T-lymphocytes of donor origin and B-lymphocytes of both patient and donor origin, demonstrating prolonged persistence of patient B-lymphocytes and suggesting that the patient's immune defect is primarily at the T-lymphocyte level.

Nonfluorescent Y chromosomes. Cytologic evidence of origin.

Twelve presumptive structurally altered Y chromosomes were studied with Q-, G-, G-11, C-, Cd, and lateral asymmetric banding techniques and were compared with normal X and Y chromosomes and with an abnormal [i(Yq)] Y chromosome that exhibited intact fluorescence. Significant to this work is the fact that the Y chromosome has a small block of Giemsa-11 heterochromatin adjacent to the centromere on the long arm, while the X chromosome does not, which allows a distinction between the X- and Y-derived chromosomes. Two of the twelve altered chromosomes of either X or Y origin are small nonfluorescent rings. Each ring has a G-11-positive band of heterochromatin at the centromere, confirming Y origin. Each of the normal-length nonfluorescent presumed Ys and a Y with a fluorescent band in the center have one G-11 band at the centromere and another at an equal distance from the end of the long arm, the bands also being Cd positive, indicating that these chromosomes are pseudodicentric. The likely mechanism of origin is a break at the distal bright heterochromatin/euchromatin junction (or within the bright segment in the chromosome with the bright center band), fusion of the sister chromatids at the breakpoints, and loss of the distal segment.