A polymorphic DNA sequence from the terminal part of chromosome 20q [D20S25]

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Genetic counselling in Duchenne and Becker muscular dystrophy is problematic when carrier studies give controversial results

DNA-analysis with flanking and intragenic markers gave confusing results in 7 out of 74 (9.5%) Finnish families with Duchenne or Becker muscular dystrophy. In five families a sister or maternal aunt of the patient had elevated serum creatine kinase (CK) activity, although DNA-analysis indicated a low risk for carriership. In one family the two affected brothers had different pERT87 alleles. In one family the intragenic deletion found in a patient was not present in his mother, who was an obligatory carrier. Deletions were detected with cDNA probes in the probands in five of the families, but the controversy regarding carriership still remained. It is necessary to combine all available data from pedigree analysis, CK measurements, and DNA studies whenever carrier studies are performed, but it appears that major problems in counselling and prenatal diagnosis will still remain in a proportion of the families.

An interspersed repeated sequence specific for human subtelomeric regions

A family of DNA loci (DNF28) from the pseudoautosomal region of the human sex chromosomes is characterized by a repeated element (STIR: subtelomeric interspersed repeat) which detects homologous sequences in the telomeric regions of human autosomes by in situ hybridization. Several STIR elements from both the pseudoautosomal region and terminal parts of autosomes were cloned and sequenced. A conserved 350 bp sequence and some characteristic structural differences between the autosomal and pseudoautosomal STIRs were observed. Screening of the DNA sequence databases with a consensus sequence revealed the presence of STIRs in several human loci localized in the terminal parts of different chromosomes. We mapped single copy probes flanking the cloned autosomal STIRs to the subtelomeric parts of six different chromosomes by in situ hybridization and genetic linkage analysis. The linkage data show a greatly increased recombination frequency in the subtelomeric regions of the chromosomes, especially in male meiosis. The STIR elements, specifically located in subtelomeric regions, could play a role in the peculiar recombination properties of these chromosomal regions, e.g. by promoting initiation of pairing at meiosis.

The etiology of XX sex reversal

The primary testis-determining function is exerted by a gene in the sex-determining region of the human Y chromosome. This gene is termed the sex-determining factor or TDF. A zinc finger gene, ZFY, residing in this region has been cloned and characterized. It is a candidate for TDF. A challenge to future molecular research is to clarify the function of a zinc finger gene on the X chromosome, ZFX, that shows high structural similarity to ZFY. Furthermore, the existence of other genes involved in sex determination is likely but so far unproven. Sex reversal leading to testes in apparently XX individuals (XX males) is most often due to the presence of TDF on the paternally derived X chromosome. The abnormality arises during meiosis in the father when an abnormal exchange leads to the transfer onto the X of the entire pseudoautosomal region plus a portion of the Y chromosome-specific region including TDF from the Y. An XX male resulting from such an exchange is described. 10-20% of XX males do not have Y DNA. Two major mechanisms to explain such Y(-) XX males are discussed. First, several published pedigrees show clear-cut dominant autosomal or X chromosomal inheritance of XX maleness. These patients are always Y(-) and usually have sexual ambiguity. This indicates the existence of other genes, obviously 'downstream' from TDF, that when mutated can trigger testis determination. Nothing concrete is presently known about these putative genes, but their phenotypic effect is slightly different from that of TDF. Second, mosaicism with a prevalent XX lineage and a hidden or scarce lineage containing a Y chromosome can explain some apparently Y(-) XX males. Two XX/XXY mosaic patients are described in detail. In one, only a combination of DNA hybridization and cytogenetic studies led to the discovery of the XXY cell line. In conclusion, XX sex reversal in man is caused by at least 3 mechanisms, viz. abnormal Y-X interchange, genes other than TDF, and mosaicism.

Molecular analysis of hemophilia A mutations in the Finnish population

We have examined the Finnish hemophilia A population for factor VIII gene mutations. This study included 83 unrelated patients and revealed 10 mutations associated with hemophilia. Using cloned cDNA, genomic, and oligonucleotide probes, we have identified three classes of mutations: five mutations causing the loss of TaqI restriction sites, a point mutation resulting in a new TaqI site, and four partial gene deletions. Although exons 5 and 6 were involved in three of the four partial gene deletions, the extent of the DNA lost differs in each case. The fourth deletion was located entirely within intron 1 and segregated with the disease in a large hemophilia pedigree. There was no history of hemophilia in eight of the 10 families. The origin of the mutation was determined in six of these pedigrees, two of which showed evidence for maternal mosaicism.

Marked amine and amine metabolite changes in Norrie disease patients with an X-chromosomal deletion affecting monoamine oxidase

Urinary and plasma amines and amine metabolites were quantified in two individuals with Norrie disease resulting from a deletion in chromosomal region Xp11.3, recently reported to be associated with absence of the gene encoding monoamine oxidase (MAO)-A and nondetectable MAO-A activity in fibroblasts and MAO-B activity in platelets. Marked (four-to 100-fold) elevations in levels of urinary phenylethylamine, o-tyramine, and m-tyramine (which are preferential substrates for MAO-B) and marked reductions (90%) in levels of 3-methoxy-4-hydroxyphenylglycol (a deaminated metabolite of norepinephrine, a preferential substrate for MAO-A) in urine and plasma confirmed the presence of a systemic, functionally significant reduction in the activities of both MAO isozymes. The magnitude of these changes, which are equivalent to those found in subjects taking MAO-inhibiting antidepressants, suggests that early initiation of dietary and drug restrictions may be clinically important in these and other patients with X-chromosomal mutations involving MAO. These findings further support the proposition that the MAOA and MAOB genes are located in close proximity on the X chromosome. Negligible changes in the metabolites of dopamine and serotonin raise the possibility that other metabolic pathways are of importance for their production, that dietary or intestinal bacterial sources contribute substantially to the presence of these amine metabolites in urine, or both.

Haplotype and multipoint linkage analysis in Finnish choroideremia families

Multipoint linkage analysis of choroideremia (TCD) and seven X chromosomal restriction fragment length polymorphisms (RFLPs) was carried out in 18 Finnish TCD families. The data place TCD distal to PGK and DXS72, very close to DXYS1 and DXYS5 (Zmax = 24 at theta = 0) and proximal to DXYS4 and DXYS12. This agrees with the data obtained from other linkage studies and from physical mapping. All the TCD males and carrier females studied have the same DXYS1 allele in coupling with TCD. In Northeastern Finland, 66/69 chromosomes carrying TCD had the same haplotype at loci DXS72, DXYS1, DXYS4, and DXYS12. The same haplotype is seen in only 15/99 chromosomes not carrying TCD. Moreover, in 71/104 non-TCD chromosomes, the haplotype at six marker loci is different from those seen in any of the 76 TCD chromosomes. This supports the previously described hypothesis that the large Northern Finnish choroideremia pedigrees, comprising a total of over 80 living patients representing more than a fifth of all TCD patients described worldwide, carry the same mutation. These linkage and haplotype data provide improved opportunities for prenatal diagnosis based on RFLP studies.

The gene encoding human low-molecular weight insulin-like growth-factor binding protein (IGF-BP25): regional localization to 7p12-p13 and description of a DNA polymorphism

The low-molecular weight insulin-like growth-factor binding protein (IGF-BP25) is synthesized by human liver, secretory endometrium and decidua, and is also present in human serum. It binds insulin-like growth factors IGF-I and IGF-II with high affinity, and is proposed to act as a paracrine regulator of cell growth. In situ hybridization studies with a cDNA encompassing the entire protein coding region of IGF-BP25 localized the gene to bands p12-p13 on chromosome 7. Southern blot analysis with the enzyme BglII revealed a common restriction fragment length polymorphism: the presence of the polymorphic BglII site results in the formation of two fragments 4.6 kb and 1.6 kb in size whereas its absence produces a single 6.2 kb fragment. The frequencies of the two alleles were 0.73 and 0.27, respectively. IGF-BP25 constitutes a useful genetic marker for the proximal short arm of chromosome 7.

Coincident maternal meiotic nondisjunction of chromosomes X and 21 without evidence of autosomal asynapsis

A family in which the proband showed phenotypic signs of both the Turner and Down syndromes was studied cytogenetically and with restriction fragment length polymorphisms. The proband's karyotype was 46,X,+21, showing double aneuploidy without any signs of mosaicism. The single X and one chromosome 21 were of paternal origin while two chromosome 21 were of maternal origin. The nondisjunction of chromosome 21 took place in maternal meiosis II. If it is assumed that the absence of mosaicism renders postzygotic mitotic loss of the X chromosome unlikely, then the X chromosome would have been lost in maternal meiosis I or II. Recombination had occurred between the nondisjoined chromosomes 21. We conclude that double nondisjunction took place in one patient and that asynapsis was not a prerequisite for the autosomal nondisjunction.

Norrie disease gene is distinct from the monoamine oxidase genes

The genes for MAO-A and MAO-B appear to be very close to the Norrie disease gene, on the basis of loss and/or disruption of the MAO genes and activities in atypical Norrie disease patients deleted for the DXS7 locus; linkage among the MAO genes, the Norrie disease gene, and the DXS7 locus; and mapping of all these loci to the chromosomal region Xp11. The present study provides evidence that the MAO genes are not disrupted in "classic" Norrie disease patients. Genomic DNA from these "nondeletion" Norrie disease patients did not show rearrangements at the MAOA or DXS7 loci. Normal levels of MAO-A activities, as well as normal amounts and size of the MAO-A mRNA, were observed in cultured skin fibroblasts from these patients, and MAO-B activity in their platelets was normal. Catecholamine metabolites evaluated in plasma and urine were in the control range. Thus, although some atypical Norrie disease patients lack both MAO-A and MAO-B activities, MAO does not appear to be an etiologic factor in classic Norrie disease.

Molecular studies of the sex chromosomes in human testicular cancer: pronounced changes in X and Y chromosome dosage in some tumors

Nine males with testicular germ cell tumors were studied by Southern blotting using probes recognizing different regions of the X and Y chromosomes. In the tumors of three patients, an imbalance was noted with a relative deficiency of DNA of Y-chromosomal and a concurrent excess of that of X-chromosomal origin. The X:Y signal ratios were 4, 4, and 2, respectively, in tumor DNA relative to normal DNA, and the ratios of Y to an autosomal locus were 0.4, 0.6, and 0.7, respectively, in the same tumors. Several loci on both arms of the Y chromosome were similarly involved. No structural abnormalities of Y chromosome DNA could be demonstrated. The X/Y change occurred in two of the three patients with nonseminomatous tumors and in two of the three patients with metastatic disease. To account for the results, two alternative models are discussed: first, loss of the Y chromosome and increase in X chromosome number in some but not all tumor cells; second, polyploidization with one Y chromosome and several X chromosomes.

Cystic fibrosis in Finland: a molecular and genealogical study

The incidence of cystic fibrosis (CF) in Finland is one tenth that in other Caucasian populations. To study the genetics of CF in Finland, we used a combined molecular and genealogical approach. Out of the 20 Finnish families with a living CF patient, 19 were typed for eight closely linked restriction fragment length polymorphisms (RFLP) at the MET, D7S8, and D7S23 loci. The birthplaces of the parents and grandparents were traced using population registries. Allele and haplotype frequencies in Finland are similar to those of other European and North American populations, but are modified by sampling: two regional CF gene clusters, evidently the results of a founder effect, were identified. Generally, the gene was evenly distributed over the population, carrier frequency being estimated at approximately 1.3%. We conclude that CF in Finland is caused by the common Caucasian mutation(s), and that the low frequency of the gene can be explained by a negative sampling effect and genetic drift.

Cytogenetic studies of 21 patients with acute lymphoblastic leukemia in relapse

Karyotypes of 21 patients, originally entered into the Third International Workshop on Chromosomes in Leukemia (3IWCL), were investigated in first, second and/or subsequent relapses. Karyotypes at diagnosis were related to the relapses in the following ways: normal to normal (N-N) (five cases); abnormal to normal (A-N) (two cases); abnormal to abnormal with no change (A-A) (five cases); abnormal to abnormal with clonal evolution (A-A+) (eight cases); and normal to abnormal (N-A) (one case). The A-A group comprised two each of t(4;11) and t(9;22) cases and one pseudodiploid case; included in this group were the only two patients who did not receive intensive treatment. Both A-N cases had been pseudodiploid at diagnosis. Clonal evolution A-A+ occurred in patients who had had 47-49 chromosomes or pseudodiploidy at diagnosis and was mainly due to the addition of structural change. The additional abnormalities were different in each case. The only de novo appearance of a clone (N-A) was in host cells in relapse following bone marrow transplantation. Clonal evolution occurred in patients who had been intensively treated and who relapsed late; the median time from diagnosis to relapse studied for the A-A group was 6 months and for the A-A+ group was 24 months. Survival following relapse was shorter for patients who had had a clonal abnormality at any time (median 10 months) than for those with no abnormality at diagnosis or in relapse (median 26 months).

The clinical significance of karyotype in acute myelogenous leukemia

To evaluate further the prognostic significance of karyotype at diagnosis of acute myelogenous leukemia (AML), we have made a follow-up study of 711 patients who were diagnosed between January 1, 1980, and March 31, 1982, and who were originally reported by the Fourth International Workshop on Chromosomes in Leukemia (4IWCL). Three different chromosomal classifications were evaluated, including presence of normal and abnormal metaphases (NN-AN-AA classification), a modification of the Chicago classification, and a complexity classification. All three chromosomal classifications were shown to correlate significantly with outcome in patients with de novo AML. Furthermore, the NN-AN-AA classification and the complexity classification had independent prognostic significance when age, sex, and FAB morphology were also considered in multivariate analyses of survival. These data provide further evidence that karyotype is an important factor in predicting the outcome of patients with AML.

Six-year follow-up of the clinical significance of karyotype in acute lymphoblastic leukemia

To evaluate the importance of pretreatment karyotype in predicting long-term outcome in acute lymphoblastic leukemia (ALL), we performed a follow-up study of the 329 patients from the Third International Workshop on Chromosomes in Leukemia. Living patients have now been followed a minimum of 6 years. Patients were divided into ten groups according to pretreatment karyotype: no abnormalities, one of the following structural abnormalities [the Philadelphia chromosome, rearrangements involving 8q24, t(4;11), 14q+, 6q-] or, in the remaining cases, modal number (less than 46, 46, 47-50, greater than 50). As previously reported for achievement and duration of complete remission, and overall survival, disease-free survival differed significantly (p less than 0.001) among chromosome groups for both adults and children. Among children, karyotype was an independent prognostic factor for predicting disease-free survival. Because of the long follow-up, we now have been able to utilize statistical models to estimate the percentage of patients cured, according to karyotype alone and combined with other risk factors. Adults with the highest likelihood of cure (21-33%) were those patients with FAB-L1, a leukocyte count of 50,000/microliters or less, and one of the following chromosome groups: greater than 50, 47-50, 6q-, or normal. In children these same characteristics were associated with the highest percentage of cure (58-71% cured). In addition, we identified several groups of children with less than 15% chance of cure who clearly need to be treated as high-risk patients at diagnosis. Future studies of patients who have received risk-adapted therapy based on these chromosome data are needed to determine if more intensive treatment will improve the outlook of patients with cytogenetically unfavorable types of ALL.

Cytogenetic studies of 103 patients with acute myelogenous leukemia in relapse

In order to investigate the cytogenetic patterns in relapsed acute myelogenous leukemia (AML), a clinical and cytogenetic follow-up of patients newly diagnosed for the Fourth International Workshop on Chromosomes in Leukemia (4IWCL) was evaluated at the 6IWCL. Information was received on 103 patients in relapse who were then classified into seven groups according to the diagnostic karyotype. These groups were: normal, t(8;21), t(15;17), +8, a single specific abnormality either numerical or structural other than those already listed, a single nonrandom or miscellaneous abnormality again either numerical or structural, and complex abnormalities. The patient's age, diagnostic FAB type, the number of relapses, the total survival time, and the karyotype in relapse were considered in each of these cytogenetic groups. The remission and survival rates were comparable in all groups except the +8 group, where patients relapsed earlier and had a shorter survival time. Multiple relapses occurred most frequently in the t(8;21) group, whereas none of the patients with t(15;17) relapsed more than once, although the total survival time was similar to the two groups. Thirty-nine percent of the patients relapsed with the same karyotype as at diagnosis. A more complex karyotype showing evolution was found in 53%, and 8% showed either a less-complicated karyotype or appeared to have reverted to normal. Numerical abnormalities in relapse frequently involved trisomy of chromosomes 8 and/or 21. There was a nonrandom development of 9q- with relapse in patients with t(8;21). A pericentric inversion of chromosome 4, and abnormality infrequently reported at diagnosis, was found in relapse in association with t(15;17), t(8;21), and +8 karyotypes. Changes considered to be typically secondary in nature involving 5q, 7q, and 12p were seen in only seven cases. Twenty-one patients who had an apparently normal karyotype at diagnosis remained normal in relapse, indicating that absence of clonal chromosome abnormality is a real observation in AML rather than a failure of detection.

Human bone marrow cytogenetics: growth factors stimulate metaphases for specific lineages

Fresh and/or frozen bone marrow cells from five healthy individuals and seven patients with myeloid leukemia were studied using growth factors and a cytogenetic technique which allows simultaneous analysis of karotype and cell lineage. Cell lineages were identified using monoclonal antibodies in an alkaline phosphatase antialkaline phosphatase staining method. In general, cultures stimulated with a colony stimulating factor containing conditioned medium (CSF) and erythropoietin (EPO) had a higher (approximately 2-fold) mitotic index (MI) than cultures without these growth factors (maximum 7.0 vs. 3.8 after 4-day culture). The significantly higher MI in cultures with growth factors was shown to result from an increase in both erythrocytic and granulocytic-monocytic mitoses. Every culture with CSF and EPO had more erythrocytic metaphases than the identical culture without these growth factors (mean erythrocytic MI 3.1 vs. 0.3, p = 0.01 in healthy subjects; 6.9 vs. 0, p = 0.05 in leukemia). In each of the three patients showing an increased MI where lineage-specific MI was studied, the granulocytic-monocytic MI increased (mean 4.0 vs. 2.1, p = 0.05). These data suggest that growth factors increase the number of metaphases available for cytogenetic analysis from fresh or frozen marrow, and may be used to stimulate metaphases from specific lineages.

The methylation pattern of normal and truncated amplified human c-myc oncogenes

COLO320DM and COLO320HSR are two human cell lines with 30-40-fold c-myc amplification. Half of the c-myc gene copies in COLO320DM are truncated and expressed as the predominant mRNA, while half are normal. Most c-myc copies in COLO320HSR are normal and expressed. Truncated c-myc genes are fully methylated, while the normal ones are fully demethylated irrespective of their stage of expression. The normal transcriptionally active c-myc from fibroblast cells is fully methylated, while c-myc from granulocytes (probably downregulated) is almost fully demethylated. These results indicate a lack of correlation between expression and the state of methylation for human c-myc oncogenes. Furthermore, exons 1 and 2 and intron 1 of c-myc are CpG-rich islands. Since these islands are constitutively demethylated, it is assumed that demethylation is the constitutive state and methylation the facultative state of the c-myc oncogene.

Determination of the breakpoints of 1;7 translocations in myelodysplastic syndrome by in situ hybridization using chromosome-specific alpha satellite DNA from human chromosomes 1 and 7

A whole-arm translocation involving the short arm of chromosome 7 and the long arm of chromosome 1 occurs nonrandomly in myelodysplastic syndrome and acute nonlymphocytic leukemia. In situ hybridization, using alpha satellite DNA specific for the centromeric regions of chromosomes 1 (probe pSD1-1) and 7 (probe p21-4), was performed to determine the exact breakpoints of the translocation. Both probes hybridized to the centromeric region of the translocation chromosome in metaphases from two patients with myelodysplastic syndrome. Both probes hybridized with approximately equal strength to either chromosome 1 or 7 and to the 1;7 translocation chromosome, suggesting that the t(1;7) had retained the chromosome-specific alpha satellite DNA from both chromosomes. These studies permit us to propose a new description, t(1;7)(cen;cen), for this translocation.

Monoamine oxidase deficiency in males with an X chromosome deletion

Mapping of the human MAOA gene to chromosomal region Xp21-p11 prompted our study of two affected males in a family previously reported to have Norrie disease resulting from a submicroscopic deletion in this chromosomal region. In this investigation we demonstrate in these cousins deletion of the MAOA gene, undetectable levels of MAO-A and MAO-B activities in their fibroblasts and platelets, respectively, loss of mRNA for MAO-A in fibroblasts, and substantial alterations in urinary catecholamine metabolites. The present study documents that a marked deficiency of MAO activity is compatible with life and that genes for MAO-A and MAO-B are near each other in this Xp chromosomal region. Some of the clinical features of these MAO deletion patients may help to identify X-linked MAO deficiency diseases in humans.

Chromosome 7 long arm deletion in myeloid disorders: a narrow breakpoint region in 7q22 defined by molecular mapping

The involvement of the erythropoietin (EPO), plasminogen activator inhibitor type I (PAI1), and multi-drug resistance (MDR2) genes located in chromosomal region 7q21-22 was studied in patients with myeloid disorders and with or without a chromosome 7 abnormality. Separated blood mononuclear cells and granulocytes from 21 patients were used in restriction fragment length polymorphism (RFLP) studies with gene-specific DNA probes. A marked weakness of one of the allelic bands was observed in granulocyte-derived DNA from heterozygous patients with monosomy 7. In four patients with a partial deletion of chromosome 7 long arm (7q-), marked weakness of an allelic band was observed in granulocyte-derived DNA with PAI1 probe (four heterozygous patients) and MDR2 probe (one heterozygous patient), implying deletion of these genes. In contrast, the EPO gene was not deleted in these patients, as demonstrated by the presence of two allelic bands of equal strength in granulocyte-derived DNA (two patients) or by gene dosage estimation (two patients). Two allelic bands of equal strength were also observed in three heterozygous patients with an arbitrary probe (pKV13) located in 7cen-q21.3. Unexpected hemizygosity or hybridization bands were not observed in any patient. We conclude that PAI1 and MDR2 are located distally of EPO in 7q22, and that none of these genes is commonly rearranged in myeloid disorders. The chromosome 7 long arm deletion breakpoint is located in a relatively narrow segment between the PAI1 and EPO genes in different patients. The deletion may involve a specific site in DNA, since the genetic distance between the PAI1 and EPO genes is only 3 cM.

The sex-determining zinc finger sequences in XY females of Akodon azarae (Rodentia, Cricetidae)

Wild populations of Akodon azarae comprise females with a karyotype indistinguishable from that of males. These individuals were formerly assumed to be Xx, the x being an X chromosome with a deletion of most of its long arm. By using a DNA probe derived from the testis-determining region of the human Y chromosome (comprising a candidate gene for the testis-determining factor, Y-linked zinc finger [ZFY]), we demonstrate that A. azarae gonosomally variant females are XY and not Xx. The ZFY sequences in A. azarae are amplified and located in two different families of EcoRI fragments derived from Y-chromosome DNA. No rearrangement or change in the state of methylation of ZFY or ZFX (X-linked zinc finger) sequences were found in XY females. We propose that sex reversal in A. azarae may be mediated by a gene or genes other than ZFX or ZFY.

Chromosome 7 long-arm deletions in myeloid disorders: terminal DNA sequences are commonly conserved and breakpoints vary

Deletions in the long arm of chromosome 7 are common recurrent abnormalities in secondary leukemias and myelodysplastic syndromes. To learn more about the basic mechanisms involved, we used Southern blot analysis to study four patients with different 7q--deletions to determine the exact break-points and to define the extent of the deletions. Several genes and DNA sequences from 16 different loci were found to be deleted, as judged by the absence or considerable weakening of an allelic band in granulocytic DNA in patients with constitutional heterozygosity. A terminal segment was present in each of the partially deleted chromosomes, as shown by heterozygosity for probes from the region 7q35----qter in granulocyte DNA. This indicated that the chromosome 7q deletions were interstitial, rather than terminal, in each of these patients. The length of the preserved terminal segment varied among the patients. Our results support gene loss as a mechanism contributing to leukemogenesis. Since the deletions are interstitial, hybrid genes may be formed at the junction, but the variation in breakpoints argues against the existence of a common hybrid gene of importance to the malignant process.

Linkage relationships and gene order around the locus for X-linked retinoschisis

X-linked recessive retinoschisis (RS) is a hereditary disorder with variable clinical features. The main symptoms are poor sight; radial, cystic macula degeneration; and peripheral superficial retinal detachment. The disease is quite common in Finland, where at least 300 hemizygous males have been diagnosed. We used nine polymorphic DNA markers to study the localization of RS on the short arm of the X chromosome in 31 families comprising 88 affected persons. Two-point linkage results confirmed close linkage of the RS gene to the marker loci DXS43, DXS16, DXS207, and DXS41 and also revealed close linkage to the marker loci DXS197 and DXS9. Only one recombination was observed between DXS43 and RS in 59 informative meioses, giving a maximum lod score of 13.87 at the recombination fraction .02. No recombinations were observed between the RS locus and DXS9 and DXS197 (lods between 3 and 4), but at neither locus was the number of informative meioses sufficient to provide reliable estimates of recombination fractions. The most likely gene order on the basis of multilocus analysis was Xpter-DXS85-(DXS207,DXS43)-RS-DXS41-DXS 164-Xcen. Because multilocus linkage analysis indicated that the most probable location of RS is proximal to DXS207 and DXS43 and distal to DXS41, these three flanking markers are the closest and most informative markers currently available for carrier detection.

Immunoglobulin kappa and lambda light chain dual genotype rearrangement in a patient with kappa-secreting B-CLL

The cytogenetics, immunophenotype and immunoglobulin gene rearrangements were analysed in a consecutive series of 56 patients with lymphoma or lymphatic leukaemia. One patient with B-CLL showed monoclonal rearrangements of the constant mu, kappa and lambda genes. The immunophenotype was kappa-secreting indicating expression of one immunoglobulin light kappa allele. Clones of kappa producing B-cells usually show germline lambda genes. The present case may thus be interpreted as a failure of the mechanisms controlling isotypic exclusion at the gene level. Further studies are needed to determine the frequency of such events and whether the patients show distinct clinical or other features.

Clonal chromosomal abnormalities showing multiple-cell-lineage involvement in acute myeloid leukemia

To determine whether one or more hematopoietic-cell lineages are involved in acute myeloid leukemia (AML), we designed a technique that simultaneously identifies a cell as malignant and determines its lineage. We used numerical clonal chromosomal abnormalities, which are readily detected, to indicate neoplasia, and monoclonal antibodies in an alkaline phosphatase-antialkaline phosphatase detection procedure to identify lineages as granulocytic-monocytic, erythrocytic, or megakaryocytic. Examination of bone marrow from 12 patients with AML showed metaphases of granulocytic-monocytic lineage with abnormal karyotypes in all patients. In seven patients, we also detected abnormal karyotypes in the erythrocytic or megakaryocytic lineage. In all four patients with monosomy 7, both granulocytic-monocytic and erythrocytic cells were affected. Two of four patients with trisomy 8 also had evidence of multiple-lineage involvement, but in two the erythrocytic lineage had normal karyotypes, suggesting an origin at a progenitor-cell stage committed to granulocytic-monocytic development. Multiple-lineage involvement was found in AML both arising de novo (four of five analyzable cases) and following another cancer (three of four analyzable cases). These data demonstrate multiple-lineage involvement in a high proportion of cases of AML and suggest that many cases originate from the multipotent hematopoietic cell or from an earlier progenitor cell.

Y;autosome translocations and mosaicism in the aetiology of 45,X maleness: assignment of fertility factor to distal Yq11

Three 45,X males have been studied with Y-DNA probes by Southern blotting and in situ hybridization. Southern blotting studies with a panel of mapped Y-DNA probes showed that in all three individuals contiguous portions of the Y chromosome including all of the short arm, the centromere, and part of the euchromatic portion of the long arm were present. The breakpoint was different in each case. The individual with the largest portion (intervals 1-6) is a fertile male belonging to a family in which the translocation is inherited in four generations. The second adult patient, who has intervals 1-5, is an azoospermic, sterile male. These phenotypic findings suggest the existence of a gene involved in spermatogenesis in interval 6 in distal Yq11. The third case, a boy with penoscrotal hypospadias, has intervals 1-4B. In situ hybridization with the pseudoautosomal probe pDP230 and the Y chromosome specific probe pDP105 showed that Y-derived DNA was translocated onto the short arm of a chromosome 15, 14, and 14, respectively. One of the patients was a mosaic for the 14p+ translocation chromosome. Our data and those reported by others suggest the following conclusions based on molecular studies in eight 45,X males: The predominant aetiological factor is Y;autosome translocation observed in seven of the eight cases. As the remaining case was a low-grade mosaic involving a normal Y chromosome, the maleness in all cases was due to the effect of the testis determining factor, TDF. There is preferential involvement of the short arm of an acrocentric chromosome (five out of seven translocations) but other autosomal regions can also be involved. The reason why one of the derivative translocation chromosomes becomes lost may be that it has no centromere.

Molecular characterization of a Y;15 translocation segregating in a family

We have used Y-specific and Y-derived DNA probes for in situ hybridization and Southern blotting analysis to characterize a Y;15 translocation showing normal Mendelian inheritance in a family. Cytogenetically there appeared to be an unbalanced translocation of Yqh to 15p; this translocation may be considered as a prototype of those translocations between Yq and the short arm of an acrocentric chromosome which have a population incidence of approximately 1 in 2,000. Our molecular studies showed that, in all probability, the breakpoints were near the border between Yq11.23 and Yq12, and in 15p11, respectively; the translocation is abbreviated t(Y;15)(q12;p11). Using the Y-specific probe pY431 in a quantitative Southern hybridization assay, normal females had no hybridization, female carriers and normal men had the same amount, and male carriers had twice that amount. Cytogenetic analysis and quantitative in situ hybridization using probes pY431 and pY3.4 were consistent with the hypothesis that the portion of Yq translocated to 15p comprised all of Yq12 and none of Yq11. The absence of Southern hybridization with probes specific for Yp and Yq11 confirmed this observation. Even though the family was ascertained through two brothers who both had schizophrenia and were carriers of the translocation, the clinical evaluation of a total of nine individuals with the translocation and five without it did not suggest its association with an abnormal phenotype.

Characterization of a (Y;4) translocation by DNA hybridization

A phenotypically normal male with azoospermia was found to have a translocation between the short arm of the Y chromosome and the distal long arm of a chromosome 4. By cytogenetic analysis it could not be determined whether the translocation was reciprocal, nor whether it was balanced. In situ DNA hybridization with two pseudoautosomal and one Y-specific probe demonstrated that the breakpoint was on distal Yp and that there was Y chromosome material on 4q. Thus the translocation was reciprocal and could be characterized as t(Y;4)(pll;q32). There was no evidence for loss of Y-DNA sequences as judged by Southern blotting with Y-DNA probes. Thus the translocation may be balanced. We conclude that DNA hybridization can be used to refine considerably the cytogenetic analysis of such translocations.

Monocytic involvement by monosomy 7 preceded acute myelomonocytic leukemia in a patient with myelodysplastic syndrome

Novel techniques were used to detect which cell lineages were affected by monosomy 7 in a patient who had myelodysplastic syndrome and later developed acute leukemia. The patient had had paroxysmal nocturnal hemoglobinuria for 20 years before developing refractory anemia with excess of blasts. Cytogenetic analysis at the myelodysplastic stage disclosed monosomy 7 in bone marrow mitoses. Restriction fragment length polymorphism analysis of fractionated white blood cells with the chromosome 7-specific probes MetH and MetD revealed that blood monocytes and most bone marrow erythroblasts but not blood granulocytes or lymphocytes were affected by monosomy 7. The patient later developed acute myelomonocytic leukemia with blast cells positive for markers of the myelomonocytic lineage but negative for granulocytic markers in a standard surface marker analysis. The leukemic blast cells had monosomy 7 as determined by direct cytogenetic investigation. Thus, the monocytes were found to be affected by monosomy 7 in this patient 8 months before her myelodysplastic syndrome progressed to acute myelomonocytic leukemia, and the affected cells had the same biologic markers at both stages of the disease.

Microdeletions in patients with X-linked muscular dystrophy: molecular-clinical correlations

The DNA from 68 patients with X-linked (Duchenne and Becker) muscular dystrophy belonging to 49 unrelated families was analyzed for microdeletions using 13 closely linked or gene-specific DNA-markers. Fourteen patients from eight families showed a deletion involving a least one of the markers used, giving a deletion frequency of 16%. The proportion of families with deletions was 36% in the Becker and 8% in the Duchenne form of the disease. With one exception, the extent of the deletion was different in different families. All living, affected males from the same family carried the same deletion. The extent or the localization of the deletion did not correlate with clinical features such as severity of disease or mental retardation.

Linkage studies in a new X-linked myopathy, suggesting exclusion of DMD locus and tentative assignment to distal Xq

We here report linkage studies in a family suffering from a recently described hereditary muscle disease named X-linked myopathy with excessive autophagy (XMEA). Significant lod scores excluding linkage to the Duchenne-Becker muscular dystrophy locus were found. Several other loci on the short and long arms of the X chromosome produced negative lod scores, whereas probe DX13-7 defining locus DXS15 showed no recombinants and a lod score of z = 0.903 at theta = .0. Further studies should be done to determine whether the gene for XMEA is (1) located at Xq and (2) caused by a mutation of the Emery-Dreifuss muscular dystrophy gene, which has been assigned to the same region.

Demethylation of two specific DNA sequences in expressed human immunoglobulin light kappa constant genes

We have analyzed the pattern of methylation of rearranged and germ line C kappa genes in DNA samples from human B-type chronic lymphatic leukemia lymphocytes and normal fibroblasts, and from granulocytes, T-, and non-T-lymphocytes separated from normal blood. C kappa alleles are flanked by one HpaII site on each side. Leukemic B-CLL DNA from five patients showed demethylation of these two sites in the productively rearranged allele and methylation of both sites in the nonexpressed allele whether rearranged or in germ-line configuration. Non-T-lymphocytes from normal individuals also showed part of the C kappa genes to have demethylation of both HpaII sites. On the other hand, C kappa genes from normal granulocytes, T-lymphocytes, and four of five fibroblast samples were methylated in one or both HpaII sites. We propose that in B-lymphocytes, demethylation of C kappa alleles is a specific event taking place in the expressed genes and being associated with an increased transcriptional activity of the gene. In addition to this specific demethylation, there is also an unspecific one that may appear in cells with silent C kappa genes and that do not modify the expression of the gene.

The sex-determining region of the human Y chromosome encodes a finger protein

The presence or absence of the Y chromosome determines whether a mammalian embryo develops as a male or female. In humans, genetic deletion analysis of "sex-reversed" individuals has identified a small portion of the Y chromosome necessary and sufficient to induce testicular differentiation of the bipotential gonad. We report the cloning of a 230-kilobase segment of the human Y chromosome that contains some or all of the testis-determining factor gene (TDF), the master sex-determining locus. The cloned region spans the deletion in a female who carries all but 160 kilobases of the Y. Certain DNA sequences within this region were highly conserved during evolution; homologs occur on the Y chromosomes of all mammals examined. In particular, homologous sequences are found within the sex-determining region of the mouse Y chromosome. The nucleotide sequence of this conserved DNA on the human Y chromosome suggests that it encodes a protein with multiple "finger" domains, as first described in frog transcription factor IIIA. The encoded protein probably binds to nucleic acids in a sequence-specific manner, and may regulate transcription. Very similar DNA sequences occur on the X chromosome of humans and other mammals. We discuss the possibility that the Y-encoded finger protein is the testis-determining factor, and propose models of sex determination accommodating the finding of a related locus on the X chromosome. The presence of similar sequences in birds suggests a possible role not only in the XX/XY sex determination system of mammals, but also in the ZZ/ZW system of birds.

Linkage, physical mapping, and DNA sequence analysis of pseudoautosomal loci on the human X and Y chromosomes

The pseudoautosomal region of the human X and Y chromosomes is subject to frequent X-Y recombination during male meiosis. We report the finding of two pseudoautosomal loci, DXYS20 and DXYS28, characterized by highly informative restriction fragment length polymorphisms (RFLPs). The pseudoautosomal character of DXYS20 and DXYS28 was formally demonstrated by comparing their transmission to 45,X and to normal individuals. Studies of the inheritance of these loci reveal that the pseudoautosomal region, though highly recombinogenic, is subject to marked recombinational interference in male meiosis; no double recombinants were observed in 143 triply informative meioses, and the coefficient of coincidence is likely less than 0.45. In female meiosis, linkage of these pseudoautosomal RFLPs to strictly sex-linked RFLPs on the short arm of the X is readily detected; the genetic length of the pseudoautosomal region in female meiosis is at least 4 cM but not more than 18 cM. The genetic map of the human X chromosome is now defined from near the short-arm telomere to band q28 on the long arm. Locus DXYS20, which maps near the X and Y short-arm telomeres, is composed of long tandem arrays of 61-bp repeats. Occasional, seemingly random base-pair substitutions within these arrays of 61-bp repeats, in combination with marked variation in the size of the array, generate the high degree of DNA polymorphism at DXYS20.

Molecular characterization of chromosome 7 long arm deletions in myeloid disorders

Partial deletion of the long arm of chromosome 7 is a common abnormality in the bone marrow cells of patients with myelodysplastic syndrome (MDS) or acute nonlymphocytic leukemia (ANLL). This study was undertaken to characterize the chromosome breakpoints in molecular terms and to determine if hemizygosity or submicroscopic deletions occur in patients without any cytogenetically detectable abnormality of chromosome 7. We studied restriction fragment length polymorphisms with 10 chromosome 7-specific DNA probes in separated WBC fractions. No molecular abnormalities occurred in lymphocyte-derived DNA. Several probes located in band 7q22 or distally thereof detected deletion of one allele in granulocyte-derived DNA from all four patients with chromosome 7 long arm deletion. In the granulocytes of one patient heterozygosity for the T cell receptor beta chain gene (in band 7q35) indicated that the deletion was interstitial. NJ-3, a proalpha2(I)collagen gene probe (in band 7q21-22) detected heterozygosity in the granulocytes of one patient. No hemizygosity or deletions were found in four patients with two normal chromosomes 7. These results confirm that mature granulocytes but not lymphocytes are derived from the abnormal clone. Interstitial deletions exist, and the extent of deleted genomic material varies among patients.

Monosomy 7 predisposes to diabetes insipidus in leukaemia and myelodysplastic syndrome

We studied the chromosomes in the bone marrow of 4 patients who had both diabetes insipidus (DI) and acute non-lymphocytic leukaemia. Clinical findings suggested that, in each case, myelodysplastic syndrome had preceded the onset of acute leukaemia. Two other such patients described in the literature had had a banded karyotype study of bone marrow cells. All 6 patients had deletions of chromosome 7. 3 had monosomy 7 as the sole cytogenetic abnormality, 2 had monosomy 7 associated with other clonal abnormalities and 1 had del(7)(q22) in association with other abnormalities. These data suggest that monosomy 7 or perhaps monosomy for 7q22-qter predisposes to DI. The mechanism by which the proposed predisposition is produced remains to be clarified.

The inheritance of fragile sites: apparent absence of fra(2)(q13) in the parents of three unrelated probands

We describe the inherited folate sensitive fragile site, fra(2)(q13), in three unrelated mentally retarded children, two of them with different forms of epilepsy. Fra(2)(q13) was detected in one healthy sib of one of the probands. Except for one cell in one of the fathers, fra(2)(q13) could not be detected in any of the six parents, who were repeatedly studied using methods known to induce fragile sites of this type. These findings suggest that fra(2)(q13) is not associated with the clinical features of our patients and can be transmitted by persons not expressing it. The expression of fra(2)(q13) may be age dependent.

Linked polymorphic DNA markers in the prediction of X-linked muscular dystrophy

Ten polymorphic DNA markers, including gene specific markers of loci DXS164 and DXS206, were tested for allele frequencies, degree of heterozygosity and linkage in 34 Finnish families with X-linked muscular dystrophy. With the exception of the BamHI RFLP of DXS164 subclone pERT87-15, allele frequencies and the degree of heterozygosity failed to show any significant deviation from the data published elsewhere. We document a high degree of linkage disequilibrium between several RFLPs belonging to locus DXS164. Our linkage data include one recombination between DMD and DXS164 enabling a tentative location of the mutation site distal to DXS164. The maximum lod score for linkage between the disease locus and DX164 was 7.828 at a recombination fraction of 0.02. According to our data DXS28 and DXS43 may be located further away from the disease locus than previously thought. We use only gene specific markers for genetic counselling. Excluding deletions, 97.1% of women were heterozygous for at least one such marker. A diagnostic procedure in which useful information can be obtained in over 90% of all diagnostic situations, using only four filters, is proposed.

An XXX male resulting from paternal X-Y interchange and maternal X-X nondisjunction

A 2-year-old boy was found to have a 47,XXX karyotype. Restriction-fragment-length-polymorphism analysis showed that, of his three X chromosomes, one is of paternal and two are of maternal origin. The results of Y-DNA hybridization were reminiscent of those in XX males in two respects. First, hybridization to Southern transfers revealed the presence in this XXX male of sequences derived from the Y-chromosomal short arm. Second, in situ hybridization showed that this Y DNA was located on the tip of the X-chromosomal short arm. We conclude that this XXX male resulted from the coincidence of X-X nondisjunction during maternal meiosis and aberrant X-Y interchange either during or prior to paternal meiosis.

Prenatal diagnosis of X-linked chronic granulomatous disease using restriction fragment length polymorphism analysis

Prenatal diagnosis of X-linked chronic granulomatous disease (CGD) was performed with restriction fragment length polymorphism (RFLP) analysis using probes flanking the gene. The male fetus and an affected male displayed the same haplotype for RFLPs belonging to six linked loci extending from DXS164 to DXS7, which encompass the CGD locus, and for which the mother was heterozygous. Diagnosis of an affected fetus was confirmed after termination of the pregnancy by the study of fetal granulocytes using the nitroblue tetrazolium reduction test. In informative families prenatal diagnosis of CGD can be made earlier by RFLP analysis than by fetal blood sampling.

X-linked retinoschisis is closely linked to DXS41 and DXS16 but not DXS85

A linkage study was carried out in nine families with 24 males affected by X-linked recessive retinoschisis (RS), using three polymorphic DNA probes from the distal segment of Xp. Close linkage of the disease locus with markers DXS41 (probe p99-6) and DXS16 (pXUT23) was found, confirming the location of the RS gene on the distal short arm of the X chromosome. Lod scores for linkage with DXS85 (probe 782) were negative.

The pattern of methylation in rearranged and germ-line human immunoglobulin constant mu genes

Human C mu genes show two different patterns of demethylation. The first is associated with gene expression; this pattern is restricted to productive C mu alleles and is detected in leukemic and normal B-lymphocytes but not in T-lymphocytes, granulocytes or fibroblasts. The second pattern, not related with gene expression, is observed in B-lymphocytes, fibroblasts and part of T-lymphocytes but not in granulocytes.

Chromosome abnormalities in peripheral T-cell lymphoma

We have studied neoplastic lymph nodes from six patients histologically, immunologically and cytogenetically. Histologically all the cases were classified as peripheral T-cell lymphomas. These were subclassified as T-zone lymphomas in three, large cell 'pale cell' variant in one, large cell immunoblastic in one, and small cell, mycosis fungoides in one. Two had features of angioimmunoblastic lymphadenopathy (AILD). Immunologically all cases expressed CD2 (OKT11) and CD4 (T4). All six cases had clonal chromosome abnormalities, although in four cases the majority of cells were chromosomally normal. Chromosome 3 was most often involved in abnormalities, occurring in five patients. The most common single chromosome abnormality, trisomy 3, was seen in all three cases classified as T-zone lymphoma and in no other cases. In the two cases with features of AILD only numerical abnormalities were seen, whereas in the other cases complicated structural rearrangements were present. Recurring structural abnormalities involved bands 1p12or13, 1q32, 3p25 and 14q11. Our data suggest that cytogenetic analysis may assist in diagnosis and classification of the peripheral T-cell lymphomas.

Exchange of terminal portions of X- and Y-chromosomal short arms in human XX males

In most human 'XX males', DNA sequences normally found on Yp, the short arm of the Y chromosome, are present on Xp, the short arm of the X chromosome. To establish whether this transfer involves a terminal portion of Yp, and whether a terminal portion of Xp is lost in the process, we followed the inheritance of pseudoautosomal restriction fragment length polymorphisms in two XX-male families. One XX male apparently inherited the entire pseudoautosomal region of his father's Y chromosome and no part of the pseudoautosomal region of his father's X chromosome. The second XX male also inherited the entire pseudoautosomal region of his father's Y, but in addition inherited a proximal portion of the pseudoautosomal region of his father's X. These findings argue that XX males result from the transfer of a terminal portion of Yp onto Xp in exchange for a terminal portion of Xp (ref. 7). This implies that the testis-determining factor gene (TDF) maps distally in the strictly sex-linked portion of Yp, near the pseudoautosomal domain. The XX males described here appear to result from single (and, at least in the second case, unequal) crossovers proximal to the pseudoautosomal region on Yp and proximal to or within the pseudoautosomal region on Xp.