Showing papers in "Human Genetics in 1990"

Detection of 98% of DMD/BMD gene deletions by polymerase chain reaction

Abstract: We describe oligonucleotide primer sequences that can be used to amplify eight exons plus the muscle promoter of the dystrophin gene in a single multiplex polymerase chain reaction (PCR). When used in conjunction with an existing primer set, these two multiplex reactions detect about 98% of deletions in patients with Duchenne or Becker muscular dystrophy (DMD, BMD). Furthermore, these primers amplify most of the exons in the deletion prone “hot spot” region around exons 44 to 53, allowing determination of deletion endpoints and prediction of mutational effects on the translational reading frame. Thus, use of these PCR-based assays will allow deletion detection and prenatal diagnosis for most DMD/BMD patients in a fraction of the time required for Southern blot analysis.

The mutational spectrum of single base-pair substitutions causing human genetic disease: patterns and predictions.

Abstract: Reports of single base-pair substitutions that cause human genetic disease and that have been located and characterized in an unbiased fashion were collated; 32% of point mutations were CG → TG or CG → CA transitions consistent with a chemical model of mutation via methylation-mediated deamination. This represents a 12-fold higher frequency than that predicted from random expectation, confirming that CG dinucleotides are indeed hotspots of mutation causing human genetic disease. However, since CG also appears hypermutable irrespective of methylation-mediated deamination, a second mechanism may also be involved in generating CG mutations. The spectrum of point mutations occurring outwith CG dinucleotides is also non-random, at both the mono- and dinucleotide levels. An intrinsic bias in clinical detection was excluded since frequencies of specific amino acid substitutions did not correlate with the ‘chemical difference’ between the amino acids exchanged. Instead, a strong correlation was observed with the mutational spectrum predicted from the experimentally measured mispairing frequencies of vertebrate DNA polymerases α and β in vitro. This correlation appears to be independent of any difference in the efficiency of enzymatic proofreading/mismatch-repair mechanisms but is consistent with a physical model of mutation through nucleotide misincorporation as a result of transient misalignment of bases at the replication fork. This model is further supported by an observed correlation between dinucleotide mutability and stability, possibly because transient misalignment must be stabilized long enough for misincorporation to occur. Since point mutations in human genes causing genetic disease neither arise by random error nor are independent of their local sequence environment, predictive models may be considered. We present a computer model (MUTPRED) based upon empirical data; it is designed to predict the location of point mutations within gene coding regions causing human genetic disease. The mutational spectrum predicted for the human factor IX gene was shown to resemble closely the observed spectrum of point mutations causing haemophilia B. Further, the model was able to predict successfully the rank order of disease prevalence and/or mutation rates associated with various human autosomal dominant and sex-linked recessive conditions. Although still imperfect, this model nevertheless represents an initial attempt to relate the variable prevalence of human genetic disease to the mutability inherent in the nucleotide sequences of the underlying genes.

R-banding and nonisotopic in situ hybridization: precise localization of the human type II collagen gene (COL2A1)

Abstract: A new mapping system, based on nonisotopic in situ hybridization combined with fluorescent staining of replicated prometaphase R-bands, is described. Replication of the bands is achieved by treatment of thymidinesynchronized cells with bromodeoxyuridine. The human COL2A1 gene was mapped to band 12q13.11–q13.12 in this manner, to illustrate the potential of the technique for improving the precision of chromosomal mapping and physical ordering of genes.

Potential genetic functions of tandem repeated DNA sequence blocks in the human genome are based on a highly conserved “chromatin folding code”

Abstract: This review is based on a thorough description of the structure and sequence organization of tandemly organized repetitive DNA sequence families in the human genome; it is aimed at revealing the locusspecific sequence organization of tandemly repetitive sequence structures as a highly conserved DNA sequence code. These repetitive so-called “super-structures” or “higher-order” structures are able to attract specific nuclear proteins. I shall define this code therefore as a “chromatin folding code”. Since locus-specific superstructures of tandemly repetitive sequence units are present not only in the chromosome centromere or telomere region but also on the arms of the chromosomes, I assume that their chromatin folding code may contribute to, or even organize, the folding pathway of the chromatin chain in the nucleus. The “chromatin folding code” is based on its specific “chromatin code”, which describes the sequence dependence of the helical pathway of the DNA primary sequence (i.e., secondary structure) entrapping the histone octamers in preferential positions. There is no periodicity in the distribution of the nucleosomes along the DNA chain. The folding pathway of the nucleosomal chromatin chain is however still flexible and determined by e.g., the length of the DNA chain between the nucleosomes. The fixation and stabilization of the chromatin chain in the space of the nucleus (i.e., its “functional state”) may be mediated by additionally unique DNA protein interactions that are dictated by the “chromatin folding code”. The unique DNA-protein interactions around the centromeres of human chromosomes are revealed for example by their “C-banding”. I wish to stress that it is not my aim to relate each block of repetitive DNA sequences to a specific “chromatin folding code”, but I shall demonstrate that there is an inherent potential for tandem repeated sequence units to develop a locus-specific repetitive higher order structure; this potential may create a specific chromatin folding code whenever a selection force exists at the position of this repetitive DNA structure in the genome.

The critical region on the human Xq

Abstract: Adult female carriers of balanced X; autosome translocations (118 cases) and of balanced X inversions (31 cases) have been collected from the literature. Forty-five of the 118 translocation carriers in whom the break was in the critical region (Xq13–q22, Xq22–q26, separated by a narrow region within Xq22) showed gonadal dysgenesis. Seven of the 31 inversion carriers in whom the break was in the same region also had gonadal dysgenesis, whereas the remaining 24 were normal in this respect. The critical region consists mainly of Q-bright material, and is the fifth brightest segment in the human genome. The region contains relatively few genes. It is possible that meiotic crossing-over, rarely, if ever, takes place in it. The critical region may therefore consist of two “supergenes” whose integrity must be maintained to allow normal ovarian development. The effect exerted by this region differs from other known position effects, in that it is independent of the break-point within the region and of the chromosome bands to which the broken ends are attached. One possible mechanism causing this effect might be a change in the replication order of the chromosome bands, which, in turn, might affect their function.

Clinical and genetic heterogeneity in retinitis pigmentosa

Abstract: The clinical course of defective vision and blindness has been investigated in relation to different modes of genetic transmission in a large series of 93 families with retinitis pigmentosa (RP). For autosomal dominant RP, two clinical subtypes could be distinguished according to the delay in macular involvement. In the severe form, macular involvement occurred within 10 years, while in the mild form, macular involvement occurred after 20 years. Interestingly, a significant increase of mean paternal age (38.8 years, mean controls in France = 29.1 years, P < 0.001) was found in this form of RP, a feature which is suggestive of new mutations. For autosomal recessive RP, four significantly different clinical subtypes could be recognized, according to both age of onset and the pattern of development (P < 0.001), namely cone-rod dystrophy and early-onset severe forms on the one hand (mean age of onset = 7.6 years), late-onset mild forms and senile forms on the other. Similarly, two significantly different clinical subtypes could be recognized in X-linked RP, according to both mode and age of onset, which were either myopia (mean age = 3.5±0.5 years) or night blindness (mean age = 10.6±4.1 years, P < 0.001). By contrast, no difference was noted regarding the clinical course of the disease, which was remarkably severe whatever the clinical subtype (blindness before 25 years). In addition, all obligate carriers in our series were found to have either severe myopia or pigment deposits in their peripheral retina. Finally, sporadic RP represented the majority of cases in our series (42%). There was a considerable heterogeneity in this group, and at least three clinical forms could be recognized, namely cone-rod dystrophy, early onset-severe forms and late onset moderate forms. At the beginning of the disease, the hereditary nature of the sporadic forms was very difficult to ascertain (especially between 7–10 years) and only the clinical course could possibly provide information regarding the mode of inheritance. However, the high level of consanguinity, and the high sex ratio in early onset and severe sporadic forms (including cone-rod dystrophy), was suggestive of an autosomal or X-linked recessive inheritance, while increased paternal age in late onset forms was suggestive of autosomal dominant mutations.

Fetal hemoglobin in normal adults and β-thalassemia heterozygotes

Abstract: A recently developed high performance liquid chromatographic (HPLC) procedure using a weak cation exchanger (PolyCAT) in columns of different sizes was used to quantify fetal hemoglobin (Hb F) in blood of normal adults and β-thalassemia (β-thal) heterozygotes with ten different types of mutations. Preparative PolyCATHPLC greatly facilitated the characterization of isolated Hb F, i.e., the determination of the relative quantities of the Gγ and Aγ chains. The method is accurate and allows quantitation of Hb F at the 0.5% level; preparative PolyCAT-HPLC allows isolation of (nearly) pure Hb F from blood samples with low (< 1%) Hb F. Adult Hb F levels were determined in 69 normal adults (including 24 diabetics); Hb F levels fell below 1% except for subjects with abnormal -Gγ-Gγ arrangement and a C→T mutation at position -158 relative to the Cap site of both Gγ genes. The effect of the same mutation in the normal-Gγ-Aγ-arrangement was variable. Certain β-thal mutations (namely, those at positions -29;-88; IVS-I-1; IVS-II-1) were associated with high Hb F levels in heterozygotes, while those at nucleotide (nt) positions IVS-I-6; IVS-I-110; codon 24; codon 39; codons 41/42; IVS-II-745 were not. Gγ values varied and often fell into two groups (high Gγ and low Gγ); high Gγ values were not associated with high Hb F values. The chromatographic procedure is ideally suited for Hb A2 quantitation. Average values of Hb A2 in β-thal heterozygotes with any one of nine of the ten mutations were twice that of normals; the one exception was the β-thal heterozygote with the IVS-I-6 (T→C) mutation with an average low Hb A2 value of 3.6%.

Gradient of distribution in Europe of the major CF mutation and of its associated haplotype

Abstract: In this collaborative European study, a total of 4871 cystic fibrosis (CF) chromosomes and 3539 normal chromosomes have been characterized for the haplotypes defined by the 2 extragenic polymorphic sequences revealed by XV2c and KM19. The association between one of these haplotypes (B haplotype) and the most frequent CF mutation, ΔF508, suggests for the latter a single origin and a subsequent diffusion according to a South East-North West gradient. The linkage disequilibrium data between CF and the B haplotype in different European populations are compatible with a relatively more recent appearance of the mutation in Northern Europe whereas in Southern Europe a longer history of the same mutation would have allowed time for recombination with other haplotypes. This model is also compatible with a selective advantage of carriers but does not account for (1) the excess of B haplotypes observed among both normal and non-ΔF508 CF chromosomes; (2) the correlation between the B haplotype and the severity of the phenotypic effect caused by CF mutations, as measured by pancreatic insufficiency and meconium ileus.

Monocyte-derived neutrophil chemotactic factor (MDNCF/IL-8) resides in a gene cluster along with several other members of the platelet factor 4 gene superfamily.

Abstract: Monocyte-derived neutrophil chemotactic factor (MDNCF/IL-8, suggested gene symbol IL8) is a cytokine that chemoattracts and activates neutrophils. Using a panel of human-rodent cell hybrids that preferentially segregate human chromosomes and in situ hybridization, the MDNCF/IL-8 gene was placed on the human gene map at position 4q12-q21. This is the same location where at least three other members (platelet factor 4, melanoma growth stimulatory activity, and interferon-γ induced factor) of the platelet factor 4 gene superfamily reside. In addition, a restriction fragment length polymorphism was identified using MDNCF as a probe in screening genomic DNA digested with HindIII from unrelated individuals.

An update on the frequency of mucopolysaccharide syndromes in British Columbia.

Abstract: ~Department of Paediatrics, Alberta Children's Hospital Research Centre, University of Calgary, 1820 Richmond Road SW, Calgary, Alberta T2T 5C7, Canada 2Department of Paediatrics, Biochemical Diseases Laboratory, British Columbia's Children's Hospital, University of British Columbia, Vancouver, BC V6H 3V4, Canada 3B. C. Health Surveillance Registry, Division of Vital Statistics Government of British Columbia, Vancouver, BC V6Z 2C5, Canada

Three point mutations in the CFTR gene in French cystic fibrosis patients: identification by denaturing gradient gel electrophoresis.

Abstract: The cystic fibrosis (CF) gene was recently identified as a gene spanning 250 kilobases (kbp) and coding for a 1480 amino acid protein, cystic fibrosis transmembrane conductance regulator (CFTR). Approximately 70% of CF mutations involve a three-base-pair deletion in CFTR exon 10, resulting in the loss of a phenylalanine at position 508 in the gene product (delta F508). In order to screen for other molecular defects, we have used a strategy based on denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR)-amplified gene segments. This method, which permits rapid detection of any sequence change in a given DNA stretch, was used successfully to analyse 61 non-delta F508 CF chromosomes from French CF patients. A study of CFTR exons 10, 11, 14a, 15 and 20 detected three mutations located in exons 14a, 15 and 20, along with several nucleotide sequence polymorphisms. These nucleotide changes were identified by direct sequencing of PCR fragments displaying altered electrophoretic behaviour, together with some of the polymorphisms and mutations previously characterized by others. The strategy presented here constitutes a valuable tool for the development of carrier testing for individuals or couples with a family history of cystic fibrosis, and will contribute to deciphering the functionally important regions of the CFTR gene.

The similarity of phenotypic effects caused by Xp and Xq deletions in the human female: a hypothesis.

Abstract: We have collected from the literature adult nonmosaic women with the following aberrant X chromosomes: Xp- (52), Xq- (67), idic(Xp-)(10), idic(Xq-)(9), and interstitial deletions (12). Lack of Xp, and especially Xcen-Xp11 (b region), may cause full-blown Turner syndrome. However, individual Turner symptoms, including gonadal dysgenesis, otherwise seem to be randomly distributed with respect to the different Xp and Xq deletions, although breakpoints distal to Xq25 do not give rise to any phenotypic anomalies except in a few cases of secondary amenorrhea or premature menopause. Of the carriers of an Xp- or Xq- chromosome, 65% and 93%, respectively, suffer from ovarian dysgenesis, whereas all idic(Xp-) and idic(Xq-) chromosomes cause primary or secondary amenorrhea. Xq deletions do not induce specific symptoms different from those caused by Xp deletions. Lack of the tip of Xp has led in 46/52 cases to short stature, but 43% of the Xq- carriers are also short. To explain these observations, we propose the following hypothesis. Since deletions of truly inactivated regions do not seem to cause any symptoms, we assume that the b region (Xcen-p11) always stays active in a normal inactive X, but is inactivated in deleted X chromosomes, especially in Xq- chromosomes. In some cases, inactivation may spread to the tip of Xp; this would explain the apparently variable behavior of the Xg and STS genes, and the short stature of some Xq- carriers. Full chromosome pairing seems to be a prerequisite for the viability of oocytes and thus for gonadal development. Deleted X chromosomes necessarily leave a portion of the normal X unpaired and isodicentrics probably interfere with pairing, resulting in atresia of oocytes. The role played by the "critical region" (Xq13-q24) in ovarian development is still unclear.

Microdissection of banded human chromosomes.

Abstract: Physical dissection of metaphase chromosomes is the most straightforward approach for the isolation of DNA sequences from specific chromosome regions. However, conventional microdissection techniques are too crude and inefficient for analysis of the human genome. Here we describe a technique for the precise dissection of single bands from GTG-banded chromosomes. Cells from normal amniotic fluid cell cultures are harvested by the pipette method. Microdissection is performed on an inverted microscope (magnification 1250 x) with the help of extended siliconized glass needles and an electronically controlled micromanipulator. Enzymatic amplification of the dissected DNA allows the construction of band-specific DNA libraries from as few as 20 dissected chromosome fragments.

Characteristic chromosome abnormalities, including rearrangements of 6p, del(7q), +12, and t(12;14), in 44 uterine leiomyomas.

Abstract: The cytogenetic analysis of 224 leiomyomas from 138 patients is presented. An insufficient number of mitoses was found in 35 tumors, normal karyotypes in 145, and clonal chromosome aberrations were detected in 44. The three previously identified cytogenetic subgroups were all represented in this series: del(7) (q21.2q31.2) was found in 11, trisomy 12 in five, and t(12;14)(q14-15;q23-24) in one leiomyoma. Rearrangements of 6p, including deletions, inversions, and various translocations, were found in eight tumors, thus delineating a new cytogenetic subgroup of uterine leiomyoma. The remaining 21 karyotypically abnormal tumors had nonrecurrent changes. One leiomyoma had two cytogenetically unrelated clones characterized by del(7)(q21.2 q31.2) and +12. Karyotypic changes in two separate leiomyomas from the same uterus were identified in five patients; in three of them, different anomalies were found in the two tumors, whereas cytogenetically identical aberrations − del(7q) and dic(21;22) − were detected in two macroscopically discrete tumors. These findings suggest that whereas some multiple leiomyomas originate independently, others may be derived from the same neoplastic clone.

Genotype-phenotype correlations in XX males and their bearing on current theories of sex determination.

Abstract: Clinical, chromosomal and molecular studies of a group of 15 XX males confirm the presence of two main groups. A Y+ve group of ten patients exhibit sex reversal as the result of transfer of the distal end of the short arm of the Y chromosome, including testis determining factors, to the short arm of one X-chromosome, presumably by accidental crossing-over in paternal meiosis. The ten patients have Klinefelter's syndrome but differ from XXY cases in that they are short and shown no impairment of intelligence. The four Y-ve XX males have no demonstrable Y sequences and differ from Y+ve cases in abnormality of the external genitalia and invariable gynaecomastia; in this, they more closely resemble XX true hermaphrodites than XY males. These observations on Y-ve XX males and an additional exceptional Y+ patient suggest that the ZFY locus is not essential for male differentiation and is not the primary testis determining factor. Male sex determination in sporadic, and familial Y-ve XX males and true hermaphrodites is likely to be the result of mutation in an X-linked TDF gene and its consequent escape from the constraints of X-inactivation. It seems premature to abandon the dosage model of sex determination on the recent evidence that ZFX does not show dosage compensation.

Studies of RFLP closely linked to the cystic fibrosis locus throughout Europe lead to new considerations in populations genetics.

Abstract: The prenatal diagnosis of cystic fibrosis is now routinely performed by using two probes tightly linked to the CF locus (XV2C and KM19). These probes have been shown to exhibit a strong linkage disequilibrium with the CF locus. Our data (103 families) have been pooled with other French data (237 families). They are consistent with the hypothesis of a unique ancestral mutation initially associated with a B (D1E2) restriction fragment length polymorphism (RFLP) haplotype, subsequently reassociated by cross-over with A, C or D haplotypes. Assuming such an hypothesis, the mutation is supposed to be 3000-6000 years old, depending on generation length and the true recombination ratio between the KM19 and CF loci. Up-to-date Spanish, Danish and Greek data are reported together with other previously published population data in order to discuss the geographic origin and age of the mutation in Europe. The action of selection in terms of heterozygote advantage and distorsion of segregation is discussed.

Viral integration, fragile sites, and proto-oncogenes in human neoplasia.

Abstract: To evaluate the trend of viral integration in the human genome, chromosomal localization of five DNA-containing viruses compiled from literature data was compared to the location of fragile sites and proto-oncogenes. A total of 35 regionally mapped viral integration sites from tumors and transformed cells were distributed over 19 chromosomes. Of the 35 integration sites 23 (66%) were at the bands of fragile sites, and 7 were one band away (20%). This statistically defines the correlation as highly significant (P = 0.0000183, Fisher's F-test). Five integration sites did not correspond to the location of a fragile site. Thirteen integration sites and proto-oncogenes mapped at the same bands (37%), 6 (17%) were one band apart, and at 16 integration sites (46%) no proto-oncogenes were localized (P = 0.00491). Eighteen viral integration sites, fragile sites, and proto-oncogenes (51%) were localized at the same bands or one band distant. This clustering of viral integration sites, fragile sites, and proto-oncogenes is statistically highly significant (P = 0.0000118), and indicates nonrandom viral integration in the human genome.

Chromosomal in situ suppression hybridization of human gonosomes and autosomes and its use in clinical cytogenetics

Abstract: DNA libraries from sorted human gonosomes were used selectively to stain the X and Y chromosomes in normal and aberrant cultured human cells by chromosomal in situ suppression (CISS-) hybridization. The entire X chromosome was stained in metaphase spreads. Interphase chromosome domains of both the active and inactive X were clearly delineated. CISS-hybridization of the Y chromosome resulted in the specific decoration of the euchromatic part (Ypter-q11), whereas the heterochromatic part (Yq12) remained unlabeled. The stained part of the Y chromosome formed a compact domain in interphase nuclei. This approach was applied to amniotic fluid cells containing a ring chromosome of unknown origin (47,XY; +r). The ring chromosome was not stained by library probes from the gonosomes, thereby suggesting its autosomal origin. The sensitivity of CISS-hybridization was demonstrated by the detection of small translocations and fragments in human lymphocyte metaphase spreads after irradiation with 60Co-gamma-rays. Lymphocyte cultures from two XX-males were investigated by CISS-hybridization with Y-library probes. In both cases, metaphase spreads demonstrated a translocation of Yp-material to the short arm of an X chromosome. The translocated Y-material could also be demonstrated directly in interphase nuclei. CISS-hybridization of autosomes 7 and 13 was used for prenatal diagnosis in a case with a known balanced translocation t(7;13) in the father. The same translocation was observed in amniotic fluid cells from the fetus. Specific staining of the chromosomes involved in such translocations will be particularly important, in the future, in cases that cannot be solved reliably by conventional chromosome banding alone.

A possible common origin of "Y-negative" human XX males and XX true hermaphrodites.

Abstract: We have studied nine patients aged 1 month to 16 years with 46, XX karyotypes and testicular tissue. Some of these patients were followed through puberty. Phenotypically, two presented normal and seven abnormal external genitalia (AG). Among this latter group, four showed hypospadias and three true hermaphroditism (TH). The endocrine data were similar in all three groups: testosterone levels were within normal limits during puberty, decreasing in adulthood; gonadotrophin levels were above the control values at mid puberty. Histologies of the two sub groups of AG patients were identical up to 5 years of age and presented differences when compared with controls, regardless of the ovarian part of the ovotestis. However, in patients older than 8 years, germ cells disappeared and dysgenesis became obvious. In one patient, the ovarian zone of the gonad was detected only after complete serial sections of the removed gonad were examined. Southern blot analysis with Y-DNA probes displayed Y-specific material for the classic 46 XX males and a lack of such sequences for all patients with AG and TH. Based on these findings, we postulate that 46, XX males with AG and 46, XX TH may represent alternative manifestations of the same genetic defect. These data together with those concerning familial cases of 46, XX males with AG and 46, XX TH suggest an autosomally (or pseudoautosomally) determined mechanism.

Increased frequency of 6-thioguanine-resistant peripheral blood lymphocytes in Werner syndrome patients

Abstract: The frequency of spontaneous 6-thioguanine (TG)-resistant peripheral blood lymphocytes in five unrelated Werner syndrome (WS) patients was determined using an autoradiographic labeling assay. The average frequency of TG-resistant lymphocytes was eightfold higher in WS patients than in sex- and age-matched normal control donors. This finding and previous identification of increased spontaneous chromosomal rearrangements and deletions in WS cells or cell lines suggest that WS is a human genomic instability or mutator syndrome.

The analysis of hypervariable DNA profiles: problems associated with the objective determination of the probability of a match

Abstract: A computerised system has been used to store DNA profiles from 3 hypervariable loci. This initial survey illustrates that band matching is only possible after analysis of the errors associated with electrophoretic systems. A number of databases have been constructed with the three probes investigated and two methods of frequency determination, ‘binning’ and ‘sliding window’ fitting, have been compared.

Direct carrier detection by in situ suppression hybridization with cosmid clones of the Duchenne/Becker muscular dystrophy locus

Abstract: A basic problem in genetic counseling of families with Duchenne/Becker muscular dystrophy (DMD/BMD) concerns the carrier status of female relatives of an affected male. In about 60% of these patients, deletions of one or more exons of the dystrophin gene can be identified. These deletions preferentially include exon 45, which can be detected by multiplex polymerase chain reaction (PCR) and Southern blot analysis of genomic cosmid clones that map to this critical region. As a new approach for definitive carrier detection, we have performed chromosomal in situ suppression (CISS) hybridization with these cosmid clones in female relatives of four unrelated patients. In normal females, most metaphases showed signals on both×chromosomes, whereas only one×chromosome was labeled in carriers. Our results demonstrate that CISS hybridization can define the carrier status in female relatives of DMD patients exhibiting a deletion in the dystrophin gene.

Unusual features in the inheritance of ataxia telangiectasia

Abstract: A prevalence study of ataxia telangiectasia was conducted in the West Midlands, with a population of over 5 million. The prevalence in those aged 50 or less was found to be 1 in 514 000 and the birth frequency to be about 1 in 300 000. A genetic study of 47 families ascertained throughout the United Kingdom was carried out concurrently. A low parental consanguinity rate was found, no parents being first cousins or more closely related, whereas 10% had been expected. The incidence of ataxia telangiectasia in the 79 sibs of index cases was 1 in 7. These two features demonstrate that ataxia telangiectasia may not always be an autosomal recessive condition. Other possible explanations are that some cases are double heterozygotes or new dominant mutations.

The human homeobox gene HOX7 maps to chromosome 4p16.1 and may be implicated in Wolf-Hirschhorn syndrome.

Abstract: A cosmid containing the human sequence (HOX7) homologous to the mouse homeogene Hox-7 was isolated from a genomic cosmid library. There is only one highly conserved homologous gene in the human genome. The C-terminal two-thirds of the HOX7 homeobox DNA sequence has been determined; there are no predicted amino acid changes from the mouse sequence. Data from mouse/human hybrid cell lines show that HOX7 maps to human chromosome 4p16.1, a region that is syntenic with part of mouse chromosome 5, the site of the murine Hox-7 gene. Analysis of chromosomes from two patients with Wolf-Hirschhorn syndrome, which is characterised by profound dysmorphologies, indicates that the HOX7 locus is deleted. Although not all Wolf-Hirschhorn syndrome patients analysed were deleted for HOX7, the combination of positional data and functional correlation with mouse expression implicates HOX7 as a candidate gene for this syndrome.

Localisation of a dystrophin-related autosomal gene to 6q24 in man, and to mouse chromosome 10 in the region of the dystrophia muscularis (dy) locus

Abstract: We have localised a dystrophin-related autosomal gene called DMDL (Duchenne muscular dystrophy-like) to human chromosome 6q24 by in situ hybridisation. Using restriction fragment length polymorphism analysis in two mouse species, we have localised the homologous gene Dmdl in the mouse to chromosome 10 proximal to the Myb oncogene. A neuromuscular disease locus dystrophia muscularis (dy) has previously been assigned to this region of mouse chromosome 10.

Painting of human chromosomes with probes generated from hybrid cell lines by PCR with Alu and L1 primers.

Abstract: Specific amplification of human sequences of up to several kb length has recently been accomplished in man-hamster and man-mouse somatic hybrid cell DNA by IRS-PCR (interspersed repetitive sequence — polymerase chain reaction). This approach is based on oligonucleotide primers that anneal specifically to human Alu- or L1-sequences and allows the amplification of any human sequences located between adequately spaced, inverted Alu- or L1-blocks. Here, we demonstrate that probe pools generated from two somatic hybrid cell lines by Alu- and L1-PCR can be used for chromosome painting in normal human lymphocyte metaphase spreads by chromosomal in situ suppression (CISS-) hybridization. The painted chromosomes and chromosome subregions directly represent the content of normal and deleted human chromosomes in the two somatic hybrid cell lines. The combination of IRS-PCR and CISS-hybridization will facilitate and improve the cytogenetic analysis of somatic hybrid cell panels, in particular, in cases where structurally aberrant human chromosomes or human chromosome segments involved in interspecies translocations cannot be unequivocally identified by classical banding techniques. Moreover, this new approach will help to generate probe pools for the specific delineation of human chromosome subregions for use in cytogenetic diagnostics and research without the necessity of cloning.

Prophase of meiosis in human spermatocytes analysed by EM microspreading in infertile men and their controls and comparisons with human oocytes.

Abstract: Observations at the electron microscope (EM) level have been made on 1883 primary spermatocytes from 40 chromosomally normal subfertile men and 566 spermatocytes from 10 fertile controls, using the technique of microspreading. Spermatocytes of infertile men in general showed greater indications of degeneration including higher levels of background silver deposition, nucleolar organising region — XY associations, fragmentation of synaptonemal complexes and overproduction of XY excrescences. A few oligospermic men also showed an immature morphology of the XY pair and/or a reduced extent of XY synapsis. Dissociation of the sex chromosome axes at prophase was found to occur with a much lower frequency than that recorded for separated X and Y chromosomes at metaphase I. In a single spermatocyte, synaptonemal complex formation was observed between Xqter and Yqter, a situation that could enable rare XqYq interchange. A proteinaceous stalked body exists on the Y axis towards its non-pairing end; this structure might have a functional relationship with the gene for spermatogenesis, (AZF), located at the euchromatin/heterochromatin interface. Compared with human oocytes, spermatocytes show fewer anomalies of synapsis, i.e. asynapsed segments or whole axes, non-homologous associations, interchanges, interlocks. These latter data agree well with findings from the mouse.

Frequency and effect of human apolipoprotein A-IV polymorphism on lipid and lipoprotein levels in an Icelandic population

Abstract: Human apolipoprotein A-IV (apo A-IV) exhibits a genetic polymorphism with two common alleles, A-IV1 and A-IV2, in Caucasian populations. We have investigated this polymorphism in the Icelandic population. The frequencies of the two alleles are significantly different from middel European populations with a higher frequency of the A-IV2 allele (0.117 versus 0.077) occurring in Iceland. The alleles at the apo A-IV locus have significant effects on plasma high density lipoprotein cholesterol (HDL-C) and triglyceride levels. The average effect of the A-IV2 allele is to raise HDL-C by 4.9 mg/dl and to lower triglyceride levels by 19.4mg/dl. We estimate that the genetic variability at the apo A-IV gene locus accounts for 3.1% of the total variability of HDL-C and for 2.8% of the total variability of triglycerides in the population from Iceland. This confirms and extends our previous observations on apo A-IV allele effects in Tyroleans in an independent population.

Neurofibromatosis-1: a maximum likelihood estimation of mutation rate

Abstract: Methods of classical segregation analysis were applied to a sample of 129 sibships with one or more individuals affected by neurofibromatosis-1 (NF-1). The sample consists only of subjects with NF-1; all the probands had been referred for genetic counselling because of cafe-au-lait spots, and a diagnostic protocol was invariably applied. No deviation from the segregation ratio expected for a fully penetrant Mendelian dominant gene was observed. A maximum likelihood estimate of the proportion of sporadic cases was obtained, and the mutation rate was estimated to be 6.5 x 10(-5) gametes per generation (95% CI 5.0-8.1).

Complex translocations, simple variant translocations and Ph-negative cases in chronic myelogenous leukaemia.

Abstract: A proportion of cases of chronic myelogenous leukaemia (CML) has been described either (1) with a variant translocation, or (2) without the apparent involvement of both 9q34 and 22q11 (Ph-negative CML). All variant translocations have been further demonstrated to be complex implicating 9q34,22q11, plus another breakpoint on a variable chromosome. Complex translocations may be due to two successive events. Some of the breakpoints on the variable chromosome appear to be recurrent, and these remain to be studied for prognostic significance. Ph-negative CML comprises (1) cases of submicroscopic (hidden) insertion of 9q34-ABL within 22q11-BCR, and (2) cases without BCR-ABL rearrangement. We propose this last category to be called "CML-like disease", not to be confused anymore with true CML, and consequently to be studied as a separate entity.