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D H Ledbetter

Publications and source records attributed to D H Ledbetter.

At least 109 records · Page 6Linked to original sources
PubMed1993

Wilms tumor in a patient with Prader-Willi syndrome.

The development of Wilms tumor in a patient with Prader-Willi syndrome prompted us to determine the parental origin of the genes implicated in both disorders because of the sex-specific parent-of-origin effects previously demonstrated for both conditions. A paternal chromosome 15q11-q13 deletion was demonstrated, but no changes were demonstrated in a limited analysis of chromosome 11p, which harbors two Wilms tumor suppressor genes, WT1 and WT2.

Chromosome Deletion↗
PubMed1993

A somatic cell hybrid map of human chromosome 13.

We have constructed a chromosome 13 somatic cell hybrid map using seven cell lines: PGMEA6, a hybrid containing the entire chromosome 13, and six hybrids containing various deletions of chromosome 13 (BARF7, PPF22, KBF11, KSF39, CF25, and CF27). We have mapped 80 markers that define 10 regions of chromosome 13 with respect to 10 breakpoints in the mapping panel; these regions range in size from 4 to 24 Mb, with an average size of 8 Mb. The 80 markers sublocalized on our mapping panel include 10 Alu-PCR clones, 6 of which were converted to sequence-tagged sites; 40 (CA)n repeat-containing clones, 27 of which are microsatellite PCR markers; 8 (AAAG)n repeat-containing PCR markers, 1 two-allele PCR marker, 4 genes or expressed sequences, and 17 anonymous DNA probes. This low-resolution physical map can be used as a backbone map for more refined physical mapping using radiation hybrids or yeast artificial chromosomes.

Animals↗
PubMed1993

A complete YAC contig of the Prader-Willi/Angelman chromosome region (15q11-q13) and refined localization of the SNRPN gene.

Since a previous report of a partial YAC contig of the Prader-Willi/Angelman chromosome region (15q11-q13), a complete contig spanning approximately 3.5 Mb has been developed. YACs were isolated from two human genomic libraries by PCR and hybridization screening methods. Twenty-three sequence-tagged sites (STSs) were mapped within the contig, a density of approximately 1 per 200 kb. Overlaps between YAC clones were identified by Alu-PCR dot-blot analysis and confirmed by STS mapping or hybridization with ends of YAC inserts. The gene encoding small nuclear ribonucleoprotein-associated peptide N (SNRPN), recently identified as a candidate gene for Prader-Willi syndrome, was localized within this contig between markers PW71 and TD3-21. Loci mapped within and immediately flanking the Prader-Willi/Angelman chromosome region contig are ordered as follows: cen-IR39-ML34-IR4-3R-TD189-1-PW71-SNRPN -TD3-21- LS6-1-GABRB3,D15S97-GABRA5-IR10-1-CMW1+ ++-tel. This YAC contig will be a useful resource for more detailed physical mapping of the region, for generation of new DNA markers, and for mapping or cloning candidate genes for the Prader-Willi and Angelman syndromes.

Angelman Syndrome↗
PubMed1993

Multiplex PCR of three dinucleotide repeats in the Prader-Willi/Angelman critical region (15q11-q13): molecular diagnosis and mechanism of uniparental disomy.

Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are distinct mental retardation disorders caused by a deficiency of paternal (PWS) or maternal (AS) contributions for chromosome 15 by either deletion or uniparental disomy (UPD). To further study the molecular mechanisms involved in these disorders and to improve molecular diagnostic methods, we have isolated three dinucleotide repeat markers in the PWS/AS critical region. An Alu-CA PCR method was used to isolate CA-repeat markers directly from yeast artificial chromosome (YAC) clones identified by probes IR4-3R (D15S11), LS6-1 (D15S113), and GABAA receptor B3 (GABRB3). Three markers with 6-11 alleles and 73-83% heterozygosities were identified and analyzed by multiplex PCR. Gene-centromere mapping was performed on a panel of ovarian teratomas of known meiotic origin, and showed the most proximal marker, IR4-3R, to be 13 cM (95% confidence limits: 7-19 cM) from the centromere of chromosome 15. Molecular diagnostic studies were performed on 20 PWS and 9 AS patients. In 17 patients with deletions, the parental origin of deletion was determined. Ten PWS patients were shown to have maternal heterodisomy. Since these markers are only 13 cM from the centromere, heterodisomy indicates that maternal meiosis I nondisjunction is involved in the origin of UPD. In contrast, two paternal disomy cases of AS showed isodisomy for all markers tested along the length of chromosome 15. This suggests a paternal meiosis II nondisjunction event (without crossing over) or, more likely, monosomic conception (due to maternal nondisjunction) followed by chromosome duplication.(ABSTRACT TRUNCATED AT 250 WORDS)

Alleles↗
PubMed1993

Nondisjunction of chromosome 15: origin and recombination.

Thirty-two cases of uniparental disomy (UPD), ascertained from Prader-Willi syndrome patients (N = 27) and Angelman syndrome patients (N = 5), are used to investigate the pattern of recombination associated with nondisjunction of chromosome 15. In addition, the meiotic stage of nondisjunction is inferred by using markers mapping near the centromere. Two basic approaches to the analysis of recombination are utilized. Standard methods of centromere mapping are employed to determine the level of recombination in specific pairwise intervals along the chromosome. This method shows a significant reduction in recombination for two of five intervals examined. Second, the observed frequency of each recombinant class (i.e., zero, one, two, three, or more observable crossovers) is compared with expected values. This is useful for testing whether the reduction in recombination can be attributed solely to a proportion of cases with no recombination at all (because of asynapsis), with the remaining groups showing normal recombination (or even excess recombination), or whether recombination is uniformly reduced. Analysis of maternal UPD(15) data shows a slight reduction in the multiple-recombinant classes, with a corresponding increase in both the zero- and one-recombinant classes over expected values. The majority, more than 82%, of the extra chromosomes in maternal UPD(15) cases are due to meiotic I nondisjunction events. In contrast, most paternal UPD(15) cases so far examined appear to have a postzygotic origin of the extra paternal chromosome.

Aneuploidy↗
PubMed1992

A randomized comparison of transcervical and transabdominal chorionic-villus sampling. The U.S. National Institute of Child Health and Human Development Chorionic-Villus Sampling and Amniocentesis Study Group.

BACKGROUND: Chorionic-villus sampling is done in early pregnancy to obtain fetal cells for the prenatal diagnosis of genetic and chromosomal defects. Transcervical chorionic-villus sampling has been shown to be safe and effective in national trials. Recently, an alternative transabdominal technique has been suggested as potentially easier and safer. METHODS: From April 1987 through September 1989, we prospectively compared transcervical and transabdominal chorionic-villus sampling in 3999 women with singleton pregnancies in whom the risk of a genetically abnormal fetus was increased. Women between 7 and 12 weeks of gestation underwent ultrasonographic evaluation of placental and uterine position. Those with active vaginal infections, active bleeding, or cervical polyps were excluded. If the obstetrician thought either sampling procedure was acceptable, the woman was asked to consent to random assignment to one of the two procedures. Both groups were followed to determine the outcome of pregnancy and the rate of spontaneous fetal loss after chorionic-villus sampling. RESULTS: Among the 3999 women who entered the study, sampling was attempted in 3873 (97 percent), 1944 of whom had been assigned to undergo transcervical sampling and 1929 to undergo transabdominal sampling. Of these 3873 women, sampling was eventually successful in 3863. Sampling was successful after a single insertion of the sampling instrument in 94 percent of the transabdominal procedures and 90 percent of the transcervical procedures. Among the women with cytogenetically normal pregnancies who had sampling because of maternal age, the rate of spontaneous fetal loss through 28 weeks of pregnancy was 2.5 percent in the transcervical-sampling group and 2.3 percent in the transabdominal-sampling group (difference, 0.26 percent; 95 percent confidence interval, -0.5 to 1.0 percent). CONCLUSIONS: Transabdominal and transcervical chorionic-villus sampling appear to be equally safe procedures for first-trimester diagnosis of fetal abnormalities.

Abdomen↗
PubMed1992

Two hereditary defects related to vitamin D metabolism map to the same region of human chromosome 12q13-14.

We have localized the locus for the vitamin D receptor (VDR) responsible for hypocalcemic vitamin D-resistant rickets (HVDRR), close to the pseudovitamin D-deficient rickets (PDDR) locus, another disorder related to impaired vitamin D metabolism. PDDR (formerly vitamin D dependency type I, VDD1) was recently mapped to human chromosome 12q14 by linkage analysis. Here we report on the assignment of VDR to 12q13-14 by in situ hybridization and by linkage analysis. Linkage analysis between VDR, PDDR, and several RFLP markers show close linkage, with no recombination (theta = 0) between VDR and PDDR (Z = 1.94), a COL2A1 haplotype (Z = 4.03), ELA1 (Z = 0.98), and D12S15 (Z = 4.17). The analysis of extended haplotypes in one of the PDDR families provides evidence for recombination between VDR and PDDR and localizes VDR together with COL2A1 proximal to PDDR. Complete allelic association detected between VDR and COL2A1 loci on PDDR chromosomes and lower association between VDR and PDDR suggests a VDR location very close to COL2A1 and one more distant to PDDR. We propose the following order of loci: (VDR, COL2A1), (PDDR, ELA1, D12S15), D12S4, (D12S14, D12S17), D12S6. Thus, two clearly distinct loci involved in the control of vitamin D activity map close to each other in the region 12q13-14.

Chromosomes, Human, Pair 12↗
PubMed1992

Cytogenetic results from the U.S. Collaborative Study on CVS.

Cytogenetic data are presented for 11,473 chorionic villus sampling (CVS) procedures from nine centres in the U.S. NICHD collaborative study. A successful cytogenetic diagnosis was obtained in 99.7 per cent of cases, with data obtained from the direct method only (26 per cent), culture method only (42 per cent), or a combination of both (32 per cent). A total of 1.1 per cent of patients had a second CVS or amniocentesis procedure for reasons related to the cytogenetic diagnostic procedure, including laboratory failures (27 cases), maternal cell contamination (4 cases), or mosaic or ambiguous cytogenetic results (98 cases). There were no diagnostic errors involving trisomies for chromosomes 21, 18, and 13. For sex chromosome aneuploidies, one patient terminated her pregnancy on the basis of non-mosaic 47,XXX in the direct method prior to the availability of results from cultured cells. Subsequent analysis of the CVS cultures and fetal tissues showed only normal female cells. Other false-positive predictions involving non-mosaic aneuploidies (n = 13) were observed in the direct or culture method, but these cases involved rare aneuploidies: four cases of tetraploidy, two cases of trisomy 7, and one case each of trisomies 3, 8, 11, 15, 16, 20, and 22. This indicates that rare aneuploidies observed in the direct or culture method should be subjected to follow-up by amniocentesis. Two cases of unbalanced structural abnormalities detected in the direct method were not confirmed in cultured CVS or amniotic fluid. In addition, one structural rearrangement was misinterpreted as unbalanced from the direct method, leading to pregnancy termination prior to results from cultured cells showing a balanced, inherited translocation. False-negative results (n = 8) were observed only in the direct method, including one non-mosaic fetal abnormality (trisomy 18) detected by the culture method and seven cases of fetal mosaicism (all detected by the culture method). Mosaicism was observed in 0.8 per cent of all cases, while pseudomosaicism (including single trisomic cells) was observed in 1.6 per cent of cases. Mosaicism was observed with equal frequency in the direct and culture methods, but was confirmed as fetal mosaicism more often in cases from the culture method (24 per cent) than in cases from the direct method (10 per cent). The overall rate of maternal cell contamination was 1.8 per cent for the culture method, but there was only one case of incorrect sex prediction due to complete maternal cell contamination which resulted in the birth of a normal male.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1992

Chorionic mosaicism: association with fetal loss but not with adverse perinatal outcome.

Cytogenetic data from the United States NICHD collaborative study of chorionic villus sampling (CVS) were used to evaluate the clinical significance of chorionic mosaicism. The 10,754 patients with normal cytogenetic results were compared with 108 patients (1.0 per cent) with placental mosaicism and 181 patients (1.6 per cent) with pseudo-mosaicism. Of the pregnancies intended to continue, the pregnancy loss rate was significantly greater in patients with placental mosaicism than in the cytogenetically normal cohort (8.6 vs. 3.4 per cent, p less than 0.05). However, there was no difference in the frequencies of abruptio placenta, preterm labour or delivery, small-for-gestational-age newborns, pregnancy-induced hypertension, or neonates with Apgar scores less than 7.

Abortion, Spontaneous↗
PubMed1992

First-trimester biochemical and molecular diagnoses using chorionic villi: high accuracy in the U.S. collaborative study.

The accuracy of biochemical and molecular prenatal diagnoses using chorionic villi as the fetal source was assessed by seven centres participating in the NICHD collaborative study on the safety and accuracy of chorionic villus sampling (CVS) and amniocentesis. Of 601 pregnancies studied, biochemical methods were used to determine the diagnosis in 283 fetuses at risk for 35 different metabolic disorders. Fifteen different lysosomal storage diseases accounted for 81 per cent of the biochemical prenatal diagnoses performed, with 57 per cent of these pregnancies at risk for Tay-Sachs disease. No errors were made in the biochemical diagnoses that predicted affected or unaffected fetuses. However, the diagnoses of certain disorders (e.g., mucopolysacchariodosis type IH, metachromatic leukodystrophy, and Krabbe disease) occasionally required confirmatory studies in cultured amniocytes because the enzyme results were inconclusive in direct and/or cultured villi or due to the presence of a pseudodeficiency allele. Of these, only the diagnosis of a fetus at risk for Krabbe disease remained inconclusive after special studies to discriminate between mutant and pseudo-deficiency alleles. Recombinant DNA techniques were used to predict the diagnosis of 318 fetuses at risk for 16 different disorders in which the defective disease gene could be detected either directly or by linkage analysis to a nearby polymorphic marker. Of these, 32 per cent were for haemoglobinopathies, 25 per cent for cystic fibrosis, 24 per cent for Duchenne or Becker muscular dystrophy, and 7 per cent for haemophilias. Pregnancies at risk for known disorders with specific molecular lesions (e.g., sickle cell disease) were accurately diagnosed in direct and/or cultured villi. Diagnoses requiring analyses with closely linked polymorphic markers were occasionally uniformative or inconclusive. Maternal contamination was not reported in any biochemical or molecular-based diagnosis. These studies document the high accuracy and rapidity of both biochemical and mutation-specific prenatal diagnoses with direct and cultured chorionic villi.

Adult↗
PubMed1992

Risk factors associated with transcervical CVS losses.

Factors found to be associated with pregnancy loss after transcervical CVS were race (higher for non-white), history of spontaneous abortion, unplanned pregnancy, history of spotting or bleeding during the pregnancy prior to CVS, and placental position (higher for fundal or lateral locations). Whether the increase in loss risk is due to the factor, per se, or the factor plus the CVS cannot be determined due to the lack of appropriate control data.

Adult↗
PubMed1992

Genetic mapping of four dinucleotide repeat loci, DXS453, DXS458, DXS454, and DXS424, on the X chromosome using multiplex polymerase chain reaction.

Dinucleotide CA repeat sequences in the human genome have been shown to be highly polymorphic due to variation in the length of the repeat-containing segment. Therefore, these markers can serve as anchor loci in the construction of a high-resolution genetic map of the human genome. In this study, we improved the efficiency of typing dinucleotide repeats using multiplex polymerase chain reaction (PCR). Dinucleotide repeat sequences of four previously identified markers (DXS453, DXS458, DXS454, and DXS424) on the long arm of the X chromosome were simultaneously amplified in a single PCR reaction. This multiplex PCR was applied to genotype individuals from the 40 CEPH reference families, and the genotypic data were used to determine the map position of the four loci with respect to eight reference markers in the Xq region by linkage analysis.

Base Sequence↗
PubMed1992

The CCAAT/enhancer binding protein (C/EBP alpha) gene (CEBPA) maps to human chromosome 19q13.1 and the related nuclear factor NF-IL6 (C/EBP beta) gene (CEBPB) maps to human chromosome 20q13.1.

The CEBPA gene encoding CCAAT/enhancer binding protein (C/EBP alpha) has been mapped to human chromosome 19 and the CEBPB (formerly TCF5) gene encoding NF-IL6 (C/EBP beta) to human chromosome 20 by Southern blot analysis of Chinese hamster x human and mouse x human somatic cell hybrids. CEBPA has been further mapped to 19q13.1 between the loci GPI and TGFB using human x hamster somatic cell hybrids containing restricted fragments of human chromosome 19. This position was confirmed by fluorescence in situ hybridization. Furthermore, CEBPB has been mapped to 20q13.1 by fluorescence in situ hybridization.

Animals↗
PubMed1992

Gene dosage is a mechanism for Charcot-Marie-Tooth disease type 1A.

Charcot-Marie-Tooth disease type 1A (CMT1A) is the most common inherited peripheral neuropathy in humans, characterized electrophysiologically by decreased nerve conduction velocities (NCVs). CMT1A is associated with a large submicroscopic DNA duplication in proximal 17p. In this report we demonstrate that a patient with a cytogenetically visible duplication, dup(17)(p11.2p12), has decreased NCV. Molecular analysis demonstrated this patient was duplicated for all the DNA markers duplicated in CMT1A as well as markers both proximal and distal to the CMT1A duplication. These data support the hypothesis that the CMT1A phenotype can result from a gene dosage effect.

Charcot-Marie-Tooth Disease↗