Search PubMed⌕ Search

Biomedical subjects

D H Ledbetter

Publications and source records attributed to D H Ledbetter.

At least 37 records · Page 2Linked to original sources
PubMed2000

Somatic segregation errors predominantly contribute to the gain or loss of a paternal chromosome leading to uniparental disomy for chromosome 15.

Paternal uniparental disomy (UPD) for chromosome 15 (UPD15), which is found in approximately 2% of Angelman syndrome (AS) patients, is much less frequent than maternal UPD15, which is found in 25% of Prader-Willi syndrome patients. Such a difference cannot be easily accounted for if 'gamete complementation' is the main mechanism leading to UPD. If we assume that non-disjunction of chromosome 15 in male meiosis is relatively rare, then the gain or loss of the paternal chromosome involved in paternal and maternal UPD15, respectively, may be more likely to result from a post-zygotic rather than a meiotic event. To test this hypothesis, the origin of the extra chromosome 15 was determined in 21 AS patients with paternal UPD15 with a paternal origin of the trisomy. Only 4 of 21 paternal UPD15 cases could be clearly attributed to a meiotic error. Furthermore, significant non-random X-chromosome inactivation (XCI) observed in maternal UPD15 patients (p < 0.001) provides indirect evidence that a post-zygotic error is also typically involved in loss of the paternal chromosome. The mean maternal and paternal ages of 33.4 and 39.4 years, respectively, for paternal UPD15 cases are increased as compared with normal controls. This may be simply the consequence of an age association with maternal non-disjunction leading to nullisomy for chromosome 15 in the oocyte, although the higher paternal age in paternal UPD15 as compared with maternal UPD15 cases is suggestive that paternal age may also play a role in the origin of paternal UPD15.

Adult↗
PubMed2000

Breakpoint sequences of an 1;8 translocation in a family with Gilles de la Tourette syndrome.

Gilles de la Tourette syndrome (GTS) is a common, heritable neurological disorder manifested by chronic motor and vocal tics with childhood onset. Previous extensive linkage analysis failed to identify a GTS gene based on an autosomal dominant pattern of inheritance. Recently, a family was reported with a balanced chromosomal translocation t(1;8)(q21.1;q22.1) in family members with GTS or tics. Chromosome 8q22.1 was previously implicated in GTS by both association and linkage results. We therefore cloned and sequenced both translocation breakpoints from this family. The CBFA2T1 gene was identified 11 kb distal to the 8q22.1 breakpoint. Sequencing of CBFA2TI exons within 37 unrelated GTS patients failed to identify any mutations. However, it is possible that the translocation altered the expression of this gene or another nearby gene. Examination of the breakpoint sequences revealed a duplication of six nucleotides from chromosome 8 but no change in the chromosome 1 sequence. The sequences immediately flanking the breakpoints on the two chromosomes were modestly similar, but the breakpoints did not occur within known interspersed repeats. Our results add to our knowledge of the genetics of GTS and the mechanisms of balanced chromosomal translocations.

Bacteriophages↗
PubMed1999

Risk of abnormal pregnancy outcome in carriers of balanced reciprocal translocations involving the Miller-Dieker syndrome (MDS) critical region in chromosome 17p13.3.

We studied the pedigrees of 14 families segregating a reciprocal translocation with one breakpoint in chromosome 17p13 and the other in the distal region of another autosome. All 14 were ascertained on the basis of an affected index case: 13 had Miller-Dieker syndrome (MDS) and one had dup(17p). In these 14 families, 38 balanced translocation carriers had 127 pregnancies, corrected for ascertainment bias by the exclusion of all index cases and carriers in the line of descent to the index cases. An abnormal phentotype, unbalanced chromosome constitution, or both, were found in 33 of 127 (26%) pregnancies: 15 of 127 (12%) had MDS and an unbalanced karyotype with del (17p); 9 of 127 (7%) had a less severe phenotype with dup(17p); and 9 were unstudied, although MDS with der(17) was usually suspected based on early death and multiple congenital anomalies. When unexplained pregnancy losses, including miscarriages and stillbirths, were excluded from the total, 33 of 99 (33%) pregnancies were phenotypically or genotypically abnormal. The overall risk of abnormal pregnancy outcome of 26% is in the upper range of the reported risk for unbalanced offspring of carrier parents assessed through liveborn aneuploid offspring [Gardner and Sutherland (1996), Oxford Univ. Press]. The risk increases to 33% when unexplained pregnancy losses are excluded from the total. These results are consistent with Daniel's model of risk based on the size of the unbalanced fragments [Daniel (1985) Clin Genet 28:216-224, Daniel et al. (1989) Am J Med Genet 31:14-53]. Pregnancy losses included 26 miscarriages (20%) and two stillbirths (2%) among the 127 pregnancies, similar to the respective population frequencies of 10-20% and 1%.

Abnormalities, Multiple↗
PubMed1999

Differences in the gyral pattern distinguish chromosome 17-linked and X-linked lissencephaly.

BACKGROUND: Classical lissencephaly or "smooth brain" is a human brain malformation that consists of diffuse agyria and pachygyria. Two genes associated with classical lissencephaly have recently been cloned-LIS1 from chromosome 17p13.3 and XLIS (also called DCX) from Xq22.3-q23. OBJECTIVE: We performed genotype-phenotype analysis in children with lissencephaly associated with mutations of different genes. METHODS: We compared the phenotype, especially brain imaging studies, in a series of 48 children with lissencephaly, including 12 with Miller-Dieker syndrome (MDS), which is associated with large deletions of LIS1 and other genes in the region, 24 with isolated lissencephaly sequence caused by smaller LIS1 deletions or mutations, and 12 with isolated lissencephaly sequence caused by XLIS mutations. RESULTS: We found consistent differences in the gyral patterns, with the malformation more severe posteriorly in individuals with LIS1 mutations and more severe anteriorly in individuals with XLIS mutations. Thus, mutations of LIS1 are associated with a posterior-to-anterior gradient of lissencephaly, whereas mutations of XLIS are associated with an anterior-to-posterior gradient. We also confirmed differences in severity between MDS and ILS17. Hypoplasia of the cerebellar vermis proved to be more common with XLIS mutations. CONCLUSION: It is often possible to predict the gene mutation from careful review of brain imaging studies.

Brain↗
PubMed1999

Genomic structure, chromosomal mapping, and expression pattern of human DCAMKL1 (KIAA0369), a homologue of DCX (XLIS).

Human DCAMKL1, also known as KIAA0369, is a homologue of DCX (Xq22. 3), a gene associated with X-linked lissencephaly and subcortical band heterotopia. This suggests that DCAMKL1 may play a role in neuronal migration. The gene also shows similarity to Ca2+/calmodulin-dependent protein kinases. We have determined its genomic structure, regional mapping, and expression pattern in human tissues. DCAMKL1 consists of at least 18 exons ranging from 58 to 3359 bp in length. We have characterized the exon/intron borders, and primers were designed to amplify each individual exon for mutation analysis. DCAMKL1 was mapped to chromosome 13q13 by fluorescence in situ hybridization. Northern blot analysis showed DCAMKL1 to be predominantly expressed in human fetal brain as a major transcript of about 5.8 kb.

Brain↗
PubMed1999

Molecular cloning and characterization of the human NUDC gene.

In both Aspergillus nidulans and the mouse, studies of the nuclear distribution gene C (NudC) have strongly suggested that the NudC protein interacts with NudF, which is the product of NudF, a homologue of human LIS1 (also know as PAFAH1B1), one of the causative genes for classical lissencephaly. We have isolated the human NUDC gene and its two processed pseudogenes. The human NUDC gene is highly conserved and its predicted amino acid sequence shows 94% identity to mouse NudC and 95% identity to rat NudC. The genomic structure of NUDC, its chromosomal localization, and expression pattern in human tissues were characterized. NUDC consists of at least 9 exons ranging from 66 bp to 266 bp in size and 8 introns from 92 bp to 2.0 kb in length, and the total genomic region spans about 8 kb. NUDC was mapped to 1p34-p35 by fluorescence in situ hybridization. Northern analysis showed a major 1.6 kb transcript in all fetal and adult tissues examined. Primers which amplify individual exons of NUDC were developed for mutation analysis.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗
PubMed1999

Significance of genetic testing for paternal uniparental disomy of chromosome 6 in neonatal diabetes mellitus.

Two patients who presented at birth with neonatal diabetes mellitus (NDM) are described: one with paternal uniparental disomy for chromosome 6 and one with normal, biparental inheritance. The first child presented with low birth weight, macroglossia, hypertelorism, and club foot in addition to NDM. In this patient hyperglycemia was transient, and insulin treatment was discontinued at 4 months of age. The second child also presented with low birth weight but was normal in appearance, and insulin dependence continues after 5 years. Genetic analysis with polymorphic DNA markers for chromosome 6 indicated the presence of paternal uniparental disomy (UPD) in the first case and normal, biparental inheritance in the second case. Paternal UPD 6 has been reported in 8 previous cases of which 6 showed NDM. Three cases with paternal UPD 6 also included additional anomalies, such as macroglossia, not usually associated with NDM. Therefore the simultaneous finding of NDM and macroglossia should be a strong indicator for genetic testing. The genetic finding of paternal UPD 6 allows prediction of a transient, rather than permanent, form of diabetes mellitus and no increased recurrence risk of transient NDM in subsequent pregnancies.

Aneuploidy↗
PubMed1999

The spectrum of mutations in UBE3A causing Angelman syndrome.

Angelman syndrome (AS) is characterized by mental retardation, absence of speech, seizures and motor dysfunction. AS is caused by maternal deletions for chromosome 15q11-q13, paternal uniparental disomy (UPD), imprinting defects or loss-of-function mutations in the UBE3A locus which encodes E6-AP ubiquitin-protein ligase. The UBE3A gene is imprinted with paternal silencing in human brain and similar silencing of the Ube3a locus in Purkinje cells and hippocampal neurons in the mouse. We have sequenced the major coding exons for UBE3A in 56 index patients with a clinical diagnosis of AS and a normal DNA methylation pattern. The analysis identified disease-causing mutations in 17 of 56 patients (30%) including 13 truncating mutations, two missense mutations, one single amino acid deletion and one stop codon mutation predicting an elongated protein. Mutations were identified in six of eight families (75%) with more than one affected case, and in 11 of 47 isolated cases (23%); no mutation was found in one family with two siblings, one with a typical and one with an atypical phenotype. Mutations were de novo in nine of the 11 isolated cases. An amino acid polymorphism of threonine substituted for alanine at codon 178 was identified, and a 3 bp length polymorphism was found in the intron upstream of exon 8. In all informative cases, phenotypic expression was consistent with imprinting with a normal phenotype when a mutation was on the paternal chromosome and an AS phenotype when a mutation was on the maternal chromosome. Laboratory diagnosis and genetic counseling for AS are complex, and mutation analysis is valuable in clinically typical AS patients with a normal methylation analysis.

Angelman Syndrome↗
PubMed1999

Large genomic duplicons map to sites of instability in the Prader-Willi/Angelman syndrome chromosome region (15q11-q13).

The most common etiology for Prader-Willi syndrome and Angelman syndrome is de novo interstitial deletion of chromosome 15q11-q13. Deletions and other recurrent rearrangements of this region involve four common 'hotspots' for breakage, termed breakpoints 1-4 (BP1-BP4). Construction of an approximately 4 Mb YAC contig of this region identified multiple sequence tagged sites (STSs) present at both BP2 and BP3, suggestive of a genomic duplication event. Interphase FISH studies demonstrated three to five copies on 15q11-q13, one copy on 16p11.1-p11.2 and one copy on 15q24 in normal controls, while analysis on two Class I deletion patients showed loss of approximately three signals at 15q11-q13 on one homolog. Multiple FISH signals were also observed at regions orthologous to both human chromosomes 15 and 16 in non-human primates, including Old World monkeys, suggesting that duplication of this region may have occurred approximately 20 million years ago. A BAC/PAC contig for the duplicated genomic segment (duplicon) demonstrated a size of approximately 400 kb. Surprisingly, the duplicon was found to contain at least seven different expressed sequence tags representing multiple genes/pseudogenes. Sequence comparison of STSs amplified from YAC clones uniquely mapped to BP2 or BP3 showed two different copies of the duplicon within BP3, while BP2 comprised a single copy. The orientation of BP2 and BP3 are inverted relative to each other, whereas the two copies within BP3 are in tandem. The presence of large duplicated segments on chromosome 15q11-q13 provides a mechanism for homologous unequal recombination events that may mediate the frequent rearrangements observed for this chromosome.

Angelman Syndrome↗
PubMed1999

Subcortical band heterotopia in rare affected males can be caused by missense mutations in DCX (XLIS) or LIS1.

Subcortical band heterotopia (SBH) are bilateral and symmetric ribbons of gray matter found in the central white matter between the cortex and the ventricular surface, which comprises the less severe end of the lissencephaly (agyria-pachygyria-band) spectrum of malformations. Mutations in DCX (also known as XLIS ) have previously been described in females with SBH. We have now identified mutations in either the DCX or LIS1 gene in three of 11 boys studied, demonstrating for the first time that mutations of either DCX or LIS1 can cause SBH or mixed pachygyria-SBH (PCH-SBH) in males. All three changes detected are missense mutations, predicted to be of germline origin. They include a missense mutation in exon 4 of DCX in a boy with PCH-SBH (R78H), a different missense mutation in exon 4 of DCX in a boy with mild SBH and in his mildly affected mother (R89G) and a missense mutation in exon 6 of LIS1 in a boy with SBH (S169P). The missense mutations probably account for the less severe brain malformations, although other patients with missense mutations in the same exons have had diffuse lissencephaly. Therefore, it appears likely that the effect of the specific amino acid change on the protein determines the severity of the phenotype, with some mutations enabling residual protein function and allowing normal migration in a larger proportion of neurons. However, we expect that somatic mosaic mutations of both LIS1 and DCX will also prove to be an important mechanism in causing SBH in males.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗
PubMed1999

Characterization of physical gap sizes at human telomeres.

Genome-wide physical and genetic mapping efforts have not yet fully addressed the problem of closure at the telomeric ends of human chromosomes. Targeted efforts at cloning human and mouse telomeres have succeeded in identifying unique sequences at most telomeres, but gap sizes between these telomere clones and the distal markers on integrated genetic/physical maps remain largely unknown. As telomeric regions are known to be the most gene-rich regions of the human genome, filling these gaps should have a high priority in completion of the Human Genome Project. We reported previously a first generation set of unique sequence probes for human telomeric regions. Of 41 human telomere regions, 33 were represented by unique clones with a known distance (</= 300 kb) from the end of the chromosome; clones for the remaining eight telomeric regions had not yet been identified and were represented by the most distal markers on the integrated genetic/physical map. We have identified unique telomere clones for four of the remaining telomeres, 9p, 12p, 15q, and 16p. To determine the telomeric gap size for these chromosomes and five other human telomeres, interphase FISH analysis was performed to measure the distance between each telomere clone and the corresponding most distal marker. These studies provide distance estimates ranging from <100 kb to >1 Mb, thus defining the physical mapping task for filling telomeric gaps.

Chromosome Mapping↗
PubMed1999

Intrauterine growth retardation associated with maternal uniparental disomy for chromosome 6 unmasked by congenital adrenal hyperplasia.

We report the first case of maternal uniparental disomy for chromosome 6 (UPD6mat) ascertained through congenital adrenal hyperplasia (CAH), which arose because of reduction to homozygosity of an autosomal recessive mutation. This case suggests that UPD6mat is associated with intrauterine growth retardation (IUGR). A case of paternal UPD (involving only the short arm of chromosome 6) ascertained as CAH has previously been reported, but was not stated to have IUGR. Our patient was born with IUGR followed by extraordinarily good catch-up growth. She had a history of a marked lag in motor development. She presented at 2.65 y of age with pubarche of 3 mo duration, clitoral enlargement, and an advanced bone age. Simple virilizing CAH was diagnosed by elevations of plasma 17-hydroxyprogesterone and testosterone. Mutation analysis showed that the CAH was due to homozygosity for the 1172N exon 4 mutation. When parental DNA was examined, the mother was found to be heterozygous for the uncommon exon 4 mutation, while the father had no detectable mutations. DNA microsatellite analysis was subsequently performed on the patient and parents using polymorphic markers spanning the entire chromosome 6. Seven markers were informative for inheritance of a single maternal allele and absence of paternal alleles in the proband. Analysis of microsatellite markers from other chromosomes confirmed biparental inheritance at these loci. This combination of findings is diagnostic of UPD6mat. The only other reported case of UPD6mat was discovered serendipitously when genotyped for renal transplantation; this patient had a history of IUGR. Since both cases of UPD6mat had IUGR, the phenotype appears to include IUGR as well as the potential to unmask an autosomal recessive trait.

Adrenal Hyperplasia, Congenital↗
PubMed1998

The human ROX gene: genomic structure and mutation analysis in human breast tumors.

We have recently isolated a human gene, ROX, encoding a new member of the basic helix-loop-helix leucine zipper protein family. ROX is capable of heterodimerizing with Max and acts as a transcriptional repressor in an E-box-driven reporter gene system, while it was found to activate transcription in HeLa cells. ROX expression levels vary during the cell cycle, being down-regulated in proliferating cells. These biological properties of ROX suggest a possible involvement of this gene in cell proliferation and differentiation. The ROX gene maps to chromosome 17p13.3, a region frequently deleted in human malignancies. Here we report the genomic structure of the human ROX gene, which is composed of six exons and spans a genomic region of less than 40 kb. In an attempt to identify possible inactivating mutations in the ROX gene in human breast cancer, we performed a single-strand conformation polymorphism analysis of its coding region in 16 sporadic breast carcinomas showing loss of heterozygosity in the 17p13.3 region. No mutations were found in this analysis. Five nucleotide polymorphisms were identified in the ROX gene, three of which caused an amino acid substitution. These nucleotide changes were present in the peripheral blood DNAs of both the patients and the control individuals. In vitro translated assays did not show a significant decrease in the ability of the ROX mutant proteins to bind DNA or to repress transcription of a driven reporter gene in HEK293 cells. Despite experimental evidence that ROX might act as a tumor suppressor gene, our data suggest that mutations in the coding region of ROX are uncommon in human breast tumorigenesis.

Basic Helix-Loop-Helix Leucine Zipper Transcriptio↗
PubMed1998

Comparative genomic hybridization: a comparison with molecular and cytogenetic analysis.

Comparative genomic hybridization (CGH) is a powerful technique for detecting copy number changes throughout the genome. We describe the development of a versatile image analysis program for CGH studies. Several methods for the production of metaphases which give optimum hybridization signals have also been assessed. CGH analysis was performed on DNA samples from several different and clinically relevant specimens: amniotic fluid cells trisomic for a single chromosome, lymphoblastoid cell lines with abnormalities involving single chromosome bands, malignant cell lines and biopsy material from primary ovarian carcinomas. The results were compared with those derived from G-banding, chromosome painting, and molecular genetic techniques. Our data demonstrate that CGH was able to detect a wide range of quantitative genetic alterations including duplication or deletion of single chromosome bands. CGH analysis also indicated the presence of genetic abnormalities that were not detected by other cytogenetic or molecular approaches. Moreover, our CGH methodology allowed the ready comparison of CGH results from different tumors, a process which greatly facilitated identification of shared genetic changes.

Amniotic Fluid↗
PubMed1998

Graded reduction of Pafah1b1 (Lis1) activity results in neuronal migration defects and early embryonic lethality.

Heterozygous mutation or deletion of the beta subunit of platelet-activating factor acetylhydrolase (PAFAH1B1, also known as LIS1) in humans is associated with type I lissencephaly, a severe developmental brain disorder thought to result from abnormal neuronal migration. To further understand the function of PAFAH1B1, we produced three different mutant alleles in mouse Pafah1b1. Homozygous null mice die early in embryogenesis soon after implantation. Mice with one inactive allele display cortical, hippocampal and olfactory bulb disorganization resulting from delayed neuronal migration by a cell-autonomous neuronal pathway. Mice with further reduction of Pafah1b1 activity display more severe brain disorganization as well as cerebellar defects. Our results demonstrate an essential, dosage-sensitive neuronal-specific role for Pafah1b1 in neuronal migration throughout the brain, and an essential role in early embryonic development. The phenotypes observed are distinct from those of other mouse mutants with neuronal migration defects, suggesting that Pafah1b1 participates in a novel pathway for neuronal migration.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗
PubMed1998

A simple VNTR-PCR method for detecting maternal cell contamination in prenatal diagnosis.

The effectiveness of variable number tandem repeats (VNTRs) was evaluated in the detection of maternal cell contamination. Nonradioactive PCRs were performed on 30 sets of prenatal tissue using VNTRs as primers. The combination of two VNTRs (YNZ22 and APOB) provided information on all 30 cases, distinguishing maternal-fetal genotype patterns and detecting maternal cell contamination in 5 of 30 prenatal cases. The amplification of these two VNTRs does not require radioactive or fluorescence labeling, and a small gel electrophoresis is sufficient to see the maternal-fetal genotype pattern. By this method, detection of maternal cell contamination in prenatal tissues can be obtained in 1 day, without the use of expensive instruments, thus providing DNA laboratories a very sensitive, rapid, and simple proof pretest on all prenatal tissues before performing the final genetic diagnostic testing.

Amniocentesis↗
PubMed1998

LIS1 and XLIS (DCX) mutations cause most classical lissencephaly, but different patterns of malformation.

Classical lissencephaly (LIS) is a neuronal migration disorder resulting in brain malformation, epilepsy and mental retardation. Deletions or mutations of LIS1 on 17p13.3 and mutations in XLIS ( DCX ) on Xq22.3-q23 produce LIS. Direct DNA sequencing of LIS1 and XLIS was performed in 25 children with sporadic LIS and no deletion of LIS1 by fluorescence in situ hybridization. Mutations of LIS1 were found by sequencing ( n = 8) and Southern blot ( n = 2) in a total of 10 patients (40%) of both sexes and mutations of XLIS in five males (20%). Combined with previous data, deletions or mutations of these two genes account for approximately 76% of isolated LIS. These data demonstrate that LIS1 and XLIS mutations cause the majority of, though not all, human LIS. The mutations in LIS1 were predicted to result in protein truncation in six of eight patients and splice site mutations in two, all of which disrupt one or more of the seven WD40 repeats contained in the LIS1 protein. Point mutations in XLIS identified the C-terminal serine/proline-rich region as potentially important for protein function. The patients with mutations were included in a genotype-phenotype analysis of 32 subjects with deletions or other mutations of these two genes. Whereas the brain malformation due to LIS1 mutations was more severe over the parietal and occipital regions, XLIS mutations produced the reverse gradient, which was more severe over the frontal cortex. The distinct LIS patterns suggest that LIS1 and XLIS may be part of overlapping, but distinct, signaling pathways that promote neuronal migration.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗