Biomedical subjects

D H Ledbetter

Publications and source records attributed to D H Ledbetter.

At least 19 recordsLinked to original sources

PubMed2001

LIS1 missense mutations cause milder lissencephaly phenotypes including a child with normal IQ.

BACKGROUND: Classical lissencephaly is a disorder of neuroblast migration with most patients having mutations of either the LIS1 or DCX genes. Most patients with lissencephaly secondary to LIS1 mutations have a severe malformation consisting of generalized agyria and pachygyria. However, increasing experience suggests that the phenotypic spectrum is wider than previously thought. METHODS: The authors describe the clinical and imaging features and mutation data of the five known patients with missense mutations of the LIS1 gene and emphasize one patient with normal intelligence. RESULTS: Patients with a missense mutation of the LIS1 gene have a wider and milder spectrum of cortical malformations and clinical sequelae compared with patients with other mutation types. CONCLUSION: Milder and more variable phenotypes seen in patients with missense mutations of LIS1 are likely a consequence of suboptimal function of the mutant LIS1 protein, rather than complete loss of function of this protein. The authors suggest that the few patients found thus far with missense mutations of LIS1 results from an underascertainment of patients with more subtle malformations and that abnormalities of the LIS1 gene may account for a greater spectrum of neurologic problems in childhood than has previously been appreciated.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗

PubMed2001

Incomplete penetrance with normal MRI in a woman with germline mutation of the DCX gene.

X-linked isolated lissencephaly sequence (ILS) and subcortical band heterotopia are allelic human disorders associated with mutations of the DCX gene in both familial and sporadic forms. The authors describe a large Sardinian family in which three brothers with ILS have a missense mutation of the DCX gene. Their mother, a nonmosaic carrier, has a normal phenotype and cranial MRI. Skewed X-inactivation in the lymphocytes was also ruled out. This is the first report of an asymptomatic carrier of a DCX mutation likely due to apparent nonpenetrance.

Adolescent↗

PubMed2001

The human aminophospholipid-transporting ATPase gene ATP10C maps adjacent to UBE3A and exhibits similar imprinted expression.

Maternal duplications of the imprinted 15q11-13 domain result in an estimated 1%-2% of autism-spectrum disorders, and linkage to autism has been identified within 15q12-13. UBE3A, the Angelman syndrome gene, has, to date, been the only maternally expressed, imprinted gene identified within this region, but mutations have not been found in autistic patients. Here we describe the characterization of ATP10C, a new human imprinted gene, which encodes a putative protein homologous to the mouse aminophospholipid-transporting ATPase Atp10c. ATP10C maps within 200 kb distal to UBE3A and, like UBE3A, also demonstrates imprinted, preferential maternal expression in human brain. The location and imprinted expression of ATP10C thus make it a candidate for chromosome 15-associated autism and suggest that it may contribute to the Angelman syndrome phenotype.

Angelman Syndrome↗

PubMed2001

Further evidence for linkage of Gilles de la Tourette syndrome (GTS) susceptibility loci on chromosomes 2p11, 8q22 and 11q23-24 in South African Afrikaners.

Utilizing DNA samples from 91 Afrikaner nuclear families with one or more affected children, five genomic regions on chromosomes 2p, 8q, 11q, 20q, and 21q that gave evidence for association with GTS in previous case-control association studies were investigated for linkage and association with GTS. Highly polymorphic markers with mean heterozygosity of 0.77 were typed and resulting genotypes evaluated using single marker transmission disequilibrium (TDT), single marker haplotype relative risk (HRR), and multi-marker "extended" TDT and HRR methods. Single marker TDT analysis showed evidence for linkage or association, with p-values near 0.05, for markers D2S139, GATA28F12, and D11S1377 on chromosomes 2p11, 8q22 and 11q23-24, respectively. Extended, two-locus TDT and HRR analysis provided further evidence for linkage or association on chromosome 2 with p-values of 0.007 and 0.025, and chromosome 8 with p-values of 0.059 and 0.013, respectively. These results provide important additional evidence for the location of GTS susceptibility loci.

Case-Control Studies↗

PubMed2001

Olfactory receptor-gene clusters, genomic-inversion polymorphisms, and common chromosome rearrangements.

The olfactory receptor (OR)-gene superfamily is the largest in the mammalian genome. Several of the human OR genes appear in clusters with > or = 10 members located on almost all human chromosomes, and some chromosomes contain more than one cluster. We demonstrate, by experimental and in silico data, that unequal crossovers between two OR gene clusters in 8p are responsible for the formation of three recurrent chromosome macrorearrangements and a submicroscopic inversion polymorphism. The first two macrorearrangements are the inverted duplication of 8p, inv dup(8p), which is associated with a distinct phenotype, and a supernumerary marker chromosome, +der(8)(8p23.1pter), which is also a recurrent rearrangement and is associated with minor anomalies. We demonstrate that it is the reciprocal of the inv dup(8p). The third macrorearrangment is a recurrent 8p23 interstitial deletion associated with heart defect. Since inv dup(8p)s originate consistently in maternal meiosis, we investigated the maternal chromosomes 8 in eight mothers of subjects with inv dup(8p) and in the mother of one subject with +der(8), by means of probes included between the two 8p-OR gene clusters. All the mothers were heterozygous for an 8p submicroscopic inversion that was delimited by the 8p-OR gene clusters and was present, in heterozygous state, in 26% of a population of European descent. Thus, inversion heterozygosity may cause susceptibility to unequal recombination, leading to the formation of the inv dup(8p) or to its reciprocal product, the +der(8p). After the Yp inversion polymorphism, which is the preferential background for the PRKX/PRKY translocation in XX males and XY females, the OR-8p inversion is the second genomic polymorphism that confers susceptibility to the formation of common chromosome rearrangements. Accordingly, it may be possible to develop a profile of the individual risk of having progeny with chromosome rearrangements.

Chromosome Breakage↗

PubMed2001

LIS1: from cortical malformation to essential protein of cellular dynamics.

The LIS1 gene was cloned following the study of children with lissencephaly and cytogenetic abnormalities involving chromosome 17p, however, the role of the LIS1 protein in normal cortical development is not precisely defined. LIS1 is a component of evolutionarily conserved intracellular multiprotein complexes and recent literature shows that these complexes are essential, not only for neuronal migration, but they might also be fundamental components of the machinery for cell proliferation and intracellular transport.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗

PubMed2001

Mutation analysis of the DCX gene and genotype/phenotype correlation in subcortical band heterotopia.

Subcortical band heterotopia (SBH) comprises part of a spectrum of phenotypes associated with classical lissencephaly (LIS). LIS and SBH are caused by alterations in at least two genes: LIS1 (PAFAH1B1) at 17p13.3 and DCX (doublecortin) at Xq22.3-q23. DCX mutations predominantly cause LIS in hemizygous males and SBH in heterozygous females, and we have evaluated several families with LIS male and SBH female siblings. In this study, we performed detailed DCX mutation analysis and genotype-phenotype correlation in a large cohort with typical SBH. We screened 26 sporadic SBH females and 11 LIS/SBH families for DCX mutations by direct sequencing. We found 29 mutations in 22 sporadic patients and 11 pedigrees, including five deletions, four nonsense mutations, 19 missense mutations and one splice donor site mutation. The DCX mutation prevalence was 84.6% (22 of 26) in sporadic SBH patients and 100% (11 of 11) in SBH pedigrees. Maternal germline mosaicism was found in one family. Significant differences in genotype were found in relation to band thickness and familial vs sporadic status.

Brain↗

PubMed2001

Molecular characterisation of four cases of intrachromosomal triplication of chromosome 15q11-q14.

CONTEXT: Chromosomal abnormalities that involve the proximal region of chromosome 15q occur relatively frequently in the human population. However, interstitial triplications involving one 15 homologue are very rare with three cases reported to date. OBJECTIVE: To provide a detailed molecular characterisation of four additional patients with interstitial triplications of chromosome 15q11-q14. DESIGN: Molecular analyses were performed using DNA markers and probes specific for the 15q11-q14 region. SETTING: Molecular cytogenetics laboratory at the University of Chicago. SUBJECTS: Four patients with mild to severe mental retardation and features of Prader-Willi syndrome (PWS) or Angelman syndrome (AS) were referred for molecular cytogenetic analysis following identification of a suspected duplication/triplication of chromosome 15q11-q14 by routine cytogenetic analysis. MAIN OUTCOME MEASURES: Fluorescence in situ hybridisation (FISH) was performed to determine the type of chromosomal abnormality present, the extent of the abnormal region, and the orientation of the extra chromosomal segments. Molecular polymorphism analysis was performed to determine the parental origin of the abnormality. Methylation and northern blot analyses of the SNRPN gene were performed to determine the effect of extra copies of the SNRPN gene on its methylation pattern and expression. RESULTS: Fluorescence in situ hybridisation (FISH) using probes within and flanking the Prader-Willi/Angelman syndrome critical region indicated that all patients carried an intrachromosomal triplication of proximal 15q11-q14 in one of the two chromosome 15 homologues (trip(15)). In all patients the orientation of the triplicated segments was normal-inverted-normal, suggesting that a common mechanism of rearrangement may have been involved. Microsatellite analysis showed the parental origin of the trip(15) to be maternal in three cases and paternal in one case. The paternal triplication patient had features similar to PWS, one maternal triplication patient had features similar to AS, and the other two maternal triplication patients had non-specific findings including hypotonia and mental retardation. Methylation analysis at exon 1 of the SNRPN locus showed increased dosage of either the paternal or maternal bands in the paternal or maternal triplication patients, respectively, suggesting that the methylation pattern shows a dose dependent increase that correlates with the parental origin of the triplication. In addition, the expression of SNRPN was analysed by northern blotting and expression levels were consistent with dosage and parental origin of the triplication. CONCLUSIONS: These four additional cases of trip(15) will provide additional information towards understanding the phenotypic effects of this abnormality and aid in understanding the mechanism of formation of other chromosome 15 rearrangements.

Blotting, Northern↗

PubMed2000

The location and type of mutation predict malformation severity in isolated lissencephaly caused by abnormalities within the LIS1 gene.

Lissencephaly is a cortical malformation secondary to impaired neuronal migration resulting in mental retardation, epilepsy and motor impairment. It shows a severity spectrum from agyria with a severely thickened cortex to posterior band heterotopia only. The LIS1 gene on 17p13.3 encodes a 45 kDa protein named PAFAH1B1 containing seven WD40 repeats. This protein is required for optimal neuronal migration by two proposed mechanisms: as a microtubule-associated protein and as one subunit of the enzyme platelet-activating factor acetylhydrolase. Approximately 65% of patients with isolated lissencephaly sequence (ILS) show intragenic mutations or deletions of the LIS1 gene. We analyzed 29 non-deletion ILS patients carrying a mutation of LIS1 and we report 15 novel mutations. Patients with missense mutations had a milder lissencephaly grade compared with those with mutations leading to a shortened or truncated protein (P = 0.022). Early truncation/deletion mutations in the putative microtubule-binding domain resulted in a more severe lissencephaly than later truncation/deletion mutations (P < 0.001). Our results suggest that the lissencephaly severity in ILS caused by LIS1 mutations may be predicted by the type and location of the mutation. Using a spectrum of ILS patients, we confirm the importance of specific WD40 repeats and a putative microtubule-binding domain for PAFAH1B1 function. We suggest that the small number of missense mutations identified may be due to underdiagnosis of milder phenotypes and hypothesize that the greater lissencephaly severity seen in Miller-Dieker syndrome may be secondary to the loss of another cortical development gene in the deletion of 17p13.3.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗

PubMed2000

Partial paternal uniparental disomy of chromosome 6 in an infant with neonatal diabetes, macroglossia, and craniofacial abnormalities.

Neonatal diabetes, which can be transient or permanent, is defined as hyperglycemia that presents within the first month of life and requires insulin therapy. Transient neonatal diabetes mellitus has been associated with abnormalities of the paternally inherited copy of chromosome 6, including duplications of a portion of the long arm of chromosome 6 and uniparental disomy, implicating overexpression of an imprinted gene in this disorder. To date, all patients with transient neonatal diabetes mellitus and uniparental disomy have had complete paternal isodisomy. We describe a patient with neonatal diabetes, macroglossia, and craniofacial abnormalities, with partial paternal uniparental disomy of chromosome 6 involving the distal portion of 6q, from 6q24-qter. This observation demonstrates that mitotic recombination of chromosome 6 can also give rise to uniparental disomy and neonatal diabetes, a situation similar to that observed in Beckwith-Wiedemann syndrome, another imprinted disorder. This finding has clinical implications, since somatic mosaicism for uniparental disomy of chromosome 6 should also be considered in patients with transient neonatal diabetes mellitus.

Aneuploidy↗

PubMed2000

An optimized set of human telomere clones for studying telomere integrity and architecture.

Telomere-specific clones are a valuable resource for the characterization of chromosomal rearrangements. We previously reported a first-generation set of human telomere probes consisting of 34 genomic clones, which were a known distance from the end of the chromosome ( approximately 300 kb), and 7 clones corresponding to the most distal markers on the integrated genetic/physical map (1p, 5p, 6p, 9p, 12p, 15q, and 20q). Subsequently, this resource has been optimized and completed: the size of the genomic clones has been expanded to a target size of 100-200 kb, which is optimal for use in genome-scanning methodologies, and additional probes for the remaining seven telomeres have been identified. For each clone we give an associated mapped sequence-tagged site and provide distances from the telomere estimated using a combination of fiberFISH, interphase FISH, sequence analysis, and radiation-hybrid mapping. This updated set of telomeric clones is an invaluable resource for clinical diagnosis and represents an important contribution to genetic and physical mapping efforts aimed at telomeric regions.

Chromosomes, Artificial, Yeast↗

PubMed2000

Inverted duplication of the distal short arm of chromosome 3 associated with lobar holoprosencephaly and lumbosacral meningomyelocele.

A fetus with lobar holoprosencephaly and lumbosacral meningomyelocele associated with duplication of the short arm of chromosome 3 is reported. The anomalies were detected on fetal ultrasound at 20 weeks' gestation and the autopsy findings correlated well with the prenatal findings. The fetal karyotype was 46,XY,der(3)del(3)(p26) dup(3)(p26p21.3). The association of holoprosencephaly with duplication 3p is well known, but to the best of our knowledge this is the first reported association of meningomyelocele with 3p duplication. These findings suggest that a gene or genes with a crucial role in central nervous system development are located on the short arm of chromosome 3.

Abnormalities, Multiple↗

PubMed2000

Lissencephaly and subcortical band heterotopia: molecular basis and diagnosis.

Magnetic resonance imaging is now used routinely in the evaluation of developmental and neurological disorders and provides exquisite images of the living human brain. Consequently, it is evident that cortical malformations are more common than previously thought. Among the most severe is classical lissencephaly, in which the cortex lacks the complex folding that characterizes the normal human brain. Lissencephaly includes agyria and pachygyria, and merges with subcortical band heterotopia. Current molecular genetic techniques combined with the identification of affected patients have enabled the detection of two of the genes responsible: LIS1 (PAFAH1B1) on chromosome 17 and DCX (doublecortin) on the X chromosome. This review highlights the discovery of these genes and discusses the advances made in understanding the molecular basis of cortical development and improvements in diagnosis and genetic counseling.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗

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↗