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M Leppert

Publications and source records attributed to M Leppert.

At least 37 records · Page 2Linked to original sources
PubMed1999

The identical 5' splice-site acceptor mutation in five attenuated APC families from Newfoundland demonstrates a founder effect.

Inherited mutations of the APC gene predispose carriers to multiple adenomatous polyps of the colon and rectum and to colorectal cancer. Mutations located at the extreme 5' end of the APC gene, however, are associated with a less severe disease known as attenuated adenomatous polyposis coli (AAPC). Many individuals with AAPC develop relatively few colorectal polyps but are still at high risk for colorectal cancer. We report here the identification of a 5' APC germline mutation in five separately ascertained AAPC families from Newfoundland, Canada. This disease-causing mutation is a single basepair change (G to A) in the splice-acceptor region of APC intron 3 that creates a mutant RNA without exon 4 of APC. The observation of the same APC mutation in five families from the same geographic area demonstrates a founder effect. Furthermore, the identification of this germline mutation strengthens the correlation between the 5' location of an APC disease-causing mutation and the attenuated polyposis phenotype.

Adenomatous Polyposis Coli↗
PubMed1999

The rod photoreceptor ATP-binding cassette transporter gene, ABCR, and retinal disease: from monogenic to multifactorial.

The ABCR gene encodes a rod photoreceptor specific ATP-binding cassette transporter. Mutations in ABCR are associated with at least four inherited retinal dystrophies: Stargardt disease, Fundus Flavimaculatus, cone-rod dystrophy, and retinitis pigmentosa. A statistically significant increase in heterozygous ABCR alterations has been identified in patients with age-related macular degeneration (AMD). A pedigree is described which manifests both Stargardt disease and AMD in which an ABCR mutation cosegregates with both disease phenotypes. These data from this case report support the hypothesis that ABCR is a dominant susceptibility locus for AMD. Recent work regarding ABCR is reviewed and a model is presented in which decreased ABCR function correlates with severity of retinal disease.

ATP-Binding Cassette Transporters↗
PubMed1999

Sequential neuromotor examination in children with intrauterine cocaine/polydrug exposure.

Data are presented on 157 newborn infants followed sequentially in a randomized home-based nursing-intervention trial for drug-exposed infants with follow up at 3 (N=118), 6 (N=124), and 12 months (N=77). The objectives of this study were to describe the longitudinal neurodevelopmental status of a cohort of children with intrauterine exposure to illicit drugs during their gestation, characterize the evolution of early tone abnormalities in a polydrug-exposed cohort, and determine whether neuromotor outcome is associated with drug-exposure patterns. For analysis, infants were grouped based on maternal drug-use pattern and the presence of drug metabolites in the neonatal drug screen. The sequential neuromotor examination was used at each age to define the neuromotor status of six domains and define categorical classifications as either normal, suspect, or abnormal. Multiple patterns of neuromotor abnormalities were observed during the neonatal period; most resolved over time. Axial hypotonia was a prominent finding in the neonatal period; however, it was infrequent in abnormal examinations at 12 months. Increased lower-extremity tone was a less frequent finding during the neonatal period. Infants whose neonatal urine drug screen was positive for both cocaine and opiates, were more likely than infants with negative urine drug screens, cocaine only, or opiate only drug screen results to have abnormal neuromotor examinations; while positive maternal drug screens for concurrent cocaine and opiate use were associated with peripheral hypertonia. Persistence of increased leg-extensor tone was found in 67% of the abnormal examinations at 12 months. Acquisition of rolling and walking was delayed in the drug-exposed cohort.

Age Factors↗
PubMed1999

Genotype/Phenotype analysis of a photoreceptor-specific ATP-binding cassette transporter gene, ABCR, in Stargardt disease.

Mutation scanning and direct DNA sequencing of all 50 exons of ABCR were completed for 150 families segregating recessive Stargardt disease (STGD1). ABCR variations were identified in 173 (57%) disease chromosomes, the majority of which represent missense amino acid substitutions. These ABCR variants were not found in 220 unaffected control individuals (440 chromosomes) but do cosegregate with the disease in these families with STGD1, and many occur in conserved functional domains. Missense amino acid substitutions located in the amino terminal one-third of the protein appear to be associated with earlier onset of the disease and may represent misfolding alleles. The two most common mutant alleles, G1961E and A1038V, each identified in 16 of 173 disease chromosomes, composed 18.5% of mutations identified. G1961E has been associated previously, at a statistically significant level in the heterozygous state, with age-related macular degeneration (AMD). Clinical evaluation of these 150 families with STGD1 revealed a high frequency of AMD in first- and second-degree relatives. These findings support the hypothesis that compound heterozygous ABCR mutations are responsible for STGD1 and that some heterozygous ABCR mutations may enhance susceptibility to AMD.

ATP-Binding Cassette Transporters↗
PubMed1999

Novel locus for autosomal dominant hereditary spastic paraplegia, on chromosome 8q.

Hereditary spastic paraplegia (HSP) is a clinically and genetically heterogeneous group of disorders characterized by insidiously progressive spastic weakness in the legs. Genetic loci for autosomal dominant HSP exist on chromosomes 2p, 14q, and 15q. These loci are excluded in 45% of autosomal dominant HSP kindreds, indicating the presence of additional loci for autosomal dominant HSP. We analyzed a Caucasian kindred with autosomal dominant HSP and identified tight linkage between the disorder and microsatellite markers on chromosome 8q (maximum two-point LOD score 5.51 at recombination fraction 0). Our results clearly establish the existence of a locus for autosomal dominant HSP on chromosome 8q23-24. Currently this locus spans 6.2 cM between D8S1804 and D8S1774 and includes several potential candidate genes. Identifying this novel HSP locus on chromosome 8q23-24 will facilitate discovery of this HSP gene, improve genetic counseling for families with linkage to this locus, and extend our ability to correlate clinical features with different HSP loci.

Adult↗
PubMed1999

Hyperparathyroidism-jaw tumor syndrome: the HRPT2 locus is within a 0.7-cM region on chromosome 1q.

Hyperparathyroidism-jaw tumor syndrome (HPT-JT) is an autosomal dominant disease characterized by the development of multiple parathyroid adenomas and multiple fibro-osseous tumors of the maxilla and mandible. Some families have had affected members with involvement of the kidneys, variously reported as Wilms tumors, nephroblastomas, and hamartomas. The HPT-JT gene (HRPT2) maps to chromosome 1q25-q31. We describe further investigation of two HPT-JT families (K3304 and K3349) identified through the literature. These two expanded families and two previously reported families were investigated jointly for linkage with 21 new, closely linked markers. Multipoint linkage analysis resulted in a maximum LOD score of 7.83 (at recombination fraction 0) for markers D1S2848-D1S191. Recombination events in these families reduced the HRPT2 region to approximately 14.7 cM. In addition, two of these four study families (i.e., K3304 and K11687) share a 2.2-cM length of their (expanded) affected haplotype, indicating a possible common origin. Combining the linkage data and shared-haplotype data, we propose a 0.7-cM candidate region for HRPT2.

Adenoma↗
PubMed1999

Delineation of the critical interval of Bardet-Biedl syndrome 1 (BBS1) to a small region of 11q13, through linkage and haplotype analysis of 91 pedigrees.

Bardet-Biedl syndrome (BBS) is a genetically heterogeneous recessive disease characterized primarily by atypical retinitis pigmentosa, obesity, polydactyly, hypogenitalism, and mental retardation. Despite the presence of at least five loci in the human genome, on chromosomes 2q, 3p, 11q, 15q and 16q, as many as 50% of the mutations appear to map to the BBS1 locus on 11q13. The recessive mode of inheritance and the genetic heterogeneity of the syndrome, as well as the inability to distinguish between different genetic loci by phenotypic analyses, have hindered efforts to delineate the 11q13 region as a first step toward cloning the mutated gene. To circumvent these difficulties, we collected a large number of BBS pedigrees of primarily North American and European origin and performed genetic analysis, using microsatellites from all known BBS genomic regions. Heterogeneity analysis established a 40.5% contribution of the 11q13 locus to BBS, and haplotype construction on 11q-linked pedigrees revealed several informative recombinants, defining the BBS1 critical interval between D11S4205 and D11S913, a genetic distance of 2.9 cM, equivalent to approximately 2.6 Mb. Loss of identity by descent in two consanguineous pedigrees was also observed in the region, potentially refining the region to 1.8 Mb between D11S1883 and D11S4944. The identification of multiple recombinants at the same position forms the basis for physical mapping efforts, coupled with mutation analysis of candidate genes, to identify the gene for BBS1.

Bardet-Biedl Syndrome↗
PubMed1999

Benign familial neonatal epilepsy with mutations in two potassium channel genes.

The significant progress made over the past year in understanding the basis for a form of neonatal seizures can be attributed to the successful positional cloning of two new voltage-gated potassium channel genes. Expression studies have increased our understanding of the biology of these channels and their role in epilepsy.

Chromosomes, Human, Pair 20↗
PubMed1999

Genetic linkage of the dentinogenesis imperfecta type III locus to chromosome 4q.

Dentinogenesis imperfecta type III (DGI-III) is an autosomal-dominant disorder of dentin formation which appears in a tri-racial southern Maryland population known as the "Brandywine isolate". This disease has suggestive evidence of linkage to the long arm of human chromosome 4 (LOD score of 2.0) in a family presenting with both juvenile periodontitis and DGI-III. The purpose of this study was to screen a family presenting with only DGI-III to determine if this locus was indeed on chromosome 4q. Furthermore, we wanted to determine if DGI-III co-localized with dentinogenesis imperfecta type II (DGI-II), which has been localized to 4q21-q23. Therefore, a large kindred from the Brandywine isolate was identified, oral examination performed, and blood samples collected from 21 family members. DNA from this family was genotyped with 6 highly polymorphic markers that span the DGI-II critical region of chromosome 4q. Analysis of the data yielded a maximum two-point LOD score of 4.87 with a marker for the dentin matrix protein 1 (DMP1) locus, a gene contained in the critical region for DGI-II. Our results demonstrated that the DGI-III locus is on human chromosome 4q21 within a 6.6 cM region that overlaps the DGI-II critical region. These results are consistent with the hypothesis that DGI-II is either an allelic variant of DGI-III or the result of mutations in two tightly linked genes.

Aggressive Periodontitis↗
PubMed1999

Human retinoic X receptor beta: complete genomic sequence and mutation search for ossification of posterior longitudinal ligament of the spine.

Ossification of the posterior longitudinal ligament of the spine (OPLL) is characterized by ectopic bone formation in the ligament. OPLL is a very common disorder, in fact it constitutes the leading cause of myelopathy among Japanese. In the previous report, we provided the genetic linkage evidence that the genetic susceptibility of OPLL mapped to HLA complex of chromosome 6. As a candidate gene approach, retinoic X receptor beta (RXR beta), assigned to chromosome 6p21.3 adjacent to HLA class II, was analyzed for a possible causality. To start screening for the molecular variants of RXR beta in OPLL subjects, we first obtained P1 phage genomic clones containing the entire human RXR beta and elucidated the genomic organization of the gene. The human RXR beta is composed of 10 exons spanning over 6.2 kb of genomic DNA. Sequence analysis of the promoter region revealed a GC-rich sequence without TATA motif. We have identified three distinct molecular variants, one was in exon 10 and two were in the intergenic region between RXR beta and collagen 11A2 (COL11A2). Two variants in the intergenic region, 3' end + 140 and 3' end + 561, exhibit statistically significant associations with OPLL in case-control study (p = 0.0028 for 3' end + 140 and p = 0.034 for 3' end + 561). These results indicate that the genetic causality of OPLL lies within or close to the RXR beta/COL11A2 locus.

Adult↗
PubMed1999

Methylenetetrahydrofolate reductase, diet, and risk of colon cancer.

Individuals with different forms of the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene, carriers of the C677T mutation versus wild type, show differences in enzyme levels; these differences have been hypothesized to be related to DNA methylation and, perhaps, to the nucleotide pool size. Using data from an incident case-control study, we evaluated the combined effect of dietary intake of folate, methionine, vitamin B6, vitamin B12, and alcohol and various forms of the MTHFR gene on risk of colon cancer. Individuals homozygous for the variant form of the MTHFR gene (TT) had a slightly lower risk of colon cancer than did individuals who were wild type [CC, odds ratio (OR) = 0.8, 95% confidence interval (CI) = 0.6-1.1 for men; and OR = 0.9, 95% CI = 0.6-1.2 for women]. High levels of intake of folate, vitamin B6, and vitamin B12 were associated with a 30-40% reduction in risk of colon cancer among those with the TT relative to those with low levels of intake who were CC genotype. Associations were stronger for proximal tumors, in which high levels of intake of these nutrients were associated with a halving of risk among those with the TT genotype. The inverse association with high levels of these nutrients in those with the TT genotype was stronger among those diagnosed at an older age. Although imprecise, the inverse association with the low-risk diet that was high in folate and methionine and without alcohol was observed for both the TT genotype (OR = 0.4 95% CI = 0.1-0.9) and the CC/CT genotype (OR = 0.6, 95% CI = 0.4-1.0), but this association was not seen with the high-risk diet for either the TT or CC/CT genotype. Although associations were generally weak, these findings suggest that those with differing MTHFR genotypes may have different susceptibilities to colon cancer, based on dietary consumption of folate, vitamin B6, and vitamin B12.

Adult↗
PubMed1999

Meat consumption, genetic susceptibility, and colon cancer risk: a United States multicenter case-control study.

Meat consumption may especially increase risk of colon cancer when the meat is prepared at high temperatures and consumed by subjects with an inherited susceptibility to well-done meat. In this United States case-control study, the association between meat consumption, genetic susceptibility, and colon cancer risk was studied. Meat consumption data were available from a detailed diet history questionnaire and from questions about methods of preparation. Molecular variants in the carcinogen-metabolizing genes NAT2 and GSTM1 were determined in DNA extracted from WBCs. A total of 1542 cases and 1860 population-based controls were included in these analyses. The amount of red and white meat consumed was not associated with overall colon cancer risk. Processed meat consumption was weakly positively associated with colon cancer risk in men only (odds ratio for highest versus lowest quintile of intake = 1.4, 95% confidence interval = 1.0-1.9). The frequency of fried, broiled, baked, or barbecued meat, use of drippings, and doneness of meat were not significantly associated with risk. The Mutagen Index, as an estimate for exposure to mutagenic or carcinogenic substances, was slightly positively associated with colon cancer risk in men (odds ratio = 1.3, 95% confidence interval = 1.0-1.7). No significant associations with colon cancer risk were observed for different NAT2 and GSTM1 gene variants. The observed associations with processed meat and the Mutagen Index were strongest for those with the intermediate or rapid NAT2 acetylator phenotype. Associations were not markedly influenced by lack of the GSTM1 gene. This study provides little support for an association between meat consumption and colon cancer risk but does provide some, albeit not strong, evidence for a modifying effect of molecular variants of the NAT2 gene.

Adult↗
PubMed1998

Inherited duplication Xq27-qter at Xp22.3 in severely affected males: molecular cytogenetic evaluation and clinical description in three unrelated families.

We describe the clinical phenotype in four males from three families with duplication (X)(qter-->q27::p22.3-->qter). This is an unusual duplication of the distal long arm segment, Xq27-qter, onto the distal short arm of the X chromosome at Xp22.3, as shown by fluorescent in situ hybridization analysis with multiple X-specific probes. The patients are young male offspring of three unrelated, phenotypically normal carrier women. The affected males have similar clinical manifestations including severe growth retardation and developmental delay, severe axial hypotonia, and minor anomalies. Such clinical similarity in three unrelated families demonstrates that this chromosome abnormality results in a new and distinct clinical phenotype. Replication studies, performed on two of the mothers, provided evidence that inactivation of the abnormal X chromosome permitted the structural abnormality to persist in these families for a generation or more in females without phenotypic expression.

Adult↗
PubMed1998

Alleles of APC modulate the frequency and classes of mutations that lead to colon polyps.

Most inherited mutant alleles of the adenomatosis polyposis coli gene (APC) cause the appearance of large numbers of colon polyps, the familial polyposis syndrome. (These mutant alleles are designated APCp alleles.) A subset of APC mutations, the attenuated or APC(AP) alleles, predispose to only a few colon polyps. This leads to the hypothesis that if mutation of the inherited normal allele is rate limiting in polyp development, the increased number of polyps associated with the APCp allele indicates that the frequency of mutations that can lead to polyp formation is higher among APCp carriers than among APC(AP) carriers. We have previously suggested that the APC protein might modulate the frequency of mutations, such as loss of heterozygosity (LOH), necessary for colon polyp formation. We thus reasoned that tumours from patients who carry an APC(AP) allele might show a reduced frequency of LOH compared with tumours from patients who carry an APCp allele. Loss of AAPC mutant alleles is designated as LOH(AP). Screening of tumours from APC(AP) carriers revealed a reduction of LOH compared with that of an unselected group of polyposis patients. In fact, no loss of the inherited APC(N) allele was observed, although sequencing showed that the inherited APC(N) allele had frequently undergone point mutations and small deletions in the tumours. A low frequency loss of the inherited APC(AP) allele was seen. These findings support the suggestion that the APC(AP) allele has residual gene activity and that this activity modulates the spectrum and frequency of mutations that lead to adenoma formation.

Adenomatous Polyposis Coli↗
PubMed1998

A novel potassium channel gene, KCNQ2, is mutated in an inherited epilepsy of newborns.

Idiopathic generalized epilepsies account for about 40% of epilepsy up to age 40 and commonly have a genetic basis. One type is benign familial neonatal convulsions (BFNC), a dominantly inherited disorder of newborns. We have identified a sub-microscopic deletion of chromosome 20q13.3 that co-segregates with seizures in a BFNC family. Characterization of cDNAs spanning the deleted region identified one encoding a novel voltage-gated potassium channel, KCNQ2, which belongs to a new KQT-like class of potassium channels. Five other BFNC probands were shown to have KCNQ2 mutations, including two transmembrane missense mutations, two frameshifts and one splice-site mutation. This finding in BFNC provides additional evidence that defects in potassium channels are involved in the mammalian epilepsy phenotype.

Amino Acid Sequence↗
PubMed1998

A pore mutation in a novel KQT-like potassium channel gene in an idiopathic epilepsy family.

Epileptic disorders affect about 20-40 million people worldwide, and 40% of these are idiopathic generalized epilepsies (IGEs; ref. 1). Most of the IGEs that are inherited are complex, multigenic diseases. To address basic mechanisms for epilepsies, we have focused on one well-defined class of IGEs with an autosomal-dominant mode of inheritance: the benign familial neonatal convulsions (BFNC; refs 2,3). Genetic heterogeneity of BFNC has been observed. Two loci, EBN1 and EBN2, have been mapped by linkage analysis to chromosome 20q13 (refs 5,6) and chromosome 8q24 (refs 7,8), respectively. By positional cloning, we recently identified the gene for EBN1 as KCNQ2 (ref. 9). This gene, a voltage-gated potassium channel, based on homology, is a member of the KQT-like family. Here we describe an additional member, KCNQ3. We mapped this new gene to chromosome 8, between markers D8S256 and D8S284 on a radiation hybrid map. We screened KCNQ3 for mutations in the large BFNC family previously linked to chromosome 8q24 in the same marker interval. We found a missense mutation in the critical pore region in perfect co-segregation with the BFNC phenotype. The same conserved amino acid is also mutated in KVLQT1 (KCNQ1) in an LQT patient. KCNQ2, KCNQ3 and undiscovered genes of the same family of K+ channels are strong candidates for other IGEs.

Amino Acid Sequence↗