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M Leppert

Publications and source records attributed to M Leppert.

At least 55 records · Page 3Linked to original sources
PubMed1998

Mutations in CYP1B1, the gene for cytochrome P4501B1, are the predominant cause of primary congenital glaucoma in Saudi Arabia.

The autosomal recessive disorder primary congenital glaucoma (PCG) is caused by unknown developmental defect(s) of the trabecular meshwork and anterior chamber angle of the eye. Homozygosity mapping with a DNA pooling strategy in three large consanguineous Saudi PCG families identified the GLC3A locus on chromosome 2p21 in a region tightly linked to PCG in another population. Formal linkage analysis in 25 Saudi PCG families confirmed both significant linkage to polymorphic markers in this region and incomplete penetrance, but it showed no evidence of genetic heterogeneity. For these 25 families, the maximum combined two-point LOD score was 15.76 at a recombination fraction of .021, with the polymorphic marker D2S177. Both haplotype analysis and homozygosity mapping in these families localized GLC3A to a 5-cM critical interval delineated by markers D2S2186 and D2S1356. Sequence analysis of the coding exons for cytochrome P4501B1 (CYP1B1) in these 25 families revealed three distinctive mutations that segregate with the phenotype in 24 families. Additional clinical and molecular data on some mildly affected relatives showed variable expressivity of PCG in this population. These results should stimulate a study of the genetic and environmental events that modify the effects of CYP1B1 mutations in ocular development. Furthermore, the small number of PCG mutations identified in this Saudi population makes both neonatal and population screening attractive public health measures.

Adult↗
PubMed1998

Parental origin-dependent, male offspring-specific transmission-ratio distortion at loci on the human X chromosome.

We have analyzed the transmission of maternal alleles at loci spanning the length of the X chromosome in 47 normal, genetic disease-free families. We found a significant deviation from the expected Mendelian 1:1 ratio of grandpaternal:grandmaternal alleles at loci in Xp11.4-p21.1. The distortion in inheritance ratio was found only among male offspring and was manifested as a strong bias in favor of the inheritance of the alleles of the maternal grandfather. We found no evidence for significant heterogeneity among the families, which implies that the major determinant involved in the generation of the non-Mendelian ratio is epigenetic. Our analysis of recombinant chromosomes inherited by male offspring indicates that an 11.6-cM interval on the short arm of the X chromosome, bounded by DXS538 and DXS7, contains an imprinted gene that affects the survival of male embryos.

Animals↗
PubMed1998

Genetic mapping of ossification of the posterior longitudinal ligament of the spine.

Ossification of the posterior longitudinal ligament of the spine (OPLL) is recognized as a common disorder among Japanese and throughout Asia. Estimates of its prevalence are in the range of 1. 9%-4.3%. Although its etiology is thought to involve a multiplicity of factors, epidemiological and family studies strongly implicate genetic susceptibility in the pathogenesis of OPLL. In this study we report an identification of a predisposing locus for OPLL, on chromosome 6p, close to the HLA complex. The evidence for this localization is provided by a genetic-linkage study of 91 affected sib pairs from 53 Japanese families. In this sib-pair study, D6S276, a marker lying close to the HLA complex, gives evidence for strongly significant linkage (P = .000006) to the OPLL locus. A candidate gene in the region, that for collagen 11A2, was analyzed for the presence of molecular variants in affected probands. Of 19 distinct variants identified, 4 showed strong statistical associations with OPLL (highest P = .0004). These observations of linkage and association, taken together, show that a genetic locus for OPLL lies close to the HLA region, on chromosome 6p.

Chromosome Mapping↗
PubMed1998

NAT2, GSTM-1, cigarette smoking, and risk of colon cancer.

Cigarette smoking has been associated inconsistently with colon cancer. The extent to which genetic profile influences susceptibility to the inducement of colon cancer by cigarette smoking is not known. In this study, we evaluated the associations between smoking cigarettes and polymorphisms of the NAT2 and GSTM-1 genes using data obtained from an incident case-control study of 1993 cases of colon cancer and 2410 age- and sex- matched controls. Neither NAT2 nor GSTM-1 polymorphisms were significantly associated with colon cancer, except among older women, in whom the intermediate/rapid imputed phenotype was associated with increased risk of colon cancer [odds ratio (OR) = 1.4, 95% confidence interval (CI) = 1.0-1.81. Using several indicators of cigarette smoking, we observed no significant interaction between these genotypes and cigarette smoking and colon cancer. The major variation in association with colon cancer was from the amount of cigarette exposure, with those smoking a pack or more of cigarettes per day being at an approximately 40% increased risk of colon cancer; this association did not vary by genotype. However, those who stopped smoking 5-14 years prior to diagnosis and who where intermediate/rapid acetylators were at a slightly greater risk than those who were slow acetylators (for men, OR = 1.6, 95% CI = 1.0-2.4; for women, OR = 2.5, 95% CI = 1.4-4.4). Associations were similar when proximal and distal tumors were examined and separated for age at the time of diagnosis. The lack of an association does not rule out the possibility of other genetic polymorphisms interacting with cigarette smoke to cause colon cancer, nor does it take into account individual phenotypic variability.

Adult↗
PubMed1997

Mutation of the Stargardt disease gene (ABCR) in age-related macular degeneration.

Age-related macular degeneration (AMD) is the leading cause of severe central visual impairment among the elderly and is associated both with environmental factors such as smoking and with genetic factors. Here, 167 unrelated AMD patients were screened for alterations in ABCR, a gene that encodes a retinal rod photoreceptor protein and is defective in Stargardt disease, a common hereditary form of macular dystrophy. Thirteen different AMD-associated alterations, both deletions and amino acid substitutions, were found in one allele of ABCR in 26 patients (16%). Identification of ABCR alterations will permit presymptomatic testing of high-risk individuals and may lead to earlier diagnosis of AMD and to new strategies for prevention and therapy.

ATP-Binding Cassette Transporters↗
PubMed1997

Do non-insulin-dependent diabetes mellitus (NIDDM) and insulin-dependent diabetes mellitus (IDDM) share genetic susceptibility loci? An analysis of putative IDDM susceptibility regions in familial NIDDM.

Non-insulin-dependent diabetes mellitus (NIDDM) has been viewed as genetically and physiologically distinct from insulin-dependent diabetes mellitus (IDDM), yet many of the recently suggested IDDM susceptibility loci are likely to increase the risk of diabetes through nonautoimmune mechanisms. To test the hypothesis that the IDDM susceptibility loci include important NIDDM susceptibility loci, we tested the linkage of 14 putative susceptibility regions with NIDDM among families and sibling pairs of Northern European descent. All regions were tested with highly informative microsatellite (simple tandem repeat) polymorphisms in up to 166 affected individuals from 42 families using both parametric and nonparametric methods (149 pairs for sibling pair analyses). We found no evidence for linkage to the majority of loci, including loci that appeared to be linked to IDDM in more than one study. We report some evidence for shared susceptibility for regions on chromosomes 1, 2, and 6. The best evidence based on multilocus affected pedigree member (APM) analysis of markers near D1S191 suggested linkage at P value .0001. This region has not yet been confirmed as an IDDM locus, and our analyses could represent a false-positive result. The role of these three regions will only be clarified by testing in additional families. In combination with other investigations in our laboratory for chromosome 11 susceptibility regions, our data generally do not provide convincing evidence that IDDM and NIDDM share common genetic factors among families of Northern European descent with ascertainment of two or more NIDDM siblings.

Adult↗
PubMed1997

A photoreceptor cell-specific ATP-binding transporter gene (ABCR) is mutated in recessive Stargardt macular dystrophy.

Stargardt disease (STGD, also known as fundus flavimaculatus; FFM) is an autosomal recessive retinal disorder characterized by a juvenile-onset macular dystrophy, alterations of the peripheral retina, and subretinal deposition of lipofuscin-like material. A gene encoding an ATP-binding cassette (ABC) transporter was mapped to the 2-cM (centiMorgan) interval at 1p13-p21 previously shown by linkage analysis to harbour the STGD gene. This gene, ABCR, is expressed exclusively and at high levels in the retina, in rod but not cone photoreceptors, as detected by in situ hybridization. Mutational analysis of ABCR in STGD families revealed a total of 19 different mutations including homozygous mutations in two families with consanguineous parentage. These data indicate that ABCR is the causal gene of STGD/FFM.

ATP-Binding Cassette Transporters↗
PubMed1997

Gastric adenocarcinoma and dysplasia in fundic gland polyps of a patient with attenuated adenomatous polyposis coli.

Gastric adenocarcinoma has been previously recognized as a potential complication of familial adenomatous polyposis coli (APC) and attenuated forms of APC (AAPC). This tumor has only been reported to originate from adenomatous polyps of the gastric mucosa in these clinical conditions. There have been no previous case reports of gastric adenocarcinoma arising from the more commonly found fundic gland polyps associated with AAPC or APC. We report the first definitive case of gastric adenocarcinoma arising from a hyperplastic polyp of the fundis of a patient with AAPC.

Adenocarcinoma↗
PubMed1997

Genetic linkage of Paget disease of the bone to chromosome 18q.

Paget disease is a common bone disease characterized by abnormal osteoclasts that are large, multinucleated, and overactive and that contain paramyxovirus-like nuclear inclusions. There is evidence for a major genetic component to Paget disease, with up to 40% of patients having affected first-degree relatives; however, the locus (loci) and gene(s) involved are unknown. Another bone disorder, familial expansile osteolysis (FEO), although extremely rare, also is characterized by similar osteoclast abnormalities but has an earlier age at onset and a more aggressive clinical progression. The causative gene for FEO has been localized to a region of human chromosome 18q. On the basis of the presence of similar clinical findings and of viral-like nuclear inclusions in osteoclasts, we hypothesized that FEO and Paget disease are allelic versions of the same locus. Therefore, a large kindred with a high incidence of Paget disease was examined to determine if Paget disease was linked to genetic markers in the same region of chromosome 18 as that for FEO. Our analysis yielded a two-point LOD score of 3.40, with the genetic marker D18S42, a marker tightly linked to the FEO locus. This demonstrates that the gene(s) responsible for FEO and that for Paget disease are either closely linked or the same locus.

Adult↗
PubMed1996

Linkage of a familial platelet disorder with a propensity to develop myeloid malignancies to human chromosome 21q22.1-22.2.

Linkage analysis was performed on a large pedigree with an autosomal dominant platelet disorder and a striking propensity in affected family members to develop hematologic malignancy, predominantly acute myelogenous leukemia. We report the linkage of the autosomal dominant platelet disorder to markers on chromosome 21q22. Four genetic markers completely cosegregate with the trait and yield maximum logarithm of difference scores ranging from 4.9 to 10.5 (theta = .001). Two flanking markers, D21S1265 and D21S167, define a critical region for the disease locus of 15.2 centimorgan. Further analysis of this locus may identify a gene product that affects platelet production and function and contributes to the molecular evolution of hematologic malignancy.

Acute Disease↗
PubMed1996

Hereditary spastic paraplegia linked to chromosome 15q: Analysis of candidate genes.

We previously reported an extended kindred with autosomal dominant uncomplicated hereditary spastic paraplegia (HSP) and found close linkage between the disorder and microsatellite polymorphisms on chromosome 15q. Multipoint linkage analysis reached a maximum LOD score (10.16) between D15S128 and D15S156, a region that includes genes encoding alpha5 and beta3 subunits of GABAA receptor. Theoretically, abnormal GABA-mediated neurotransmission could produce spasticity and possibly other changes of HSP. We used genetic linkage analysis to evaluate these two HSP candidate genes and observed obligate recombinants for polymorphisms immediately adjacent to (or within untranslated regions of) genes encoding alpha5 and beta3 GABAA receptor subunits. Although these genes are linked tightly to the HSP locus, our findings conclusively exclude these genes from being responsible for HSP in this kindred.

Adult↗
PubMed1996

Heritability of X chromosome--inactivation phenotype in a large family.

One of the two X chromosomes in each somatic cell of normal human females becomes inactivated very early in embryonic development. Although the inactivation of an X chromosome in any particular somatic cell of the embryonic lineage is thought to be a stochastic and epigenetic event, a strong genetic influence on this process has been described in the mouse. We have attempted to uncover evidence for genetic control of X-chromosome inactivation in the human by examining X chromosome-inactivation patterns in 255 females from 36 three-generation pedigrees, to determine whether this quantitative character exhibits evidence of heritability. We have found one family in which all seven daughters of one male and the mother of this male have highly skewed patterns of X-chromosome inactivation, suggesting strongly that this quantitative character is controlled by one or more X-linked genes in some families.

Alleles↗
PubMed1996

Paroxysmal dystonic choreoathetosis: tight linkage to chromosome 2q.

Paroxysmal dystonic choreoathetosis (PDC) is characterized by attacks of involuntary movements that last up to several hours and occur at rest both spontaneously and following caffeine or alcohol consumption. We analyzed a Polish-American kindred with autosomal dominant PDC and identified tight linkage between the disorder and microsatellite markers on chromosome 2q (maximum two-point LOD score 4.77; recombination fraction 0). Our results clearly establish the existence of a locus for autosomal dominant PDC on distal chromosome 2q. The fact that three other paroxysmal neurological disorders (periodic ataxia with myokymia and hypo- and hyperkalemic periodic paralysis) are due to mutation in ion-channel genes raises the possibility that PDC is also due to an ion-channel gene mutation. It is noteworthy that a cluster of sodium-channel genes is located on distal chromosome 2q, near the PDC locus. Identifying the PDC locus on chromosome 2q will facilitate discovery of the PDC gene and enable investigators to determine whether PDC is genetically homogeneous and whether other paroxysmal movement disorders are also genetically linked to the PDC locus.

Athetosis↗
PubMed1996

Bilineal transmission and phenotypic variation of Tourette's disorder in a large pedigree.

OBJECTIVE: Variability in the clinical phenotype of Tourette's disorder (TD) was assessed in a single large family, with a focus on the influence of bilineal transmission. METHOD: Tics, obsessive-compulsive symptoms, and attention-deficit symptoms were evaluated through interview and standardized checklists for 175 descendants and 16 spouses who married into a single four-generation pedigree. RESULTS: Some form of tic disorder was diagnosed in 67% of descendants and 44% of married-in spouses. TD was found in 36% of descendants and in 31% of married-in spouses. Impairment was minimal in most cases, but age at onset and location and number of tics were typical of TD described in clinic samples. Obsessive-compulsive symptoms were found in 38% of descendants and 62% of those with current TD, but obsessive-compulsive disorder was found in only four individuals. Attention-deficit hyperactivity disorder occurred in 25% of children. Multivariate analysis indicated that offspring of two parents with tic disorders manifested significantly more lifetime tics, more severe categories of tic disorders, and an earlier age at onset for TD compared with offspring of one or no affected parents. CONCLUSIONS: TD in this family is most often a mild disorder but otherwise similar to published clinical cases. Increased morbidity is significantly associated with bilineality. The frequency and impact of bilineality raise questions about possible assortative mating, the prevalence of TD, and assumed mechanisms of transmission and etiology.

Adolescent↗
PubMed1996

A gene for primary congenital glaucoma is not linked to the locus on chromosome 1q for autosomal dominant juvenile-onset open angle glaucoma.

BACKGROUND: Primary congenital glaucoma is an uncommon autosomal recessive condition that results from a developmental defect in the trabecular meshwork and anterior chamber angle, manifesting in the neonatal or infantile period with increased intraocular pressure, corneal enlargement and edema, and optic nerve cupping with consequent loss of vision. Nothing is known about its genetic location. PATIENTS AND METHODS: Linkage analysis was performed in 25 primary congenital glaucoma Saudi Arabian families with six polymorphic DNA markers on chromosome 1q in a region that has shown tight linkage to a locus for autosomal dominant juvenile-onset open angle glaucoma (GLC1A). Twenty-four of these families are highly consanguineous. RESULTS: Each family was shown separately to exclude the 8-centimorgan (cM) interval containing the GLC1A locus. Four families independently demonstrated overlapping regions of exclusion (theta < or = -2) that spanned the entire 8-cM interval. Assignment of a primary congenital glaucoma locus in this region could be excluded by a cadre of 21 families because a primary congenital glaucoma disease locus did not segregate in an autosomal recessive manner on haplotypes constructed with markers in this region. For all families, no affected individuals demonstrated homozygosity of alleles in regions tightly linked to the GLC1A locus. CONCLUSION: These results exclude the 8-cM region on chromosome 1q shown to contain the GLC1A locus from containing a disease locus for primary congenital glaucoma in this population of 25 Saudi Arabian families.

Chromosome Mapping↗