Biomedical subjects

J M Hebert

Publications and source records attributed to J M Hebert.

At least 19 recordsLinked to original sources

PubMed1996

Autism and the X chromosome. Multipoint sib-pair analysis.

BACKGROUND: Genetic factors undoubtedly play a major etiologic role in autism, but how it is inherited remains unanswered. The increased incidence in males suggests possible involvement of the X chromosome. METHODS: Using data from 38 multiplex families with autism (2 or more autistic siblings), we performed a multipoint sib-pair linkage analysis between autism and 35 microsatellite markers located on the X chromosome. The model included a single parameter, the risk ratio lambda xs (i.e., ratio of risk to siblings compared with the population prevalence), owing to an X-linked gene. Different lambda xs values were assumed and regions of exclusion were established. RESULTS: The entire X chromosome could be excluded for a lambda xs value of 4. The ability to exclude an X-linked gene decreased with smaller lambda xs values, and some positive evidence was obtained with smaller values. A maximum lod score of 1.24 was obtained at locus DXS424 with a lambda xs value of 1.5. CONCLUSIONS: We were able to exclude any moderate to strong gene effect causing autism on the X chromosome. Smaller gene effects (lambda xs < 4) could not be excluded, in particular, a gene of small effect located between DXS453 and DXS1001.

Adolescent↗

PubMed1996

Geographic clustering of human Y-chromosome haplotypes.

Five polymorphic markers on the Y-chromosome (mostly microsatellites) were typed in 121 individuals from 13 populations around the world. With these markers 78 different haplotypes were detected. Haplotypes present more than once tend to be shared by individuals from the same population or continent. A reconstruction of haplotype phylogeny also indicates significant geographic structure in the data. Based on the similarity of the haplotypes, population relationships were examined and found to be largely concordant with those obtained with other markers. Even though the sample size and the number of markers are small, there is very signficant clustering of the haplotypes by continent of origin.

Alleles↗

PubMed1995

Demographic history of India and mtDNA-sequence diversity.

The demographic history of India was examined by comparing mtDNA sequences obtained from members of three culturally divergent Indian subpopulations (endogamous caste groups). While an inferred tree revealed some clustering according to caste affiliation, there was no clear separation into three genetically distinct groups along caste lines. Comparison of pairwise nucleotide difference distributions, however, did indicate a difference in growth patterns between two of the castes. The Brahmin population appears to have undergone either a rapid expansion or steady growth. The low-ranking Mukri caste, however, may have either maintained a roughly constant population size or undergone multiple bottlenecks during that period. Comparison of the Indian sequences to those obtained from other populations, using a tree, revealed that the Indian sequences, along with all other non-African samples, form a starlike cluster. This cluster may represent a major expansion, possibly originating in southern Asia, taking place at some point after modern humans initially left Africa.

Base Sequence↗

PubMed1994

Construction of human Y-chromosomal haplotypes using a new polymorphic A to G transition.

We report the discovery of a polymorphic A to G transition found on the human Y chromosome by sequencing Y-specific sequence-tagged sites (STSs). It shows maximal linkage disequilibrium with a previously described Alu insertional polymorphism. We analyze further an apparently African Y chromosome which seems to have entered a Mexican Mayan population several generations ago. Using the newly discovered transition and the Y-specific polymorphic Alu insertion, we discuss how the chromosome's haplotype information might be used to answer questions of human origins and migrations.

Animals↗

PubMed1994

Comparison of 79 DNA polymorphisms tested in Australians, Japanese and Papua New Guineans with those of five other human populations.

Seventy-nine DNA polymorphisms from 57 loci (28 genes and 29 anonymous DNA segments) have been typed in eight human populations. Here we present allele frequencies for three populations (Japanese, New Guineans, and Australians) as well as revised frequencies for a Chinese sample: allele frequencies for five additional populations (Biaka and Mbuti Pygmies, Melanesians, Chinese, and Europeans) were described previously [Bowcock et al 1991a]. Evaluation of Hardy-Weinberg equilibrium for these polymorphisms suggested that the New Guinean sample may be from a highly substructured population. Average FST value for the 79 markers (polymorphisms) was 0.147 +/- 0.011 across the eight populations: Fst values for some markers changed dramatically with the addition of three populations--in particular, Australians and New Guineans. Average heterozygosity for eight populations was 0.307 +/- 0.014. Genetic distances indicated that the Australian sample may have some European ancestry. An average linkage tree inferred from these distances suggested that the first split of modern humans was between Africans and non-Africans, while the second major split was between Australians/New Guineans and all other non-Africans. The neighbor-joining tree also separated the African populations from all others. European polymorphism ascertainment bias and European admixture appear to have influenced both estimation of population heterozygosity and tree inference.

Alleles↗

PubMed1991

Drift, admixture, and selection in human evolution: a study with DNA polymorphisms.

Accuracy of evolutionary analysis of populations within a species requires the testing of a large number of genetic polymorphisms belonging to many loci. We report here a reconstruction of human differentiation based on 100 DNA polymorphisms tested in five populations from four continents. The results agree with earlier conclusions based on other classes of genetic markers but reveal that Europeans do not fit a simple model of independently evolving populations with equal evolutionary rates. Evolutionary models involving early admixture are compatible with the data. Taking one such model into account, we examined through simulation whether random genetic drift alone might explain the variation among gene frequencies across populations and genes. A measure of variation among populations was calculated for each polymorphism, and its distribution for the 100 polymorphisms was compared with that expected for a drift-only hypothesis. At least two-thirds of the polymorphisms appear to be selectively neutral, but there are significant deviations at the two ends of the observed distribution of the measure of variation: a slight excess of polymorphisms with low variation and a greater excess with high variation. This indicates that a few DNA polymorphisms are affected by natural selection, rarely heterotic, and more often disruptive, while most are selectively neutral.

Animals↗

PubMed1991

A contiguous linkage map of chromosome 13q with 39 distinct loci separated on average by 5.1 centimorgans.

A fine-structure linkage map of chromosome 13q is presented. This map contains 39 continuously linked loci defined by genotypes generated from the CEPH family DNAs with 56 probe and enzyme combinations. An alpha-satellite probe for sequences on chromosome 13 was included, resulting in a complete map of 13q with 39 distinct loci. The map spans 1.715 M in males and 2.099 M in females and the mean genetic distance between adjacent loci is 5.1 cM. Although there was generally a several-fold excess of female recombination in the interstitial portion of 13q, an excess of recombination in males was observed at both ends of this chromosomal arm. This map should be useful for the localization of any additional marker, gene, or disease locus of interest on chromosome 13q.

Chromosome Mapping↗

PubMed1991

Predictive testing for Wilson's disease using tightly linked and flanking DNA markers.

We studied DNA polymorphisms for five new chromosome 13 markers in 52 Wilson's disease (WD) families from Europe, North America, and the Middle East. There was significant evidence for linkage between the Wilson's disease locus (WND) and all the marker loci. Multilocus linkage analysis, using a genetic linkage map established from reference pedigrees, suggested that WND is most likely between D13S31 and D13S59, at distances of 0.4 and 1.2 centimorgans, respectively. Our results suggest that the chromosomal location of the Wilson's disease gene is the same in all families from the populations studied. This evidence and the availability of many close, flanking, and polymorphic DNA markers make possible accurate and informative testing of potential carriers and WD homozygotes in families with at least one previously affected child. An advantage of a genetic linkage test over other laboratory methods for prediction of genotype in WD is that a reliable diagnosis can be made at a much earlier stage in life, including prenatally. In addition, DNA testing can be used in place of an invasive liver biopsy procedure to confirm a diagnosis in patients with borderline serum ceruloplasmin levels. Presymptomatic identification will also allow therapeutic intervention to prevent symptoms before irreparable liver or neurologic damage occurs. We describe the implementation of prenatal and preclinical diagnosis for two families with WD.

Chromosome Mapping↗

PubMed1991

Study of an additional 58 DNA markers in five human populations from four continents.

One hundred DNA polymorphisms from 73 loci (42 genes and 31 anonymous DNA segments) were investigated in five populations (Biaka and Mbuti Pygmies, Melanesians, Chinese and Caucasoids). Data for 47 polymorphisms, including 42 of those discussed here, were described previously [Bowcock et al 1987]. Here we report statistical quantities of genetic importance for each gene and population. The average FST for the 100 markers is 0.137 and the average heterozygosity is 0.325. When known genes and anonymous segments are compared there is no significant difference in the average FST values or in the average heterozygosities.

Africa↗

PubMed1990

The serotonin receptor subtype 2 locus HTR2 is on human chromosome 13 near genes for esterase D and retinoblastoma-1 and on mouse chromosome 14.

Serotonin (5-hydroxytryptamine) functions as a neurotransmitter and a hormone. Its diverse actions are mediated by at least seven distinct cell surface receptor subtypes. The serotonin receptor subtype 2 (gene symbol HTR2) is a G-protein-coupled receptor, expressed primarily in the cerebral cortex, where upon stimulation it stimulates the hydrolysis of inositol phospholipids. We have mapped the HTR2 locus to human chromosome 13 and to mouse chromosome 14 by somatic cell hybrid analysis. Linkage studies in CEPH families, using a PvuII RFLP detected with the HTR2 probe, revealed tight linkage between HTR2 and ESD, the locus for esterase D. The most likely position for HTR2 is between ESD and RB1, the retinoblastoma-1 gene. The homologous loci in mouse, Rb-1 and Esd(Es-10) are on mouse chromosome 14, close to ag, agitans, a recessive neurological mutation. Having mapped Htr-2 to mouse chromosome 14, we predict that it falls into this known conserved gene cluster.

Animals↗

PubMed1990

Wilson's disease in Israel: a genetic and epidemiological study.

Clinical and family history data on persons affected with Wilson disease (WD) living in Israel between 1958 and 1984 were ascertained from the literature, hospital records and neurological and gastroenterological clinics. From this population of 51 families, representing a diversity of Middle Eastern. North African and European backgrounds, blood samples were collected from affected individuals in 21 families, their parents, sibs and other relatives for quantitative determinations of plasma copper and ceruloplasmin, liver tests and DNA analysis. Although the majority of patients have the hepatic form of the disease, hepatic and neurological cases were found among all ethnic groups. In fact, affected sibs in several inbred families who most likely inherited two copies of the same mutant allele had different symptoms. Gene frequencies were calculated for each of the populations taking into account inbreeding, probability of ascertainment, and estimated incidence. Although many of these communities have gene frequencies which are comparable to worldwide estimates, high prevalence of disease is maintained by consanguineous mating patterns. Probabilities of WND genotypes were calculated for 129 unaffected relatives who had an a priori risk of inheriting at least one WND allele using information from 10 DNA markers closely linked to the WND locus. There was no evidence that multiple loci are responsible for the observed clinical variability in this sample of families. Furthermore, studies of serum copper and ceruloplasmin levels in unaffected relatives suggest that phenotypic variability in WD may be due in part to an interaction of the WND locus with other genetic or non-genetic modifiers such as age.

Adolescent↗

PubMed1990

Exclusion of the retinoblastoma gene and chromosome 13q as the site of a primary lesion for human breast cancer.

Chromosome 13q has been suggested as the site of a gene predisposing to human breast cancer, because loss of heterozygosity of alleles on this chromosome has been observed in some ductal breast tumors and because two breast cancer lines are altered at the retinoblastoma gene (RB1) at 13q14. To test this possibility, linkage of breast cancer susceptibility to 14 loci on chromosome 13q loci was assessed in extended families in which breast cancer is apparently inherited as an autosomal dominant trait. RB1 was excluded as the site of a breast cancer gene by a lod score of Z = -7.60 at close linkage for 13 families. Multipoint analysis yielded negative lod scores throughout the region between 13q12 and 13q34; over most of this distance, Z less than -2.0. Therefore, chromosome 13q appears to be excluded as the site of primary lesion for breast cancer in these families. In addition, comparison of tumor versus normal tissues of nonfamilial breast cancer patients revealed an alteration at the 5' end of RB1 in a mucoid carcinoma but no alterations of RB1 in five informative ductal adenocarcinomas. Linkage data and comparisons of tumor and normal tissues suggest that changes in the RBI locus either are secondary alterations associated with progression of some tumors or occur by chance.

Breast Neoplasms↗

PubMed1989