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PubMed1991

Population genetics in forensic DNA typing.

Variable number of tandem repeat (VNTR) sequences are used to link defendants with crimes by matching DNA patterns. The probative value of a match is often calculated by multiplying together the estimated frequencies with which each particular VNTR pattern occurs in a reference database. However, this method is liable to potentially serious errors because ethnic subgroups within major racial categories exhibit genetic differences that are maintained by endogamy. The multiplication procedure currently in use can be made scientifically valid only by extensive sampling of VNTR frequency distributions in a variety of ethnic groups, similar to the ethnic studies of various blood groups done in the past. Alternative approaches for dealing with subpopulation heterogeneity are discussed.

Alleles↗
PubMed1993

Population genetics of human, animal, and environmental Yersinia strains.

Multilocus enzyme electrophoresis was used to analyze 244 strains of nine Yersinia species isolated from the environment, animals, and humans at 18 genes encoding metabolic enzymes. All 18 enzymes were polymorphic. Among the 137 electrophoretic types (ETs) distinguished, the mean allelic diversity per locus was 0.531. Yersinia frederiksenii ETs were divided into three major clusters that were separated by a large genetic distance, and one ET was more closely related to Yersinia enterocolitica. Thus, strains classically identified as Y. frederiksenii may represent more than one species. Furthermore, two strains identified as Yersinia kristensenii proved to be more closely related to Yersinia mollaretii. Environmental strains formed independent groups. A very interesting ET consisting of as many as 61 isolates of Yersinia enterocolitica was detected, and the epidemiologic relevance of this ET is discussed. Human strains of Y. enterocolitica biotype 4 and Yersinia pseudotuberculosis were recognized as being closely related to animal strains of the same species. Therefore, animal strains of these two species may be considered potential human pathogens.

Animals↗
PubMed1989

Population genetics of human and animal enteric Campylobacter strains.

A total of 125 strains of Campylobacter jejuni and Campylobacter coli from human and animal hosts were analyzed by multilocus enzyme electrophoresis. Ten genetic loci were characterized by the electrophoretic mobilities of their products, and all were found to be polymorphic. The nine loci considered for genetic analysis had an average allele number of 6.9 and a mean genetic diversity of 0.634. The strains were grouped into 64 electrophoretic types (ETs) forming two principal clusters; the first cluster consisted of 50 ETs represented by 104 isolates of C.jejuni, and the second included 14 ETs represented by 21 isolates of C. coli. The genetic distance between the two species was 0.939. The data support the conclusions that (i) campylobacteriosis caused by C. jejuni and C. coli is a zoonosis, (ii) human and animal strains do not constitute subpopulations, and (iii) every animal strain may be considered a potential human pathogen. The frequency of intraspecies gene transfer seems to be moderately high whereas interspecies gene transfer is very rare at best, which suggests the existence of a biological barrier between C. jejuni and C. coli.

Alleles↗
PubMed1999

17Beta-hydroxysteroid dehydrogenase-3 deficiency: diagnosis, phenotypic variability, population genetics, and worldwide distribution of ancient and de novo mutations.

17Beta-hydroxysteroid dehydrogenase-3 (17betaHSD3) deficiency is an autosomal recessive form of male pseudohermaphroditism caused by mutations in the HSD17B3 gene. In a nationwide study on male pseudohermaphroditism among all pediatric endocrinologists and clinical geneticists in The Netherlands, 18 17betaHSD3-deficient index cases were identified, 12 of whom initially had received the tentative diagnosis androgen insensitivity syndrome (AIS). The phenotypes and genotypes of these patients were studied. Endocrine diagnostic methods were evaluated in comparison to mutation analysis of the HSD17B3 gene. RT-PCR studies were performed on testicular ribonucleic acid of patients homozygous for two different splice site mutations. The minimal incidence of 17betaHSD3 deficiency in The Netherlands and the corresponding carrier frequency were calculated. Haplotype analysis of the chromosomal region of the HSD17B3 gene in Europeans, North Americans, Latin Americans, Australians, and Arabs was used to establish whether recurrent identical mutations were ancient or had repeatedly occurred de novo. In genotypically identical cases, phenotypic variation for external sexual development was observed. Gonadotropin-stimulated serum testosterone/androstenedione ratios in 17betaHSD3-deficient patients were discriminative in all cases and did not overlap with ratios in normal controls or with ratios in AIS patients. In all investigated patients both HSD17B3 alleles were mutated. The intronic mutations 325 + 4;A-->T and 655-1;G-->A disrupted normal splicing, but a small amount of wild-type messenger ribonucleic acid was still made in patients homozygous for 655-1;G-->A. The minimal incidence of 17betaHSD3 deficiency in The Netherlands was shown to be 1: 147,000, with a heterozygote frequency of 1:135. At least 4 mutations, 325 + 4;A-->T, N74T, 655-1;G-->A, and R80Q, found worldwide, appeared to be ancient and originating from genetic founders. Their dispersion could be reconstructed through historical analysis. The HSD17B3 gene mutations 326-1;G-->C and P282L were de novo mutations. 17betaHSD3 deficiency can be reliably diagnosed by endocrine evaluation and mutation analysis. Phenotypic variation can occur between families with the same homozygous mutations. The incidence of 17betaHSD3 deficiency is 0.65 times the incidence of AIS, which is thought to be the most frequent known cause of male pseudohermaphroditism without dysgenic gonads. A global inventory of affected cases demonstrated the ancient origin of at least four mutations. The mutational history of this genetic locus offers views into human diversity and disease, provided by national and international collaboration.

17-Hydroxysteroid Dehydrogenases↗