Search

The tetranucleotide repeat locus C2_4_4 situated in the HLA class I region (6p21.3) and the HLA-ABC specificities were investigated in an Austrian population sample of 240 unrelated Caucasoid individuals. The analysis of the linkage disequilibrium between C2_4_4 and HLA class I showed several significant values, especially when factors coded for by so-called "superhaplotypes" were considered; such linkage disequilibria are of importance for the practical use of HLA coded short tandem repeats.

During the past few years, the DNA Commission of the International Society of Forensic Genetics has published a series of documents providing guidelines and recommendations concerning the application of DNA polymorphisms to the problems of human identification. This latest report addresses a relatively new area - namely, Y-chromosome polymorphisms, with particular emphasis on short tandem repeats (STRs). This report addresses nomenclature, use of allelic ladders, population genetics and reporting methods.

The Human Leukocyte Antigen (HLA) system can be defined as a set of glycoproteins which take up peptides intracellulary and become ligands for immune receptors once they are expressed on the cell membrane. Functional HLA molecules are trimers consisting of a heavy chain and a light chain which bind a peptide. The production of HLA molecules in the endoplasmic reticulum, their assembly and their trafficking to the cell membrane have been studied in great detail. A salient feature of HLA molecules is their polymorphism which is essentially a tremendous amount of variation in the amino acid sequence of mainly the heavy chain between different HLA types. Polymorphic chains of HLA molecules are encoded in the human major histocompatibility complex (MHC) on the short arm of chromosome 6. A map of the nucleotide sequence of the human MHC has been established. The polymorphism of HLA molecules, i.e. the HLA type, is intimately associated with the nature of the peptides bound. In principle, HLA molecules can bind a variety of different peptides. However, peptides with distinct biochemical features are preferentially bound according to the HLA-type. HLA-typing is applied clinically in transplantation and disease association. Recently, recombinant HLA molecules have been used as a tool to define the T cell receptor repertoire.

A case of dispermic chimerism is presented. The use of DNA polymorphisms in order to differentiate between blood chimerism and dispermy is shown.

We investigated the (AAAG)n short tandem repeat (STR) polymorphism HumF13A01 an Austrian Caucasoid population sample (n = 674). PCR amplified fragments were detected on an automatic A.L.F. DNA sequencer using laser-induced fluorescence. A total of 14 alleles could be identified including a new 179 bp allele which was designated allele 3. Sequence determination of allele 3 confirmed the typing results by revealing three continuous copies of the core repeat, whereas in sequencing of 54 additional alleles no further variants or microheterogeneities could be observed. The population data showed no significant deviation from Hardy-Weinberg equilibrium.

The short tandem repeat (STR) polymorphism HumLPL (TTTA)n, which is located in intron 6 of the lipoprotein lipase gene, was investigated by AMPFLP (amplification fragment length polymorphism)-technique using an allelic ladder consisting of amplified alleles of this locus as a standard size marker. The allelic ladder was prepared by pooling equal concentrations of six separate alleles, which were identified by their different electrophoretic mobility in native polyacrylamide gel, eluted and subsequently amplified. Sequence analysis of the ladder alleles and allele 7, which is not included in the ladder, showed a regular repeat structure with 7 and 9 to 14 repetitions of the core repeat. The allelic ladder was employed in the analysis of the genotypes of 550 unrelated Caucasoids of Austria. No new alleles were found. The population investigated showed no deviation from Hardy-Weinberg equilibrium (P = 0.195).

The short tandem repeat (STR) polymorphism at the CD4 locus, designated HUMCD4, was examined by PCR, native polyacrylamide electrophoresis and subsequent silver staining using an allelic ladder of eight distinguishable alleles occurring in an Austrian Caucasian population sample as a standard size marker. The ladder was produced by pooling equal concentrations of eluted, separately amplified and sequenced alleles, which were previously identified by their different electrophoretical migration. Components of the ladder are in regular intervals of five basepairs. Alleles 4 to 8 were designated according to the number of AAAAG repeat units. The four longer alleles 8' to 11 showed a stable A to G transition in one of the repeat units and were designated counting the AAAGG unit for a AAAAG. Allele 8' was not included in the ladder because it showed the same electrophoretic mobility as allele 8. This ladder proved to be a precise and reliable tool in the analysis of 600 chromosomes of the Austrian population. The population investigated showed no deviation from Hardy-Weinberg equilibrium (P = 0.23).

After a description of the various DNA polymorphisms which can be used in forensic medicine, the use of these markers for solving cases of disputed paternity is discussed in detail. VNTR polymorphisms detectable after amplification of the relevant loci by the PCR seem to be the best tools for paternity testing.

The genetic structure of the HLA gene complex, which represents the major histocompatibility complex of man, is described. The polymorphisms at the various HLA loci as well as the biologic function of the HLA system with respect to the immune response are discussed.

The basis and efficiency of paternity testing using conventional markers (alloantigens or electrophoretically defined polymorphisms in blood) for individuals involved in cases of affiliation are shown. A possible use of DNA polymorphisms in paternity cases is discussed. Due to the fact that the formal genetics of DNA polymorphisms have not been fully validated by the analysis of large numbers of informative meioses, it is not yet possible to include these systems in routine paternity testing. As the vast majority of cases can be resolved by conventional markers, the inclusion of DNA polymorphisms is not usually necessary; in some cases, however, they can provide additional information.

By isoelectric focusing in a pH range of pH 3.5-9.5 or of pH 5-8, and by using a functional or an immunological detection, a genetic polymorphism of plasminogen can be demonstrated. In Caucasoids, 2 common alleles--PLGA (frequency 0.67) and PLGB (frequency 0.30)--as well as several rare variants (sum of their frequencies 0.03) exist. Systematic studies on the functional activity of the various plasminogen gene products should be performed in order to analyse whether or not a difference of plasminogen activity can be observed amongst the possible phenotypes and in order to see whether or not the various plasminogen phenotypes have any clinical significance.

Phenotype and gene frequencies of the GLO I polymorphism in Vienna are given. No exception to the postulated rule of inheritance could be found in 23 families with 51 children and 132 mother-child pairs. Linkage with the HLA system is confirmed, but no linkage disequilibrium between GLO alleles and HLA-A, B, C genes was detected. The use of the GLO I polymorphism in paternity cases is discussed.

The advances reached by using DNA polymorphisms (restriction fragment length polymorphisms) in blood group serology are demonstrated by means of the HLA system. The potentialities for various applications (e.g. better definition of alloantigens, association with diseases, paternity testing, forensic medicine or genetic counselling) are mentioned.