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Background and Objectives The aim of this study was to investigate whether in-line filtration, using a polyester filter for the preparation of red cell concentrates (RCC) and plasma (PL), leads to an altered proportion of T and B lymphocytes in the fraction of residual white blood cells (WBC). Materials and Methods The capacity of Pall WBF-2 in-line filters to reduce the numbers of T and B lymphocytes from red blood cell concentrates (RCC) and plasma (PL) of 22 donations was investigated by three-colour flow cytometry (FC) using the Tritest-Trucount kit. T and B lymphocytes were identified using monoclonal antibodies (mAbs) against CD3, CD19 and CD45, conjugated with fluorescein isothiocyanate, phycoerythrin or peridinin chlorophyll protein-A, respectively. As the number of B cells was below the detection limit of the FC method, WBC of the respective blood components of healthy donors were concentrated 25-fold by Percoll density-gradient centrifugation. In this fraction the absolute numbers of T and B cells, as well as their ratio, were determined using the Attractor software, which provides a discrimination of rare cell counts from FC in relation to debris. Results The mean numbers, as well as minima and maxima of T and B lymphocytes per unit, were as follows. T cells in RCC: 4·51 × 103 (1·68 × 102−4·09 × 104) and in PL: 1·35 × 103 (2·21–1·78 × 104); B cells in RCC: 2·33 × 103 (7·10 × 101−9·15 × 103) and in PL: 2·33 × 102 (7·5 × 102−2·8 × 103). T cells were retained, on average, at a higher level than B cells: 3·01 times higher in RCC and 1·01 times higher in PL. Conclusion After filtration, the ratio of T and B lymphocytes changed in RCC (1·95 : 1) compared with unfiltered blood, where it was 5·83 : 1. In PL the ratio did not change notably compared to unfiltered blood. The results of this research show that cell concentration (using gradient centrifugation) in combination with an appropriate FC acquisition and analysis procedure, allows both residual T and B lymphocytes (being under the detection limit without cell concentration) to be determined.

Background and Objectives Platelet count, thrombopoetin (TPO) level and the compartment of megakaryocyte progenitor cells (CFU-Mk) are major determinants in the regulation of thrombopoiesis. The aim of this study was to investigate the potential changes in the compartment of CFU-Mk and their correlation with serum TPO levels and platelet count after plateletpheresis. Materials and methods Twelve healthy individuals were randomly assigned to undergo single-donor plateletpheresis. A collagen-based in vitro culture system was used to determine the number of peripheral blood (PB) CFU-Mk before and after donation and on days 1, 4 and 7 thereafter. TPO levels were measured by a specific enzyme-linked immunosorbent assay and whole blood counts were performed using an automated cell counter. Results The pre-apheresis platelet count (mean ± SEM: 276 ± 13 × 109/l) decreased after plateletpheresis to a nadir of 194 ± 8 × 109/l (P

The highly polymorphic STR locus D12S391 was investigated in an Austrian population sample (N = 150) by PCR-amplification, comparative detection on native and denaturing polyacrylamide gels and solid phase single stranded sequencing of three size variant alleles and several additional alleles. A total of 15 alleles, distinguishable by size under denaturing conditions, could be detected. No deviations from Hardy-Weinberg equilibrium were observed in the population investigated (P = 0.52). Sequencing of size variants designated 17.3 and 18.3 showed an incomplete (GAT) repeat unit at position two of the tandem region. Additional new sequence variants due to varying compositions of the number of (AGAT) and (AGAC) repeats could be identified. Due to distinct electrophoretical mobilities of alleles of the same size but different sequence structures, denaturing detection conditions should be employed when the aim is standardization.

Background and objectives New-generation polyester filters provide significant depletion of white blood cells (WBC) and platelets (PLT) in filtered red blood cell concentrates (FRCC) and in filtered plasma preparations (FP). The aim of this study was to elaborate a sensitive flow cytometric method for monitoring residual WBC and PLT in FRCC and FP. Materials and methods We determined the number of WBC in 500 microliters FRCC of FP using 50 microliters of a combination of monoclonal antibodies (MAB) against CD45 (FITC labeled) and CD19 (PE labeled). After lysis of red blood cells, we mixed a specific number of reference beads with the remaining WBC. The number of residual WBC related to the acquisition volume was defined by the acquired reference beads. Using this method, the detection limit (DL) was 3 WBC/microliter. Alternative methods used MAB against CD45 (FITC and PerCP labeled) and CD14 (PE labeled) or lymphocyte subsets such as CD3 (FITC labeled) and CD19, CD4, CD8, CD16 and CD56 (PE labeled) in combination with CD45 (PerCP labeled). The DL values were 10 WBC/microliter for the CD45/CD14 staining and 0.1 WBC/microliter for the determination of both CD3+ and CD19+ lymphocytes. For residual PLT in FRCC or FP, we used an FITC-conjugated MAB against CD41, with reference beads to determine the acquisition volume. PLT were demonstrated in a green-fluorescence (FL1) single histogram after gating in the forward light scatter x 90 degrees light scatter signal dot plot. PLT counting was as described for WBC. The DL value was about 2 PLT/microliter. Results Filtration with Pall WBF-1 filters reduces WBC by 4 log and PLT by 3-4 log, resulting in cell counts which are below the critical limit for causing adverse transfusion reactions. Conclusions Flow cytometry techniques provide a reproducible and objective tool for counting residual WBC and PLT in blood preparations compared with the Nageotte hemocytometer. Absolute numbers of leukocyte and lymphocyte subpopulations are obtainable.

Typing for HLA-B27 by serological methods is routinely performed using the microlymphocytotoxic test (MLCT). Since monoclonal antibodies (MAB) against HLA-B27 are available, flow cytometry (FC), which requires less time than the MLCT has been developed as an alternative technique. The aim of the present study was to check the accuracy and reliability of this method using different MAB against HLA-B27 in comparison to MLCT (using polyclonal antibodies against HLA-B27 and cross-reacting specificities [CRS]). FC was performed in 144 patients with HLA-B27-related rheumatic disorders (seronegative spondarthritides) using a special software package which requires corresponding calibration beads in order to achieve a standardized setup of the flow cytometer. MAB from the following producers were used: Becton & Dickinson (BD), Behringwerke (BE), One Lambda (OL), and Immunotech (IT). In addition to the critical limit of fluorescence intensity (FI) which indicates positivity if exceeded, provided by the software (but valid only for the MAB from BD), empirically twice the value of the STD calculated from the mean of the FI values of HLA-B27 positive patients was regarded a good cut off for the HLA-B27 positivity in FC measurements with the MAB used. Using a standard protocol including an incubation of whole EDTA-anticoagulated blood for 15 min with MAB against HLA-B27 (FITC-conjugated) and CD3 (PE-conjugated) and a lysis of erythrocytes, good discrimination between HLA-B27 positive and negative patients was obtained. Cross reactions with HLA-B27 positive patients occurred except when the MAB from OL was used. One false-negative result was found with OL's MAB (out of 22) and false-positive results occurred in HLA-B7+ patients when MAB from BD, BE, and IT were used. Unfortunately also 1 false-positive result (out of 57) was obtained in HLA-B7−, B27− patients with IT's MAB. Errors in the interpretation of the FC analysis might be avoided if more than one MAB (including those not cross reacting with HLA-B7) are used. © 1996 Wiley-Liss, Inc.

In order to estimate the residual risk of transfusion-transmitted HCV infection, we have analyzed data from two transfusion centers in Austria (Vienna) and Germany (G6ttingen) from 1990 to 1995. In Vienna, the seroprevalence (RIBA-confirmed third-generation anti-HCV tests) was 0.28% in first-time donors (FTD) and the incidence of seroconversion in repeat donors (RD) was 0.049 (per 100 person years) from 1994 to 1995. In Gottingen, the prevalence of a PCR-confirmed positive third-generation anti-HCV test was 0.22% in FTDs and the incidence was 0.093 (per 100 person years). A continuous decline of the rate of anti-HCV-positive donations and donors was observed with first- and second-generation anti-HCV tests in the years 1990–1994. The introduction of the third-generation anti-HCV test resulted in increased numbers of anti-HCV positive repeat donors, mainly due to false-positive results. Only 9% of anti-HCV-positive repeat donors were either PCR positive or RIBA positive or indeterminate. Based on a mathematical model which takes (a) the window period, (b) the false-negative rate of anti-HCV tests, and (c) human and operational errors into consideration, we have calculated the residual risk of HCV infection. We used a window period of 74 days, a sensitivity of 98%, and an error rate of 0.1%. The residual risk (for third-generation anti-HCV test-negative blood components) was calculated to be 1:9000 (95% confidence interval 1:16390–1:6210) and 1:4800 (95% confidence interval 1:40000–1:1320) for Vienna and Gottingen, respectively, in 1994 and 1995. Since this conservative approach does not take the impact of ALAT screening into account, the actual risk is probably lower.

Flow cytometry (FC) provides a reproducible investigation of cell surface antigens on platelets. The aim of this study was to elaborate appropriate protocols and to compare them with other techniques that have already been published. (1) Venipuncture with tubes containing citrate was better for the preservation of the antigenicity than using ACD tubes. The isolated platelets could not be completely distinguished from detritus and protein aggregates. Therefore a platelet concentration between 10(7) and 10(8)/ml measurement buffer was necessary to obtain a sufficient resolution by FC. (2) Isolation methods using either differential centrifugation or diluted Ficoll-Hypaque as a flotation medium provided platelets of equal purity. The method with Ficoll-Hypaque resulted in a higher number of isolated platelets than differential centrifugation. The demonstration of platelets and their antigens in whole blood without isolation gave good results provided the platelets were not activated. Activation of platelets with 1 NIH-U thrombin/l resulted in the loss of a part of the highly activated platelets because of their aggregation. (3) Comparing different concentrations of paraformaldehyde in PBS, fixation with 1% for 15 min provided the best antigen preservation for most of the antigens investigated. Isolation induced platelet activation. In order to avoid this effect, the whole anticoagulated blood was fixed with 1% paraformaldehyde for 15 min immediately after venipuncture. Then the platelets were isolated using diluted Ficoll-Hypaque. In this way, systemic activation of platelets can be detected with antibodies against glycoproteins which are translocated from the alpha-granules or lysosomes to the cell membrane. These activation markers can be determined on immediately fixed platelets (already in the whole blood) without any interference due to unspecific activation caused by the isolation procedure. (4) Platelet treatment with citric acid at pH 3, in order to remove the antigenicity of HLA-class I molecules, was sensitive to immediate fixation with paraformaldehyde in the whole blood. Fixation after isolating the platelets made it possible to demonstrate antigen stripping, and the free heavy chain, devoid of the beta 2-microglobulin, could be clearly demonstrated. (5) Using standardization beads, the average number of antigenic sites per platelet could be determined for the investigated specificities. It was shown that antibodies which have been directly conjugated or biotinylated and combined with streptavidin-phycoerythrin yielded similar results in terms of the number of antigenic binding sites while unconjugated antibodies in combination with FITC-conjugated anti-mouse-IgG led to overestimation of antigenic binding sites.

In a follow up study, DNA typing of short tandem repeat polymorphisms, HLA and ABO antigen typing was carried out on a pair of chimeric twins, which had already been investigated by serological and cytogenetical methods two decades ago. The aim of the study was to find out whether or not DNA typing of short tandem repeat polymorphisms is an appropriate method to characterize twin chimeras.

One to two per cent of patients in need of red cell transfusion carry irregular antibodies to red blood cell (RBC) antigens and have to be supplied with specially selected blood units. To be able to respond to those requests, blood centres have to screen a significant number of donors for a variety of antigens serologically, which is a costly and through the shortage of reagents, also limited procedure. To make this procedure more efficient, the Austrian Red Cross has developed a genotyping assay as an alternative approach for high throughput RBC typing.A multiplex polymerase chain reaction (PCR) assay was designed for typing 35 RBC antigens in six reaction mixes. The assay includes both common as well as high-frequency-alleles: MNS1, MNS2, MNS3 and MNS4; LU1, LU2, LU8 and LU14; KEL1, KEL2, KEL3, KEL4, KEL6, KEL7, KEL11, KEL17 and KEL21; FY1, FY2, FYB(WK) and FY0 (FYB(ES)); JK1 and JK2; DI1, DI2, DI3 and DI4; YT1 and YT2; DO1 and DO2; CO1 and CO2; IN1 and IN2. The assay was validated using 370 selected serologically typed samples. Subsequently 6000 individuals were screened to identify high frequency antigen (HFA)-negative donors and to facilitate the search for compatible blood for alloimmunized patients.All controls showed complete concordance for the tested markers. The screening of 6000 donors revealed 57 new HFA-negative donors and the blood group database was extended by approximately 210,000 results.The study shows that in practice, this high-throughput genotyping assay is feasible, fast and provides reliable results. Compared to serological testing, this molecular approach is also very cost-efficient.

The locus ACTBP2 (SE33) is localized on chromosome 6 (band 6q14). This has been demonstrated by typing a large Caucasoid three-generation kindred of Austrian origin for SE33 and several chromosome 6 markers.

The aim of this study was to investigate whether in-line filtration, using a polyester filter for the preparation of red cell concentrates (RCC) and plasma (PL), leads to an altered proportion of T and B lymphocytes in the fraction of residual white blood cells (WBC).The capacity of Pall WBF-2 in-line filters to reduce the numbers of T and B lymphocytes from red blood cell concentrates (RCC) and plasma (PL) of 22 donations was investigated by three-colour flow cytometry (FC) using the Tritest-Trucount kit. T and B lymphocytes were identified using monoclonal antibodies (mAbs) against CD3, CD19 and CD45, conjugated with fluorescein isothiocyanate, phycoerythrin or peridinin chlorophyll protein-A, respectively. As the number of B cells was below the detection limit of the FC method, WBC of the respective blood components of healthy donors were concentrated 25-fold by Percoll density-gradient centrifugation. In this fraction the absolute numbers of T and B cells, as well as their ratio, were determined using the Attractor software, which provides a discrimination of rare cell counts from FC in relation to debris.The mean numbers, as well as minima and maxima of T and B lymphocytes per unit, were as follows. T cells in RCC: 4.51 x 10(3) (1.68 x 10(2)-4.09 x 10(4)) and in PL: 1.35 x 10(3) (2.21-1.78 x 10(4)); B cells in RCC: 2.33 x 10(3) (7.10 x 10(1)-9.15 x 10(3)) and in PL: 2.33 x 102 (7.5 x 10(2)-2.8 x 10(3)). T cells were retained, on average, at a higher level than B cells: 3.01 times higher in RCC and 1.01 times higher in PL.After filtration, the ratio of T and B lymphocytes changed in RCC (1.95 : 1) compared with unfiltered blood, where it was 5.83 : 1. In PL the ratio did not change notably compared to unfiltered blood. The results of this research show that cell concentration (using gradient centrifugation) in combination with an appropriate FC acquisition and analysis procedure, allows both residual T and B lymphocytes (being under the detection limit without cell concentration) to be determined.

Allele and genotype frequencies were determined in a population sample from Catalonia (northeast Spain) for two short tandem repeat loci (HUMCD4 and HUMF13A1), using the polymerase chain reaction (PCR). After denaturing PAG electrophoresis, 6 alleles were identified for HUMCD4 in a sample of 157 unrelated individuals, and 11 alleles for HUMF13A1 in a sample of 141 individuals. No deviation from Hardy-Weinberg equilibrium was found. The HUMCD4 and HUMF13A1 loci demonstrated a heterozygosity of 0.6815 and 0.7305 respectively.

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).

Short tandem repeat polymorphisms (STR’s) are tracts of di- to hexa- or heptanucleotides, which are tandemly repeated. They are highly polymorphic in respect to the number of repeats and widely spread throughout the human genome (Tautz 1989; Edwards 1992).

Human DNA microsatellite polymorphisms (Variable Number of Tandem Repeats, VNTR) with short repeat sizes (2–5bp) have become very useful markers in forensic haemogenetics in the last few years. For a number of reasons, typing for these markers is more and more preferred to conventional techniques in forensic casework: The large number, high polymorphism and thus the high information content of microsatellite markers The use of just one technique (PCR-Amplification Fragment Length Polymorphism, AMPFLP) for all markers The possibility to successfully employ these markers even for very low amounts of highly degraded stains However, it must be stated that there are still some problems and restrictions with these systems. Typing by AMPFLP on polyacrylamide gels is not always very clear-cut, especially with certain markers (e.g. APOB, SE33) because of interalleles (variants with incomplete repeats or sequence variants with distinct electrophoretic mobility) and/or the limited resolution capability of electrophoresis. The allele frequency distribution in different populations has shown significant differences for certain systems, whereas other loci showed a more uniform distribution, at least in the populations studied so far. Since the amount of data is limited, especially for the microsatellites with short core repeat length (Short Tandem Repeats, STR) population studies are still required. Furthermore, detailed sequencing studies should also be performed for all markers in forensic use since only with this technique the polymorphism can be determined to the ultimate level. For routine use the AMPFLP technique will still stay the standard, but it is required that a marker consisting of alleles with known sequence is used with this technique [DNA comission of the ISFH, 1994].

Typing for HLA-B27 is routinely performed in patients with seronegative spondarthritides. Besides the microlymphocytotoxic test (MLCT), other serological techniques have been developed such as enzyme immunoassays (EIA) using serum or plasma as a source for the determination of soluble HLA-B27 (sHLA-B27) and flow cytometric (FC) methods. The aim of the present study was to check the accuracy and reliability of the EIA for sHLA-B27 in comparison to the MLCT using antibodies against HLA-B27 and cross-reacting specificities (CRS), as well as an FC method and a molecular biological method. Any discrepant results should be typed with the MLCT using a complete panel of anti-HLA-class I antibodies, with FC and with a molecular biological technique. The EIA should also be repeated in those patients, using serum and plasma from a new venipuncture. In 81 patients with rheumatic disorders, the EIA and the MLCT using antibodies against HLA-B27 and CRS were performed. Based on the MLCT with a complete panel of anti-HLA-class I antibodies as a standard, discrepant test results were obtained for 9 out of 81 patients with the MLCT using antibodies against HLA-B27 and CRS and with the EIA. The following wrong results occurred: in the MLCT with anti-HLA-B27 and CRS, there were two false-negative results; in the EIA there were four false-negative and one false-positive results: one sample was undeterminable. In comparison with the MLCT, including the complete panel of HLA-class I antibodies, as well as with a molecular biological technique, typing with FC showed a complete concordance. Our investigations demonstrated that for routine typing for HLA-B27 the MLCT cannot be replaced by EIA because of a significant number of mistypings. The MLCT performed only with antibodies against HLA-B27 and CRS may also lead to typing errors. No errors were detected using flow cytometry. If only serological methods can be performed in a laboratory a combination of flow cytometry and MLCT could therefore enhance the safety of HLA-B27 typing.

tetranucleotide polymorphism in intron 40 of the human von Willebrand factor gene 12p12–12pter; Genbank Acession No.25858 [Kimpton 1992]

Short tandem repeat (STR) polymorphisms are microsatellite loci containing repeat motifs 2 to 7 nucleotides long. Several hundred STR marker systems have been described until now. They are widely spread throughout the human genome and most of them show high levels of heterozygosity. Since STR sequences may even be amplified from small amounts of highly degraded template DNA, they have become very useful in human identification e.g. for forensic casework and paternity testing.

In order to estimate the residual risk of transfusion-transmitted HIV infection we have analyzed the data from two transfusion centers in Austria (Vienna) and Germany (Göttingen) from 1985 to 1994. In Vienna, an incidence of 1:42,000 positive anti-HIV tests in repeat donors and a prevalence of 1:7000 in first-time donors were found in 1993. In Göttingen, the indicence was 1:67,000 and the prevalence 1:7900 from 1985 to 1993. Based on a mathematical model which takes (a) the window period and (b) the false-negative rate of anti-HIV tests, as well as (c) human and operational errors into consideration, we have calculated the residual risk of HIV infection. The residual risk (third generation anti-HIV test) was found to be 1:520,000 (95% confidence interval 1:1340,000-1:210,000), and 1:900,000 (95% confidence interval 1:2340,000-1:380,000) for Vienna and Göttingen, respectively, in 1993. Look-back studies from 1985 till 1994 revealed transfusion-transmitted HIV infections in three recipients (for 1.9 million donations in Vienna) and one recipient (for 160,000 donations in Göttingen) of blood components. Based on our model, as well as on prevalence and incidence rates of HIV infection, it is also possible to predict the efficacy of additional measures introduced to further decrease the risk of transfusion-transmitted HIV infection through blood components.

Short tandem repeat (STR) microsatellite loci (Edwards et al 1991) are becoming increasingly important in forensic haemogenetics. Like the VNTR-AMPFLP microsatellite loci they represent highly polymorphic markers for genetic linkage studies, human identification and paternity testing and can be typed by direct high resolution polyacrylamide gel electrophoresis (PAGE). Because of their short overall size (100-500bp) STR loci may still be successfully amplified by PCR from highly degraded material (stains) when other methods fail to produce a typeable result. In order to establish procedures and references for reliable typing of the STR-loci SE33 (Polymeropoulos et al 1992) and TC11 (Edwards et al 1992) we optimized conditions for high resolution PAGE with subsequent silver staining of the amplification products and employed this method for typing a local population sample.

The invention of the Polymerase Chain Reaction (PCR, Saiki et al 1988) has opened a wide new field of applications in molecular biology. Many new PCR-based techniques to type for polymorphic markers are now available and thus forensic haemogenetics is certainly moving to a new age. The highly polymorphic Variable Number of Tandem Repeat (VNTR) -loci offer a system of markers with high informativeness and have already been employed for paternity and identity testing for a few years. So far, most work has been done by analysis of enzyme-digested amplification products (RFLP) which is a cumbersome method with limited sensitivity. Therefore, typing of VNTR’s and STR’s (Short Tandem Repeats, a subset of VNTR’s with very short repeat sequences: 2–4bp) by Amplification Fragment Length Polymorphism (AMPFLP) is about to become the method of choice, since DNA-sequencing, of course the most precise way to type for a genetic polymorphism, will presumably not be available to most workers in the forensic field in the near future. We have undertaken studies to optimize conditions for high resolution electrophoresis on rehydratable polyacrylamide gels for the VNTR marker systems ApoB, COL2A1, D1S80, YNZ22 and for the STR loci SE33 and TC11 in order to obtain a simple protocol that leads to reproducible and reliable results and to further employ this protocol for local population and family studies and for the forensic casework in the future.

The HLA system (for review, see Tsuji et al, 1992) which represents the major histocompatibility complex (MHC) of man, encompasses approximately one thousandth of the human genome (3.8 centi-Morgans corresponding to 3800 kilobases, kb) and is localised on the short arm of chromosome 6 (band 6p21).

Microsatellite loci (VNTR, Variable Number of Tandem Repeats), a highly polymorphic system of non-coding marker loci dispersed throughout the whole human genome with constant rates were introduced to paternity and identity testing by Jeffreys et al (1988). Initially, typing has been carried out by Restriction Fragment Length Polymorphism (RFLP). Since this method has its limitaions and moreover, is time-consuming and difficult to perform and to analyze, typing by Amplification Fragment Length Polymorphism (AMPFLP, Budowle et al 1991) represents a major improvement to the typing of VNTR-loci. Since this is a simple and reliable technique and sufficently high exclusion chances can easily be achieved, it will presumably replace conventional systems for paternity and identity testing in the near future. Population and family studies that are necessary to select and to introduce new marker systems to forensic haemogenetics have already been performed by a number of workers(see Lit.). In this paper, we present the allele and phenotype frequencies of an Austrian population sample typed for the VNTR-loci ApoB, COL2A1, D1S80 and YNZ22.

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).