Study on aneuploidy and p53 mutations in astrocytomas

To determine whether a correlation exists between aneuploidy and p53 status in astrocytic tumors we analyzed 48 astrocytomas with different grades of malignancy for the presence of p53 mutations and aneuploidy of chromosomes 10 and 17 (Ch10, Ch17), known to be particularly involved with this type of tumor. We used polymerase chain reaction (PCR)-based denaturing gradient gel electrophoresis (DGGE) analysis on exons 5-8 of the p53 gene, and fluorescence in situ hybridization (FISH) analysis on interphase nuclei using chromosome specific pericentromeric probes, respectively. Our results showed that Ch10/Ch17 aneuploidy is a common early event in astrocytomas (90% of low grade tumors are aneuploid). p53 mutations and Ch17 aneuploidy are early events, but their incidence is not dependent on tumor grade. Loss of Ch10 is the only alteration that significantly correlates with tumor progression. No significant correlation between the presence of Ch10/Ch17 aneuploidy and p53 mutations was found. However, the coexistence of p53 mutations and aneuploidy, was observed in a subset of cases. The presence of p53 mutations appeared to be a significant predictor of a poor prognosis. In conclusion, genomic instability may or may not be associated with p53 mutations in astrocytomas, thus suggesting that other cellular determinants can also be responsible for the aneuploidy observed.

Loss of heterozygosity for chromosome 11 in adenocarcinoma of the stomach

Loss of heterozygosity (LOH) at several chromosomal loci is a common feature of the malignant progression of human tumors. In the case of chromosome 11, LOH has been well documented in several types of solid neoplasms, including gastric carcinoma, suggesting the presence of suppressor gene(s) at 11p15 and 11q22-23. Little is currently known about the molecular events occurring during the development of gastric cancer. To define the regions of chromosome 11 involved in gastric cancer progression, we used high-density polymorphic markers to screen for LOH in matched normal and tumor tissue DNA from 60 primary gastric carcinomas. We found that 21% of the tumors showed LOH simultaneously at 11p15 and 11q22-23, 41% had LOH at 11p15, and 30% had LOH at 11q22-23. We confirm that the minimal critical area of LOH for 11p15.5 is the approximately 2-Mb region between loci D11S1318 and D11S988. However, when we analyzed the pattern of LOH according to the country of origin of the patient, LOH for 11q22-23 alone was found only in cases from Italy. The minimal critical region of LOH at 11q22-23 is identical to that identified for other solid tumors, suggesting that the same putative tumor suppressor gene(s) contained within this region is involved in the pathogenesis of several common human tumors.

Intestinal and diffuse gastric cancers arise in a different background of Helicobacter pylori gastritis through different gene involvement

Investigation of extensively sampled nontumor gastric mucosa from 205 early gastric cancers showed Helicobacter pylori colonization in 85% of cases, including 100% of diffuse and 78% (83% in 97 cases with Swiss rolls) of glandular or mixed cancers. Intestinal metaplasia, including its type III variant, was prominent in the mucosa associated with glandular and mixed (but not diffuse) early cancers. Both glandular (usually called "intestinal") and diffuse-type cancers showed admixtures of intestinal and gastric tumor cell phenotypes. Both p53 gene mutations and p53 protein immunostaining were essentially restricted to glandular or mixed cancers and associated dysplastic lesions. Their appearance in the advanced stage of diffuse cancer was partly due to a change of the histologic pattern from glandular to diffuse during progression of some tumors. Loss of laminin, beta I integrin, or zonula adherens junctions was a common finding in both early and advanced diffuse cancer. It is concluded that two main pathways operate in gastric carcinogenesis, both starting from H. pylori gastritis and both leading to phenotypically variable, often mixed gastric/intestinal tumor growth. However, only one of the two pathways involves intestinal metaplasia, its type III variant, p53 gene alteration, and dysplasia to end in glandular cancer. In the other pathway, diffuse cancer apparently arises directly from hyperplastic, sometimes atypical necks of mostly nonmetaplastic gastric glands, through primary involvement of genes affecting cell-cell and cell-matrix junctional proteins.

p53 gene mutations and protein nuclear accumulation are early events in intestinal type gastric cancer but late events in diffuse type

We screened for p53 alterations in 71 early gastric cancers of differing histological types and growth patterns, 18 advanced cancers of diffuse type, 19 dysplastic lesions, and 12 extensive intestinal metaplasia cases. Tumors were investigated for gene mutations (exons 5-8) with PCR-based denaturing gradient gel electrophoresis and sequencing techniques, and for protein accumulation with immunohistochemical methods. Nontumor samples were studied with immunohistochemistry alone. Of the early cancers, intestinal tumors showed a much higher p53 mutation frequency (41%) than did diffuse cancers (4%). When comparing early and advanced tumors of the same type, we observed a similarity in mutation frequency (41 versus about 50%) for intestinal tumors, and a significant increase for diffuse tumors (from 4 to 33%). Immunopositive case distribution between tumor types and stages paralleled that of mutated cases. Immunohistochemical and genetic analysis gave concordant results for all samples with gene mutations. Eighteen of the 65 (28%) nonmutated tumors displayed significant immunoreactivity. Early tumors that massively penetrated the submucosa, i.e., the early tumors for which prognosis is worst, showed the highest frequency both of p53 gene mutation and of nonmutated protein accumulation. Twelve of 19 dysplastic lesions showed significant immunoreactivity, whereas intestinal metaplasias proved unreactive in all but a few cells. Our results yield two implications: that p53 alterations have a crucial and early role in gastric carcinogenesis of intestinal type, likely acting at the transition step between metaplasia and dysplasia; and that the alterations are mainly associated with tumor progression in cancer of diffuse type.

Analysis and clinical implications of K-ras gene mutations and infection with human papillomavirus types 16 and 18 in primary adenocarcinoma of the uterine cervix

Experimental models indicate that activated ras genes and HPV oncogenic sequences may cooperate in inducing a completely transformed phenotype in epithelial cells. We searched for K-ras gene mutations and HPV type-16 and -18 sequences in 67 primary adenocarcinomas of the uterine cervix by analyzing DNAs from formalin-fixed, paraffin-embedded tissue samples. Target sequences were amplified by PCR and analyzed by denaturing gradient gel electrophoresis (DGGE) and sequencing for the detection of K-ras gene mutations and by Southern blotting for the detection of HPV infection. We found 16 mutations in 15 cases; 14 were at codon 12 and 2 at codon 13; 11 were base transitions and 5 were transversions. Mutations were more frequent in mucin-secreting than in non-mucinous tumors. HPV oncogenic sequences were detected in 58 cases with no significant difference between K-ras-mutated and wild-type tumors. HPV oncogenic sequences were also more frequent in mucin-secreting than in non-mucinous tumors. Both molecular events were present simultaneously in 13 out of 58 cases, all of which had histologically grade-2 and grade-3 tumors. Clinico-pathological parameters of the disease and the overall survival, however, were independent of K-ras mutations and of HPV-16 and -18 infection, as shown by univariate and multivariate analysis. In contrast, stage of disease, lymph-node metastases, deep infiltration, clear-cell histology and low grade of differentiation were risk factors for tumor-related death.

Intraductal papillary-mucinous tumours represent a distinct group of pancreatic neoplasms: an investigation of tumour cell differentiation and K-ras, p53 and c-erbB-2 abnormalities in 26 patients

Intraductal papillary growth of mucin producing hypersecreting, columnar cells characterizes a group of rare pancreatic exocrine neoplasms which we propose to call intraductal papillary-mucinous tumors (IPMT). We analysed the histopathology of 26 IPMT in relation to gastro-enteropancreatic marker expression, genetic changes and biology. Four IPMT showing only mild dysplasia were considered to be adenomas. Nine tumours displayed moderate dysplasia and were regarded as borderline. Severe dysplasia-carcinoma in situ changes were found in 13 IPMT which were therefore classified as intraductal carcinomas. Six of these carcinomas were frankly invasive and two of these had lymph node metastases. The invasive component resembled mucinous non-cystic carcinoma in all but one tumour which showed a ductal invasion pattern. Immunohistochemically, an intestinal marker type was found in most carcinomas, while gastric type differentiation prevailed among adenomas or borderline tumours. K-ras mutations (seven at codon 12 and one at codon 13) were found in 31% of IPMT (2 adenomas, 1 borderline, 5 carcinomas). Nuclear p53 overexpression was detected in 31% of IPMT (6 carcinomas and 2 borderline IPMT) and correlated with p53 mutations (one at exon 8 and the other at exon 5) in two carcinomas. p53 abnormalities were unrelated to K-ras mutation. c-erbB-2 overexpression was observed in 65% of IPMT, with various grades of dysplasia. Twenty-two of 24 patients are alive and well after a mean post-operative follow-up of 41 months. Only two patients, both with invasive cancer at the time of surgery, died of tumour disease. It is concluded that pancreatic IPMT encompass neoplasms which, in general, have a favorable prognosis, but are heterogeneous in regard to grade of dysplasia and marker expression. Adenoma, borderline tumour, intraductal carcinoma and invasive carcinoma can be differentiated. p53 changes but not K-ras mutation or c-erbB-2 overexpression are related to the grade of malignancy. Most IPMT differ in histological structure, marker expression and behaviour from ductal adenocarcinoma.

K-ras gene mutations: an unfavorable prognostic marker in stage I lung adenocarcinoma

Activation of K-ras gene by point mutations, a common finding in lung adenocarcinomas, has been suggested to decrease patient survival. We investigated 109 lung adenocarcinomas, mostly small, peripheral, stage I tumours (81/109) for presence of K-ras gene mutations at codons 12 and 13. Mutations were detected by denaturing gradient gel electrophoresis analysis of specific sequences amplified by polymerase chain reaction from DNA extracted from archival pathological material. Thirty-three of 109 (30.3%) tumours showed mutations at codon 12 (28/33, 84.8%) or 13 (5/33, 15.2%) of the gene. Mutations and type of nucleotide substitutions were differently distributed among cytological subtypes, being more prevalent among less differentiated (G2 and G3) tumours and among bronchial than bronchiolo-alveolar type adenocarcinomas. Survival analysis showed an adverse effect of K-ras mutation on survival, restricted to stage I tumours. Median survival for 81 stage I patients was 30 months for non-mutated tumours versus 20 months for mutated tumours (p = 0.016). Multivariate analysis showed that age of patient (p = 0.001) and K-ras mutation status (p = 0.04) were the only independent factors influencing survival significantly. These data strengthen the hypothesis that K-ras gene mutations may be useful in identifying a subgroup of patients with poor outcome.

K-ras and p53 gene mutations in pancreatic cancer: ductal and nonductal tumors progress through different genetic lesions

We studied K-ras and p53 gene mutations in a panel of 57 primary pancreatic cancers including ductal and nonductal tumors. DNAs were obtained from formalin-fixed, paraffin-embedded material. Target sequences were amplified by polymerase chain reaction and analyzed by denaturing gradient gel electrophoresis and sequencing. Both K-ras and p53 genes were frequently mutated in ductal cancers (25 of 35, 71.4%; 18 of 35, 51.4%, respectively). K-ras mutations were confined to the second position of codon 12 where base transitions and transversions were equally observed. p53 changes were mainly missense mutations. Transitions and transversions were found equally with a prevalence of G:C-->A:T changes among transitions. No gene alterations were present in the 6 exocrine nonductal tumors and (with one exception) in the 12 endocrine tumors analyzed. Our results indicate that mutated K-ras and p53 genes can cooperate in the establishment of ductal pancreatic cancers, whereas other genetic events have to be present in nonductal tumors. Moreover, K-ras alterations may represent an early event in ductal tumorigenesis, as suggested both by the high gene mutation frequency and by the presence of mutations in low-grade tumors. On the contrary, p53 gene changes seem to represent an event required for the malignancy progression of ductal tumors from lower to higher grades.

Primary retroperitoneal mucinous cystoadenocarcinomas: an immunohistochemical and molecular study

Special immunohistochemical stains for the identification of gastroenteropancreatic antigens in two cases of primary retroperitoneal mucinous cystoadenocarcinomas (PRMC) show that these tumours have patterns similar to ovarian mucinous tumours. Markers of pyloric type gastric mucosa differentiation (M1, cathepsin E, concavavalin A, pepsinogen II) are mostly positive in benign and borderline areas with endocervical type differentiation, while immunoreactivity for intestinal cell markers (M3SI and CAR-5) and for DU-PAN-2 is present mainly in frankly malignant areas, regardless of differentiation type. DNA analysis shows a point mutation of K-ras oncogene at codon 12 (GGT to CGT) in one case. The immunohistochemical and genotypic similarity of PRMC and ovarian mucinous tumours may indicate similar mechanisms in their histogenesis.

Loss of heterozygosity and K-ras gene mutations in gastric cancer

In order to identify relevant genetic lesions in gastric carcinoma, we searched for tumor suppressor gene inactivation and K-ras gene mutations by analyzing tumor and control DNAs from 34 patients. These were from an epidemiologically defined area of Italy characterized by one of the world's highest incidences of stomach cancer. Allele losses were investigated by the Southern blotting procedure at 16 polymorphic loci on 11 different chromosomes. Our data demonstrate that chromosomal regions 5q, 11p, 17p and 18q are frequently deleted, and that 7q and 13q chromosome arms are also involved, although at a lower frequency. Loss of heterozygosity (LOH) at region 11p was not found during other surveys carried out on patients of different geographic origins. No specific combination of allelic losses could be recognized in the samples analyzed, the only exception being that tumors with 17p allelic loss also showed LOH on the 18q region. When matching frequent LOH events and the stage of progression of the tumors, we observed a trend of association between advanced stages and allelic losses on 17p and 18q chromosome arms. The analysis of K-ras, carried out by the polymerase chain reaction and denaturing gradient gel electrophoresis, demonstrated transforming mutations in only 3 out of 32 cases. Colorectal tumorigenesis proceeds by the accumulation of genetic alterations, including K-ras mutations and inactivation of tumor suppressor genes on the 5q, 17p and 18q regions. Our data indicate that, although gastric and colorectal neoplasias share common genetic alterations, they probably progress through different pathways.

Base transitions are the most frequent genetic changes at P53 in gastric cancer

We searched for P53 mutations in gastric carcinoma by analyzing tumor DNAs from 29 patients. We detected 13 different somatic mutations in 15 patients (52%) and a biallelic polymorphism in exon 6 (5 heterozygous subjects). The somatic mutations were mainly localized in the sequences corresponding to the highly conserved domains of the protein. Twelve samples showed a single base change: 11 missense and 1 nonsense mutations. Three samples showed deletions leading to a frame shift, to the in-frame loss of 2 amino acids, and to the deletion of a splicing site. All point mutations, except one, were transitions, and 91% of them were G:C-->A:T changes. We previously analyzed this panel of tumors for allelic loss at the 17p13 chromosomal region, where the P53 gene had previously been located: the results showed an increasing incidence of allelic loss in late-stage tumors. On the contrary, in the present study no trend between P53 mutations and tumor stages was found. This observation indicates that mutation events precede allelic loss in gastric cancer. Half (54%) of the mutations occurred in samples without allelic loss, suggesting that specific mutated alleles, acting in a dominant negative fashion, can alter in vivo the P53 protein function.

DNA amplification in human gastric carcinomas

We recently identified a genomic domain at chromosome 10q26 that is highly amplified in the gastric carcinoma cell lines KATO III and SNU-16 and contains the BEK/K-sam gene, which encodes several growth factor receptors. A contiguous segment of 200 kb spanning this gene was amplified in five of 139 (3.6%) primary gastric carcinomas, all of them classified as poorly differentiated tumors. There was no amplification of this genomic region in a variety of other solid tumors. The overall frequency of gene amplification among the gastric carcinomas rose to 19.4% when MYC, ERBB2, and INT2 were included in the analysis, with significant association with advanced tumor stage. Amplification of various genomic regions in solid tumors may be more frequent than previously estimated.

Detection of K-ras mutations by denaturing gradient gel electrophoresis (DGGE): a study on pancreatic cancer

In pancreatic neoplasias mutations in the first exon (codon 12) of K-ras gene occur at high frequency and seem to have a diagnostic significance. We set up the DGGE conditions to search for these mutations in pancreatic tumor sample DNAs. All samples were directly classified by simply comparing their DGGE patterns with those of control cell lines carrying known K-ras base substitutions. We found a mutation frequency of 73% in pancreatic adenocarcinoma, whereas no mutations were observed in benign lesions. The non-isotopic method we used turned out to be rapid and sensitive. DGGE could therefore be utilized for the detection of K-ras mutations in pancreatic lesions, to evaluate their actual or potential malignancy. In general, DGGE could be useful for K-ras gene screening on pathological tissue samples.

DNA sequences amplified in cancer cells: an interface between tumor biology and human genome analysis

There is growing evidence that amplification of specific genes is associated with tumor progression. While several proto-oncogenes are known to be activated by amplification, it is clear that not all the genes involved in DNA amplification in human tumors have been discovered. Our approach to the identification of such genes is based on the 'reverse genetics' methodology. Anonymous amplified DNA fragments are cloned by virtue of their amplification in a given tumor. These sequences are mapped in the normal genome and hence define a new genetic locus. The amplified domain is isolated by long-range cloning and analyzed along three lines of investigation: new genes are sought that can explain the biological significance of the amplification; the structure of the domain is studied in normal cells and in the amplification unit in the cancer cell; attempts are made to identify molecular probes of diagnostic value within the amplified domain. This application of genome technology to cancer biology is demonstrated in our study of a new genomic domain at chromosome 10q26 which is amplified specifically in human gastric carcinomas.

A 5'-truncated c-myc gene variant not associated with a risk of cancer

By analyzing c-myc specific fragments from white blood cell DNAs of 98 gastric cancer patients and 46 control subjects, we observed 6 unexpected patterns due to presence of a variant c-myc gene in addition to the normal gene. Restriction enzyme mapping indicated that the variant c-myc gene was the result of a 5' deletion including the first exon and part of the first intron. The deleted region, non-coding for the functional c-myc protein, contains sequences involved in the regulation of transcription. We therefore analyzed the c-myc mRNAs from a subject carrying the truncated gene and from a subject homozygous for the normal gene in Northern blotting experiments: the mRNAs were indistinguishable, both qualitatively and quantitatively. Family analysis demonstrated that the truncated gene is inherited in a Mendelian fashion. Population studies showed that the allele, both in patients and in control subjects, reaches a polymorphic frequency (2.1% for the whole sample) and that it is not associated with a risk of cancer.

Heterogeneous protooncogene amplification correlates with tumor progression and presence of metastases in gastric cancer patients

In order to evaluate the relevance of protooncogene alterations in gastric cancer and to specifically relate these alterations to types and stages of the neoplasia, we studied oncogenes of possible interest in gastric tumors with different clinical parameters. Fifty DNAs from primary gastric adenocarcinoma were analyzed, by the Southern blotting technique, for the presence of amplification or rearrangements of seven different protooncogenes: c-myc, c-erbB2, c-Ki-ras, c-Ha-ras, c-N-ras, hst, and c-mos. All the tumors analyzed were histologically classified and staged. Amplification of the following genes was found: c-myc (2 of 50), hst (3 of 50), c-erbB2 (3 of 50), and c-Ki-ras (5 of 50). The simultaneous amplification of hst (3 cases), c-myc (1 of 3), or c-Ki-ras (2 of 3) was observed. Analysis of DNAs from atrophic and metaplastic gastric mucosa (which can be regarded as preneoplastic lesions) of the 10 patients showing gene amplification demonstrated that this was limited to neoplastic cells. Considering protooncogene amplification in general (i.e., involving different genes and occurring to different degrees) and clinical parameters of tumors, we found a statistically significant association between amplification and both tumor progression and presence of metastases. Therefore, at least for the genes analyzed, amplification is a relatively infrequent phenomenon and represents a late event in the temporal development of gastric cancer.

Red cell and serum polymorphisms in the Oltrepò Pavese population (northern Italy)

A sample of about 300 subjects from the Italian population of the Oltrepò Pavese, in Lombardy, was studied for 6 polymorphic genetic markers: ACP1, ADA, ESD, GLO1, PGM1 subtyping and HP. The observed gene frequencies were: ACP1*A = .267, ACP1*B = .697, ACP1*C = .036; ADA*2 = .060; ESD*2 = .119; GLO1*1 = .375; PGM1*1S = .688, PGM1*1F = .095, PGM1*2S = .175, PGM1*2F = .042; HP*1 = .362.

Study of the c-Ha-ras-1 locus polymorphism in an Italian population with high incidence of gastric cancer

The c-Ha-ras-1 proto-oncogene locus is characterized by a restriction fragment length polymorphism resulting from length variation in a variable tandem repetition (VTR) region downstream from the structural part of the gene. The presence of uncommon alleles at this region has been suggested to be an informative marker for the development of different malignancies, including solid tumours. In order to identify possible genetic markers of cancer risk, we studied the c-Ha-ras-1 locus polymorphism in an Italian population characterized by a high incidence of stomach tumours. Gastric cancer patients, some having first-degree relatives affected by the same malignancy, and control subjects were studied. A total of 176 DNAs was analysed by the Southern blotting technique with TaqI restriction enzyme. This yields a fragment containing the sequence of variable length (VTR) and also allows detection of a cleavage site polymorphism. Thirteen different alleles were detected and some new common and rare variants were found. Our results do not provide evidence that the inheritance of any allele may predispose to gastric malignancies. Segregation analysis carried out on 13 patients' families demonstrated, without exception, a Mendelian inheritance of patterns.

Migration pattern and genetic marker distribution of the Afro-American population of Bluefields, Nicaragua

On a sample of the population of mixed African ancestry living in Bluefields, Nicaragua, the pattern of migration and the distribution of red cell and serum genetic markers have been studied. It is concluded that, in spite of a considerable level of internal and external migration, a distinctive genetic structure is maintained by the population. Moreover, a strongly negative assortative mating can be observed between people inhabiting the western and eastern areas of Nicaragua. It is estimated that most, if not all, of the genetic pool of the population is accounted for by a process of admixture between African and Indian peoples.

A study of several red cell enzyme markers in two samples of the Italian population. Report of new CA1 and PGD variant phenotypes

Gene frequencies for 17 red cell enzymatic markers have been determined in two samples of the Italian population (Lombardy and Tuscany regions). A significant difference was found between the two samples for the AK1 and PGM1 systems (AK1*2 .028 and .044, PGM1*2 .254 and .301 in Lombardy and Tuscany respectively). Variant phenotypes, for PEPA, PEPB, CA2, PGM2, PGD and GPT markers, have been observed; some of these are due to new alleles occurring at the CA2 and PGD loci.

Electrophoretic subtyping of phosphoglucomutase locus 1 (PGM1) polymorphism in the Italian and Czechoslovakian populations

About 3,500 subjects from Italy and Czechoslovakia have been analyzed by acid starch gel electrophoresis for the subtyping of PGM1 polymorphism. The Italian sample included three different subgroups, from Northern, Central and Southern Italy. The allele frequencies found in the three groups do not differ significantly from each other; the observed values in the pooled sample are: PGM1S1 = 0.594, PGM1F1 = 0.118, PGM2S1 = 0.231, PGM2F1 = 0.057. In the Czechoslovakian group, which differs significantly from the Italian population, the following allele frequencies were found: PGM1S1 = 0.639, PGM1F1 = 0.118, PGM2S1 = 0.180, PGM2F1 = 0.063. The analysis of 217 families did not show any exception to Mendelian inheritance of the patterns.

Inheritance of rDNA spacer length variants in man

We studied the rDNA spacer length polymorphism in a sample of 121 individuals belonging to families of 2-3 generations. Our data, obtained by restriction pattern analysis of genomic DNA, confirmed the limited and discrete nature of this polymorphism. Using the pattern as a genetic marker, we analyzed the segregation of length variants in the different families and we investigated the possible occurrence of unequal crossing-over events among homologous and nonhomologous rDNA clusters. No direct evidence of recombination in the spacer region that we analyzed emerged from our study. All the differences in the restriction patterns observed among individuals from the same family could be explained as resulting from meiotic segregation. Family data showed a multichromosomal distribution of NTS length variants and demonstrated a direct correspondence between the frequency of a variant in the population and its degree of spreading on the different rDNA clusters.

A study of ten red cell enzymatic markers in the Naples' population. Report of a new GPT variant phenotype

A sample of the population of Naples has been examined for several red cell enzyme markers. About 2,000 newborn have been analyzed for ACP, GLO I, and UMPK; 1,000 of them were also analyzed for PepA and PepB, and 500 for PGM1 and PGM2. In addition about 400 school children have been typed for the PGD and PGP polymorphisms. The observed gene frequencies for the polymorphic systems are: ACPA = 0.293, ACPB = 0.667 and ACPC = 0.040; GLO1 = 0.372; GPT2 = 0.462; UMPK2 = 0.029; PGM21 = 0.279; PGDC = 0.037; PGP1 = 0.953, PGP2 = 0.038 and PGP3 = 0.009. Moreover during the screening of PepA, PepB and GPT markers, some rare alleles have been encountered, one of which, at the GPT locus, has never been reported before. We propose for it the name GPT10.

Subtyping of phosphoglucomutase locus 1 (PGM1) polymorphism in some populations of Rwanda: description of variant phenotypes, "haplotype" frequencies, and linkage disequilibrium data

Some populations of Rwanda (South Twa Pygmies, Hutu, and Tutsi) have been analyzed by acid starch gel electrophoresis for the subtyping of PGM1 polymorphism. The new polymorphic third PGM11 allele, the PGM1(1Twa), which we recently detected in Twa Pygmies from North Rwanda, has not been found in this survey, whereas the rare PGM1(6) allele attains subpolymorphic frequencies in all groups. Comparison between the various populations of Rwanda shows that they differ significantly from each other with the exception of South Twa Pygmies and Tutsi. A relatively low frequency (9.6%) of the PGM1(2S) allele appears to be typical of North Twa Pygmies; a low frequency of PGM1(2F) (1.2%-3.6%) has been found in all these groups but not in the Hutu (6.4%); and a particularly high incidence of the PGM1(1F) allele (the highest so far reported) has been observed in the South Twa Pygmies (20%) and in the Tutsi (18%). The PGM1(1Twa) and PGM1(6) enzymes, which in acid starch gel are not distinguishable, can be clearly differentiated by isoelectric focusing. In addition, the same technique has shown that the rare PGM1(7) allele observed in one Hutu is different from that found at polymorphic frequency in the Japanese and from a rare PGM1(7) allele found in Germany. On the very likely hypothesis that the PGM1(1S), PGM1(1F), PGM1(2S), and PGM1(2F) result from variations at two different polymorphic sites, 1/2 and F/S, within the PGM1 structural gene, all the available population data have been analyzed to investigate whether preferential combinations (haplotypes) were identifiable. Whereas Caucasians show a prevalence of 2F and 1S combination with an 8.02% mean value of linkage disequilibrium expressed as % Dmax, from the very few and scattered African data, it is impossible to draw any inference at present.