Apolipoprotein A polymorphisms and plasma lipoprotein(a) concentrations in non-Hispanic Whites and Hispanics

Elevated levels of plasma lipoprotein(a) [Lp(a)] are thought to be a risk factor for atherosclerosis and coronary heart disease. Plasma levels of Lp(a) are highly variable between individuals, ranging from 0.1 mg/dL to > 100 mg/dL These levels are under strict genetic control, and genetic variation in the apolipoprotein A (APOA) gene accounts for almost all variation in Lp(a) levels. In this study, we investigated the relationship between two APOA polymorphisms (kringle 4 and 5' pentanucleotide repeat) and plasma Lp(a) levels in normoglycemic non-Hispanic Whites (NHWs) (n = 390) and Hispanics (n = 214) from the San Luis Valley, Colorado. Mean (+/- SD) and median Lp(a) levels were 9.6 +/- 12.5 mg/dL and 3.8 mg/dL, respectively, in NHWs and 12.1 +/- 15.6 mg/dL and 4.9 mg/dL, respectively, in Hispanics. The number of observed kringle 4 repeats ranged from 11 to 38 in NHWs and from 10 to 41 in Hispanics. Spearman rank correlation revealed an inverse relationship between the size of the kringle 4 repeat and plasma Lp(a) levels in both populations (r = -0.38; p < 0.0001 in NHWs and r = -0.64; p < 0.0001 in Hispanics). About 30% and 48% of the variation in plasma Lp(a) was explained by this polymorphism in NHWs and Hispanics, respectively. This study confirms that the kringle 4 polymorphism in the APOA gene is a significant determinant of Lp(a) levels in both study groups. A pentanucleotide repeat polymorphism in the 5' promoter region of the APOA gene did not show significant impact on plasma Lp(a) levels in either NHWs or Hispanics.     

The relationship among apolipoprotein(a) polymorphisms, the low-density lipoprotein receptor-related protein, and the very low density lipoprotein receptor genes, and plasma lipoprotein(A) concentration in the Czech population

Increased plasma concentration of lipoprotein(a) [Lp(a)] is an established independent risk factor for coronary artery disease (CAD), which is strongly genetically determined. This study was designed to investigate the relationship between the K-IV and (TTTTA)n apolipoprotein(a) [apo(a), protein; APOA, gene] polymorphisms, as well as the C766T low-density lipoprotein receptor-related protein (LRP) and the (CGG)n very low density lipoprotein receptor (VLDLR) polymorphisms on the one hand, and plasma Lp(a) levels in Czech subjects who underwent coronary angiography on the other hand. The lengths of the alleles of the APOA K-IV and (TTTTA)n polymorphisms were strongly inversely correlated with plasma Lp(a) levels in univariate analysis (r = -0.41, p < 10(-4) and r = -0.20, p < 0.01, respectively). Multivariate analysis revealed significant associations between the APOA polymorphisms studied and plasma Lp(a) levels in subjects expressing only one APOA K-IV allele (p < 10(-6) for K-IV and p < 0.001 for TTTTA). In subjects expressing both APOA K-IV alleles, the multivariate analysis revealed that only the APOA K-IV alleles were inversely correlated with plasma Lp(a) levels (p < 0.001). Associations between both the LRP and VLDLR gene polymorphisms and plasma Lp(a) levels were only of borderline significance (p < 0.06 and p < 0.07, respectively) and were not confirmed in multivariate analysis. In conclusion, both APOA length polymorphisms significantly influenced plasma Lp(a) concentration in the Czech population studied, and this circumstance could explain the association in this population observed earlier between APOA (TTTTA)n polymorphism and CAD (Benes et al. 2000). Only a minor role in the regulation of plasma Lp(a) levels is suggested for the C766T LRP and the (CGG)n VLDLR polymorphisms.     

Apolipoprotein A-IV genetic polymorphism and its impact on quantitative traits in normoglycemic and non-insulin-dependent diabetic Hispanics from the San Luis Valley, Colorado.

Apolipoprotein A-IV exhibits a common two-allele polymorphism in several human populations studied to date. Using isoelectric focusing and immunoblotting, we have analyzed plasmas from 188 non-insulin-dependent diabetic and 238 normoglycemic Hispanic individuals from the San Luis Valley, Colorado, to determine APOA4 genotype frequencies and to estimate the impact of the genotypes on quantitative traits. The frequencies of the two common alleles, APOA4*1 and APOA4*2, were 0.929 and 0.069, respectively, in normal subjects and 0.901 and 0.096, respectively, in diabetics. The third rare allele, APOA4*3, was detected sporadically in both groups. We studied the impact of APOA4 polymorphism on the levels of total plasma cholesterol, HDL cholesterol and its subfractions (HDL3 and HDL2), LDL cholesterol, triglycerides, glucose, and insulin. We observed no significant effect of the APOA4 polymorphism on any trait in diabetics. However, we did note a significant sex-specific effect in normoglycemic females on the level of total HDL cholesterol (p = 0.001) and its subfractions HDL2 (p = 0.043) and HDL3 (p = 0.001). The effect of the APOA4*2 allele in normal Hispanic females was to lower the total HDL, HDL2, and HDL3 cholesterol by 8.75 mg/dl, 2.37 mg/dl, and 5.36 mg/dl, respectively, compared to the common APOA4*1 allele.     

Plasma lipoprotein(a) distribution and its correlates among Samoans

Plasma lipoprotein(a) [Lp(a)]-consisting of a disulfide-linked complex of apolipoprotein B and apolipoprotein (a)--levels are considered to be an independent risk factor for coronary heart disease. There are considerable ethnic group differences in the distribution of plasma Lp(a) levels that raise public health concerns. Although plasma Lp(a) distribution has been determined in various ethnic groups, no such information is available in Pacific Islanders. In this study we have determined the distribution and correlates of plasma Lp(a) in population-based samples of 361 American Samoans (145 men, 216 women) and 560 Western Samoans (265 men, 295 women), aged 20-70 years. Plasma Lp(a) levels were measured using a commercial enzyme-linked immunosorbent assay. The distribution of plasma Lp(a) levels in both groups was highly skewed with 73% and 65% of values in the 0-5 mg/dl range in American Samoans and Western Samoans, respectively. The mean (6.4 mg/dl) and median (2.2 mg/dl) Lp(a) levels in pooled Samoans were significantly lower when compared with other ethnic groups using the same measurement kit. Plasma Lp(a) correlated significantly with total and LDL cholesterol in both genders after correcting for the contribution of Lp(a) cholesterol, and with apolipoprotein B in women after the correction for Lp(a)-apoB, but not with age, smoking, alcohol intake, or body mass index. Our data show that Samoans, Polynesians of Pacific Islands, have strikingly lower Lp(a) levels than all other reported population groups. These data are consistent with the hypothesis that genetic factors account for interethnic group variation in plasma Lp(a) levels.     

The apolipoprotein (a) gene: a transcribed hypervariable locus controlling plasma lipoprotein (a) concentration

Lipoprotein(a) [Lp(a)] is a quantitative trait in human plasma. Lp(a) consists of a low-density lipoprotein and the plasminogen-related apolipoprotein(a) [apo(a)]. The apo(a) gene determines a size polymorphism of the protein, which is related to Lp(a) levels in plasma. In an attempt to gain a deeper insight into the genetic architecture of this risk factor for coronary heart disease, we have investigated the basis of the apo(a) size polymorphism by pulsed field gel electrophoresis of genomic DNA employing various restriction enzymes (SwaI, KpnI, KspI, SfiI, NotI) and an apo(a) kringle-IV-specific probe. All enzymes detected the same size polymorphism in the kringle IV repeat domain of apo(a). With KpnI, 26 different alleles were identified among 156 unrelated subjects; these alleles ranged in size from 32kb to 189kb and differed by increments of 5.6kb, corresponding to one kringle IV unit. There was a perfect match between the size of the apo(a) DNA phenotypes and the size of apo(a) isoforms in plasma. The apo(a) DNA polymorphism was further used to estimate the magnitude of the apo(a) gene effect on Lp(a) levels by a sib-pair comparison approach based on 253 sib-pairs from 64 families. Intra-class correlation of log-transformed Lp(a) levels was high in sib-pairs sharing both parental alleles (r = 0.91), significant in those with one common allele (r = 0.31), and absent in those with no parental allele in common (r = 0.12). The data show that the intra-individual variability in Lp(a) levels is almost entirely explained by variation at the apo(a) locus but that only a fraction (46%) is explained by the DNA size polymorphism. This suggests further heterogeneity relating to Lp(a) levels in the apo(a) gene.     

The Apo(a) gene is the major determinant of variation in plasma Lp(a) levels in African Americans.

The distributions of plasma lipoprotein(a), or Lp(a), levels differ significantly among ethnic groups. Individuals of African descent have a two- to threefold higher mean plasma level of Lp(a) than either Caucasians or Orientals. In Caucasians, variation in the plasma Lp(a) levels has been shown to be largely determined by sequence differences at the apo(a) locus, but little is known about either the genetic architecture of plasma Lp(a) levels in Africans or why they have higher levels of plasma Lp(a). In this paper we analyze the plasma Lp(a) levels of 257 sibling pairs from 49 independent African American families. The plasma Lp(a) levels were much more similar in the sibling pairs who inherited both apo(a) alleles identical by descent (IBD) (r = .85) than in those that shared one (r = .48) or no (r = .22) parental apo(a) alleles in common. On the basis of these findings, it was estimated that 78% of the variation in plasma Lp(a) levels in African Americans is attributable to polymorphism at either the apo(a) locus or sequences closely linked to it. Thus, the apo(a) locus is the major determinant of variation in plasma Lp(a) levels in African Americans, as well as in Caucasians. No molecular evidence was found for a common "high-expressing" apo(a) allele in the African Americans. We propose that the higher plasma levels of Lp(a) in Africans are likely due to a yet-to-be-identified trans-acting factor(s) that causes an increase in the rate of secretion of apo(a) or a decrease in its catabolism.     

The dinucleotide (CA) repeat polymorphism of estrogen receptor beta but not the dinucleotide (TA) repeat polymorphism of estrogen receptor alpha is associated with venous ulceration

Venous ulcers are the predominant form of chronic wound in the elderly, accounting for around 70% of all cases. The steroid sex hormone estrogen plays a crucial role in normal human skin maintenance and during cutaneous wound repair following injury. Estrogen can reverse age-related impaired wound healing by dampening the inflammatory response and increasing matrix deposition at the wound site. The molecular actions of estrogen are mediated through two nuclear sex steroid hormone receptors, estrogen receptor alpha (ERalpha) and beta (ERbeta). We have conducted a case-control study to investigate whether dinucleotide repeat polymorphisms in the estrogen receptor genes are associated with venous ulceration in the UK Caucasian population. Genomic fragments containing the ERalpha dinucleotide (TA)(n) repeat polymorphism or the ERbeta dinucleotide (CA)(n) repeat polymorphism were amplified by polymerase chain reaction in subject DNA samples and genotyped according to fragment length by capillary electrophoresis. There was no evidence to suggest that the TA repeat polymorphism of ERalpha was associated with venous ulceration. However, the CA*18 allele of the ERbeta CA repeat polymorphism was significantly associated with venous ulceration (n = 120, OR = 1.8, 95% CI = 1.1-2.8, P = 0.02). When the CA repeats alleles were grouped together into either low (L < or = 18) or high (H > 18) numbers of CA repeats, the low (L) repeat allele was significantly associated with venous ulceration (OR = 1.5, 95% CI = 1.0-2.2, P = 0.03). Our results show that a specific ERbeta variant is associated with impaired healing in the elderly, predisposing individuals to venous ulceration.     

The world-wide distribution of allele frequencies at the human dopamine D4 receptor locus

The dopamine D4 receptor gene (DRD4) has an expressed polymorphism in the third exon that may have functional relevance. The polymorphism exists at two levels. At the higher level there is an imperfect tandem repeat of 48 base pairs (bp) coding for 16 amino acids; alleles have been identified with 2 (32 amino acids) to 10 (160 amino acids) repeats. The imperfect nature of the repeats is responsible for a more subtle level of variation since alleles with the same number of repeats can differ in the exact sequences or in the order of the variants of the 48-bp unit. We have undertaken a global survey of this expressed polymorphism as one approach to understanding the evolutionary significance and origins of the polymorphism as well as understanding what selective forces, if any, may be operating at this locus. As the first step, we have determined the repeat number genotype of the DRD4 repeat polymorphism in 1,327 individuals from 36 different populations. The allele frequencies differ considerably among the different populations. The 4-repeat allele was the most prevalent (global mean allele frequency = 64.3%) and appeared in every population with a frequency ranging from 0.16 to 0.96. The 7-repeat allele was the second most common (global mean = 20.6%), appearing quite frequently in the Americas (mean frequency = 48.3%) but only occasionally in East and South Asia (mean frequency = 1.9%). The 2-repeat allele was the third most common (global mean frequency = 8.2%) and was quite frequent in East and South Asia (mean frequency = 18.1%) while uncommon in the Americas (mean frequency = 2.9%) and Africa (mean frequency = 1.7%). The universality of the polymorphism with only three common repeat-number alleles (4, 7, and 2) indicates that the polymorphism is ancient and arose before the global dispersion of modern humans. The diversity of actual allele frequencies for this expressed polymorphism among different populations emphasizes the importance of population considerations in the design and interpretation of any association studies carried out with this polymorphism. Received: 18 July 1995 / Revised: 18 December 1995     

High degree of genetic polymorphism in apolipoprotein(a) associated with plasma lipoprotein(a) levels in Japanese and Chinese populations

We have developed a sensitve, high-resolution method for the analysis of the apolipoprotein(a) [apo(a)] isoforms using sodium dodecyl sulfate (SDS)-agarose/ gradient polyacrylamide gel electrophoresis. In an analysis of the genetic polymorphism of apo(a) isoforms and their relationship with plasma lipoprotein(a) [Lp(a)] levels in Japanese and Chinese, this method identified 25 different apo(a) isoforms and detected one or two apo(a) isoforms in more than 99.5% of the individuals tested. The apparent molecular weights of the apo(a) isoforms ranged from 370 kDa to 950 kDa, and 22 of the 25 different apo(a) isoforns had a higher molecular weight than of apo B-100. Studies on Japanese families confirmed the autosomal codominant segregation of apo(a) isoforms and the existence of a null allele at the apo(a) locus. The observed frequency distribution of apo(a) isoform phenotypes fit the expectations of the Hardy-Weinberg equilibrium in both the Japanese and Chinese populations. Our data indicate the existence of at least 26 alleles, including a null allele, at the apo(a) locus. The frequency distribution patterns of the apo(a) isoform alleles in Japanese and Chinese were similar to each other and also similar to that of apo(a) gene sizes reported in Caucasian American individuals. The average heterozygosity at the apo(a) locus was 92% in Japanese and 93% in Chinese. A highly significant inverse correlation was observed between plasma Lp(a) levels and the size of apo(a) isoforms in both the Japanese (r=-0.677, P=0.0001) and the Chinese (r=-0.703, P=0.0001). A highly skewed distribution of Lp(a) concentrations towards lower levels in the Japanese population may be explained by high frequencies of alleles encoding large apo(a) isoforms and the null allele.     

Apo[a] size and PNR explain African American-Caucasian differences in allele-specific apo[a] levels for small but not large apo[a

Apolipoprotein [a] (apo[a]) gene size is a major predictor of lipoprotein [a] level. To determine genetic predictors of allele-specific apo[a] levels beyond gene size, we evaluated the upstream C/T and pentanucleotide repeat (PNR) polymorphisms. We determined apo[a] sizes, allele-specific apo[a] levels, and C/T and PNR in 215 Caucasians and 139 African Americans. For Caucasians, apo[a] size affected allele-specific levels substantially greater in subjects with apo[a] < 24 K4; for African Americans, the size effect was smaller than in Caucasians, <24 K4, but did not decrease at higher repeats. In both groups, the level decreased with increasing size of the other allele. Controlling for apo[a] sizes, PNR decreased allele-specific apo[a] levels in Caucasians with increasing PNR > 8. In a multiple regression model, apo[a] allele size and size and expression of the other apo[a] allele (and PNR > 8 for Caucasians) significantly predicted allele-specific apo[a] levels. For a common PNR 8 allele, predicted values were similar in the two ethnicities for small size apo[a]. Allele-specific apo[a] levels were influenced by the other allele size and expression. Observed differences between Caucasians and African Americans in allele-specific apo[a] levels were explained for small apo[a] sizes by the other allele size and PNR; the ethnicity differences remain unexplained for larger sizes.     

In vivo characterization of human APOA5 haplotypes

Increased plasma triglyceride concentrations are an independent risk factor for cardiovascular disease. Numerous studies support a reproducible genetic association between two minor haplotypes in the human apolipoprotein A5 gene (APOA5) and increased plasma triglyceride concentrations. We thus sought to investigate the effects of these minor haplotypes (APOA5*2 and APOA5*3) on ApoAV plasma levels through the precise insertion of single-copy APOA5 haplotypes at a targeted location (Hprt) in the mouse genome. While we found no difference in the amount of human plasma ApoAV in mice containing the common APOA5*1 or minor APOA5*2 haplotype, the introduction of the single APOA5*3-defining allele (19W) resulted in three fold lower ApoAV plasma levels, consistent with existing genetic association studies. These results indicate that the S19W polymorphism is likely to be functional and explain the strong association of this variant with plasma triglycerides, supporting the value of sensitive in vivo assays to define the functional nature of human haplotypes.     

A polymorphic (CA)n repeat element maps the human glucokinase gene (GCK) to chromosome 7p.

A compound imperfect dinucleotide repeat element, [CA]4TTTGT[CT]7[CA]9AA[CA]4CCACATA[CA]3, was found approximately 10 kb 3' to the human glucokinase gene (GCK) from analysis of contiguous genomic DNA obtained from a bacteriophage lambda chromosome walk. Direct human genomic sequencing revealed the source of polymorphism to be variable numbers of CT and CA repeats. Altogether six alleles that range in length from +10 to -15 nucleotides compared to the most common (Z) allele have been identified. Alleles Z, Z + 2, and Z + 4 were present in American Blacks, Pima Indians, and Caucasians, with somewhat varied frequencies among the groups. Two alleles, Z + 10 and Z - 15, appear to be unique to American Blacks, while a Z + 6 allele was observed only in the Caucasian population studied. Observed heterozygosity of the polymorphism in the CEPH reference pedigree collection is 44% and the PIC 0.44. The polymorphism is assayed by PCR amplification and resolution of 32P-end-labeled products (ranging in length from 180 to 205 bp) on denaturing polyacrylamide sequencing gels. Using the PCR assay, the human glucokinase gene was physically localized to chromosome 7 in a panel of rodent/human somatic cell lines. Genetic analysis in CEPH pedigrees placed the dinucleotide repeat element, and thereby the human glucokinase gene, on chromosome 7p between TCRG and a RFLP locus D7S57. The glucokinase dinucleotide repeat genetic marker can now be used to assess the role of the glucokinase gene in diabetes by population association studies. In addition, this repeat marker and others flanking it on chromosome 7 can be used in linkage studies with families segregating the disorder.     

Hypervariability of intronic simple (gt)n(ga)m repeats in HLA-DRB genes

We have investigated the extent of DNA variability in intronic simple (gt)_n(ga)_m repeat sequences and correlated this to sequence polymorphisms in the flanking exon 2 of HLA-DRB genes. The polymerase chain reaction (PCR) was used to amplify a DNA fragment containing exon 2 and the repeat region of intron 2. The PCR products were separated on sequencing gels in order to demonstrate length hypervariability of the (gt)_n(ga)_m repeats. In a parallel experiment, the PCR products were cloned and sequenced (each exon 2 plus adjacent simple repeats) to characterize the simple repeats in relation to the HLA-DRB sequences. In a panel of 25 DRB1, DRB4, and DRB5 alleles new sequences were not detected. Restriction fragment length polymorphism (RFLP) subtyping of serologically defined haplotypes corresponds to translated DNA sequences in 85% of the cases, the exceptions involving unusual DR/DQ combinations. Many identical DRB1 alleles can be distinguished on the basis of their adjacent simple repeats. We found group-specific organization of the repeats: the DRw52 supergroup repeats differ from those of DRB1*0101, DRB4*0101, and DRB5*0101 alleles and from those of pseudogenes. Finally, we amplified baboon DNA and found a DRB allele with extensive similarity to DRB1 sequences of the DRw52 supergroup. The simple repeat of the baboon gene, however, resembles that of human pseudogenes. In addition to further subtyping, the parallel study of polymorphic protein and hypervariable DNA alleles may allow conclusions to be drawn on the relationships between the DRB genes and perhaps also on the theory of trans-species evolution.The nucleotide sequence data reported in this paper have been submitted to the GenBank nucleotide sequence database and have been assigned the accession number M 34258.     

Genetics of the quantitative Lp(a) lipoprotein trait

Summary Lp(a) glycoprotein exhibits an apparent size polymorphism that is associated with genetically controlled Lp(a) lipoprotein concentrations in plasma (Utermann et al. 1988). We have tested the hypothesis that this polymorphism is genetically controlled by studying 15 matings with a total of 44 offspring. This confirmed our conclusion that Lp(a) types are controlled by a series of codominant alleles Lp^F, Lp^B, Lp^S1, Lp^S2, Lp^S3 and Lp^S4 and by a null allele Lp^o. Together with the data from the accompanying paper this indicates that the structural gene for the Lp(a) protein is the major gene locus determining Lp(a) lipoprotein concentrations in plasma.     

Association of the (TAAAA)n repeat and Asp327Asn polymorphisms in the sex hormone-binding globulin (SHBG) gene with idiopathic male infertility and relation to serum SHBG concentrations

Sex hormone binding globulin (SHBG) is involved in delivering sex hormones to target tissues. We investigated the association between the (TAAAA)n repeat polymorphism, and Asp327Asn polymorphism in the SHBG gene with semen quality and idiopathic male infertility. We studied 168 men with idiopathic infertility [oligoasthenoteratozoospermia (OAT)] and equal number of age-matched normal controls. The serum levels of SHBG, reproductive and thyroid hormones, and Inhibin B were measured. Semen parameters were also assessed. The genotype assays for the SHBG polymorphism were done using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique. Baseline SHBG levels tended to be lower in infertile men (21.1±7.2nmol/l) compared to normal fertile men (24.7±7.9nmol/l). SHBG levels tended to be higher among the subjects with the Asn/Asn (25.84±3.6nmol/l) and S/S (24.50±5.4nmol/l) genotypes compared to subjects with the Asp/Asn (24.38±3.2nmol/l) and L/L (18.44±4.2nmol/l) genotypes of the SHBG gene. The genotype frequencies of Asp/Asp were 80.9% in cases and 71.4% in controls (P=0.001). The variant Asp/Asn genotype was associated with a more than 50% reduced risk of infertility (OR: 0.46, 95% CI: 0.25-0.80, P=0.001). Genotype analysis demonstrated six SHBG (TAAAA)n alleles with 6-11 repeats. Long SHBG (TAAAA)n alleles (>8 repeats) were at greater frequency in infertile men than fertile subjects (P=0.001), whereas short SHBG (TAAAA)n alleles (≤8 repeats) tended to be more frequent in fertile men than cases (P=0.001). Men with the 9/X TAAAA repeat genotype displayed a 2.82-fold increased risk of infertility (95% CI: 1.27-4.79, P=0.01). There were strong and significant positive correlations between plasma SHBG and sperm count (r=0.672, P=0.01), sperm motility (r=0.721, P=0.01) and sperm morphology (r=0.574, P=0.02). We concluded that the SHBG Asp237Asn and (TAAAA)n polymorphisms may influence SHBG levels and as a result, male infertility. Multicenter large scale studies are warranted to better elucidate the role of SHBG gene polymorphism in male infertility.     

Mapping the human liver/islet glucose transporter (GLUT2) gene within a genetic linkage map of chromosome 3q using a (CA)n dinucleotide repeat polymorphism and characterization of the polymorphism in three racial groups.

The human liver/islet glucose transporter (GLUT2), a candidate gene for diabetes, has been incorporated into a genetic linkage map for chromosome 3q using a (CA)n dinucleotide repeat polymorphism adjacent to the 3'-end of exon 4a. We have found a total of nine alleles ranging in length from 153 to 169 nucleotides in three racial groups and have determined the precise structure of the variable region for four of the alleles by DNA sequencing. Five alleles were found to be common to the American Black, Caucasian, and Pima Indian racial groups studied. One allele (169 bp) was unique to American Blacks, and another rare allele (153 bp) was found only in the Caucasian population studied. Observed heterozygosity of the polymorphism in the Caucasian (CEPH) reference pedigree collection is 60%, for American Blacks 71%, and for Pima Indians 53%. An independent study recently identified the same dinucleotide repeat and found six alleles in a Caucasian population (Froguel et al., 1991), a result that we confirm; however, our sequencing data indicate a different molecular structure for the polymorphism for some of the alleles. We have constructed a new genetic linkage map of chromosome 3q uniquely placing the GLUT2 gene between flanking markers D3S26 and D3S43. The genetic map consists of 23 loci (25 RFLPs and 2 (CA)n dinucleotide repeat markers) with 14 markers uniquely localized with odds of at least 1000:1. Three genes (FTHL4, TF, GLUT2) are integrated into the map, which spans a sex-average distance of 147.3 cM, 103.8 cM in males and 227.0 cM in females.(ABSTRACT TRUNCATED AT 250 WORDS)     

CTG repeats distribution and Alu insertion polymorphism at myotonic dystrophy (DM) gene in Amhara and Oromo populations of Ethiopia

Myotonic dystrophy (DM) is a dominantly inherited neuromuscular disease, highly variable and multisystemic, which is caused by the expansion of a CTG repeat located in the 3′ untranslated region of the DMPK gene. Normal alleles show a copy number of 5–37 repeats on normal chromosomes, amplified to 50–3000 copies on DM chromosomes. The trinucleotide repeat shows a trimodal allele distribution in the majority of the examined population. The first class includes alleles carrying (CTG)₅, the second class, alleles in the range 7–18 repeats, and the third class, alleles (CTG)_{≥ 19}. The frequency of this third class is directly related to the prevalence of DM in different populations, suggesting that normal large-sized alleles predispose toward DM. We studied CTG repeat allele distribution and Alu insertion and/or deletion polymorphism at the myotonic dystrophy locus in two major Ethiopian populations, the Amhara and Oromo. CTG allele distribution and haplotype analysis on a total of 224 normal chromosomes showed significant differences between the two ethnic groups. These differences have a bearing on the out-of-Africa hypothesis for the origin of the DM mutation. In addition, (CTG)_{≥ 19} alleles were exclusively detected in the Amhara population, confirming the predisposing role of these alleles compared with the DM expansion-mutation. Electronic Publication     

中国人端粒酶催化亚基(hTERT)基因第六内含子VNTR多态性研究

端粒酶的激活在肿瘤发生、衰老以及细胞永生化过程中起重要作用,端粒酶催化亚基(hTERT)的表达是诱导端粒酶活性的限制性步骤,hTERT的表达受到复杂的调控。hTERT基因组全长40kh,包含16个外显子及15个内含子,其中,在第2和第6内含子中各存在2个可变数目串联重复(VNTR)多态性序列(VNTR2—1st、VNTR2—2nd以及VNTR6—1st和VNTR6—2nd),在第12内含子存在另一个单态性串联重复序列。通过对北京地区210例汉族健康人群hTERT基因第6内含子中36-bpVNTR6—1st的多态性进行调查研究．结果在调查人群中观察到18、20、21、22、23、26和35次重复共7种等位基因型以及14种基因型。基因型频率分布符合Hardy—Weinberg平衡。与韩国浦山地区调查人群类似,20、22及35次重复为最常见的等位基因型,这3种等位基因型频率占调查人群总数的94．76％。除了35次重复等位基因型频率与浦山地区人群存在差异外,其他基因型频率差异不显著。此外,除了在部分重复22次的等位基因型中VNTR5′端与浦山地区人群相同外,其他等位基因型中,北京地区汉族人VNTR6—1st5′端均存在53bD插入片段,显示出不同人种vNTR6—1st周边序列的差异性。北京地区汉族正常人群hTERT VNTR基因多态性资料为研究多态性与肿瘤或衰老的相关性提供了资料。     

Population Genetic Characteristics of the D1S80 locus in seven human populations

We have analyzed the allele frequency distribution at the highly polymorphic variable number of tandem repeat (VNTR) locus D1S80 (pMCT118) in seven ethnic populations (namely, New Guinea Highlanders of Papua New Guinea, Dogrib Indians of Canada, Pehuenche Indians of Chile, American and Western Samoans, Kacharis of Northeast India, and German Caucasians) using the polymerase chain reaction (PCR) technique. In the pooled sample of 443 unrelated individuals 20 segregating alleles were detected. A trimodal pattern of allelic distribution is present in the majority of populations and is indicative of the evolutionary antiquity of the polymorphism at this locus. In spite of the observed high degree of polymorphism (expected heterozygosity 56%–86%), with a single exception — the marginally significant P value (0.04) of the exact test in American Samoans — the genotype distributions in all populations conform to their respective Hardy-Weinberg expectations. Summary statistics indicate that, in general, the allele frequency distribution at this locus may be approximated by the infinite allele model. The data also demonstrate that alleles that are shared by all populations have the highest average frequency within populations. Furthermore, the kinship bioassay analysis demonstrates that the extensive variation observed at the D1S80 locus is at the interindividual within population level, which dwarfs any interpopulation allele frequency variation, consistent with the population dynamics of hypervariable polymorphisms. These characteristics of the D1S80 locus make it a very useful marker for population genetic research, genetic linkage studies, forensic identification of individuals, and for determination of biological relatedness of individuals.