The genotype determines the B cell response in mercury-treated mice

Gaucher disease (GD) is an autosomal recessive disorder caused by mutations in the lysosomal beta-glucocerebrosidase (GBA) gene. As the disease is particularly prevalent among Ashkenazi Jews, most studies have been carried out on this ethnic group. In the current study, we present a mutation analysis of the GBA gene in Spanish patients together with the clinical findings. We conducted a systematic analysis in 53 unrelated GD patients. The GBA gene was initially scanned for nine previously described mutations by ASO hybridization or restriction analysis after PCR amplification. The remaining unidentified alleles were screened by nonisotopic PCR-SSCP analysis and sequenced. This approach allowed the identification of 101 of 106 GD alleles (95.3%) involving 24 different mutations, 11 of which are described for the first time: G113E (455G-->A), T134P (517A-->C), G389E (1283G-->A), P391L (1289C-->T), N392I (1292A-->T), Y412H (1351T-->G), W(-4)X (108G-->A), Q169X (662C-->T), R257X (886C-->T), 500insT, and IVS5+1G-->T. Most mutations are present in one or few GD chromosomes. However, two mutations, N370S (1226A-->G) and L444P (1448T-->C), are very frequent and account for 66.1% of the total number of alleles. Linkage disequilibrium was detected between these two mutations and an intragenic polymorphism, indicating that expansion of founder alleles occurred in both cases. Analysis of several microsatellite markers close to the GBA gene allowed us to establish the putative haplotype of the ancestral N370S chromosome.     

Evolution of precipitates in lead-implanted aluminum: A backscattering and channeling study

BACKGROUND: Thirty-six mutations that cause Gaucher disease, the most common glycolipid storage disorder, are known. Although both alleles of most patients with the disease contain one of these mutations, in a few patients one or both disease-producing alleles have remained unidentified. Identification of mutations in these patients is useful for genetic counseling. MATERIALS AND METHODS: The DNA from 23 Gaucher disease patients in whom at least one glucocerebrosidase allele did not contain any of the 36 previously described mutations has been examined by single strand conformation polymorphism (SSCP) analysis, followed by sequencing of regions in which abnormalities were detected. RESULTS: Eight previously undescribed mutations were detected. In exon 3, a deletion of a cytosine at cDNA nt 203 was found. In exon 6, three missense mutations were identified: a C-->A transversion at cDNA nt 644 (Ala176-->Asp), a C-->A transversion at cDNA nt 661 that resulted in a (Pro182-->Thr), and a G-->A transition at cDNA nt 721 (Gly202-->Arg). Two missense mutations were found in exon 7: a G-->A transition at cDNA nt 887 (Arg257-->Gln) and a C-->T at cDNA nt 970 (Arg285-->Cys). Two missense mutations were found in exon 9: a T-->G at cDNA nt 1249 (Trp378-->Gly) and a G-->A at cDNA nt 1255 (Asp380-->Asn). In addition to these disease-producing mutations, a silent C-->G transversion at cDNA nt 1431, occurring in a gene that already contained the 1226G mutation, was found in one family. CONCLUSIONS: The mutations described here and previously known can be classified as mild, severe, or lethal, on the basis of their effect on enzyme production and on clinical phenotype, and as polymorphic or sporadic, on the basis of the haplotype in which they are found. Rare mutations such as the new ones described here are sporadic in nature.     

ThioTEPA pharmacokinetics during intravesical chemotherapy: the influence of dose and volume of instillate on systemic uptake and dose rate to the tumour

Hereditary tyrosinaemia type I (HTI), an autosomal recessive inborn error of metabolism, is caused by a deficiency of the enzyme fumarylacetoacetate hydrolase. The highest incidence of HTI is observed in the Saguenay-Lac-St-Jean region (SLSJ) (Québec, Canada), where 1 out of 22 individuals is thought to be a carrier. A splice mutation (IVS12 + 5G-->A) has recently been identified in this particular region. Here, we have determined the frequency of this mutation in a population of obligate carriers from the SLSJ region by allele-specific oligonucleotide hybridization and a method using a restriction enzyme digestion. Over 95 per cent of the HTI carriers were found to have the IVS12 + 5G-->A splice mutation. Screening for this mutation based on the two methods reported here is thus a reliable and rapid way of detecting carriers of hereditary tyrosinaemia type I in that region at high risk.     

Hypolactasia and metabolic changes in post-menopausal women

The polymorphic cytochrome P450 CYP2D6 is involved in the metabolism of various drugs of wide therapeutic use and is a presumed susceptibility factor for certain environmentally-induced diseases. Our aim was to define the mutations and alleles of the CYP2D6 gene and to evaluate their frequencies in the European population. Using polymerase chain reaction-single strand conformation polymorphism analysis, 672 unrelated subjects were screened for mutations in the 9 exons of the gene and their exon-intron boundaries. A total of 48 point mutations were identified, of which 29 were novel. Mutations 1749 G-->C, 2938 C-->T and 4268 G-->C represented 52.6%, 34.3% and 52.9% of the mutations in the total population, respectively. Of the eight detrimental mutations detected, the 1934 G-->A, the 1795 Tdel and the 2637 Adel accounted for 65.8%, 6.2% and 4.8% respectively, within the poor metabolizer subgroup. Fifty-three different alleles were characterized from the mutation pattern and by allele-specific sequencing. They are derived from three major alleles, namely the wild-type CYP2D6*1A, the functional CYP2D6*2 and the null CYP2D6*4A. Five allelic variants (CYP2D6*1A, *2, *2B, *4A and *5) account for about 87% of all alleles, while the remaining alleles occur with a frequency of 0.1%-2.7%. These data provide a solid basis for future epidemiological, clinical as well as interethnic studies of the CYP2D6 polymorphism and highlight that the described single strand conformation polymorphism method can be successfully used in designing such studies.     

Response to ICRF-159 in cell lines resistant to cleavable complex-forming topoisomerase II inhibitors

Gaucher disease is the most common lysosomal storage disease with a high prevalence in the Ashkenazi Jewish population but it is also present in other populations. The presence of eight mutations (1226G, 1448C, IVS2+1. 84GG, 1504T, 1604T, 1342C and 1297T) and the complete deletion of the beta-glucocerebrosidase gene was investigated in 25 unrelated non-Jewish patients with Gaucher's disease in Germany. In the Jewish population, three of these mutations account for more than 90% of all mutated alleles. In addition, relatives of two patients were included in our study. Restriction fragment length polymorphism analysis and sequencing of PCR products obtained from DNA of peripheral blood leukocytes was performed for mutation analysis. Gene deletion was detected by comparison of radioactively labelled PCR fragments of both the functional beta-glucocerebrosidase gene and the pseudogene. Among the unrelated patients, 50 alleles were investigated and the mutations identified in 35 alleles (70%), whereas 15 alleles (30%) remained unidentified. The most prevalent mutation in our group of patients was the 1226G (370Asn-->Ser) mutation, accounting for 18 alleles (36%), followed by the 1448C (444Lcu-->Pro) mutation, that was found in 12 alleles (24%). A complete gene deletion was present in two alleles (4%). The IVS1+2 (splicing mutation), the 1504T (463Arg-->Cys) as well as the 1342C (409Asp-->His) mutations were each present in one allele (2%). None of the alleles carried the 84GG (frame-shift), 1604A (496Arg-->His) or the 1297T (394Val-->Leu) mutation. This distribution is different from the Ashkenazi Jewish population but is similar to other Caucasian groups like the Spanish and Portuguese populations. Our results confirm the variability of mutation patterns in Gaucher patients of different ethnic origin. All patients were divided into nine groups according to their genotype and their clinical status was related to the individual genotype. Genotype/phenotype characteristics of the 1226G, 1448C, and 1342C mutations of previous studies were confirmed by our results.     

High incidence of the CD8/9 (+G) beta 0-thalassemia mutation in Spain

BACKGROUND AND OBJECTIVE: In Spain, as in other Mediterranean regions the most common beta-thalassemia mutations are due to point mutations in gene regions that are critical for production of mRNA, such as [IVS-I-nt1 (G-->A), IVS-I-nt6 (T-->C), IVS-I-nt110 (G-->A)] which interrupt normal RNA processing or nonsense mutations [CD39 (C-->T)] which interrupt the translation of mRNA. The frameshift mutation CD8/9 (+G) is a very common allele in Asian Indians but is rare in the Mediterranean regions in which isolated alleles with this mutation have been found in Israel, Greece, Portugal and Turkey. DESIGN AND METHODS: We performed a molecular analysis of 175 chromosomes corresponding to 233 beta-thalassemia patients (221 heterozygous, 10 homozygous and 2 compound heterozygous) who belong to 169 Spanish families. The study of beta-thalassemia was made by PCR-ARMS, the alpha genes by Southern blot, the phenotype of Hb Lepore by enzymatic amplification and the presence of -158 gamma G C-->T mutation by PCR and digestion with the restriction enzyme XmnL. RESULTS: Twenty of these 233 patients showed the beta-thalassemia mutation CD8/9 (+G) (17 were heterozygous, 2 homozygous and in one patient the mutation was associated with a structural variant Hb Lepore Boston). INTERPRETATION AND CONCLUSIONS: These data reveal the heterogeneity of beta-thalassemia in Spain and the relatively high frequency (8.6%) of the frameshift mutation CD8/9 (+G). It is surprising that homozygotes for beta zero-thalassemia due to this mutation with very high Hb F values (around 90%) present a phenotype of intermediate thalassemia.     

W474C amino acid substitution affects early processing of the alpha-subunit of beta-hexosaminidase A and is associated with subacute G(M2) gangliosidosis

Mutations in the HEXA gene, encoding the alpha-subunit of beta-hexosaminidase A (Hex A), that abolish Hex A enzyme activity cause Tay-Sachs disease (TSD), the fatal infantile form of G(M2) gangliosidosis, Type 1. Less severe, subacute (juvenile-onset) and chronic (adult-onset) variants are characterized by a broad spectrum of clinical manifestations and are associated with residual levels of Hex A enzyme activity. We identified a 1422 G-->C (amino acid W474C) substitution in the first position of exon 13 of HEXA of a non-Jewish proband who manifested a subacute variant of G(M2) gangliosidosis. On the second maternally inherited allele, we identified the common infantile disease-causing 4-bp insertion, +TATC 1278, in exon 11. Pulse-chase analysis using proband fibroblasts revealed that the W474C-containing alpha-subunit precursor was normally synthesized, but not phosphorylated or secreted, and the mature lysosomal alpha-subunit was not detected. When the W474C-containing alpha-subunit was transiently co-expressed with the beta-subunit to produce Hex A (alphabeta) in COS-7 cells, the mature alpha-subunit was present, but its level was much lower than that from normal alpha-subunit transfections, although higher than in those cells transfected with an alpha-subunit associated with infantile TSD. Furthermore, the precursor level of the W474C alpha-subunit was found to accumulate in comparison to the normal alpha-subunit precursor levels. We conclude that the 1422 G-->C mutation is the cause of Hex A enzyme deficiency in the proband. The resulting W474C substitution clearly interferes with alpha-subunit processing, but because the base substitution falls at the first position of exon 13, aberrant splicing may also contribute to Hex A deficiency in this proband.     

Pseudodeficiency of arylsulphatase A: strategy for clarification of genotype in families of subjects with low ASA activity and neurological symptoms

A benign deficiency (pseudodeficiency) of the lysosomal enzyme arylsulphatase A (ASA) (EC 3.1.6.8) towards synthetic substrates complicates the diagnosis of metachromatic leukodystrophy (MLD). The pseudodeficiency is due to a single base substitution in the 3'-untranslated region of the ASA gene (1524+95 A-->G) and it has been reported that this mutation (PD2) always occurs on a chromosome carrying a second mutation in the ASA gene (PD1), which abolishes an N-glycosylation site (N350S). Analysis of the two PD mutations in the ASA gene separately was carried out in a large group of subjects with neurological symptoms and low ASA activity, including close relatives and MLD patients. The relationship between ASA enzyme activity and the different genotypes identified is presented. Evidence for the existence of an allele containing the PD2 mutation alone is presented. A strategy for cases with low ASA activity and neurological symptoms in families carrying a PD allele or both PD and MLD alleles is proposed.     

The arylamine N-acetyltransferase (NAT2) polymorphism and the risk of adverse reactions to co-trimoxazole in children

OBJECTIVE: The evaluation of the importance of the genetically determined acetylation defect for the development of adverse reactions to co-trimoxazole in children. METHODS: The study comprised 48 children aged 3 months to 3 years, who were being treated for interstitial pneumonia with co-trimoxazole. During the treatment, daily clinical examinations and biochemical tests to monitor the functions in various organs enabled us to detect adverse reactions to the drug. The therapy was continued or discontinued according to the results of these examinations. In all children we identified the genotype coding for N-acetyltransferase (NAT2). For this purpose, DNA was isolated from peripheral blood. Polymerase chain reaction (PCR) was then carried out, followed by restriction mapping with the KpnI, Ddel, TaqI, and BamHI endonucleases in order to identify the four mutations at the NAT2 gene locus: 481C-->T; 803A-->G; 590G-->A and 857G-->A, respectively. RESULTS: In 29 children (60%) various adverse effects occurred and in 19 children (40%) no adverse reactions to treatment occurred. We found statistically significant differences in the occurrence of the identified wt alleles, and alleles with 590A and 857A mutations between the two groups of children studied. In the group with adverse effects, 87% of children had genotype coding for slow acetylation and only 13% had genotypes containing the wt allele. In the group without adverse effects the results were reversed: 89% had genotypes with the wt allele, and only 2 children (10%) were found to have the homozygotic mutation (slow acetylation). CONCLUSION: The results show that the occurrence of adverse effects from co-trimoxazole is closely connected with the genotype coding for slow acetylation.     

The usefulness of single-strand DNA conformation polymorphism analysis to detect mutations in protein C deficiency

The standard approach for the molecular genetic analysis of protein C deficiency, polymerase chain reaction (PCR) amplification followed by direct sequencing, although very accurate, is time-consuming. The aim of this study is to investigate the usefulness of a simplified, time-saving screening method for the detection of protein C mutations consisting of the combination of multiplex PCR amplifications using the same primers that were designed for sequencing, followed by single-strand DNA conformation polymorphism (SSCP) electrophoresis analysis performed with one set of conditions. The study was designed in two phases. First, we tested six known point mutations located in different exons of the protein C gene by SSCP. Second, we prospectively studied nine patients with protein C deficiency type I using SSCP as the first screening technique. All the exons were amplified with a common PCR protocol, either as single fragments or as multiplex combinations of several of them. In the retrospective study, three out of the six point mutations were visible as a band shift: 40 T-->G (exon 2), 1432 C-->T (exon 3) and 7253 C-->T (exon 8). In the prospective analysis SSCP detected three different mutations. These mutations were: 6128 T-->C (exon 7), 6216 C-->T (exon 7) and in two probands 8631 C-->T (exon 9). In the five remaining patients we identified only two different mutations by direct sequencing: 6246 G-->A (exon 7) in two patients and 8589 G-->A (exon 9) in four patients. In summary, the results from both studies show that only 60% of all mutations can be detected using this simplified method. It also suggests that a multiple set of conditions, smaller PCR fragments, or both, should be used in order to achieve a sensitivity comparable to sequencing.     

Mutations in haemophilia A

In the present study DNA from 281 unrelated haemophilia A patients including 15 inhibitor patients has been analysed by Southern blotting technique. Using various restriction enzymes, cloned factor VIII cDNA probes and genomic fragments we have identified 14 mutations. Six of the mutations are novel partial factor VIII gene deletions. One deletion affects exon 1, two deletions concern exon 6, another deletion, of which breakpoints are sequenced, takes part of exon 16 and two deletions affect exon 26. Besides the deletions, eight point mutations have been found at the TaqI restriction sites of exons 18, 24 and 26. Five C-->T mutations resulted in nonsense mutations, one in exon 18, one in exon 26 and three in exon 24. Two G-->A mutations caused a missense mutation in exon 24 leading to an arginine/glutamine exchange. Although two patients showed this mutation, their clinical phenotypes were different, possibly due to an additional unidentified sequence polymorphism. A G-->T mutation in exon 26 substituted the arginine with leucine. All deletions and seven of the point mutations are associated with severe disease with a detectable inhibitor in the patient with the TaqI-point mutation in exon 18. One of the G-->A mutations is associated with mild haemophilia but the patient also has developed an inhibitor. Amongst these mutations the origin of the mutation could be determined in four kindred, one of which showed maternal mosaicism.     

Glucosephosphate isomerase (GPI) deficiency mutations associated with hereditary nonspherocytic hemolytic anemia (HNSHA)

Five unrelated patients with hereditary glucosephosphate isomerase (GPI) deficiency resulting in nonspherocytic hemolytic anemia were studied. Three new mutations were found in the coding region of the GPI gene: two patients were heterozygous for 223 A-->G (R75G) and 898 G-->C(R300P), respectively and one was homozygous for 1415G-->A(R472H). Surprisingly, 2 previously reported mutations, 286 C-->T and 1039 C-->T, were found in 2 and 3 patients respectively. Until now only 4 of 18 GPI mutations had been found more than once in unrelated patients and these 4 in only 2 patients each. Eleven of the 20 known point mutations have occurred at CpG "hot spots" and the 286 C-->T and 1039 C-->T are among these. The 489 G/A polymorphism in the GPI coding region was used to demonstrate unequivocally that the 1039 C-->T mutation occurred in both haplotypes and therefore probably originated more than once. Because no common GPI mutation has been found we suggest that heterozygosity for GPI confers little if any selective advantage.     

Six previously undescribed pyruvate kinase mutations causing enzyme deficiency

Erythrocyte pyruvate kinase deficiency is the most common cause of hereditary nonspherocytic hemolytic anemia. We present 6 previously undescribed mutations of the PKLR gene associated with enzyme deficiency located at cDNA nt 476 G-->T (159Gly-->Val), 884 C-->T (295Ala-->Val), 943 G-->A (315Glu-->Lys), 1022 G-->A (341Gly-->Asp), 1511 G-->T (504Arg-->Leu), and 1528 C-->T (510Arg-->Ter). Two of these mutations are near the substrate binding site: the 315Glu-->Lys (943A) mutation may be involved in Mg2+ binding and 159Gly-->Val (476T) mutation has a possible effect on ADP binding. Four of six mutations produce deduced changes in the shape of the molecule. Two of these mutations, 504Arg-->Leu (1511T) and 510Arg-->Ter (1528T), are located at the interface of domains A and C. One of them (510Arg-->Ter) is a deletion of the C-terminal residues affecting the integrity of the protein. The 504Arg-->Leu mutation eliminates a stabilizing interaction between domains A and C. Changes in amino acid 341(nt 1022) from Gly to Asp cause local perturbations. The mutation 295Ala-->Val (884T) might affect the way pyruvate kinase interacts with other molecules. We review previously described mutations and conclude that there is not yet sufficient data to allow us to draw conclusions regarding genotype/phenotype relationship.     

Joint load considerations in total knee replacement

We have characterized the mutations in 1050 carriers of the beta-thalassemia gene and analyzed their regional distribution in India. The majority of beta-thalassemia carriers were migrants from Pakistan and their pattern of mutations differed from the rest. The frequency of the 619-bp deletion was 33.3% among the migrants from Pakistan, 8-17% in the northern states, and less than 5% in the other states. Among non-migrant subjects, the predominant mutation was IVS-I-5 (G-->C), varying from 85% in the southern states and 66-70% in the eastern states to 47-60% in the northern states. The mutation IVS-I-1 (G-->T) was observed at high frequency among the migrants from Pakistan (26.2%), but with very low/zero frequency in the other states. Mutations at codons 8/9 (+G) and codons 41/42 (-CTTT) were distributed in all regions of India with a frequency varying from 3% to 15%. Only eight of 12 published rare mutations were observed in subjects from different parts of India. Mutations of codon 5 (-CT) and codons 47/48 (+ATCT) were found exclusively in migrants from Pakistan, and mutation -88 (C-->T) was detected only in subjects from Punjab, Haryana, and Uttar Pradesh. Using the amplification refractory mutation system technique, mutations were successfully identified in 98.2% of subjects. Overall, 91.8% of the subjects had one of the five commonest mutations [IVS-I-5 (G-->C), 34.1%; 619-bp deletion, 21.0%; IVS-I-1 (G-->T) 15.8%; codons 8/9 (+G), 12.1%, and codons 41/42 (-CTTT), 8.7%], 5.9% of the subjects had a less common mutation, while 1.8% of the carriers remained uncharacterized. The application of this knowledge has helped to successfully establish a program of genetic counselling and prenatal diagnosis of beta-thalassemia in order to reduce the burden of this disease in India.     

Cytologic diagnosis and subtyping of rhabdomyosarcoma

Ornithine transcarbamylase (OTC) deficiency is an X-linked disorder of urea synthesis. Among females who carry a mutant OTC allele, there is a wide range of phenotypic variability, ranging from apparent normality to a severe onset and the resulting profound neurologic impairment observed in hemizygous males. This study was designed to define the phenotypic variability of OTC deficiency in ostensibly healthy carrier females and to compare them to noncarrier females from their own and other families. One hundred seventy-five women from 89 families participated in this study. Each completed a mailed questionnaire, allopurinol testing, and fasting plasma amino acid determinations. OTC carrier status was determined by pedigree analysis, allopurinol test results, and/or DNA mutation analysis. Overall, 79 women were identified as carriers of a mutant OTC allele (60 proband mothers, 19 relatives), and 96 women (32 proband mothers, 64 female relatives) were determined to be noncarriers. Comparison of biochemical phenotypes indicated that carriers and noncarriers do not differ in daily urinary creatinine excretion, but that carriers excrete significantly less urea nitrogen and total nitrogen, reflecting their significantly lower historically reported daily protein intake. Carriers had significantly higher levels of fasting plasma glutamine and alanine, and significantly lower levels of citrulline and arginine compared with noncarriers. Carriers and noncarriers reported similar demographic characteristics, anthropometric measurements, level of education, and medical and pregnancy histories. There was no indication of increased incidence of migraine headaches among carriers. Thus, we found no evidence that asymptomatic adult female OTC heterozygotes are at increased risk for previously unidentified health problems apart from an unknown risk for hyperammonemic encephalopathy as occurred in 3 of the carriers in this study. Because these episodes appear to be related to physiologic stress (fracture, parturition), it would seem medically prudent for carriers to be aware of this risk.     

Cloning and sequencing of the URA3 gene of Kluyveromyces marxianus CBS 6556

More than 250 mutations have been detected in the cystic fibrosis (CF) transmembrane regulator (CFTR) gene, most of which are single point mutations or small deletions or insertions of a few nucleotides. Here we report the first large deletion identified in the CFTR gene, which involves 50 kb in two stretches of DNA: one of 10 kb from exon 4 to exon 7, and another of 40 kb, spanning exons 11 to 18. The deletion has been detected via uniparental inheritance of CFTR microsatellite alleles (IVS17BTA and IVS17BCA) in 3 independent CF families. Clinical status of the 3 CF patients, of which two have the delta F508 mutation as the other CF allele, suggests that this mutation is responsible for a severe clinical phenotype, indistinguishable from homozygous delta F508 patients. The deletion detected here suggests that other large, but less complex molecular defects could also exist in the CFTR gene.     

Determination of serum pancreatic polypeptide and its clinical significance in patients with end state renal failure

A screening program for the detection of Tay-Sachs disease (TSD) carriers in the ultra Orthodox community of Ashkenazi Jews has operated in Israel since 1986. The purpose of this program is the prevention of marriages of 2 heterozygotes. The screened individuals are mostly couples in the engagement process or students in religious high schools. Two mandatory requirements guide this program. First, anonymity of the tested individuals who are identified only by code numbers; second completion of the test results of couples in the engagement process within a few days. The screening program is performed by the determination of hexosaminidase A (Hex A) activity in serum which is repeated in serum and leukocyte extracts in couples where both partners were found in the heterozygote range in the initial tests. The minimal carrier frequency was estimated to be 1:26 or higher, which is higher then in the general Jewish Ashkenazi population. This higher carrier frequency apparently stems from the fact that most members of this community originate from central Europe where the TSD carrier frequency was previously reported to be the highest in the Ashkenazi population. Since the beginning of the screening program no TSD child has been born to newlywed couples of this community in Israel.     

Bias in somatic hypermutation of human VH genes

Translationally silent mutations, which are not antigen selected, of human VH6 Ig gene rearrangements isolated from human spleen were analyzed for bias to gain insight into intrinsic features of the mutation process. Sixty-three clones representing 38 VH6DJ rearrangements had an overall mutation frequency of 4.5%, a replacement/silent (R/S) mutation ratio of 2.1 and 167 unique silent mutations. The silent mutations showed bias in: (i) targeting to CDR1 and CDR2, (ii) an increased frequency of mutations of A compared to T nucleotide bases on the coding strand, and (iii) an increased frequency of transitions versus transversions. Bias of C-->G over C-->A, of G-->C over G-->T and of A-->C over A-->T transversions was also present. Hot spots of mutation were observed, some which corresponded to potential sites of stem-loop formation. The results suggest that the somatic mutation process in man may be targeted to the complementarity determining region for some V genes, exhibits specific base substitutions favoring transitions and specific types of transversions, and may be occurring on only one DNA strand.     

G-->A substitution at position -75 of the apolipoprotein A-I gene promoter. Evidence against a direct effect on HDL cholesterol levels

The present study sought to resolve the contradictory evidence as to whether the G-->A substitution at position -75 of the apoA-I gene promoter raises HDL cholesterol (HDL-C) levels by examining the effect of this polymorphism in French Canadians, a relatively genetically homogeneous population. Among 308 women, carriers of the A allele displayed 12% and 10% higher mean plasma HDL-C and apoA-I concentrations, respectively, than did noncarriers. Among 345 men, no effect of the A allele was noted. The frequency distribution of HDL-C levels in women carrying the A but not the G allele appeared bimodal, with one peak corresponding to the mean of the noncarriers and a second to higher HDL-C. Thus it appears that only a subset of A alleles confers high HDL-C levels. This hypothesis was supported by data from four kindreds within which some but not all A alleles segregated with hyperalphalipoproteinemia. The data suggest that the A substitution in the apoA-I gene promoter does not directly confer high HDL-C levels but may be in linkage disequilibrium with other sequence polymorphism(s) at this locus in a subset of alleles that raise HDL-C levels.