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Joann M Moulds

Publications and source records attributed to Joann M Moulds.

8 recordsLinked to original sources
PubMed2005

Genetic mechanisms of Rhesus box variation.

BACKGROUND: The RHD gene is flanked by two highly homologous DNA segments of approximately 9000 bp, the upstream and downstream Rhesus boxes. In haplotypes with an RHD deletion, the fusion of the two Rhesus boxes generates the single-hybrid Rhesus box, the detection of which has been applied for RHD zygosity determination. Aberrant Rhesus boxes can confound this application and appear to be frequent among African individuals. STUDY DESIGN AND METHODS: A total of 5850 bp of the upstream and of the downstream Rhesus boxes were sequenced in 18 samples that were representative for all four D clusters and of the hybrid Rhesus boxes in four samples that were mistyped in assays for the hybrid Rhesus box. RESULTS: The known differences between upstream and downstream Rhesus boxes were in part restricted to subsets of RHD alleles. Forty-six additional polymorphisms were detected and caused by single-nucleotide substitutions, short insertions, or deletions. Gene conversions were found in the upstream Rhesus boxes of RHDpsi, DAU-1, and DAU-3 and in the downstream Rhesus boxes of Ccdes, weak D type 4.1, type 4.2 (DAR), and DAU-0. Recombinations between haplotypes were likely in several alleles like DIII type 4. Four nonstandard hybrid Rhesus boxes were suggestive of multiple RHD deletion events. CONCLUSION: There is considerable variation of Rhesus box sequences associated with distinct RHD alleles. RHD zygosity diagnostics in African persons is best based on quantitative polymerase chain reaction or amplification of the full-length hybrid Rhesus box. Because aberrant Rhesus boxes were observed among European persons, use of more than one method for hybrid Rhesus box detection may even be advisable in European persons.

Africa↗
PubMed2003

A human complement receptor 1 polymorphism that reduces Plasmodium falciparum rosetting confers protection against severe malaria.

Parasitized red blood cells (RBCs) from children suffering from severe malaria often adhere to complement receptor 1 (CR1) on uninfected RBCs to form clumps of cells known as "rosettes." Despite a well documented association between rosetting and severe malaria, it is controversial whether rosetting is a cause or a correlate of parasite virulence. CR1-deficient RBC show greatly reduced rosetting; therefore, we hypothesized that, if rosetting is a direct cause of malaria pathology, CR1-deficient individuals should be protected against severe disease. In this study, we show that RBC CR1 deficiency occurs in up to 80% of healthy individuals from the malaria-endemic regions of Papua New Guinea. This RBC CR1 deficiency is associated with polymorphisms in the CR1 gene and, unexpectedly, with alpha-thalassemia, a common genetic disorder in Melanesian populations. Analysis of a case-control study demonstrated that the CR1 polymorphisms and alpha-thalassemia independently confer protection against severe malaria. We have therefore identified CR1 as a new malaria resistance gene and provided compelling evidence that rosetting is an important parasite virulence phenotype that should be a target for drug and vaccine development.

Adult↗
PubMed2003

RHD allele distribution in Africans of Mali.

BACKGROUND: Aberrant and non-functional RHD alleles are much more frequent in Africans than in Europeans. The DAU cluster of RHD alleles exemplifies that the alleles frequent in Africans have evaded recognition until recently. A comprehensive survey of RHD alleles in any African population was lacking. RESULTS: We surveyed the molecular structure and frequency of RHD alleles in Mali (West Africa) by evaluating 116 haplotypes. Only 69% could be attributed to standard RHD (55%) or the RHD deletion (14%). The aberrant RHD allele DAU-0 was predicted for 19%, RHDPsi for 7% and Ccdes for 4% of all haplotypes. DAU-3 and the new RHD allele RHD(L207F), dubbed DMA, were found in one haplotype each. A PCR-RFLP for the detection of the hybrid Rhesus box diagnostic for the RHD deletion in Europeans was false positive in 9 individuals, including all carriers of RHDPsi. Including two silent mutations and the RHD deletion, a total of 9 alleles could be differentiated. CONCLUSION: Besides standard RHD and the RHD deletion, DAU-0, RHDPsi and Ccdes are major alleles in Mali. Our survey proved that the most frequent alleles of West Africans have been recognized allowing to devise reliable genotyping and phenotyping strategies.

Alleles↗
PubMed2002

The molecular genetics of the human I locus and molecular background explain the partial association of the adult i phenotype with congenital cataracts.

The human i and I antigens are characterized as linear and branched repeats of N-acetyllactosamine, respectively. Conversion of the i to the I structure requires I-branching beta-1,6-N-acetylglucosaminyltransferase activity. It has been noted that the null phenotype of I, the adult i phenotype, is associated with congenital cataracts in Asians. Previously, the identification of molecular changes in the IGnT gene, associated with the adult i phenotype, has been reported. In the present study, we demonstrate that the human I locus expresses 3 IGnT forms, designated IGnTA, IGnTB, and IGnTC, which have different exon 1, but identical exons 2 and 3, coding regions. The molecular genetics proposed for the I locus offer a new perspective on the formation and expression of the I antigen in different cells and provide insight into the questions derived from investigation of the adult i phenotype. Molecular genetic analyses of the I loci of the 2 adult i groups, with and without congenital cataracts, were performed, and enzyme function assays and expression patterns for the 3 IGnT transcripts in reticulocytes and lens-epithelium cells were analyzed. The results suggest a molecular genetic mechanism that may explain the partial association of the adult i phenotype with congenital cataracts and indicate that a defect in the I locus may lead directly to the development of congenital cataracts. The results also suggest that the human blood group I gene should be reassigned to the IGnTC form, not the IGnTB form, as described previously.

Adult↗
PubMed2002

The molecular basis of complete complement C4A and C4B deficiencies in a systemic lupus erythematosus patient with homozygous C4A and C4B mutant genes.

The disease course of a complete C4-deficient patient in the U.S. was followed for 18 years. The patient experienced multiple episodes of infection, and he was diagnosed with systemic lupus erythematosus at age 9 years. The disease progressed to WHO class III mild lupus nephritis and to fatal CNS vasculitis at age 23 years. Immunochemical experiments showed that the patient and his sibling had complete absence of C4A and C4B proteins and were negative for the Rodgers and Chido blood group Ags. Segregation and definitive RFLP analyses demonstrated that the patient and his sibling inherited two identical haplotypes, HLA A2 B12 DR6, each of which carries a defective long C4A gene and a defective short C4B gene. PCR and DNA sequencing revealed that the mutant C4A contained a 2-bp insertion in exon 29 at the sequence for codon 1213. The identical mutation was absent in the mutant C4B. The C4B mutant gene was selectively amplified by long range PCR, and its 41 exons were completely sequenced. The C4B mutant had a novel single C nucleotide deletion at the sequence for codon 522 in exon 13, leading to frame-shift mutation and premature termination. Thus, a multiplex PCR is designed by which known mutations in C4A and C4B can be elucidated conveniently. Among the 28 individuals reported with complete C4 deficiency, 75-96% of the subjects (dependent on the inclusion criteria) were afflicted with autoimmune or immune complex disorders. Hence, complete C4 deficiency is one of the most penetrant genetic risk factors for human systemic lupus erythematosus.

Adult↗
PubMed2002

Human complement receptor type 1 (CR1) binds to a major malarial adhesin.

Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1), a major adhesin molecule expressed on Plasmodium-falciparum-infected erythrocytes, interacts with several receptors on endothelial cells and uninfected erythrocytes. This 'stickiness', known as rosetting, is a strategy used by the parasite to remain sequestered in the microvasculature to avoid destruction in the spleen and liver. Erythrocyte rosetting causes obstruction of the blood flow in microcapillaries. Recent data suggest a direct interaction between PfEMP1 and a functional site of complement receptor type 1 (CR1; CD35) on uninfected erythrocytes. Consistent with the hypothesis that CR1 is important in malaria pathogenesis is a 40-70-fold increase in the frequency of two CR1 blood-group antigens (at least one of which might rosette less efficiently) in malaria-exposed African populations. Furthermore, structural differences in erythrocyte CR1 between human and non-human primates are probably explained by the selective pressure of malaria.

Animals↗
PubMed2002

Understanding the Knops blood group and its role in malaria.

The antibodies that once were referred to as "HTLAs" have now help to define an entire blood group system with a well characterized genetic basis. Although not "clinically significant" in transfusion medicine, the Knops blood group has gained importance in the field of infectious disease. Its further role in protein (CR1) function and autoimmune diseases remains unknown but may provide interesting work for years to come.

Blood Group Antigens↗