Beta-2-glycoprotein specificity of human anti-phospholipid antibody resides on the light chain: a novel mechanism for acquisition of cross-reactivity by an autoantibody

We have recently shown that the anti-cardiolipin activity of human anti-phospholipid antibody UK4 (lambda) resides on its heavy chain. We now show that UK4 possesses strong reactivity to the plasma-protein beta2-Glycoprotein I (beta2-GPI) also. Utilizing chain shuffling experiments involving an unrelated anti-p185 antibody 4D5 (kappa) with no reactivity to beta2-GPI, we now demonstrate that both the constructs possessing the auto-antibody-derived light chain exhibited significant binding to beta2-GPI. However, the construct possessing UK4 heavy chain in association with 4D5 light chain, exhibited no anti-beta2-GPI activity. Furthermore, there was a low increase (approximately 10%) in the binding of UK4 to cardiolipin in the presence of beta2-GPI. The results demonstrate that anti-beta2-GPI activity resides on UK4 light chain and, importantly, this activity could be transferred to a novel antibody construct via the light chain alone. Computer-generated models of the three-dimensional structures of UK4 and its hybrids, suggest predominant interaction of UK4 light chain with domain IV of beta2-GPI. Molecular docking experiments highlight a number of potential sites on beta2-GPI for interaction of UK4 and indicate as to how beta2-GPI recognition may occur primarily via the autoantibody light chain. The study provides first demonstration of the occurrence of anti-phospholipid and anti-beta2-GPI activities separately on heavy and light chains of an autoantibody. The possible mechanisms that such antibodies may employ to recognise their antigens, are discussed.     

A comprehensive haplotype analysis of CYP19 and breast cancer risk: the Multiethnic Cohort

The CYP19 gene encodes for aromatase (P450arom), a key steroidogenic enzyme that catalyzes the final step of estrogen biosynthesis. Apart from rare mutations in CYP19 which result in severe phenotypes associated with estrogen insufficiency, little is known about whether common variation in CYP19 is associated with risk of hormone-related diseases. In this study, we employed a haplotype-based approach to search for common disease-associated variants in this candidate breast cancer susceptibility gene among African-American, Hawaiian, Japanese, Latina and White women in the Multiethnic Cohort Study (MEC). We utilized 74 densely spaced single-nucleotide polymorphisms (SNPs) (one every approximately 2.6 kb) spanning 189.4 kb of the CYP19 locus to characterize linkage disequilibrium (LD) and haplotype patterns among 69-70 individuals from each ethnic population. We detected four regions of strong LD (blocks 1-4) that were quite closely conserved across populations. Within each block there was a limited diversity of common haplotypes (5 to 10 with a frequency >/=5%) and most haplotypes were observed to be shared across populations. Twenty-five haplotype-tagging SNPs (htSNPs) were selected to predict the common haplotypes with high probability (average Rh2=0.92) and genotyped in a breast cancer case-control study in the MEC (cases, n=1355; controls, n=2580). We first performed global tests for differences in risk according to the common haplotypes and observed significant haplotype-effects in block 2 [P=0.01; haplotypes 2b (OR=1.23; 95% CI, 1.07-1.40), 2d (OR=1.28; 95% CI, 1.01-1.62)]. We also found a common long-range haplotype comprised of block-specific haplotypes 2b and 3c to be associated with increased risk of breast cancer (haplotype 2b-3c: OR=1.31; 95% CI, 1.11-1.54). Our findings suggest the hypothesis that women with the long-range CYP19 haplotype 2b-3c may be carriers of a predisposing breast cancer susceptibility allele.     

Prenatal detection of D trisomy

The second instance of a prenatally diagnosed fetus of D trisomy is reported in a 45-year-old woman. The fetus had bilateral hare lip and cleft palate, arrhinencephaly, and numerous other malformations.     

Mapping of B-Cell Epitopes in a Trypanosoma cruzi Immunodominant Antigen Expressed in Natural Infections

Tc40 is an immunodominant antigen present in natural Trypanosoma cruzi infections. This immunogen was thoroughly mapped by using overlapping amino acid sequences identified by gene cloning and chemical peptide synthesis. To map continuous epitopes of the Tc40 antigen, an epitope expression library was constructed and screened with sera from human chagasic patients. A major, linear B-cell epitope spanning residues 403 to 426 (PAKAAAPPAA) was identified in the central domain of Tc40. A synthetic peptide spanning this region reacted strongly with 89.8% of the serum samples from T. cruzi-infected individuals. This indicates that the main antigenic site is defined by the linear sequence of the peptide rather than a conformation-dependent structure. The major B-cell epitope of Tc40 shares a high degree of sequence identity with T. cruzi ribosomal and RNA binding proteins, suggesting the existence of cross-reactivity among these molecules.     

Hearing impairment as an early sign of alpha‐mannosidosis in children with a mild phenotype: Report of seven new cases

Alpha‐mannosidosis (AM) is a very rare (prevalence: 1/500000 births) autosomal recessive lysosomal storage disorder. It is characterized by multi‐systemic involvement associated with progressive intellectual disability, hearing loss, skeletal anomalies, and coarse facial features. The spectrum is wide, from very severe and lethal to a milder phenotype that usually progresses slowly. AM is caused by a deficiency of lysosomal alpha‐mannosidase. A diagnosis can be established by measuring the activity of lysosomal alpha‐mannosidase in leucocytes and screening for abnormal urinary excretion of mannose‐rich oligosaccharides. Genetic confirmation is obtained with the identification of MAN2B1 mutations. Enzyme replacement therapy (LAMZEDE^R) was approved for use in Europe in August 2018. Here, we describe seven individuals from four families, diagnosed at 3–23 years of age, and who were referred to a clinical geneticist for etiologic exploration of syndromic hearing loss, associated with moderate learning disabilities. Exome sequencing had been used to establish the molecular diagnosis in five cases, including a two‐sibling pair. In the remaining two patients, the diagnosis was obtained with screening of urinary oligosaccharides excretion and the association of deafness and hypotonia. These observations emphasize that the clinical diagnosis of AM can be challenging, and that it is likely an underdiagnosed rare cause of syndromic hearing loss. Exome sequencing can contribute significantly to the early diagnosis of these nonspecific mild phenotypes, with advantages for treatment and management.     

Three highly polymorphic microsatellites at the human myelin oligodendrocyte glycoprotein locus, 100 kb telomeric to HLA-F : Characterization and relation to HLA haplotypes

The MOG locus, located on chromosomal bands 6p21.3-p22 and mapped about 100 kb telomeric to HLA-F, was isolated from cosmid ICRFcl09A2434 and shown to contain three microsatellites. These CA-repeat polymorphic markers were characterized in a sample of 173 healthy unrelated individuals and 84 DNAs from the HLA Workshop reference panel, by a method combining fluorescence labeling of PCR products and use of an automated DNA sequencer. For the three markers, frequencies of heterozygotes are well predicted from allele frequencies by the Hardy—Weinberg rule, which suggests that problems of allele nonamplification are unlikely. Typing of cell lines homozygous in the HLA region allowed unambiguous definition of 81 HLA-MOG haplotypes and showed that several HLA ancestral haplotypes extended to the MOG region. The high degree of polymorphism (59%, 51%, and 81% at the three loci, respectively, and 87% at the haplotype level) makes these new markers informative for association or linkage studies with diseases such as hemochromatosis or multiple sclerosis, and for studies aimed at precisely delineating the site of crossover in chromosomes in which recombination occurred in the distal part of the HLA class I region.