Seidman, Jonathan G

Abstract Background and Aims Truncating variants in the TTN gene (TTNtv) are the most common genetic cause of dilated cardiomyopathy (DCM) but also occur as incidental findings in the general population. This study investigated factors associated with the clinical manifestation of TTNtv. Methods An international multicentre retrospective observational study was performed in families with TTNtv-related DCM. Shared frailty models were used to estimate associations of variant characteristics with lifetime risk of DCM, and logistic regression to estimate odds ratios (ORs) for individual-level clinical risk factor profiles (cardiac conditions, cardiovascular comorbidities, lifestyle) and DCM. Results A total of 3158 subjects in 1043 families with TTNtv-related DCM were studied. TTNtv-positive subjects were 21-fold more likely to develop DCM [OR, 21.21; 95% confidence interval (CI), 14.80–30.39]. Disease onset was earlier in males, but was similar for TTNtv of different types and locations. The presence of clinical risk factors was associated with earlier DCM onset (OR, 3.41; 95% CI, 2.06–5.64), with a prior history of atrial fibrillation having a two-fold increased odds of DCM (OR, 2.05; 95% CI, 1.27–3.32). The prevalence of clinical risk factors increased with age; however, the strength of the DCM association was greatest for young-onset (<30 years) disease (OR, 4.75; 95% CI, 2.35–9.60). Administration of beta-adrenergic receptor or renin-angiotensin system-blocking drugs prior to overt DCM was associated with 87% reduced odds of DCM (OR, .13; 95% CI, .08–.23). Conclusions Disease onset in TTNtv-associated familial DCM is dependent on individual patient context and is potentially modifiable by risk factor management and prophylactic therapeutic intervention.

Abstract A20.2J B lymphoma cells have been co-transfected with the A alpha b, A beta b or with the A alpha b, A beta bm12 and neomycin resistance genes. The transfected cell lines constitutively express the I-Ab or I-Abm12 class II molecules at a level comparable with that of the endogenous I-Ad antigen. The I-Ab antigens expressed on three independently transfected B cell clones (A20.Ab.1, A20.Ab.2, and A20.Ab.3) are serologically and functionally indistinguishable from the I-Ab molecules expressed by control H-2bxd B hybridoma cells (LB cells). These transfected cell lines were potent I region-restricted antigen-presenting cells to a large panel of antigen-specific, autoreactive and alloreactive T cell hybridomas, as well as normal T cell clones. There were not significant differences in the efficiency of antigen presentation by the Ia molecules encoded by the transfected, as compared with the endogenous, I-A genes. The expression of a functional I-Ab antigen on the surface of cells transfected with A beta bm12 and A alpha b genes is consistent with previous work that implicated the A beta-chain alone in the bm 12 mutation. Furthermore, because the transfected A20.Ab and A20.Abm12 cells display the serologic and functional properties of normal spleen cells from the wild-type and mutant mouse strains, respectively, it is clear that class II genes do not undergo unexpected and unpredictable alterations after transfection in this system. This system permits us to investigate the structural requirements for interactions between class II major histocompatibility complex antigens, a foreign antigen, and the T cell receptor by in vitro site-directed mutagenesis coupled with DNA-mediated gene transfer.

Abstract Several Ia-negative variants of a homozygous Iad-expressing antigen-presenting B lymphoma cell line, M12, have been obtained by repeated cycles of negative immunoselection after mutagenesis with ethylmethane sulfonate or gamma-irradiation. Two such Iad-negative cell lines, selected with a mixture of alpha I-Ad and alpha I-Ed monoclonal antibodies, failed to present antigen to all cloned Iad-restricted T cells tested, whereas the third cell line, selected with alpha I-Ad reagents only, stimulated I-Ed but not I-Ad-restricted T cells. The mutations in all three cell lines resulted in the absence of RNA specific for the A beta d gene. In addition, two-dimensional gel electrophoresis of immunoprecipitates from one of the I-Ed-negative cell lines demonstrated the presence of intracytoplasmic Ed polypeptides that exhibited significantly decreased amounts of oligosaccharide-induced heterogeneity. The introduction of class II A beta b and A alpha b genes by DNA-mediated transfection resulted in the serologic and functional expression of a class II I-Ab molecule but not the reexpression of the endogenous class II molecules; thus a transacting regulatory element is unlikely to be the target of the mutagenic event. The analysis of these and other Ia variant cell lines may prove useful in understanding the molecular mechanisms that control the expression of class II molecules in B cells.

Abstract A segment of the murine immune response-associated (Ia) antigen A beta chain mRNA has been cloned, and this cDNA clone has been used to examine the organization of the genes encoding these highly polymorphic cell surface proteins. To isolate this clone, pIA beta-1, we screened 5000 cDNA clones by a filter hybridization-selection assay using a rabbit heteroantiserum to identify the A beta chain produced in in vitro translation reactions. This clone corresponds to a segment of the mRNA encoding the beta chain of the murine I-A antigen. The 464 bp nucleotide sequence of the insert is consistent with a cDNA clone encoding the carboxyl end of the murine A beta chain. Comparison of this nucleotide sequence to a human Ia beta chain-derived cDNA clone suggests that the two clones could encode proteins that are about 90% homologous in this region. Southern blot analysis using pIA beta-1 as a probe to investigate the structure of the A beta chain gene in inbred strains of mice allows two conclusions. First, there is only one A beta chain gene homologous to this cDNA clone in each haploid mouse genome. Second, the restriction fragments encoding this gene are highly polymorphic. We postulate that the mechanism which generates polymorphic variation of the A beta chain may be involved in generating the restriction site polymorphism within or near the A beta chain gene.