Genetic counselling for hypertrophic cardiomyopathy: are we ready for it?

Hypertrophic cardiomyopathy (HCM) is a dominant genetic disorder of the myocardium associated with dysfunctional contractile proteins. The major risk of HCM is sudden cardiac death, which may occur even in asymptomatic carriers. Causes are highly heterogeneous. Over 140 different mutations in nine sarcomeric genes have been described to date. The majority of cases (80% or more) may eventually be traced to one of these genes. Although genetic counselling is suggested even if mutations are not known, molecular diagnosis implies new options such as carrier identification or - theoretically - preclinical risk stratification. A scheme according to which cardiologists and clinical and molecular geneticists could cooperate in counselling patients and managing HCM clinically is proposed.     

The polymerase chain reaction: an improved method for the analysis of nucleic acids

Summary The polymerase chain reaction (PCR) is a method for the selective amplification of DNA or RNA segments of up to 2 kilobasepairs (kb) or more in length. Synthetic oligonucleotides flanking sequences of interest are used in repeated cycles of enzymatic primer extension in opposite and overlapping directions. The essential steps in each cycle are thermal denaturation of double-stranded target molecules, primer annealing to both strands and enzymatic synthesis of DNA. The use of the heat-stable DNA polymerase from the archebacterium Thermus aquaticus (Taq polymerase) makes the reaction amenable to automation. Since both strands of a given DNA segment are used as templates, the number of target sequences increases exponentially. The reaction is simple, fast and extremely sensitive. The DNA or RNA content of a single cell is sufficient to detect a specific sequence. This method greatly facilitates the diagnosis of mutations or sequence polymorhisms of various types in human genetics, and the detection of pathogenic components and conditions in the context of clinical research and diagnostics; it is also useful in simplifying complex analytical or synthetic protocols in basic molecular biology. This article describes the principles of the reaction and discusses the applications in different areas of biomedical research.     

Monoclonal anti-mouse macrophage antibodies recognize the globular portions of C1q, a subcomponent of the first component of complement

One of seven monoclonal antibodies generated against mouse macrophages (M phi) was found to recognize isolated heterologous C1q. This antibody was shown to be cytotoxic and to react in a strain-independent way with mouse M phi derived from bone marrow cells as well as with M phi from the peritoneal cavity; it did not react, however, with mouse granulocytes, thymocytes, or T and B lymphocytes. The hemolytic activity of fluid phase C1q was inhibited to 50% at a 2 X 10(-4) dilution of hybridoma supernatant, whereas a 100-fold higher concentration was required to inhibit C1q bound to immune complexes ( EAC1q ) to the same extent. It was demonstrated that this antibody recognizes the isolated globular, Fc-binding portions of the C1q molecule and reacts with the A and B chains. Because M phi have been shown to synthesize C1q, the Fc-recognizing subcomponent of the first component of complement, evidence was provided that endogeneous C1q can serve as an Fc receptor on M phi during secretion. This fact was demonstrated by a dose-dependent inhibition of Fc-receptor activity for EIgG by the F(ab')2 fragment of this monoclonal antibody. These experiments further support the concept that C1q produced by M phi functions on the surface as an Fc-recognizing molecule before it is released and incorporated into the macromolecular complex of serum C1.     

Carbonic anhydrase subunits of the mitochondrial NADH dehydrogenase complex (complex I) in plants

The mitochondrial nicotinamide adenine dinucleotide, reduced (NADH) dehydrogenase complex (complex I) of plants has a molecular mass of about 1000 kDa and is composed of more than 40 distinct protein subunits. About three quarter of these subunits are homologous to complex I subunits of heterotrophic eukaryotes, whereas the remaining subunits are unique to plants. Among them are three to five structurally related proteins that resemble an archaebacterial γ-type carbonic anhydrase (γCA). The γCA subunits are attached to the membrane arm of complex I on the matrix-exposed side and form an extra spherical domain. At the same time, they span the inner mitochondrial membrane and are essential for assembly of the protein complex. Expression of the genes encoding γCA subunits is reduced if plants are cultivated in the presence of elevated CO₂ concentration. The functional role of these subunits within plant mitochondria is currently unknown but might be related to photorespiration. We propose that the complex I–integrated γCAs are involved in mitochondrial HCO₃⁻ formation to allow efficient recycling of inorganic carbon for CO₂ fixation in chloroplasts under high light conditions.