Location of loops of the Sinskey modified J loop posterior chamber lens. A histopathological study.
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Aged↗
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Results for “looping”
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[Mechanisms of the control of movement: comparison of the models of closed-loop and open-loop].
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Adult↗
[Implantation technic for 4-loop and 2-loop lenses].
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Humans↗
[Comparison between coronary arteriographic observation and vectorcardiographic changes of QRS loop and T loop].
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Angiography↗
Temporary decompression after colorectal surgery: randomized comparison of loop ileostomy and loop colostomy.
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Anastomosis, Surgical↗
Conformational analysis and clustering of short and medium size loops connecting regular secondary structures: a database for modeling and prediction.
Loops are regions of nonrepetitive conformation connecting regular secondary structures. We identified 2,024 loops of one to eight residues in length, with acceptable main-chain bond lengths and peptide bond angles, from a database of 223 protein and protein-domain structures. Each loop is characterized by its sequence, main-chain conformation, and relative disposition of its bounding secondary structures as described by the separation between the tips of their axes and the angle between them. Loops, grouped according to their length and type of their bounding secondary structures, were superposed and clustered into 161 conformational classes, corresponding to 63% of all loops. Of these, 109 (51% of the loops) were populated by at least four nonhomologous loops or four loops sharing a low sequence identity. Another 52 classes, including 12% of the loops, were populated by at least three loops of low sequence similarity from three or fewer nonhomologous groups. Loop class suprafamilies resulting from variations in the termini of secondary structures are discussed in this article. Most previously described loop conformations were found among the classes. New classes included a 2:4 type IV hairpin, a helix-capping loop, and a loop that mediates dinucleotide-binding. The relative disposition of bounding secondary structures varies among loop classes, with some classes such as beta-hairpins being very restrictive. For each class, sequence preferences as key residues were identified; those most frequently at these conserved positions than in proteins were Gly, Asp, Pro, Phe, and Cys. Most of these residues are involved in stabilizing loop conformation, often through a positive phi conformation or secondary structure capping. Identification of helix-capping residues and beta-breakers among the highly conserved positions supported our decision to group loops according to their bounding secondary structures. Several of the identified loop classes were associated with specific functions, and all of the member loops had the same function; key residues were conserved for this purpose, as is the case for the parvalbumin-like calcium-binding loops. A significant number, but not all, of the member loops of other loop classes had the same function, as is the case for the helix-turn-helix DNA-binding loops. This article provides a systematic and coherent conformational classification of loops, covering a broad range of lengths and all four combinations of bounding secondary structure types, and supplies a useful basis for modelling of loop conformations where the bounding secondary structures are known or reliably predicted.
Databases, Factual↗
PDB-based protein loop prediction: parameters for selection and methods for optimization.
An approach to loop prediction that starts with a database search is presented and analyzed. To obtain meaningful statistics, 130 loops from 21 proteins were studied. The correlation between the internal conformation of the loop and the conformation of the neighboring stem residues was examined. Distances between C(alpha) and C(beta) of the immediate neighbor residues at each end select template loops as well as more complex (e.g. three residues on either side) matching criteria. To have a high probability that the best possible loop candidate in the database is included in the set, relatively large cutoffs for matching the interatomic distances of the stem residues have to be used in the template loop selection procedure; for loops of length 5, this results in an average of 1000 loops and for loops of length 9, the number is about 1500. The required number increases only slowly with loop length, in contrast to the exponential time increase involved in direct searches of the conformational space. The best loops among the large number of candidates can be determined by ranking them with the standard CHARMM non-bonded energy function (without electrostatics) applied to the backbone and C(beta) atoms. The same representation (backbone plus C(beta)) can be used to optimize the loop orientations relative to the rest of the protein by constrained energy minimization. Target loops that have many non-bonded contacts with the protein yield better results so that analysis of the non-bonded contacts of the selected template loops is useful in determining the expected accuracy of a prediction. The method for loop selection and optimization predicted eight (out of 18) loops of up to nine residues to an RMSD better than 1.07 A relative to the crystal structure; for 17 of the 18 loops, one of the three lowest energy template loops had an RMSD of less than 1.79 A. The prediction of antibody loops from a database search is more effective than that for non-antibody loops. Provided that they belong to one of the canonical classes, very similar antibody loops are certain to exist in the database. Superposition of the stem residues for antibody loops also results in a better orientation than with arbitrary target loops because the neighboring residues tend to have a more similar beta-strand structure. Two H3 loops (for which no canonical structures have been proposed) were predicted with reasonable accuracy (RMSD of 0.49 A and 1.07 A) even though no corresponding antibody loops were in the database.
Algorithms↗
End-to-end vs interior loop formation kinetics in unfolded polypeptide chains.
The conformational search for favorable intramolecular interactions during protein folding is limited by intrachain diffusion processes. Recent studies on the dynamics of loop formation in unfolded polypeptide chains have focused on loops involving residues near the chain ends. During protein folding, however, most contacts are formed between residues in the interior of the chain. We compared the kinetics of end-to-end loop formation (type I loops) to the formation of end-to-interior (type II loops) and interior-to-interior loops (type III loops) using triplet-triplet energy transfer from xanthone to naphthylalanine. The results show that formation of type II and type III loops is slower compared to type I loops of the same size and amino acid sequence. The rate constant for type II loop formation decreases with increasing overall chain dimensions up to a limiting value, at which loop formation is about 2.5-fold slower for type II loops compared to type I loops. Comparing type II loops of different loop size and amino acid sequence shows that the ratio of loop dimension over total chain dimension determines the rate constant for loop formation. Formation of type III loops is 1.7-fold slower than formation of type II loops, indicating that local chain motions are strongly coupled to motions of other chain segments which leads to faster dynamics toward the chain ends. Our results show that differences in the kinetics of formation of type I, type II, and type III loops are mainly caused by differences in internal flexibility at the different positions in the polypeptide chain. Interactions of the polypeptide chain with the solvent contribute to the kinetics of loop formation, which are strongly viscosity-dependent. However, the observed differences in the kinetics of formation of type I, type II, and type III loops are not due to the increased number of peptide-solvent interactions in type II and type III loops compared to type I loops as indicated by identical viscosity dependencies for the kinetics of formation of the different types of loops.
Amino Acid Sequence↗
Reduced R-loop abundance at proinflammatory loci: a shared epigenetic mechanism in inflammatory and metabolic diseases.
INTRODUCTION: R-loops, RNA-DNA hybrid structures with a displaced single-stranded DNA loop, are key regulators of transcriptional control, chromatin architecture, and genome stability and have emerging roles in inflammatory signaling. However, the relationship between R-loop abundance and strongly modulated inflammatory effector genes in metabolic inflammation and influenza virus infection remains underexplored. METHODS: We performed a locus-centric integrative analysis combining robust differentially expressed genes (DEGs) from multiple inflammatory and infection-related murine and human transcriptomic disease models with experimentally validated multi-cell R-loop annotations from the reference atlas RLoopBase. Our correlation framework evaluated the directional relationship between R-loop abundance and inflammatory gene expression rather than assuming disease-sample-matched R-loop measurements. We further analyzed R-loop regulatory proteins, NRF2-associated R-loop regulators, and overlaps between R-loop regulators and CRISPRi-identified mitochondrial and cellular reactive oxygen species (ROS) regulators. RESULTS: In angiotensin II-infused apolipoprotein E-deficient (ApoE-/-) mice, a model of abdominal aortic aneurysm (AAA), genomic regions encoding the top significantly upregulated genes exhibited significantly fewer R-loops than those encoding downregulated genes at days 14 and 28. Similarly, in atherosclerotic ApoE-/- mice fed a high-fat diet for 32 and 78 weeks, upregulated genes were associated with fewer R-loops than downregulated genes. Reduced R-loop abundance was also observed in genomic regions encoding the top significantly upregulated genes in liver tissues from patients with non-alcoholic steatohepatitis (NASH), as well as in monosodium urate (MSU)-stimulated lymphatic endothelial cells (LECs) and influenza virus-infected human umbilical vein endothelial cells (HUVECs). R-loop regulatory proteins upregulated during metabolic inflammation were enriched in immune and inflammatory pathways. NRF2 was identified as a regulator of 27 R-loop regulatory proteins, including 10 positively and 17 negatively regulated proteins. Furthermore, 54 R-loop regulatory proteins overlapped with CRISPRi-identified mitochondrial and cellular ROS regulators, suggesting potential reciprocal regulation between R-loop homeostasis and ROS signaling. Disease-associated changes in pro-ROS and anti-ROS R-loop regulatory proteins further linked R-loop regulation to inflammatory and oxidative stress pathways. DISCUSSION: These findings identify reduced R-loop abundance at genomic regions encoding strongly upregulated inflammatory genes as a shared feature across multiple models of metabolic inflammation and influenza virus infection. The results further suggest that immune-associated R-loop regulatory proteins and the NRF2-ROS axis may contribute to R-loop remodeling during inflammatory disease. This integrative framework provides new insight into the potential role of R-loops and ROS-sensitive R-loop regulators in inflammatory and metabolic diseases and identifies candidate pathways for future mechanistic investigation and therapeutic targeting.
R-loop regulatory proteins↗
Influence of loop residues on the relative stabilities of DNA hairpin structures.
We have determined the relative stabilities and melting behaviors of DNA hairpin structures as a function of the nonbonded residues in the loop. The specific family of hairpin structures we investigated in this work is formed by the 16-mer sequence d[CGAACG(X)4CGTTCG], where X is deoxyadenosine, deoxycytidine, deoxyguanosine, or deoxythymidine. As shown below, this 16-mer can fold back on itself to form a family of DNA hairpin structures that possess a common hexameric stem duplex and a nonbonded loop of 4 nucleotides. For the hairpin structures investigated in this work, we varied the loop composition from all purine residues to all pyrimidine residues. (Formula: see text). We thermodynamically characterized the relative stabilities and melting profiles of these hairpin structures by a combination of spectroscopic and calorimetric techniques. To establish a thermodynamic "baseline," we also conducted parallel studies on the isolated hexameric duplex d[CGAACG).(CG-TTCG)], which corresponds to the common stem duplex present in each hairpin structure. Our spectroscopic and calorimetric data reveal the following: (i) The hairpin structure with four dT residues in the loop exhibits the highest melting temperature, while the corresponding hairpin structure with four dA residues in the loop exhibits the lowest melting temperature. (ii) The free energy data at 25 degrees C reveal the following order of DNA hairpin stability for the four structures studied here: T loop greater than C loop greater than G loop greater than A loop. In other words, the pyrimidine-looped hairpins of four residues are more stable than the purine-looped hairpins. (iii) The loop-dependent order of hairpin stability is paralleled by a similar trend in the calorimetrically determined transition enthalpies for hairpin disruption. Thus, the enhanced stability of the pyrimidine-looped hairpin structures relative to purine-looped hairpin structures is enthalpic in origin. To develop insight into the molecular basis for the thermodynamic differences, proton NMR spectroscopy was used to probe for structural disparities between the most stable hairpin structure (T loop) and the least stable hairpin structure (A loop). Two-dimensional nuclear Overhauser enhancement spectroscopy revealed connectivities between the residues in the stem duplexes of both hairpin structures that are consistent with B-form DNA. In addition, the nonbonded residues in both the T and A loops exhibited the same connectivity patterns. However, on the 5' side of the stem-loop junction, the T-loop residue exhibited a connectivity with the adjacent base pair of the stem duplex that is not observed for the corresponding A-loop residue. This difference in connectivities at the stem-loop junction may provide a structural basis for our observation that the T-looped hairpin structure is more stable than the corresponding A-looped hairpin structure.
Calorimetry, Differential Scanning↗
Studies of DNA dumbbells. VI. Analysis of optical melting curves of dumbbells with a sixteen-base pair duplex stem and end-loops of variable size and sequence.
Optical melting curves of 22 DNA dumbbells with the 16-base pair duplex sequence 5'-G-C-A-T-C-A-T-C-G-A-T-G-A-T-G-C-3' linked on both ends by single-strand loops of A, or C, sequences (iota = 2, 3, 4, 6, 8, 10, 14). T sequences (iota = 2, 3, 4, 6, 8, 10), and G iota sequences (iota = 2, 4) were measured in phosphate buffered solvents containing 30, 70, and 120 mM Na+. For dumbbells with loops comprised of at least three nucleotides, stability is inversely proportional to end-loop size. Dumbbells with loops comprised of only two nucleotide bases generally have lower stabilities than dumbbells with three base nucleotide loops. Experimental melting curves were analyzed in terms of the numerically exact (multistate) statistical thermodynamic model of DNA dumbbell melting previously described (T. M. paner, M. Amaratunga & A. S. Benight (1992), Biopolymers 32, 881). Theoretically calculated melting curves were fitted to experimental curves by simultaneously adjusting model parameters representing statistical weights of intramolecular hairpin loop and single-strand circle states. The systematically determined empirical parameters provided evaluations of the energetics of hairpin loop formation as a function of loop size, sequence, and salt environment. Values of the free energies of hairpin loop formation delta Gloop(n > iota) and single-strand circles, delta Gcir(N) as a function of end-loop size, tau = 2-14, circle size, N = 32 + 2 iota, and loop sequence were obtained. These quantities were found to depend on end-loop size but not loop sequence. Their empirically determined values also varied with solvent ionic strength. Analytical expressions for the partition function Q(T) of the dumbbells were evaluated using the empirically evaluated best-fit loop parameters. From Q(T), the melting transition enthalpy delta H, entropy delta S, and free energy delta G, were evaluated for the dumbbells as a function of end-loop size, sequence, and [Na+]. Since the multistate analysis is based on the numerically exact model, and considers a statistically significant number of theoretically possible partially melted states, it does not require prior assumptions regarding the nature of the melting transition, i.e., whether or not it occurs in a two-state manner. For comparison with the multistate analysis, thermodynamic transition parameters were also evaluated directly from experimental melting curves assuming a two-state transition and using the graphical van't Hoff analysis. Comparisons between results of the multistate and two-state analyses suggested dumbbells with loops comprised of six or fewer residues melted in a two-state manner, while the melting processes for dumbbells with larger end-loops deviate from two-state behavior. Dependence of thermodynamic transition parameters on [Na+] as a function of loop size suggests single-strand end-loops have different counterion binding properties than the melted circle. Results are compared with those obtained in an earlier study of dumbbells with the slightly different stem sequence 5'-G-C-A-T-A-G-A-T-G-A-G-A-A-T-G-C-3' linked on the ends by T iota loops (iota = 2, 3, 4, 6, 8, 10, 14).
Base Composition↗
Analysis, clustering and prediction of the conformation of short and medium size loops connecting regular secondary structures.
Loops are regions of non-repetitive conformation connecting regular secondary structures. They are both the most difficult and error prone regions of a protein to solve by X-ray crystallography and the hardest regions to model using knowledge-based procedures. While the core of a protein can be straight forwardly modelled from the structurally conserved regions of homologues of known structure, loops must be modelled from a selected homologue or from a loop chosen from outside the family. Here we present a loop prediction procedure that attempts to identify the conformational class of the loop rather than to select a specific loop from a database of fragments. The structures of some 2083 loops of one to eight residues in length were extracted from a database of 225 protein and protein domain structures. For each loop, the relative disposition of its bounding secondary structures is described by the separation between the tips of their axes, the angle and dihedral angle between their axes. From the clustering of the loops according to the root mean square deviation of their spatial fit, a total of 162 loop conformational classes, including 79% of loops, were identified. One-hundred and eight of these, involving 66% of the loops, were populated by at least four non-homologous loops or four loops sharing a low sequence identity. Another 54 classes, including 13% of the loops, were populated by at least three loops of low sequence similarity from three or fewer non-homologous groups. Most of the previously described loop conformations were found among the populated classes. For each class a template was constructed containing both sequence preferences and the relative disposition of bounding secondary structures among member loops. During comparative modelling, the conformation of a loop can be predicted by identifying a loop class with which its sequence and disposition of bounding secondary structures are compatible.
Amino Acid Sequence↗
Thiol cross-linking of cytoplasmic loops in the lactose permease of Escherichia coli.
The N- and C-terminal halves of lactose permease, each with a single-Cys residue in a cytoplasmic loop, were coexpressed, and cross-linking was studied in the absence or presence of ligand. Out of the 68 paired-Cys mutants in cytoplasmic loops IV/V and VIII/IX or X/XI, three pairs in loop IV/V and X/XI, (i) Arg135 --> Cys/Thr338 --> Cys, (ii) Arg134 --> Cys/Val343 --> Cys, and (iii) Arg134 --> Cys/Phe345 --> Cys, form a spontaneous disulfide bond, indicating that loops IV/V and X/XI are in close proximity. In addition, specific paired-Cys residues in loop IV/V (132-138) and loop VIII/IX (282-290) or loop X/XI (335-345) cross-link with iodine and/or the homobifunctional cross-linking agents N, N'-o-phenylenedimaleimide, N,N'-p-phenylenedimaleimide, and 1, 6-bis(maleimido)hexane. The results demonstrate that loop IV/V is close to both loop VIII/IX and loop X/XI. On the other hand, similar though less extensive cross-linking studies indicate that neither the N terminus nor loop II/III appear to be close to loops VIII/IX or X/XI. The findings suggest that the longer cytoplasmic loops are highly flexible and interact in a largely random fashion. However, although a Cys residue at position 134 in loop IV/V, for example, is able to cross-link with a Cys residue at each position in loop VIII/IX or loop X/XI, Cys residues at other positions in loop IV/V exhibit markedly different cross-linking patterns. Therefore, although the domains appear to be very flexible, the interactions are not completely random, suggesting that there are probably at least some structural constraints that limit the degree of flexibility. In addition, evidence is presented suggesting that ligand binding induces conformational alterations between loop IV/V and loop VIII/IX or X/XI.
Binding Sites↗
A hierarchical approach to all-atom protein loop prediction.
The application of all-atom force fields (and explicit or implicit solvent models) to protein homology-modeling tasks such as side-chain and loop prediction remains challenging both because of the expense of the individual energy calculations and because of the difficulty of sampling the rugged all-atom energy surface. Here we address this challenge for the problem of loop prediction through the development of numerous new algorithms, with an emphasis on multiscale and hierarchical techniques. As a first step in evaluating the performance of our loop prediction algorithm, we have applied it to the problem of reconstructing loops in native structures; we also explicitly include crystal packing to provide a fair comparison with crystal structures. In brief, large numbers of loops are generated by using a dihedral angle-based buildup procedure followed by iterative cycles of clustering, side-chain optimization, and complete energy minimization of selected loop structures. We evaluate this method by using the largest test set yet used for validation of a loop prediction method, with a total of 833 loops ranging from 4 to 12 residues in length. Average/median backbone root-mean-square deviations (RMSDs) to the native structures (superimposing the body of the protein, not the loop itself) are 0.42/0.24 A for 5 residue loops, 1.00/0.44 A for 8 residue loops, and 2.47/1.83 A for 11 residue loops. Median RMSDs are substantially lower than the averages because of a small number of outliers; the causes of these failures are examined in some detail, and many can be attributed to errors in assignment of protonation states of titratable residues, omission of ligands from the simulation, and, in a few cases, probable errors in the experimentally determined structures. When these obvious problems in the data sets are filtered out, average RMSDs to the native structures improve to 0.43 A for 5 residue loops, 0.84 A for 8 residue loops, and 1.63 A for 11 residue loops. In the vast majority of cases, the method locates energy minima that are lower than or equal to that of the minimized native loop, thus indicating that sampling rarely limits prediction accuracy. The overall results are, to our knowledge, the best reported to date, and we attribute this success to the combination of an accurate all-atom energy function, efficient methods for loop buildup and side-chain optimization, and, especially for the longer loops, the hierarchical refinement protocol.
Algorithms↗
Structure and function in bacteriorhodopsin: the effect of the interhelical loops on the protein folding kinetics.
The loops connecting the seven transmembrane helices of bacteriorhodopsin have each been replaced in turn by structureless linkers of Gly-Gly-Ser repeat sequences, and the effect on the protein folding kinetics has been determined. An SDS-denatured state of each loop mutant bacterio-opsin was folded in l-alpha-1,2-dihexanoylphosphatidylcholine/l-alpha-1,2-dimyristoylphosphatidylcholine micelles, containing retinal, to give functional bacteriorhodopsin. Stopped-flow mixing was used to initiate the folding reaction, giving a time resolution of milliseconds, and changes in protein fluorescence were used to monitor folding. All loop mutant proteins folded according to the same reaction scheme as wild-type protein. The folding kinetics of the AB, BC and DE loop mutants were the same as wild-type protein, despite the blue-shifted chromophore band of the BC loop mutant bR state. A partially folded apoprotein intermediate state of the AB loop mutant did however appear to decay in the absence of retinal. The most significant effects on the folding kinetics were seen for mutant protein with structureless linkers in place of the CD, EF and FG loops. The rate-limiting apoprotein folding step of the CD loop mutant was about ten times slower than wild-type, whilst that of the EF loop mutant was almost four times slower than wild-type. Wild-type behaviour was observed for the other folding and retinal binding events of the CD and EF loop mutant proteins. These effects of the CD and EF loop mutations on apoprotein folding correlate with the fact that these two loop mutants also have the least stable, partially folded apoprotein intermediate of all the loop mutants, and are the most affected by a decrease in lipid lateral pressure. In contrast, the FG loop mutant exhibited wild-type apoprotein folding, but altered covalent binding of retinal and final folding to bacteriorhodopsin. This correlates with the fact that the FG loop mutant bacteriorhodopsin is the most susceptible to denaturation by SDS of all the loop mutants, but its partially folded apoprotein intermediate is more stable than that of the CD and EF mutants. Thus the CD and EF loops may contribute to the transition state for the rate-limiting apoprotein folding step and the FG loop to that for final folding and covalent binding of retinal.
Apoproteins↗
Size influence on shape of handwritten characters loops.
In the practice of forensic handwriting experts, the size of the writing on a questioned document may be different from that of known samples. In this study, the hypothesis of shape invariance of handwritten closed loops across size increasing was tested. A Fourier methodology was applied to 2325 small letters (591 a loops, 547 d loops, 596 o loops and 591 q loops) and 692 enlarged letters (162 a loops, 173 d loops, 173 o loops and 184 q loops), in a population of 13 writers who were asked to write letters in their usual size and about three times larger. Most of the writers presented similar modifications when increasing the size of the loops; they produced enlarged loops significantly more round and less slanted towards the right or the left. Furthermore, a discrimination was demonstrated between the writers on the basis of the enlarged loops, with a correct classification rate superior to 90%, whatever the letter (a, d, o or q). A classification of the enlarged loops in their corresponding writer was then possible. On the contrary, when comparing the enlarged loops to the small ones, almost one half of the enlarged loops were allocated to a wrong writer. Shape invariance was thus not supported for this particular application. Consequently, when comparing documents with a different writing size, differences in loops shape should be interpreted cautiously because they may be due to a different writer, but they may also be due to an enlargement of the loops. Therefore, reference material of similar writing size to that of the questioned writing should be requested for the comparison of handwritten loops.
Journal Article↗
M/F ratios of four different closing loops: 3D analysis using the finite element method (FEM).
BACKGROUND: It has been claimed that the opus loop is capable of delivering a constant and optimum M/F ratio without the need for gable bends. OBJECTIVE: To compare the forces, moments and moment/force (M/F) ratios of the opus loop, L-loop, T-loop and vertical helical closing loop (VHC loop) in a segmented arch with the finite element method (FEM). METHODS: The FEM was used to compare 3D models of closing loops in rectangular (0.016 x 0.022 inch) stainless steel wire. The L-, T- and VHC loops were designed with and without preactivation bends. The opus loop had no preactivation bends. The T-Loops were 10 mm in height and 10 mm in length. The horizontal and vertical forces, the moments and the M/F ratios at the alpha and beta ends were recorded at 0, 0. 1, 0.4, 0.7 and 1 mm intervals. RESULTS: The highest horizontal and vertical forces were produced by the L-loop (with and without preactivation bends) and in most cases the lowest forces were produced by the VHC loop. Loops with preactivation bends produced marked changes in the M/F ratio and loops without preactivation bends low, but relatively constant, M/F ratios over the full range of activation. Of the loops modelled without preactivation bends the opus and T-loop had the highest M/F ratios (7.20 - 7.67 mm at the anterior ends). CONCLUSION: Stainless steel opus and T-loops without preactivation bends had constant M/F ratios, but both loops failed to deliver the optimum M/F ratio of 10:1.
Biomechanical Phenomena↗
[Mitral regurgitation due to abnormal reinsertion of chordae tendineae (looping) of the posterior mitral leaflet: clinical and echocardiographic features].
Two-dimensional (2D) echocardiographic and clinical characteristics of patients with mitral regurgitation (MR) due to abnormal reinsertion of chordae tendineae (looping) in the middle scallop of the posterior leaflet were described and compared with those of patients with chordal rupture of the posterior leaflet. Twenty-five patients with posterior mitral valve prolapse who underwent mitral valve replacement were studied. They were categorized in three groups; 14 patients with MR due to ruptured chordae tendineae (RCT) of the posterior leaflet (RCT group); three patients with looping of the chordae tendineae in the middle scallop of the posterior leaflet (looping group); and eight patients with both RCT and looping (looping + RCT group). It was difficult to distinguish the looping group from the other two groups by their 2D echocardiographic findings, which were characteristic of those of RCT. However, the following findings were more frequently encountered in the patients with looping than in those without: 1) aberrant or absent systolic coaptation with salient arc of the posterior leaflet, observed in six of the RCT group (43%), two in the looping group (67%) and seven in the looping + RCT group (88%); 2) with thickened edges of the posterior leaflet, shown in three of the RCT group (21%), two of the looping group (67%) and five of the looping + RCT group (63%) in the long-axis view, and also noticed in four of the RCT group (29%), two of the looping group (67%) and six of the looping + RCT group (75%) in the short-axis view. In the clinical history, the onset of a heart murmur, congestive heart failure and surgical treatment occurred at significantly younger ages in the looping group than in the RCT group. As for hemodynamic parameters, pulmonary hypertension was significantly milder in the looping group than in the RCT group. In conclusion, although 2D echocardiographic findings of patients with looping were similar to those of patients with RCT, it seemed possible to differentiate the looping group from the RCT group by the 2D finding of a prolapsed posterior mitral valve with a salient arc and a thickened edge. It was also suggested that the looping of chordae tendineae in the middle scallop of the posterior leaflet was congenital in origin.
Adolescent↗