Improved Accuracy of Cardiac Tissue-Level Simulations by Considering Membrane Resistance as a Cellular-Level Optimization Objective.

Cardiac cellular models are utilized as the building blocks for tissue simulation. One of the imprecisions of conventional cellular modeling, especially when the models are used in tissue-level modeling, stems from the mere consideration of cellular properties (e.g., action potential shape) in parameter tuning of the model. In our previous work, we put forward an accurate framework in which membrane resistance (Rm) reflecting inter-cellular characteristics, i.e., electrotonic effects, was considered alongside cellular features in cellular model fitting. This paper, for the first time, examines the hypothesis that considering Rm as an additional optimization objective improves the accuracy of tissue-level modeling. To study this hypothesis, after cellular-level optimization of a well-known model, source-sink mismatch configurations in a 2-dimensional model are investigated. The results demonstrate that including Rm in the optimization protocol yields a substantial improvement in the relative error of the critical transition border which is defined as the minimum window size between source and sink that wave propagates. Model developers can utilize the proposed concept during parameter tuning to increase the accuracy of models.

A Novel Bi-Level Framework for Fitting the Parameters in Cardiac Cellular Models.

Cardiac models constructed from sets of differential equations provide invaluable information about heart mechanism and disorder of both human and animals. As tuning the parameters is a profoundly important step of modeling, this paper presents a novel parametrization technique based on a bilevel framework that benefits from two solution approaches, namely mixed integer genetic algorithm (MIGA) and linear least squares (LLS). In the upper-level optimization step, the action potential (AP) of the model is fitted to the reference AP using MIGA. In the lower-level optimization step, the mismatch between the total current of the model and reference is minimized via a clamp concept-based linearization and LLS solution approach. Notably, the clamp concept can diminish the nonlinearity of the parameter fitting problem. The issue of dependency on initial parameters in the lower-level problem, as well as the sensitivity of model parameters to linearization, are circumvented by MIGA in the upper-level optimization. For evaluation of MIGA-LLS performance, two complex human ventricular models are employed. The results demonstrate that in comparison to the genetic algorithm (GA)-based approach, the proposed framework significantly reduces the average and variation of normalized root-mean-squared error (NRMSE) in terms of the AP and total current in different trials. Variability in the resulting parameter values is considerably decreased as well.

Arrhythmia Vulnerability in Diabetic Cardiac Tissue is Species-Dependent: Effects of I KATP, Uncoupling, and Connexin Lateralization.

Amongst the complications of diabetes is arrhythmia, the risk of which depends on multiple factors. This study was designed to investigate several factors, including the effects of ATP-sensitive potassium current, lateralized connexins, and gap junction uncoupling. ATP-sensitive potassium channel (I KATP) opening is caused by ischemia, which can occur in diabetic or non-diabetic hearts. I KATP opening was simulated in this work to determine if the risk of ischemia-induced arrhythmias is affected by diabetes. Simulations were performed using healthy and diabetic models of rat and rabbit ventricle. Results showed that the diabetic rat model is less vulnerable to reentrant arrhythmia than the healthy rat model. The diabetic rabbit model was more vulnerable to reentrant arrhythmia than the healthy rabbit model. In both rabbit models, the vulnerability increased as the gap junctional coupling decreased. Opening of I KATP resulted in larger window of vulnerability. Conduction reserve was simulated based on 1D simulations for both rat and rabbit models. There was no difference between rat and rabbit conduction reserve. Our results showed that the simulation results are model-dependent, i.e., results from the rabbit model are similar to human clinical data, while the results from the rat model contradict human clinical observations, suggesting a significant species-dependence in arrhythmia vulnerability in the diabetic heart.

Pressure-dependent changes in haematocrit and plasma volume during anaesthesia, a randomised clinical trial.

BACKGROUND: Induction of general anaesthesia has been shown to cause haemodilution and an increase in plasma volume. The aim of this study was to evaluate whether prevention of hypotension during anaesthesia induction could avoid haemodilution. METHODS: Twenty-four cardiac surgery patients, 66 ± 10 years, were randomised to receive either norepinephrine in a dose needed to maintain mean arterial blood pressure (MAP) at pre-anaesthesia levels after induction or to a control group that received vasopressor if MAP decreased below 60 mmHg. No fluids were infused. Changes in plasma volume were calculated with standard formula: 100 × (Hct(pre)/Hct(post) - 1)/(1 - Hct(pre)). Arterial blood gas was analysed every 10 minutes and non-invasive continuous haemoglobin (SpHb) was continuously measured. RESULTS: Pre-anaesthesia MAP was 98 ± 7 mmHg. Ten minutes after anaesthesia induction, the haematocrit decreased by 5.0 ± 2.5% in the control group compared with 1.2 ± 1.4% in the intervention group, which corresponds to increases in plasma volume by 310 ml and 85 ml respectively. MAP decreased to 69 ± 15 mmHg compared to 92 ± 10 mmHg in the intervention group. The difference maintained throughout the 70 min intervention period. The change in haemoglobin level measured by blood gas analysis could not be detected by SpHb measurement. The mean bias between the SpHb and blood gas haemoglobin was 15 g/l. CONCLUSION: During anaesthesia induction, haematocrit decreases and plasma volume increases early and parallel to a decrease in blood pressure. This autotransfusion is blunted when blood pressure is maintained at pre-induction levels with norepinephrine.

Single cell analysis of cancer cells using an improved RT-MLPA method has potential for cancer diagnosis and monitoring.

Single cell analysis techniques have great potential in the cancer genomics field. The detection and characterization of circulating tumour cells are important for identifying metastatic disease at an early stage and monitoring it. This protocol is based on transcript profiling using Reverse Transcriptase Multiplex Ligation-dependent Probe Amplification (RT-MLPA), which is a specific method for simultaneous detection of multiple mRNA transcripts. Because of the small amount of (circulating) tumour cells, a pre-amplification reaction is performed after reverse transcription to generate a sufficient number of target molecules for the MLPA reaction. We designed a highly sensitive method for detecting and quantifying a panel of seven genes whose expression patterns are associated with breast cancer, and optimized the method for single cell analysis. For detection we used a fluorescence-dependent semi-quantitative method involving hybridization of unique barcodes to an array. We evaluated the method using three human breast cancer cell lines and identified specific gene expression profiles for each line. Furthermore, we applied the method to single cells and confirmed the heterogeneity of a cell population. Successful gene detection from cancer cells in human blood from metastatic breast cancer patients supports the use of RT-MLPA as a diagnostic tool for cancer genomics.

Motion estimation in cardiac fluorescence imaging with scale-space landmarks and optical flow: a comparative study.

Motion artifacts are a major disadvantage of cardiac optical mapping studies. Pixel misalignment due to contraction is a main cause of the presence of gross motion artifacts in action potential recordings. This study is focused on methods for identifying landmarks and tracking the motion of cardiac tissue for preparations in optical mapping recordings. This is a first step toward our long-term goal to implement a landmark-based image registration technique to correct for pixel misalignment in cardiac optical mapping fluorescence videos and, hence, for gross motion artifacts. Preliminary results for the registration step are presented as an initial proof of concept. The characteristics of the optical mapping images are challenging, since their lack of contrast and well-defined features impose a limitation on the techniques than can be used for landmark selection and motion tracking. This paper compares results of motion estimation of the cardiac surface with two approaches that do not rely on high-contrast features: 1) Scale-invariant feature transform (SIFT) detected "keypoints," to be used as landmarks for motion tracking, as well as 2) a classical global optical flow (OF) algorithm. Both are applied to low-contrast and low-resolution cardiac fluorescence images. We demonstrate that the performance of SIFT is superior to that of OF for pixel motion tracking in cardiac optical mapping images with simulated motion. Results for action potential recovery and action potential duration calculation after landmark-based image registration show that SIFT landmark-based registration yields superior performance in this regard as well.

Computer simulation of cardiac propagation: effects of fiber rotation, intramural conductivity, and optical mapping.

Cardiac propagation characteristics such as anisotropy ratio and conduction velocities are often determined experimentally from epicardial measurements. We hypothesize that these measurements have inaccuracies due to intramural fiber rotation and transmural electrotonic interactions. We also hypothesize that optical mapping (OM) recordings compound the error, due to contributions from deeper layers. In this study, we studied propagation in a three-dimensional computer model of a slab of tissue with varying thickness and a 120° fiber rotation. Simulation results were further processed to reconstruct OM signals. As expected, simulation results demonstrated that the direction of wave propagation on the epicardial surface is not aligned with the epicardial fiber orientation. This angle difference was most pronounced for thin tissue, and decreased with decreasing intramural conductivity and increasing tissue thickness. This difference also increased with time elapsed poststimulus, as the contribution from deeper layers increased. Observations were confirmed experimentally with OM measurements from isolated rat hearts. Simulations also predicted that OM causes an additional error in measurements due to activity in deeper layers being less aligned. Several alternative approaches for the estimation of fiber orientation and anisotropy ratio were evaluated. Those based on conduction velocity measurements yielded the most accurate estimates when applied to noise-free simulated data.

Two apparently unrelated groups of symbiotic annelids, Nautiliniellidae and Calamyzidae (Phyllodocida, Annelida), are a clade of derived chrysopetalid polychaetes.

Nautiliniellidae Miura and Laubier, 1989 is a small family of marine polychaetes with 20 currently described species in 11 genera, most of which are known to live symbiotically in the mantle cavity of bivalves, mainly from cold seeps and hydrothermal vents, while Calamyzidae (Hartmann-Schröder, 1971) including only one described species, Calamyzas amphictenicola Arwidsson 1932 lives as an ectoparasite on ampharetid polychaetes in Swedish waters. Nautiliniellidae and Calamyzidae have both been considered to belong to Phyllodocida, but the few phylogenetic studies including these taxa have found their positions unstable. The internal relationships within Nautiliniellidae are also poorly understood. Using molecular information from both nuclear and mitochondrial genes and morphological data we assessed the systematic placement of Nautiliniellidae (seven species; collected from Pacific hydrothermal vents and cold seeps and one from Atlantic waters) and Calamyzas amphictenicola. Our results show that C. amphictenicola and Nautiliniellidae formed a well-supported clade that is nested within Chrysopetalidae, a free-living group of polychaetes. The chrysopetalid genus Vigtorniella Kiseleva 1992; a bacterial mat grazer found at methane seeps, anoxic basins and whalefalls, formed a paraphyletic grade with respect to the Nautiliniellidae-Calamyzas clade. The internal relationships within the Nautiliniellidae-Calamyzas clade as well as the relationships with their hosts are also examined. As a result we synonymize Calamyzidae and Nautiliniellidae with Chrysopetalidae, with the last as the oldest available family-group name. Within Chrysopetalidae we refer to the subfamilies Chrysopetalinae Ehlers 1864; Dysponetinae Aguado, Nygren & Rouse, herein; and Calamyzinae Hartmann-Schröder, 1971. Calamyzinae contains C. amphictenicola, all taxa formerly in Nautiliniellidae, and the chrysopetalid genus Vigtorniella.

Cardiac fiber rotation distorts surface measurements of anisotropic propagation.

Anisotropy is often determined experimentally from epicardial propagation measurements. We hypothesize that the direction of wave propagation on the epicardial surface is not aligned with the epicardial fiber orientation, due to intramural fiber rotation. In this paper, we modeled the effect of cardiac tissue fiber rotation on wave propagation. We used a three dimensional computer model of varying thickness with a 120 degree fiber rotation through the thickness. The angle difference between the direction of propagation and fiber orientation was most pronounced for thin tissue, and decreased with increasing tissue thickness. This angle also increased with the time elapsed since stimulation. Finally, we demonstrated that the fiber rotation from epicardium to endocardium results in inaccurate measurements of conduction velocities at the epicardium, particularly in thin tissues.

Application of scale-space descriptors for the reliable detection of keypoints for image registration in optical mapping studies in whole heart preparations.

Data acquired using Optical Mapping (OM) studies are affected by motion artifacts due to the inherent contraction of the heart. Those artifacts can be reduced by registering the images obtained by the OM system or by the combination of approaches like physical restraint of the heart or ratiometry with image registration. Due to the lack of high contrast features most registration methods are not suitable for this application. This paper is focused on the utilization of scale space theory and local descriptors to enhance the detection of local features in OM images and to describe the movement of keypoints. This information can be used to determine a suitable set of transformations to perform the registration process.

Norepinephrine causes a pressure-dependent plasma volume decrease in clinical vasodilatory shock.

BACKGROUND: Recent experimental studies have shown that a norepinephrine-induced increase in blood pressure induces a loss of plasma volume, particularly under increased microvascular permeability. We studied the effects of norepinephrine-induced variations in the mean arterial pressure (MAP) on plasma volume changes and systemic haemodynamics in patients with vasodilatory shock. METHODS: Twenty-one mechanically ventilated patients who required norepinephrine to maintain MAP > or =70 mmHg because of septic/postcardiotomy vasodilatory shock were included. The norepinephrine dose was randomly titrated to target MAPs of 60, 75 and 90 mmHg. At each target MAP, data on systemic haemodynamics, haematocrit, arterial and mixed venous oxygen content and urine flow urine were measured. Changes in the plasma volume were calculated as 100 x (Hct(pre)/Hct(post)-1)/ (1-Hct(pre)), where Hct(pre) and Hct(post) are haematocrits before and after intervention. RESULTS: Norepinephrine doses to obtain target MAPs of 60, 75 and 90 mmHg were 0.20+/-0.18, 0.29+/-0.18 and 0.42+/-0.31 microg/kg/min, respectively. From 60 to 90 mmHg, increases in the cardiac index (15%), systemic oxygen delivery index (25%), central venous pressure (CVP) (20%) and pulmonary artery occlusion pressure (33%) were seen, while the intrapulmonary shunt fraction was unaffected by norepinehrine. Plasma volume decreased by 6.5% and 9.4% (P<0.0001) when blood pressure was increased from 60 to 75 and 90 mmHg, respectively. MAP (P<0.02) independently predicted the decrease in plasma volume with norepinephrine but not CVP (P=0.19), cardiac index (P=0.73), norepinephrine dose (P=0.58) or urine flow (P=0.64). CONCLUSIONS: Norepinephrine causes a pressure-dependent decrease in the plasma volume in patients with vasodilatory shock most likely caused by transcapillary fluid extravasation.

Low-dose vasopressin increases glomerular filtration rate, but impairs renal oxygenation in post-cardiac surgery patients.

BACKGROUND: The beneficial effects of vasopressin on diuresis and creatinine clearance have been demonstrated when used as an additional/alternative therapy in catecholamine-dependent vasodilatory shock. A detailed analysis of the effects of vasopressin on renal perfusion, glomerular filtration, excretory function and oxygenation in man is, however, lacking. The objective of this pharmacodynamic study was to evaluate the effects of low to moderate doses of vasopressin on renal blood flow (RBF), glomerular filtration rate (GFR), renal oxygen consumption (RVO2) and renal oxygen extraction (RO2Ex) in post-cardiac surgery patients. METHODS: Twelve patients were studied during sedation and mechanical ventilation after cardiac surgery. Vasopressin was sequentially infused at 1.2, 2.4 and 4.8 U/h. At each infusion rate, systemic haemodynamics were evaluated by a pulmonary artery catheter, and RBF and GFR were measured by the renal vein thermodilution technique and by renal extraction of 51chromium-ethylenediaminetetraacetic acid, respectively. RVO2 and RO2Ex were calculated by arterial and renal vein blood samples. RESULTS: The mean arterial pressure was not affected by vasopressin while cardiac output and heart rate decreased. RBF decreased and GFR, filtration fraction, sodium reabsorption, RVO2, RO2Ex and renal vascular resistance increased dose-dependently with vasopressin. Vasopressin exerted direct antidiuretic and antinatriuretic effects. CONCLUSIONS: Short-term infusion of low to moderate, non-hypertensive doses of vasopressin induced a post-glomerular renal vasoconstriction with a decrease in RBF and an increase in GFR in post-cardiac surgery patients. This was accompanied by an increase in RVO2, as a consequence of the increases in the filtered tubular load of sodium. Finally, vasopressin impaired the renal oxygen demand/supply relationship.

Vasopressin decreases intestinal mucosal perfusion: a clinical study on cardiac surgery patients in vasodilatory shock.

BACKGROUND: Low to moderate doses of vasopressin have been used in the treatment of cathecholamine-dependent vasodilatory shock in sepsis or after cardiac surgery. We evaluated the effects of vasopressin on jejunal mucosal perfusion, gastric-arterial pCO2 gradient and the global splanchnic oxygen demand/supply relationship in patients with vasodilatory shock after cardiac surgery. METHODS: Eight mechanically ventilated patients, dependent on norepinephrine to maintain mean arterial pressure (MAP) > or = 60 mmHg because of septic/post-cardiotomy vasodilatory shock and multiple organ failure after cardiac surgery, were included. Vasopressin was sequentially infused at 1.2, 2.4 and 4.8 U/h for 30-min periods. Norepinephrine was simultaneously decreased to maintain MAP at 75 mmHg. At each infusion rate of vasopressin, data on systemic hemodynamics, jejunal mucosal perfusion, jejunal mucosal hematocrit and red blood cell velocity (laser Doppler flowmetry) as well as gastric-arterial pCO2 gradient (gastric tonometry) and splanchnic oxygen and lactate extraction (hepatic vein catheter) were obtained. RESULTS: The cardiac index, stroke volume index and systemic oxygen delivery decreased and systemic vascular resistance and systemic oxygen extraction increased significantly, while the heart rate or global oxygen consumption did not change with increasing vasopressin dose. Jejunal mucosal perfusion decreased and the arterial-gastric-mucosal pCO2 gradient increased, while splanchnic oxygen or lactate extraction or mixed venous-hepatic venous oxygen saturation gradient were not affected by increasing infusion rates of vasopressin. CONCLUSIONS: Infusion of low to moderate doses of vasopressin in patients with norepinephrine-dependent vasodilatory shock after cardiac surgery induces an intestinal and gastric mucosal vasoconstriction.

Cost effectiveness of two rehabilitation programmes for neck and back pain patients: A seven year follow-up.

The cost effectiveness of work-oriented rehabilitation for persons on long-term sick leave needs to be assessed. This prospective observational study presents a follow-up seven years after rehabilitation using two different evidence-based work-oriented regimens. Individuals on sick leave for neck and back pain were referred to two rehabilitation programmes in Sweden. The first programme was a relatively low-intensity programme based on orthopaedic manual therapy and exercise programme (OMTP). The second programme was a full-time multidisciplinary programme (MDP). The primary outcome was sickness absence seven years after intervention. Cost effectiveness was calculated on the basis of loss of production due to sickness absence. The results show that participants referred to MDP and with less than 60 sick days before rehabilitation have reduced sickness absence after intervention as compared to matched controls. This corresponds to a cost reduction of about 94,494 EUR per referred individual. Further, the results indicate that participants of the OMTP who have more than 60 sick days before rehabilitation have a statistically significant increased risk of disability pension. This means increased cost in terms of loss of production of 44,593 EUR per referred individual. The results of this study show that MPD but not OMTP achieves the goal of working life-oriented rehabilitation. A direct comparison between the rehabilitation programmes strengthened the assumption that long-term sickness absence prior to rehabilitation is associated with more days on sick leave after rehabilitation. This analysis also indicated the importance of participants' pain self-efficacy beliefs and recovery beliefs on rehabilitation outcome.

Relative cardiac expression of growth hormone receptor and insulin-like growth factor-I mRNA in congenital heart disease.

GH may exert direct growth-promoting and metabolic actions on target tissues, but most of its effects are mediated by circulating (endocrine) or local (auto-/paracrine) IGF-I. The GH/IGF-I system has an important role in cardiac development and in maintaining the structure and function of the heart. A subgroup of children with pronounced heart defects will eventually need transplants, owing to congestive heart failure. Since the symptoms are often severe and may progress while waiting for surgery, it is necessary to develop supportive medical treatment. GH has been proposed as a therapeutic agent in adults with heart failure, but to date studies are lacking on children and more information is necessary. We have examined the expression of IGF-I mRNA and GH-receptor (GH-R) mRNA in children undergoing surgery for congenital heart disease. Eighteen children scheduled for open-heart surgery were included in the study. Right auricular biopsies were taken at the time of venous catheterization preceding cardiac bypass. The specimens were analysed using realtime PCR. We were able to show expression of both IGF-I mRNA and GH-R mRNA in the pediatric heart. The relative expressions were intercorrelated (r=0.75, p<0.001). GH-R mRNA correlated positively to standardized weight (r=0.65, p=0.004), body mass index (BMI) (r=0.59, p=0.01), and standardized BMI (r=0.59, p=0.01). IGF-I mRNA only correlated to BMI (r=0.50, p=0.04). This is the first study displaying cardiac expression of IGF-I mRNA and GH-R mRNA in children with congenital heart disease, although further studies are needed to define a role for GH in the treatment of these patients.

Methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) robustly detects and distinguishes 11p15 abnormalities associated with overgrowth and growth retardation.

BACKGROUND: A variety of abnormalities have been demonstrated at chromosome 11p15 in individuals with overgrowth and growth retardation. The identification of these abnormalities is clinically important but often technically difficult. Methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) is a simple but effective technique able to identify and differentiate methylation and copy number abnormalities, and thus is potentially well suited to the analysis of 11p15. AIMS: To customize and test an MS-MLPA assay capable of detecting and distinguishing the full spectrum of known 11p15 epigenetic and copy number abnormalities associated with overgrowth and growth retardation and to assess its effectiveness as a first line investigation of these abnormalities. METHODS: Five synthetic probe pairs were designed to extend the range of abnormalities detectable with a commercially available MS-MLPA assay. To define the normal values, 75 normal control samples were analysed using the customized assay. The assay was then used to analyse a "test set" of 24 normal and 27 abnormal samples, with data analysed by two independent blinded observers. The status of all abnormal samples was confirmed by a second technique. RESULTS: The MS-MLPA assay gave reproducible, accurate methylation and copy number results in the 126 samples assayed. The blinded observers correctly identified and classified all 51 samples in the test set. CONCLUSIONS: MS-MLPA robustly and sensitively detects and distinguishes epigenetic and copy number abnormalities at 11p15 and is an effective first line investigation of 11p15 in individuals with overgrowth or growth retardation.

Reduced conduction reserve of the propagating cardiac impulse in the diabetic rat heart: a model study.

Conduction velocity is dependent on two main factors: intercellular electrical coupling and cellular electrical excitability. There is significant redundancy, 'conduction reserve', in these parameters such that significant reduction in the conduction velocity of the action potential requires either a severe change in one of these parameters or a combined change in both parameters. Studies in diabetic rat hearts have shown a significant reduction in the conduction reserve and it was hypothesized that this is mainly due to the lateralization of the gap junction protein connexin 43 (Cx43). To gain a better understanding of the effect of reduced intercellular coupling, a rat ventricle myocyte model was used to simulate propagation along a strand of cells. Simulations were performed to assess the effect of reduction of intercellular conductance on the conduction velocity. As the conductance of the gap junction decreased a significant reduction in the conduction velocity was observed. The relationship between conduction velocity and intercellular coupling became steeper with decreasing coupling, such that conduction velocity became increasingly sensitive to further uncoupling. This is consistent with experimental results, in which application of the gap junction uncoupler heptanol caused a larger conduction slowing in diabetic hearts than in controls.

Sequential gene promoter methylation during HPV-induced cervical carcinogenesis.

We aimed to link DNA methylation events occurring in cervical carcinomas to distinct stages of HPV-induced transformation. Methylation specific-multiplex ligation-dependent probe amplification (MS-MLPA) analysis of cervical carcinomas revealed promoter methylation of 12 out of 29 tumour suppressor genes analysed, with MGMT being most frequently methylated (92%). Subsequently, consecutive stages of HPV16/18-transfected keratinocytes (n=11), ranging from pre-immortal to anchorage-independent phenotypes, were analysed by MS-MLPA. Whereas no methylation was evident in pre-immortal cells, progression to anchorage independence was associated with an accumulation of frequent methylation events involving five genes, all of which were also methylated in cervical carcinomas. TP73 and ESR1 methylation became manifest in early immortal cells followed by RARbeta and DAPK1 methylation in late immortal passages. Complementary methylation of MGMT was related to anchorage independence. Analysis of nine cervical cancer cell lines, representing the tumorigenic phenotype, revealed in addition to these five genes frequent methylation of CADM1, CDH13 and CHFR. In conclusion, eight recurrent methylation events in cervical carcinomas could be assigned to different stages of HPV-induced transformation. Hence, our in vitro model system provides a valuable tool to further functionally address the epigenetic alterations that are common in cervical carcinomas.

Detection of a novel familial deletion of four genes between BP1 and BP2 of the Prader-Willi/Angelman syndrome critical region by oligo-array CGH in a child with neurological disorder and speech impairment.

Two common classes of deletions are described in the literature in individuals with Prader-Willi/Angelman syndrome (PWS/AS): one between breakpoint 1 (BP1) to BP3 and the other between BP2 to BP3 of the PWS/AS critical region on chromosome 15q11-->q13. We present here a novel observation of an approximately 253-kb deletion between BP1 and BP2 on 15q11.2, in a 3(1/2)-year-old boy, who was referred to us with a clinical suspicion of having Angelman syndrome and presenting with mental retardation, neurological disorder, developmental delay and speech impairment. Karyotype and FISH results were found to be normal. The microdeletion between BP1 and BP2 includes four genes - NIPA1, NIPA2, CYFIP1 and TUBGCP5 which was detected by a high-resolution oligonucleotide array-CGH that was further validated by a Multiplex Ligation-dependent Probe Amplification (MLPA) assay. The same deletion was observed in the father who presented with similar but relatively milder clinical features as compared to the affected son. Methylation studies by methylation-specific MLPA (MS-MLPA) of the SNRPN imprinting center (IC) showed a normal imprinting pattern, both in the patient and the father. To our knowledge a microdeletion limited only to the BP1-BP2 region has not yet been reported. The familial genetic alteration together with the striking clinical presentation in this study are interesting, but from our single case study it is difficult to suggest if the deletion is causative of some of the abnormal features or if it is a normal variant. The study however further strengthens the fact that genome-wide analysis by array CGH in individuals with developmental delay and mental retardation is very useful in detecting such hidden interstitial chromosomal rearrangements.