Investigating the potential of single-cell DNA methylation data to detect allele-specific methylation and imprinting

Allele-specific methylation (ASM) is an epigenetic modification whereby one parental allele becomes methylated and the other unmethylated at a specific locus. ASM is most often driven by the presence of nearby heterozygous variants that influence methylation, but also occurs somatically in the context of genomic imprinting. In this study, we investigate ASM using publicly available single-cell reduced representation bisulfite sequencing (scRRBS) data on 608 B cells sampled from six healthy B cell samples and 1,230 cells from 11 chronic lymphocytic leukemia (CLL) samples. We developed a likelihood-based criterion to test whether a CpG exhibited ASM, based on the distributions of methylated and unmethylated reads both within and across cells. Applying our likelihood ratio test, 65,998 CpG sites exhibited ASM in healthy B cell samples according to a Bonferroni criterion (p < 8.4 × 10-9), and 32,862 CpG sites exhibited ASM in CLL samples (p < 8.5 × 10-9). We also called ASM at the sample level. To evaluate the accuracy of our method, we called heterozygous variants from the scRRBS data, which enabled variant-based calls of ASM within each cell. Comparing sample-level ASM calls to the variant-based measures of ASM, we observed a positive predictive value of 76%-100% across samples. We observed high concordance of ASM across samples and an overrepresentation of ASM in previously reported imprinted genes and genes with imprinting binding motifs. Our study demonstrates that single-cell bisulfite sequencing is a potentially powerful tool to investigate ASM, especially as studies expand to increase the number of samples and cells sequenced.

A comparative atlas of single-cell chromatin accessibility in the human brain

Recent advances in single-cell transcriptomics have illuminated the diverse neuronal and glial cell types within the human brain. However, the regulatory programs governing cell identity and function remain unclear. Using a single-nucleus assay for transposase-accessible chromatin using sequencing (snATAC-seq), we explored open chromatin landscapes across 1.1 million cells in 42 brain regions from three adults. Integrating this data unveiled 107 distinct cell types and their specific utilization of 544,735 candidate cis-regulatory DNA elements (cCREs) in the human genome. Nearly a third of the cCREs demonstrated conservation and chromatin accessibility in the mouse brain cells. We reveal strong links between specific brain cell types and neuropsychiatric disorders including schizophrenia, bipolar disorder, Alzheimer's disease (AD), and major depression, and have developed deep learning models to predict the regulatory roles of noncoding risk variants in these disorders.

Single-cell DNA methylation and 3D genome architecture in the human brain

Delineating the gene-regulatory programs underlying complex cell types is fundamental for understanding brain function in health and disease. Here, we comprehensively examined human brain cell epigenomes by probing DNA methylation and chromatin conformation at single-cell resolution in 517 thousand cells (399 thousand neurons and 118 thousand non-neurons) from 46 regions of three adult male brains. We identified 188 cell types and characterized their molecular signatures. Integrative analyses revealed concordant changes in DNA methylation, chromatin accessibility, chromatin organization, and gene expression across cell types, cortical areas, and basal ganglia structures. We further developed single-cell methylation barcodes that reliably predict brain cell types using the methylation status of select genomic sites. This multimodal epigenomic brain cell atlas provides new insights into the complexity of cell-type-specific gene regulation in adult human brains.

Differential DNA methylation and changing cell-type proportions as fibrotic stage progresses in NAFLD

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is characterized by changes in cell composition that occur throughout disease pathogenesis, which includes the development of fibrosis in a subset of patients. DNA methylation (DNAm) is a plausible mechanism underlying these shifts, considering that DNAm profiles differ across tissues and cell types, and DNAm may play a role in cell-type differentiation. Previous work investigating the relationship between DNAm and fibrosis in NAFLD has been limited by sample size and the number of CpG sites interrogated.

RESULTS

Here, we performed an epigenome-wide analysis using Infinium MethylationEPIC array data from 325 individuals with NAFLD, including 119 with severe fibrosis and 206 with no histological evidence of fibrosis. After adjustment for latent confounders, we identified 7 CpG sites whose DNAm associated with fibrosis (p < 5.96 × 10^-8). Analysis of RNA-seq data collected from a subset of individuals (N = 56) revealed that gene expression at 288 genes associated with DNAm at one or more of the 7 fibrosis-related CpGs. DNAm-based estimates of cell-type proportions showed that estimated proportions of natural killer cells increased, while epithelial cell proportions decreased with disease stage. Finally, we used an elastic net regression model to assess DNAm as a biomarker of fibrotic stage and found that our model predicted fibrosis with a sensitivity of 0.93 and provided information beyond a model based solely on cell-type proportions.

CONCLUSION

These findings are consistent with DNAm as a mechanism underpinning or marking fibrosis-related shifts in cell composition and demonstrate the potential of DNAm as a possible biomarker of NAFLD fibrosis.

Ten-eleven translocation protein 1 modulates medulloblastoma progression

BACKGROUND

Medulloblastoma (MB) is the most common malignant pediatric brain tumor that originates in the cerebellum and brainstem. Frequent somatic mutations and deregulated expression of epigenetic regulators in MB highlight the substantial role of epigenetic alterations. 5-hydroxymethylcytosine (5hmC) is a highly abundant cytosine modification in the developing cerebellum and is regulated by ten-eleven translocation (TET) enzymes.

RESULTS

We investigate the alterations of 5hmC and TET enzymes in MB and their significance to cerebellar cancer formation. We show total abundance of 5hmC is reduced in MB, but identify significant enrichment of MB-specific 5hmC marks at regulatory regions of genes implicated in stem-like properties and Nanog-binding motifs. While TET1 and TET2 levels are high in MBs, only knockout of Tet1 in the smoothened (SmoA1) mouse model attenuates uncontrolled proliferation, leading to a favorable prognosis. The pharmacological Tet1 inhibition reduces cell viability and platelet-derived growth factor signaling pathway-associated genes.

CONCLUSIONS

These results together suggest a potential key role of 5hmC and indicate an oncogenic nature for TET1 in MB tumorigenesis, suggesting it as a potential therapeutic target for MBs.

Age-related DNA hydroxymethylation is enriched for gene expression and immune system processes in human peripheral blood

DNA methylation (DNAm) has a well-established association with age in many tissues, including peripheral blood mononuclear cells (PBMCs). Compared to DNAm, the closely related epigenetic modification known as DNA hydroxymethylation (DNAhm) was much more recently discovered in mammals. Preliminary investigations have observed a positive correlation between gene body DNAhm and cis-gene expression. While some of these studies have observed an association between age and global DNAhm, none have investigated region-specific age-related DNAhm in human blood samples. In this study, we investigated DNAhm and gene expression in PBMCs of 10 young and 10 old, healthy female volunteers. Thousands of regions were differentially hydroxymethylated in the old vs. young individuals in gene bodies, exonic regions, enhancers, and promoters. Consistent with previous work, we observed directional consistency between age-related differences in DNAhm and gene expression. Further, age-related DNAhm and genes with high levels of DNAhm were enriched for immune system processes which may support a role of age-related DNAhm in immunosenescence.

Non-linear patterns in age-related DNA methylation may reflect CD4+ T cell differentiation

DNA methylation (DNAm) is an important epigenetic process involved in the regulation of gene expression. While many studies have identified thousands of loci associated with age, few have differentiated between linear and non-linear DNAm trends with age. Non-linear trends could indicate early- or late-life gene regulatory processes. Using data from the Illumina 450K array on 336 human peripheral blood samples, we identified 21 CpG sites that associated with age (P<1.03E-7) and exhibited changing rates of DNAm change with age (P<1.94E-6). For 2 of these CpG sites (cg07955995 and cg22285878), DNAm increased with age at an increasing rate, indicating that differential DNAm was greatest among elderly individuals. We observed significant replication for both CpG sites (P<5.0E-8) in a second set of peripheral blood samples. In 8 of 9 additional data sets comprising samples of monocytes, T cell subtypes, and brain tissue, we observed a pattern directionally consistent with DNAm increasing with age at an increasing rate, which was nominally significant in the 3 largest data sets (4.3E-15<P<0.039). cg07955995 and cg22285878 reside in the promoter region of KLF14, which encodes a protein involved in immune cell differentiation via the repression of FOXP3. These findings may suggest a possible role for cg07955995 and cg22285878 in immunosenescence.

Global epigenomic reconfiguration during mammalian brain development

DNA methylation is implicated in mammalian brain development and plasticity underlying learning and memory. We report the genome-wide composition, patterning, cell specificity, and dynamics of DNA methylation at single-base resolution in human and mouse frontal cortex throughout their lifespan. Widespread methylome reconfiguration occurs during fetal to young adult development, coincident with synaptogenesis. During this period, highly conserved non-CG methylation (mCH) accumulates in neurons, but not glia, to become the dominant form of methylation in the human neuronal genome. Moreover, we found an mCH signature that identifies genes escaping X-chromosome inactivation. Last, whole-genome single-base resolution 5-hydroxymethylcytosine (hmC) maps revealed that hmC marks fetal brain cell genomes at putative regulatory regions that are CG-demethylated and activated in the adult brain and that CG demethylation at these hmC-poised loci depends on Tet2 activity.

Impact of lymphocyte and monocyte recovery on the outcomes of allogeneic hematopoietic SCT with fludarabine and melphalan conditioning

We have recently shown that lymphocyte and monocyte recovery by day +100 are associated with survival post myeloablative allogeneic hematopoietic transplant for acute leukemia. We hypothesized that lymphocyte and monocyte recovery would have a similar impact on survival in the reduced intensity setting. To test this hypothesis, we analyzed clinical data from 118 consecutive fludarabine/melphalan-conditioned patients by correlating peripheral blood absolute lymphocyte counts and monocyte counts (ALC and AMC, respectively) at days +15, +30, +60 and +100 with the outcomes. Multivariate analysis revealed that day +100 AMC (risk ratio (RR) 0.22, 95% confidence interval (CI) 0.07-0.73, P=0.01) and mild chronic GVHD (RR 0.09, 95% CI 0.005-0.43, P=0.008) were independently associated with survival. To explore whether the patterns of lymphocyte and monocyte recovery had a prognostic value, we performed unsupervised hierarchical clustering on the studied hematopoietic parameters and identified three patient clusters, A-C. Patient clusters A and B both had improved OS compared with cluster C (77.8 months vs not reached vs 22.3 months, respectively, P<0.001). No patient in cluster C had a day +100 AMC >300. Both severe acute GVHD and relapse occurred more frequently in cluster C. Our data suggest that patients with low AMC by day +100 post fludarabine/melphalan-conditioned allogeneic hematopoietic SCT may be at risk for poor outcomes.

Knee in early juvenile rheumatoid arthritis: MR imaging findings

PURPOSE

To determine the magnetic resonance (MR) imaging findings in the knee in early juvenile rheumatoid arthritis.

MATERIALS AND METHODS

MR imaging (1.5 T) was performed in the more symptomatic knee in 30 children with juvenile rheumatoid arthritis with a symptom duration 1 year or less. Conventional, fast spin-echo, three-dimensional gradient-echo, and gadolinium-enhanced T1-weighted images were assessed. Two radiologists independently read the images, and a third resolved disagreements. These images were compared with knee radiographs in 27 children.

RESULTS

Mean maximal synovial thickness was 4.8 mm +/- 2.4 (SD). Mean synovial volume was 15.4 mL +/- 10.8. Suprapatellar joint effusions were seen in 26 (87%) of 30 knees, meniscal hypoplasia in 11 (37%) of 30 knees, and abnormal epiphyseal marrow in eight (27%) of 30 knees. Three knees had articular cartilage contour irregularity, fissures, and/or thinning. One knee had a bone erosion. Knee radiographs showed suprapatellar fullness in 78% of the knees, joint space narrowing in one knee, and no bone abnormalities.

CONCLUSION

Synovial hypertrophy and joint effusions are the most frequent MR imaging findings of knees in early juvenile rheumatoid arthritis. Early in the disease, radiographically occult cartilage and bone erosions are uncommonly seen at MR imaging. The potential relationship of synovitis to cartilage abnormalities deserves further study.

Absent peritoneal fluid on screening trauma ultrasonography in children: a prospective comparison with computed tomography

BACKGROUND

Although the accuracy of focused abdominal sonography for trauma (FAST) in adults has been demonstrated, results of this technique in children have been conflicting with few comparisons against computed tomography (CT), the imaging gold standard.

METHODS

A total of 160 hemodynamically stable pediatric trauma victims referred for abdominal CT initially underwent rapid screening sonography looking for free fluid. Both studies were interpreted in blinded fashion.

RESULTS

Forty-four of the 160 patients had an intraabdominal injury on CT, 24 (55%) of which had normal screening sonography. Fifteen of the 44 (34%) had no free fluid on either modality. Accuracy of sonography compared with CT was 76% with a negative predictive value 81%.

CONCLUSIONS

Sonography for free fluid alone is not reliable to exclude blunt intraabdominal injury in hemodynamically stable children given the considerable percentage of injured patients without free fluid. J Pediatr Surg 36:565-569.

Pediatric peripherally inserted central catheters: complication rates related to catheter tip location

OBJECTIVE

To compare complication rates between central venous catheter tip location and noncentral tip location after peripherally inserted central catheter (PICC) placement in children.

METHODS

Between 1994 and 1998, data from all children who underwent PICC placement were analyzed. Patient demographics, catheter characteristics, catheter duration, infusate composition, and catheter complications were entered prospectively into a computerized database. Catheter tip locations were determined by fluoroscopy and were defined as central if they resided in the superior vena cava, right atrium, or high inferior vena cava at or above the level of the diaphragm, and as noncentral if located elsewhere. Differences in complication rates between the central and noncentral groups were analyzed.

RESULTS

Data from a total of 1266 PICCs were analyzed from 1053 patients with a mean age of 6.49 +/-.2 years (range: 0-45.0 years). Of the 1266 PICCs, 1096 (87%) were central in tip location, and 170 (13%) were noncentral in tip location. The central group had 42 complications of 1096 catheters (3.8%), while the noncentral group had 49 complications of 170 catheters (28.8%). Controlling for patient age, catheter size, gender, and catheter duration with a logistic regression model, there remained a statistically significant increased likelihood of complication in the noncentral group versus the central group (adjusted odds ratio: 8.28; 95% confidence interval: 5.11-13.43).

CONCLUSIONS

Centrally placed catheter tips are associated with fewer complications than are noncentrally placed catheter tips. Clinicians should ensure that catheter tips reside centrally after PICC placement in infants and children.

Demystifying the hospital information system/radiology information system integration process

Most organizations planning to implement picture archiving and communications systems (PACS) are aware of the need to integrate the hospital information system (HIS) and radiology information system (RIS) with the PACS, yet few are acutely aware of the challenges associated with this requirement. This report highlights the results of collaborative efforts between Children's Hospital Medical Center-Cincinnati (CHMC) applications specialists with expertise in the HIS and CHMC information system, radiology staff familiar with the enterprise and radiology workflow and data flow requirements; and General Electric integration engineers familiar with the SMS HIS and RIS, and GE PACS. CHMC received Board approval, including full funding of the entire PACS project, in October 1998. An aggressive time frame for installation was established, as CHMC's PACS leadership committed to the selection, design, and implementation of PACS and computed radiography (CR) within 18 to 20 months. CHMC selected GE (Milwaukee, WI) as its PACS vendor in July 1999, and began its implementation in November 1999. We will present the four-stage integration process undertaken at CHMC: (1) planning the integration effort, (2) designing the Interface, (3) building the interface, and (4) testing the Interface.

Effect of surrogate tolerogenesis on the vascular rejection of pig heart xenografts

BACKGROUND

Organ xenografts are fulminantly rejected by antibody-mediated vascular rejection. Surrogate tolerogenesis (ST), the induction of tolerance within the donor, is effective with aorta xenografts. This preliminary study assesses the effect of ST on preformed antibodies and rejection of porcine heart xenografts.

METHODS

Tolerance to the donor pig was induced by infusing recipient marrow into fetal pigs. Later, pig splenocytes were transfused and heterotopic pig hearts transplanted using chimeric or nonchimeric pigs. Anti-pig antibodies were assessed.

RESULTS

With ST alone, xenografts developed cellular rejection at 4-6 days, whereas control grafts developed vascular rejection at 3-4 days (cellular vs. vascular, P<0.03). There was a reduction in preformed antibodies (P<0.03). ST combined with moderate cyclosporine prevented rejection at 9+ and 25 days in sensitized recipients compared with vascular rejection at 0.5-2 days for controls (P<0.07).

CONCLUSIONS

ST seems to provide protection against vascular rejection. The cellular rejection seems sensitive to cyclosporine.

Imaging and radiological interventional techniques for gastrointestinal bleeding in children

Causes of pediatric gastrointestinal (GI) bleeding in children are numerous. The role of radiology in defining associated pathology, pinpointing the bleeding site, and intervening to control hemorrhage is discussed here. Barium studies, computed tomography (CT), and magnetic resonance imaging (MRI) each may play a role in identifying the underlying pathology associated with the bleeding. The exact source of bleeding may be localized by means of nuclear scintigraphy as well as selective angiography. In cases of life-threatening or persistent hemorrhage, once a bleeding source is identified, the interventional radiologist may offer percutaneous transcatheter therapy with selective intraarterial vasopressin infusion or embolotherapy.

Peripherally inserted central venous catheters: success of scalp-vein access in infants and newborns

The authors assessed the feasibility of placing peripherally inserted central venous catheters via scalp veins in infants and newborns. In 60 newborns and infants, aged 3 days to 10 months, placement of 62 2-F peripherally inserted central venous catheters was attempted with scalpvein access. The tip location was central in 30 of the 62 catheters (48%) and long peripheral intravenous in 17 (27%); access failed in 15 (24%). Scalp-vein access for peripherally inserted central venous catheters offers a safe and effective alternative route for gaining central venous access in infants and newborns.

Tarsal coalition: a blinded comparison of MRI and CT

OBJECTIVE

To determine how well MRI can detect tarsal coalition compared with CT, the current imaging standard.

MATERIALS AND METHODS

Coronal and axial CT and MRI were performed within 3 weeks of each other on 40 feet in 20 consecutive patients referred with symptoms of possible tarsal coalition. Scans were read independently in blinded fashion by different imagers. Coalitions were either complete (osseous) or incomplete (non-osseous). Results were compared with available surgical data and clinical follow-up.

RESULTS

Both modalities prospectively identified 15 coalitions (9 patients) and each missed 1 calcaneonavicular coalition. Twenty-three of the remaining 24 feet were negative for coalition on both CT and MRI. An atypical incomplete talocalcaneal coalition seen on CT was not identified prospectively on MRI.

CONCLUSION

MRI is very good for detecting tarsal coalition and has a high rate of agreement with CT, the imaging "gold standard." When clinical suspicion for coalition is high, CT remains a more cost-effective diagnostic modality. If other causes for ankle pain are also entertained, MRI can be performed and provide nearly equivalent diagnostic accuracy for detecting tarsal coalition.

Fibrolipoma of the median nerve: MRI

The MRI findings of two patients with fibrolipoma of median nerve are presented. A characteristic 'cable-like' appearance of the tumour was present on T1-weighted images. Unique imaging features of these cases included extension of the lesion into the radial digital nerve of the index finger in case 1 and extraneuronal extension of a exophytic fatty mass from the median nerve into the thenar eminence in case 2.

MR imaging of biliary cysts in children with biliary atresia: clinical associations and pathologic correlation

OBJECTIVE

We used MR imaging to determine the prevalence of biliary cysts in children with end-stage biliary atresia and evaluated the association of cysts with cholangitis, choleretic therapy, portoenterostomy, biochemical abnormalities, and MR findings of end-stage liver disease. The MR features of these cysts were correlated with their gross and histopathologic appearances.

MATERIALS AND METHODS

We retrospectively reviewed 48 MR studies, clinical history, and laboratory data of 44 consecutive children with biliary atresia.

RESULTS

MR images showed cysts in eight patients (18%). Cysts were statistically (p < .04) more common in patients who had a history of cholangitis, but were not associated with choleretic therapy or portoenterostomy surgery. Cysts were not statistically correlated with abnormalities in hepatic biochemical function or MR features of end-stage liver disease. Four livers with cysts were available for histopathologic study. Cysts were filled with bile, and most had an epithelial lining, consistent with a biliary origin. The epithelium was frequently ulcerated, accompanied by periportal extravasation of bile and inflammation. These findings suggest chronic obstruction with microscopic perforation.

CONCLUSION

Biliary cysts are common in biliary atresia and may be related to previous episodes of cholangitis with attendant obstruction of biliary radicles. The presence of these cysts did not correlate with hepatic function, portoenterostomy surgery, or the extent of liver disease.

Caval thrombolysis in neonates using low doses of recombinant human tissue-type plasminogen activator

Four neonates suffered caval thrombosis secondary to indwelling central catheters. Dissolution of thrombus with recombinant tissue plasminogen activator (rt-PA) as a low-dose infusion (0.05 mg/kg/hr) directly into thrombus was successful in three patients. rt-PA was ceased after three days in the fourth patient because of catheter malposition. Thrombolysis was achieved between four and ten days. Rethrombosis occurred in one patient despite heparin prophylaxis. Plasminogen activator infusions were titrated to maintain fibrinogen levels above 100 mg/dl. One neonate suffered an intracranial haemorrhage. Regional rt-PA is an alternative to thrombectomy in critically ill neonates.

Prothrombinex-induced thrombosis and its management with regional plasminogen activator in hepatic failure

Fulminant hepatic failure causes a bleeding diathesis as a result of impaired synthesis of hepatic clotting factors, thrombocytopenia, fibrinolysis and disseminated intravascular coagulation. Administration of clotting factor concentrates can cause thrombosis in patients with acute hepatic failure. Regional infusion of recombinant tissue-type plasminogen activator may be used to induce local thrombolysis. A case report of a five-year-old child is presented and the literature is reviewed.

Vesicoureteric reflux in children: prediction with color Doppler imaging. Work in progress

Unlike gray-scale sonography, color Doppler ultrasonography allows reliable visualization of the ureteric jet phenomenon. A study was undertaken to determine whether any measurable parameter predicts the presence of vesicoureteric reflux. Measurements of mean urine jet velocity, longitudinal angle, transverse angle, and distance of the origin of the jet from the midline of the bladder were obtained on 31 infants and children (62 ureters) with a proved urinary tract infection. Of these measurements, only the distance of the ureteric orifice from the midline of the bladder was found to correlate with vesicoureteric reflux (mean distance in the reflux group, 10.25 mm +/- 2.40 (standard deviation [SD]); in the nonreflux group, 7.98 mm +/- 2.40 [P = .004]). The authors conclude that the more laterally positioned the ureteric orifice, the more likely it is to reflux. Color Doppler ultrasound measurement of the laterality of the ureteric orifice may be useful for predicting which children with a urinary tract infection would benefit from voiding cystourethrography.

Complex infantile and congenital hip dislocation: assessment with MR imaging

Twenty-five magnetic resonance hip studies were performed on 19 infants with congenital hip dislocation. These patients had a poor initial treatment response, a teratologic dislocation, or a late presentation. Detailed images of single hips obtained with small surface coils resulted in excellent visualization of all the clinically important soft-tissue and cartilaginous structures of the hip. No other imaging modality demonstrates all of these structures simultaneously.

Pediatric musculoskeletal magnetic resonance imaging

MRI has demonstrated clinical applicability and improved diagnostic capability in the musculoskeletal system to a degree rivaling its success in the neurologic system. For certain regions such as the joints, the superficial nature of these structures is ideal for the application of localized radiofrequency coils, enabling considerably improved signal, spatial resolution, and detectable contrast. The multiplanar capability is often invaluable in assessing such regions as the weight-bearing surfaces of the hips. It has been shown to be the most sensitive single test for diagnosing avascular necrosis, and has yielded very high resolution images of the internal architecture of the joints and soft tissues in an entirely noninvasive manner and without the need for the administration of exogenous contrast agents. Short TE images are quite useful in evaluating fatty background regions of interest, such as the bone marrow and subcutaneous tissue, whereas long TR and TE studies are frequently more suitable for soft tissue pathology. The lack of ionizing radiation and the continued failure of intensive research to disclose any deleterious effects at the levels used for clinical diagnostic imaging make this tool especially appealing for application to the pediatric population. With the continual development of new pulsing sequences, contrast agents, and further advances in imaging/spectroscopic correlation, magnetic resonance imaging of the musculoskeletal system is ensured of a solid role in the clinical diagnostic evaluation of the pediatric population.

The seasonal dynamics of leaf resin, nitrogen, and herbivore damage in Eriodictyon californicum and their parallels in Diplacus aurantiacus

The chaparral shrub Eriodictyon californicum produces a flavonoid leaf resin with a chemically similar composition to that previously reported for the sympatric shrub Diplacus aurantiacus. We determined the phenology, resin content, and nitrogen content of Eriodictyon leaves and the leaf area lost to herbivores. Nitrogen content and resin content were both negatively correlated with leaf age at each sampling date, but nitrogen decreased during the growing season while resin increased. The fraction of leaf area lost during the growing season averaged less than 7% and was highest on the oldest leaves. The seasonal pattern of resin production in Eriodictyon corresponds to that in Diplacus, indicating that the similar environments of Eriodyctyon and Diplacus have led to convergent leaf resins. This convergence in these two plants has implications for chemicals of similar function in other chaparral shrubs.

Chitosan: a new hemostatic

Chitosan is a deacetylated derivative of arthropod chitin. We found that it formed a coagulum in contact with defibrinated blood, heparinized blood, and washed red cells. When knitted DeBakey grafts were treated with chitosan, they were impermeable to blood. Examination of these grafts at 24 hours revealed no rebleeding. Examination at one, two, three, and four months showed the grafts to be encased in smooth muscle with a living endothelial lining and an abundant vasa vasorum. Control grafts showed the usual fibrous healing.

Late objective assessment of venous value surgery

To evaluate the contribution of an isolated femoral venous value to venous hemodynamics, ten patients (12 limbs) who had undergone femoral valve transposition without saphenous vein stripping or ligation of perforators were followed up for 12 to 18 months after surgery. Ascending and descending venography were performed to document anatomic patency. Dynamic venous pressures and venous refilling times were recorded to evaluate muscle pump function and cutaneous congestion, respectively. Signs of venous hypertension and the need for elastic support were noted. No patient attained normal venous pressure at any time after surgery. Normalization of venous refilling time was transient: nine of 12 limbs had reverted to preoperative abnormal levels at 12 to 18 months and all required elastic support. Femoral value reconstruction performed alone for venous stasis is not sufficient. In postthrombotic venous ulcer, incompetent calf perforators remain a central problem.

Assessment of a modified technique of distal splenorenal shunting

Warren's distal splenorenal shunt has been effective in treatment of recurrent variceal hemorrhage. To simplify the operative procedure, two alterations in the technique were used in this study. The first was to approach the splenic and renal veins simultaneously through a single inframesocolonic retroperitoneal incision in the plane of the pancreatic fusion fossa. The second was abandonment of the portoazygos disconnection. Since 1974, twenty-nine patients have undergone this modified operation. The patients ranged in age from 21 to 76 years. Fourteen patients had alcoholic cirrhosis, 13 had nonalcoholic cirrhosis, and the etiology was unknown in two. There were 14 Child's class A patients, 12 class B, and three class C. Significant ascites was present at operation in seven patients. Hepatofugal flow was demonstrated angiographically in four patients. The follow-up period ranged from 6 months to 6 years; 19 patients were followed up for 1 year or longer. There were three early postoperative deaths (10.3%), and one patient died 2 months postoperatively. Recurrent variceal bleeding was seen early in one patient and late (2 months) in another. Only one of the surviving patients developed encephalopathy. Technical modification to simplify performance of the distal splenorenal shunt did not compromise the results of the operation. However, four of seven patients with ascites died either immediately or early after the procedure, and two of these four patients also had hepatofugal flow. Ascites and hepatofugal flow may adversely influence the results of the operation.

Respiratory distress in newborn infants: contribution to current mortality

A review of infants with respiratory distress born at the Mercy Maternity Hospital, Melbourne, during the years from 1975 to 1977 showed that live-born infants totalled 13304; 288 (2.2%) had respiratory distress. Of the 13304 infants, 197 died; 75 (38.1%) were infants with respiratory distress. Hyaline membrane disease was the cause of the respiratory distress in 153 (53.1%) infants; 58 (37.9%) infants with that problem died. Hyaline membrane disease accounted for 58 (77.3%) of the 75 deaths in infants with respiratory distress. Assisted ventilation was required in 147 (51.0%) infants with respiratory distress and chronic complications of its use acceptable as bronchopulmonary dysplasia occurred in only 8.2% and retrolental fibroplasia in only 3.4%; it is suggested that assisted ventilation was commenced too late in 23 (34.0%) infants. Twenty-eight (42.0%) infants with respiratory distress died despite correct usage of assisted ventilation. This number attests to the dangers of prematurity; hence the decision to deliver an infant prematurely should not be taken lightly.

IgG antibodies to phosphorylcholine exhibit more diversity than their IgM counterparts

An amino acid sequence analysis of the N-terminal immunoglobulin heavy and light chain variable regions (VH and VL) from 16 hybridoma proteins which bind phosphorylcholine as well as the complete sequence analysis of 9 of these VH regions is presented. There seem to be more VH regions participating in the phosphorylcholine response than can be encoded directly by germ-line VH gene segments. Moreover, the V regions from IgG antibodies are considerably more variable than those from their IgM counterparts. These observations raise the possibility that a somatic mechanism for V region diversification produces greater diversity in IgG than in IgM antibodies.

Recognition and surgical management of patent but hemodynamically failed arterial grafts

During a five-year period, 34 patients had persistence or recurrence of abnormal hemodynamic measurements in limbs after arterial reconstruction depsite graft patency documented by arteriography. Initial operations included aortofemoral (four), femorofemoral (ten), femoropopliteal (18), and femorotibial (two) bypass. Immediate postoperative hemodynamic failure was documented in seven patients by a mean ankle/brachial systolic pressure index increase of only 0.05 +/- 0.04 following the initial reconstruction. The remaining 27 patients had delayed hemodynamic failure; mean increase in ankle pressure was only 0.06 +/- 0.05 from the preoperative period until time of detection of failure (average duration 2.5 years). In all 34 patients, arteriography demonstrated patency of the initial graft. In conjunction with the vascular laboratory examination, arteriography identified the cause of hemodynamic failure to be inadequate inflow in 10 patients, poor outflow in 16, combined inflow and outflow obstruction in one, and graft stenosis in seven. Unrecognized stenosis in areas proximal (two patients) and distal (three patients) to the bypass emphasized the importance of complete biplanar arteriography before initial operation. Reoperation was successful in correcting hemodynamic failure in 26 patients (76.5%) with a mean increase in ankle index of 0.41 +/- 0.15. Operation was technically not feasible in four patients and was not performed in another four patients because of concomitant medical problems. In two of these patients, progression to graft thrombosis was documented. The results of this study suggest that early objective recognition of an anatomically patent but hemodynamically failed graft is possible by frequent noninvasive testing. Prompt investigation by arteriography defines the cause and location of failure, and reoperation restores normal limb hemodynamics. Most important, reoperation permits salvage of the majority of these patent grafts prior to ultimate failure from thrombosis.

Boomslang bite with haemorrhage and activation of complement by the alternate pathway

A case of Boomslang poisoning is reported for the first time in North West Europe. The treatment is described and activation of complement by the alternate pathway in vivo was shown.