Assays of Monitoring and Measuring Autophagic Flux for iPSC-Derived Human Neurons and Other Brain Cell Types

Autophagy is a highly conserved, cytoprotective, catabolic process induced in response to conditions of cellular stress and nutrient deprivation. It is responsible for the degradation of large intracellular substrates such as misfolded or aggregated proteins and organelles. This self-degradative mechanism is crucial for proteostasis in post-mitotic neurons, requiring its careful regulation. Due to its homeostatic role and the implications, it has for certain disease pathologies, autophagy has become a growing area of research. We describe here two assays that can be used as part of a tool kit for measuring autophagy-lysosomal flux in human iPSC-derived neurons.One way to measure autophagic flux is through a western blotting assay, which can be used to analyze two important autophagy proteins: microtubule-associated protein 1 light chain 3 (LC3) and p62. In this chapter, we describe a western blotting assay for use in human iPSC neurons that can be used to quantify these two proteins of interest to measure autophagic flux.In addition to conventional western blotting techniques, more sophisticated tools have come available to readout autophagic flux in a sensitive and high-throughput manner. In the latter portion of this chapter, we describe a flow cytometry assay which utilizes a pH-sensitive fluorescent reporter which can also be used to measure autophagic flux.

Structural variants shape driver combinations and outcomes in pediatric high-grade glioma

We analyzed the contributions of structural variants (SVs) to gliomagenesis across 179 pediatric high-grade gliomas (pHGGs). The most recurrent SVs targeted MYC isoforms and receptor tyrosine kinases (RTKs), including an SV amplifying a MYC enhancer in 12% of diffuse midline gliomas (DMG), indicating an underappreciated role for MYC in pHGG. SV signature analysis revealed that tumors with simple signatures were TP53 wild type (TP53WT) but showed alterations in TP53 pathway members PPM1D and MDM4. Complex signatures were associated with direct aberrations in TP53, CDKN2A and RB1 early in tumor evolution and with later-occurring extrachromosomal amplicons. All pHGGs exhibited at least one simple-SV signature, but complex-SV signatures were primarily restricted to subsets of H3.3K27M DMGs and hemispheric pHGGs. Importantly, DMGs with complex-SV signatures were associated with shorter overall survival independent of histone mutation and TP53 status. These data provide insight into the impact of SVs on gliomagenesis and the mechanisms that shape them.

HGG-60. Structural variants shape driver combinations and outcomes in pediatric high-grade glioma

Pediatric high-grade gliomas (pHGGs), encompassing hemispheric and diffuse midline gliomas (DMGs), remain a devastating disease. The last decade has revealed oncogenic drivers including single nucleotide variants (SNVs) in histones. However, the contribution of structural variants (SVs) to gliomagenesis has not been systematically explored due to limitations in early SV analysis approaches. Using SV algorithms, we recently created, we analyzed SVs in whole-genome sequences of 179 pHGGs including a novel cohort of treatment naïve samples–the largest WGS cohort assembled in adult or pediatric glioma. The most recurrent SVs targeted MYC isoforms and receptor tyrosine kinases, including a novel SV amplifying a MYC enhancer in the lncRNA CCDC26 in 12% of DMGs and revealing a more central role for MYC in these cancers than previously known. Applying de novo SV signature discovery, we identified five signatures including three (SVsig1-3) involving primarily simple SVs, and two (SVsig4-5) involving complex, clustered SVs. These SV signatures associated with genetic variants that differed from what was observed for SV signatures in other cancers, suggesting different links to underlying biology. Tumors with simple SV signatures were TP53 wild-type but were enriched with alterations in TP53 pathway members PPM1D and MDM4. Complex signatures were associated with direct aberrations in TP53, CDKN2A, and RB1 early in tumor evolution, and with extrachromosomal amplicons that likely occurred later. All pHGGs exhibited at least one simple SV signature but complex SV signatures were primarily restricted to subsets of H3.3K27M DMGs and hemispheric pHGGs. Importantly, DMGs with the complex SV signatures SVsig4-5 were associated with shorter overall survival independent of histone type and TP53 status. These data inform the role and impact of SVs in gliomagenesis and mechanisms that shape them.

CloneSifter: enrichment of rare clones from heterogeneous cell populations

BACKGROUND

Many biological processes, such as cancer metastasis, organismal development, and acquisition of resistance to cytotoxic therapy, rely on the emergence of rare sub-clones from a larger population. Understanding how the genetic and epigenetic features of diverse clones affect clonal fitness provides insight into molecular mechanisms underlying selective processes. While large-scale barcoding with NGS readout has facilitated cellular fitness assessment at the population level, this approach does not support characterization of clones prior to selection. Single-cell genomics methods provide high biological resolution, but are challenging to scale across large populations to probe rare clones and are destructive, limiting further functional analysis of important clones.

RESULTS

Here, we develop CloneSifter, a methodology for tracking and enriching rare clones throughout their response to selection. CloneSifter utilizes a CRISPR sgRNA-barcode library that facilitates the isolation of viable cells from specific clones within the barcoded population using a sequence-specific retrieval reporter. We demonstrate that CloneSifter can measure clonal fitness of cancer cell models in vitro and retrieve targeted clones at abundance as low as 1 in 1883 in a heterogeneous cell population.

CONCLUSIONS

CloneSifter provides a means to track and access specific and rare clones of interest across dynamic changes in population structure to comprehensively explore the basis of these changes.

Generation of Human Neurons and Oligodendrocytes from Pluripotent Stem Cells for Modeling Neuron-Oligodendrocyte Interactions

In Alzheimer's disease (AD) and other neurodegenerative disorders, oligodendroglial failure is a common early pathological feature, but how it contributes to disease development and progression, particularly in the gray matter of the brain, remains largely unknown. The dysfunction of oligodendrocyte lineage cells is hallmarked by deficiencies in myelination and impaired self-renewal of oligodendrocyte precursor cells (OPCs). These two defects are caused at least in part by the disruption of interactions between neuron and oligodendrocytes along the buildup of pathology. OPCs give rise to myelinating oligodendrocytes during CNS development. In the mature brain cortex, OPCs are the major proliferative cells (comprising ~5% of total brain cells) and control new myelin formation in a neural activity-dependent manner. Such neuron-to-oligodendrocyte communications are significantly understudied, especially in the context of neurodegenerative conditions such as AD, due to the lack of appropriate tools. In recent years, our group and others have made significant progress to improve currently available protocols to generate functional neurons and oligodendrocytes individually from human pluripotent stem cells. In this manuscript, we describe our optimized procedures, including the establishment of a co-culture system to model the neuron-oligodendrocyte connections. Our illustrative results suggest an unexpected contribution from OPCs/oligodendrocytes to the brain amyloidosis and synapse integrity and highlight the utility of this methodology for AD research. This reductionist approach is a powerful tool to dissect the specific hetero-cellular interactions out of the inherent complexity inside the brain. The protocols we describe here are expected to facilitate future studies on oligodendroglial defects in the pathogenesis of neurodegeneration.

Neuronal differentiation and cell-cycle programs mediate response to BET-bromodomain inhibition in MYC-driven medulloblastoma

BET-bromodomain inhibition (BETi) has shown pre-clinical promise for MYC-amplified medulloblastoma. However, the mechanisms for its action, and ultimately for resistance, have not been fully defined. Here, using a combination of expression profiling, genome-scale CRISPR/Cas9-mediated loss of function and ORF/cDNA driven rescue screens, and cell-based models of spontaneous resistance, we identify bHLH/homeobox transcription factors and cell-cycle regulators as key genes mediating BETi's response and resistance. Cells that acquire drug tolerance exhibit a more neuronally differentiated cell-state and expression of lineage-specific bHLH/homeobox transcription factors. However, they do not terminally differentiate, maintain expression of CCND2, and continue to cycle through S-phase. Moreover, CDK4/CDK6 inhibition delays acquisition of resistance. Therefore, our data provide insights about the mechanisms underlying BETi effects and the appearance of resistance and support the therapeutic use of combined cell-cycle inhibitors with BETi in MYC-amplified medulloblastoma.

Clinical targeted exome-based sequencing in combination with genome-wide copy number profiling: precision medicine analysis of 203 pediatric brain tumors

Background

Clinical genomics platforms are needed to identify targetable alterations, but implementation of these technologies and best practices in routine clinical pediatric oncology practice are not yet well established.

Methods

Profile is an institution-wide prospective clinical research initiative that uses targeted sequencing to identify targetable alterations in tumors. OncoPanel, a multiplexed targeted exome-sequencing platform that includes 300 cancer-causing genes, was used to assess single nucleotide variants and rearrangements/indels. Alterations were annotated (Tiers 1-4) based on clinical significance, with Tier 1 alterations having well-established clinical utility. OncoCopy, a clinical genome-wide array comparative genomic hybridization (aCGH) assay, was also performed to evaluate copy number alterations and better define rearrangement breakpoints.

Results

Cancer genomes of 203 pediatric brain tumors were profiled across histological subtypes, including 117 samples analyzed by OncoPanel, 146 by OncoCopy, and 60 tumors subjected to both methodologies. OncoPanel revealed clinically relevant alterations in 56% of patients (44 cancer mutations and 20 rearrangements), including BRAF alterations that directed the use of targeted inhibitors. Rearrangements in MYB-QKI, MYBL1, BRAF, and FGFR1 were also detected. Furthermore, while copy number profiles differed across histologies, the combined use of OncoPanel and OncoCopy identified subgroup-specific alterations in 89% (17/19) of medulloblastomas.

Conclusion

The combination of OncoPanel and OncoCopy multiplex genomic assays can identify critical diagnostic, prognostic, and treatment-relevant alterations and represents an effective precision medicine approach for clinical evaluation of pediatric brain tumors.

SvABA: genome-wide detection of structural variants and indels by local assembly

Structural variants (SVs), including small insertion and deletion variants (indels), are challenging to detect through standard alignment-based variant calling methods. Sequence assembly offers a powerful approach to identifying SVs, but is difficult to apply at scale genome-wide for SV detection due to its computational complexity and the difficulty of extracting SVs from assembly contigs. We describe SvABA, an efficient and accurate method for detecting SVs from short-read sequencing data using genome-wide local assembly with low memory and computing requirements. We evaluated SvABA's performance on the NA12878 human genome and in simulated and real cancer genomes. SvABA demonstrates superior sensitivity and specificity across a large spectrum of SVs and substantially improves detection performance for variants in the 20–300 bp range, compared with existing methods. SvABA also identifies complex somatic rearrangements with chains of short (<1000 bp) templated-sequence insertions copied from distant genomic regions. We applied SvABA to 344 cancer genomes from 11 cancer types and found that short templated-sequence insertions occur in ∼4% of all somatic rearrangements. Finally, we demonstrate that SvABA can identify sites of viral integration and cancer driver alterations containing medium-sized (50–300 bp) SVs.

MYB-QKI rearrangements in angiocentric glioma drive tumorigenicity through a tripartite mechanism

Angiocentric gliomas are pediatric low-grade gliomas (PLGGs) without known recurrent genetic drivers. We performed genomic analysis of new and published data from 249 PLGGs including 19 Angiocentric Gliomas. We identified MYB-QKI fusions as a specific and single candidate driver event in Angiocentric Gliomas. In vitro and in vivo functional studies show MYB-QKI rearrangements promote tumorigenesis through three mechanisms: MYB activation by truncation, enhancer translocation driving aberrant MYB-QKI expression, and hemizygous loss of the tumor suppressor QKI. This represents the first example of a single driver rearrangement simultaneously transforming cells via three genetic and epigenetic mechanisms in a tumor.

Erdheim-Chester disease: a rare cause of acute renal failure

Erdheim-Chester disease (ECD) is a rare systemic histiocytic infiltrative disease of unknown aetiology. In radiology it is characterized by symmetrical sclerotic bone lesions predominantly affecting the diaphyses and metaphyses of long bones. Perivascular fibrosis has been reported in the literature as being a feature of this disease and we report one such case that presented with an encased aorta and renal arteries leading to acute renal failure. The diagnosis of ECD was delayed until a biopsy of the retroperitoneal infiltrate was performed. Further imaging with fluorine 18 deoxyglucose positron emission tomography, bone scintigraphy, plain films of the long bones and CT of the chest, abdomen and pelvis were performed to assess the extent of the patient's systemic disease involvement. To our knowledge, this is the first reported case of ECD presenting with acute renal failure secondary to bilateral occlusion of the renal arteries.

A novel assay for fungal ketol-isomerase activity

2-Deoxy-D-glucose-6-phosphate ketol-isomerase (EC 2.6.1.16) forms glucosamine-6-phosphate and glutamate from fructose-6-phosphate and glutamine and plays an important role in chitin synthesis in fungi. We have established a new assay for fungal ketol-isomerase activity that is amenable to high throughput screening to identify enzyme inhibitors. Aspergillus fumigatus crude lysate was incubated with substrates and after incubation, reactions were terminated. Glutamate dehydrogenase, nitro blue tetrazolium chloride, phenazine methosulfate and beta-NAD were added and the amount of glutamate formed by ketol-isomerase activity was determined by measuring OD585nm. A feedback inhibitor, UDP-N-acetylglucosamine, of fungal ketol-isomerase was successfully detected by this assay (IC50=0.48 mM). In a pilot scale screening, an active extract from an extremophilic bacterium was found, and the extract showed antifungal activity against A. fumigatus, Candida albicans and C. glabrata.

Differential protection in two transgenic lines of NOD/Lt mice hyperexpressing the autoantigen GAD65 in pancreatic beta-cells

Although expressed at very low levels in islets of NOD mice, GAD65 is a candidate islet autoantigen. Two transgenic lines of NOD/Lt mice expressing high levels of human GAD65 from a rat insulin promoter were generated. Transgenes were integrated on proximal chromosome 15 of the A line and on the Y chromosome of the Y line. Transgenic A-line mice were obligate hemizygotes, since homozygous expression resulted in developmental lethality. A twofold higher level of hGAD65 transcripts in A-line islets from young donors was associated with higher GAD protein and enzyme activity levels. Y-line males developed diabetes at a similar rate and incidence as standard NOD/Lt males. In contrast, A-line mice of both sexes exhibited a markedly lowered incidence of diabetes. Insulitis, present in both transgenic lines, developed more slowly in A-line mice and correlated with a reduction in the ratio of gamma-interferon to interleukin-10 transcripts. Splenic leukocytes from young A-line donors transferred diabetes into NOD-scid recipients at a retarded rate compared with those from nontransgenic donors. Further, nontransgenic NOD T-cells transferred diabetes more slowly in NOD-scid recipients that were congenic for A-line transgenes as compared with standard NOD-scid recipients. Primed T-cell responses and spontaneous humoral reactivity to GAD65 failed to distinguish transgenic from nontransgenic mice. Quantitative differences in expression level or insertional mutagenesis are possible mechanisms of protection in the A line.

Reduction of serum lactate by sodium dichloroacetate, and human pharmacokinetic-pharmacodynamic relationships

Sodium dichloroacetate (DCA) or placebo, two infusions 30 min in duration and 8 h apart, was administered to healthy subjects under double-blind conditions. The objectives were to characterize accurately the tolerability of DCA, its pharmacokinetics, and the reduction of resting serum lactate concentration by DCA. A hybrid, one-compartment pharmacokinetic model fitted best, with zero-order elimination mean of 27.9 micrograms/ml/h at concentrations above about 80 to 120 micrograms/ml, and with first-order elimination (mean kelim = 0.54) at lower serum concentrations of DCA. Resting serum lactate was dose-independently, maximally reduced within 15 min of the end of all active infusions. The duration of suppression of resting serum lactate was dose-dependent, from 4.5 h (30 mg/kg) to > 8 h (100 mg/kg). Second infusions (15-50 mg/kg) again promptly and maximally reduced resting serum lactate. Hysteresis loops were asymmetrical for all doses but exhibited change in shape that was dose-dependent; no good pharmacokinetic-pharmacodynamic model could be fitted that was consistent between doses. Infusions were well tolerated, 100 mg/kg + 50 mg/kg being the highest doses. Somnolence, the only dose-related adverse event, was reported by 3 of 37 subjects at times corresponding to the highest serum DCA concentrations. This study demonstrates the tolerability of i.v. DCA, proposes a simple pharmacokinetic model for its elimination, characterizes the dose-response relationship in terms of time course of effect, shows the dissociation between elimination of DCA and offset of response and will guide further studies of DCA in patients with head injury or stroke.

An additional breakpoint region in the BCL-1 locus associated with the t(11;14)(q13;q32) translocation of B-lymphocytic malignancy

The t(11;14)(q13;q32) translocation is associated with human B-lymphocytic malignancy. This translocation divides the IgH locus on chromosome 14q32 and may activate a postulated proto-oncogene, bcl-1, located on chromosome 11q13. Two samples of chronic lymphocytic leukemia with the t(11;14)(q32;q13) translocation were studied. The break in one sample was shown to join Jh sequences with the previously described bcl-1 major translocation cluster. DNA blots of the second sample suggested that Jh sequences were joined to a different breakpoint region on chromosome 11. This translocation was cloned and found to link the human Jh3 region and a new breakpoint region 63 kb telomeric of the major translocation cluster. This translocation occurred in part as the result of an aberrant D-J recombination. Recurrent translocations human B-lymphocytic malignancy. The definition of a new breakpoint region may aid the identification of the postulated bcl-1 gene.

Colony-stimulating factor gene expression in human acute myeloblastic leukemia cells is posttranscriptionally regulated

Normal human myeloid cells require certain colony stimulating factors (CSFs) for growth and differentiation. These CSFs are normally produced exogenously by accessory cells. However, human acute myeloid leukemia cells have been found, in certain instances, to have constitutive, endogenous production of one or more of these CSFs. In order to address the molecular basis of this apparently anomalous production of CSFs, we studied granulocyte-, monocyte-, and granulocyte/monocyte colony stimulating factor gene expression, gene structure, transcription rate, message stability, and message inducibility in human acute myeloid leukemia samples. CSF gene expression by Northern analysis was variable from no transcripts detectable to transcripts present for all three CSFs. No CSF gene structure abnormalities were detected by Southern blot analysis. Nuclear run-on assays found ongoing and relatively uniform CSF gene transcription irrespective of the levels of CSF expression detected by Northern analysis. However, the stability of the CSF transcripts appeared to correlate with the level detected on Northern blots. Despite the apparent similarity in the regulation of these CSFs to that seen in mature monocytes, the inducibility of the expression of these CSFs was found to differ significantly from that seen in these mature myeloid cells. Taken together, these results suggest that the expression of CSF genes in human myeloid leukemias is primarily mediated through posttranscriptional mechanisms. These mechanisms are separate for each of the CSFs and apparently different from that found in normal blood monocytes.

Lack of detectable somatic hypermutation in the V region of the Ig H chain gene of a human chronic B lymphocytic leukemia

Monoclonal human B cell tumors are a model system for the study of somatic hypermutation of the Ig genes of humans. It was previously shown that a number of B cell lymphomas exhibited striking V region point mutation, hypothesized to result from the somatic hypermutation mechanism. In this study we have extended the analysis to chronic lymphocytic leukemia. We have cloned and sequenced the productive Vh representing five different cells from a monoclonal chronic lymphocytic leukemia. All five Vh sequences were identical. Therefore, the Vh region in this leukemia was not the subject of detectable somatic mutation. These data suggest that chronic lymphocytic leukemia might lack the mechanism for somatic hypermutation and represent a stage of normal B lymphocyte differentiation in which the somatic hypermutation mechanism is not active.

Lack of detectable somatic hypermutation in the V region of the Ig H chain gene of a human chronic B lymphocytic leukemia

Monoclonal human B cell tumors are a model system for the study of somatic hypermutation of the Ig genes of humans. It was previously shown that a number of B cell lymphomas exhibited striking V region point mutation, hypothesized to result from the somatic hypermutation mechanism. In this study we have extended the analysis to chronic lymphocytic leukemia. We have cloned and sequenced the productive Vh representing five different cells from a monoclonal chronic lymphocytic leukemia. All five Vh sequences were identical. Therefore, the Vh region in this leukemia was not the subject of detectable somatic mutation. These data suggest that chronic lymphocytic leukemia might lack the mechanism for somatic hypermutation and represent a stage of normal B lymphocyte differentiation in which the somatic hypermutation mechanism is not active.

Myocardial infarction. How representative are autopsied subjects with this clinical entity?

We documented the differences in clinical features between 86 autopsied and 54 nonautopsied subjects who died of myocardial infarction to ascertain any bias that might be present in use of postmortem data. More than 200 historical, clinical, noninvasive, and hemodynamic aspects were compared. Of noninvasive aspects examined in all subjects, only 13 had significant differences (by chi 2 or unpaired t tests) between autopsied and nonautopsied subjects. However, there had been greater impairment of vital signs and hemodynamic aspects during early hospitalization in the autopsied vs the nonautopsied subjects. Further, the one-month survival rate was lower in autopsied subjects (31% vs 72%; P less than .01). We conclude that patients in severe congestive heart failure or shock and, presumably, with relatively large or complicated myocardial infarcts are more likely to die early and be autopsied. Those with better cardiac function live longer, and often die after having been released from the initial hospitalization; these subjects, presumably with smaller and uncomplicated infarcts, do not undergo autopsy. Before correlating pathological and clinical data from subjects with acute myocardial infarction, it is important to carefully analyze bias inherent in the selection of subjects to undergo autopsy.

[The perioperative myocardial infarct after aortocoronary bypass]

Two sets of criteria are developed for the diagnosis of perioperative myocardial infarction: 1) new, persistent Q waves and either an elevated 48-hour MB-CPK area or a positive pyrophosphate scan, 2) severe ischemic ST-T wave changes and both elevated MB-CPK area and a positive scan.

Predictive factors and mechanism of arrhythmias and myocardial ischaemic changes in elderly patients during barium enema

The incidence of significant arrhythmias and ST segment changes during barium enema examination (BE) was evaluated by Holter monitoring of 58 unselected patients over the age of 60 years. Forty percent of the group developed new significant arrhythmias of which the most common were frequent and/or multifocal premature ventricular contractions. Seven percent demonstrated ST segment depression. Administration of glucagon did not diminish the incidence of arrhythmias. Predictive factors for ECG abnormalities were advancing age, abnormal pre-BE-ECG, and pre-BE orthostatic hypotension. Analysis of arhythmias and response to phywiologic tension. Analysis of arrhythmias and response to physiologic manoeuvres suggested that the abnormalities were related to increased sympathetic tone which may be intensified by hypovolaemia resulting from routine bowel preparation.

Multiple crystal cross-sectional echocardiography in the diagnosis of cyanotic congenital heart disease

A new multiple crystal echocardiographic system was used to assess cross-sectional cardiac anatomy in real time in fifty infants and children with cyanotic heart disease, and the findings were compared to normals. Four standard transducer positions were employed to evaluate sagittal and transverse cardiac cross-sections. Studies in patients with tetralogy of Fallot demonstrated an enlarged aorta overriding the septum with preservation of mitral-aortic continuity. In the absence of pulmonary atresia the main pulmonary artery could be identified in all of these patients. The diagnosis of d -transposition of the great vessels was established by viewing great vessel orientation in transverse section at the second intercostal space and observing a rightward and anteriorly placed great artery. In sagittal projections a retrosternal aorta and mitral-pulmonic continuity was observed. In one patient with d -transposition, apposition in systole of the ventricular septum and anterior leaflet of the mitral valve was identified as the cause of left ventricular outflow tract obstruction. Descriptions are provided of the findings in patients with l -transposition, double outlet right ventricle, and truncus arteriosus. The new multiscan method allows a substantially more precise determination of intra- and extra-cardiac spatial relationships than single crystal techniques. Multiscan echocardiography is safe, widely applicable, and provides clinically important information to assist in the diagnosis and management of infants and children with cyanotic heart disease.

Multiple crystal echocardiographic evaluation of endocardial cushion defect

A prototype multiple crystal echocardiographic system developed by Bom and associates was used to evaluate cross-sectional cardiac anatomy in real time in twenty infants and children with endocardial cushion defect (ECD). The findings were compared to fifty normal infants and children and nineteen patients with normal mitral valve anatomy but right ventricular enlargement (RVE). Three standard transducer positions for evaluation of sagittal and transverse cardiac cross-sections are outlined and the normal group and RVE subgroup described. Studies in patients with ECD demonstrated several distinctive abnormalities, consisting of multiple echoes in the mitral valve area, anterior mitral leaflet - septal apposition in diastole with reduced posterior motion in systole, and reduced excursion of the anterior mitral leaflet. In patients with complete atrioventricular (A-V) canal defects, the anterior leaflet was often observed passing across the plane of the ventricular septum into the right ventricle during diastole, and in some of these patients the anterior mitral leaflet was related to the tricuspid annulus. Multiple crystal cardiac ultrasonography allows a more precise determination of intra- and extracardiac spatial relationships and is easier to perform than single crystal echo. The new technique provides clinical information helpful in evaluating patients with possible ECD and gives some indication of the severity of the defect.