Understanding the informal aspects of medication processes to maintain patient safety in hospitals: a sociotechnical ethnographic study in paediatric units.

Adverse drug events (ADEs) are common in hospitals, affecting one in six child in-patients. Medication processes are complex systems. This study aimed to explore the work-as-done of medication safety in three English paediatric units using direct observation and semi-structured interviews. We found that a combination of the physical environment, traditional work systems and team norms were among the systemic barriers to medicines safety. The layout of wards discouraged teamworking and reinforced professional boundaries. Workspaces were inadequate, and interruptions were uncontrollable. A less experienced workforce undertook prescribing and verification while more experienced nurses undertook administration. Guidelines were inadequate, with actors muddling through together. Formal controls against ADEs included checking (of prescriptions and administration) and barcode administration systems, but these did not integrate into workflows. Families played an important part in the safe administration of medication and provision of information about their children but were isolated from other parts of the system.

Formal medicines safety processes in paediatric units are disjointed and disconnected. This has led actors in the system (e.g. nursing and medical staff) to develop informal adaptations to increase resilience. There is a need to incorporate these adaptations into a systems-focussed consideration of safety processes, in order to properly inform the development of medication safety interventions.

De novo variants in RNF213 are associated with a clinical spectrum ranging from Leigh syndrome to early-onset stroke.

PURPOSE: RNF213, encoding a giant E3 ubiquitin ligase, has been recognized for its role as a key susceptibility gene for moyamoya disease. Case reports have also implicated specific variants in RNF213 with an early-onset form of moyamoya disease with full penetrance. We aimed to expand the phenotypic spectrum of monogenic RNF213-related disease and to evaluate genotype-phenotype correlations. METHODS: Patients were identified through reanalysis of exome sequencing data of an unselected cohort of unsolved pediatric cases and through GeneMatcher or ClinVar. Functional characterization was done by proteomics analysis and oxidative phosphorylation enzyme activities using patient-derived fibroblasts. RESULTS: We identified 14 individuals from 13 unrelated families with (de novo) missense variants in RNF213 clustering within or around the Really Interesting New Gene (RING) domain. Individuals presented either with early-onset stroke (n = 11) or with Leigh syndrome (n = 3). No genotype-phenotype correlation could be established. Proteomics using patient-derived fibroblasts revealed no significant differences between clinical subgroups. 3D modeling revealed a clustering of missense variants in the tertiary structure of RNF213 potentially affecting zinc-binding suggesting a gain-of-function or dominant negative effect. CONCLUSION: De novo missense variants in RNF213 clustering in the E3 RING or other regions affecting zinc-binding lead to an early-onset syndrome characterized by stroke or Leigh syndrome.

Genetic landscape of pediatric acute liver failure of indeterminate origin.

BACKGROUND AIMS: Pediatric acute liver failure (PALF) is a life-threatening condition. In Europe, main causes are viral infections (12-16%) and inherited metabolic diseases (14-28%). Yet, in up to 50% of cases the underlying etiology remains elusive, challenging clinical management, including liver transplantation. We systematically studied indeterminate PALF cases referred for genetic evaluation by whole-exome sequencing (WES), and analyzed phenotypic and biochemical markers, and the diagnostic yield of WES in this condition. METHODS: With this international, multicenter observational study, patients (0-18 y) with indeterminate PALF were analyzed by WES. Data on the clinical and biochemical phenotype were retrieved and systematically analyzed. RESULTS: In total, 260 indeterminate PALF patients from 19 countries were recruited between 2011 and 2022, of whom 59 had recurrent PALF (RALF). WES established a genetic diagnosis in 37% of cases (97/260). Diagnostic yield was highest in children with PALF in the first year of life (46%), and in children with RALF (64%). Thirty-six distinct disease genes were identified. Defects in NBAS (n=20), MPV17 (n=8) and DGUOK (n=7) were the most frequent findings. When categorizing, most frequent were mitochondrial diseases (45%), disorders of vesicular trafficking (28%) and cytosolic aminoacyl-tRNA synthetase deficiencies (10%). One-third of patients had a fatal outcome. Fifty-six patients received liver transplants. CONCLUSION: This study elucidates a large contribution of genetic causes in PALF of indeterminate origin with an increasing spectrum of disease entities. The high proportion of diagnosed cases and potential treatment implications argue for exome or in future rapid genome sequencing in PALF diagnostics.

Genotypic and phenotypic spectrum of infantile liver failure due to pathogenic TRMU variants.

PURPOSE: This study aimed to define the genotypic and phenotypic spectrum of reversible acute liver failure (ALF) of infancy resulting from biallelic pathogenic TRMU variants and determine the role of cysteine supplementation in its treatment. METHODS: Individuals with biallelic (likely) pathogenic variants in TRMU were studied within an international retrospective collection of de-identified patient data. RESULTS: In 62 individuals, including 30 previously unreported cases, we described 47 (likely) pathogenic TRMU variants, of which 17 were novel, and 1 intragenic deletion. Of these 62 individuals, 42 were alive at a median age of 6.8 (0.6-22) years after a median follow-up of 3.6 (0.1-22) years. The most frequent finding, occurring in all but 2 individuals, was liver involvement. ALF occurred only in the first year of life and was reported in 43 of 62 individuals; 11 of whom received liver transplantation. Loss-of-function TRMU variants were associated with poor survival. Supplementation with at least 1 cysteine source, typically N-acetylcysteine, improved survival significantly. Neurodevelopmental delay was observed in 11 individuals and persisted in 4 of the survivors, but we were unable to determine whether this was a primary or a secondary consequence of TRMU deficiency. CONCLUSION: In most patients, TRMU-associated ALF was a transient, reversible disease and cysteine supplementation improved survival.

Navigating uncertain illness trajectories for young children with serious infectious illness: a modified grounded theory study.

BACKGROUND: Infectious illness is the biggest cause of death in children due to a physical illness, particularly in children under five years. If mortality is to be reduced for this group of children, it is important to understand factors affecting their pathways to hospital. The aim of this study was to retrospectively identify organisational and environmental factors, and individual child, family, and professional factors affecting timing of admission to hospital for children under five years of age with a serious infectious illness (SII). METHODS: An explanatory modified grounded theory design was used in collaboration with parents. Two stages of data collection were conducted: Stage 1, interviews with 22 parents whose child had recently been hospitalised with a SII and 14 health professionals (HPs) involved in their pre-admission trajectories; Stage 2, focus groups with 18 parents and 16 HPs with past experience of SII in young children. Constant comparative analysis generated the explanatory theory. RESULTS: The core category was 'navigating uncertain illness trajectories for young children with serious infectious illness'. Uncertainty was prevalent throughout the parents' and HPs' stories about their experiences of navigating social rules and overburdened health services for these children. The complexity of and lack of continuity within services, family lives, social expectations and hierarchies provided the context and conditions for children's, often complex, illness trajectories. Parents reported powerlessness and perceived criticism leading to delayed help-seeking. Importantly, parents and professionals missed symptoms of serious illness. Risk averse services were found to refer more children to emergency departments. CONCLUSIONS: Parents and professionals have difficulties recognising signs of SII in young children and can feel socially constrained from seeking help. The increased burden on services has made it more difficult for professionals to spot the seriously ill child.

Glutaric aciduria type 1: Diagnosis, clinical features and long-term outcome in a large cohort of 34 Irish patients.

Glutaric aciduria type 1 (GA1) is a rare neurometabolic disorder that can lead to encephalopathic crises and severe dystonic movement disorders. Adherence to strict dietary restriction, in particular a diet low in lysine, carnitine supplementation and emergency treatment in pre-symptomatic patients diagnosed by high-risk screen (HRS) or newborn screen (NBS) leads to a favourable outcome. We present biochemical and clinical characteristics and long-term outcome data of 34 Irish patients with GA1 aged 1-40 years. Sixteen patients were diagnosed clinically, and 17 patients by HRS, prior to introduction of NBS for GA1 in the Republic of Ireland in 2018. One patient was diagnosed by NBS. Clinical diagnosis was at a median of 1 year (range 1 month to 8 years) and by HRS was at a median of 4 days (range 3 days to 11 years). 14/18 (77.8%) diagnosed by HRS or NBS had neither clinical manifestations nor radiological features of GA1, or had radiological features only, compared to 0/16 (0%) diagnosed clinically (p < 0.001). Patients diagnosed clinically who survived to school-age were more likely to have significant cerebral palsy and dystonia (7/11; 63.6% vs. 0/13; 0%, p < 0.001). They were less likely to be in mainstream school versus the HRS group (5/10; 50% vs. 12/13; 92.3%; p = 0.012). Clinical events occurring after 6 years of age were unusual, but included spastic diplegia, thalamic haemorrhage, Chiari malformation, pituitary hormone deficiency and epilepsy. The exact aetiology of these events is unclear.

Humanizing harm: Using a restorative approach to heal and learn from adverse events.

BACKGROUND: Healthcare is not without risk. Despite two decades of policy focus and improvement efforts, the global incidence of harm remains stubbornly persistent, with estimates suggesting that 10% of hospital patients are affected by adverse events. METHODS: We explore how current investigative responses can compound the harm for all those affected-patients, families, health professionals and organizations-by neglecting to appreciate and respond to the human impacts. We suggest that the risk of compounded harm may be reduced when investigations respond to the need for healing alongside system learning, with the former having been consistently neglected. DISCUSSION: We argue that incident responses must be conceived within a relational as well as a regulatory framework, and that this-a restorative approach-has the potential to radically shift the focus, conduct and outcomes of investigative processes. CONCLUSION: The identification of the preconditions and mechanisms that enable the success of restorative approaches in global health systems and legal contexts is required if their demonstrated potential is to be realized on a larger scale. The policy must be co-created by all those who will be affected by reforms and be guided by restorative principles. PATIENT OR PUBLIC CONTRIBUTION: This viewpoint represents an international collaboration between a clinician academic, safety scientist and harmed patient and family members. The paper incorporates key findings and definitions from New Zealand's restorative response to surgical mesh harm, which was co-designed with patient advocates, academics and clinicians.

Secondary Hyperparathyroidism in Children with Mucolipidosis Type II (I-Cell Disease): Irish Experience.

Mucolipidosis type II (ML II) is an autosomal recessive lysosomal targeting disorder that may present with features of hyperparathyroidism. The aim of this study was to describe in detail the clinical cases of ML II presenting to a tertiary referral centre with biochemical and/or radiological features of hyperparathyroidism. There were twenty-three children diagnosed with ML II in the Republic of Ireland from July 1998 to July 2021 inclusive (a 23-year period). The approximate incidence of ML II in the Republic of Ireland is, therefore, 1 per 64,000 live births. Medical records were available and were reviewed for 21 of the 23 children. Five of these had been identified as having biochemical and/or radiological features of hyperparathyroidism. Of these five, three children were born to Irish Traveller parents and two to non-Traveller Irish parents. All five children had radiological features of hyperparathyroidism (on skeletal survey), with evidence of antenatal fractures in three cases and an acute fracture in one. Four children had biochemical features of secondary hyperparathyroidism. Three children received treatment with high dose Vitamin D supplements and two who had antenatal/acute fractures were managed with minimal handling. We observed resolution of secondary hyperparathyroidism in all cases irrespective of treatment. Four of five children with ML II and hyperparathyroidism died as a result of cardiorespiratory failure at ages ranging from 10 months to 7 years. Biochemical and/or radiological evidence of hyperparathyroidism is commonly identified at presentation of ML II. Further studies are needed to establish the pathophysiology and optimal management of hyperparathyroidism in this cohort. Recognition of this association may improve diagnostic accuracy and management, facilitate family counseling and is also important for natural history data.

Biomarkers and biosensors for the diagnosis of noncompliant pH, dark cutting beef predisposition, and welfare in cattle.

Meat quality can be affected by stress, exhaustion, feed composition, and other physical and environmental conditions. These stressors can alter the pH in postmortem muscle, leading to high pH and low-quality dark cutting (DC) beef, resulting in considerable economic loss. Moreover, the dark cutting prediction may equally provide a measure for animal welfare since it is directly related to animal stress. There are two needs to advance on-site detection of dark cutters: (1) a clear indication that biomarker (signature compounds) levels in cattle correlate with stress and DC outcome; and (2) measuring these biomarkers rapidly and accurately on-farm or the abattoir, depending on the objectives. This critical review assesses which small molecules and proteins have been identified as potential biomarkers of stress and dark cutting in cattle. We discuss the potential of promising small molecule biomarkers, including catecholamine/cortisol metabolites, lactate, succinate, inosine, glucose, and ß-hydroxybutyrate, and we identify a clear research gap for proteomic biomarker discovery in live cattle. We also explore the potential of chemical-sensing and biosensing technologies, including direct electrochemical detection improved through nanotechnology (e.g., carbon and gold nanostructures), surface-enhanced Raman spectroscopy in combination with chemometrics, and commercial hand-held devices for small molecule detection. No current strategy exists to rapidly detect predictive meat quality biomarkers due to the need to further validate biomarkers and the fact that different biosensor types are needed to optimally detect different molecules. Nonetheless, several biomarker/biosensor combinations reported herein show excellent potential to enable the measurement of DC potential in live cattle.

Long term food stability for extended space missions: a review.

At present, human spaceflight is confined to low Earth orbit but, in future, will again go to the Moon and, beyond, to Mars. The provision of food during these extended missions will need to meet the special nutritional and psychosocial needs of the crew. Terrestrially grown and processed food products, currently provided for consumption by astronauts/cosmonauts, have not yet been systematically optimised to maintain their nutritional integrity and reach the shelf-life necessary for extended space voyages. Notably, space food provisions for Mars exploration will be subject to extended exposure to galactic cosmic radiation and solar particle events, the impact of which is not fully understood. In this review, we provide a summary of the existing knowledge about current space food products, the impact of radiation and storage on food composition, the identification of radiolytic biomarkers and identify gaps in our knowledge that are specific in relation to the effect of the cosmic radiation on food in space.

Shared education as a contact-based intervention to improve intergroup relations among adolescents in postconflict Northern Ireland.

Past research has shown that intergroup contact can be a promising intervention to improve intergroup relations and that contact-based interventions might be most effective during adolescence. In postconflict Northern Ireland, widespread residential segregation and a largely separate school system limit opportunities for intergroup contact between adolescents from the Catholic and Protestant communities. We evaluated whether a large-scale intervention to facilitate intergroup contact between students attending separate schools (the 'Shared Education' program) improves a range of outcomes relevant for intergroup relations in Northern Ireland. We conducted a 5-wave longitudinal, quasi-experimental study that followed a large sample of school students (N = 5,159, Mage = 12.4, age range: 10-14 years; 2,988 girls, 2,044 boys) from 56 predominantly Catholic or Protestant schools from sixth to tenth grade. We compared the developmental trajectories of students who, in 9th (14-15 years) and 10th (15-16 years) grade, shared some classes with students from the other community, as part of the program, to students who did not. We found that participating in shared classes had a medium-size, positive effect on the amount of intergroup contact students had outside of class, and small, positive effects on students' outgroup attitudes, outgroup trust, and intergroup empathy (but not on their intergroup anxiety, future contact intentions, deprovincialization, or multicultural beliefs). Our findings show that a school-based program of shared education can provide a viable and effective intervention to facilitate intergroup contact, improve intergroup relations, and foster social integration among adolescents at a large scale in a postconflict society. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Caring for a sick or injured child during the COVID-19 pandemic lockdown in 2020 in the UK: An online survey of parents' experiences.

BACKGROUND: During the COVID-19 pandemic, the first UK lockdown (March to May 2020) witnessed a dramatic reduction in children presenting to primary/emergency care, creating concern that fear of the virus was resulting in children presenting late. METHODS: An online survey was co-developed with UK parents to understand the impact of the lockdown on parents' help-seeking for, and care of, their sick/injured child(ren). The survey was advertised through social media and snowballing to parents whose children had been ill/injured during the lockdown. Analysis used descriptive statistics, SPSSv25 and thematic analysis. RESULTS: The survey was fully completed by 198 UK parents. The majority asked for help (144/198): from their family doctor (78), national helplines (48) or an Emergency Department (23). Most reported that their decision-making had not changed, although how they sought help had changed. A few parents reported that the severity and duration of illness had increased because of uncertainty about and/or difficulty accessing services. Parents did not always report seeking help for symptoms rated red or amber by the Royal College of Paediatrics and Child Health. Parents reported accessing information through the internet or using information that they already had. PARENT CONTRIBUTION: This was a collaboration with parents from survey development to dissemination, with two parents being integral members of our research team. CONCLUSIONS: Our questionnaire was completed by parents who were not deterred from seeking help for their sick or injured children. Even for these parents, the lockdown changes to services created uncertainty about, and barriers to, accessing medical help for their children.

Enzyme replacement therapy and hematopoietic stem cell transplant: a new paradigm of treatment in Wolman disease.

BACKGROUND: Wolman disease is a rare, lysosomal storage disorder in which biallelic variants in the LIPA gene result in reduced or complete lack of lysosomal acid lipase. The accumulation of the substrates; cholesterol esters and triglycerides, significantly impacts cellular function. Untreated patients die within the first 12 months of life. Clinically, patients present severely malnourished, with diarrhoea and hepatosplenomegaly, many have an inflammatory phenotype, including with hemophagocytic lymphohistiocytosis (HLH). Hematopoietic stem cell transplant (HCT) had been historically the only treatment available but has a high procedure-related mortality because of disease progression and disease-associated morbidities. More recently, enzyme replacement therapy (ERT) with dietary substrate reduction (DSR) has significantly improved patient survival. However, ERT is life long, expensive and its utility is limited by anti-drug antibodies (ADA) and the need for central venous access. RESULTS: We describe five Wolman disease patients diagnosed in infancy that were treated at Royal Manchester Children's Hospital receiving ERT with DSR then HCT-multimodal therapy. In 3/5 an initial response to ERT was attenuated by ADA with associated clinical and laboratory features of deterioration. 1/5 developed anaphylaxis to ERT and the other patient died post HCT with ongoing HLH. All patients received allogeneic HCT. 4/5 patients are alive, and both disease phenotype and laboratory parameters are improved compared to when they were on ERT alone. The gastrointestinal symptoms are particularly improved after HCT, with reduced diarrhoea and vomiting. This allows gradual structured normalisation of diet with improved tolerance of dietary fat. Histologically there are reduced cholesterol clefts, fewer foamy macrophages and an improved villous structure. Disease biomarkers also show improvement with ERT, immunotherapy and HCT. Three patients have mixed chimerism after HCT, indicating a likely engraftment-defect in this condition. CONCLUSION: We describe combined ERT, DSR and HCT, multimodal treatment for Wolman disease. ERT and DSR stabilises the sick infant and reduces the formerly described prohibitively high, transplant-associated mortality in this condition. HCT abrogates the problems of ERT, namely attenuating ADA, the need for continuing venous access, and continuing high cost drug treatment. HCT also brings improved efficacy, particularly evident in improved gastrointestinal function and histology. Multimodal therapy should be considered a new paradigm of treatment for Wolman disease patients where there is an attenuated response to ERT, and for all patients where there is a well-matched transplant donor, in order to improve long term gut function, tolerance of a normal diet and quality of life.

Rapid Evaporative Ionization Mass Spectrometry: A Review on Its Application to the Red Meat Industry with an Australian Context.

The red meat supply chain is a complex network transferring product from producers to consumers in a safe and secure way. There can be times when fragmentation can arise within the supply chain, which could be exploited. This risk needs reduction so that meat products enter the market with the desired attributes. Rapid Evaporative Ionisation Mass Spectrometry (REIMS) is a novel ambient mass spectrometry technique originally developed for rapid and accurate classification of biological tissue which is now being considered for use in a range of additional applications. It has subsequently shown promise for a range of food provenance, quality and safety applications with its ability to conduct ex vivo and in situ analysis. These are regarded as critical characteristics for technologies which can enable real-time decision making in meat processing plants and more broadly throughout the sector. This review presents an overview of the REIMS technology, and its application to the areas of provenance, quality and safety to the red meat industry, particularly in an Australian context.

Maple syrup urine disease: Clinical outcomes, metabolic control, and genotypes in a screened population after four decades of newborn bloodspot screening in the Republic of Ireland.

Since 1972, 18 patients (10 females/8 males) have been detected by newborn bloodspot screening (NBS) with neonatal-onset maple syrup urine disease (MSUD) in Ireland. Patients were stratified into three clusters according to clinical outcome at the time of data collection, including developmental, clinical, and IQ data. A fourth cluster comprised of two early childhood deaths; a third patient died as an adult. We present neuroimaging and electroencephalography together with clinical and biochemical data. Incidence of MSUD (1972-2018) was 1 in 147 975. Overall good clinical outcomes were achieved with 15/18 patients alive and with essentially normal functioning (with only the lowest performing cluster lying beyond a single SD on their full scale intelligence quotient). Molecular genetic analysis revealed genotypes hitherto not reported, including a possible digenic inheritance state for the BCKDHA and DBT genes in one family. Treatment has been based on early implementation of emergency treatment, diet, close monitoring, and even dialysis in the setting of acute metabolic decompensation. A plasma leucine ≥400 µmol/L (outside therapeutic range) was more frequently observed in infancy or during adolescence, possibly due to infections, hormonal changes, or noncompliance. Children require careful management during metabolic decompensations in early childhood, and this represented a key risk period in our cohort. A high level of metabolic control can be achieved through diet with early implementation of a "sick day" regime and, in some cases, dialysis as a rescue therapy. The Irish cohort, despite largely classical phenotypes, achieved good outcomes in the NBS era, underlining the importance of early diagnosis and skilled multidisciplinary team management.

Meat color is determined not only by chromatic heme pigments but also by the physical structure and achromatic light scattering properties of the muscle.

Meat color is important for consumer acceptability, with excessively dark meat often associated with consumer rejection. It is determined chromatically by pigment content (measured by hue and chroma) and achromatically by scattering of light by the microstructure (measured by lightness), the latter of which has received minimal research focus. This review discusses the individual components of the meat microstructure that cause differences in achromatic contributions to color. Differences in achromatic light scattering between light and dark extremes of meat color are most likely explained by structural attributes within the muscle cell. These differences are proposed to arise from variations in (a) transverse shrinkage of the structural lattice of the myofilaments, myofibrils, and muscles fibers, (b) longitudinal shrinkage of the sarcomere, and (c) different protein composition of the surrounding medium (sarcoplasm and extracellular space). These are discussed at a mechanistic level, in relation to six parameters of the muscle cell: (a) protein surface charge altering the myofilament spacing, (b) protein solubility, (c) sarcoplasmic protein binding to myofilaments and myofibrils, (d) integrity of the cytoskeleton and cell adhesion proteins, (e) sarcomere integrity and myofibrillar proteins, and (f) myosin denaturation and rigor bond modification. New data are presented to support the proposed role of structural elements in muscle causing achromatic light scattering and their contribution to the surface color of meat. In addition, the relationships between lightness and water holding capacity and pH are explored and the economic impact of dark meat for the meat industry is discussed.

Genotypic diversity and phenotypic spectrum of infantile liver failure syndrome type 1 due to variants in LARS1.

PURPOSE: Biallelic variants in LARS1, coding for the cytosolic leucyl-tRNA synthetase, cause infantile liver failure syndrome 1 (ILFS1). Since its description in 2012, there has been no systematic analysis of the clinical spectrum and genetic findings. METHODS: Individuals with biallelic variants in LARS1 were included through an international, multicenter collaboration including novel and previously published patients. Clinical variables were analyzed and functional studies were performed in patient-derived fibroblasts. RESULTS: Twenty-five individuals from 15 families were ascertained including 12 novel patients with eight previously unreported variants. The most prominent clinical findings are recurrent elevation of liver transaminases up to liver failure and encephalopathic episodes, both triggered by febrile illness. Magnetic resonance image (MRI) changes during an encephalopathic episode can be consistent with metabolic stroke. Furthermore, growth retardation, microcytic anemia, neurodevelopmental delay, muscular hypotonia, and infection-related seizures are prevalent. Aminoacylation activity is significantly decreased in all patient cells studied upon temperature elevation in vitro. CONCLUSION: ILFS1 is characterized by recurrent elevation of liver transaminases up to liver failure in conjunction with abnormalities of growth, blood, nervous system, and musculature. Encephalopathic episodes with seizures can occur independently from liver crises and may present with metabolic stroke.

Variations in meat colour due to factors other than myoglobin chemistry; a synthesis of recent findings (invited review).

This review focuses on the mechanisms responsible for some the achromatic aspects of meat colour (paleness or darkness) due to light scatter from structures within the tissue. Recent investigations have highlighted the role of three key mechanisms contributing to variations in the lightness of meat: (1) Variations in the myofilament lattice spacing, and the resultant changes in myofibril diameter and muscle fibre diameter. A 20% increase in lightness (L* value) between muscles with ultimate pH of 6.1 versus 5.4 is accompanied by a 17% change in muscle fibre diameter. (2) Variations in sarcomere length, if these are associated with changes in myofilament and myofiber diameter, (3) Variations in sarcoplasmic protein distribution, including whether these are bound or precipitated onto the myofilaments, as demonstrated by an increase of 1.24 in the ratio of X-ray diffraction intensities from mass centered on the thin filaments versus thick filaments in dark (pH 6.15) versus light (pH 5.47) muscles. For clarity, the discussion of these mechanisms is principally in relation to pH and temperature at rigor (5 °C-35 °C), although the possibility of contributions from numerous other factors is acknowledged.