Phosphorylase Deficiency Research Articles

Methylthioadenosine phosphorylase deficiency in tumors: A compelling therapeutic target.

The methionine salvage pathway is responsible for recycling sulfur-containing metabolites to methionine. This salvage pathway has been found to be implicated in cell apoptosis, proliferation, differentiation and inflammatory response. Methylthioadenosine phosphorylase (MTAP) catalyzes the reversible phosphorolysis of 5'-methylthioadenosine, a by-product produced from polyamine biosynthesis. The MTAP gene is located adjacent to the cyclin-dependent kinase inhibitor 2A gene and co-deletes with CDKN2A in nearly 15% of tumors. Moreover, MTAP-deleted tumor cells exhibit greater sensitivity to methionine depletion and to the inhibitors of purine synthesis. In this review, we first summarized the molecular structure and expression of MTAP in tumors. Furthermore, we discussed PRMT5 and MAT2A as a potential vulnerability for MTAP-deleted tumors. The complex and dynamic role of MTAP in diverse malignancies has also been discussed. Finally, we demonstrated the implications for the treatment of MTAP-deleted tumors.

Thymidine Phosphorylase Deficiency or Inhibition Preserves Cardiac Function in Mice With Acute Myocardial Infarction.

Background Ischemic cardiovascular disease is the leading cause of death worldwide. Current pharmacologic therapy has multiple limitations, and patients remain symptomatic despite maximal medical therapies. Deficiency or inhibition of thymidine phosphorylase (TYMP) in mice reduces thrombosis, suggesting that TYMP could be a novel therapeutic target for patients with acute myocardial infarction (AMI). Methods and Results A mouse AMI model was established by ligation of the left anterior descending coronary artery in C57BL/6J wild-type and TYMP-deficient (Tymp-/-) mice. Cardiac function was monitored by echocardiography or Langendorff assay. TYMP-deficient hearts had lower baseline contractility. However, cardiac function, systolic left ventricle anterior wall thickness, and diastolic wall strain were significantly greater 4 weeks after AMI compared with wild-type hearts. TYMP deficiency reduced microthrombus formation after AMI. TYMP deficiency did not affect angiogenesis in either normal or infarcted myocardium but increased arteriogenesis post-AMI. TYMP deficiency enhanced the mobilization of bone marrow stem cells and promoted mesenchymal stem cell (MSC) proliferation, migration, and resistance to inflammation and hypoxia. TYMP deficiency increased the number of larger MSCs and decreased matrix metalloproteinase-2 expression, resulting in a high homing capability. TYMP deficiency induced constitutive AKT phosphorylation in MSCs but reduced expression of genes associated with retinoid-interferon-induced mortality-19, a molecule that enhances cell death. Inhibition of TYMP with its selective inhibitor, tipiracil, phenocopied TYMP deficiency, improved post-AMI cardiac function and systolic left ventricle anterior wall thickness, attenuated diastolic stiffness, and reduced infarct size. Conclusions This study demonstrated that TYMP plays an adverse role after AMI. Targeting TYMP may be a novel therapy for patients with AMI.

Valuing Mundane Manifestations of Rare, but Underdiagnosed, Diseases in Portugal: The Example of McArdle Disease

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Metabolic adaptations in McArdle's disease and its mechanisms.

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Patient-Reported Experiences with a Low-Carbohydrate Ketogenic Diet: An International Survey in Patients with McArdle Disease

The low-carbohydrate ketogenic diet (LCKD) has attracted increased attention in recent years as a potential treatment option for individuals with McArdle disease (glycogen storage disease type V), and despite the absence of strong scientific evidence of the LCKD's benefits, increased numbers of individuals with McArdle disease have tried a LCKD. The objective of this study was to collect patient-reported experiences with a LCKD. We aimed to estimate the immediate prevalence of individuals that had tried a LCKD in an international McArdle disease cohort, and we aimed to report on the patient-reported experiences with the diet, both positive and negative. A total of 183 responses were collected from individuals with McArdle disease from 18 countries. We found that one-third of the cohort had tried a LCKD, and almost 90% experienced some degree of positive effect, with the most prominent effects on McArdle disease-related core symptoms (e.g., activity intolerance, muscle pain, and muscle fatigue). Adverse effects were rare and generally rated as mild to moderate. These patient-reported findings underline the need for randomized clinical trials to decisively determine if a LCKD is a suitable nutritional strategy for patients with McArdle disease. The results from this study can prompt and contribute to the design of such a clinical trial.

Proximal myopathy: causes and associated conditions.

Proximal myopathy presents as generalized muscle weakness commonly involving the muscles of upper and/or lower limbs. Toxins, long-term use of statins, corticosteroids, alcohol, SGLT2 inhibitors, COVID-19 vaccination, and antimalarials have been attributed to its development. In endocrine and metabolic disorders, adrenal dysfunction including both overproduction and insufficiency of the adrenal gland hormones has been reported to cause myopathy. Moreover, parathyroid and thyroid disorders along with pituitary gland disorders can also directly or indirectly contribute to this condition. In idiopathic inflammatory myopathies including polymyositis, dermatomyositis, inclusion body myositis (IBM), and Systemic Lupus Erythematosus (SLE), Sjögren's Syndrome, and overlap syndromes, moderate to severe muscle weakness has been observed. IBM has been reported to be the most prevalent acquired myopathy above the age of 50. Hereditary or congenital myopathies include limb girdle muscular dystrophies, facioscapulohumeral muscular dystrophy, Duchenne and Becker muscular dystrophy, and proximal myotonic myopathy. In addition to these, glycogen storage diseases such as the McArdle disease can also cause fast exhaustion, myalgia, and cramping in working muscles. It is pertinent to mention here that a class of hereditary metabolic myopathies, referred to as "lipid deposition myopathy" causes lipids to accumulate in skeletal muscle fibers, leading to lesions and degeneration. Among viral causes, HIV, dengue virus, influenza virus, hepatitis B virus, hepatitis C virus, SARS-CoV2 are also associated with muscle weakness. Sarcoidosis, an inflammatory disease, can also manifest as muscle weakness and myalgia. Owing to this complicated pathophysiology of proximal myopathy, this review aims to summarize the existing literature on conditions associated with this phenomenon and other recent developments that have been made regarding events leading to development of generalized muscle weakness. To the authors' knowledge this is the first narrative review that discusses causes and conditions associated with proximal myopathy in thorough detail.

МИТОХОНДРИАЛЬНАЯ НЕЙРОГАСТРОИНТЕСТИНАЛЬНАЯ ЭНЦЕФАЛОМИОПАТИЯ: КЛИНИЧЕСКОЕ НАБЛЮДЕНИЕ

A clinical case of mitochondrial neurogastrointestinal encephalopathy (MNGIE), a rare autosomal recessive multisystem disease caused by TYMP gene mutations and thymidine phosphorylase (TP) deficiency, is presented. Authors draw the specialists’ attention to the complexity of making a diagnosis and the importance of an interdisciplinary approach in the diagnosis and management of such patients with the purpose of increasing the pediatric practitioners’ MNGIE awareness thereby reducing the time to diagnosis, which in its turn improves the prognosis for the course of the disease for the patients.

Muscle glycogen unavailability and fat oxidation rate during exercise: Insights from McArdle disease.

Carbohydrate availability affects fat metabolism during exercise; however, the effects of complete muscle glycogen unavailability on maximal fat oxidation (MFO) rate remain unknown. Our purpose was to examine the MFO rate in patients with McArdle disease, comprising an inherited condition caused by complete blockade of muscle glycogen metabolism, compared to healthy controls. Nine patients (three women, aged 36±12 years) and 12healthy controls (four women, aged 40±13 years) were studied. Several molecular markers of lipid transport/metabolism were also determined in skeletal muscle (gastrocnemius) and white adipose tissue of McArdle (Pygm p.50R*/p.50R*) and wild-type male mice. Peak oxygen uptake ( ), MFO rate, the exercise intensity eliciting MFO rate (FATmax) and the MFO rate-associated workload were determined by indirect calorimetry during an incremental cycle-ergometer test. Despite having a much lower (24.7±4 vs. 42.5±11.4mLkg-1 min-1 , respectively; P<0.0001), patients showed considerably higher values for the MFO rate (0.53±0.12 vs. 0.33±0.10 gmin-1 , P=0.001), and for the FATmax (94.4±7.2 vs. 41.3±9.1 % of , P<0.0001) and MFO rate-associated workload (1.33±0.35 vs. 0.81±0.54Wkg-1 , P=0.020) than controls. No between-group differences were found overall in molecular markers of lipid transport/metabolism in mice. In summary, patients with McArdle disease show an exceptionally high MFO rate, which they attained at near-maximal exercise capacity. Pending more mechanistic explanations, these findings support the influence of glycogen availability on MFO rate and suggest that these patients develop a unique fat oxidation capacity, possibly as an adaptation to compensate for the inherited blockade in glycogen metabolism, and point to MFO rate as a potential limiting factor of exercise tolerance in this disease. KEY POINTS: Physically active McArdle patients show an exceptional fat oxidation capacity. Maximal fat oxidation rate occurs near-maximal exercise capacity in these patients. McArdle patients' exercise tolerance might rely on maximal fat oxidation rate capacity. Hyperpnoea might cloud substrate oxidation measurements in some patients. An animal model revealed overall no higher molecular markers of lipid transport/metabolism.

Low aerobic capacity in McArdle disease: A role for mitochondrial network impairment?

BackgroundMcArdle disease is caused by myophosphorylase deficiency and results in complete inability for muscle glycogen breakdown. A hallmark of this condition is muscle oxidation impairment (e.g., low peak oxygen uptake (VO2peak)), a phenomenon traditionally attributed to reduced glycolytic flux and Krebs cycle anaplerosis. Here we hypothesized an additional role for muscle mitochondrial network alterations associated with massive intracellular glycogen accumulation. MethodsWe analyzed in depth mitochondrial characteristics-content, biogenesis, ultrastructure-and network integrity in skeletal-muscle from McArdle/control mice and two patients. We also determined VO2peak in patients (both sexes, N = 145) and healthy controls (N = 133). ResultsBesides corroborating very poor VO2peak values in patients and impairment in muscle glycolytic flux, we found that, in McArdle muscle: (a) damaged fibers are likely those with a higher mitochondrial and glycogen content, which show major disruption of the three main cytoskeleton components-actin microfilaments, microtubules and intermediate filaments-thereby contributing to mitochondrial network disruption in skeletal muscle fibers; (b) there was an altered subcellular localization of mitochondrial fission/fusion proteins and of the sarcoplasmic reticulum protein calsequestrin-with subsequent alteration in mitochondrial dynamics/function; impairment in mitochondrial content/biogenesis; and (c) several OXPHOS-related complex proteins/activities were also affected. ConclusionsIn McArdle disease, severe muscle oxidative capacity impairment could also be explained by a disruption of the mitochondrial network, at least in those fibers with a higher capacity for glycogen accumulation. Our findings might pave the way for future research addressing the potential involvement of mitochondrial network alterations in the pathophysiology of other glycogenoses.

Generation of the First Human In Vitro Model for McArdle Disease Based on iPSC Technology.

McArdle disease is a rare autosomal recessive disorder caused by mutations in the PYGM gene. This gene encodes for the skeletal muscle isoform of glycogen phosphorylase (myophosphorylase), the first enzyme in glycogenolysis. Patients with this disorder are unable to obtain energy from their glycogen stored in skeletal muscle, prompting an exercise intolerance. Currently, there is no treatment for this disease, and the lack of suitable in vitro human models has prevented the search for therapies against it. In this article, we have established the first human iPSC-based model for McArdle disease. For the generation of this model, induced pluripotent stem cells (iPSCs) from a patient with McArdle disease (harbouring the homozygous mutation c.148C&gt;T; p.R50* in the PYGM gene) were differentiated into myogenic cells able to contract spontaneously in the presence of motor neurons and generate calcium transients, a proof of their maturity and functionality. Additionally, an isogenic skeletal muscle model of McArdle disease was created. As a proof-of-concept, we have tested in this model the rescue of PYGM expression by two different read-through compounds (PTC124 and RTC13). The developed model will be very useful as a platform for testing drugs or compounds with potential pharmacological activity.

ODP208 Hypoglycemia as a Presenting Feature of McArdle's Disease

Abstract Introduction McArdle's disease (glycogen storage disease type V) is an autosomal recessive disease caused by mutations in the gene encoding for the muscle isoform of glycogen phosphorylase (PYGM). Characteristic symptoms include exercise intolerance, myalgia, muscle stiffness. Approximately half develop rhabdomyolysis, myoglobinuria, and renal failure. Hypoglycemia is an uncommon presenting symptom. Case report A 36-year-old male, previous college football athlete presented with jitteriness and blurry vision while exercising over the last one year. Symptoms occur 12-15 minutes into aerobic exercise. Fingerstick blood sugar during these episodes were as low as 30 mg/dl and afterwards the patient reported fatigue all day long. Consuming high carbohydrate foods and fluids supplemented with dextrose prior to exercise mitigate his symptoms. He reported no fasting hypoglycemia. Retrospectively, the patient reports that for years he noticed feeling fatigued a few minutes into starting exerice which improves after short periods of rest "second wind phenomenon." He can perform heavy resistance exercise like weightlifting but struggles with sustained aerobic activity. Past medical history is significant for HLA B27 positivity, alopecia areata and uveitis. Medications include multivitamin and creatine supplements. Physical exam revealed a healthy, well developed muscular individual with no other remarkable findings. Family history is significant for McArdle's disease in his brother, diagnosed at age 20 based on a muscle biopsy after multiple episodes of rhabdomyolysis. Grandfather had diabetes mellitus and pancreatic carcinoma. Labs revealed a creatine kinase (CK) level of 1638.7 U/L (49-397 U/L), CK-MB 49.1 ((0.1-5.9 ng/ml), 8 AM morning cortisol of 12.3 ug/dl (4.2-22.4 ug/dl), A1c 5.3%. There was no myoglobinuria. Thyroid function tests were within normal limits. Investigations done during an episode of exercise induced hypoglycemia - fingerstick blood sugar 44 mg/dl, plasma blood glucose 56 mg/dl(65-99 mg/dl), Insulin &amp;lt;0.5 mU/L(3-25mU/l), C-Peptide 0.5ng/ml(1.1-4.4ng/ml), Proinsulin 1.1 pmol/L(0-10. 0 pmol/L). Insulin autoantibody was negative. This ruled out exercise induced hyperinsulinemia. IGF-1 and IGF-2 levels were normal. Genetic study performed by the Glycogen Storage Disease Panel showed PYGM c.2262del (p. Lys754Asnfs*49), Pathogenic, PYGM c.1537A&amp;gt;G (p. Ile513Val), Uncertain Significance, PYGM c.833G&amp;gt;C (p. Arg278Pro), Uncertain Significance. Subsequently, the patient's brother underwent genetic testing, which confirmed the presence of all three before-mentioned PYGM variants. His father was found to carry the two variants of undetermined significance, suggesting that the patient and his brother inherited the pathogenic variant from their deceased mother. Discussion The patient's medical history, along with his personal and family's genetic findings were found to be consistent with McArdle's disease. Our patient's presentation is unique in that his exercise tolerance is much higher as compared to most individuals with McArdle's and his presenting complaint was hypoglycemia. Additionally, one of the variants of uncertain significance is likely to be recognized as pathogenic in the future. Presentation: No date and time listed

First Case Report of McArdle Disease and Alive Renal Transplantation

First Case Report of McArdle Disease and Alive Renal Transplantation

MTAP deficiency contributes to immune landscape remodelling and tumour evasion.

Methylthioadenosine phosphorylase (MTAP) deficiency occurs in various malignancies and is associated with poor survival in cancer patients. However, the mechanisms underlying tumour progression due to MTAP loss are yet to be elucidated. Utilizing integrated analyses of the transcriptome, proteome and secretome, we demonstrated that MTAP deficiency alters tumour-intrinsic, immune-related pathways and reprograms cytokine profiles towards a tumour-favourable environment. Additionally, MTAP-knockout cells exhibited a marked increase in the immune checkpoint protein PD-L1. Upon co-culturing primary T cells with cancer cells, MTAP loss-mediated PD-L1 upregulation inhibited T cell-mediated killing activity and induced several T cell exhaustion markers. In two xenograft tumour models, we showed a modest increase in average volume of tumours derived from MTAP-deficient cells than that of MTAP-proficient tumours. Surprisingly, a remarkable increase in tumour size was observed in humanized mice bearing MTAP-deficient tumours, as compared to their MTAP-expressing counterparts. Following immunophenotypic characterization of tumour-infiltrating leukocytes by mass cytometry analysis, MTAP-deficient tumours were found to display decreased immune infiltrates with lower proportions of both T lymphocytes and natural killer cells and higher proportions of immunosuppressive cells as compared to MTAP-expressing tumour xenografts. Taken together, our results suggest that MTAP deficiency restructures the tumour immune microenvironment, promoting tumour progression and immune evasion.

FP.18 Modified ketogenic diet in patients with McArdle disease: A double-blind, placebo-controlled, cross-over study

McArdle disease is caused by myophosphorylase deficiency leading to blocked glycogen breakdown in skeletal muscle. Patients present with exercise intolerance and muscle pain, which can progress to muscle damage. To date there is no cure for McArdle disease. A modified ketogenic diet regime as treatment option has shown promising early results in a previously published pilot-study. The positive effects were partly caused by provision of alternative fuels in the form of ketone bodies and by improvement of fat metabolism. The present study investigates if the modified ketogenic diet regimes investigated in the pilot study are effective in improving exercise capacity in a larger cohort of patients with McArdle disease in a controlled set up. Patients are randomized in this ongoing double-blind, placebo-controlled, cross-over study to receive a modified ketogenic diet or placebo diet first for 3 weeks followed by a wash-out period of a minimum of 2 weeks followed by the opposite diet. The primary outcome is changes in heart rate during constant load cycling. Secondary outcomes include changes in plasma metabolites including ketone bodies, reduction in perceived exertion and changes in indirect calorimetry measures. So far, 18 patients with verified McArdle disease from Denmark and the United Kingdom have been included. Half of the patients (10) received placebo and a ketogenic diet regime containing 75%/15%/10% (fat/protein/carbohydrate) of which 8 completed and 2 dropped out. The other half (8) received a ketogenic diet containing 80%/15%/5% (fat/protein/carbohydrate) or placebo. In this part, 2 have completed, 5 are ongoing and 1 dropped out. The goal is to include a total of 20 patients. The study remains blinded and the results will be analyzed when the last participant has completed the study. The results will be presented at the conference.

P.74 Using high-field magnetic resonance spectroscopy to measure muscle glycogen in patients with McArdle disease

Glycogen plays a critical role as an energy source in skeletal muscle. McArdle disease is a recessively inherited disorder in which muscle glycogen breakdown is blocked due to myophosphorylase deficiency. The patients suffer from severe exercise intolerance marked by premature fatigue with muscle contractures and episodic rhabdomyolysis. Additionally, some patients show progressive muscular atrophy when they get older, mainly in lumbar paraspinal muscles but not in thigh or calf muscles. The cause of fat replacement in older McArdle patients is unknown but could relate to a higher glycogen accumulation in their muscles. Utilizing the high sensitivity of 13C magnetic resonance spectroscopy at 7 Tesla field strength, we wanted to quantify muscle glycogen in lumbar, thigh and calf muscles in young McArdle patients as well as healthy controls to test the hypothesis of variable glycogen content in muscles of patients with McArdle disease. Preliminary results from 5 patients and 8 controls, show increased muscle glycogen concentration in the calf (4.4 times normal levels, p = 0.002), hamstrings (2.7 times normal levels, p = 0.02) and anterior thigh compartment (3.2 times normal levels, p = 0.01), while there was no difference in the lumbar muscle glycogen content vs. healthy (p = 0.6). No clear pattern of muscle glycogen distribution was seen in neither the McArdle nor the control groups. Our results are in line with previous studies in that we see a 3-5 times increase in glycogen compared to control. Surprisingly, this is not seen in the lumbar muscle group, which is the muscle group most prone to fat replacement with age. Thus, it does not appear that a difference in glycogen concentration between muscles of McArdle patients can explain the fat replacement seen in specific muscles groups of older patients.

FP.06 Use of an exercise challenge system to define a universal proteomic signature of muscle injury in a diverse set of adults with inherited myopathy

Several inherited myopathies are defined by an enhanced injury response to exercise. However, current understanding of muscle injury depending on the underlying genetic lesion is poorly understood. We used an established exercise intervention along with the SOMAscan 7K platform to characterize serum proteomic signatures of exercise-induced muscle injury in a diverse set of adults with myopathy. Participants included healthy volunteers, Becker muscular dystrophy (BMD), Limb-girdle muscular dystrophies R9 (LGMDR9) and R12 (LGMDR12), and McArdle disease (McA). Muscle injury was induced by an exercise challenge consisting of high-intensity interval cycling exercise followed by a leg strength test, which has been shown to cause injury in BMD and McA. Blood samples were collected before exercise and at intervals of up to 24 hours post-exercise. We identified an indication-independent novel cluster of 27 plasma-based biomarkers that distinguished pre-exercise myopathy individuals from healthy controls. The exercise response of this distinguishing cluster revealed two subsets of proteins, those that further changed after exercise and those that were exercise-independent. Exercise-dependent biomarkers demonstrated a clear time-dependency, with >90% increasing to maximal levels at 2-4 hours post-injury. When comparing indication-specific injury responses, BMD, LGMDR9, and McA revealed a surprising degree of overlap (33 proteins), including 15 proteins that were not increased at baseline in any indication. In comparison, LGMDR12 individuals demonstrated elevated baseline signature markers but no significant injury response. The controls showed no significant biomarker response to the exercise challenge. These data not only provide several new biomarker candidates for distinguishing muscle injury but highlight significant common features between indications, suggesting a common mechanism of muscle injury and breakdown, independent of the underlying pathophysiology.

Seltene Erkrankungen in der Differenzialdiagnose bei Myalgien

Myalgia describes pain in the skeletal muscles. According to the current German clinical guidelines from 2020 (AWMF register number: 030/051), the initial diagnostic assessment consists of the anamnesis, clinical examination, electrophysiological examination and standard laboratory tests. Additional special examinations, such as molecular genetic investigations, special laboratory tests, medical imaging and muscle biopsy are only needed in certain cases. This article focuses on rare neurological diseases that are classically associated with myalgia. In this context etiologically different diseases are considered, whereby some genetically linked diseases (fascioscapulohumeral dystrophy, FSHD, dystrophia myotonica, McArdle's disease, Pompe's disease, limb girdle muscular dystrophy) are contrasted with diseases with an (auto)immune-related pathogenesis (stiff-person syndrome, Isaacs syndrome). The aspects relevant for the diagnosis are particularly highlighted. The therapeutic aspects of the diseases are not part of this article.

Immunodeficiency and autoimmunity: companions not opposites.

Autoimmunity has long been regarded as the polar opposite of immunodeficiency, but clinical and experimental evidence refute this notion. Indeed, numerous inborn or acquired immunodeficiency syndromes are characterized by the development of autoimmune complications in the setting of deficient immune defenses against microbial pathogens. Appreciation that much of the daily business of a healthy immune system is the avoidance of potentially harmful responses to innocuous environmental antigens or components of the host organism helps provide a context for these observations. In this issue of the JCI, Abt and colleagues report on purine nucleoside phosphorylase (PNP) deficiency, exploring the basis for the autoimmune complications that develop in this particular form of T cell immune deficiency and assigning a key role for overactivation of TLR7.

Genomic landscape of non-small-cell lung cancer with methylthioadenosine phosphorylase (MTAP) deficiency.

New treatment strategies for advanced non-small-cell lung carcinoma (NSCLC) include synthetic lethality targets focused on protein arginine methyl transferases such as PRMT5 that exploit the impact of genomic loss of methylthioadenosine phosphorylase (MTAP). Twenty nine thousand three hundred seventy nine advanced NSCLC cases underwent hybrid-capture based comprehensive genomic profiling between June 1, 2018 and May 31, 2020. PD-L1 expression was determined by immunohistochemistry (Dako 22C3 PharmDx assay). 13.4% (3928/29,379) NSCLC cases exhibited MTAP loss distributed in adenocarcinoma (59%), squamous cell carcinoma (22%), NSCLC not otherwise specified (16%), and 1% each for large-cell neuroendocrine, sarcomatoid, and adenosquamous carcinoma. Statistically significant differences in mitogenic driver alterations included more KRAS G12C mutations in MTAP-intact versus MTAP-lost (12% vs. 10%, p=0.0003) and fewer EGFR short variant mutations in MTAP-intact versus MTAP-lost NSCLC (10% vs. 13%, p < 0.0001). Statistically significant differences in currently untargetable genomic alterations included higher frequencies of TP53 (70% vs. 63%, p < 0.0001) and RB1 inactivation (10% vs. 2%, p < 0.0001) in MTAP-intact compared to MTAP-lost NSCLC. SMARCA4 inactivation (7% vs. 10%, p < 0.0001) was less frequent in MTAP-intact versus MTAP-lost NSCLC. Alterations in ERBB2, MET, ALK, ROS1, and NTRK1 did not significantly differ between the two groups. Predictors of immunotherapy efficacy were higher in MTAP-intact versus MTAP-lost NSCLC including tumor mutational burden (9.4 vs. 8.6 mut/Mb, p=0.001) and low (30% vs. 28%, p=0.01) and high PD-L1 (32% vs. 30%, p=0.01) expression. Alterations in biomarkers potentially predictive of immune checkpoint inhibitor resistance (STK11, KEAP1, and MDM2) were similar in the two groups. MTAP loss occurs in 13% of NSCLC, supporting the development of targeted therapies to exploit PRMT5 hyper-dependence. MTAP loss is accompanied by small differences in targeted and immunotherapy options which may impact future combination strategies.

Purine nucleoside phosphorylase deficiency induces p53-mediated intrinsic apoptosis in human induced pluripotent stem cell-derived neurons

Purine nucleoside phosphorylase (PNP) is an important enzyme in the purine degradation and salvage pathway. PNP deficiency results in marked T lineage lymphopenia and severe immunodeficiency. Additionally, PNP-deficient patients and mice suffer from diverse non-infectious neurological abnormalities of unknown etiology. To further investigate the cause for these neurologic abnormalities, induced pluripotent stem cells (iPSC) from two PNP-deficient patients were differentiated into neurons. The iPSC-derived PNP-deficient neurons had significantly reduced soma and nuclei volumes. The PNP-deficient neurons demonstrated increased spontaneous and staurosporine-induced apoptosis, measured by cleaved caspase-3 expression, together with decreased mitochondrial membrane potential and increased cleaved caspase-9 expression, indicative of enhanced intrinsic apoptosis. Greater expression of tumor protein p53 was also observed in these neurons, and inhibition of p53 using pifithrin-α prevented the apoptosis. Importantly, treatment of the iPSC-derived PNP-deficient neurons with exogenous PNP enzyme alleviated the apoptosis. Inhibition of ribonucleotide reductase (RNR) in iPSC derived from PNP-proficient neurons with hydroxyurea or with nicotinamide and trichostatin A increased the intrinsic neuronal apoptosis, implicating RNR dysfunction as the potential mechanism for the damage caused by PNP deficiency. The findings presented here establish a potential mechanism for the neurological defects observed in PNP-deficient patients and reinforce the critical role that PNP has for neuronal viability.