The Danger of Constipation with TANGO2 Deficiency Disorder (TDD)
Robin Mitchell, Bob Mitchell
TANGO2 Research Foundation, Middletown, CT, USA
Background/Purpose: Our daughter was diagnosed with TDD at age 27 years old in 2022 when she experienced a life-threatening metabolic crisis that we believe was caused, in part, by chronic and severe constipation and an ileus (intestines cannot push out waste). The crisis was the unfortunate culmination of two months of poor health characterized by the reappearance of spells of ataxia after many years of being spell-free and a non-specific and vague feeling of being "unwell". Although she was not able to specifically identify her constipation, we now realize that she was experiencing many of the symptoms for months: fullness in her stomach that led to eating only bites of her meals, extreme discomfort, backache, and nausea. When the crisis occurred, she was in the ICU for 11 days, and the constipation and an ileus were confirmed.
Intervention: Our daughter was hospitalized for almost two months and during that time she began daily use of Miralax (polyethylene glycol 3350) and Senokot (docusate sodium), both are a laxative and stool softener. Because she is prone to constipation which we believe leads to dehydration and poor nutrition absorption, her care providers recommended continuing these laxatives on a daily basis.
Maintenance: Over the past two years since her crisis and TDD diagnosis, we have continued daily use of Miralax and Senokot when we suspect constipation. In addition to Miralax and Senokot we try to keep her constipation-free by encouraging daily walks and exercise, lots of fiber in her meals, and most importantly good daily hydration (i.e., drinking lots of water).
Conclusion: Becoming aware of when our daughter might be constipated is challenging, but we have found that constipation triggers a severe and unpleasant mood that is alleviated when she is “constipation-free”. Furthermore, we believe this care regimen supports our daughter in staying out of metabolic crisis.
Dealing with Spasticity in Daily Movements Through Botox Injections
Lisa Wilson
TANGO2 Research Foundation, Middletown, CT, USA
Background/Purpose: Tyler is a 24 years old male. He uses a posterior walker for short distances. A wheelchair is used for fatigue and long durations of time. He has spastic quadriparesis and dystonia. Increased tightness is interfering with function, hygiene and positioning, despite oral antispasticity medication (15mg Baclofen) twice daily.
Intervention: At 105 pounds Tyler receives Onabotulinumtoxin A (OBT-A), also known by the brand name Botox, injections under stimulation guidance as follows:
Bilateral hip adductors 75 units each side
Bilateral Hamstrings 75 units each side
Bilateral Soleus 75 units each side
Botox reduces the spasticity of the muscle into which it was injected. Prior to the injections Tyler is given a large quantity of ice as a numbing agent for the targeted areas. The following are important after receiving the injections: 1) Stretch the muscle which was tight previously and 2) Strengthen the opposite muscles so they can counteract the strength of the tight muscles.
Maintenance: In the days directly following his Botox injections appointment, Tyler’s physical therapy sessions will target the injected areas with stretching twice within a week.
Tyler’s physiatrist recommends he repeat the Botox injections every 3 months. The effectiveness of the injections varies between visits. This is dependent on Tyler’s health during this time. If he is struggling with illness or fatigue there is minimal improvement in his spasticity in the duration between injection appointments.
Quality of life: Tyler’s spasticity makes daily movements very difficult for him. The Botox injections do allow him some fluidity in certain movements and independence with basic tasks.
Conclusion: Tyler has received Botox injections for 12 years. The effectiveness varies depending on his health proceeding the injections. Our family continues to pursue these injections every 3 months as we do see the overall effectiveness these provide him in his activities of daily living.
Podcast Short Series: Discussion of Personal Well-Being for Carers of TDD
Amanda Hull
TANGO2 Research Foundation, Middletown, CT, USA
Background/Purpose: Research tells us the emotional toll of caring for a rare disease child is complex & “many parents are fearful of the long-term implications of a rare disease, which inevitably has an effect on the entire family” (Kenny et al, 2022). Because rare diseases are unique and uncommon, often caregivers assume they have to travel the rare disease journey alone and are unaware of disease specific social support in its many forms. Research also suggests rare diseases “still lag behind other diseases in terms of published guidelines on psychosocial management, support and education. At present, patient advocacy organizations are often the only source of trustworthy information and support” (Bogart et al, 2017).
Intervention: As part of an 8 episode podcast supported by Amgen and produced by The TANGO2 Research Foundation and its stakeholder community, Educational Psychologist and TANGO2 parent, Dr. Amanda Hull developed 3 guided emotional distress reduction coaching podcasts. Each podcast discusses useful tips and strategies to support personal well-being whilst being the carer to a loved one with TANGO2 deficiency disorder. She uses both her personal and professional experiences to explore emotional wellbeing whilst being a carer for a loved one who has a diagnosis of TANGO2 deficiency disorder.
In the first episode she explores the use of strategies to stay present amongst difficult times. She looks at the use of mindfulness and even explores this through eating some chocolate! Another episode explores reducing personal distress using breathing techniques and visualization strategies. Listeners will learn and be reminded of how to set personal goals via a guided goal setting activity. She explores the use of various strategies and activities that can help with personal wellbeing. The third podcast episode focuses on how to make use of keeping a personal journal. Dr Amanda Hull discusses the type of thing that can be included in a journal in order to help focus the mind and safeguard personal wellbeing. She also explores gratitude practices and helps you to remember the benefits of such mindsets.
Maintenance: By visiting the TANGO2 Research Foundation YouTube Channel, these podcasts remain easy to access and an essential educational social support resource.
Conclusion: The series is aimed to help caregivers make time for themselves, understand how to safeguard emotional health and wellbeing while caring for a loved one with a rare disease. It is not designed to replace any direct therapeutic support and listeners should always consult personal medical caregivers if they have any concerns about their wellbeing and emotional health.
TANGO2 Deficiency Disorder (TDD) in the “Lyme” Light
Kasha Morris1, Cheyenne Beach2
1Parent and Co-Founder, TANGO2 Research Foundation, Middletown, CT, USA, 2Pediatric Cardiologist, Yale New Haven Children’s Hospital, New Haven, CT, USA
Background/Purpose: An individual with TDD can have atypical presentations of common illnesses. An emergency action plan (EP), careful monitoring for arrhythmias and metabolic decompensation and alternative methods of nutritional intake are key to recovery.
A 20 year old male with TDD presented with 3 days of fever, headache and vomiting. He had a tick removed from his leg two weeks prior and subsequently received a single empiric dose of doxycycline.
Intervention: Due to high risk of metabolic crisis and life-threatening arrhythmias associated with TDD with illness, an EP was presented and followed in the ED. Vital signs were normal, but he appeared lethargic and uncomfortable. Initial labs including glucose, electrolytes, complete blood count, procalcitonin and swabs for COVID, RSV, and influenza were unrevealing. EKG was normal. He started dextrose fluids, received tylenol and zofran and was admitted with a presumed diagnosis of viral gastroenteritis.
Shortly after admission a tick was found in his groin area and removed. He was given a dose of ceftriaxone for empiric Lyme disease treatment with tick-borne testing sent. Genetics and cardiology teams consulted, and he continued his home medications with dextrose IVF. He did not tolerate oral medications, fluids, or food, so a peripherally inserted central catheter (PICC) and nasojejunal (NJ) tube were placed. Lyme studies eventually returned positive. Ceftriaxone was continued for treatment of Lyme meningitis.
Maintenance: Throughout hospitalization he had cardiac monitoring and frequent assessment for signs of metabolic crisis (elevated CK, AST). Once he could tolerate a regular diet, IV ceftriaxone was switched to PO doxycycline. Lethargy, neck pain, headache, and activity improved and eventually resolved. He was sent home in good condition once at baseline mental/activity status to complete a 21-day course of doxycycline for lyme meningitis.
Quality of life/Conclusion: Acute illness in a person with TDD might have atypical and more severe presentation, making diagnosis and appropriate treatment challenging. The EP and close monitoring for arrhythmia and metabolic crisis help to prevent decompensation. Consistent nutritional support and B vitamins, which are not typically high priority in management of acute illness, are vital in preventing the most dangerous symptoms of TANGO2.
Finding Your Way with Things You Love
Amy Clay, Katie Clay
TANGO2 Research Foundation, Middletown, CT, USA
Background/Purpose: Life’s paths are different for everyone, especially someone with a disability. These challenges can affect various aspects of life, including higher education, employment, independence, and social integration.
Interventions: Post high school we are finding opportunities for Katie, our daughter with TDD to not only continue to do things she loves but also continue to grow her community and generate revenue.
Katie continues to overcome her fears/hesitation of doing new things. This started years ago with beginning to take DJ lessons and playing ice hockey. Today both are front and center in her life and are her favorite things to do. Both have opened opportunities to expand her circle of friends, build self confidence, develop a sense of importance, develop a work ethic, and to find employment.
We had no idea at the time how starting to play hockey or starting to take DJ lessons would impact her life. She has had so many successful opportunities just by taking that leap.
Maintenance/Quality of Life: Success number 1 - Katie is the first from her high school to attend the LifePrep Program at Nazareth University. The process required us to apply, get approval from her high school (as this was not the normal path for their Special Ed students), and interview with multiple people.
Success number 2 - Connecting with the Women’s hockey coach Katie was invited to come to the games and hang with one of the grad students (who happened to also help with her hockey team). With the help of the grad student, Katie was the first in her program to become employed by the Nazareth University Athletic Department.
Success number 3 - Katie has always loved music but was not interested in playing an instrument or singing. 4 years ago she reluctantly attended a DJ camp at a local music school and it has taken off. She now has her own DJ equipment and has had the opportunity to earn some money playing music at a number of parties.
Conclusion: In conclusion, we would like to show how sometimes you have to forge your own path, make your own opportunities. Life with a disability like TANGO2 does not have to limit or define you. Taking the leap of doing new things can be AWESOME!
Why Every Child Deserves Marmite!
Hannah Driffill, Hope Driffill
TANGO2 Research Foundation, Middletown, CT, USA
Background/Purpose: Marmite. . . love it or hate could save your life especially if you are a TANGO2 affected individual. Marmite is a savory spread made from yeast extract and fortified with B vitamins. It’s especially popular in the United Kingdom, where it’s frequently spread onto toast, crackers and sandwiches. Its strong, salty flavor profile makes it divisive too—either you love it or you hate it.
While research on the specific benefits of B vitamins for individuals with TANGO2 deficiency disorder (TDD) is limited, B vitamins have emerged as a potential treatment for rescuing TANGO2 deficiency disorder patients from life-threatening metabolic and cardiac crises and significantly improve quality life for affected TANGO2 individuals.
Intervention: Diagnosed with TDD aged 6 years old, Phoebe struggled with many of the symptoms associated with TDD. However, she always requested a daily spoonful of Marmite from around age 2. As her parents we tried to restrict this, worrying about the salt content. Little did we know she was asking for a potentially life-saving vitamin supplement!
Maintenance: So, now thanks to research supported by the TANGO2 Research Foundation (T2RF) we know the benefits and protective effects of Marmite and its advertised vitamin B complex. Now, our daughter can have all the Marmite she fancies . . . and extra vitamin drops, sprays, and/or gummies.
Quality of Life: With the inclusion of B-vitamin complex daily Phoebe’s progress in just 1 year has blown our minds. We are forever thankful that we now know about B vitamins and the research that supports it as a potential TDD treatment.
Conclusion: Love it or hate it. We now all have Marmite!!!
A Winding Education Path: Our TANGO2 Son’s Hard Fought Journey to a Diploma
Jamie Angus, Oliver Angus
TANGO2 Research Foundation, Middletown, CT, USA
Background/Purpose: The educational path for our TANGO2 son has included 6 schools, 3 districts, and both public and private placements in 2 states. The constant search for the right educational "fit" has been exhausting and rewarding, as we wondered if the next move would provide more opportunities or challenges. As a medically fragile student, schools have not always understood how best to support him. Throughout his journey, he has had to shorten his school day or be absent altogether due to fatigue. His resilience is a story of hope.
Intervention: Our son has always been classified as a special education student, receiving support at school, but it wasn’t enough. He also needed speech, occupational and vision therapy intervention for several years outside of school. When your child has chronic fatigue, it can be very difficult to have them go to school all day and participate in extra therapy sessions as well. Due to his language disorder, navigating social interactions has also been a challenge. Luckily, he started B5 at the age of 4, along with CoQ10 and Carnitine, the mitochondrial cocktail to support energy needs throughout the school day.
Maintenance: Navigating the challenges of school and puberty have been tough, as we tried to maintain our son’s energy, especially during the middle and high school years. Maintaining supplements or increasing them as needed has been very important as well as maintaining friendship and social support when his energy has flagged.
Quality of Life: It has been a struggle to maintain quality of life during the high school years, as the academic and social demands continued to increase. At a large public high school, navigating the campus and the pressure to perform at a level with typical peers began to weigh on him, so during his senior year he moved to a private school with a smaller environment and a 1:1 teaching model. He has thrived there. He now remembers that learning can be fun, positive, and challenging.
Conclusion: It has been a long and winding educational road, but we couldn’t be prouder of our son for receiving his high school diploma in June 2024.
A Systematic Approach to Identifying 22q11.2 Deletion Syndrome Patients with a Dual Diagnosis of TANGO2 Deficiency Disorder
Grayson Northcutt
Baylor College of Medicine, Houston, TX, USA
Objective: TANGO2 deficiency disorder (TDD) is both a serious and life-threatening autosomal recessive condition, caused by biallelic variants in TANGO2. Recent studies have discovered a sub-group of patients within the TDD population who have a secondary diagnosis of 22q11.2 deletion syndrome (22qDS). Low numbers of affected individuals, overlapping cardiac complications and lack of key identifying features complicates ascertaining a second genetic diagnosis among this cohort. This abstract summarizes a novel approach to discerning a secondary diagnosis of TDD in those with a pre-existing 22qDS diagnosis.
Methods: This study was a retrospective chart review to analyze 22qDS patients within the Texas Children’s hospital EPIC database for likelihood of a secondary diagnosis of TDD. A query of all patients within the EMR was performed to identify any individuals with a medical history or diagnosis of 22qDS or Velocardiofacial syndrome. In total, 793 patient charts were returned with 704 being eligible to participate in the study. Manual review of all eligible participants utilized the electronic medical records (EMRs) search function to return results for 11 key clinical features associated with TDD. In addition, a summary of pertinent medical information was recorded for each patient. Six groups with increasing likelihood of TDD were established with group 1 having the lowest likelihood and group 6 the highest for a secondary diagnosis of TDD. Patient charts were separated into these groups with a holistic approach using both the number of TDD clinical features and medical summary to determine TDD likelihood. A parental survey, inquiring about TDD features seen at home, was distributed to 126 patient guardians using purposeful sampling with individuals in higher likelihood groups being prioritized.
Results: Twelve individuals responded with a surprising number noting features of TDD or TDD spells at home.
Conclusion: By developing a method to identify TDD patients in the 22qDS population lethal metabolic crisis can be avoided with proper medical management. The number of clinical features alone is not an effective means of ascertaining TDD in the 22qDS population. We suggest that inclusion of parental experience in addition to features and clinical gestalt will lead to the highest likelihood of finding those with a dual diagnosis.
Multicenter Appraisal of Comorbid TANGO2 Deficiency Disorder in Patients with 22q11.2 Deletion Syndrome
Owlett, Laura D.1, Zapanta, Bianca2, Sandkuhler, Sarah E.1, Ames, Elizabeth G.3, Hickey, Scott E.2, Mackenzie, Samuel J.1, Meisner, Joshua K.3
1University of Rochester Medical Center, Rochester, NY, USA, 2Nationwide Children’s Hospital, Columbus, OH, USA, 3University of Michigan, Ann Arbor, MI, USA
Objective: TANGO2 deficiency disorder (TDD) is a rare, autosomal recessive condition caused by pathogenic variants in TANGO2, a gene residing within the region commonly deleted in 22q11.2 deletion syndrome (22q11.2DS). Although patients with 22q11.2DS are at substantially higher risk for comorbid TDD, it remains underdiagnosed within 22q11.2DS, likely due to overlapping symptomatology and lack of knowledge about TDD. Initiation of B-vitamin supplementation may provide therapeutic benefit in TDD, highlighting the need for effective screening methods to improve diagnosis rates in this at-risk group.
Methods: In this retrospective, multicenter study, we evaluated two cohorts of patients with 22q11.2DS (total N=435) for possible comorbid TDD using two different symptom-based screening methods (free text-mining and manual chart review versus manual chart review alone). Methodology of cohort 1 screening method successfully identified a known 22q11.2DS patient with TDD. Combined, these two cohorts identified 21 living patients meeting consensus recommendation for TANGO2 testing for suspected comorbid TDD.
Results: Of the nine patients undergoing TANGO2 sequencing with del/dup analysis, none were ultimately diagnosed with TDD. Of the 12 deaths in the suspected comorbid TDD cohort, some of these patients exhibited atypical symptoms (rhabdomyolysis, cardiac arrhythmia, or metabolic crisis) suspicious for comorbid TDD contributing to their death.
Conclusion: Collectively, these findings highlight the need for robust prospective screening tools for diagnosing comorbid TDD in patients with 22q11.2DS.
Dystonia, Ataxia, and Episodic Weakness are Common in TANGO2 Deficiency Disorder and May Respond to B-Vitamin Supplementation
Sandkuhler, Sarah E.1,* Myers, Samantha1,* Hewitt, Angela L.1, Vermilion, Jennifer1, Hull, Miriam2, Mink, Jonathan W.1, Mackenzie, Samuel J.1
1University of Rochester Medical Center, Rochester, NY, USA, 2Baylor College of Medicine, Houston, TX, USA
Objective: To characterize the presence of movement disorders or episodic fatigue or weakness (“TANGO2 spells”) in TANGO2 Deficiency Disorder (TDD) and examine the impact of B-vitamin supplementation on these symptoms.
Methods: Subjects in this study are participants in the ongoing TDD Natural History Study and were recruited through outreach from TANGO2 Research Foundation. Caregivers of recruited subjects provided representative videos demonstrating subjects’ abnormal movements. All submitted videos were reviewed by at least three pediatric movement disorder specialists and one physician with expertise in TDD. Reviewers met and achieved consensus on the movement disorder phenomenologies present in each video. Finally, semi-structured interviews were conducted with caregivers via Zoom to collect additional information on the qualities, timing, and treatments tried for subjects’ movement disorders.
Results: Videos were reviewed for a total of 26 participants and follow-up interviews were completed for 16/26 at time of submission. 15/16 (94%) subjects had movement disorders or TANGO2 spells (1 ataxia, 3 dystonia, 2 TANGO2 spells, 2 ataxia and dystonia, 5 dystonia and TANGO2 spells, 2 all), and 8/16 (50%) reported a movement disorder or spell as the first presenting symptom. The one subject without movement disorders or TANGO2 spells received early treatment and has no symptoms of TDD. 13/16 (81%) subjects receive B-vitamin supplementation including B5, and 7/13 (54%) reported complete resolution of movement disorders and TANGO2 spells after initiating B-vitamin supplementation.
Conclusions: Movement disorders or TANGO2 spells are a common symptom in TDD and are often among the first symptoms of the disorder, presenting a key opportunity for early recognition and diagnosis of TDD prior to the onset of metabolic crisis. Movement disorders may be amenable to treatment with B-vitamin supplementation.
Mechanistic Investigation Using a C. elegans Model of TANGO2 Deficiency Disorder Suggests a Dual Role for TANGO2 in Coenzyme A Maintenance and Redox Homeostasis
Youngs, Kayla S.1, Sandkuhler, Sarah E.1, Owlett, Laura1, Leonardi, Roberta2, Wojtovich, Andrew P.1, Mackenzie, Samuel J.1
1University of Rochester Medical Center, Rochester, NY, USA, 2West Virginia University School of Medicine, Morgantown, WV, USA
Background: C. elegans is a powerful model system for studying rare disease given its well-defined genome and anatomy, genetic similarity to humans, low cost, high reproductive rate, and transparent body. C. elegans harbors two homologs of the TANGO2 gene, previously named hrg-9 and hrg-10 due to their up-regulation under low-heme conditions. While emerging evidence implicates TANGO2 as a critical protein for mitochondrial function, potentially through the degradation and salvage of coenzyme A (CoA), it was recently proposed that TANGO2 functions as a heme chaperone.
Objectives: We first sought to replicate key experiments related to heme trafficking in double knockout nematodes (DKO) lacking HRG-9 and HRG-10. We then performed expanded phenotyping of these worms and investigated the potential therapeutic effects of pantothenate and cysteamine, two byproducts of CoA metabolism.
Results: Using the previously generated DKO nematodes, we were unable to validate previous experiments implicating TANGO2 as a heme chaperone. RT-qPCR analysis revealed a marked 12.1-fold enrichment of hrg-9 and a modest 1.3-fold enrichment of hrg-10 in response to paraquat, a ROS generator. We also noted several previously undescribed phenotypic features in DKO worms including a 62% decrease in median survival, a 66% reduction in brood size, poor swim motility, 20% slower pharyngeal pumping, and lawn avoidance behavior. Strikingly, HPLC analysis coupled with fluorescence detection revealed a 65% decrease in total CoA levels in DKO worms after 24 hours of fasting, whereas wildtype worms maintained CoA levels. Pantothenate and cysteamine were able to partially rescue the brood size and lawn avoidance phenotypes in DKO worms.
Conclusions: Overall, there is insufficient evidence to support heme transport as a primary function for TANGO2. C. elegans harboring deletions in TANGO2 homologs demonstrate a phenotype reminiscent of bioenergetic dysfunction and increased oxidative stress. Our lab is actively exploring the potential role of TANGO2 in the hydrolysis of pantetheine, a degradative byproduct of CoA and a precursor of pantothenate and cysteamine.
Human iPSCs-derived neuronal model to study the pathogenic mechanisms behind TANGO2 disease
Silvia Carestiato*1,2, Sofia Galli2, Aldamaria Puliti2,3, Paolo Scudieri2,3, Lisa Pavinato1, Giovanni Battista Ferrero4, Federico Zara2,3, Alfredo Brusco5,6
1University of Turin, Department of Medical Sciences, Turin, Italy, 2Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics, Maternal and Child Health (DiNOGMI), University of Genoa, Genoa, Italy, 3Medical Genetics Unit, IRCSS Giannina Gaslini Institute, Genoa, Italy, 4University of Turin, Department of Clinical and Biological Sciences, Orbassano, Italy, 5Città della Salute e della Scienza University Hospital, Medical Genetics Unit, Turin, Italy, 6University of Turin, Department of Neurosciences Rita Levi Montalcini, Turin, Italy
Background: The TANGO2 gene encodes the homonymous protein mainly involved in vesicular trafficking, mitochondrial oxidation, and cellular homeostasis. While its subcellular localization is still unclear, TANGO2-biallelic LoF variants are associated with an autosomal recessive disorder characterized by cardiac arrhythmia, metabolic crises, rhabdomyolysis, and kidney damage. Remarkably, the vast majority of T2D patients present with neurological impairment, characterized by developmental delay, intellectual disability, speech difficulties, motor delay, seizures, and MRI abnormalities, including microcephaly, brain atrophy, and white matter reduction.
Although a possible role in neuronal migration has been suggested, the effect of TANGO2 loss in neurons has never been investigated, constituting a major gap in understanding the disease.
Objective: This study focuses on the function of TANGO2 in neural stem cells and mature neurons, providing new insights into the pathogenesis of the disease.
Methods: We generated hiPSCs from two siblings with clinically different symptoms due to TANGO2 variants (c.262C>T (p.Arg88*); c.338delG (p.Gly113Alafs*10)), along with two healthy individuals serving as controls. Human iPSCs were employed to derive neural rosettes (NRs), neural progenitor cells (NPCs), and mature neurons. Lineage and morphological characterization were performed using immunofluorescence techniques, wound-healing and ROS detection assays, comparing the two siblings with control subjects.
Results: Analysis of NRs showed a significant area reduction (~45%) and impaired morphological organization in the severely affected patient. Furthermore, in the same patient, the wound-healing assay demonstrated altered migration in NPCs, supporting the previously reported role of TANGO2 in migration. Additionally, during the maturation of neurons, an increase in cell death was also observed. In this regard, the Reactive Oxygen Species (ROS) assay showed an oxidative stress condition supporting the involvement of TANGO2 in mitochondrial functions and cellular homeostasis. In contrast, no significant differences were found in NRs, NPCs, and mature neurons in the asymptomatic patient compared to controls.
Conclusion: In conclusion, we demonstrated the role of TANGO2 in the early stages of neurodevelopment, particularly in neural tube formation, cell migration, and neuronal maturation. Considering the peculiar siblings’ case, this study suggests potential protective gene/genetic modifiers influencing patient phenotypes, highlighting the need for further transcriptomic and proteomic analyses for future therapies.
Modeling TANGO2 Deficiency Disorder with Induced Pluripotent Stem Cell Cardiomyocytes Reveals Lipid Homeostasis Defects
Olivia Rechsteiner1, Sabrina Friedline2, Adam S Helms2, Joshua K Meisner2
1University of Rochester Medical Center, 2University of Michigan
Background: TANGO2 Deficiency Disorder (TDD) is a rare autosomal recessive disorder caused by a loss of function TANGO2 variants characterized by recurrent metabolic crises triggered by illness or fasting. During crises TDD patients are at risk of cardiomyopathy and sudden cardiac death from ventricular arrhythmias. Emerging evidence suggests loss of TANGO2 causes a secondary mitochondrial, lipid metabolism defect, and altered fatty acid oxidation.
Objective: Given the reproducible cardiac phenotype and reliance on fatty acid oxidative metabolism, cardiomyocytes offer a uniquely strong model for molecular mechanistic and therapeutic investigation, but optimal metabolic stress conditions to elicit TDD phenotype are currently unknown.
We performed systematic manipulation of metabolic stress conditions and phenotyping using lipid accumulation, contractile, and electrophysiology features in a human induced pluripotent stem cell cardiomyocyte (iPSC CMs) model of TDD to determine optimal metabolic stress conditions.
Methods: TANGO2 deficient (TANGO2-/-) iPSC line was generated using CRISPR-Cas9 for comparison to isogenic controls. Loss of TANGO2 protein was determined using western blot. Electrophysiological phenotyping was performed using a genetically encoded voltage sensitive fluorescent protein (Quasar2-mOrange lentiviral vector). Under varying metabolic stress conditions, action potential duration and contractile parameters were quantified in control and TANGO2-/- iPSC CMs using brightfield and fluorescent confocal microscopy. Lipid processing defects were quantified in TANGO2-/- and isogenic control iPSC-CMs using a neutral lipid stain (LipidTox) to assess for abnormalities in lipid accumulation under varying metabolic stress conditions. Lipid droplet size and intensity in fixed iPSC CMs were quantified using confocal microscopy and analyzed in CellProfiler. Metabolic stresses included combinatorial removal of glucose and addition of oleic and palmitic long chain fatty acids.
Results: Contractile and electrophysiological tests showed no significant differences between the TANGO2-/- and isogenic control iPSC CMs under individual metabolic stress conditions with similar trends across stress conditions. Preliminary data suggest increased lipid accumulation in the TANGO2-/- iPSC CMs compared to isogenic controls with minimal differences across metabolic stressor conditions.
Conclusions: Optimal metabolic stress conditions to induce TDD metabolic crisis in iPSC CMs remain elusive. However, these data suggest a baseline lipid metabolism defect in iPSC CMs with loss of TANGO2 that be further interrogated.
