I am extremely grateful to the PSI Foundation for its generous and critical support of our research endeavours in metabolic myopathies with a primary focus on fatty acid oxidation (FAO) disorders. This seminal support has furnished the basis for a number of clinical and basic research projects, the development of novel therapeutic interventions and a series of educational initiatives over the years.
Clinical relevance of fatty acid oxidation disorders
The metabolism of fatty acids (fatty acid oxidation) provides energy (ATP) for all high energy-dependent tissues such as muscle, heart, kidney, bowel, sperm, etc. The partial oxidation of fatty acids to ketones by the liver provides the brain with a critical alternative source of energy during times of hypoglycemia. The early recognition of fatty acid oxidation (FAO) disorders is very important for both pediatricians and child neurologists as they present with a spectrum of clinical disorders including progressive limb girdle lipid storage myopathy, recurrent episodes of life-threatening muscle breakdown (myoglobinuria), neuropathy, pigmentary retinopathy with night blindness, progressive cardiomyopathy, recurrent episodes of hypoglycemic hypoketotic coma or Reye-like syndrome, seizures, and mental retardation. They constitute a critical group of diseases because they are potentially rapidly fatal and a source of major morbidity. There is frequently a family history of sudden infant death syndrome (SIDS) in siblings. Early recognition and prompt institution of therapy and appropriate preventative measures, and in certain cases specific therapy, may be life saving and may significantly decrease long-term morbidity, particularly with respect to neurological sequelae, thereby significantly improving the quality of life for the child and their family. All currently known conditions are inherited as autosomal-recessive traits. There are now at least 25 known enzymes and specific transport proteins in the pathway of ß-oxidation and 18 have been associated with human disease. The most common defect is medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, which is one of the milder disorders, and which may have an incidence as high as 1 in 5000 live births. In the case of MCAD deficiency, if triggers for metabolic crisis such as fasting, prolonged exercise, shivering and stress are avoided and if there is rapid acute treatment of hypoglycemia with intravenous glucose infusion such as during infections with vomiting, the affected children should have an excellent outcome with a normal lifespan. Tissue dysfunction in FAO disorders arises from insufficient energy (ATP) production, deficient ketone body production by the liver, lipid storage in tissues and the toxicity of excessive metabolites that accumulate proximal to the metabolic block. The identification of abnormal serum acylcarnitines by electrospray ionization-tandem mass spectrometry of dried blood spots on filter paper in newborn screening programs has significantly enhanced the early recognition of these disorders which has allowed earlier intervention with an improvement in clinical outcome.
Results of our PSI supported research projects in fatty acid oxidation
Through PSI support, we have investigated the mechanisms of disease pathogenesis at a clinical, biochemical and molecular level through the intensive study of specific FAO disorders in vivo (in patients) and in vitro (in cell models) in order to provide insight into the precise correlation between genotype and phenotype and to provide key information regarding the protein and molecular basis of both normal and abnormal fatty acid oxidation. Using a translational bench-to-bedside approach, we have identified novel phenotypes and genotypes.
Carnitine palmitoyltransferase II (CPT II) deficiency
We identified carnitine palmitoyltransferase II (CPT II) deficiency, which is the most common cause overall of recurrent myoglobinuria (muscle breakdown) in males and females and in adults and in children, as a new cause for recurrent pancreatitis (Tein et al 1994). Furthermore on intensive clinical, biochemical and genetic study of a family pedigree with CPT II deficiency due to the common mutation (p.Ser113Leu), we demonstrated interesting clinical and biochemical heterogeneity in which the affected girl, who was homozygous for the mutation, had an unexpectedly high residual activity and her carrier brothers (who were heterozygous for the mutation) had lower than expected residual activities with unexpected clinical symptoms (Rafay et al 2005). This suggested that there were genetic, environmental and sex hormonal factors that influenced the biochemical and clinical presentations and highlighted the potential vulnerability of carriers if exposed to adequate FAO stressors, which was important for the counseling of the family.
Short-chain acyl-CoA dehydrogenase (SCAD) deficiency
In short-chain acyl-CoA dehydrogenase (SCAD) deficiency, we described a new clinical phenotype with progressive external ophthalmoplegia (limitation of eye movements) and multicore myopathy with severe contractures and early wheelchair dependence (Tein et al 1999). Based on the additional features of cataracts and cardiomyopathy, we investigated this young girl for evidence of elevated markers of free radical toxicity which we demonstrated in her blood. Based on this finding, we instituted a prospective treatment trial with antioxidant therapy which increased the power in her shoulder girdle muscles by six-fold, markedly improving her functional abilities in the upper extremities. Through our international network of colleagues, we then identified a series of children with the same mutation (c.319C>T) in the SCAD gene and identified common features of myopathy (30 % with multicore changes), developmental delay and the classic biomarkers but also found a wide clinical variability (Tein et al 2008). Of note, all patients were of Ashkenazi origin. Given the wide clinical variability, we concluded that this particular mutation could lead to wide clinical and biochemical phenotypic variability, suggesting a complex multifactorial/polygenic condition. Furthermore, we proposed that SCAD deficiency should be screened for in individuals with multicore myopathy, particularly among the Ashkenazim, given the potential for improvement or reversal of the muscle weakness with antioxidant therapy, particularly if instituted early before the development of severe muscle wasting and joint contractures. We then developed a cell model from the cultured skin fibroblasts of children with SCAD deficiency and with long-chain FAO defects such as CPT II and long-chain L-3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency in which we exposed the cells to an agent that enhanced free radical production. In order to simulate the typical stressors that lead to FAO crisis in affected children, we then exposed the cells to both hypoglycemia (as seen with fasting and vomiting) and hyperthermia (as seen with fever which is a stressor and also predisposes to the misfolding of certain proteins such as SCAD). We were able to demonstrate the extreme vulnerability of the SCAD and CPT II and LCHAD deficient cell lines to very early demise in culture, in sharp contrast to normal control cells and MCAD deficient cells which survived for significantly longer time periods. We were then able to increase cell survival in our SCAD and CPT II and LCHAD deficient cell lines by two- to seven-fold using specific antioxidants and an agent that increases the biogenesis of mitochondria (Zolkipli et al 2011). These remarkable results in cell culture will now form the basis for future clinical trials in children with these disorders.
Long-chain L-3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency
In LCHAD deficiency, we identified a new clinical phenotype with recurrent myoglobinuria and progressive neuropathy due to a novel genetic mutation (Ibdah et al 1998). Based on our careful clinical evaluation of our index case with this novel presentation and the apparent fragility of his muscle membranes to very minor walking exertion with release of muscle CK into the bloodstream, signifying muscle breakdown, and based on our knowledge of the membrane toxicity of long-chain fatty acids, we instituted a trial of oral prednisone. Prior to the prednisone the affected patient had marked limb girdle weakness and was almost wheelchair dependent. Following prednisone therapy, he had full restoration of muscle power to normal strength which was maintained on very low dose prednisone into adulthood (Tein et al 1995). His further course was complicated by progressive neuropathy leading to foot drop and marked weakness of the hands with a claw hand deformity whereby he could no longer write more than two lines at a time before fatigue. Again, based on emerging information regarding the importance of omega-3 very long-chain fatty acids (DHA) in nerve, mitochondrial and retinal membranes and the potential for deficiency in LCHAD deficiency, we supplemented our index case with a source of DHA which served to regenerate the peripheral nerves in his upper extremities leading to fully restored power of his hands and led to the reappearance of his formerly absent nerve conductions in the lower extremities which were also maintained on continuing DHA therapy (Tein et al 1999).
Carnitine/organic cation transporter family
In another project related to the clinical role of carnitine deficiency in male infertility, given that the highest concentrations of carnitine in the human body are found in spermatozoa and epididymal fluid (2000 X the serum carnitine concentrations), we demonstrated the different patterns of expression of the organic cation/carnitine transporter family (OCTN1, OCTN2 and OCTN3) in human sperm underlining the importance of carnitine transport and potentially reversible causes and treatment targets for male infertility (Xuan et al. 2003) as demonstrated in the mouse model of OCTN2 deficiency in which the associated male infertility is reversed with high dose L-carnitine therapy.
Knowledge Translation and Dissemination
In 1991, I founded and continue to direct the Neurometabolic Clinic, Neuroinvestigational Unit and Neurometabolic Research Laboratory at the Hospital for Sick Children, University of Toronto for the priorized clinical, biochemical and molecular investigation of children with metabolic myopathies and FAO disorders. We receive referrals from throughout Canada, the US, Caribbean, Europe, Middle East, Asia and South America. With the above investigations and PSI support, we have been able to expand the clinical phenotypes and genotypes, develop new diagnostic screening tests, and provide insight into the pathophysiological mechanisms of disease which has formed the basis for the development of new translational therapies aimed at bypassing or correcting the specific metabolic block, which have decreased long-term morbidity and mortality in affected individuals and have been successfully implemented internationally.
In 2010, the groundwork from our studies served as the basis for our formation of an International Metabolic Myopathies Focus Group which hosted over 150 international participants at the XIth International Child Neurology Congress in Cairo, May 2010. At each of the International Child Neurology Congresses in 2006, 2010, 2012, and 2014, we have organized a series of Neurometabolic Plenary Symposia as well as day-long Neurometabolic Satellite Symposia for the education of child neurologists, scientists, fellows, residents and nurses in different neurometabolic disorders including FAO disorders and metabolic myopathies with updates on new treatment strategies and novel pathophysiologic mechanisms. Given the participation by international colleagues, this has served to promote widespread dissemination of knowledge of the clinical recognition, diagnostic approach and treatment intervention as well as genetic counseling in these disorders.
PSI support has directly contributed to our publication of over 31 peer-reviewed articles in high impact journals such as Neurology, the Journal of Clinical Investigation and PLoS One and chapters in state-of-the-art Textbooks of Neurology such as Pediatric Neurology (Edited by Swaiman, Ashwal and Ferriero) and the Handbook of Clinical Neurology. The further impact of our clinical and basic research findings has elicited over 144 invitations for talks on Fatty Acid Oxidation Disorders and Metabolic Myopathies, 68 of which I have given as plenary talks at international congresses. This has included four Keynote Lectures at the Annual Scientific Congress of the Hong Kong Society of Child Neurology and Developmental Pediatrics, Nov. 2007; Presidential Symposium of the 10th Asian and Oceanian Congress of Child Neurology in Daegu, Korea June 2009; the Annual Garrod Association Congress, St. John’s Nfld, June 2010; the 2nd International Saudi Pediatric Neurology Congress, Nov. 2010. This work, in which PSI Foundation support was so critical, has also been honoured through my receipt of international awards (John Stobo Prichard Young Investigator Award, 8th International Congress of Child Neurology, Ljubljana, Slovenia. Sept. 1998; John H. Menkes Award, UCLA, Los Angeles, California, March 2012; Colleen Giblin Award Memorial Lectureship. Columbia University, NY, NY. May 2013).
Finally and very importantly, the funding from the PSI Foundation has enabled me to facilitate and nurture the training and development of a series of neurology residents, post-doctoral fellows and research trainees both locally and internationally who will serve as the next generation of clinician-scientists in this field.
Ingrid Tein BSc, MD, FRPC(C)
Director, Neurometabolic Clinic and Research Laboratory
Staff Neurologist, Division of Neurology
Associate Professor of Pediatrics, Laboratory Medicine and Pathobiology
Senior Associate Scientist, Genetics and Genome Biology Program, The Research Institute
The Hospital for Sick Children, University of Toronto
President, The International Child Neurology Association
Dr. Ingrid Tein obtained her BSc, MD, Pediatric fellowship and Pediatric Neurology fellowship at the University of Toronto. She completed her post-doctoral research in fatty acid oxidation disorders at Hopital Necker-Enfants Malades, University of Paris with Prof. Jean-Marie Saudubray and Prof. Jean Aicardi and in the Dept of Neurology, Columbia University, New York, NY with Dr. Darryl De Vivo and Dr. Salvatore DiMauro. Dr. Tein is Associate Professor of Pediatrics and of Laboratory Medicine and Pathobiology at the University of Toronto and founder and Director of the Neurometabolic Clinic, Investigational Unit and Neurometabolic Research Laboratory and Staff Neurologist in the Division of Neurology at the Hospital for Sick Children in Toronto. She is also a Senior Associate Scientist in the Genetics and Genomic Biology Program in the Research Institute of the Hospital for Sick Children. Dr. Tein currently serves as the President of the International Child Neurology Association (2014-18).